Content:

SSP – Stratigraphy, Sedimentology & Palaeontology

SSP1.1 – Open session on stratigraphy, sedimentology and palaeontology

EGU2020-748 | Displays | SSP1.1

Glacio-eustatic variability in the sedimentation pattern over northern Japan during the past 600 ka

Sushree Sova Barik, Raj K. Singh, Pratik K. Upadhyaya, Lisantaraj Biswal, Nishant Vats, and Manisha Das

The Japan Sea is a semi-enclosed marginal sea affected by global sea-level fluctuation, expansion of seasonal and permanent sea-ice cover, having a significant influence on the regional climate neighboring Japan Sea. Middle Pleistocene to Holocene sediments of the Integrated Ocean Drilling Program site U1423 situated in the northeastern part of Japan Sea was processed for the grain size analysis, semi-quantitative mineral analysis, and clay mineral analysis to access glacio-eustatic control on sedimentation pattern over Japan Sea during the past 610 ka. The average time resolution per sample is ~10 kyr. The mean grain size data suggest the dominance of silt size fraction over the sand and clay. The end member modeling of grain size data suggests the presence of two different energy conditions that varied with the time and influenced by the glacio-eustatic changes over the Japan Sea. The grain size data are relatively coarser and deposited in the higher energy condition during the glacial periods in comparison to interglacial periods except for MIS 2, 4, and 8. The higher energy condition during the glacial intervals suggesting deposition of grains due to the melting of seasonal/permanent ice sheets in the northern Japan Sea. The eolian dust brought from the Chinese loess deposits are relative finer in size and dominated by a higher proportion of quartz. During the glacial phases, illite and kaolinite (%) show a decreasing trend than the interglacial phases suggesting less terrigenous input. The high illite and decreased smectite (%) during interglacial phases suggest a higher degree of physical weathering. The significant increase in the smectite/(illite+chlorite) ratio suggests a higher degree of chemical weathering of the nearby source area, which varied over time. The overall study suggests the phase-wise variability in the presence of permanent/seasonal ice sheets and East Aian Winter Monsoon strength during the past 600 ka.

How to cite: Barik, S. S., Singh, R. K., Upadhyaya, P. K., Biswal, L., Vats, N., and Das, M.: Glacio-eustatic variability in the sedimentation pattern over northern Japan during the past 600 ka , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-748, https://doi.org/10.5194/egusphere-egu2020-748, 2020.

EGU2020-21991 | Displays | SSP1.1

Cosmogenic-nuclide burial ages for Quaternary drilling core sediments in the Yangtze River De, China

Xiao Qi

EGU2020-13000 | Displays | SSP1.1

On the application of confidence limits to biostratigraphy: an example from diatoms

Cristina Lopes and João Velez

For years, diatom-based biostratigraphy has been settings bio-events based on a qualitatively approach. This means that the biostratigraphy would set an age based on the findings or not of a certain species. However, how many species are needed to consider a certain datum as certain? One, ten, 100? Moreover, each biostratigrapher sets its on limits. One might consider one as enough and another 10. Therefore, the scale more often used is the absent, rare, frequent, common, dominant or abundant with an explanation of what of these definitions mean. This is very common in, for example, IODP expeditions.

However, what would happen to these biostratigraphy levels if one would apply, for example, a concept of 95% confidence level? Moreover, what would happen to an age model if this concept would be applied to all the biostratigraphy microfossil?

Here we will show Expedition 346 age model differences with and without confidence levels applied to diatoms. The differences can be significant and even considering the existence of a hiatus can be reconsider if confidence limits are applied, turning a possible hiatus into a very slow sedimentation rate having serious implications to the initial paleoceanographic interpretations.

How to cite: Lopes, C. and Velez, J.: On the application of confidence limits to biostratigraphy: an example from diatoms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13000, https://doi.org/10.5194/egusphere-egu2020-13000, 2020.

EGU2020-11213 | Displays | SSP1.1

Scarce population of malacofauna from MIS8/L3, at Titel loess plateau, Serbia

Milica Radaković, Bojan Gavrilović, Luka Bosnić, Milivoj Gavrilov, Pal Sümegi, David Molnár, and Slobodan Marković

We present our preliminary findings from the survey of malacofauna of the Titel loess plateau – Mošorin site (Serbia), conducted during 2018/2019. Titel loess plateau is situated near the confluence of Tisa and Danube rivers, in the southern central part of the Vojvodina province, the region known for having valuable continental climate record for the past million years. The study aims to gather palaeoenvironmental data and discern patterns of environmental changes during the Pleistocene in the loess domain. Previous surveys were done at the loess sites in Batajnica, Zemun, Crvenka and Irig. The exposed part of the Mošorin loess-paleosol section is 30 m high and covers the last three glacial periods. It is the first time we carried out a malacological analysis on the L3 segment of the profile. A total of 26 samples were collected from 5.2 m long cleaned profile section (ending of S3 to the beginning of S2). Nine species of snails were present in this horizon, including Chondrula tridens, Granaria frumentum, Helicopsis striata, Pupilla muscorum, Pupilla triplicata, Punctum pygmaeum, Succinella oblonga, Vallonia costata, Vitrina pellucida, and certain as-yet-unidentified slug taxa (Limacidae, Agriolimacidae, Milacidae). Greatest diversity and abundance was found near the S3 paleosol. Samples with no snail shells are continuous, and they are situated in the middle and upper part of the studied profile section. The first three samples that are closest to S3 include 65% of all snails shells found in the profile. The number of snail taxa and their abundance gradually increases again toward the S2 paleosol. Based on ecological preferences of discovered species (mostly thermophilous and xerophilous) we deduced that the environment during the L3 time period was an opened grassland, while the climate was mild and mostly dry.

How to cite: Radaković, M., Gavrilović, B., Bosnić, L., Gavrilov, M., Sümegi, P., Molnár, D., and Marković, S.: Scarce population of malacofauna from MIS8/L3, at Titel loess plateau, Serbia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11213, https://doi.org/10.5194/egusphere-egu2020-11213, 2020.

Micropaleontological and isotopic analyses were performed on 93 samples covering the first 50m of borehole U1460 in aim to reconstruct the paleo-environmental and paleo-climatic conditions of western australian shelf. Borehole U1460 was drilled at a water depth of 214 m during IODP (International Ocean Discovery Program) 356 expedition.

The distribution of benthic foraminifera and ostracod assemblages associated with planktonic foraminifera variation allow to characterized two main climatic phases : one dominated by generally cold conditions (glacial-like, from 50 to 20m) and another interglacial-like phase (from 20 to 0m), characterized by warmer climate. Those have been identified on the basis of distribution of tropical warm water Goloborotalia menardii (planktonic foraminifera) that shows high abundance only from 20 to 0 m, attributed to the interglacial-like phase, coherent with δ18O values curve.

The glacial assemblage is composed by an assemblage dominated by ostracod genera/species such as Pterigocytherei ssp., Krithe spp.,Argilloecia sp., Pseudocythere caudata, Trachyleberi ssp. and by benthic foraminifera such as Cibicides lobatulus, Elphidiumsp., Hyalineasp., Rosalina bradyi. These assemblages indicate cold bottom conditions with probably poorly oxygenated and organic-rich sediment environment.

The interglacial assemblage is characterized by ostracods species as Neonesidea sp., Bradleya sp., Cytherella sp., and by benthic foraminifera as Meloni ssp., Uvigerina spp., Quinqueloculina sp., Textularia sp., Trifarina sp., Cassidulina sp., Brizalina sp., Bulimina sp., Sigmoilopsis schlumbergeri. This assemblage suggests warm bottom conditions under well-oxygenated, high energy regimes and food input that would be important.

Those two phases include probably multiple glacial and interglacial stages but the most spectacular result indicates that after the onset of MIS12, one of the major glaciation in the Quaternary), the oceanographic conditions in the Western Australia sector changed deeply, either because of oceanic current re-organization or because of the continental climate change (dry/wet climate transition) that controls the amount of micronutrient input into the ocean.

How to cite: Angue Mintoo, C., Courtillat, M., and Bassetti, M.-A.: Paleoceanographic variations in SE sector of Indian Ocean (Australian shelf, IODP-U1460 site): is the MIS12 the trigger for long-term oceanic circulation re-organisation? Insights from benthic meiofauna (ostracods and foraminifera), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22609, https://doi.org/10.5194/egusphere-egu2020-22609, 2020.

EGU2020-425 | Displays | SSP1.1

Chemical evidence for the preservation of collagen in Eocene turtle shell using Py-GCxGC-TOFMS

Raman Umamaheswaran, Suryendu Dutta, Hukam Singh, Sumit Kumar, and Ashok Sahni

Studies on organic preservation in fossil tissues have been a contentious topic, as fossils have been thought to preserve little, if any, organic content after diagenesis. Several studies have previously reported the presence of collagen in fossils from deep time including in Cretaceous dinosaur bones (e.g.: Schweitzer et al., 2007, Science v. 316, 277-280). These findings have also been the subject of criticism with respect to the reproducibility of their results (e.g.: Buckley et al., 2017, Proceedings of the Royal Society B v. 284: 20170544). In the present study, we analysed a turtle shell from Eocene to ascertain a suitable proxy for the preservation of collagen, by using comprehensive pyrolysis gas chromatography – time-of-flight mass spectrometry (Py-GCxGC-TOFMS) and comparing the pyrolytic products obtained to those of modern turtle shell and collagen standard. 

In order to add to the robustness of the study, industry standards of chitin, melanin and collagen were analysed using Py-GCxGC-TOFMS and their chromatograms compared for characteristic pyrolytic products that can be used to differentiate between them. Collagen could be differentiated from the other nitrogen-bearing biopolymers based on the presence of characteristic cyclic dipeptides known as 2,5-diketopiperazines (DKPs) which are formed by the recombination of peptides during pyrolysis. We compared the chromatogram of collagen standard to that of a modern turtle shell and found that the two chromatograms could be correlated based on the presence of diketodipyrrole, 2,5-DKP(Pro-Pro), 2,5-DKP(Pro-Ala), 2,5-DKP(Pro-Gly), 2,5-DKP(Pro-Hyp), 2,5-DKP(Pro-Arg) and 2,5-DKP(Pro-Lue/Ile). We then compared the chromatogram of modern turtle shell to the Eocene shell and confirmed the presence of diketodipyrrole and 2,5-DKP(Pro-Pro) in the fossil shell thus unambiguously indicating that collagen is preserved.

How to cite: Umamaheswaran, R., Dutta, S., Singh, H., Kumar, S., and Sahni, A.: Chemical evidence for the preservation of collagen in Eocene turtle shell using Py-GCxGC-TOFMS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-425, https://doi.org/10.5194/egusphere-egu2020-425, 2020.

EGU2020-1466 | Displays | SSP1.1

Life and Death in the Jurassic Seas of Dorset, Southern England

Malcolm Hart, Gloria Arratia, Chris Moore, and Benjamin Ciotti

There are very few examples of predatory behaviour by coleoids in the fossil record (e.g., Jenny et al., 2019) and, in the known cases, the victims are always fish. The examples described by Jenny et al. (2019) involve Clarkeiteuthis conocauda (Quenstedt, 1849) from the Toarcian (Jurassic) Posidonienschiefer of Southern Germany and the capture of fish assigned to Leptolepis bronni (Agassiz, 1832). In all the described examples, the fish appears to be held in the arms of the coleoids: arms which are identified by the lines of hooks preserved in the position of the arms.

The Jurassic succession of the Wessex Basin, especially that cropping out along the Dorset Coast, contains important Lagerstätten for squid-like coleoid cephalopods. The Blue Lias and Charmouth Mudstone formations have, since the nineteenth century, provided large numbers of important body fossils that inform our knowledge of coleoid palaeontology. In many of these mudstones specimens of palaeobiological significance have been found, especially those with the arms and hooks with which the living animals caught their prey. This is particularly true in the case of a specimen in the collections of the British Geological Survey (GSM 87477), identified, as Clarkeiteuthis sp. cf. C. montefiorei (Buckman, 1879), which was found in the nineteenth century from an un-specified location near Lyme Regis. This specimen is seen to have a fish, identified as Dorsetichthyes bechei (Agassiz, 1837), being held by two arms that are positioned on each side of the fish which is aligned with the jaws of the ‘squid’.  The bones in the head of the fish are broken in a manner that suggests a quite violent attack, and not simple crushing during burial and taphonomy. While the fish is damaged in ways that are suggestive of it already being dead, has the ‘squid’ choked to death, or was its death the result of sinking to the sea floor and being overcome by, for example, reduced oxygen conditions in the water column? Whatever the cause of death this unique specimen and is the oldest that shows a direct feeding attack by a ‘squid’ on a fish that was ca. 200 mm in length.

Jenny, D., Fuchs, D., Arkhipkin, A.I., Hauff, R. B., Fritschi, B. and Klug, C. 2019. Predatory behaviour and taphonomy of a Jurassic belemnoid coleoid (Diplobelida, Cepahlopoda). Scientific Reports, 9: 7944, 11pp. [doi.org/10.1038/s41598-019-44260-w].

How to cite: Hart, M., Arratia, G., Moore, C., and Ciotti, B.: Life and Death in the Jurassic Seas of Dorset, Southern England, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1466, https://doi.org/10.5194/egusphere-egu2020-1466, 2020.

A key topic in paleoecology and macroevolution is whether assemblages of species show patterns of persistence over millions of years; a phenomenon that has been variously referred to as ‘Turnover Pulse’ or ‘Coordinated Stasis’. It has generally been presumed that any abrupt environmental changes discernible in the geological record will often lead to community turnover and the establishing of a new community that is discrete from the previous iteration, even if environmental conditions return to those that existed prior to the disruptive event. A related topic is, if patterns of stability can and do prevail despite disruption, what are the processes that allow for this. Potential options include the degree of change in the physical environment, which may not be great enough to exceed the threshold required for community collapse, or due to ‘Ecological Locking’, where directional selection is constrained by ecological processes.

Our touchstone to consider these topics is the detailed fossil record of Carboniferous brachiopod communities from the Mid-continent of North America. These were highly diverse communities that persisted in a very dynamic environmental setting. In particular, these communities were subjected to frequent and geologically rapid phases of marine transgression and regression associated with climate change over approximately a 20-million-year period. These changes likely resulted in repeated community destruction and renewal as suitable habitat was lost and then subsequently re-established.

Using a suite of statistical techniques, we characterized the nature and scope of changes in these fossil communities over time. We found that, at one scale, fossil communities were not stable throughout this interval, both in terms of taxonomic composition and the associated abundance of those taxa. Thus, there is no evidence of obdurate ecological stasis, as new discrete communities, statistically dissimilar from previous and subsequent iterations, form following each environmental disruption. However, at a higher scale, stability is manifest, as diversity patterns are stable across time and despite episodes of environmental change. In particular, we identify a form of qualified ecological stasis for both the different environments present during this interval and for the larger region as a whole. Ultimately, whilst the individual taxa that comprise each community differ, there is a consistent number of species that can exist in any given community, such that communities remain functionally similar. This indicates that whilst the individual taxa that come to form communities arrive via the exigencies of recruitment, the overall diversity of the communities is set by some higher-level ecological rules. Specifically, the rules for taxon packing are seemingly constant in distinct environments, likely due to energetic controls that limit how many taxa can be maintained in an environmental setting and/or perhaps because the amount of space needed for any individual to develop into an adult is invariant across different taxa within the same clade. Further, these ecological rules lead to stability even in the face of constant disequilibrium, which matches patterns identified in the recovery of marine invertebrate communities from disruptive events in modern systems.

How to cite: Strotz, L. and Lieberman, B.: Ecological stability despite environmental disruption – searching for ecological rules governing Carboniferous brachiopod assemblages from the North American Mid-continent, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2909, https://doi.org/10.5194/egusphere-egu2020-2909, 2020.

SSP1.2 – New and re-interpreted Pleistocene sea-level records from around the Globe

EGU2020-7153 | Displays | SSP1.2 | Highlight

Molecular fossils inferring Quaternary sea-level changes

Martina Conti, Martin Bates, Natasha Barlow, Richard Preece, Kirsty Penkman, and Brendan Keely

Targeted analysis of organic matter in soils and sediments is useful for evaluating past environmental conditions, as specific compounds may be directly linked to organisms and hence to the conditions in which they inhabited the environment.  Variations in molecular fossil distributions have become a powerful tool for understanding changes in palaeoclimate conditions.  This work uses molecular fossils to give an insight into the impact of transgressive events on primary producers inhabiting the studied basin, and hence a more detailed record of sea-level change.

The cores studied consisted of unconsolidated immature sediments from the mid-late Pleistocene (< 500,000 years) and the Holocene.  Molecular fossils, such as chlorophyll pigments and lipids, exhibit fluctuations as a response to changes in palaeoenvironmental conditions, providing a useful marker for sea-level changes.  Fluctuations in the pigment and n-alkane distribution reflect changes in primary producer activity, while the GDGT-based index of branched and isoprenoid tetraether lipids (BIT) differentiates between terrigenous and marine organic matter inputs.  Lipids were analysed by GC-FID and HPLC-MS while analysis of chlorophyll pigments was carried out using a new UHPLC-DAD method.

The results from biomarker analyses show excellent time-resolved agreement with previous lithological and ecological studies, but enabled a more sensitive response of different primary producers to changing conditions to be observed.  The molecular fossils were able to detect the onset and cessation of the studied transgressions earlier than it was possible with microfossil evidence.  Linking the pigment and lipid record with more secure dating will enable a more accurate record of Quaternary relative sea-level change.

How to cite: Conti, M., Bates, M., Barlow, N., Preece, R., Penkman, K., and Keely, B.: Molecular fossils inferring Quaternary sea-level changes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7153, https://doi.org/10.5194/egusphere-egu2020-7153, 2020.

EGU2020-13660 | Displays | SSP1.2

The sea-level signal in Pleistocene shallow-marine records – examples from carbonate and siliciclastic sequences

Barbara Mauz, Zhixiong Shen, Natasha Barlow, David Hodgson, and Colin Woodroffe

It is generally accepted that sea-level change represents the most important boundary condition that controls stratigraphic architecture in the shallow-marine area and further downdip. The shallow-marine stratigraphic body is then a result of the changing ratio between sediment supply and accommodation space with a range of local (autogenic) processes interplaying with the eustatic (allogenic) sea level. Extracting the sea-level signal from this interplay is typically approached through rigorous interpretation of the indicative meaning of relevant sea-level markers and through comparison with the most appropriate glacio-isostatic adjustment (GIA) model. The latter comparison is insightful for the last glacial period, but for the Pleistocene it suffers from the dilemma that the GIA contribution to sea-level change cannot be predicted for a specific location unless the ice history is known but this is what the shallow-marine record is trying to reconstruct.

Here we aim for Pleistocene sea-level reconstructions that are largely independent of GIA predictions. For this we present Pleistocene shallow-marine records from high-, mid- and low-latitudinal settings. The presentation focuses on four aspects: type and quality of the data (e.g. outcrop, borehole, etc), preservation of the record, separation of allogenic versus autogenic signal and completeness of the eustatic cycle.

We show that in siliciclastic systems the preservation depends on sediment supply and on the coastal energy with which ravinement and regression surfaces obliterate the stratigraphic record. Separating autogenic from allogenic signals depends very much on data quality and the ability to reconstruct the antecedent topography. None of our records show a complete eustatic cycle from lowstand to highstand and back to lowstand where the missing part of the cycle seems to be indicative for the type of shallow-marine record and its location on earth.

We discuss reasons and implications of our findings and emphasise the need for far greater consideration of stratigraphic architecture, carbonate facies and facies correlation.

How to cite: Mauz, B., Shen, Z., Barlow, N., Hodgson, D., and Woodroffe, C.: The sea-level signal in Pleistocene shallow-marine records – examples from carbonate and siliciclastic sequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13660, https://doi.org/10.5194/egusphere-egu2020-13660, 2020.

EGU2020-17606 | Displays | SSP1.2

High resolution topography and modeling of the Huon coral reef terrace sequence (Papua New Guinea)

Gino de Gelder, Anne-Morwenn Pastier, Denovan Chauveau, David Fernández-Blanco, Kevin Pedoja, Christine Authemayou, and Laurent Husson

Coral reef terraces (CRT) are amongst the most important indicators of Quaternary sea level fluctuations, and are therefore relevant to a wide spectrum of climatic and tectonic studies. The Huon Peninsula in Papua New Guinea accomodates one of the first CRT sequences to be mapped, measured and dated in detail through pioneering studies several decades ago. Those studies were limited by the available techniques to assess the large scale terrace sequence morphology, and thus to constrain spatiotemporal uplift rate variations that are key to determine past relative sea-level (RSL). We re-visit the Huon CRTs with the aim of refining tectonic uplift rates and RSL, using digital surface models calculated from 0.5m Pleiades satellite imagery. This allows us to constrain variations in CRT elevation, and assess tectonic deformation wavelengths in detail. We then use a numerical code for coral reef modeling to reconstruct the sequence morphology and constrain the possible range of RSL over the past few glacial-interglacial cycles. We find that large-scale tilting of the terrace sequence is generally N- instead of NW-directed, which is more compatible with the regional tectonic setting. It also implies changes of several meters for RSL highstand estimates compared to previous studies. We compare our results to other terrace sequences, and discuss the potential of combining high-resolution topography with landscape evolution modeling to constrain RSL.

How to cite: de Gelder, G., Pastier, A.-M., Chauveau, D., Fernández-Blanco, D., Pedoja, K., Authemayou, C., and Husson, L.: High resolution topography and modeling of the Huon coral reef terrace sequence (Papua New Guinea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17606, https://doi.org/10.5194/egusphere-egu2020-17606, 2020.

EGU2020-640 | Displays | SSP1.2

3D mapping of Quaternary coral reef terraces on Curacao Island, Southern Carribean Sea

Ciro Cerrone, Ann-Kathrin Petersen, Paolo Stocchi, Alessio Rovere, and Elisa Casella

Detailed geological field mapping is essential for the study of Relative Sea Level (RSL) indicators, that are in turn the only direct proxies to assess paleo sea level changes and long-term land movements. In the last decades, traditional mapping methods started to be complemented by small Remotely Piloted Aircraft Systems (RPAS, a.ka.a. drones) and high-resolution remote sensing datasets.

In this contribution, we show the results of geological mapping in the island of Curaçao (Netherlands Antilles). Here, we mapped a staircase sequence of coral reef terraces. In particular, we used TerraceM-2 Maptools (a Matlab® interface for mapping marine terraces) to extract wide-scale marine terrace elevations from TanDEM-X Digital Elevation Models (DEMs) (German Aerospace Center, DLR and Airbus). We detail the elevation information available for each single terrace with RPAS data processed with Agisoft Metashape, that allows obtaining as final products DEMs and orthophotos of selected sites at the inner margin of reef terraces. We then use land-based photogrammetry coupled with traditional facies analysis to identify geological discontinuities on the lower terrace.

The facies analysis allowed to precisely map the unconformity between the Hato (MIS 5.5) and Cortalein (MIS 7) Units (as identified by Muhs et al., 2012). The top of the Hato Unit forms the so-called “Curaçao Lower Terrace”. The top of the Hato Unit, extending few kilometres from the coast, has been mapped with both TanDEM-X and RPAS data up to the paleo-cliff of the Middle Terrace (formerly attributed to MIS 11), where a well-defined notch is preserved. We attribute this notch to the maximum sea ingression during MIS 5e. We compare its elevation with the RSL predicted by Glacio-Isostatic Adjustment (GIA) models.    

We discuss the new data and models for Curaçao in terms of long-term tectonic uplift and eustatic sea level.

Reference: Muhs DR, Pandolfi JM, Simmons KR, Schumann RR (2012) Sea-level history of past interglacial periods from uranium-series dating of corals, Curaçao, Leeward Antilles islands. Quat Res 78:157–169. doi: 10.1016/j.yqres.2012.05.008

Acknowledgments: TanDEM-X digital elevation data is used with permission within the Project DEM GEOL1210 (A. Rovere / M.E. Raymo). The fieldwork for this work was funded by the Helmholtz Exzellenznetzwerks “The Polar System and its Effects on the Ocean Floor (POSY)”. The authors acknowledge also the ZMT,  the Center for Tropical Marine Ecology, and the DAAD, the German Academic Exchange Service.

How to cite: Cerrone, C., Petersen, A.-K., Stocchi, P., Rovere, A., and Casella, E.: 3D mapping of Quaternary coral reef terraces on Curacao Island, Southern Carribean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-640, https://doi.org/10.5194/egusphere-egu2020-640, 2020.

As contribution to the ongoing research programmes RISeR (Dr. Barlow, Univ. Leeds, UK), WARMCOASTS (Dr. Rovere, Marum Bremen, GER) and LOSS (Dr. Stouthamer and consortium, Utrecht Univ., NL), and in more general effort to correctly deal with legacy geological data in the current era of Open Science and Geodata Science, we are populating the WARMCOASTS-WALIS database with entries for the Last-Interglacial sea-level indicator data points as available for the Southern North Sea area. This part of the world in in the immediate near field of the Scandinavian-British ice mass centre at interglacial temperate latitudes.

The majority of the sea-level indicator data points are of siliciclastic sedimentary type: transgressive contacts of marine muds over basal peats, insolation basin lakes becoming brackish marine, regressive peats establishing on tidal flat tops and so on. The abundance of peat and tradition of palynological investigation of these beds is important to date stratigraphical levels. The floating varve-count based PAZ-duration chronology for the Eemian vegetation succession in NW Europe (Zagwijn1996:QSR) allows to resolve floating ages to submillenial scale in the transgressive limb (PAZs E1-E4 and subzones), and to millennial scale in the high stand (coincident with PAZ E5) and regressive limb (starting at the PAZ E5/E6 break; Zagwijn1983:GeologieMijnbouw). Chronostratigraphical database entries for each zone and subzone have been filed in the WALIS database, informing on the varve count durations (floating time scale). Absolute age is left more broad, as there is some uncertainty and wiggle room and difference of opinion in the timing of the palynological NW European Eemian relative to that Termination II in the MIS and coral records (SierEtAl2015:QGeochron; LongEtAl2015:QSR).

Sedimentary environment analogies are drawn with the Holocene transgression and high stand to identify and classify localities as being sea-level indicator points (SLIPs), Marine limiting points, or Terrestrial limiting points. Analogies with the Holocene relative sea-level rise reconstruction practice (e.g. Hijma&Cohen2019:QSR) also echo in the protocols followed to characterize and document the vertical position of the indicator. Data entry requires to assess depth of contact (at present, expressed to a specified datum), implied depth position of past mean sea level (factoring in tidal range, palaeowater depth, background vertical movement, (de)compaction), and uncertainties to that depth (added up according to error propagation rules).

We compare our re-assessed and standardized database entries for longer established sites to the originally reported reconstructed sea-level positions (e.g. Zagwijn1983) and to their discussion in later publications (2000s, 2010s). What is one point in Zagwijn1983, often becomes an assemblage of terrestrial limiting, SLIPs and marine limiting entries in WALIS. We find the North Sea data in some earlier ‘table style’ global compilations to have suffered from generalisations. We find the protocolised database approaches as established by PALSEA activities (e.g. ShennanEtAl(Eds)2015: Handbook of Sea-Level Research; KahnEtAl(Eds)2019: QSR special issue) a more suitable environment to store and open up regional data for correct in-take and reuse by second/third parties - whether LOSS, WARMCOAST, RISeR, or you.

How to cite: Cohen, K.: Opening up a Last-Interglacial Sea Level Database for the Southern North Sea area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3135, https://doi.org/10.5194/egusphere-egu2020-3135, 2020.

EGU2020-18309 | Displays | SSP1.2

Last Interglacial Sea-Level Indicators in the Western Indian Ocean

Patrick Boyden, Jennifer Weil Accardo, Pierre Deschamps, and Alessio Rovere

With global average temperatures 2°C higher than pre-industrial and eustatic sea-level ranging between 5 and 9 m above present, the Last Interglacial is often regarded as a good process-analogue for a future warmer climate.  Large uncertainties are associated with Last Interglacial eustatic sea-level estimations. To quantify these uncertainties through standardization of sea-level metadata, the World Atlas of Last Interglacial Shorelines (WALIS) provides a community-wide standard for documenting the geological context of sea-level indicators and their chronology. By applying this standard, WALIS allows for the quantitative cross-comparison between previous studies, often times separated by decades.

 

We use WALIS to review published sea-level indicators for the Last Interglacial within the Western Indian Ocean basin. Located in the far field with respect to past glaciations, the Western Indian Ocean has the potential to provide precisely measured and dated sea level proxies, enabling a reliable estimation of maximum eustatic sea level for the Last Interglacial. This, in turn, would allow to better constrain upper boundaries of melting within ice-sheet models. Furthermore, this review highlights localities that should be revisited based on the presence of geological facies indicative of former highstands where not enough detail has been reported or where advanced dating and geodetic techniques can increase the accuracy of metadata.

How to cite: Boyden, P., Weil Accardo, J., Deschamps, P., and Rovere, A.: Last Interglacial Sea-Level Indicators in the Western Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18309, https://doi.org/10.5194/egusphere-egu2020-18309, 2020.

EGU2020-13281 | Displays | SSP1.2

Holocene sea-level changes in the Spermonde Archipelago, Indonesia: implications for vertical land movements

Alessio Rovere, Maren Bender, Thomas Mann, Paolo Stocchi, Dominik Kneer, Tilo Schöne, Julia Illigner, and Jamaluddin Jompa

We surveyed the elevation and age (14C) of paleo sea-level indicators in five islands of the Spermonde Archipelago. We describe 24 new sea-level index points from fossil microatolls, and we compare our dataset with both previously published proxies and sea-level predictions from a set of 54 Glacial Isostatic Adjustment (GIA) models, using different assumptions on both ice melting histories and mantle structure and viscosity. We then investigate the implications of our data and models in terms of vertical land movements in the study area, with two main results.

First, data from the heavily populated island of Barrang Lompo are significantly lower (ca. 80 cm) than those at all the other islands. In absence of instrumental data (e.g., GPS or tide gauges) in any of the islands, we advance the hypothesis that this difference may be due to groundwater extraction and loading of buildings on Barrang Lompo, that would cause this island to subside at rates in the order of ~3-11 mm/a.

Second, Common Era data (0-400 a BP) seem to indicate that the islands in the archipelago may be affected by tectonically-driven vertical land motions in the order of -0.88±0.61 mm/a (1-sigma), albeit slight uplift cannot be excluded. Different assumptions on vertical land motions affect, in turn, the assessment of which GIA model shows the best match with Late Holocene (ca. 4-5 ka) sea level data. Tectonic stability or slight uplift would favor iterations of ANICESELEN (De Boer et al., 2014), while subsidence would cause the sea level data to fit better with iterations of ICE-6G (Peltier et al., 2015).

References

De Boer, Bas, Paolo Stocchi, and Roderik Van De Wal. A fully coupled 3-D ice-sheet-sea-level model: algorithm and applications." Geoscientific Model Development 7.5 (2014): 2141-2156.

Peltier, W. R., D. F. Argus, and R. Drummond. Space geodesy constrains ice age terminal deglaciation: The global ICE‐6G_C (VM5a) model. Journal of Geophysical Research: Solid Earth 120.1 (2015): 450-487.

Acknowledgments

This project is funded by SEASCHANGE (RO-5245/1-1) and HAnsea (MA-6967/2-1) from the Deutsche Forschungsgemeinschaft (DFG), part of the Special Priority Program (SPP)-1889 "Regional Sea Level Change and Society". Parts of this study are under review in Climate of the Past (https://www.clim-past-discuss.net/cp-2019-63/)

How to cite: Rovere, A., Bender, M., Mann, T., Stocchi, P., Kneer, D., Schöne, T., Illigner, J., and Jompa, J.: Holocene sea-level changes in the Spermonde Archipelago, Indonesia: implications for vertical land movements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13281, https://doi.org/10.5194/egusphere-egu2020-13281, 2020.

EGU2020-12416 | Displays | SSP1.2

Driving mechanisms of sea-level variability in the U.S. mid-Atlantic during the last millennium

Jennifer Walker, Robert Kopp, Nicole Khan, Timothy Shaw, Niamh Cahill, Don Barber, Matt Brain, Jennifer Clear, Reide Corbett, and Benjamin Horton

Last millennium relative sea-level (RSL) changes along the U.S. Atlantic coast are spatially variable. Glacial isostatic adjustment (GIA) has been a significant driving factor in RSL rise during the last millennium, producing maximum rates of vertical land motion in the mid-Atlantic region due to its proximity to the margin of the former Laurentide Ice Sheet. However, there is uncertainty surrounding the influence of other regional and local processes on RSL changes such as ocean and atmosphere circulation dynamics; gravitational, rotational, and deformational signals associated with ice mass and distribution changes; sediment compaction; and tidal range change.

Here, we examined the high spatial density of high-resolution RSL records along a ~200 km stretch of coastline from New York City to southern New Jersey to distinguish between local, regional, and global scale drivers. We produced a new high-resolution (decimeter vertical, decadal temporal) RSL record of the last millennium in northern New Jersey and integrated it into an updated global database of instrumental and proxy sea-level records of the Common Era. We used a spatiotemporal empirical hierarchical model to estimate past RSL and rates of RSL change and their associated uncertainties in the context of broader regional changes by decomposing the records into global, regional linear, regional non-linear, and local components.

We found that RSL in northern New Jersey continuously rose over the last 1000 years at a rate of 1.2 ± 0.2 mm/yr (2σ) from 1000 to 1700 CE before increasing to 1.3 ± 0.7 mm/yr from 1700-1800 CE to 1.8 ± 0.6 mm/yr from 1800-1900 CE to 3.0 ± 0.6 mm/yr from 1900-2000 CE. Most of the RSL rise during the past 1000 years is attributed to regional-scale linear processes that we interpret primarily as GIA. The linear component of the RSL records exhibits a north to south gradient, with a greater contribution of RSL rise in southern New Jersey and a smaller contribution in New York City. The regional-scale non-linear contribution from the records have a magnitude <10 cm and are nearly identical because they fall within the same regional scale determined by the spatiotemporal model. The rate of the regional non-linear component fluctuated between -0.1 and 0.1 mm/yr until the late 19th century when it increased to a rate of 0.6 ± 0.1 mm/yr in the late 20th century. These trends are likely explained by a combination of physical processes, including the evolving mass of the Greenland Ice Sheet, steric effects, or ocean mass changes from atmospheric circulation and ocean currents. The local-scale contribution is <10 cm at all sites, but varies in magnitudes and rates of change, which may be due to sediment compaction or tidal range change.

How to cite: Walker, J., Kopp, R., Khan, N., Shaw, T., Cahill, N., Barber, D., Brain, M., Clear, J., Corbett, R., and Horton, B.: Driving mechanisms of sea-level variability in the U.S. mid-Atlantic during the last millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12416, https://doi.org/10.5194/egusphere-egu2020-12416, 2020.

EGU2020-1678 | Displays | SSP1.2

Relative sea level highstands of the Yucatán Peninsula, Mexico, constrained by speleothem growth periods

Simon Dominik Steidle, Sophie Warken, Norbert Frank, Julius Förstel, Nils Schorndorf, Andrea Schröder-Ritzrau, Gina Moseley, Wolfgang Stinnesbeck, and Jerónimo Avilés Olguín

The loading of the North American continent with ice sheets causes a geomorphologic response. As a result of this process, a NW-SE gradient of relative sea level developed in the Caribbean during periods of glaciation. In order to distinguish geomorphologic and eustatic contributions it is important to resolve timing and amplitude of relative sea level at different positions in the Caribbean.

The cave systems around Tulum, Quintana Roo, Mexico are presently submerged and well-connected to the nearby Atlantic with a low hydraulic head gradient. Speleothems must have formed during periods of lower sea level, thus providing constraints on the maximum elevation of relative sea level for given periods of time. Conversely, periods of growth cessation could have been caused by sea level rise thus indicating minimum relative sea level during highstands.

Here, we present 230Th/U dated submerged speleothems that grew during MIS5a-d as well as MIS1/2, MIS6 and MIS11/12.

Growth of a single stalagmite (QUE01) at -10.8±0.1m (relative to today's sea level) was interrupted twice. Petrographical studies and trace element analysis indicate that submergence caused millennial-scale growth stops in QUE01 during MIS5. The proposed highstands are between 109.4±0.3ka and 105.0±0.3ka as well as between 104.5±0.4ka and 96.9±0.4ka.

While a previous study [1] constrains the amplitude to <9.9m, this study further improves the timing. This is the first record in this area that yields bracketing ages for those highstands from a speleothem that is very close to the peak height. In order to reconstruct a Caribbean sea level gradient, the combined Yucatán record acts as a counterpiece to a similar study from the northern end of the Caribbean sea level gradient which reports highstands at that time with a higher relative sea level [4].

Speleothem growth during MIS1/2 (19-8ka) relates to conflicting local sea level markers [2,3] and contains century-scale growth stops. Samples dating back to MIS6 and MIS11/12 highlight the potential for sea level reconstruction in this area before MIS5.

[1] Moseley et al. (2013) Journal of Quaternary Science 28 293-300
[2] Moseley et al. (2015) The Holocene 25 1511-1521
[3] Hering et al. (2018) Journal of Quaternary Science 33 444-454
[4] Wainer et al. (2017) Earth and Planetary Science Letters 457 325-334

How to cite: Steidle, S. D., Warken, S., Frank, N., Förstel, J., Schorndorf, N., Schröder-Ritzrau, A., Moseley, G., Stinnesbeck, W., and Olguín, J. A.: Relative sea level highstands of the Yucatán Peninsula, Mexico, constrained by speleothem growth periods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1678, https://doi.org/10.5194/egusphere-egu2020-1678, 2020.

EGU2020-18523 | Displays | SSP1.2

Pleistocene sea-level record in low latitude settings: the Cape Verde Islands.

Teresa Bardají, José Luis Goy, Caridad Zazo, Claude Hillaire-Marcel, Cristino J. Dabrio, Ángel Gozález, Bassam Ghaleb, Ana Cabero, Vicente Soler, and Javier Lario

The volcanic Cape Verde archipelago constitutes one of the few sites in low latitude eastern Atlantic Ocean, where a long record of Pleistocene sea-level indicators develops, particularly beach deposits and marine terraces. The extreme aridity of the easternmost islands (Sal, Boa Vista and Maio) allows the exposure of long sedimentary sequences, the altitudinal and spatial distribution of which must be related both to sea level behaviour in low latitude settings and also to the volcanic nature of the archipelago.

The particular case of Maio Island reveals the occurrence of a flight of at least 18 marine terraces, between +85 and 0m. The chronology has been approached by a paleomagnetic sequence (Early - Middle Pleistocene transition), U-series measurements (Last Interglacial deposits) and 14C (Holocene units).

The results have revealed a differential behaviour in the vertical motion of the island along the Pleistocene, with unequal uplift rates during Early and Middle Pleistocene. An anomalously low-lying MIS5 unit in this island fits well with the predictions done by GIA models of Crevelling et al., (2017) although the proper evolution of volcanic islands cannot be discarded.

A comparison with Sal (Zazo et al., 2007, 2010) and Boa Vista islands is done, especially in what the MIS5 sea level record is concerned. MIS 5e deposits are scarce along the coasts of Maio and Boa Vista, and always at very low heights above mean sea level (0-0,5 m). On the island of Sal the deposits corresponding to the MIS 5e are located at a maximum height of +2.5m asml, in its most southern sector, being also very frequent to find them at 0m (Zazo et al., 2010).

The geomorphological distribution of the Pleistocene sedimentary sequences along these three islands reveals a complex history of uplift and subsidence that must be conciliated with the far-field sea level behavior, especially for the MIS5 units.

Creveling et al., 2017. QSR 163.

Zazo et al., 2007. QSR 26.

Zazo et al., 2010. GPCh 72.

Acknowledgements: This work has been supported by FEDER-MINECO Spanish project CGL15-69919-R.

How to cite: Bardají, T., Goy, J. L., Zazo, C., Hillaire-Marcel, C., Dabrio, C. J., Gozález, Á., Ghaleb, B., Cabero, A., Soler, V., and Lario, J.: Pleistocene sea-level record in low latitude settings: the Cape Verde Islands., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18523, https://doi.org/10.5194/egusphere-egu2020-18523, 2020.

EGU2020-10423 | Displays | SSP1.2

Last Interglacial fossiliferous sequences from Santiago Island (Cabo Verde Archipelago): the palaeoecology of the Nossa Senhora da Luz section, a rare example of a protected bay in volcanic oceanic islands

Carlos Melo, José Madeira, Ricardo S. Ramalho, Ana C. Rebelo, Michael Rasser, Esther González, Alfred Uchman, Patrícia Madeira, Emílio Rolán, Luís Silva, Carlos M. da Silva, Deirdre Ryan, Alessio Rovere, Mário Cachão, and Sérgio P. Ávila

The world-wide study of the geological record of the Last Interglacial is key to reconstruct the climatic and oceanographic conditions during that time interval. Here we present preliminary results of a comprehensive field analysis of one of the most extensive and least studied Quaternary fossiliferous sequences in Cabo Verde attributed to the Last Interglacial. It is located at Nossa Senhora da Luz, which is a protected inlet at the SE coast of Santiago Island. The studied sequence shows a set of transitions between fluvial and marine environments, and emersion and immersion events within a confined, highly protected bay environment. The presence, in the upper part of the sequence, of a thick layer of very fine-branched rhodoliths indicates particular ecological conditions within this bay (e.g., shallow and turbidity free waters, stable environmental conditions and/or fast growth) that are absent today and presumably played an important role for the presence of particular invertebrate species during that time. The presence of tidal specimens of the clam Senilia senilis in life position at an altitude of ~12m above sea-level allowed a re-interpretation of relative sea-level changes, suggesting that the uplift trend of Santiago Island for the Last Interglacial period onwards (3m/100ky) is possibly 70% lower than previously calculated (10m/100ky). Fossils include five phyla, with molluscs being the most diverse and abundant. Despite the abundance of some species (e.g., the bivalves Saccostrea cuccullata, S. senilis, and Aequipecten opercularis, and the gastropods Persististrombus latus and Thais nodosa), the general biodiversity is low. The presence of S. cuccullata and S. senilis, absent from extant Cabo Verdean faunas, indicates a more humid climate, unlike the dry climate found today. Some horizons are intensively bioturbated with the crustacean burrow Thalassinoides suevicus. Our new data agree with the hypothesised palaeoclimatic framework of more wet conditions than today for the Last Interglacial in the archipelago.

Keywords: Eemian, Cabo Verde Archipelago, sheltered bay, Senilia senilis, volcanic oceanic islands, NE Atlantic

Acknowledgments

C.S.M. and A.C.R. acknowledge, respectively, his PhD grant M3.1.a/F/100/2015 from FRCT/Açores 2020 and her Post-Doc grant SFRH/BPD/117810/2016 by FCT. R.R. and S.Á. acknowledges his IF/01641/2015 and IF/ 00465/2015 grants funded by FCT. A.R. and M.R. were supported by the by DFG grant RA1597/3-1. This work was supported by FCT project PTDC/CTA-GEO/28588/2017 and LISBOA-01-0145-FEDER-028588 UNTIeD and DRCT 2019-2022 – ACORES-01-0145_FEDER-000078 – VRPROTO.

How to cite: Melo, C., Madeira, J., Ramalho, R. S., Rebelo, A. C., Rasser, M., González, E., Uchman, A., Madeira, P., Rolán, E., Silva, L., Silva, C. M. D., Ryan, D., Rovere, A., Cachão, M., and Ávila, S. P.: Last Interglacial fossiliferous sequences from Santiago Island (Cabo Verde Archipelago): the palaeoecology of the Nossa Senhora da Luz section, a rare example of a protected bay in volcanic oceanic islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10423, https://doi.org/10.5194/egusphere-egu2020-10423, 2020.

EGU2020-14805 | Displays | SSP1.2 | Highlight

The southern North Sea as a natural palaeo-laboratory to reconstruct the coastal response to Last Interglacial sea-level rise

Natasha Barlow, Victor Cartelle, Oliver Pollard, Lauren Gregoire, Natalya Gomez, David Hodgson, Stephen Eaton, Freek Busschers, Kim Cohen, Carol Cotterill, Claire Mellett, and Ivan Haigh

Current models that project sea-level rise beyond 2100 have large uncertainties because recent observation encompass a too limited range of climate variability to provide robust tests against which to simulate future changes. It is crucial to turn to the geological record where there are large-scale changes in climate, but the current interglacial provides limited evidence for how the Earth-system responds to increased temperatures, and therefore it is necessary to study previous climatically-warm periods. Global temperatures during the Last Interglacial were ~1oC warmer than pre-industrial values and 3-5oC warmer at polar latitudes, during which time global mean sea level was likely 6-9 m above present. Though the drivers of warming during the Last Interglacial are different to those of today, it is the amplified warming at polar latitudes, the primary locations of the terrestrial ice masses likely to contribute to long term sea-level rise, which makes the Last Interglacial an ideal palaeo-laboratory to understand coastal response to sea-level rise.  However, our understanding of Last Interglacial sea level change is primarily limited to tropical and sub-tropical latitudes and it is important to understand the response of temperate estuarine settings to rising sea level.

The ERC-funded RISeR project (Rates of Interglacial Sea-level Change, and Responses) focuses on specifically targeting palaeo shorelines buried within the southern North Sea, preserved beyond the limit of the Last Glacial Maximum ice sheets. Buried Last Interglacial sequences in this area provide a valuable record of marine transgression and are being unveiled in new geophysical and geotechnical datasets acquired to support the offshore renewable energy development. This offshore sedimentary archives offer significant advantages over the geomorphologically restricted onshore records allowing us to trace the transgression over a much large area, and should capture the earliest flooding of the Last Interglacial North Sea basin, when the far-field data suggests ice sheet melt was at it maximum. By integrating the already available datasets with newly acquired samples as part of the project, we aim to develop new palaeoenvironmental reconstructions of the Last Interglacial sea-level change from northwest Europe, providing the first chronological constraints on timing, and therefore rates. This has the potential to allow us to ‘fingerprint’ the source of melt (Greenland and/or Antarctica) during the interglacial sea-level highstand.

How to cite: Barlow, N., Cartelle, V., Pollard, O., Gregoire, L., Gomez, N., Hodgson, D., Eaton, S., Busschers, F., Cohen, K., Cotterill, C., Mellett, C., and Haigh, I.: The southern North Sea as a natural palaeo-laboratory to reconstruct the coastal response to Last Interglacial sea-level rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14805, https://doi.org/10.5194/egusphere-egu2020-14805, 2020.

EGU2020-4450 | Displays | SSP1.2

Late Pleistocene – Holocene sea level and climate changes in the Black Sea

Andrei Briceag, Gabriel Ion, Mihaela Melinte-Dobrinescu, Dan Vasiliu, and Naliana Lupascu

The Danube Deep-Sea Fan, situated in NW Black Sea, is one of the most developed deep-sea sedimentary structures in Europe (Panin & Jipa, 2002). In 2018, in the framework of the uBiogas Project (24PCCDI/2018), several cores were acquired from the aforementioned area. In this study, high resolution microfaunal analyses coupled with sedimentological and geochemical ones, were performed on two gravity cores that revealed changes since the Last Glacial Maximum. The cores have been collected from two secondary canyons, situated in the E of the Danube Canyon, at 655,7 m (MN183_3_GC_1) and 1315 m water depths (MN183_8_GC_1). In both cores, three stratigraphic units as described by Ross & Degens (1974) were identified (oldest first): Unit 3 (Lacustrine lutite), Unit 2 (Sapropel Mud) and Unit 1 (Coccolith Mud).

The sediments of Unit 3 correspond to the Last Glacial Maximum and are marked by the presence of the cold-water ostracod species. The cores contain a reddish-brown clay and silty interval belonging to the post-glacial melt-water pulse of the Heinrich Event 1. In these deposits the ostracod assemblages display a high diversity and abundance. The CaCO3 amount is very low, i.e. below 15%, except for the upper part where it reaches more than 50%. The samples of Unit 3 contain nannofossil assemblages that are entirely composed of reworked species from Cretaceous, Paleogene, Early and Middle Miocene intervals.

In Unit 2 (the sapropel), very few specimens of ostracods were identified, towards the top. During this depositional interval CaCO3 values are dropping again below 15%. The high abundance of the calcareous nannoplankton species Braarudosphaera bigelowii in the upper part of Unit 2 suggests the first strong influx of marine waters into the Black Sea basin.

In the youngest Unit 1, a brackish-marine ostracod assemblage, with low diversity and abundance was identified. This interval is characterized by the presence of polyhaline ostracods with Mediterranean origin. The ostracods from this assemblage tolerate salinities comprised between 17-21 ‰ and characterize a sub-littoral environment. The CaCO3 values are increasing to more than 50%. During the depositional interval of Unit 1 the environmental was definitely a marine one, probably with a constant salinity of surface waters over 17 ppm, allowing the calcareous nannoplankton species Emiliania huxleyi and Braarudosphaera bigelowii to proliferate. The great abundance of the two taxa and especially of Emiliania huxleyi indicates the existence in the basin of a high nutrient input.

The financial support for this paper was provided by the Romanian Ministry of Research and Innovation, through the Programme 1 – Development of the National System of Research – Institutional Performance, Project of Excellence in Research-Innovation, Contract No. 8PFE/2018 and by the Project uBiogas, contract no. 24PCCDI/ 2018.

 

Panin, N., Jipa, D., 2002. Danube river sediment input and its interaction with the northwestern Black Sea. Estuarine Coastline Shelf Science 54: 551–562.

Ross, D.A., Degens, E.T., 1974. Recent sediments of the Black Sea. In: Degens E.T. and Ross D.A. (Eds.), The Black Sea: Geology, Chemistry, and Biology. American Association of Petroleum Geologists, Tulsa, USA: 183–199.

How to cite: Briceag, A., Ion, G., Melinte-Dobrinescu, M., Vasiliu, D., and Lupascu, N.: Late Pleistocene – Holocene sea level and climate changes in the Black Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4450, https://doi.org/10.5194/egusphere-egu2020-4450, 2020.

SSP1.3 – Earth System Paleobiology: closing the geological and biological gap

EGU2020-832 | Displays | SSP1.3 | Highlight

Morphology in time and space: how does shape change with sequence stratigraphic architecture?

Judith Sclafani, Max Christie, Marjean Cone, Brooke Roselle, Audrey Bourne, Caroline Gazze, and Monika O'Brien

In their seminal work on stratigraphic paleobiology, Patzkowsky and Holland highlighted the need for more morphological data that are placed within a stratigraphic context in order to more robustly study the impact of environmental change on morphological disparity. The ability to collect morphological data within sequence stratigraphic architecture has been limited by technique. As a result, most morphological data are collected from museum specimens, usually without sequence stratigraphic information. We used the photogrammetry technique, Structure-from-Motion, to collect brachiopod morphological data from outcrops in the Late Ordovician Cincinnati Arch (Indiana, Ohio, Kentucky; USA) and quantify morphological change within an established sequence stratigraphic architecture.

SfM uses 2D photographs taken from different angles to reconstruct a 3D shape. We photographed external valves of brachiopods in the field in 360 degrees (approximately 24 photos per specimen) and used the SfM software ‘Agisoft Metashape’ to make 3D models of those specimens. We exported these models into R and used the package ‘geomorph’ to generate a set of semi-landmarks. We used these to create a morphospace to explore the effects of environment and time on 3D shape.

Results indicate that brachiopod shells separate in morphospace according to their degree of inflation and roundness. These differences are likely controlled by environmental conditions at each position along a water depth gradient. Additionally, our results are consistent with the previously observed breakdown of the environmental gradient in response to the Richmondian invasion. In particular, for the genera Rafinesquina and Cincinitina, pre-invasion specimens inhabit a larger proportion of morphospace, with more specimens exhibiting an ovular outline. Post-invasion specimens contract in morphospace, exhibiting a more rectangular shape. However, Cincinitina is missing from the offshore environment in the C2 sequence and the deep subtidal environment in the C5 sequence, making it difficult to distinguish the effects of invasion from ecophenotypic variation.

Ultimately, our study demonstrates that SfM makes gathering 3D morphological data from the field possible. Because this is a low-cost and easily accessible method, possibilities of applying it more broadly within paleobiology abound. Further development of this technique will not only provide a better understanding of the distribution of morphological form within stratigraphic architecture, but also increase the quantity of morphological data from key intervals throughout the Phanerozoic. These data can be stored as a digital archive that could facilitate large-scale meta-analyses as well as education and outreach activities.

How to cite: Sclafani, J., Christie, M., Cone, M., Roselle, B., Bourne, A., Gazze, C., and O'Brien, M.: Morphology in time and space: how does shape change with sequence stratigraphic architecture?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-832, https://doi.org/10.5194/egusphere-egu2020-832, 2020.

EGU2020-126 | Displays | SSP1.3 | Highlight

Estimating Downcore Decline in Skeletal Disintegration Risk in Holocene Environments

Niklas Hohmann and Adam Tomašových

Preservation of skeletal remains is thought to be positively linked to rate of burial, i.e., they are exposed to destructive processes for a shorter time under higher burial. However, downcore changes in time-averaging documented in Holocene skeletal assemblages implies that per-individual burial rates of skeletal remains of the same age cohort can be variable, e.g., owing to bioturbation, and estimation of time (and sediment depth) over which skeletal remains are exposed to destruction is not straightforward.

This variability in the depth of burial exposes them to different intensities of destructive processes that is typically highest in sediments on or close to the seafloor, and accordingly changes their probability of disintegration. This hinders both the reconstruction of taphonomic conditions downcore and the reconstruction of biological archives from age cohorts of skeletal remains.

We present the AALPS (Aging ALong burial PathS) model to estimate downcore disintegration risk and taphonomic age, based on sediment-depth distribution of postmortem age of individual skeletal remains. This model can be applied to individual cores and taxa, accounts for sediment mixing and time-averaging, and incorporates knowledge of changing sediment input.

As an application, we discriminate between distinct hypotheses of changes in skeletal disintegration rates in cores from the Adriatic Sea.

The method provides new insights into the taphonomy of skeletal remains in Holocene and Anthropocene environments and age unmixing of paleoecological time series, which can be used in conservation paleobiology to reconstruct ecological baselines to guide future conservation efforts.

How to cite: Hohmann, N. and Tomašových, A.: Estimating Downcore Decline in Skeletal Disintegration Risk in Holocene Environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-126, https://doi.org/10.5194/egusphere-egu2020-126, 2020.

EGU2020-1049 | Displays | SSP1.3

Reconstruction of the trophic levels of a fossil fish community from the Late Jurassic Solnhofen Archipelago

Danijela Dimitrijevic, Martin Ebert, Martina Kölbl-Ebert, and Axel Munnecke

Trophic interactions of extinct fishes are central to our understanding of evolution, paleoecology and their role in the paleo-communities, but can be challenging, as these are limited by the incompleteness of the fossil record and by a lack of behavioural data. The extensive fossil record of Actinopterygii comes mostly from Conservation-Lagerstätten. They provide exceptionally rich information on fossil ecosystems and open outstanding windows into the evolution of life. The best-preserved Late Jurassic actinopterygians are known from the Solnhofen Archipelago, Germany. Despite that the diversity ichthyofauna of the Solnhofen Archipelago has been extensively explored in the last several decades, the dietary preferences of most fish remain unknown or have to be deduced by analogy from dentition and jaw morphology.

The aim of this study was to reconstruct the trophic levels of Late Jurassic fish assemblages using Sr/Ca and Ba/Ca measured from phosphatic fish remains, mostly ganoin and cycloid scales recovered from the Ettling locality, which is characterized by exceptionally well-preserved fossil fishes and moderate diagenetic alteration. We classified fish species into four trophic levels (durophagous, lower, middle, and higher trophic level) based on morphology available from the literature. Mean values of Sr, Ca, Ba and their ratios measured by Thermo Scientific iCAP Q inductively coupled plasma mass spectrometer in this study are in accordance with the mean values of previous studies. Differences in values between cleaned and uncleaned samples showed that the cleaning process successfully isolated primary dietary Sr content while dissolving away the diagenetic strontium present in carbonate in the pore spaces. All trophic levels showed low variation of Sr/Ca (0.003 - 0.008 μg/g) and high variation of Ba/Ca values (0.0003 - 0.0014 μg/g). The results showed significant differences between the middle and higher trophic levels (p = 0.03), while durophagous and lower trophic levels fell into the same range of values as the higher trophic level. 

We demonstrate that enamel of fossil vertebrates from the Solnhofen Archipelago still contains near-in vivo Sr, Ba, and Ca. The clear distinction between middle and higher trophic levels offers a new functional perspective on the ecological and evolutionary relationships among fishes. However, future studies should not neglect the importance of diagenetic alteration of the samples; proper sample cleaning before measuring isotopic signatures, and careful selection of the analyzed tissue (i.e. tooth enamel instead of scales or bones due to its resistance to diagenesis).

How to cite: Dimitrijevic, D., Ebert, M., Kölbl-Ebert, M., and Munnecke, A.: Reconstruction of the trophic levels of a fossil fish community from the Late Jurassic Solnhofen Archipelago , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1049, https://doi.org/10.5194/egusphere-egu2020-1049, 2020.

EGU2020-3456 | Displays | SSP1.3

Cenozoic plankton diversity dynamics and the impact of macroevolution on the marine carbon cycle.

Johan Renaudie, David Lazarus, Sarah Trubovitz, Volkan Özen, Gabrielle Rodrigues de Faria, Gayane Asatryan, and Paula Noble

The marine biological carbon pump is one of the most important mechanism to extract carbon from the atmosphere and export it to the deep-sea and the sediments, and thus take it out from the cycle for millions of years. Today, marine planktonic diatoms are the main element of that pump; however at the beginning of the Cenozoic they were too rare and not diverse enough to have much geochemical significance. Calcareous nannofossils and foraminifera on the other hand were already important components of the carbonate carbon pump; however they also contribute to the alkalinity pump which on shorter timescales have an adverse effect on carbon sequestration. In addition, heterotrophic, amoeboid protists, in particular polycystine radiolarians, are also known to contribute significantly to the carbon export to the deep-sea due to their role in forming rapidly sinking particles of aggregated organic material. We present new diversity reconstructions using the Neptune database (NSB) and case studies focussed on the Late Neogene and the Eocene-Oligocene transition using newly collected full-fauna/flora diversity data. We will then show how the diversity and abundance history of these groups changed throughout the Cenozoic, what the role of climate/oceanographic changes and competition on their evolution was, and, in the end, what consequences their evolution had on the marine carbon cycle.

How to cite: Renaudie, J., Lazarus, D., Trubovitz, S., Özen, V., Rodrigues de Faria, G., Asatryan, G., and Noble, P.: Cenozoic plankton diversity dynamics and the impact of macroevolution on the marine carbon cycle., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3456, https://doi.org/10.5194/egusphere-egu2020-3456, 2020.

EGU2020-5799 | Displays | SSP1.3 | Highlight

The impact of the Messinian Salinity Crisis on marine biota

Konstantina Agiadi, Niklas Hohmann, Giorgio Carnevale, Elsa Gliozzi, Constanza Faranda, Francesca Lozar, Mathias Harzhauser, George Iliopoulos, Antonio Caruso, George Kontakiotis, Marco Taviani, Alan Maria Mancini, Enrico Borghi, Ildefonso Bajo Campos, Pierre Moissette, Danae Thivaiou, Stergios Zarkogiannis, Eva Besiou, Daniel Garcia-Castellanos, and Angelo Camerlenghi

The Messinian Salinity Crisis (MSC) was the greatest paleoenvironmental perturbation the Mediterranean has ever seen. The literature is abundant in hypotheses on the repercussions of the MSC on organisms. However, all these are based on incomplete and still uncertain scenarios about the MSC evolution, as well as on the assumption that such a paleoenvironmental perturbation must have completely reset marine biota. Having prevailed for many decades now, this assumption has leaked from paleontology and geosciences to biological sciences, with numerous studies taking this scenario for granted instead of using it as a starting hypothesis to be tested. Here, we review and revise the marine fossil record across the Mediterranean from the Tortonian until the Zanclean to follow the current rules of nomenclature, correct misidentifications, and control for stratigraphic misplacements. We examine the composition of marine faunas, both taxonomically and considering the function of each group in the marine ecosystem and the transfer of energy through the marine food web. Specifically, we investigate the following functional groups: 1) primary producers, 2) secondary producers, 3) primary consumers, 4) secondary consumers, and 5) top predators. Our study includes sea grasses, phytoplankton, corals, benthic and planktonic foraminifera, bivalves, gastropods, brachiopods, echinoids, bryozoans, fishes, ostracods, and marine mammals. We calculate biodiversity indexes to provide independent evidence quantifying to what degree the marine fauna underwent:

How to cite: Agiadi, K., Hohmann, N., Carnevale, G., Gliozzi, E., Faranda, C., Lozar, F., Harzhauser, M., Iliopoulos, G., Caruso, A., Kontakiotis, G., Taviani, M., Mancini, A. M., Borghi, E., Bajo Campos, I., Moissette, P., Thivaiou, D., Zarkogiannis, S., Besiou, E., Garcia-Castellanos, D., and Camerlenghi, A.: The impact of the Messinian Salinity Crisis on marine biota, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5799, https://doi.org/10.5194/egusphere-egu2020-5799, 2020.

Although the temporal resolution and incompleteness of the fossil record are strongly determined by the thickness of the taphonomic active zone and by the depth and rate of mixing, it is unclear whether changes in time-averaging associated with the burial of assemblages that form in the surface mixed layer (SML) can be generalized across environments. Here we extend our previous models, which estimated disintegration on the basis of shell-age distributions (AFDs) in the SML, to stochastic transition matrices, and then apply them to discrete stratigraphic layers in sediment cores. This permits us to: (1) predict downcore trends in the shape of shell AFDs, and (2) estimate burial, disintegration, and mixing rates on the basis of age distributions observed in sediment cores. We find that, first, if the time to burial of individual shells to a specific sediment depth is stochastic due to bioturbation, then the inter-quartile age range will increase and skewness and kurtosis will decrease downcore to the top of permanent, historical layers (because the deepest layers reached by bioturbators are affected by mixing for a longer time than are surface layers). Systematic dm- to meter-scale changes in AFDs downcore can thus arise without changes in rates of sedimentation or mixing. Second, in contrast to expectations that species with durable shells will exhibit greater time averaging (larger inter-quartile age ranges) than species with fragile shells (an effect typical of assemblages in the SML), this difference will be minimized below the taphonomically active zone. Third, the median and modes of the AFDs of species differing in durability will differ, however, in those subsurface assemblages, producing age offsets (geologic age discordance) among species. These three predictions are clearly relevant for Holocene-Anthropocene studies, but also inform our understanding of deeper time fossil records, where episodically rapid burial can move surface assemblage to historical layers. In such case, the downcore decline in time averaging associated predicted by the surface-subsurface transition will characterize some subsets of stratigraphic successions in the fossil record.

How to cite: Tomašových, A., Kidwell, S. M., and Dai, R.: Modeling the transition of death assemblages from surface to subsurface: predicting the effects of burial, mixing, and disintegration on time averaging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7099, https://doi.org/10.5194/egusphere-egu2020-7099, 2020.

Environmental gradients are among the primary drivers of change in ecological communities through time and space. However, what is rare are combined data sets of community composition and the environmental factors that may have caused ecological turnover, largely because many environmental variables are difficult to measure in the stratigraphic record. In this study we integrate quantitative abundance estimates of benthic macroinvertebrates with a multivariate dataset of geochemical proxies to potentially estimate the environmental drivers of faunal change through the 13 m.y. history of the Middle–Late Jurassic Sundance Seaway, western United States.

Faunal counts of macroinvertebrates were obtained from marine rocks of the Gypsum Spring, Sundance and Twin Creek formations at 19 localities in Wyoming, Montana and South Dakota. From the same localities, calcitic shells of selected species (Gryphaea planoconvexa, Gryphaea nebrascensis, Gryphaea sp., Liostrea strigilecula, Deltoideum sp.), were analysed for stable isotope (carbon and oxygen) and elemental (Mg/Ca, Sr/Ca, Na/Ca, Ba/Ca) geochemistry. The studied interval was subdivided into seven third-order depositional sequences representing carbonate ramp, wave-dominated, siliciclastic shelf, siliciclastic tidal coast, and mixed evaporite-siliciclastic desert systems. Of these, five depositional sequences were fossiliferous.

Ordination plots (nMDS) of the two palaeoecological and geochemical datasets are very similar (procrustes correlation: 0.75, p: 0.0001). Vector fitting of geochemical data on the palaeoecological ordination shows that a main faunal turnover event, corresponding to the shift from carbonate to siliciclastic deposition at the Middle–Late Jurassic transition, correlates with an increase in productivity (increase of δ13C) and a decrease in temperature (decrease of Mg/Ca ratio) through time. Position of fauna in the seaway (craton vs. foredeep) correlates instead with variations of δ18O and Ba/Ca ratio, suggesting a strong salinity gradient, with decreasing salinity moving from the craton towards the foredeep. A critical discussion of these results will also include factors that could potentially affect temporal changes of proxy data, such as species-specific vital effects.

How to cite: Danise, S., Holland, S., and Price, G.: Combining palaeontological and geochemical data to reconstruct environmental gradients, a case study from the Jurassic Sundance Seaway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9795, https://doi.org/10.5194/egusphere-egu2020-9795, 2020.

Despite much scientific effort aimed over the past three decades to better constrain the fossil record of chemosynthesis-based communities, our understanding of their early evolution remains fragmentary. Until recently, a dominant perception was that, unlike the Cenozoic, bivalve-dominated chemosynthetic ecosystems, the Paleozoic to mid-Mesozoic methane seeps and hydrothermal vents were dominated by brachiopods. Similarly, the pattern of brachiopod vs. bivalve predominance at seeps and vents over the Phanerozoic was believed to have crudely followed that observed in normal-marine benthic shelly assemblages. Recent discoveries from the Middle Palaeozoic of Morocco have questioned this simple perception, documenting the presence of late Silurian and Middle Devonian seeps dominated by mass accumulations of large, semi-infaunal, modiomorphid bivalves (Hryniewicz et al., 2017; Jakubowicz et al., 2017). While representing a lineage unrelated to modern seep-obligate bivalve taxa, the mid-Palaeozoic seep bivalves developed a set of morphological adaptations strikingly similar to those of their modern ecological counterparts, and formed analogous, densely-packed, nearly monospecific assemblages, both suggesting their chemosymbiotic lifestyle. The new documentation of Palaeozoic establishment of the bivalve-dominated seep communities provides a fresh look at the concept of modern chemosynthetic ecosystems as a 'glimpse of antiquity', showing that although it is largely not true taxonomically, it clearly is in terms of recurring morphological themes. At the same time, this refined Palaeozoic record makes the factors responsible for the apparent scarcity of seep-related bivalves during the upper Devonian to early Mesozoic, a period of the remarkable success of brachiopod-dominated seep assemblages, ever more enigmatic.

How to cite: Jakubowicz, M. and Hryniewicz, K.: Are modern chemosynthesis-based communities a ‘glimpse of antiquity’? The changing fate of bivalves and brachiopods at ancient methane seeps as recorded in the Middle Palaeozoic of Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22640, https://doi.org/10.5194/egusphere-egu2020-22640, 2020.

EGU2020-20678 | Displays | SSP1.3

Macrobenthic community response to long-term climate change in the Adriatic Sea (Italy)

Daniele Scarponi, Michele Azzarone, Rafal Nawrot, and Michal Kowalewski

The ecological consequences of climate change on marine ecosystems remains poorly understood, particularly for ecological communities that reside in enclosed basins, which limit marine species in their ability to migrate. Here we use assemblages of late Quaternary fossils mollusks preserved in nearshore sediments to explore how nearshore marine benthic communities responded to past climate changes in the northern Adriatic.   We focus on three time periods: (1) the last interglacial (<125ka BP), when regional temperatures were higher than today, representing a possible analogue for the near-future global warming; (2) the last late glacial 14.5-18.0 ka BP; and (3) the mid-Holocene 6.0-1.0 ka BP, when conditions were similar to today but with a minimal human impact. Temporal dynamics of benthic communities was assessed by applying multivariate and resampling approaches to abundance data for core-derived samples of fossil mollusks. Results demonstrate that the penultimate interglacial benthic assemblages shifted to a new community state during the subsequent glacial period. The shift represented a decline in abundance of exclusively Mediterranean nearshore species and a concurrent increase in abundance of nearshore species of cosmopolitan and boreal affinity. This shift was, most likely, driven by global climate cooling. Following this major community restructuring, the local nearshore communities had reversed back to their previous state during the mid-Holocene, when interglacial climate conditions were fully reestablished again. We conclude that the nearshore community responded to long-term climate changes by displaying a resilient (rather than persistent or stochastic) behavior, with Holocene biota reversing back to the pre-existing interglacial state. However, regional pollution, trawling and the threat of spreading invasive species are already taking their toll and the present-day communities are shifting to a novel, historical unprecedented community state. Nonetheless, our findings indicate that if local and regional threats can be mitigated, the coastal marine communities of the northern Adriatic would be resilient against limited climate warming in the near future.

How to cite: Scarponi, D., Azzarone, M., Nawrot, R., and Kowalewski, M.: Macrobenthic community response to long-term climate change in the Adriatic Sea (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20678, https://doi.org/10.5194/egusphere-egu2020-20678, 2020.

EGU2020-650 | Displays | SSP1.3

Micropredators skulking in Silurian oceans?

Isabella Leonhard, Bryan Shirley, Duncan Murdock, and Emilia Jarochowska

Predation is potentially one of the most impactful evolutionary traits to have ever developed. Conodonts, an extinct group of early vertebrates, developed the first phosphatic dental tools, known as elements. Elements ranged from simple coniform types to more complex morphologies, predominantly in more derived species. Unlike the teeth of other vertebrates, these continuously grew throughout their lifetime by the periodic accretion of new lamellar tissues. This unique growth process continuously records chemical and physical characteristics throughout its lifespan which, when accessed, gives direct insight into the animal’s ecology and mode of life. Multiple lines of evidence, such as microwear studies and growth allometry, indicate that adult conodonts fed as predators and/or scavengers. There is little direct independent evidence for feeding ecologies in the earliest conodonts with coniform elements apparatuses, although previous modelling of element position and mechanical properties indicate these were capable of processing or manipulation of food. A direct test would be provided through evidence of tissue damage and its chemical composition. Our research focuses on samples of the coniform genus Panderodus (Family: Panderodontidae) from the Silurian of Poland and Ukraine. Panderodus has the best constrained apparatus reconstruction of any coniform conodont. Here we employ Backscatter electron (BSE) imaging and Energy-dispersive X-Ray spectroscopy (EDX) to identify growth dynamics, microwear, and chemical sclerochronology recorded within this unique mode of growth. Our results have direct implications not just for understanding the feeding mode of Panderodus, but also the origination of predation in the earliest vertebrates in the fossil record.

How to cite: Leonhard, I., Shirley, B., Murdock, D., and Jarochowska, E.: Micropredators skulking in Silurian oceans?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-650, https://doi.org/10.5194/egusphere-egu2020-650, 2020.

EGU2020-950 | Displays | SSP1.3

High-resolution assessment of the Valgu event: conodont diversity and δ18Ophos during the early Telychian (Silurian) in the Baltic Basin

Monica Alejandra Gomez Correa, Emilia Jarochowska, Peep Männik, Axel Munnecke, and Michael Joachimski

The influence of global climate and oceanographic system dynamics over biological patterns throughout Earth’s history is one of the main concerns in paleobiology. Periods that record changes in biodiversity of various magnitude are of particular interest in this field. Previous studies of major Silurian bioevents (e.g. Ireviken, Mulde and Lau) suggest that these events affected different faunas and have been correlated with positive carbon isotope (δ13Ccarb) excursions and positive shifts in oxygen isotopes (δ18Ophos) ratios, suggesting there was a disturbance in the carbon cycle, a drop in temperature, and potential glaciations. However, the impact of the biological events has not been fully assessed, and the influence of climate change remains unclear.

Here, we focus on the Valgu event, a minor episode of proposed environmental and faunistic changes in the early Telychian, which has been recognized in Baltica and Laurentia paleocontinents by changes in conodont succession and a positive excursion in δ13Ccarb. In this study, we assess a limestone-marl alternation core section in Estonia deposited below the storm wave base during the Valgu event. We test for a substantial decrease in the biodiversity of conodont communities, for extent perturbation in the carbon cycle, manifest in a positive δ13Ccarb excursion, and an abrupt positive δ18Ophos shift, which might be indicative of rapid cooling and a rapid sea-level fall typical for glacio-eustatic cycles. To this aim, we measured bulk-rock δ13Ccarb as well as δ18Ophos in monogeneric conodont samples and analyzed the conodont diversity from the event interval.

The lower part of the investigated section is characterized by shallow-water bioclastic limestones containing green algae. On top of this facies, a pronounced hardground indicates a gap in deposition and marks the boundary between the bioclastic limestones and the overlying sediments composed of nodular limestones and marls, which were deposited below the storm wave base. They show a positive carbon shift of ca. 1.4 ‰ during the Valgu interval, but no indication of an extreme change in the conodont biodiversity is evident. Likewise, the δ18Ophos in conodonts remains constant in the section, arguing against cooling or glacially-driven sea-level fluctuations as drivers for the observed changes.

How to cite: Gomez Correa, M. A., Jarochowska, E., Männik, P., Munnecke, A., and Joachimski, M.: High-resolution assessment of the Valgu event: conodont diversity and δ18Ophos during the early Telychian (Silurian) in the Baltic Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-950, https://doi.org/10.5194/egusphere-egu2020-950, 2020.

EGU2020-1057 | Displays | SSP1.3

You Are Where You Live: Using the size of conodont dental tools to shed light on environmental conditions and community complexity

Laura Mulvey, Bryan Shirley, Fiona Pye, Nussaïbah B. Raja, and Emilia Jarochowska

One of the most versatile tools in a palaeontologists’ “tool-kit” is body size analysis, which can be used to characterise and quantify a wide range of ecological and physiological traits.  Utilisation of these data allows insight into predator prey relationships, respiration rates, mortality rates, and even population dynamics. Body size analysis becomes essential when studying extinct organisms where few other clues to their ecology are available. An extreme example of such organisms are conodonts, which are hypothesised to be among the first predators.  Here, changes are tracked  through the Silurian Period using coniform conodont elements as a proxy for body size. Previous research focuses primarily on species turnover, however the data collected in this study is independent of species identification, relying purely on body size changes to reflect the ecology of the community. The size of coniform elements are measured across a number of bathymetries spanning approximately 10 million years. This allows a comparison of body size change not only across differing environments, but also through time. The morphometric measurements were determined using FossilJ, a plugin for ImageJ which facilitates semi-automated measurement of two-dimensional images. Firstly, our results show a clear correlation between body size change and onshore offshore gradients with smaller organisms residing at shallower water depths, unlike what is seen in today’s oceans. Secondly, specimens span across two of the three recorded isotopic excursions during the Silurian Period, the Mulde and Lau events. The impact of these events on conodont communities is represented by a reduction in body size directly after each. Furthermore, the results suggest the Mulde event may have had a stronger effect on these communities and could potentially reflect a time of stress and/or extinction for coniform conodonts.

How to cite: Mulvey, L., Shirley, B., Pye, F., B. Raja, N., and Jarochowska, E.: You Are Where You Live: Using the size of conodont dental tools to shed light on environmental conditions and community complexity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1057, https://doi.org/10.5194/egusphere-egu2020-1057, 2020.

EGU2020-21707 | Displays | SSP1.3

Determinants of Mollusk Abundance in Quaternary cores of Po Basin, Italy

Michał Kowalewski, Rafał Nawrot, Daniele Scarponi, and Michele Azzarone

Absolute abundance of fossils observed in cores and outcrops can be governed by extrinsic processes (e.g., net accumulation rates, intensity of taphonomic processes, post-mortem transport), intrinsic determinants of shell production rates (e.g., fecundity, spawning frequency, growth patterns), or some combination of those interdependent factors. Understanding the role of drivers of fossil abundance can enhance stratigraphic and biological interpretations of the fossil record. To assess the importance of extrinsic and intrinsic processes for fossil mollusks, we used a total of over 400 samples (each representing a 10-cm core interval and ∼0.375 dm3 of sediment) derived from 12 cores from the late Quaternary sedimentary succession of the Po basin (Italy). The results indicate that although extrinsic factors such as compaction, net accumulation rates, and sequence stratigraphic context are to some degree controlling mollusk abundance in the cores, they cannot account for extremely shell-rich deposits. The results suggest instead that shell-rich core intervals record, primarily, episodes of high shell production rates. First, samples with very high shell density (> 4000 specimens per dm3) were characterized by extremely low evenness reflecting dominance by one super-abundant species, typically a small r-selective species capable of an explosive population growth (Lentidium mediterraneum and Ecrobia ventrosa). Second, a taphonomic test supported further the biological (R-hardparts model) rather than sedimentological (R-sediment model) origin of very dense shell concentrations: the quality of shell preservation correlates positively with shell density as predicted by R-hardparts model. The results suggest that intervals of high abundance of mollusk shells in cores record intervals of high biological productivity driven by opportunistic shelly species from lower trophic levels. Integrative studies of facies architecture, sequence stratigraphy, and paleontological data can help to differentiate biologically and physically produced fossil concentrations thus allowing for more informed ecological interpretations of the fossil record.

How to cite: Kowalewski, M., Nawrot, R., Scarponi, D., and Azzarone, M.: Determinants of Mollusk Abundance in Quaternary cores of Po Basin, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21707, https://doi.org/10.5194/egusphere-egu2020-21707, 2020.

EGU2020-9349 | Displays | SSP1.3

Microbial regeneration and respiration of Fe(III) outcompetes sulphate respiration in ferruginous, high-sulphate oligotrophic ecosystems

Ingrid Steenbergen, Roman Špánek, Dagmara Sirova, Jakub Borovec, and Daniel Petrash
 

In anoxic lacustrine systems, at low-sulphate concentrations, sulphidisation acts as a crucial pathway driving the reductive dissolution of amorphous and nanocrystalline Fe-(oxyhydr)oxides in the presence of dissolved organic matter. The cycling of intermediate sulphur through a disproportionation reaction with the available Fe(III) stocks supports a continued intermediate sulphur-based respiration mechanism often referred to as cryptic. The prevalence of the so-called cryptic mechanism in meromictic, low-sulphate lakes could be attributed to the abundance of crystalline as opposed to more reactive amorphous iron (oxyhyd)roxides, which by immobilizing ferric iron also favour microbial sulphate reduction (MSR) promoting the accumulation of solid phase intermediate sulphur and sulphides[1]. In a ferruginous, sulphate-rich and oligotrophic post-mining lake (Lake Medard, Czech Republic) we observed a departure from this condition as dissolved sulphide does not accumulate in the bottom water column nor precipitate in the anoxic sediments.[2] Analyses of the bacterioplankton abundance in the hypolimnion indicate a marked niche compartmentalization, with Fe(II)-oxidising microbes, such as Gallionella sp., Rhodopseudomonas sp. and Sideroxydans sp., being important at the dysoxic to anoxic (ferruginous) interface where they drive the regeneration of ferric iron. On the other hand, Fe(III)-reducers, such as Geobacter sp. and Rhodoferax sp. are present at the O2-depleted monimolimnion and in the uppermost anoxic sediments. Toward the redox interface, the chemolithotrophic community described above allows for Fe-(re)cycling and drives the oxidation and turnover of the scarcely available volatile fatty acids. Sulphate reducers (e.g. Desulfobulbaceae, Chrostridia, Desulfarculus) and microorganisms capable of anammox, such as Nitrosomonas  and Nitrosospira where found below the redoxcline. However, together these obligate anaerobes account for < 4% of the total bacterial OTUs identified in the monimolimnion. Our observations in this purported modern analogue to ferruginous, relatively sulphate-enriched Precambrian coastal zones raise the possibility that limited dissimilatory sulphate reduction in the Earth’s primitive ferruginous oceans was rather linked to the scarcity of suitable organic substrates and high rates of Fe-(re)cycling than to low levels of dissolved sulphate. The co-precipitation of minor amounts of gypsum/anhydrite and siderite, with Fe(II,III)-(oxyhydr)oxides further support a potential link between the deep Lake Medard precipitation environment and certain mid- to Late-Archean marginal settings, where these phases have been described to be primary and/or early diagenetic in origin. 

[1] Hansel, C.M., Lentini, C.J., Tang, Y., et al. ISME J. 9, 2400–2412 (2015). 

[2] Petrash, D.A., Jan, J., Sirová, et al. Environ. Sci. Process. Impacts 20, 1414–1426 (2018). 

 

How to cite: Steenbergen, I., Špánek, R., Sirova, D., Borovec, J., and Petrash, D.: Microbial regeneration and respiration of Fe(III) outcompetes sulphate respiration in ferruginous, high-sulphate oligotrophic ecosystems , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9349, https://doi.org/10.5194/egusphere-egu2020-9349, 2020.

EGU2020-7245 | Displays | SSP1.3

Current palynological pattern of steppe-tundra at the Altai highland depressions

Ivan Strelkov, Ekaterina Nosevich, Mikhail Amosov, and Kirill Chistyakov

The landscape and climate research in Altai highlands were carried out in 2018 – 2019. The results of our investigation at the Khindiktig-Khol’ Lake Basin (Mongun-Taiga massif, Tuvan Republic) and Bertek depression (plateau Ukok, Altai Republic) are presented. In frame of study 75 samples (56 – subfossil, 13 flower buds, 6 recent) were collected for pollen analysis. Two key questions are to define the possible steppe-tundra palynological pattern based on project BIOME 6000 relying on steppe and tundra data and to compare palynological pattern with the subfossil data from Altai expeditions (2018-2019). The study was financially supported by Russian Foundation for Basic Research (RFBR) (Grant 18-05-00860).

Within international investigation project BIOME 6000 the palynological patterns of tundra and steppe vegetation were composed (Bigelow et al., 2003). Tundra is characterized by several biomes, such as low- and high-shrub tundra (SHRU; Alnus fruticosa, Betula nana, Salix vestita, Eriophorum, Sphagnum), erect dwarf-shrub tundra (DWAR; Betula nana, Salix herbacea, Cassiope, Empetrum, Vaccinium, Poaceae, Cyperaceae), prostrate dwarf-shrub tundra (PROS; Salix herbacea, Dryas, Pedicularis, Asteraceae, Caryophyllaceae, Poaceae, true mosses), cushion-forb tundra (CUSH; Draba, Papaver, Caryophyllaceae, Saxifragaceae, lichens, true mosses) and graminoid and forb tundra (DRYT; Artemisia, Kobresia, Asteraceae, Brassicaceae, Caryophyllaceae, Poaceae, true mosses). Steppe is described by two biomes: temperate grassland (STEP; Asteraceae, Chenopodiaceae, Liliaceae, grasses) and temperate xerophytic shrubland (STEP; Artemisia, Chrysothamnus, Hippophae, Purshia, grasses). In spite of the absence of steppe-tundra palynological pattern, it may include the pollen data both from steppe (Artemisia, Chrisotamnus, Hippophae, Kobresia, Purshia, Brassicaceae, Chenopodiaceae) and tundra (Alnus fruticosa, Betula nana, Salix herbacea, Cassiope, Draba, Dryas, Empetrum, Eriophorum, Papaver, Pedicularis, Vaccinium, Cyperaceae, Saxifragaceae, Sphagnum, lichens) patterns.

In pollen spectra of western Mongun-Taiga trees mean values vary from 36.4% to 45.4%. The predominance of dwarf birch (Betula nana) dust with the average number 28.7% is identified. As for the Bertek depression, the values change from 36.4% in Muzdy-Bulak to 59.3% in Argamdzhi (2019). Data from subfossil samples in 2018 show the dominance of Betula nana pollen (23.0%), whereas in 2019 it is indicated the significant and constant wind drift of Betula sect. Albae particles (average number – 36.7%) through the massif valleys to the region of sample collection.

In pollen spectra of herbs in Mongun-Taiga region mean value equals 57.9%, whereas at the Bertek depression the values differ from 62.8% (2018) to 37.3% (2019). Those spectra mostly consist of dust samples, such as Carex, Cyperaceae and Poaceae. Asteraceae, Caryophyllaceae, Chenopodiaceae and Fabaceae are also present in both regions.

Artemisia and Chenopodiaceae are the prime indicators of steppe conditions. The vegetation description of the landscapes, where the subfossil samples were collected, proves those conditions. Both vegetation and pollen data are also correlated with the DRYT and STEP biomes from project BIOME 6000. The only difference is that Artemisia prevails at the steppe sites of central and eastern part of Bertek depression, whereas Chenopodiaceae is mostly found within the coexistence of tundra and steppe cenoses in Khindiktig-Khol’ area and western part of Bertek depression.

How to cite: Strelkov, I., Nosevich, E., Amosov, M., and Chistyakov, K.: Current palynological pattern of steppe-tundra at the Altai highland depressions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7245, https://doi.org/10.5194/egusphere-egu2020-7245, 2020.

EGU2020-7873 | Displays | SSP1.3

The impact of the Pliensbachian-Toarcian crisis on belemnite diversity and size distribution

Kenneth De Baets, Patrícia Rita, Luís Vítor Duarte, Pascal Neige, Laura Piñuela, José Carlos García-Ramos, and Robert Weis

The Pliensbachian–Toarcian transition has been considered a major bottleneck in the early evolution of belemnites, probably related to major palaeoenvironmental and climatic changes during the Early Toarcian. Previous research has focused on the study of belemnites from higher, temperate latitudes, while high-resolution studies on diversity and size of subtropical belemnite assemblages in the northwest Tethys are comparatively rare. The lack of high-resolution (ammonoid subzone) abundance data on diversity and size distributions of belemnite assemblages does not allow separating changes during the Pliensbachian–Toarcian boundary event from those during the Toarcian anoxic event. Sample standardized diversity analyses on new data from Iberian sections suggest the Pliensbachian–Toarcian corresponds to a slight decrease in diversity and an adult size decrease within dominant species. Cluster and non-metric multidimensional scaling analyses, however, indicate that the largest changes in diversity and palaeogeographic distribution of belemnite assemblages occurred during the Toarcian oceanic anoxic event (TOAE) rather than the Pliensbachian–Toarcian boundary. In southern basins like the Lusitanian Basin and Riff Mountains, belemnites even disappear entirely during the TOAE. More generally, the TOAE corresponds with an increase in body size of belemnite assemblages driven by species turnover. The lack of widespread anoxia in southern basins of the northwest Tethys indicates that direct impact of warming or increased pCO2 triggered by volcanism as well as indirect effects on nutrient availability and productivity might have played an important role during both crises.

How to cite: De Baets, K., Rita, P., Duarte, L. V., Neige, P., Piñuela, L., García-Ramos, J. C., and Weis, R.: The impact of the Pliensbachian-Toarcian crisis on belemnite diversity and size distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7873, https://doi.org/10.5194/egusphere-egu2020-7873, 2020.

EGU2020-7994 | Displays | SSP1.3

Optimization of SIMS-based stable isotope measurements with regression diagnostics

Martin Schobben and Lubos Polerecky

Stable isotope measurements with secondary ion mass spectrometry (SIMS) have become an increasingly popular tool for Earth scientists to investigate natural phenomena such as biomineralization and sediment diagenesis, or to track the fate of labelled tracers in stable isotope probing experiments. The random nature of secondary ions emitted from a sample is described by Poisson statistics, which can be used to predict the precision of SIMS measurements under ideal circumstances (e.g., the predicted standard error can be deduced from the total counts of secondary ions). However, besides this fundamental source of imprecision, real SIMS measurements are additionally affected by other factors such as sample heterogeneity, instrument instability, the development and geometry of the sputter pit, and sample charging. Although some of these biases can be avoided by proper instrument tuning and sample documentation (e.g. T/SEM to characterise the textural properties of a rock sample) prior to SIMS measurement, factors such as instrument instability or sample heterogeneity can never be fully eliminated. Here we propose a data treatment procedure capable of identifying the underlying cause of the loss of precision due to instrument instability and sample heterogeneity. The reduced chi-squared statistic, which compares the predicted precision with the precision derived from descriptive statistics, is traditionally used to flag problematic measurements but without pinpointing the cause of precision-loss. We constructed a more sensitive method by the application of regression diagnostics, which calculates the influence of outliers on the regression model, and thus allows for augmentation of the raw count data. Simulations show that the recalculated descriptive and predictive statistics deviate from the original precision along trajectories specific to sample heterogeneity and instrument instability. Thus the proposed diagnostic procedure increases information yield of SIMS isotope measurements.

How to cite: Schobben, M. and Polerecky, L.: Optimization of SIMS-based stable isotope measurements with regression diagnostics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7994, https://doi.org/10.5194/egusphere-egu2020-7994, 2020.

EGU2020-9271 | Displays | SSP1.3

Pliocene-Pleistocene stratigraphic paleobiology at Altavilla Milicia (Palermo, Sicily): tectonic, climatic and eustatic forcing

Stefano Dominici, Marco Benvenuti, Vittorio Garilli, Alfred Uchman, Francesco Pollina, and Arpad David

The integration of sedimentary facies analysis, ichnology and benthic mollusc quantitative paleoecology allowed to interpret factors controlling deposition of the Altavilla Milicia alluvial to marine succession, near Palermo, Sicily. Two major composite units are recognised, separated by an angular unconformity and internally subdivided into elementary depositional sequences. Calcareous nannoplankton biostratigraphy allowed to recognize the upper Pliocene and lower Pleistocene, a time interval that covers the onset of the Quaternary glaciation. The main asset of the succession is driven by tectonic compression and accommodation by transpressional faults, a regime that led to a change in the direction of fluvial sediment delivery, from axial to transverse with respect to the basin elongation. High-frequency eustatic changes have driven the formation of elementary depositional sequences. The upper Piacenzian is characterised by marine bioclastic strata, deposited during maximum flooding intervals of the two large composite units. Mixed carbonate-siliciclastic lithosomes show a good correlation with shallow marine shell-rich detrital carbonates of Northern and Southern Italy and with Mediterranean deep-water sapropel clusters, suggesting common climatic forcing. Some tropical species previously thought to disappear from the Mediterranean at around 3.0 Ma, are instead present in the upper Piacenzian of Sicily. The study suggests that the Pliocene macrobenthos with tropical affinities disappeared from different sectors of the Mediterranean at different times.

How to cite: Dominici, S., Benvenuti, M., Garilli, V., Uchman, A., Pollina, F., and David, A.: Pliocene-Pleistocene stratigraphic paleobiology at Altavilla Milicia (Palermo, Sicily): tectonic, climatic and eustatic forcing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9271, https://doi.org/10.5194/egusphere-egu2020-9271, 2020.

EGU2020-10213 | Displays | SSP1.3 | Highlight

Primary productivity, deoxygenation, and the Gulliver-absence effect determine bivalve body size following the end-Permian mass extinction

Melanie Tietje, William J. Foster, Jana Gliwa, Clara Lembke, Autumn Pugh, Richard Hofmann, Sara Varela, Louise C. Foster, Dieter Korn, and Martin Aberhan

The impact of mass extinctions on the body sizes of animals has received considerable attention and debate, as to whether the reduced size of post-extinction organisms is due to the selective extinction of large species, absence of large species as a stochastic effect of low-diversity faunas, or a size decrease within surviving genera and species. Here, we investigated the body sizes of bivalves following the end-Permian mass extinction event and show that the shell size increase of bivalve genera was driven by both evolutionary and ecophenotypic responses. First, some genera show significant increases in body size with the evolution of new species. Further, the same genera record significant within-species increases in average and maximum body size into the late Induan, indicating that ecophenotypic changes were also involved on long-term body size trends. These increases are associated with invigorated ocean circulation, improved oxygenation of the seafloor, and probably increased food supply.

How to cite: Tietje, M., Foster, W. J., Gliwa, J., Lembke, C., Pugh, A., Hofmann, R., Varela, S., Foster, L. C., Korn, D., and Aberhan, M.: Primary productivity, deoxygenation, and the Gulliver-absence effect determine bivalve body size following the end-Permian mass extinction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10213, https://doi.org/10.5194/egusphere-egu2020-10213, 2020.

A small but rather unique reef type occurs in the Silurian of Gotland mainly composed of encrusting bryozoans and microbial crusts, forming a complex intergrowth, which can be characterized as bryozoan-rich stromatolites, so-called “bryoliths”. The alternation of bryozoans and microbes is assumingly driven by a repeated change of hostile and more favorable conditions for metazoan growth. The surfaces of the reef bodies are composed of characteristic cauliflower structures, created by bryozoans, which are performing a finger-like growth in every direction. Other common features are bioerosion (mostly by bivalves), enigmatic encrusting echinoderms, a high abundance of organophosphatic fossil remains such as bryozoan pearls and discinid brachiopods, a high abundance of epi- and endobionts, vadose silt, and gypsum pseudomorphs.

Altogether, ten of these special reefs have been identified on Gotland so far. All of them were formed during periods of strong positive δ 13C excursions at the Ireviken and Lau isotope excursions in the early Wenlock and late Ludlow, respectively. The unusual features of the bryoliths as well as their occurrence exclusively during strong positive δ 13C excursions indicate very specific environmental requirements. This leads to the assumption, that whatever caused the isotope excursions also has affected these reef systems. Hence, investigating the bryoliths will hopefully increase our knowledge to what has happened during the – still enigmatic – Silurian stable isotope excursions.

How to cite: Claussen, A. L., Munnecke, A., and Ernst, A.: Bryozoan-rich stromatolites (“bryoliths”) from the Silurian of Gotland and their relation to climate-related perturbations of the carbon cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22300, https://doi.org/10.5194/egusphere-egu2020-22300, 2020.

EGU2020-22617 | Displays | SSP1.3 | Highlight

Extreme reefs: Analyses of modern bryostromatolite ("bryolith") reefs from marginal environments in the Netherlands with comparisons to ancient analogues

George William Harrison, Lene Claußen, Christian Schulbert, and Axel Munnecke

Marginal environments sometimes serve as natural time machines, replicating conditions of ancient environments and thus inducing similar adaptations and symbioses. Few environments are more marginal than the brackish, arsenic and titanium rich, and periodically euxinic ponds found in the Zeeland (Netherlands). These ponds contain layered, stationary bioherms of alternating bryozoans and microbialites (bryostromatolites); similar structures are known from the Late Miocene of the Paratethys and the isotopic excursions in the Silurian as well as recent hypersaline lagoons in Australia. Critical study of the modern bryostromatolites will help paleontologists understand the conditions under which bryostromatolites formed in the past.

This study applied modern methods to analyze the microstructures and minerology of bryostromatolites from the Netherlands. These bryostromatolites contained alternations of Einhornia crustulenta bryozoans and gypsum-cemented microbes. Bryostromatolites formed in distinct stages, alternating between a phase of bryozoan layers and a phase where microbes and cements grew in tandem over the dead bryozoans; this microbial phase likely coincides with temporary anoxia/euxinia. The microbes, tentatively identified as cyanobacteria, showed a thrombolitic texture cemented with gypsum. This gypsum was deposited while the microbes were alive, suggesting they were alive during the euxinic phases and participating in sulfide-based photosynthesis. The bryoliths were otherwise poor in fauna, containing only a few species of mollusks, arthropods, polychaetes, and diatoms. All of these factors highlight the extreme environment under which modern and possibly ancient bryoliths formed.

How to cite: Harrison, G. W., Claußen, L., Schulbert, C., and Munnecke, A.: Extreme reefs: Analyses of modern bryostromatolite ("bryolith") reefs from marginal environments in the Netherlands with comparisons to ancient analogues, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22617, https://doi.org/10.5194/egusphere-egu2020-22617, 2020.

SSP1.4 – Achievements and perspectives in scientific ocean and continental drilling

EGU2020-20880 | Displays | SSP1.4 | Highlight

A Plate Too Far: Lessons Learned and Insight Gained from scientific and operational achievements during IODP Expedition 358 in the Nankai Trough.

Adam Wspanialy, Sean Toczko, Nobu Eguchi, Lena Maeda, Kan Aoike, Tomo Saruhashi, Takehiro Hirose, Matt Ikari, Kyuichi Kanagawa, Gaku Kimura, Masataka Kinoshita, Hiroko Kitajima, Demian Saffer, Harold Tobin, Asuka Yamaguchi, and International Ocean Discovery Program Exp 358 Scientists

IODP Expedition 358 planned to access and sample the subducting plate boundary at the Nankai Trough, Japan, and commenced on 7 October 2018, and ended on 31 March 2019, marking the ultimate stage of the NanTroSEIZE project. The goal was to drill down to the plate boundary fault, about 5 km below the ocean floor, where >8M earthquakes occur regularly at every 100–150 years. The successful completion would have represented the deepest borehole in the history of scientific ocean drilling and ultimately greatly deepen our understanding about fault mechanics, earthquake inception and tsunami generation processes.

The IODP Expedition 358 intended to access the plate boundary fault zone system through deepening the previously drilled and suspended C0002P hole. The original operational objective of the Exp 358 was to reach a total depth of 7267.5 mbrt (+/- 5200 mbsf) in 4 drilled sections. Previous major riser drilling efforts during the IODP Expeditions 338 and 348 advanced the main riser hole at Site C0002 (Hole C0002F/N/P) to 3058.5 mbsf meters below sea floor (mbsf). Extensive downhole logging data and limited intervals of core were collected during those expeditions.

Due to the nature of the drilling operation and the anticipated challenges ahead, JAMSTEC adopted oil & gas industry drilling standards and performed two detailed Drilling Well on Paper (DWOP) workshops as part of the very rigorous preparatory stage. Great deal of time was spent on selecting new and state-of-the-art drilling/circulating techniques, logging tools, bits and drilling fluid formulation including a new mud sealant additive “FracSeal” to make sure borehole integrity issues can be minimized as much as possible. Drilling stages seen implementation of a novel concept of near real-time geomechanics to continuously monitor and assess borehole integrity.

The challenges born from side-tracking near the bottom of the previously drilled Hole C0002P (2014 Exp. 348), proved greater than the multi-disciplinary teams expected and the overall objectives set for Exp.358 were not achieved. Nevertheless, despite the significant problems seen during several attempts, the hole was deepened 204 m. This is a minor success and it is believed, once away from the highly damaged area of the C0002P hole, drilling can produce a high-integrity hole following excellent communication and recommendations between drilling and scientific teams during complex drilling operations, especially in complex environments such as the Nankai Accretionary Prism.

Despite not achieving the ultimate goal of the expedition, the implemented industry drilling standards, real-time surveillance system, real time geomechanics, improved and strict communication protocols, and integrating both scientific and drilling teams have demonstrated their value and should become standard practice during future IODP/ICDP operations.

How to cite: Wspanialy, A., Toczko, S., Eguchi, N., Maeda, L., Aoike, K., Saruhashi, T., Hirose, T., Ikari, M., Kanagawa, K., Kimura, G., Kinoshita, M., Kitajima, H., Saffer, D., Tobin, H., Yamaguchi, A., and Exp 358 Scientists, I. O. D. P.: A Plate Too Far: Lessons Learned and Insight Gained from scientific and operational achievements during IODP Expedition 358 in the Nankai Trough., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20880, https://doi.org/10.5194/egusphere-egu2020-20880, 2020.

EGU2020-10122 | Displays | SSP1.4 | Highlight

ICDP project Drilling the Eger Rift – present status and further plans

Torsten Dahm, Tomas Fischer, Heiko Woith, Pavla Hrubcova, Josef Vicek, Michael Korn, Frank Krüger, Josef Horalek, Tomas Vylita, and ICDP-Eger ScienceTeam

Within the ICDP-Eger drilling project we are developing one of the most modern and comprehensive laboratories at depth worldwide to study the interrelations between the flow of mantle-derived fluids through the crust and their degassing at the surface, the occurrence and characteristics of crustal earthquake swarms, and the relation to the geo-biosphere. The Cheb basin located in the western Eger Rift at the Czech-German border provides an ideal natural laboratory for such a purpose. In October 2016 the ICDP proposal was accepted for complementing two existing shallow monitoring wells with five new, distributed, medium depth (<400 m) drill holes F3 and S1-S4.

The resulting natural laboratory at depth will comprise five drilling sites for studying above mentioned phenomena. The F1-F3 drillings form a unique facility of three wells at one site within an active CO2 mofette of Hartoušov for continuous recordings of fluid composition and fluid flow rate, as well as for intermittent GeoBio fluid sampling. Drillings S1-S4 are planned for seismological monitoring to reach a new level of high-frequency, near source observations of earthquake swarms and related phenomena such as seismic noise and tremors generated by fluid movements. Instrumentation of the seismic wells S1-S3 will include 8-element geophone chains and a bottom-hole broadband sensor. The borehole sensors will be complemented at S1 by small-scale surface array of approximately 400 m diameter to obtain truly 3D-array configurations. If possible, broadband surface stations and other sensors will be added to each drill location.

So far, we have completed drillings at sites S1, S2 and S3, with depth of 402, 480 and 400 m. The drilling of S4 is planned in 2020 at one of the recently discovered Maars at the Czech-German border region. Drilling F3 was completed in September 2019 at a depth of 239 m. It has reached several over-pressurized, CO2 bearing layers. The three boreholes have been connected by underground tubes system to the nearby field laboratory equipped by flowmeters and mass spectrometers allowing for long time precise monitoring of the degassing process. The S1 borehole (Landwust) will be instrumented in January 2020 by a test geophone chain allowing, along with the DAS fibre-optic cable installed behind the casing, to carry out a VSP measurement.

In our presentation we provide information on the status of drillings, sensor installation and plans for the complete monitoring and data handling concept.

How to cite: Dahm, T., Fischer, T., Woith, H., Hrubcova, P., Vicek, J., Korn, M., Krüger, F., Horalek, J., Vylita, T., and ScienceTeam, I.-E.: ICDP project Drilling the Eger Rift – present status and further plans , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10122, https://doi.org/10.5194/egusphere-egu2020-10122, 2020.

EGU2020-8872 | Displays | SSP1.4 | Highlight

IODP Expedition 378 South Pacific Paleogene Climate: New high-resolution high-latitude Cenozoic Section

Ursula Röhl, Deborah J Thomas, and Laurel Childress and the Expedition 378 Science Party

As the world’s largest ocean, the Pacific Ocean is intricately linked to major changes in the global climate system. International Ocean Discovery Program (IODP) Expedition 378 is designed to recover Paleogene sedimentary sections in the South Pacific to reconstruct key changes in oceanic and atmospheric circulation. These cores will provide an unparalleled opportunity to add crucial new data and geographic coverage to existing reconstructions of Paleogene climate and as part of a major regional slate of expeditions in the Southern Ocean to fill a critical need for high-latitude climate reconstructions. Appropriate high-latitude records are unobtainable in the Northern Hemisphere of the Pacific Ocean.

The drilling strategy included a transect of sites strategically positioned in the South Pacific to recover Paleogene carbonates buried under red clay sequences at present latitudes of 40°–52°S in 4650 – 5075 meters of water depth. Due to technical issues we no longer will be able to reach the deeper sites. Therefore, the focus of Expedition 378 will be now to obtain a continuous sedimentary record of a previously single hole, rotary-drilled, spot-cored, classic Cenozoic high-latitude DSDP Site 277 and provide a crucial, multiple hole, mostly APC-cored, continuous record of the intermediate-depth Subantarctic South Pacific Ocean from the Latest Cretaceous to late Oligocene.

How to cite: Röhl, U., Thomas, D. J., and Childress, L. and the Expedition 378 Science Party: IODP Expedition 378 South Pacific Paleogene Climate: New high-resolution high-latitude Cenozoic Section, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8872, https://doi.org/10.5194/egusphere-egu2020-8872, 2020.

EGU2020-12094 | Displays | SSP1.4 | Highlight

The seismogenic zones of an M2.0-5.5 earthquakes successfully recovered in deep South African gold mines: the outcomes and the follow-up plan

Hiroshi Ogasawara, Bennie Liebenberg, Yasuo Yabe, Yuki Yokoyama, Tetsuro Hirono, Devan M. Nisson, Tullis C. Onstott, Thomas L. Kieft, Esta van Heerden, Thomas Wiersberg, Taku Noda, Musa S.D. Manzi, Siyanda B. Mngadi, Raymond J. Durrheim, Yuhji Yamamaoto, Takatoshi Ito, Akio Funato, Martin Ziegler, James J. Mori, and Carsten Dinske and the The ICDP DSeis team

This paper reports on the outcomes of the ICDP drilling into seismogenic zones of M2.0-5.5 earthquakes in South African (SA) gold mines (DSeis; 2017-2018), the follow-up work in 2019, and planned post-drilling activity from 2020 onwards.

In deep SA gold mines, seismogenic zones evolve ahead of thin tabular excavations. Normal faulting prevails because mining enhances the vertical maximum principal stress. At 1km depth at the Cooke 4 mine, we elucidated the evolution of the seismogenic zone with a dense acoustic emission network. In 2017, we successfully recovered both the metasedimentary host rock (mainly quartzite ~2.8 Ga) and samples of the seismogenic zone with well-preserved fracture systems using a triple-tube (BQ 1.5m-long). Subsequent laboratory work investigated critical characteristics of rock-rock friction.

In 2014, an M5.5 earthquake, the largest in deep South African gold mining districts, took place. Dense seismic networks, both on the Earth’s surface and at 2-3 km depth, showed that this event was atypical because it was a sinistral event on an unknown geological structure below the mining horizon in West Rand Group strata (~2.9 Ga). Inversion and back-projection of the ground motion showed complicated but unilateral rupture propagation. The densest population of aftershocks shows a sharp upper cut-off and streaks, both dipping to the south.  Its centroid lies outside the significant main rupture zone. In 2017, we commenced drilling at a site at 2.9km depth in a tension quadrant of the sinistral faulting, several hundreds of meters above the upper fringe of the M5.5 aftershock plane. During 2017-2018, we drilled holes, of a total length of 1.6 km. With a 1.5m NQ triple-tube for the critical section, we could recover the fault materials and the host rock with the seismic fracture system well preserved. Borehole logging and core curation in SA and laboratory work at international organizations, including Kochi Core Center Japan (KCC), followed during 2017-2019. With the geology data mapped on the mining horizons and the legacy seismic reflection data as additional information, the following picture is emerging: (a) transition of the stress regime from normal-faulting to sinistral-faulting; (b) stress localization; (c) heterogeneity in the aftershock distribution as well as the segregation between the main rupture and aftershocks, potentially correlated with significant heterogeneity in mechanical properties; (d) a role of an altered lamprophyre dike; (e) hypersaline brine with salinity even higher than measurements at other deep gold mines, potentially as old as brine found at Kidd Creek mine, Canada; and (f) abiogenic gas and organic carbon.

These data sets allow us to address questions in earthquake and deep-life sciences raised in the ICDP Science Plan (2014-2019). In 2019, the ICDP Executive Committee described DSeis as a ‘successful’ project. To integrate and discuss the outcomes in greater depth and plan additional follow-up work, we are planning a post-drilling workshop in November 2020 or January 2021 at KCC before we return the imported critical section of the core to South Africa.

How to cite: Ogasawara, H., Liebenberg, B., Yabe, Y., Yokoyama, Y., Hirono, T., Nisson, D. M., Onstott, T. C., Kieft, T. L., van Heerden, E., Wiersberg, T., Noda, T., Manzi, M. S. D., Mngadi, S. B., Durrheim, R. J., Yamamaoto, Y., Ito, T., Funato, A., Ziegler, M., Mori, J. J., and Dinske, C. and the The ICDP DSeis team: The seismogenic zones of an M2.0-5.5 earthquakes successfully recovered in deep South African gold mines: the outcomes and the follow-up plan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12094, https://doi.org/10.5194/egusphere-egu2020-12094, 2020.

EGU2020-4886 | Displays | SSP1.4 | Highlight

Towards a Continuous Cenozoic Arctic Climate Record - A Challenge for IODP Expedition 377 in 2021

Ruediger Stein, Estella Weigelt, Frank Niessen, and Kristen St. John

Although the Arctic Ocean is a major player in the global climate/earth system, this region is one of the last major physiographic provinces on Earth where the short- and long-term geological history is still poorly known. This lack in knowledge is mainly due to the major technological/logistical problems in operating within the permanently ice-covered Arctic region which makes it difficult to retrieve long and undisturbed sediment cores. Continuous central Arctic Ocean sedimentary records, allowing a development of chronologic sequences of climate and environmental change through Cenozoic times and a comparison with global climate records, however, were missing prior to the IODP Expedition 302 (Arctic Ocean Coring Expedition – ACEX), the first scientific drilling in the central Arctic Ocean in 2004. By studying the unique ACEX sequence, a large number of scientific discoveries that describe previously unknown Arctic paleo-environments, were obtained during the last 15 years (for most recent review and references see Stein, 2019a). While these results from ACEX were unprecedented, key questions related to the climate history of the Arctic Ocean remain unanswered, in part because of poor core recovery, and in part because of the possible presence of a major mid-Cenozoic hiatus or interval of starved sedimentation within the ACEX record. Following-up ACEX and its cutting-edge science, a second scientific drilling on Lomonosov Ridge with a focus on the reconstruction of the continuous and complete Cenozoic Arctic Ocean climate history, has been proposed and now scheduled as IODP Expedition 377 "Arctic Ocean Paleoceanography - ArcOP") for late summer/early autumn 2021. Based on new seismic and coring data obtained during Polarstern Expedition PS87 in 2014 (Stein, 2015) and Polarstern Expedition PS115/2 in 2018 (Stein, 2019b), several locations for potential drill sites have been proposed and further optimized. At the primary drill site location, about 230 m of Plio-Pleistocene, 460 m of Miocene, and >200 m of Oligocene-Eocene may be recovered. These new detailed climate records spanning time intervals from the Paleogene Greenhouse world to the Neogene-Quaternary Icehouse world will give new insights into our understanding of the Arctic Ocean within the global climate system and provide an opportunity to test the performance of climate models used to predict future climate change. Within this presentation an update of the primary objectives and the drilling strategy of ArcOP Expedition 377 will be outlined. For further details as well as the drilling proposal we refer to http://www.ecord.org/expedition377/ .

 

Reference:

Stein, R. (Ed.), 2015. Cruise Report of Expedition PS115/2 of the Research Vessel POLARSTERN to the Arctic Ocean in 2014 (http://epic.awi.de/37728/1/BzPM_0688_2015.pdf).

Stein, R. (Ed.), 2019b. Cruise Report of Expedition PS115/2 of the Research Vessel POLARSTERN to the Arctic Ocean in 2018. (https://epic.awi.de/id/eprint/49226/1/BzPM_0728_2019.pdf ).

Stein, R., 2019a. The late Mesozoic-Cenozoic Arctic Ocean climate and sea ice history: A challenge for past and future scientific ocean drilling. Paleoceanography & Paleoclimatology, ,  https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018PA003433

How to cite: Stein, R., Weigelt, E., Niessen, F., and St. John, K.: Towards a Continuous Cenozoic Arctic Climate Record - A Challenge for IODP Expedition 377 in 2021, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4886, https://doi.org/10.5194/egusphere-egu2020-4886, 2020.

EGU2020-13955 | Displays | SSP1.4

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden

Felix Kästner, Simona Pierdominici, Judith Elger, Christian Berndt, Alba Zappone, Jochem Kück, and Anja Maria Schleicher

Deeply rooted thrust zones are key features of tectonic processes and the evolution of mountain belts. Exhumed and deeply-eroded orogens like the Scandinavian Caledonides allow to study such systems from the surface. Previous seismic investigations of the Seve Nappe Complex have shown indications for a strong but discontinuous reflectivity of this thrust zone, which is only poorly understood. The correlation of seismic properties measured on borehole cores with surface seismic data can help to constrain the origin of this reflectivity. In this study, we compare seismic velocities measured on cores to in situ velocities measured in the borehole. The core and downhole velocities deviate by up to 2 km/s. However, velocities of mafic rocks are generally in close agreement. Seismic anisotropy increases from about 5 to 26 % at depth, indicating a transition from gneissic to schistose foliation. Differences in the core and downhole velocities are most likely the result of microcracks due to depressurization of the cores. Thus, seismic velocity can help to identify mafic rocks on different scales whereas the velocity signature of other lithologies is obscured in core-derived velocities. Metamorphic foliation on the other hand has a clear expression in seismic anisotropy. To further constrain the effects of mineral composition, microstructure and deformation on the measured seismic anisotropy, we conducted additional microscopic investigations on selected core samples. These analyses using electron-based microscopy and X-ray powder diffractometry indicate that the anisotropy is strongest for mica schists followed by amphibole-rich units. This also emphasizes that seismic velocity and anisotropy are of complementary importance to better distinguish the present lithological units. Our results will aid in the evaluation of core-derived seismic properties of high-grade metamorphic rocks at the COSC-1 borehole and elsewhere.

How to cite: Kästner, F., Pierdominici, S., Elger, J., Berndt, C., Zappone, A., Kück, J., and Schleicher, A. M.: Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13955, https://doi.org/10.5194/egusphere-egu2020-13955, 2020.

EGU2020-22367 | Displays | SSP1.4 | Highlight

Investigating the Dynamics of the Pacific Antarctic Circumpolar Current – Initial Results from International Ocean Discovery Program Expedition 383 (DYNAPACC)

Frank Lamy, Gisela Winckler, Carlos Zarikian, and Expedition 383 Scientists

The Antarctic Circumpolar Current (ACC) is the world’s strongest zonal current system that connects all three major basins of the global ocean, and therefore integrates, forces and responds to global climate variability. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, the Pacific sector of the ACC lacks information on its Cenozoic paleoceanography from deep-sea drilling records.

To advance our knowledge and understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, IODP Expedition 383 recovered sedimentary sequences at: (1) Three sites located in the central South Pacific (Sites U1539, U1540 and U1541); (2) two sites at the Chilean Margin (U1542, U1544); and (3) one site from the hemipelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Age control based on magneto and bio-stratigraphically constrained orbital tuning of physical properties in the Plio-Pleistocene sediments is remarkable, with Sites U1541 and U1543 extending the record back to the late Miocene, and Site U1540 to the earliest Pliocene. Pleistocene sedimentary sequences with high sedimentation rates in the order of 40 cm/kyr were drilled in the Central South Pacific (U1539) and along the Chilean Margin. Taken together, the sites represent a depth transect from ~1100 m at the Chilean margin (U1542) to ~4070 m in the Central South Pacific (U1539), and allow reconstructing changes in the vertical structure of the ACC – a key issue for understanding the role of the Southern Ocean in the global carbon cycle- to be investigated. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic, carbonate, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep ocean variations and their relation to atmosphere and cryosphere changes through stadial-to-interstadial, glacial-to-interglacial and warmer than present time intervals.

How to cite: Lamy, F., Winckler, G., Zarikian, C., and 383 Scientists, E.: Investigating the Dynamics of the Pacific Antarctic Circumpolar Current – Initial Results from International Ocean Discovery Program Expedition 383 (DYNAPACC), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22367, https://doi.org/10.5194/egusphere-egu2020-22367, 2020.

In Early Cretaceous, Shahezi Formation developed in syn-rift stage which belongs to the deep strata of the Songliao Basin, China. Due to the poor outcrop development, there is no previous study or report on the provenance of detrital zircons from Shahezi Formation before. The Songke 2 well is a part of Songliao Basin drilling project which belongs to the International Continental Scientific Drilling Projects (ICDP). The conduct of this scientific drilling is to obtain a nearly complete Cretaceous terrestrial sedimentary record, as determined from basin-filling history. Therefore, this research will focus on the sample from Songke 2 well. This study based on continuous and complete sampling which are unique research materials. What’s more, Songliao Basin is one of the largest continental sedimentary basins in the world, which holds the most important reserves of Chinese oil and natural gas. Consequently, this study is a kind of significance for oil and natural gas prospects of deep strata in Songliao Basin.

Through the detailed description about cores, fan delta facies and lacustrine facies can be identified in this study. Also, the detailed information and sedimentary environment at Early Cretaceous can be clarified. The upper member of Shahezi formation shows the characteristics of fan delta facies intersecting shore-shallow lakes, reflecting the multistage cyclicity changes under the sufficient source supply during the syn-rift stage. In order to define the provenance of the upper member of Shahezi Formation in the north-central area of the Songliao Basin, five sandstone sample (DZ01~05) of the upper member of Shahezi Formation were continuous sampling from Songke 2 well. U-Pb dating was performed on detrital zircons separated from the five sandstone samples. Detrital zircons from DZ01 to DZ05 has dominant ages of 105~140 Ma (268 grains), 155~200 Ma (160 grains), and 220~260 Ma (44 grains). This paper demonstrates that the provenance of the upper member of Shahezi Formation is came from the Central Great Xing’an Range. The depositional period of the Shahezi Formation constraints of maximum sedimentary age and reached to 111-115 Ma. At the same time, the Great Xing’an Range also provides sediments for the western Hailar Basin, which indicates that the Great Xing’an Range uplift and denudation during this period. The closure and collision of the Mongolia-Okhotsk ocean to the north and Pacific Plate subduction beneath the Asian continent to the east were the major tectonic events affecting the tectonic environment of the Great Xing’an Range.

How to cite: An, D.: Early Cretaceous (Aptian) provenance and tectonic response in Songliao Basin, NE China: Evidence from detrital zircon U-Pb ages from the Shahezi Formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5621, https://doi.org/10.5194/egusphere-egu2020-5621, 2020.

EGU2020-7686 | Displays | SSP1.4

Uncharted archives – imprints of tsunami backwash deposits on the Algarve shelf (Portugal)

Piero Bellanova, Klaus Reicherter, Pedro J.M. Costa, Mike Frenken, Lisa Feist, Jan Schwarzbauer, Juan I. Santisteban, Andreas Vött, Ivana Bosnic, Helmut Brückner, Holger Schüttrumpf, César Andrade, João F Duarte, Jannis Kuhlmann, and the M152 scientfic Team

Research on offshore tsunami deposits is scarce and their depositional processes and preservation potential are virtually unexplored. Therefore, the RV Meteor cruise M152 mapped and sampled one coast-parallel and two coast-perpendicular transects at water depths from 65 to 114 m off the Algarve coast (Portugal). This coast was strongly affected by the well-known Lisbon earthquake and tsunami of November 1st, 1755 AD. Numerous onshore locations have been well documented and studied with historic damage reports and modern scientific investigations of the onshore tsunami deposits. However, very scarce information about the backwash, the water masses flowing back into the sea, exists and their imprint on the shelf is unexplored.

In order to fill this gap, a total of 19 vibracores were recovered during the RV Meteor cruise M152. For tracing the sedimentary imprint of the AD 1755 tsunami and potential predecessors, a multi-proxy analysis was carried out (sedimentology, micropaleontology, inorganic and organic geochemistry, radiocarbon and OSL dating). Within the offshore Holocene stratigraphic record, at least two event layers of likely tsunami backwash origin were identified based on their significantly different properties compared to the background shelf sediments. The uppermost tsunami layer (at a depth of 16-25 cm in most cores) displays an erosional contact at the base with heterogeneous compositional changes; its bounding radiocarbon ages allow a correlation with the AD 1755 Lisbon tsunami. Organic-geochemical markers, such as n-alkanes, polycyclic aromatic hydrocarbons, steroids and fatty acids, show an increased input of terrestrial matter in this offshore AD 1755 event layer.

A surprising discovery was another distinct high-energy deposit, i.e. a potential predecessor to the AD 1755 Lisbon tsunami, at a core depth of about 122-155 cm, which was 14C-dated to approx. 3700 yrs cal BP. Due to its erosional base and coarse-grained composition (well-sorted medium sand), as well as the increased terrestrial influence (displayed by biomarkers), it can be assumed that this deposit originates from the backwash of a paleo-tsunami.

This multi-proxy approach with sedimentological, micropaleontological, inorganic and organic-geochemical criteria, enabled us to (1) identify of backwash tsunami deposits; (2) establish a recurrence interval; and (3) estimate the hazard potential for the related coastal areas. Results of the M152 cruise demonstrate for the first time that the depositional basins on the Algarve shelf have the potential to reliably archive Holocene tsunami backwash deposits. The low-energy environment of the outer Algarve shelf sets prime conditions for the preservation of tsunami backwash deposits. Thus, these geoarchives offer the possibility to study the mechanisms and hydrodynamics of backwash currents, and to investigate tsunami strata that are not preserved elsewhere.

How to cite: Bellanova, P., Reicherter, K., Costa, P. J. M., Frenken, M., Feist, L., Schwarzbauer, J., Santisteban, J. I., Vött, A., Bosnic, I., Brückner, H., Schüttrumpf, H., Andrade, C., Duarte, J. F., Kuhlmann, J., and M152 scientfic Team, T.: Uncharted archives – imprints of tsunami backwash deposits on the Algarve shelf (Portugal), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7686, https://doi.org/10.5194/egusphere-egu2020-7686, 2020.

EGU2020-20571 | Displays | SSP1.4

Planning a drilling campaign in a petroleum province using high resolution 3D seismic data – IODP proposal 909

David Cox, Andrew M. W. Newton, Paul C. Knutz, and Mads Huuse

A drilling hazard assessment has been completed for a large area of the NW Greenland-Baffin Bay continental shelf. This assessment was in relation to International Ocean Discovery Program (IODP) proposal 909 that aims to drill several sites across the shelf in an attempt to better understand the evolution and variability of the northern Greenland Ice Sheet. The assessment utilised high quality and extensive 3D seismic data that were acquired during recent hydrocarbon exploration interest in the area – a fact that highlights the risk of drilling in a petroleum province and therefore, the importance of this assessment with regards to safety.

Scattered seismic anomalies are observed within the Cenozoic sedimentary succession covering the rift basins of the Melville Bay region. These features, potentially representing the presence of free gas or gas-rich fluids, vary in nature from isolated anomalies, fault flags, stacked fluid flow features and canyons; all of which pose a significant drilling risk and were actively avoided during site selection. In areas above the Melville Bay Ridge – a feature that dominates the structure of this area – free gas is also observed trapped beneath extensive gas hydrate deposits, identified via a spectacularly imaged bottom simulating reflector marking the base of the gas hydrate stability zone. The location of the hydrate deposits, and the free gas beneath, are likely controlled by a complicated migration history, due to large scale rift-related faulting and migration along sandy aquifer horizons. In other areas, gas is interpreted to have reached the shallow subsurface due to secondary leakage from a deeper gas reservoir on the ridge crest.

It is clear that hydrocarbon related hazards within this area are varied and abundant, making it a more challenging location to select sites for an IODP drilling campaign. However, due to the extensive coverage and high resolution (up to 11 m vertical resolution (45 Hz at 2.0 km/s velocity) of the 3D seismic data available, as well as the use of recently acquired ultra-high resolution site survey lines, these features can be accurately imaged and confidently mapped. This allowed for the development of a detailed understanding of the character and distribution of fluids within the shallow subsurface, and the use of this knowledge to select site localities that maximise the potential for drilling to be completed safely and successfully if proposal 909 were to be executed.

How to cite: Cox, D., Newton, A. M. W., Knutz, P. C., and Huuse, M.: Planning a drilling campaign in a petroleum province using high resolution 3D seismic data – IODP proposal 909, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20571, https://doi.org/10.5194/egusphere-egu2020-20571, 2020.

EGU2020-8069 | Displays | SSP1.4

Extending Ocean Drilling Pursuits [eODP]: Making Scientific Ocean Drilling Data Accessible Through Searchable Databases

Andrew Fraass, Leah LeVay, Jocelyn Sessa, and Shanan Peters

Scientific ocean drilling through the International Ocean Discovery Program (IODP) and its predecessors, has a far-reaching legacy. They have produced vast quantities of marine data, the results of which have revolutionized many geoscience subdisciplines. Meta-analytical studies from these efforts exist for micropaleontology, paleoclimate, and marine sedimentation, and several outstanding resources have curated and made available elements of offshore drilling data (e.g., Neptune), but much of the data remain heterogeneous and dispersed. Each study, therefore, requires reassembling a synthesis of data from numerous sources; a slow, difficult process that limits reproducibility and slows the progress of hypothesis testing and generation. A computer programmatically-accessible repository of scientific ocean drilling data that spans the globe will allow for large-scale marine sedimentary geology and micropaleontologic studies and may help stimulate major advances in these fields.

The eODP project, funded through the NSF’s EarthCube program, seeks to facilitate access to, and visualization of, these large microfossil and stratigraphic datasets. To achieve these goals, eODP will be linking and enhancing the existing database structures of the Paleobiology Database (PBDB) and Macrostrat. This project is targeting shipboard drilling-derived data, but the infrastructure will be put in place to allow the addition of data generated post-cruise. eODP will accomplish the following goals: (1) enable construction of sediment-grounded and flexible age models in an environment that encompasses the deep-sea and outcrops; (2) expand existing lithology and age model construction approaches in this integrated offshore-onshore stratigraphically-focused environment; (3) adapt key microfossil data into the PBDB data model; (4) develop new API-driven web user interfaces for easily discovering and acquiring data; and (5) establish user working groups for community input and feedback. The success of eODP hinges upon interaction, feedback, and contribution of the scientific ocean drilling community, and we invite anyone interested in participating in this project to join the eODP team.

How to cite: Fraass, A., LeVay, L., Sessa, J., and Peters, S.: Extending Ocean Drilling Pursuits [eODP]: Making Scientific Ocean Drilling Data Accessible Through Searchable Databases , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8069, https://doi.org/10.5194/egusphere-egu2020-8069, 2020.

EGU2020-5089 | Displays | SSP1.4 | Highlight

More than ten years of successful operation of the MARUM-MeBo sea bed drilling technology: Highlights of recent scientific drilling campaigns

Tim Freudenthal, Gerhard Bohrmann, Karsten Gohl, Johann Philipp Klages, Michael Riedel, Klaus Wallmann, and Gerold Wefer

Over the last two decades sea bed drilling technology has proven to provide a valuable complement to the services of classical drill ships. Especially for shallow drillings up to 200 mbsf and when working in remote areas difficult to access, sea bed drill rigs are a cost-effective alternative. Recent developments especially concerning borehole logging techniques add to the capabilities of sea bed drilling technology.

The MARUM-MeBo is a robotic drilling system that is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen (Freudenthal and Wefer, 2013). The drill rig is deployed on the sea bed and remotely controlled from the vessel. It is used for core drilling in soft sediments as well as hard rocks in the deep sea. Especially since an upgrade in 2007/2008 for the use of wireline drilling technique, the first-generation drill rig MARUM-MeBo70 with a drilling capacity of about 70 m was successfully deployed on more than 15 research expeditions. Since 2014 the second-generation drill rig MARUM-MeBo200 with an increased drilling capacity of up to 200 m below sea floor is successfully in operation.

In this presentation we focus on results of three recent drilling campaigns, exemplifying the exploitation of the potential of the sea bed drilling technology:

  1. In early 2017 the MeBo70 was deployed from the ice breaking vessel RV POLARSTERN on the West Antarctic shelf (Gohl et al., 2017), an area difficult to access by a drill ship. We were able to recover a sedimentary sequence of the upper Cretaceous time period as one of the very few terrigenous records from this time in Antarctica. This sequence indicates that about 92 to 83 Mio years ago at a paleolatitude of about 82°S this area was covered by a temperate coastal rain forest, making any Antarctic ice sheet formation at this time period unlikely (Klages et al., in press).
  2. Also, in 2017 the MeBo70 was deployed in the Arctic off Svalbard. Next to coring a temperature probe was used to assess in situ temperatures and local geothermal gradients (Riedel et al. 2018). Combining these temperature data with the porewater geochemistry of the drilled cores Wallmann et al (2018) were able to prove the effect of isostatic rebound after deglaciation on gas hydrate dissociation.
  3. In late 2017 the MeBo200 was deployed in the Black Sea. Geophysical borehole log data of P-wave velocity, electrical resistivity, and spectral gamma ray were combined with core-derived physical properties of porosity, magnetic susceptibility, and bulk density and compared with seismic data of the region (Riedel et al., in press). This study shows the potential of core-log seismic integration for shallow drilling campaigns conducted with a sea bed drill rig.

References:

Freudenthal, T and Wefer, G (2013) Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-2013

Gohl, K, et al. (2017) Geochemistry, Geophysics, Geosystems, 18, 4235–4250. https://doi.org/10.1002/2017GC007081

Klages, JP et al. (in press) Nature, 2019-10-14805B

Riedel, M et al. (2018) Geochemistry, Geophysics, Geosystems, 19, 1165–1177. doi:10.1002/2017GC007288

Riedel, M et al. (in press) Marine and Petroleum Geology, doi.org/10.1016/j.marpetgeo.2019.104192

Wallmann, K et al. (2018) Nature Communications, 9:83, DOI: 10.1038/s41467-017-02550-9

 

How to cite: Freudenthal, T., Bohrmann, G., Gohl, K., Klages, J. P., Riedel, M., Wallmann, K., and Wefer, G.: More than ten years of successful operation of the MARUM-MeBo sea bed drilling technology: Highlights of recent scientific drilling campaigns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5089, https://doi.org/10.5194/egusphere-egu2020-5089, 2020.

EGU2020-13070 | Displays | SSP1.4

Lake Constance sediments recovered using novel piston coring system

Ulrich Harms, Ulli Raschke, Antje Schwalb, and Volker Wittig

Key archives in environmental and past climate research are buried in soft sediment but investigations are often hampered by the lack of continuous, complete and undisturbed samples. We have developed the new core-drilling instrument Hipercorig to overcome these issues and we have tested this tool successfully on the perialpine Lakes Mondsee and Constance at up to 204 m water depths and down to 64 m core length.

Hipercorig comprises a hydraulically hammered down-the-hole piston coring system capable to reach up to 100 m core length in up to 200 m water depths. The well-proven piston system ensures high-quality intact cores while the hydraulic hammer drive allows penetrating hard-layers such as sand, gravel or tephra. The piston-hammer system, casing string and ground plate is connected via Kevlar ropes to a coring rig and deployment is controlled via underwater cameras. For lake, estuarine and shallow marine projects buoyance and working space is provided through a barge with four anchors and winches. The complete system is consisting of modular elements to be shipped in four 20-foot-containers including two boats and outboard motors. Hipercorig allows for about 10 m rate of penetration per shift and produces 7.5 cm cores in 2 m long core runs.

A first deployment on Lake Mondsee to initially test and modify Hipercorig recovered 64 m sediment core from glacial tills. A follow on shake-down cruise on Lake Constance served as deep-water trial and to sample so far unearthed pre-Holocene strata below about 12 m sediment depth. Coring was performed in summer 2019 in 204 m water depth, 2 km SSW of Hagnau, Germany. The site is located close to the deepest part of this basin with best possible preservation of a continuous and undisturbed depositional record. Two sediment cores of 24 and 20.5 mblf were retrieved and complemented by three 2-m-long surface cores. The uppermost 11 m of sediments consist of Holocene lacustrine clays with increasing intercalations of silt, while late Quaternary glacial sands dominate below 11 m. The piston coring device was modified to allow for penetrating these rigid sand layers, but the sands slowed down core recovery and caused core loss of ~15 cm at the end of each core run but overlapping coring was used to compensate the loss. While samples for microbiology have been taken immediately, core opening, description, and sampling will be performed at Bern University, Switzerland, in October 2019.

Currently Hipercorig receives final upgrades for safety and flexibility so that the whole system will be available from spring 2020 on for scientific coring projects on a non-for-profit base to teams with funded research projects. They will have to raise transport and operations costs as well as a maintenance fee that will serve to sustain the tool. The German Scientific Earth Probing Consortium GESEP will provide an oversight board to prioritize projects and support projects in implementation.

How to cite: Harms, U., Raschke, U., Schwalb, A., and Wittig, V.: Lake Constance sediments recovered using novel piston coring system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13070, https://doi.org/10.5194/egusphere-egu2020-13070, 2020.

EGU2020-4270 | Displays | SSP1.4

Preliminary report on the sedimentary record of SCORE Site C9035 of Tokai, Nankai Trough, southwest Japan

Kan-Hsi Hsiung, Toshiya Kanamatsu, Ken Ikehara, Io Miura, Juichiro Ashi, Shuichi Kodaira, Kohsaku Arai, Natsumi Okutsu, and Kan Aoike

Chikyu Shallow Core Program (SCORE) is a short and shallow ocean drilling program arranged by Japan Drilling Earth Science Consortium (J-DESC), Japan. SCORE provides opportunities for scientific ocean drilling test and project which can complete in a short period of time by using the ocean drilling vessel D/V Chikyu except for IODP expedition period. The title of this project is “Enigmatic recurrence pattern of Tokai earthquake in Nankai Trough, southwest Japan: the link between great earthquakes and ridge subduction”. The objective of our program is to investigate the past earthquake occurrence from a continuous sedimentary sequence at a local tectonic basin (i.e., Kanasunose Trough) in Nankai Trough. The target of this drilling program is to find an enigmatic recurrence pattern of Tokai earthquake in Nankai Trough, southwest Japan. Hydraulic Piston Coring System (HPCS) of the ocean drilling vessel (D/V) Chikyu can provide an opportunity to obtain an excellent long and continuous sedimentary record to unravel the earthquake recurrence pattern of this study area.

 

Expedition 912 was conducted by D/V Chikyu sailing from Shimizu to Sasebo, Japan from 4 January - 15 January 2020. The Leg 1 of Expedition 912 was cored Hole A and B in Site C9035 which are located in 34°05.7’N, 138°08.03’E with 2442 meters of water depth in the Kanasunose Trough, Tokai, Nankai Trough. The Penetration depth at site C9035 is 80.19 meters with HPCS drilled from 5 January to 8 January 2020. The thickness of Hole C9035A sediments was 9.5 m with a recovery of 105%. The thickness of cored sediments was 80.19 meters at Hole C9035B, with a recovery of 104.7%. The shipboard measurements of whole-round core samples involved X-ray CT scan and Physical properties. After splitting, the visual core description (VCD), smear slides, split surface image, Natural Remanent Magnetisation (NRM), penetration strength, and moisture and density (MAD) measurements, and Vane shear test were conducted.

 

The sedimentary succession is dominated by silty sediments with numerous coarse-grained (coarse silt–very fine sand) layers and some volcanic ash layers and spots. Two lithological units (Unit I and II) can be distinguished on the basis of sedimentary facies. Unit I consists of bioturbated silt and layered coarse silt–very fine sand with massive silt. Three ashes can be founded in Unit I and will provide good age control. Unit II is characterized by matrix-supported gravelly mud–muddy gravel and angular mudstone gravel. After measurements, the extended work of the recurrence intervals of seismo-turbidite in geological time will be built to stimulate the link between great earthquakes and ridge subduction.

How to cite: Hsiung, K.-H., Kanamatsu, T., Ikehara, K., Miura, I., Ashi, J., Kodaira, S., Arai, K., Okutsu, N., and Aoike, K.: Preliminary report on the sedimentary record of SCORE Site C9035 of Tokai, Nankai Trough, southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4270, https://doi.org/10.5194/egusphere-egu2020-4270, 2020.

EGU2020-4219 | Displays | SSP1.4

Rift propagation north of Iceland: A case of asymmetric plume - rift interaction?

Hans Christian Larsen, Anett Blischke, and Bryndís Brandsdóttir and the IODP Proposal 976-Pre working group

Drilling by the Ocean drilling Program (ODP Legs 104, 152, 163) and geophysical studies have inferred a widespread and strong influence by the Iceland plume on the structure of the ~2500 km long volcanic rifted margins that formed between East Greenland and NW Europe during continental breakupat  ~56-54 Ma. A persistent, but spatially much reduced impact by the plume on crustal structure is evident along the ~250 km Greenland-Iceland-Faeroe ridge (GIFR). Spreading south of the GIFR has remained comparatively stable along the Reykjanes Ridge (RR). By contrast, spreading between the GIFR and northwards to the Jan Mayen Fracture Zone (JMFZ) involved northward rift propagation (~50-25 Ma) away from the Iceland plume and into the East Greenland margin. This was paired with a northward retreat of the initial spreading axis (Aegir ridge (AER)) further to the east. Slivers of the East Greenland continental crust topped by continental plateau basalts extruded during initial breakup were torn off by this northward rift propagation, and form segments of the Jan Mayen microcontinent (JMMC). Rift propagation resulted in the formation of the Iceland Plateau (IP) underlain by anomalously thick and shallow oceanic crust. The striking asymmetry in plate kinematics and crustal structures south and north of Iceland seems associated with a less enriched mantle source feeding the spreading system north of Iceland. This suggests a potentially long-lived north-south asymmetry in the composition and dynamics of the plume that, if confirmed, will favor the existence of distinctly different mantle reservoirs rather than a mixing (entrainment) process followed by a compositional de-convolution process during decompression melting and melt distribution. IODP proposal 976-Pre will address these topics by investigating the temporal and compositional development of the crust of the IP, as well as the transition from rift propagation by the IP rift (IPR) into the present day Kolbeinsey ridge (KR). Drilling will sample 2-3 stages of four IPR propagation stages we have mapped, the transition from the IPR to KR spreading, rifting and timing of transpressive movements along the pseudo-transform zone that linked the propagating IPR to the retreating AER. One drill site hopefully will establish the stratigraphic relationship between the JMMC basalts and the East Greenland plateau basalts. Sediment cover at the drill sites will constrain subsidence history and the paleo-environmental evolution of the high-latitude north-east Atlantic and its connectivity to the global ocean.The proposed drilling addresses long-standing ocean drilling themes of continental breakup, rift propagation, mantle plume reservoirs and structure, and north Atlantic paleoceanography.

How to cite: Larsen, H. C., Blischke, A., and Brandsdóttir, B. and the IODP Proposal 976-Pre working group: Rift propagation north of Iceland: A case of asymmetric plume - rift interaction?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4219, https://doi.org/10.5194/egusphere-egu2020-4219, 2020.

EGU2020-19204 | Displays | SSP1.4

Indian subcontinent hydroclimate and vegetation changes during the last glacial reconstructed by leaf wax stable isotope and pollen analyses on sediments from IODP Site U1446, NW Bay of Bengal

Stefan Lauterbach, Nils Andersen, Charlotte Clément, Stéphanie Desprat, Coralie Zorzi, Krishnamurthy Anupama, Srinivasan Prasad, Dulce Oliveira, Thomas Blanz, Kaustubh Thirumalai, Steven C. Clemens, Philippe Martinez, and Ralph R. Schneider

Understanding past variability and forcing mechanisms of the Asian monsoon system is of key importance for better forecasting its behaviour under future global warming scenarios and how this may affect modern societies and economies. So far, knowledge about long-term monsoon variability in mainland Asia is mainly based on proxy records from Chinese speleothems, primarily recording changes of the East Asian Summer Monsoon (EASM). These records have provided evidence for orbital-scale monsoon variability, driven by Northern Hemisphere summer insolation changes, but also for centennial- to millennial-scale reductions in monsoon precipitation. These so-called Weak Monsoon Intervals (WMIs) occurred synchronously to cold intervals in the North Atlantic realm, e.g. during Heinrich Events, pointing at a close hemisphere-scale climatic teleconnection between the North Atlantic and Asia. However, the exact mechanisms that control short-term monsoon variability are still elusive. Moreover, long-term palaeomonsoon proxy records from the core zone of the Indian Summer Monsoon (ISM) are still relatively scarce compared to those from the EASM realm. To identify possible short-term changes in ISM intensity and reconstruct related hydroclimate and vegetation changes on the Indian subcontinent during the interval ~6–74 ka BP, sediments from IODP Site U1446 in the NW Bay of Bengal have been analysed. This site, being located within the reach of the Mahanadi River, is characterized by high riverine input of terrestrial organic matter and thus ideal for high-resolution analyses of pollen content and the stable hydrogen (δD) and carbon (δ13C) isotope composition of n-alkanes from terrestrial plant leaf waxes. Here we present preliminary results of δD and δ13C analyses on odd-numbered long-chain n-alkanes (n-C27 to n-C33,) extracted from the IODP Site U1446 sediments. These indicate several reductions in ISM precipitation during the last glacial, which occurred parallel to cold events in the North Atlantic realm, e.g. during Heinrich events H1, H2, H4, H5 and H6. In combination with pollen and alkenone-based (UK’37) sea surface temperature data from the same sediments, we aim at (1) providing a comprehensive and high-resolution reconstruction of past ISM variability and associated vegetation changes on the Indian subcontinent and (2) understanding the trigger mechanisms of centennial- to millennial-scale WMIs, particularly in relation to changes in Indian Ocean oceanography.

How to cite: Lauterbach, S., Andersen, N., Clément, C., Desprat, S., Zorzi, C., Anupama, K., Prasad, S., Oliveira, D., Blanz, T., Thirumalai, K., Clemens, S. C., Martinez, P., and Schneider, R. R.: Indian subcontinent hydroclimate and vegetation changes during the last glacial reconstructed by leaf wax stable isotope and pollen analyses on sediments from IODP Site U1446, NW Bay of Bengal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19204, https://doi.org/10.5194/egusphere-egu2020-19204, 2020.

EGU2020-10110 | Displays | SSP1.4

Drilling the Tore seamount- Archive of a natural oceanic sediment trap

Susana M. Lebreiro, Silvia Nave, Laura Antón, Elizabeth Michel, Catherine Kissel, Claire Waelbroeck, Nick McCave, David Hodell, Jose-Abel Flores, Francisca Martinez-Ruiz, Belén Martrat, Cristina Roque, Alex Piotrowski, Luke Skinner, Francisco Sierro, Pedro Terrinha, Guy Cornen, María Isabel Reguera, Rocío Lozano-Luz, and Natalia Bravo

Located 300 km off West Iberia in the open NE Atlantic Ocean, the Tore seamount emerges from the 5.5 km surrounding abyssal plains to a summit rim at 2.2 km, which has an elliptical crater-like shape with a central depression 100 km in diameter. The ~5.5 km depth of the Tore internal basin is connected to the surrounding deep ocean basin by a single narrow gateway down to 4.3 km depth. This basin is exceptional because it is 1) a giant sediment-trap for vertical fluxes, with sediments unaffected by deep currents and erosion, containing a record of enhanced biogenic subtropical productivity during deglaciations, which can be examined mechanistically, 2) a natural laboratory to examine carbonate dissolution at 5.5 km water depth constrained by NADW deep ventilation during glacials, and 3) an excellent location to test sediment processes distant from continental margins and understand triggering mechanisms of downslope flows in the open, deep ocean. Not many cores have been recovered in the area at such 5.5 km depth and unite this singular environment. At the larger scale of North Atlantic circulation and productivity, the semi-isolated Tore seamount is a most valuable site to assess crucial scientific hypotheses related to thermohaline circulation, carbon cycling and climate variability. These challenging questions are framed in the IODP Initial Science Plan illuminating Earth´s Past, Present and Future, 2013-2023, theme Climate and Ocean Change.

Our APL applies for drilling one site in the middle of the Tore seamount at 5.5 km depth, to retrieve a complete Quaternary sedimentary sequence (180 m long). This carbonate rich archive will be compared with records available in the Northeast Atlantic and to be recovered during Expedition #771-Full2 (Hodell et al.).

We present results from a 24 long giant Calypso core taken in the APL-site proposed which covers 430 thousand years and 5 glacial-interglacial cycles (Spanish project “TORE5deglaciations”, CTM2017-84113-R, 2018-2020).

How to cite: Lebreiro, S. M., Nave, S., Antón, L., Michel, E., Kissel, C., Waelbroeck, C., McCave, N., Hodell, D., Flores, J.-A., Martinez-Ruiz, F., Martrat, B., Roque, C., Piotrowski, A., Skinner, L., Sierro, F., Terrinha, P., Cornen, G., Reguera, M. I., Lozano-Luz, R., and Bravo, N.: Drilling the Tore seamount- Archive of a natural oceanic sediment trap, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10110, https://doi.org/10.5194/egusphere-egu2020-10110, 2020.

EGU2020-2475 | Displays | SSP1.4

Evidence for polar surface-water incursions into the Gulf of Cadiz (SW Iberia) during the Early-to-Mid Pleistocene Transition

Aline Mega, Emilia Salgueiro, and Antje Helga Luise Voelker

The Mid Pleistocene Transition (MPT) was a global climatic event characterized by a drastic change in the deep thermohaline circulation during the glacial periods that resulted in more intense and longer lasting cold periods and cooler sea-surface temperature (SST). These changes might be linked to the atmospheric pCO2 reduction which in turn led to colder atmospheric temperatures and the expansion of continental ice sheets. In the mid-latitude North Atlantic, high-resolution records documenting the MPT's impact are still limited. Thus, this study's objective is to contribute to the knowledge by reconstructing circulation changes in the subtropical gyre realm off the southwestern Iberian Margin.  We use planktonic foraminifera faunal data from Integrated Ocean Drilling Program (IODP) Site U1387 (Faro Drift, Gulf of Cadiz) to characterize centennial-scale SST variations during the interval from Marine Isotope Stage (MIS) 18 to MIS 28. The results indicate relative stable SSTs during the interglacial and interstadial periods with temperatures around 20°C during summer and 16°C during winter. During MIS 20, 22, 24, and 25 short-termed extreme cold events were recorded when winter temperatures dropped below 5°C, during late MIS 22 even close to 0°C. They mark the terminal stadial events during deglaciation and were related to increased abundance of polar planktonic foraminifera species N. pachyderma that reached values near to 80%. N. pachyderma values. Percentages of that species between 90 and 50% can be found in the polar regions near the Arctic Front and those between 50 and 5% are indicative of subarctic waters. Whereas the terminal stadial events and the first stadial phase of MIS 22 were marked by incursions of polar surface waters to the southern Iberian margin, abrupt cold events during periods of continental ice shield growth of MIS 19, 21, 25 and 28 were associated with subarctic surface waters. During the MPT, the waters off southern Iberia, therefore, experienced cooling events more extreme than during the last glacial cycle.

How to cite: Mega, A., Salgueiro, E., and Voelker, A. H. L.: Evidence for polar surface-water incursions into the Gulf of Cadiz (SW Iberia) during the Early-to-Mid Pleistocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2475, https://doi.org/10.5194/egusphere-egu2020-2475, 2020.

EGU2020-5452 | Displays | SSP1.4

Serpentinite mud volcanism and exhumation of fore arc- and lower plate material in the Mariana convergent margin system (IODP Expedition 366)

Walter Kurz, Irena Miladinova, Arianna V. Del Gaudio, Werner Piller, and Kurt Krenn

Serpentine seamounts located in the forearc region of a subduction zone setting represent an excellent natural laboratory for studying the geochemical processes acting along convergent plate margins and the associated natural hazards as well as the forearc structure and fault patterns. Active serpentinite mud volcanoes are currently restricted only to the Izu-Bonin-Mariana system, where old (presumably Cretaceous) oceanic lithosphere is subducting in the absence of an accretionary prism.

IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench (Yinazao, Fantangisña and Asùt Tesoru). Most of the material consists of serpentinite mud containing lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific plate. A thin cover of pelagic sediments and volcanic ash deposits underlying the mud volcanos were also recovered. Recycled materials from the subducted slab are found at all three mud volcanoes and consist of metavolcanics rocks, metamorphosed pelagic sediments including cherty limestone as well as fault rocks.

Preliminary investigation of recovered sedimentary clasts from the summit of Fantangisña Seamount revealed that they contain primary calcite veins, whereas the latest veins are composed of aragonite (CaCO₃) and barite (BaSO₄).

Recovered clasts from the flank consist mainly of ultramafic rocks with various degrees of serpentinization. The serpentinite veins consist of lizardite and chrysotile, which suggests rather low temperatures of serpentinization (below 200 °C). Petrological analysis of metabasalt clasts from the same drilling hole shows changes in the mineral composition within the different intervals of the core. The composition of clinopyroxene varies between aegirine-augite and omphacite, but augite is also present. The presence of phengite with Si content of 3.5-3.8 a.p.f.u. indicates minimum pressure of 0.7 GPa at ~250 °C.

Furthermore, providing a detailed characterization of the fluids composition and transport would allow the better constraining of the tectonic and metamorphic history as well as the physical properties of the subducting Pacific Plate. Obtaining data on that point is in progress and will be presented additionally.

How to cite: Kurz, W., Miladinova, I., Del Gaudio, A. V., Piller, W., and Krenn, K.: Serpentinite mud volcanism and exhumation of fore arc- and lower plate material in the Mariana convergent margin system (IODP Expedition 366), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5452, https://doi.org/10.5194/egusphere-egu2020-5452, 2020.

The oceanographic cruise 89 (RRS James Cook) sailed in 2013 off the Iberian margin in support of an IODP proposal centred on IODP Site 1385. JC089 collected a range of hydrographic data and recovered a set of short sediment cores. We focus on 11 of the later, sampling the hydrography of the last c.400 years along a bathymetric gradient (600-4600 m). The stable isotopes (δ18O & δ13C) for: 8 common benthic foraminifer species with varied habitat preferences, the sediment pore-water and the bottom water above the sites were measured. The geochemical data is compared to various sedimentary and micropalaeontological data. The later comprises abundances of the main benthic foraminifera species >212μm, checking for living position of the endo-fauna in Rose-Bengal stained samples and for the abundances of phytodetritus-loving species E.exigua in the >90μm for all the 0-1cm samples. The study of the planktonic foraminifer assemblages along a gradient stretching 170 km offshore confirms the major influence of the upwelling to the East. Except for the epi-benthic species C.wuellestorfi, which records the bottom water δ13C at equilibrium, all other species failed to record the δ13C of the (pore) water at the depth of their living-position. We find that G.affinis could record the δ13CDIC near equilibrium with the pore-water at a depth of c.-1cm; therefore above its living population peak. This could be explained by vertical migrations through the sediment column at sites where the supply of organic matter is pulsed. The later assumption seems supported by a reverse correlation between high relative abundances of E.exigua and that of the planktonic upwelling indicator species G.bulloides under productivity pulses corresponding to higher Δδ13C(epi-G.affinis).

The Δδ13C varies from 1.7 to 4.9‰ (n=6) across a decreasing but increasingly pulsed surface productivity gradient further away from the coast. Across this range, G.affinis is observed living at increasing depths in the sediment but always peaks in oxic sediments. The absence of G.affinis from water deeper than 3100 meters prevents Δδ13C estimates at deeper water depths. For 6 of the 11 sites where G.affinis was present C.wuellestorfi occurred only twice. The δ13C for H.elegans and C.mundulus adjusted by -1.08 and +0.25‰ respectively (this study) were used instead for the shallower sites. Off the Iberian Margin the style of seasonally fluctuating food supply could be the main factor on Δδ13C. The implication on future and long-ranging IODP-based palaeoclimatic studies is that the Δδ13C could be used to estimate the type of productivity regime back in time. In the one hand the sites mostly influenced by the main upwelling cell exhibit Δδ13C < 3‰ & correspond to less than 10% of the time spent in an oligotrophic setting below 0.2mg (chla)/m3. In the other hand Δδ13C >3‰ trace offshore rare productive surface filaments in an environment otherwise corresponding to c.90% of the time under oligotrophic surface water. The absence G.affinis (for the range of depths studied) could indicate a record sitting outside either of these productive systems' influence.

How to cite: Mleneck-Vautravers, M. and Hodell, D.: Recent Foraminifers and Stable Isotopes Records on a Bathymetric Transect off Portugal (Cruise JC089) and implications for the Palaeoxygenation proxy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7567, https://doi.org/10.5194/egusphere-egu2020-7567, 2020.

EGU2020-11898 | Displays | SSP1.4

Controls on stratigraphic variability in a semi-closed rift basin over the Late Quaternary, Gulf of Corinth, Greece

Sofia Pechlivanidou, Spyros Sergiou, Maria Geraga, Robert Gawthorpe, Dimitra Antoniou, Dimitra Angelopoulou, Mary Ford, and Natacha Fabregas

The Corinth Gulf is a semi-closed active rift basin, which alternated between marine and isolated/semi-isolated conditions as sea level fluctuated with respect to basin sills during Quaternary glacial/interglacial cycles. Results from the recent IODP Expedition 381 reveal cyclic variations of 10s-100s of kyr in sedimentation rates and basin paleoenvironment. In this study we investigate the controls on stratigraphic development of the Corinth basin during the last eustatic cycle and the Holocene based on core data from the IODP Expedition 381 Site M0079. We perform a multi-proxy analysis of the upper ~200 mbsf of core covering Marine Isotope Stages (MIS) 1-5 (i.e. last 130 kyr). Our analyses include grain size and micropaleontological (foraminifera) analyses at regular intervals (~0.5 m), Computed Tomography (CT-scanning) of selected u-channels and specific microscopic work (smear slides, SEM) on targeted samples. Our results show pronounced variability in sedimentation patterns during the isolated/semi-isolated phases compared to the marine intervals. Low density, thinly bedded and laminated muds alternating with high density homogenous mud beds and occasionally sandy, organic rich beds prevail during isolated/semi-isolated conditions. In contrast, homogenous and/or highly bioturbated successions characterize the marine sequences. The transitions from marine to isolated/semi-isolated conditions and vise-versa are often associated with authigenic carbonate deposition. Fine grained sediments (sand < 10%) dominate both the marine and the isolated sequences. Nevertheless, sandy turbidites (sand > 10%) are also present and are more often observed in the isolated phases, likely associated with climatic-driven changes in erosional processes onshore. Our analysis reveals short-lived isolated/semi-isolated sub-phases within the lower marine interval corresponding to the MIS5b and MIS5d lowstands. Short marine spikes also interrupt the isolated/semi-isolated conditions of the last glacial period indicating temporary sea level rises within MIS3. Overall, the marine intervals display significant paleoenvironmental differences although they share similar sedimentary patters. In particular, we observe more diverse palaeoceanographic conditions in the MIS5 marine sub-phases compared to the MIS1, especially regarding temperature and eutrophication levels of the water column.  

How to cite: Pechlivanidou, S., Sergiou, S., Geraga, M., Gawthorpe, R., Antoniou, D., Angelopoulou, D., Ford, M., and Fabregas, N.: Controls on stratigraphic variability in a semi-closed rift basin over the Late Quaternary, Gulf of Corinth, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11898, https://doi.org/10.5194/egusphere-egu2020-11898, 2020.

EGU2020-3407 | Displays | SSP1.4

Integration of drilling mud gas monitoring, downhole geophysical logging and drill core analysis identifies gas inflow zones in borehole COSC-1, Sweden

Simona Pierdominici, Thomas Wiersberg, Henning Lorenz, Bjarne Almqvist, and Iwona Klonowska and the COSC Science Team

The continuous wireline core drilling of the COSC-1 borehole (Jämtland, Central Sweden) offered the unique opportunity to combine data and findings from drilling mud gas monitoring, downhole geophysical logging and drill core analysis. The COSC project aims to better understand deep orogenic processes in mountain belts in a major mid-Paleozoic environment in western Scandinavia. The 2.5 km deep fully cored borehole COSC-1 was drilled in 2014 into the lower part of the Seve Nappe Complex, characterized by a thick sequence of high-grade metamorphic rocks. Here, we present results from a combination of drill mud gas monitoring with data from geophysical logging and core analysis to identify and characterize fluid-bearing open fractures during drilling of metamorphic rocks. Geophysical downhole logging is an established technique for extracting information from the underground. Online monitoring of drilling mud gas (OLGA) is also increasingly used in scientific drilling operations, but a combined interpretation of the data sets obtained with these methods has rarely been carried out in the past. Nearly complete gas records were obtained by OLGA with three meter depth resolution from 662 m to 1709 m and six meter resolution from 1709 m to 2490 m depth (COSC-1 total depth: 2496 m) for hydrogen, methane, carbon dioxide and helium by on-line drilling mud gas monitoring. Between 662 m and approx. 1550 m, both He and CH4 form broad peaks superimposed by several spike-like features. Zones with gas spikes coincide with high resistivity intervals identified by dual laterolog measurements and show fractures in optical drill core scans, borehole televiewer images, and visual core inspection. Therefore, we assume gas inflow through open fractures where deep/shallow resistivity ratios is greater than 1.5 imply the presence of free gas. The correlation between helium and deep/shallow resistivity ratios no longer appears at depths greater than 1550 m, probably because the formation gases are dissolved in formation fluids at higher pressure. 13 gas zones found in the depth interval 662 – 1550 m match with areas of higher resistivity and with open fractures identified by optical core logging. Below 1550 m depth, He drops significantly, whereas CH4 remains relatively high and H2 and CO2 reach maximum values. The high amount of hydrogen and methane at depths below 1616 m, from where friction between the casing and the drill string was reported, imply that these gases are most certainly artificially generated at depths below 1616 m and at least partly of artificial origin at shallower depths. Comparison between OLGA data and resistivity downhole logging data can help to estimate degassing depths: at depths where OLGA identified formation gases, concurrent high resistivity would be diagnostic for free gas, whereas low resistivity would imply gases dissolved in saline formation fluids.

How to cite: Pierdominici, S., Wiersberg, T., Lorenz, H., Almqvist, B., and Klonowska, I. and the COSC Science Team: Integration of drilling mud gas monitoring, downhole geophysical logging and drill core analysis identifies gas inflow zones in borehole COSC-1, Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3407, https://doi.org/10.5194/egusphere-egu2020-3407, 2020.

EGU2020-3891 | Displays | SSP1.4

Investigating glacial/interglacial cyclicity from downhole logging data and mineralogical composition: an example from the ICDP drilling project Lake Junín, Peru

Anja Schleicher, Simona Pierdominici, Christian Zeeden, Jochem Kück, Donald Rodbell, and Mark Abbott

Reconstructing the history of continental records covering the glacial-interglacial cycles was the main objective of the ICDP Lake Junín drilling project. Located at 4000 m above sea level, Lake Junín is characterized by a thick sediment package (>125 m) deposited with a sedimentation rate of 14-15 cm/kyr. In fact, the lake predates the maximum extent of glaciation, and is in a geomorphic position to record the waxing and waning of glaciers in the nearby Cordillera. Drilling was performed in 2015 at three sites and a suite of downhole logging measurements were applied. Downhole logging measurements were used to recognize the glacial and interglacial cycles, to reconstruct an age–depth model, to estimate sedimentation rates and to identify electrofacies. Initially, we investigate the consistency of cyclic sediment behavior and see that the interval from ~30-90 m shows a rather stable cyclicity with a wavelength of ~10 m. Natural and spectral gamma ray data were used for cyclostratigraphic analysis, and the astronomical spectral misfit (ASM) method was used to reconstruct the sedimentation rate. The results indicate a sedimentation rate of about 5-20 cm/kyr in the Lake Junín record. Furthermore, the TimeOpt method was applied to test for a fit of precession amplitude with eccentricity; it results in an average sedimentation rate of 15 cm/kyr. Both ASM and TimeOpt are astronomical testing approaches for untuned stratigraphic data in the depth domain that comprehensively evaluate a range of plausible time scales for the deposition history. This method suggests a good fit of the precession amplitude and an eccentricity filter when applying an average sedimentation rate of 14-15 cm/kyr. Based on these information on sedimentation rate, we establish a correlation of the spectral gamma ray data to the LR04 benthic isotope stack. In addition, the downhole logging data were used for cluster analysis to construct a lithological profile, called the electrofacies log.  Three major groups (carbonate-silt, peat and silt) have been identified by spectrum gamma ray, magnetic susceptibility, and p-wave velocity logs. With this method we are able to attribute the lithology in correspondence of core gaps. Finally, the properties of the clusters are analyzed and converted into lithological units according to the lithological information from the visual core description or mineralogical analysis or core material. To achieve this, 68 samples were taken in total from two core runs, in order to compare and characterize the minerals in the lake sediments at different depths. The mineralogical analyses performed by X-ray diffraction (XRD) show quartz, calcite, feldspar and clay minerals. The clay size fraction (< 2 micron) contains illite, smectite and kaolinite in different amounts. Linking the abundance and the lack of clay minerals in core samples with the downhole logging data, a relationship between geological history of the lake and climate change processes can be recognized. Consequently, the different mineralogical composition of the sediments, especially the presence or absence of smectite in the clay bulk, reflects a glacial/interglacial climate cyclicity.

How to cite: Schleicher, A., Pierdominici, S., Zeeden, C., Kück, J., Rodbell, D., and Abbott, M.: Investigating glacial/interglacial cyclicity from downhole logging data and mineralogical composition: an example from the ICDP drilling project Lake Junín, Peru, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3891, https://doi.org/10.5194/egusphere-egu2020-3891, 2020.

EGU2020-19628 | Displays | SSP1.4

Rock Magnetic and Magnetostratigraphic Study of Chicxulub Crater Impact Breccias and Post-Impact Carbonates in the Yaxcopoil-1 and Santa Elena Boreholes

Jaime Urrutia-Fucugauchi, Ligia Perez-Cruz, Elia Escobar-Sanchez, Miriam Velasco-Villarreal, and Edgar Garcia-Garnica

Chicxulub crater was formed ~66 Ma ago by an asteroid impact at the Cretaceous/Paleogene (K/Pg) boundary on the Yucatan carbonate platform in the southern Gulf of Mexico. The crater is the youngest and best preserved of the three large impact basins, with a ~200 km diameter and multi-ring and peak ring morphology. The crater, covered by post-impact carbonate sediments with thickness up to ~1.1 km, has been investigated by geophysical studies and drilling programs. Initial drilling in Yucatan was carried out by the Pemex oil company, followed by the National University UNAM Chicxulub program, the ICDP Yaxcopoil-1 project and the IODP-ICDP Expedition 364 marine drilling. Here, results of combined paleomagnetic, rock magnetic, petrographic and geochemical studies are used to characterize the sequence and constrain the unit’s emplacement and crater formation. We analyze core samples of suevitic breccias and Paleogene carbonates from the Yaxcopoil-1 and Santa Elena boreholes drilled in the southern sector, inside and to the south of the crater rim marked by the ring of cenotes.  Magnetic hysteresis, low-field susceptibility and coercitivity analyses indicate that main carriers are titanomagnetites and magnetite. Mineralogical and magnetic properties indicate effects of hydrothermal alteration, associated with the high temperature system generated by the impact. Higher coercitivity minerals are also observed in some samples. In the carbonate sections, hydrothermal effects as marked by the geochemical logs decrease upwards from the breccia-carbonate contact. Alternating field and thermal demagnetization is used to investigate the magnetization vector composition and isolate the characteristic remanent components. Magnetic polarities defined from the inclination data show a sequence of reverse to normal, which correlate to polarity chrons 29r to 26r, with impact occurring within 29r chron.  The correlations of the magnetostratigraphy and stable isotopes indicate a hiatus at the basal Paleocene section. In Santa Elena cores, d13C values range from 1.2 to 3.5%0 and d18O values range from -1.4 to -4.8%0, with variation trends correlating with the marine carbon and oxygen isotope records for the late Maastrichtian and early Paleocene. The positive carbon isotopes indicate high productivity after the K/Pg extinction event, while the oxygen isotope values are more negative reflecting regional and local effects. Silica contents decrease from high in the suevites to low values in carbonates showing higher variability and then increased contents at the Paleocene-Eocene Thermal Maximum (PETM). The geochemical trends correlate in other elements including iron, titanium, potassium and aluminum that record impact-induced hydrothermal effects and possibly changing depositional conditions. Ca shows an opposite trend, with lower values in the upper suevitic breccias, higher values in the Paleocene carbonates and lower values in the PETM.

How to cite: Urrutia-Fucugauchi, J., Perez-Cruz, L., Escobar-Sanchez, E., Velasco-Villarreal, M., and Garcia-Garnica, E.: Rock Magnetic and Magnetostratigraphic Study of Chicxulub Crater Impact Breccias and Post-Impact Carbonates in the Yaxcopoil-1 and Santa Elena Boreholes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19628, https://doi.org/10.5194/egusphere-egu2020-19628, 2020.

Kerguelen Plateau (KP), one of the world’s largest Large Igneous Provinces, is located in a key region in the southern Indian Ocean. Its complex topography has a strong influence on pathways of water masses within the Antarctic Circumpolar Current (ACC) and the Antarctic Bottom Water (AABW). Thick sediment packages deposited on top and around KP are a high-fidelity recorders of significant modifications in pathways and intensities of water masses flowing across the KP during the Cenozoic. Already the previously ODP spot cored sedimentary sequences demonstrated their outstanding potential as a far-field monitor for the evolution of the Antarctic Ice Sheet, for the climate variability in the Warmhouse World of the middle to late Eocene, for changes in ocean circulation, and for migration of the Polar Frontal System. Here we propose to revisited KP and recover a complete, multiple-hole drilled, carbonate rich sedimentary successions from Labuan and Ragatt Basin area by an IODP Expedition. Only high-quality drilled, undisturbed new material will allow studying the interaction of climatic and tectonic changes of the last 66 million years and provide important information on the formation and dynamics of the Antarctic ice sheet due to the unique location of the KP.

How to cite: Westerhold, T. and Uenzelmann-Neben, G.: Kerguelen Plateau Drift Deposits: outstanding high-resolution chronicle of Cenozoic climatic and oceanographic changes in the southern Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3121, https://doi.org/10.5194/egusphere-egu2020-3121, 2020.

EGU2020-3671 | Displays | SSP1.4

Detecting and using Milankovic cycles in borehole logging data: Comparing methods and application to Lake Ohrid

Thomas Wonik, Arne Ulfers, Matthias Sinnesael, Mingsong Li, and Christian Zeeden

Borehole logging data are not yet systematically assessed using cyclostratigraphic methods. In order to obtain a reliable understanding of (long) borehole logging datasets, and especially data from complex settings, a good understanding of the potential and specifics of relevant (time/depth) evolutive methods in cyclostratigraphy are an essential prerequisite. Therefore, we test a suite of evolutive cyclostratigraphic methods using several artificial datasets consisting of modelled Milankovic signals and noise.

Aim of this work is the comparison of different cyclostratigraphic methods for an understanding of which methods are suitable for Quaternary lake records, also for a good understanding of ICDP logging data. Once artificial datasets are discussed, we apply these methods to real data. A discussion of the possible issues and potential of especially uncommon methods gives insight in further potential of cyclostratigraphy.

Lake Ohrid is a tectonic lake located on the border of North Macedonia and Albania. With 1.36 Ma, it is considered Europe’s oldest lake and an important link between Mediterranean climate and African monsoon systems (Wagner et al. 2019). In 2013, an ICDP drilling campaign recovered 2100 m of sediments from four sites (Wagner et al. 2014).

Datasets from geophysical downhole logging provided by the Leibniz Institute for Applied Geophysics are used in a cyclostratigraphic analysis, which provides further insight into the sedimentation history of Lake Ohrid. Here we present initial results from the full succession in this sedimentary archive.

 

References:

Wagner, B., Wilke, T., Krastel, S., Zanchetta, G., Sulpizio, R., Reicherter, K., Leng, M. J., Grazhdani, A., Trajanovski, S., Francke, A., Lindhorst, K., Levkov, Z., Cvetkoska, A., Reed, J. M., Zhang, X., Lacey, J. H., Wonik, T., Baumgarten, H., and Vogel, H.: The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid. Sci. Dril., 17, 19–29, doi:10.5194/sd-17-19-2014 (2014).

Wagner, B., Vogel, H., Francke, A. et al.  Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years. Nature, 573, 256–260 (2019).

How to cite: Wonik, T., Ulfers, A., Sinnesael, M., Li, M., and Zeeden, C.: Detecting and using Milankovic cycles in borehole logging data: Comparing methods and application to Lake Ohrid, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3671, https://doi.org/10.5194/egusphere-egu2020-3671, 2020.

SSP1.5 – (Bio)mineral archives of past environmental conditions: from the Precambrian to the present

The formation of a solid-state material from solution is a ubiquitous process of fundamental importance not only for synthesis in solid-state chemistry but for a wide range of disciplines such as geosciences and biology. However, established classical crystallization theories fall short in explaining the outcome of crystallization and mineralization processes in complex environments, such as in biomineralizing organisms or geochemical and industrial settings.  The misfit between classical textbook knowledge and the plurality of conflicting experimental evidence facilitated the advent of an array of new crystallization concepts. These so-called nonclassical crystallization processes are fuelled by the attachment of multiatomic assemblies rather than by attachment of single ions drive crystal formation. Some of these models, such as oriented attachment, were unequivocally backed by experimental evidence and thus accepted by the science community. Other models have encountered distinct resistance from peers. At the centre of this intense dispute, we find the calcium carbonate system, which is of crucial importance for a range of disciplines. For this system, in particular, the existence of prenucleation clusters in the form of dynamically ordered liquid-like polyoxoanions (DOLLOP) has been suggested, and it has been claimed that nonclassical nucleation processes take place. However several groups have challenged this claim, claiming an entirely classical crystallization behaviour

Based on our results, we will draw a different picture of calcium carbonate formation. We show that the issues with this very systems root in its solute chemistry and the fact that this renders a calcium carbonate solution into a multicomponent system. We show liquid-liquid phase separation of near-neutral calcium carbonate solutions along with the first ultrastructural model of amorphous calcium carbonate (ACC). This findings give insight into the formation mechanisms of calcium carbonate under kinetically controlled conditions. Our findings further demonstrate that the formation of a liquid-condensed mineral precursor phase is not solely a “quirk of the peculiar calcium carbonate system” but a general phenomenon: it is an early stage precursor in the formation pathway of calcium carbonate under geo- and biochemical relevant conditions. Moreover, we show that this unexpected demixing behaviour is widespread, many inorganic components go through spinodal decomposition, when the reaction conditions are kinetically controlled and the solution chemistry disadvantage burst nucleation. Our data suggest that it is not the misconception and oversimplification of classical theories but our oversimplification of the solution chemistry which causes the current dispute on classical vs nonclassical nucleation of inorganic compounds. Currently, we see no need for invoking “non-classical” notions of nucleation since our exceptional observations can entirely be explained by established physicochemical concepts apart from CNT. Our results raise the awareness that a supramolecular solution and coordination chemistry provides the key to a thorough understanding of the genesis of inorganic solids under kinetically controlled conditions.

How to cite: Wolf, S.: From solutes to solids: towards a supramolecular view on mineralization processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21861, https://doi.org/10.5194/egusphere-egu2020-21861, 2020.

EGU2020-8680 | Displays | SSP1.5

Authigenic pyrite formation in iron-dominated marine sediments of the Mozambique Margin

Mark Zindorf, Jurjen Rooze, Christof Meile, Gwenael Jouet, Christian März, Robert Newton, Olivier Rouxel, Ewan Pelleter, Christophe Brandily, Nicolas Gayet, and Lucie Pastor

Sediment deposition along continental margins and especially close to the outlets of major river systems is highly dynamic and influenced by changing environmental conditions, such as sea-level variations and the shifting of ocean currents.
The upper slope of the Mozambique margin (SE Africa) receives its sediments from the Zambezi River and is the largest river-fed deposition center along the Eastern African Margin. Global sea level rise during the last glacial-Holocene transition led to a re-routing of the Zambezi River sediment plume. This caused order-of-magnitude changes in sedimentation rates along the shelf break of the Mozambique margin. The variable sediment input as well as changing organic matter load and quality resulted in non-steady state early diagenesis leading to changes in formation and upward flow of methane. This is reflected in temporally and spatially variable formation conditions of authigenic minerals (such as pyrite), especially at the sulfate-methane transition zone (SMTZ) where upward-diffusing methane is anaerobically oxidized by sulfate. Pyrite accumulations in sediment cores can be used to define the past positioning of SMTZs. The isotopic composition of sulfur in pyrite can provide information about the geochemical and environmental factors (e.g., availability of methane, sulfate, reactive iron) controlling the formation of these authigenic minerals during different times of sediment deposition.

We present geochemical data from sediment cores acquired in 2015 during the PAMELA-MOZ4 campaign onboard R/V Pourquoi Pas? offshore Mozambique. A reactive transport model is used to simulate the evolution of early diagenetic conditions over the time of sediment deposition (i.e., the last 27,000 years). By reproducing the currently observed mineral accumulations, the temporal development of methane generation and upward flux, and the past positioning of the SMTZ, can be reconstructed. With this, we are able to put a time constraint on past events of authigenic mineral accumulation and reveal their response to sedimentation rate changes caused by sea-level rise. We further discuss isotope signatures of small-scale diagenetic processes at the Mozambique margin.

This research was co-funded by TOTAL and IFREMER as part of the PAMELA scientific project.

How to cite: Zindorf, M., Rooze, J., Meile, C., Jouet, G., März, C., Newton, R., Rouxel, O., Pelleter, E., Brandily, C., Gayet, N., and Pastor, L.: Authigenic pyrite formation in iron-dominated marine sediments of the Mozambique Margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8680, https://doi.org/10.5194/egusphere-egu2020-8680, 2020.

EGU2020-2104 | Displays | SSP1.5

New insight into spheroidal iron (oxyhydr)oxide concretion formation models: Diagenetic concretion nucleation associated with neutral fluids from a mafic intrusion

Sally Potter-McIntyre, Justin Filiberto, Susanne Schwenzer, Jake Crandall, Scott Perl, and Bea Baharier

Directly west of the San Rafael Swell on the Colorado Plateau in the western U.S., the Jurassic Entrada Sandstone is intruded by a ~2 km long mafic dike. The dike is Miocene; however, the area is also crosscut by Laramide (~50Ma) clusters of deformation bands that are up 500 m long and up to ~3 m wide. The mafic intrusions infused the area with fluids that bleached the red sandstone directly surrounding the dike. On one side of the dike, the bleached area terminates at an adjacent deformation band set ~475 m south of the dike. Field observations suggest that the dike acted as a baffle preventing fluids from migrating further into the sandstone. Spheroidal calcite and iron (oxyhydr)oxide concretions are present in the bleached host rock, although calcite concretions (1-3 cm diameter) are present throughout the area on both sides of the deformation bands and in both red and white host rock. Iron (oxyhydr)oxide concretions (1-5 cm diameter) are limited to the uppermost bleached section between the dike and the deformation band set. Some iron concretions have solid interiors, and some have well-cemented rinds with interiors depleted of cement. Additionally, some iron concretions are nucleated on individual deformation bands that are ~2 mm wide and iron (oxyhydr)oxide cemented joint faces are also present. Thermochemical modeling shows the infiltrating Miocene fluids were CO2-bearing, but near neutral pH. The restricted location of the iron (oxyhydr)oxide concretions and relation to the calcite concretions suggest that stagnation of fluid is needed for spheroidal iron oxyhydroxide concretion formation. Calcite concretion nucleation and growth may be quicker resulting in more widespread occurrences, and/or may have preceded the Miocene fluids that infiltrated the unit. The evidence presented here shows that recently proposed models calling for calcite concretion precursors and acidic fluids for iron (oxyhydr)oxide concretion formation may not be correct.

How to cite: Potter-McIntyre, S., Filiberto, J., Schwenzer, S., Crandall, J., Perl, S., and Baharier, B.: New insight into spheroidal iron (oxyhydr)oxide concretion formation models: Diagenetic concretion nucleation associated with neutral fluids from a mafic intrusion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2104, https://doi.org/10.5194/egusphere-egu2020-2104, 2020.

EGU2020-19949 | Displays | SSP1.5

Palygorskite in a Paleosol from Zagros mountain belt, NE Iraq

Axel Mentler, Polla Khanaqa, Kamal Karim, Franz Ottner, Jasmin Schomakers, Katharina Keiblinger, and Rosana Kral

In the semi-arid region south of Sulaimani city, paleosols can be found. The genesis of these paleosols needs to be elucidated. Here, we investigated a section of an Oligocene paleosol from that region. The section is about 7m thick with lower, middle and upper horizons, which consisted of partially weathered dolomitic limestone; conglomerate or lithified pebbly paleosol; and sandy-silty claystone or lithified clayey paleosol, respectively. These horizons were studied mineralogically and stratigraphically using X-ray diffraction, scanning electron microscopy, Simultaneous Thermal Analysis (STA) and granulometric analysis. Palygorskite content was higher in the conglomerate (lithified gravely paleosol) and in the partially weathered dolomitic limestone than in clayey paleosol.

Palygorskite is a trace mineral that allows to estimate climatic conditions during soil genesis. In hand specimen, palygorskite occurs as green patches of crystalline coating that covers pores and cavities on limestone and dolostone. Under scanning electron microscope, it appears as linear and fibrous loose bundles that occupy the interstice between the dolomite crystals and is mainly associated with dolostone and limestone facies.

We thus conclude that the climate was arid, and that the terrestrial land cover in this part of the Oligocene Basin in Northern Iraq was limestone and dolostone.

On this land, soil genesis and intermittent stream and sheet erosion was occurring during the entire Oligocene and it is well known, stratigraphically, as Oligocene Unconformity.

The possible origin of the palygorskite was the development during Oligocene by upward accumulation under hydrothermal condition in partially high weathered dolomitic limestone of Pila Spi formation during burial. Palygorskite occurs in marine, lacustrine and soil environments. Limited occurrences are associated with hydrothermal activity, in both marine and continental environments. Palygorskite-containing soils are limited almost exclusively to arid and semiarid areas of the world and are rather unstable in humid conditions.

The present paleosol was developed on Oligocene terrestrial land that bordered the sea covering Middle and Southern Iraq. Due to non-deposition weathering and mass wasting, calcareous gravely soil (limestone conglomerate) was generated. Sandy and clay soil were developed on the terrestrial land which stratigraphically formed an unconformity. This land was covered by water of a closed lagoon. Limestones are deposited as Lower Fars Formation.

These occurrences are associated with aquatic conditions characterized by alkaline solutions with high activities of Si and Mg. The most common setting for lacustrine palygorskite genesis are playa deposits, ancient lacustrine terraces, or closed-basin deposits of other types. While traces of palygorskite can be identified in a wide variety of soils, significant amounts of the pedogenically formed mineral are commonly associated with one specific situation of soil genesis like soils have been affected by fluctuating ground water, soil morphology that includes distinct and sharp textual transitions. This groups includes many paleosols. Most of these Paleosols are non-saline or only slightly saline.

How to cite: Mentler, A., Khanaqa, P., Karim, K., Ottner, F., Schomakers, J., Keiblinger, K., and Kral, R.: Palygorskite in a Paleosol from Zagros mountain belt, NE Iraq, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19949, https://doi.org/10.5194/egusphere-egu2020-19949, 2020.

EGU2020-11006 | Displays | SSP1.5

Laser-induced fluorescence (LiF) spectroscopy for detecting REE cross-contaminations in the Smithsonian rare-earth element phosphate standards

Margret C. Fuchs, Jan Beyer, Sandra Lorenz, Suchinder K. Sharma, Axel D. Renno, Johannes Heitmann, and Richard Gloaguen

Spectroscopy based methods have proven great potential in efficient, non-invasive material characterization. Recording the material-specific optical properties delivers instant information on the composition of an investigated sample surface without chemical sample preparation and may be operated in spatially continuous mode. In minerals, laser-induced fluorescence (LiF) provides a promising method to address the challenges of robust and efficient rare-earth element (REE) detection. The method is based on the characteristic electronic transitions within the incompletely filled f-shell of REE. The corresponding emission shows distinct features (spectral fingerprints) in the visible and near-infrared (VNIR) range of the electromagnetic spectrum that allow to distinguish between individual REE and mineral matrix luminescence. Only REE with completely filled or empty f-orbitals miss characteristic luminescence (i.e. Y3+, Sc3+, La3+, Lu3+), while the emissions of Gd3+ lie at lower wavelengths than the observed VNIR range.

We test the suitability of LiF in applications of REE identification by (1) building a spectral LiF library from a sample set of luminescent REE phosphates and (2) evaluating observed emissions in samples of non-luminescent REE, and (3) comparing indicated REE cross-contamination to results of neutron activation analysis (NAA). As samples, we use the Smithsonian REE phosphate standards for electron microprobe analysis. The synthetic material delivers a simple, well-defined host composition, is well investigated and NAA results are available on additional trace REE concentration resulting from the material production procedure. The trace REE concentrations are at the order of 10-4 given in mass fraction. We employ laser-induced fluorescence at three commonly used laser wavelengths (325 nm, 442 nm, 532 nm) to acquire our REE sample spectra and record LiF signals in the visible to near-infrared spectral range (350 – 1080 nm).

The comparison of spectra from non-luminescent REE phosphates shows clear similarities in emission patterns that can be assigned to specific luminescent REE using the spectral LiF library. Our results demonstrate the suitability of LIF for REE detection along with the benefits of selective element excitation and highlight the high sensitivity of the LiF method. The detected emissions in the non-luminescent samples indicate a detection limit below mass fractions of 10-4, when compared to NAA results, but also show that not all REE are equally responsive. Here, the co-existence of REE with complex interactions such as charge transfer contributes to the observed emission pattern. Adding to the spectral LiF library data and expanding investigations to further mineral hosts will facilitate new applications of LIF for REE analysis in natural samples and its implementation in raw material exploration.

How to cite: Fuchs, M. C., Beyer, J., Lorenz, S., Sharma, S. K., Renno, A. D., Heitmann, J., and Gloaguen, R.: Laser-induced fluorescence (LiF) spectroscopy for detecting REE cross-contaminations in the Smithsonian rare-earth element phosphate standards , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11006, https://doi.org/10.5194/egusphere-egu2020-11006, 2020.

The diameter of framboidal pyrites was widely used as a measure of redox condition in modern and ancient sedimentary environments, the proposed critical values of average size and standard deviation of framboids are about 8μm and 3μm respectively. However, a few reports proposed that the exceptionally large size and standard deviation of framboidal pyrites in cored sediments from northeastern South China Sea is closely related to the anaerobic oxidation of methane (AOM) processes mainly dominated in sulfate-methane transition zones (SMTZ). Here we investigate the occurrence of framboidal pyrites in two cored sediments of sites SC-W02B-2017 and SC-W03B-2017 at Shenhu area during the first offshore gas hydrate production test in northern South China Sea. Combined with the statistics of size and standard deviation of framboidal pyrites, the relative concentrations and sulfur isotopic compositions of bulk pyrites, we verified that the AOM could enhance the framboidal pyrite formation. Our data show that both the size and the standard deviation of framboidal pyrite present an unusual positive excursion in cored sediment column. By interpreting the coupling occurrence of positive excursions both pyrite concentrations and sulfur isotopes, four main paleo-sulfate-methane transition zones (Paleo-SMTZ) are roughly recognized in depths around 50 meter below seafloor (mbsf), 90-100 mbsf, 135-225 mbsf and 180 mbsf, where unusual strong AOM and unusual methane releases might happened. The morphology shows most of the pyrite framboids occur in framboidal cluster with a rod-like, irregular block shape and secondary overgrowth. The size of pyrite framboids in site W02B ranges from 8.1μm to 40.1μm with maximal about 40.1μm and in site W03B from 8.6μm to 25.3μm with maximal about 101.2μm (n=2686 from 13 samples). Our data show the average size and the standard deviation of pyrite framboids are more than 20μm and 3.0μm respectively, and the higher δ34S value and larger size of framboid mainly occur near the intervals of paleo-SMTZs in marine sediment columns. Therefore, we propose again that the enhancing AOM in SMTZs could flourish the growth of pyrite framboids and enlarge the standard deviation of framboidal size, which might be implication for more precise interpretation of redox condition of sedimentary environments using framboidal pyrite diameter.

How to cite: Wang, J. and Wei, Q.: Framboidal pyrites flourished in sulfate-methane transition zones of cored sediments in the northern South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3979, https://doi.org/10.5194/egusphere-egu2020-3979, 2020.

EGU2020-15902 | Displays | SSP1.5

Building amorphous calcium carbonate into geochemical biomineralisation models

David Evans, William Gray, James Rae, Rosanna Greenop, Paul Webb, Kirsty Penkman, Roland Kröger, and Nicola Allison

Amorphous calcium carbonate (ACC) has been observed, or inferred to exist, in the majority of the major phyla of marine calcifying organisms. The CaCO3 produced by these organisms represents one of the largest long-term carbon sinks on Earth’s surface, such that identifying how calcification will respond to anthropogenic climate change is an urgent priority. A substantial portion of our knowledge of the biomineralisation process of these organisms is derived from inferences based on skeletal geochemical data, yet such models typically do not include an ACC component because little is known about trace element and isotope fractionation into ACC. In order to address this, we present, to our knowledge, the first structural and geochemical data of ACC precipitated from seawater under varying carbonate system conditions, seawater Mg/Ca ratios, and in the presence of three of the most common intracrystalline amino acids (aspartic acid, glutamic acid, and glycine). Based on these data we identify the carbonate system conditions necessary to produce ACC from seawater [Evans et al., 2019], and identify the dominant controls on ACC geochemistry. As an example, we utilise these data to build a simple biomineralisation model for the low-Mg (e.g. planktonic) foraminifera, based on precipitation of low-Mg calcite through an ACC precursor phase in a semi-enclosed pool. This exercise demonstrates that the observed shell geochemistry of this group of organisms can be fully reconciled with a model that includes an ACC component, and moreover that constraints can be placed on the degree of ACC utilisation and the ACC-calcite transformation process. More broadly, the exercise demonstrates that knowledge of the characteristics and geochemistry of ACC is important in the development of a process-based understanding of marine calcification.

Evans, D., Webb, P., Penkman, K. Kröger, R., & Allison, N. [2019] The Characteristics and Biological Relevance of Inorganic Amorphous Calcium Carbonate (ACC) Precipitated from Seawater. Crystal Growth & Design 19: 4300.

How to cite: Evans, D., Gray, W., Rae, J., Greenop, R., Webb, P., Penkman, K., Kröger, R., and Allison, N.: Building amorphous calcium carbonate into geochemical biomineralisation models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15902, https://doi.org/10.5194/egusphere-egu2020-15902, 2020.

EGU2020-19690 | Displays | SSP1.5 | Highlight

Microbial control on Anthropocene carbonates in slag drainage waters

Cees van der Land, Keziah Cowan, Angela Sherry, Laura Bastianini, Neil Gray, Mike Rogerson, Ramon Mercedes-Martin, Timothy Prior, Edgley Cesar, and William Mayes

Over the last decennia, alkaline leachates from the weathering of legacy steel slag disposal sites have affected the surrounding soils and drainage streams. The hyperalkaline and hypersaline conditions around these sites are comparable to extreme paleo environments such as alkaline lakes in rift volcanic settings. Investigating the carbonate deposits forming in these man-made systems provides a unique opportunity to link the ongoing physical and microbial processes to their resultant carbonate morphologies.

Here we present data from 3 sites across Dene Burn, a slag drainage stream in Consett, County Durham, UK. After 100 years, iron and steel production ceased in 1980, leaving over 20 million tons of slag in the form of several large mounds. Analysis showed Dene Burn to be typical of slag drainage waters with an elevated pH (>9) and saturated with different secondary phase minerals- particularly calcite. However, the physical distribution of carbonates is more comparable with estimated local kinetic precipitation rate than it is to thermodynamic saturation, indicating that the fundamental control on carbonate formation arises from crystal surface processes. A microbial community comprising predominantly Proteobacteria (Alpha-, Gamma-, Beta- and Deltaproteobacteria), Cyanobacteria, Bacillariophyta (diatoms) and Bacteroidetes (Flavobacterium) was identified at the 3 sites. The microbial communities and an abundance of extracellular polymeric substances (EPS) were shown in close association with the mineral phases detected at the sites. The presence and composition of these biofilms appears to control local carbonate mineralisation rates and carbonate morphologies.

Drainage streams from steel slag provide a unique opportunity to study carbonate mineral formation under extreme environmental conditions. Furthermore, maximising carbonate formation at such sites could be utilised as a remediation and carbonate sequestration technique.

How to cite: van der Land, C., Cowan, K., Sherry, A., Bastianini, L., Gray, N., Rogerson, M., Mercedes-Martin, R., Prior, T., Cesar, E., and Mayes, W.: Microbial control on Anthropocene carbonates in slag drainage waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19690, https://doi.org/10.5194/egusphere-egu2020-19690, 2020.

EGU2020-20253 | Displays | SSP1.5

Biogeohemical significance of Intracellular calcification by Cyanobacteria

Neha Mehta, Feriel-Skouri Panet, and Karim Benzerara

Cyanobacteria are an abundant and diverse group of photosynthetic bacteria that have shaped Earth’s environment for billions of years and play a vital role in the cycling of numerous elements such as carbon, calcium, and phosphorus. In particular, their impact on the global carbon cycle is of significant interest in the context of carbon capture and climate change, as they sequester atmospheric CO2 into organic carbon and biogenic calcium carbonates (CaCO3) through a process called calcification.  The process of calcification has long been considered as extracellular and non-biologically controlled. However, recently, several cyanobacterial species have been reported to form intracellular amorphous calcium carbonate (ACC) inclusions. These cyanobacteria were found in diverse environments and accumulate high concentrations of AEE (Ca, Ba and Sr) from solutions undersaturated with respect to AEE-carbonate phases. Moreover, one of these cyanobacteria species, G. lithophora was shown to selectively accumulate stable and radioactive alkaline earth elements (AEE) within the intracellular amorphous carbonates and/or polyp inclusions (Mehta et al., 2019). Recently, it was confirmed that cyanobacteria forming intracellular ACC contained a much higher content of alkaline earth elements (AEE) than all other cyanobacteria (DeWever et al., 2019). The high concentration of Ba and Sr within these intracellular inclusions was surprising because Ba and Sr have usually been considered as having no physiological role at all. The high concentration of Ca within these intracellular inclusions was directly in contrast with the traditional paradigm of cells maintaining a state of homeostasis with respect to Ca. Furthermore, Sr/Ca and Ba/Ca ratios in these ACC inclusions were very different from those expected from abiotic precipitation in the solution surrounding the cells (Cam et al. 2015). To understand the biological driver behind these observations, first, I will present a review of the above mentioned “vital effects” in the context of intracellular calcification in cyanobacteria. Second, using batch incubation experiments, I will show that high Ca concentrations are vital not only for the growth of G. lithophora, but also for the uptake of Ba by G. lithophora. Lastly, I will examine Ca homeostasis in ACC forming cyanobacterial strains by using an antagonist/inhibitor of a known channel/transporter involved in Ca transport.  Overall, these insights will shed some light on the role of cyanobacteria forming intracellular ACC on carbonate (bio)mineralization, in both modern and ancient Earth’s environment. 

Reference:

N Mehta, K Benzerara, B Kocar, V Chapon, Sequestration of radionuclidesRadium-226 and Strontium-90 by cyanobacteria forming intracellular calcium carbonates, ES&T 2019

De Wever, A.; Benzerara, K. et al. Evidence of High Ca Uptake by Cyanobacteria Forming Intracellular CaCO 3 and Impact on Their Growth. Geobiology 2019

Cam, N., Georgelin, T., Jaber, M., Lambert, J.-F., and Benzerara, K, In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: what do we learn about intracellular calcification by cyanobacteria? Geochim. Cosmochim. Acta 2015

 

How to cite: Mehta, N., Panet, F.-S., and Benzerara, K.: Biogeohemical significance of Intracellular calcification by Cyanobacteria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20253, https://doi.org/10.5194/egusphere-egu2020-20253, 2020.

EGU2020-21988 | Displays | SSP1.5 | Highlight

Boron proxies and biomineralisation: the possible, the impossible and the likely.

Oscar Branson and Alex Gagnon

The abundance and isotopic content of boron in carbonate biominerals provide our best records of ocean carbon chemistry and pH, which have proved instrumental in studying past episodes of CO2-induced climate change. The boron proxies are based on the theory that carbonates solely incorporate B(OH)4- in proportion to seawater B(OH)4-/HCO3- or B(OH)4-/CO32-, capturing both the state of the ocean C system and the pH-dependent isotopic composition of B(OH)4-. However, models of biomineralisation invoke significant modification of internal carbon chemistry to facilitate calcification, and substantial proton export has been observed during carbonate formation. The pH, carbon and boron chemistry at the site of calcification cannot be the same as that of external seawater. How, then, do biominerals appear to record seawater B(OH)4-? While unanswered, this question raises serious problems for our interpretation and use of the B proxies.

We explore this question using a quantitative model of B transport and incorporation in biomineralisation. Three key fluxes dominate biomineral formation: CaCO3 precipitation, the exchange of seawater with the external environment, and ion transport across membranes by diffusion or active pumping. By reducing the problem to the balance between these three key fluxes, it is possible to explore a wide range of biomineralisation scenarios with minimally restrictive assumptions. Within this framework, we consider both the transport of B(OH)4-, and the transport and passive diffusion of membrane-permeable B(OH)3, allowing us to explore a comprehensive range of candidate biomineralisation scenarios and B transport processes.

By explicitly including the independent transport of both B species, our model offers two key insights into the mechanisms behind the boron proxies and biomineralisation:

  1. We identify biomineralisation mechanisms that allow B geochemistry to record external seawater conditions, despite the modified chemistry at the calcification site.

  2. We constrain the dynamics of the calcification environment (e.g. ‘closed’ vs. ‘open’ or Rayleigh- vs. transport-dominated system) by inverting the model to consider paired B/Ca and δ11B data, offering key new constraints on ion transport processes in biomineralisation.

How to cite: Branson, O. and Gagnon, A.: Boron proxies and biomineralisation: the possible, the impossible and the likely., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21988, https://doi.org/10.5194/egusphere-egu2020-21988, 2020.

EGU2020-19994 | Displays | SSP1.5

δ11B and B/Ca ontogenetic variability within Globigerina bulloides

Matthieu Buisson, Pascale Louvat, Szabina Karancz, Ruchen Tian, Markus Raitzsch, Jelle Bijma, and Claire Rollion-Bard

Understanding the atmosphere-continent-ocean carbon cycle and its associated oceanic carbon system is one of the keystones to face the Anthropocene’s climate change. Since the 1990s the isotopic ratio of boron (δ11B) in calcitic shells of planktonic foraminifera has proven to be a powerful geochemical proxy to determine the oceanic paleo-pH and its link to atmospheric CO2 level over geological times1, whereas the ratio B/Ca as proxy of the seawater carbonate chemistry is still questionable2,3.

However, the use of planktonic foraminifera in paleoclimatic reconstructions requires calibrations of the pH – δ11B relationships to correct what is known as « vital effect »4: each species controls differently its calcification process and consequently slightly modifies the seawater chemistry during biomineralization5,6. Moreover, shell size effect on δ11B has been reported for some symbiont-bearing species due to photosynthetic increase of pH7,8.

Calibrations for the symbiont-barren Globigerina bulloides have been already determined9,10 but sparse data have been reported so far for the test size effect on δ11B 11.

Here we measured the δ11B of three different fractions (250-315, 315-400 and >400 μm) of G. bulloides sampled along the coretop PS97-122 from the Chilean margin (54.10°S, 74.91°W), by using a new protocol developed at IPGP and dedicated to small samples which couple a microsublimation technique and a micro-direct injection device (μ-dDIHEN12). Our preliminary results show significantly higher δ11B values for the large fractions compared to the small ones, as found for symbiont-bearing planktonic species such as Globigerinoides sacculifer7 and Globigerinoides ruber8.

 

  • (1) Pearson & Palmer, 2000, Nature 406, 695-699
  • (2) Yu et al., 2007, Paleoceanography 22, PA2202
  • (3) Allen et al., 2012, EPSL 351-352, 270-280
  • (4) Urey et al., 1951, Soc. Am. Bull. 62, 399-416
  • (5) Erez, 2003, Rev. in Min. and Geochem. 54 (1), 115-149
  • (6) de Nooijer et al., 2014, Earth-Science Reviews 135, 48-58
  • (7) Hönisch & Hemming, 2004, Paleoceanography 19, PA4010
  • (8) Henehan et al., 2013, EPSL 364, 111-122
  • (9) Martínez-Botíet al., 2015, Nature 518, 219-222
  • (10) Raitzsch et al., 2018, EPSL 487, 138-150
  • (11) Henehan et al., 2016, EPSL 454, 282-292
  • (12) Louvat et al., 2019, JAAS 8, 1553-1563

How to cite: Buisson, M., Louvat, P., Karancz, S., Tian, R., Raitzsch, M., Bijma, J., and Rollion-Bard, C.: δ11B and B/Ca ontogenetic variability within Globigerina bulloides , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19994, https://doi.org/10.5194/egusphere-egu2020-19994, 2020.

Despite being some of the largest bio-constructions on the planet, coral reefs are made by many millions of cm- to mm-sized polyps of Scleractinian corals. Calcification occurs in a micron sized space sandwiched between the coral animal and the existing skeleton, known as the extra cellular medium (ECM). The coral animal has a tight control on the carbonate system in this space through deploying enzymatic pumps (e.g. Ca-ATPase) and secreting acidic-rich proteins. Tracking the state of the carbonate system in the ECM is therefore key to forming a mechanistic understanding of how environmental change, such as ocean acidification, influences skeletal formation and ultimately the growth and resilience of these important ecosystems.

Traditional means to examine ECM composition is through the use of micro-electrodes. While these approaches have revealed many key insights they are, by their nature, invasive.  They also only provide snap shots of information for corals grown in the laboratory. The boron isotopic composition of the coral skeleton and its boron content (expressed as B/Ca ratio) have recently emerged as a viable alternative approach to fully characterise the carbonate system in the ECM.  However, most studies employ bulk sampling techniques which require averaging across both structural elements of the coral skeleton and many months to years of growth. Laser ablation MC-ICP-MS approaches are now available as an alternative sampling protocol (e.g. Standish et al. 2019), and along with B/Ca (and other trace element) measurements this not only allows a reconstruction of the full carbonate system of the ECM from an analysis of the skeleton of any coral (cultured or wild) at unprecedented spatial and temporal resolution, but it also allows an examination of the influence of the carbonate system in the ECM on trace element incorporation. 

Here we present boron isotope and trace element analyses of several tropical, reef-building, corals to examine the nature and magnitude of fine scale variation in ECM composition.  By studying corals from locations where external seawater is well known we also gain insights into trace element incorporation and whether external seawater pH can be accurately reconstructed from the boron-based proxies at weekly (or better) resolution. 

 

Standish, C.D., Chalk, T.B., Babila, T.L., Milton, J.A., Palmer, M.R., Foster, G.L. (2019) The effect of matrix interferences in situ boron isotope analysis by laser ablation MC-ICP-MS, Rapid Communications in Mass Spectrometry 33: 959–968 https://doi.org/10.1002/rcm.8432

How to cite: Foster, G. L., Chalk, T. B., and Standish, C. D.: Boron isotope analysis of coral skeletons by laser ablation MC-ICP-MS: new insights into calcification and environmental reconstruction at high temporal resolution , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8202, https://doi.org/10.5194/egusphere-egu2020-8202, 2020.

A widespread phenomenon in biogenic and inorganic carbonates that are formed out of isotopic equilibrium is a nearly ubiquitous co-variation (slope) of carbon vs. oxygen isotopes, in e.g., speleothem and cryogenic carbonates, shells and skeletons of foraminifera, corals etc. For proxy calibrations, it is critical to understand such isotope variations (often labeled kinetic or vital effects) in proxies widely used for paleo-reconstructions. Given that this phenomenon is observed in inorganic carbonates and biogenic carbonates across different phyla suggest a common underlying mechanism, possibly independent of biological controls, that is, likely of inorganic origin. Here we present results from laboratory experiments on synthetic carbonate precipitation to constrain the kinetic isotope fractionation factor (KFF) of carbon and oxygen during CO2 hydration. We used an experimental setup similar to that of an earlier study but with important modifications and tight temperature and pH control. The average d13C and d18O values of our carbonate samples (BaCO3) produced at 25 deg C and pH = 8.0 (NBS) are -29.7 +- 0.71 per mil (VPDB) and 18.8 +- 0.56 per mil (VSMOW), respectively. From the isotope data, we calculate our experimental 13KFF and 18KFF, which refer to the 13C/12C and 18O/16O fractionation between CO2(g) and BaCO3, where the d13C and d18O values of CO2(g) were calculated using known equilibrium fractionation factors. Our results show that our KFFs are the largest values compared to previously reported experimental KFFs (except for one study), suggesting that our values are closest to the full isotopic disequilibrium during CO2 hydration. Based on our KFFs, we will present the expected slope of carbon vs. oxygen isotopic disequilibrium from kinetic effects during CO2 hydration. We will also discuss the expected slope from equilibrium effects of solution pH on oxygen isotopes. Comparison with field and culture data will reveal the origin of the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates.

How to cite: Zeebe, R., Yumol, L., and Uchikawa, J.: Solution to an enigma: Explaining the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10573, https://doi.org/10.5194/egusphere-egu2020-10573, 2020.

EGU2020-3051 | Displays | SSP1.5

Combined clumped isotope measurements resolve kinetic biases in carbonate formation temperatures

David Bajnai, Weifu Guo, Niklas Löffler, Katharina Methner, Emilija Krsnik, Tyler B. Coplen, Eberhard Gischler, Maximilian Hansen, Daniela Henkel, Gregory D. Price, Jacek Raddatz, Denis Scholz, and Jens Fiebig

Reaction kinetics involved in the precipitation of carbonates can introduce large scatter and inaccuracies in the temperatures derived from their δ18O and ∆47 values. Advances in mass spectrometry instrumentation recently enabled high-precision analysis of the 18O–18O clumping in carbonate minerals (48), despite the relatively low natural abundance of 12C18O18O, the main isotopologue contributing to the 48 signal (1). Measurements of 48, when combined with 47, can yield additional insights into kinetic effects and the carbonate formation environment (2).

Here we report high-precision 47 and 48 values of speleothem carbonates, modern coral skeletons, a brachiopod, and a belemnite. We constrained equilibrium in 47 vs 48 space by anchoring empirically derived 47 vs temperature and 48 vs temperature relationships to a Devils Hole mammillary calcite, known to be precipitated at extremely slow rates at a constant 33.7(±0.8) °C and water oxygen isotope composition. Our results, compared to theoretical predictions, provide the most substantial evidence to date that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Data from an ancient belemnite imply it precipitated near isotopic equilibrium and confirm the warmer-than-present temperatures at Early Cretaceous southern high latitudes. The presence of similar kinetic departure in a brachiopod but not in a belemnite suggests that the current discrepancy between belemnite and brachiopod-based temperature estimates in the geologic record is most likely related to a greater kinetic bias in the isotopic composition of brachiopod shells.

We demonstrate that the combined clumped isotope method makes it possible to identify carbonates that did not precipitate in thermodynamic equilibrium from their parent water. Our results highlight the potential that the combined clumped isotope analyses hold for accurate paleoclimate reconstructions and the identification of the kinetic fractionation processes dominant in carbonate (bio)mineralisation.

(1) Fiebig et al. (2019), https://doi.org/10.1016/j.chemgeo.2019.05.019

(2) Guo, W. (2020), https://doi.org/10.1016/j.gca.2019.07.055

How to cite: Bajnai, D., Guo, W., Löffler, N., Methner, K., Krsnik, E., Coplen, T. B., Gischler, E., Hansen, M., Henkel, D., Price, G. D., Raddatz, J., Scholz, D., and Fiebig, J.: Combined clumped isotope measurements resolve kinetic biases in carbonate formation temperatures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3051, https://doi.org/10.5194/egusphere-egu2020-3051, 2020.

The Mg/Ca paleotemperature proxy in planktic foraminifera is one of the most widely-used proxies for sea surface temperature. However, this ratio is not constant throughout the test, varying systematically by several fold independent of temperature between faster and slower growing diurnal bands. This phenomenon has yet to be explained mechanistically, however, changing calcification rates may be a contributing factor. Observing the relationship between calcification rate and trace metal incorporation for multiple proxies at the scale of this banding will allow us to better understand the contribution of kinetic effects to heterogeneity. In this study, we examine Me/Ca ratios on a diurnal cycle in Orbulina universa, utilizing a novel approach based on multiple isotopic spikes that allows us to measure Sr/Ca, Li/Ca and Mg/Ca with the precision of isotope dilution while still maintaining the time resolution of microanalytical techniques. Using independently measured growth rates derived from NanoSIMS measurements of diurnal Mg/Ca heterogeneity, we examine the effect of crystal growth rate on foraminiferal Sr/Ca and Li/Ca.  We observe that Sr/Ca ratios in foraminifera are ~3% higher during the night than during the day, which initially appears opposite to the expected signal based on growth rate. However, we also observe a positive correlation between Sr and Mg in foraminiferal calcite, which falls on the same mineralogical line as the Sr/Ca and Mg/Ca of other biogenic and inorganic calcites. We attribute offsets in calcite composition from this mineralogical relationship to kinetics. Interpreted within that framework, day Sr/Ca ratios appear more affected by kinetics than night Sr/Ca ratios, which is consistent with observed calcification rates. The difference between any given data point and the mineralogical line can be explained by kinetic processes, and correlates with oceanographic properties in cultured foraminifera, which could help separate temperature from growth rate effects in the paleorecord.

How to cite: Bonnin, E., Spero, H., and Gagnon, A.: Testing the effect of crystal growth rate on foraminiferal calcite microchemistry using Sr/Ca of individual day/night bands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13960, https://doi.org/10.5194/egusphere-egu2020-13960, 2020.

EGU2020-7573 | Displays | SSP1.5

Exploring the biomineral morphology of crossed-lamellar bivalve shells as a water temperature proxy

Nils Höche, Melita Peharda, Julien Thébault, and Bernd R. Schöne

Bivalve shells serve as excellent high-resolution archives of marine paleoclimate. Recently, ultrastructural features of the shells were investigated as potential temperature proxies that can overcome the limitations of the stable oxygen isotope method (i.e., missing data on past seawater oxygen isotope signature and diagenetic overprint). According to previous studies, the size of individual biomineral units of prismatic, nacreous and crossed-lamellar ultrastructures in cross-sections along the axis of maximum growth was solely related to water temperature. Despite being present in 90% of all mollusks, the crossed-lamellar ultrastructure was only studied for environmental relationships in one species (Glycymeris bimaculata) until now. To determine whether this new proxy can be applied to other bivalves with crossed-lamellar ultrastructure, further studies are needed.

We analyzed the shells of other Glycymerididae collected at near-shore and shelf environments (G. nummaria and G. pilosa: Adriatic Sea, Croatia; G. glycymeris: Iroise Sea, France; Glycymeris sp: Southern Pacific, New Zealand) by means of SEM, using a previously developed automatic image analysis procedure. Morphological changes of the biomineral units of the shells were assessed for relationships with temperature, salinity and food availability. Additionally, the crossed-lamellar architectures of phylogenetically more distantly related taxa (Venus verrucosa and Callista chione: Adriatic Sea, Croatia) were assessed.

Our results show that all studied Glycymerididae species, irrespective of environmental setting and locality, formed larger biomineral units in warmer waters. However, biomineral properties of ontogenetically old shell portions are more difficult to interpret, because declining growth rates condense the shell record and aggravate ultrastructural analyses. The crossed-lamellar shell layers of V. verrucosa and C. chione exhibited hierarchical organizations very similar to those of the Glycymerididae. The ultrastructural temperature proxy can therefore be applied to crossed-lamellar shells of bivalves from a wide range of coastal settings, preferably in ontogenetically young shell portions.

How to cite: Höche, N., Peharda, M., Thébault, J., and Schöne, B. R.: Exploring the biomineral morphology of crossed-lamellar bivalve shells as a water temperature proxy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7573, https://doi.org/10.5194/egusphere-egu2020-7573, 2020.

EGU2020-4724 | Displays | SSP1.5

Ba/Ca, P/Ca, Li/Ca and Mn/Ca ratios in the deep-sea bivalve Acesta excavata: Valuable tools to reconstruct plankton dynamics in cold-water coral ecosystems?

Nicolai Schleinkofer, Jacek Raddatz, David Evans, Axel Gerdes, Silke Voigt, and Max Wisshak

Phytoplankton is one of the most important producers of oxygen, and plays an important role in the export of large amounts of carbon to the deeper ocean. Since phytoplankton is also the basis of most food webs in the ocean, understanding the dynamic system of phytoplankton is a crucial part to understand past carbon- and nutrient cycles and paleoclimatic changes. The export of nutrients is also an important factor impacting cold-water coral (CWC) reefs and may play a role in controlling their distribution. Here we present laser ablation inductively coupled mass spectrometer (LA-ICP-MS) Element/Ca measurements from Acesta excavata, a file clam, often associated with cold-water coral reefs along the European continental margin. Environmental parameters were recorded with lander systems directly deployed in the CWC reefs, which allows us to compare our geochemical data to in-situ ocean data.

Our results reveal, that Ba/Ca ratios show stable baseline values with intermittent sharp peaks. The location of these peaks in between major growth lines and temperature reconstructions with Mg/Sr ratios (Schleinkofer et al., submitted) show that these peaks occur during Winter and are repeatable between samples from the same location. This indicates a strong external forcing mechanism and allows cross-dating of different bivalve shells. While the occurrence of Ba/Ca peaks correlates with phytoplankton maxima, the absolute Ba/Ca ratio does not correlate with the phytoplankton abundance.

Mn/Ca ratios show similar trends as Ba/Ca ratios but the peaks are phase shifted and occur slightly delayed. These peaks could be triggered by decreasing oxygen concentrations in the water caused by the decomposition of organic material.

As A. excavata does not show easily distinguishable growth lines under the light microscope despite of Mutvei staining or fluorescence microscopy, we hypothesize that P/Ca ratios might be usable to locate highly phosphorylated shell areas that usually correlate with major growth lines. P/Ca ratios show no perceivable features in the vicinity of major growth lines. Instead we recognize that Ba/Ca peaks follow a minimum in P/Ca which is possibly caused by the uptake of phosphor by plankton.

These results suggest that A. excavata have potential as a promising tool for high resolution paleoenvironmental reconstructions of both intermediate and overlying surface water masses.

References

Schleinkofer N, Raddatz J, Evans D, Gerdes A, Flögel S, Voigt S, et al. Elemental to calcium ratios in the marine bivalve Acesta excavata: an archive for high-resolution paleoceanographic reconstructions of intermediate water masses. PLoS One. Submitted

How to cite: Schleinkofer, N., Raddatz, J., Evans, D., Gerdes, A., Voigt, S., and Wisshak, M.: Ba/Ca, P/Ca, Li/Ca and Mn/Ca ratios in the deep-sea bivalve Acesta excavata: Valuable tools to reconstruct plankton dynamics in cold-water coral ecosystems?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4724, https://doi.org/10.5194/egusphere-egu2020-4724, 2020.

EGU2020-18358 | Displays | SSP1.5

Paleotemperature and paleosalinity evolution across Eocene-Oligocene Transition in North Atlantic Ocean: Insights from geochemical analysis of bivalve shells.

Justine Briard, Marc de Rafélis, Emmanuelle Vennin, Mathieu Daëron, Valérie Chavagnac, Laurent Emmanuel, Didier Merle, and Emmanuelle Pucéat

The Cenozoic period encompasses the last transition from the “greenhouse” climate of the late Early Eocene (~50 Ma) to our modern “icehouse” climate with its much lower CO2 levels, significant polar glaciation and major sea level drop. The Eocene-Oligocene transition (EOT), that marks the first major ice-sheet build-up on Antarctica, has been extensively studied as it represents the entrance into an icehouse mode. Identification of this major step of Antarctic ice-sheet build-up strongly relies on δ18O and Mg/Ca benthic foraminifera records from ODP / DSDP sites. By contrast, few records currently exist from coastal environments despite the presence of abundant fossil archives, like bivalve shells. Yet palaeoenvironmental records from these peculiar coastal sites could bring information on how they react to global climate changes and help to further understand the behavior of our climate system. In this study, we applied a multi-proxy strategy coupling δ18O, δ13C, clumped isotopes (Δ47), strontium isotopes (87Sr/86Sr) analyses on aragonitic and calcitic bivalves and sediments recovered from the Isle of Wight (London-Paris Basin, Northeastern Atlantic Ocean) to provide additional constrain on environmental changes in this region across the Eocene-Oligocene Transition (~37.8–33 Ma).

Our new coupled δ18O and Δ47 dataset highlights a marked decrease in local seawater temperatures (~ 8°C) coupled to a drop in local seawater δ18O, likely linked to the sea level drop associated with ice-cap formation and an evolution toward more proximal, brackish environment in this region (that is apparent from sediment facies evolution). We estimate the salinity decrease recorded at the local scale from the Eocene to the Oligocene as reaching about 6 PSU, from 31 to 25 PSU. Strontium isotope analyses of the bivalves support this interpretation, showing values close to that of seawater up to the EOT but a marked deviation from contemporaneous global seawater 87Sr/86Sr values toward more radiogenic values afterward. This positive deviation is in agreement with an evolution toward more proximal environments, subjected to larger freshwater inputs.

How to cite: Briard, J., de Rafélis, M., Vennin, E., Daëron, M., Chavagnac, V., Emmanuel, L., Merle, D., and Pucéat, E.: Paleotemperature and paleosalinity evolution across Eocene-Oligocene Transition in North Atlantic Ocean: Insights from geochemical analysis of bivalve shells., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18358, https://doi.org/10.5194/egusphere-egu2020-18358, 2020.

EGU2020-7732 | Displays | SSP1.5 | Highlight

Zn isotopes in deep sea corals: a useful palaeoceanographic archive?

Susan Little, Tina van De Flierdt, David Wilson, Mark Rehkämper, Jess Adkins, and Laura Robinson

Zinc (Zn) is an important bioessential trace element. Its distribution in the modern oceans reflects a combination of biological uptake, remineralization and the physical ocean circulation. Furthermore, the partitioning behaviour of Zn (DZn) and its isotopes (δ66Zn) in carbonates has been linked to ambient seawater carbonate chemistry [1-3].

Development of Zn isotopes in carbonates as a palaeoceanographic tool has been hampered by the high concentrations of Zn in contaminating material, such as lithogenic or authigenic (e.g. Fe-Mn oxide) phases. However, deep-sea corals are large enough to be subjected to aggressive physical and chemical cleaning, enabling effective removal of contaminating phases. They also have several other advantages over traditional palaeoclimate archives, including the ability to assign precise absolute ages to individual specimens based on uranium-series dating [4].

Here we present Zn/Ca and δ66Zn data for a suite of modern and recent (<1000 yr) deep sea corals from six ocean regions spanning the far North Atlantic to the Tasman Sea. We observe what appears to be species-specific Zn partitioning behaviour, but no clear links between DZn or coral δ66Zn and ambient seawater carbonate chemistry. Overall, there is good agreement between measured or best-guess modern seawater δ66Zn and coral aragonite δ66Zn values, suggesting that corals of species Desmophyllum dianthus and genus Caryophyllia do not significantly fractionate Zn isotopes during calcification. Deep sea corals may thus provide a useful archive of the past ocean Zn isotope composition and its spatial variability.

[1] Marchitto T. M., Curry W. B. and Oppo D. W. (2000). Paleoceanography 15, 299–306. 
[2] van Dijk, I., de Nooijer, L. J., Wolthers, M., & Reichart, G. J. (2017). Geochimica et Cosmochimica Acta 197, 263-277. 
[3] Mavromatis, V., González, A. G., Dietzel, M., & Schott, J. (2019). Geochimica et Cosmochimica Acta 244, 99-112. 
[4] Robinson, L. F., Adkins, J. F., Frank, N..., & van de Flierdt, T. (2014), DSR Part II 99, 184-198.

 

How to cite: Little, S., van De Flierdt, T., Wilson, D., Rehkämper, M., Adkins, J., and Robinson, L.: Zn isotopes in deep sea corals: a useful palaeoceanographic archive? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7732, https://doi.org/10.5194/egusphere-egu2020-7732, 2020.

EGU2020-8653 | Displays | SSP1.5

Early diagenesis in benthic foraminifera under anoxic conditions from the Landsort Deep, Baltic Sea (IODP Site M0063)

Sha Ni, Nadine Quintana Krupinski, Jeroen Groeneveld, Karen Luise Knudsen, Per Persson, Andrea Somogyi, Inda Brinkmann, Marit-Solveig Seidenkrantz, and Helena L. Filipsson

The chemical composition of foraminiferal calcite is widely used for studying past environmental conditions and biogeochemistry. However, high rate of microbial-derived organic matter degradation and abundant dissolved metal sources in sediment and pore waters may impede the application of paleoenvironmental proxies due to formation of secondary carbonates on the outside and/or inside of foraminiferal tests. Secondary carbonate precipitation severely alters the foraminiferal geochemistry and can be difficult to eliminate through standard cleaning procedures for foraminiferal trace element analyses. Here we present results of the mineral composition and formation sequence of diagenetic coatings on the tests of foraminifera formed under extreme anoxic conditions in the Baltic Sea deepest basin (the Landsort Deep, IODP Exp. 347, Site M0063), as well as changing trace element concentrations of authigenic carbonates on the test on a millennial time-scale. The focus is on the diagenetic carbonates present on the tests of the low-oxygen tolerant benthic foraminiferal species Elphidium selseyensis and Elphidium clavatum. We applied geochemical and imaging methods by using scanning electron microscope imaging (SEM) and energy dispersive spectroscopy (EDS), synchrotron-based x-ray fluorescence microscopy (nano-XRF), RAMAN spectroscopy and laser ablation (LA)-ICP-MS, in order to ascertain the sedimentary diagenetic processes, and the foraminiferal authigenic mineral formation sequence. The authigenic carbonates were enriched in Mg, Mn, Fe and Ba, depending on the redox environmental conditions when the authigenic carbonates were precipitated. In particular, concentrations of redox-sensitive elements such as Mn and Fe were increased in bottom waters and sedimentary pore waters under oxygen-depleted conditions in the Landsort Deep, which resulted in Mn- and Fe-enriched carbonate formation. The diagenetic alteration on foraminiferal tests provides potential opportunity to investigate past sedimentary redox environment and primary productivity in the Baltic Sea.

How to cite: Ni, S., Quintana Krupinski, N., Groeneveld, J., Knudsen, K. L., Persson, P., Somogyi, A., Brinkmann, I., Seidenkrantz, M.-S., and Filipsson, H. L.: Early diagenesis in benthic foraminifera under anoxic conditions from the Landsort Deep, Baltic Sea (IODP Site M0063), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8653, https://doi.org/10.5194/egusphere-egu2020-8653, 2020.

EGU2020-2094 | Displays | SSP1.5

The carbon-isotope signature of diagenetic carbonates

Patrick Meister and Carolina Reyes

Diagenetic carbonates often show large variations in their carbon isotope compositions. Variations are mainly the result of isotope fractionation effects during microbial metabolic processes, and these processes themselves may induce carbonate formation. Inorganic carbon from dissimilatory microbial activity shows negative carbon isotope values (d13C), in particular if methane is used as a carbon source. In turn, inorganic carbon produced during methanogenesis shows positive d13C values. The range of isotope values preserved in the carbonate phase ultimately depends on the reservoir sizes, diffusive mixing of different carbon sources, and episodic formation of carbonate (Meister et al., 2019; Meister and Reyes, 2019). The carbon-isotope signature of diagenetic carbonates therefore represents an archive of past biogeochemical activity in the subsurface.

 

References:

Meister, P. and Reyes, C. (2019) The carbon-isotope record of the sub-seafloor biosphere. In: "Tracking the Deep Biosphere through Time" (Eds. H. Drake, M. Ivarsson, C. Heim), Geosciences 9, 507, 1-25. https://doi:10.3390/geosciences9120507

Meister, P., Liu, B., Khalili, A., Böttcher, M.E., and Jørgensen, B.B. (2019) Factors controlling the carbon isotope composition of dissolved inorganic carbon and methane in marine porewater: An evaluation by reactive-transport modelling. J. Marine Systems 200, 103227, 1-18. https://doi.org/10.1016/j.jmarsys.2019.103227

 

 

How to cite: Meister, P. and Reyes, C.: The carbon-isotope signature of diagenetic carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2094, https://doi.org/10.5194/egusphere-egu2020-2094, 2020.

EGU2020-9810 | Displays | SSP1.5

Microbial alkalinity production and clay mineral alteration in marine methanogenic sediments: implications for diagenetic carbonate formation

Gerhard Herda, Elena Petrishcheva, Susanne Gier, Bo Liu, and Patrick Meister

A numerical reaction transport model was developed to simulate the effects of microbial activity and mineral reactions on the composition of the porewater in a 150-m-thick sedimentary interval drilled in the Peruvian deep-sea trench (Ocean Drilling Program, Site 1230). This site shows a zone of intense methanogenesis below 10 m sediment depth. The simulation shows that microbial activity accounts for most alkalinity production of up to 150 mmol/l, while the excess of CO2 produced during methanogenesis causes a strong acidification of the porewater. Ammonium production from organic matter degradation significantly contributes to alkalinity production, whereby ion exchange was simulated to compensate for hidden ammonium production not otherwise accounted for. Although clay minerals are reacting far too slowly to equilibrate with the porewater over millions of years, additional alkalinity is provided by alteration of chlorite, illite, and feldspar to kaolinite. Overall, alkalinity production in methanogenic zones is sufficient to prevent dissolution of carbonates and to induce carbonate formation either continuously as disseminated cryptic dolomite or episodically as hard lithified beds along a supersaturation front. The simulation presented here provides fundamental insight into the diagenetic effects of the deep biosphere and may also be applicable for the long-term prediction of the stability and safety of deep CO2 storage reservoirs.

 

How to cite: Herda, G., Petrishcheva, E., Gier, S., Liu, B., and Meister, P.: Microbial alkalinity production and clay mineral alteration in marine methanogenic sediments: implications for diagenetic carbonate formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9810, https://doi.org/10.5194/egusphere-egu2020-9810, 2020.

EGU2020-3170 | Displays | SSP1.5

Continental carbonates growth pathways, fabrics and diagenesis

Silvia Frisia, Andrea Borsato, and Giovanna Della Porta

Continental carbonates are a repository of exceptional climate and environmental changes at scales from sub-annual to decadal to millennial. Their fabrics and chemistry encapsulate information about temperature and rainfall variability, volcanic eruptions, earthquakes, vegetation changes, as well as microbial interaction. Yet, fabric and chemical properties are influenced by the crystallization pathways and, crucially, growth mechanisms and diagenesis of the carbonate crystals. Here we present examples from diverse continental settings and discuss why fabrics are extremely important to determine the accuracy of preservation of a “primary” signal.

Most continental carbonate formation is driven by degassing. This is the case of cave carbonate deposits (speleothems), which allowed tremendous breakthrough in palaeoclimate science. Speleothems form in the dark, from drip waters poor in nutrients and organic compounds. Their most common fabric consist of columnar crystals. Nanoscale investigation shows that speleothem crystals have diverse growth pathways, including particle attachment (Frisia et al., 2018). The distribution of climate-sensitive trace elements, thus, rather than following crystallographic sector zoning, follows “parallel growth layers” reflecting environmental changes. The critical parameter in growth process is the drip rate. By contrast, subglacial and cryogenic carbonates, which also grow in the dark and consist of columnar crystals, form in micro-phreatic environment where supersaturation is not attained by degassing, but by concentration of elements by slow freezing.  In this situation trace elements are incorporated following crystallographic faces and provide exceptional information of subglacial processes including volcanic eruptions (Frisia et al., 2017).

Lacustrine, spring and fluvial carbonates grow at Earth’s surface, being exposed to Sun’s light. These carbonates’ precipitation, similarly to speleothems, is promoted by degassing, but also by the presence of photosynthetic organisms and high substances organic interaction. Their fabrics are commonly characterized by micrite, which is rare in caves and in subglacial samples.

Evaporitic lake (Great Salt Lake, GSL) and spring deposits described in Della Porta (2015) were observed by TEM. One typical microfabric is peloidal micrite. The GSL peloidal micrite consists of calcite nanocrystals, and the peloids are associated with aragonite and filaments. Spring deposits peloidal micrite also consists of nanocrystal aggregates surrounded by filaments. 

Most speleothems and spring/lake carbonates document a phase of growth that involves nanocrystal aggregation, which we did not observe in the phreatic subglacial samples.

Implications for palaeoenvironmental research: In speleothems, Ostwald ripening likely transforms nanoparticle aggregates into larger crystals. Critically, in speleothems, Ostwald ripening processes result in removal of some tracers, such as Si, associated to first growth phases, and preservation of those that we use to reconstruct palaeo hydrology. In lake and spring deposits it would seem that micrite preserves the original environmental data, because micrite means that the crystals were protected from ripening by the organic part of the deposit. In subglacial carbonates, growth appears to follow a classical ion attachment at growth sites, thus, their fabrics preserve pristine primary signals.   

 

References:

Della Porta, G. (2015) Geological Society, London, Special Publications 418, 17-68.

Frisia, S. et al (2018) Earth-Science reviews 178, 68-91.

Frisia, S.,  et al. (2017) Nature Communications 8.

 

How to cite: Frisia, S., Borsato, A., and Della Porta, G.: Continental carbonates growth pathways, fabrics and diagenesis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3170, https://doi.org/10.5194/egusphere-egu2020-3170, 2020.

EGU2020-3040 | Displays | SSP1.5

Stable isotope data of modern and ancient microbialites

Alexandra S. Rodler, Sylvie Bruggmann, Steven Goderis, and Philippe Claeys

Carbonate-based reconstructions of environmental conditions in the Precambrian rely heavily on shallow-water and typically microbially-mediated carbonates. This is because Precambrian carbonate rocks formed either microbially or abiotically. Consequently, organo-sedimentary carbonate structures (microbialites) are extensively used as archives of physico-chemical conditions of early Earth environments using traditional isotopes such as stable carbon and oxygen isotopes. When post-depositional alteration is carefully evaluated, valuable information on local seawater chemistry may be gained. More recently, non-traditional isotope systems are applied to microbialites for reconstructing, for example, the redox evolution of our planet. However, interpretations of non-traditional isotope data are challenging, and information on diagenetic alteration is crucial. We present geochemical analyses of modern and ancient microbialites, which are part of an ongoing study on the chromium isotope systematics in modern and fossil microbialites (1). Here, we focus on stable C- and O-isotope data and diagenetic alteration of the analysed microbialites. This approach aims to build a framework for interpreting paleo-environmental reconstructions using non-traditional isotope systems. First results of powdered sub-samples of the modern microbialites show that stable C- and O-isotope data reliably reflect the environmental conditions of their depositional setting: high δ13C values (+2 to +8 ‰) indicate extensive microbial activity and high δ18O values point to evaporative settings. One set of Precambrian microbialite samples also has high δ13C values (~+4 ‰), similar to the modern microbialites, but in comparison to modern samples, relatively low δ18O values (~-3 ‰). Yet, another set of Precambrian microbialite samples display both low δ13C (~-0.5 ‰) and δ18O values (-3 to -6 ‰). The results are interpreted to indicate a different depositional environment and/or more likely, a stronger degree of post-depositional diagenetic alteration that might also explain the comparatively low δ53Cr values of these samples.

How to cite: Rodler, A. S., Bruggmann, S., Goderis, S., and Claeys, P.: Stable isotope data of modern and ancient microbialites , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3040, https://doi.org/10.5194/egusphere-egu2020-3040, 2020.

EGU2020-6909 | Displays | SSP1.5

Carbonate and chert genesis in the 3.35 Ga old Strelley Pool Formation (Australia): Insights from trace metals and Sm/Nd dating

Sebastian Viehmann, Simon V. Hohl, Nathalie Tepe, Martin Van Kranendonk, Joachim Reitner, Thilo Hofmann, Christian Koeberl, and Patrick Meister

Stromatolites are laminated, presumably microbial structures, consisting largely of an authigenic precipitate, thus, providing potential geochemical archives of early Earth aqueous environments and their habitability. In this study, we report trace element and Sm/Nd isotope data from Palaeoarchean stromatolites and adjacent cherts of the Strelley Pool Formation (NW Australia), obtained by ICP-MS and TIMS, to test their reliability as archives for palaeo-environmental reconstruction and to understand authigenic mineral formation.

Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a linear Sm-Nd regression line yielding an age of 3253 ±320 Ma.. In contrast, associated crystal-fan carbonates yield 2718 ±220 Ma, suggesting that their Sm-Nd isotope system was altered after deposition. Geochronological information via Sm-Nd dating of black and white cherts is limited, probably due to a reset of the isotope system during an unknown Paleoproterozoic or younger alteration event.

Carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns (REYSN; except for redox-sensitive Ce and Eu) parallel to those of modern seawater, indicating a seawater-derived origin. Positive EuSN anomalies (2.1 - 2.4), combined with heterogeneous ɛNd3.35Ga values (-3.2 to +5.8) within alternating stromatolite laminae, support that seawater chemistry was variably affected by both continental weathering and high-temperature hydrothermal fluids contributing elements of both young mafic or older felsic rocks. In contrast, black cherts show non-seawater like REYSN patterns and significant amounts of elements leached from the surrounding rocks, masking the pristine geochemical composition of ancient seawater. In conclusion, Archaean stromatolites indeed preserve pristine authigenic phases at the mm-scale that contain signatures representative of the water chemistry prevailing in the depositional environment.

How to cite: Viehmann, S., Hohl, S. V., Tepe, N., Van Kranendonk, M., Reitner, J., Hofmann, T., Koeberl, C., and Meister, P.: Carbonate and chert genesis in the 3.35 Ga old Strelley Pool Formation (Australia): Insights from trace metals and Sm/Nd dating , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6909, https://doi.org/10.5194/egusphere-egu2020-6909, 2020.

EGU2020-5285 | Displays | SSP1.5

Lutetian conid snails from the Paris and Hampshire Basins as seasonality archives of the middle Eocene

Alexander Clark, Johan Vellekoop, Zita Keleman, and Robert Speijer

During the Lutetian (middle Eocene, 48-41 Ma), Earth’s climate was in transition from greenhouse to icehouse conditions, sometimes referred to as a “doubthouse climate”. These circumstances allowed the Paris Basin (France) and Hampshire Basin (UK) to be hotspots for marine biodiversity, hosting a diverse assemblage of molluscs, including members of the Conidae family. Most species within the family are known to live for multiple years, possibly up to a decade, in fully marine conditions and mostly in shallow waters. Under these fully marine conditions, Conidae shells would be excellent recorders of sea water temperatures, allowing paleotemperature reconstruction for the two basins. However, climatic parameters such as temperature extremes or seasonality have not been well documented in the two basins during the Lutetian, with only a handful of studies available [Andreasson & Schmitz 2000, Huyghe et al. 2015]. Here, we made longitudinal and latitudinal comparisons between the two basins, using carbon and oxygen stable isotope data measured on different Conidae species, in order to provide seasonality reconstructions in north-western Europe. The focus of this research is mainly on assessing isotopic variation of seasonality within a basin and comparison between basins, including previously published data. SEM and cold cathodoluminescence shows that for both basins the preservation of the mollusc carbonate is sufficient to allow for approximations of the original environmental conditions. Three specimens from each basin were sampled by means of manual drilling along the growth axis of the shells. Obtained stable carbon and oxygen isotope data were used to reconstruct variation in paleotemperature and productivity. Following the methodology of Kobashi & Grossman 2003, patterns in the isotopic signature throughout the life of each specimen give an indication of the environmental reconstruction and any internal variability. By comparing existing and newly collected data from the same localities and family, we examine whether differences in seasonality are species-specific, due to climatic variation, or reflect environmental differences. 
Andreasson, F.P., Schmitz, B. (2000) Temperature seasonality in the early middle Eocene North Atlantic region: Evidence from stable isotope profiles of marine gastropod shells, GSA Bulletin, 112, 628-640. 
Huyghe, D., Lartaud., F., Emmanuel, L., Merle, D., Renard, M. (2015) Palaeogene climate evolution in the Paris Basin from oxygen stable isotope (δ18O) compositions of marine molluscs. Journal of the Geological Society, 172, 576-587. 
Kobashi, T., Grossman, E.L. (2003) The oxygen isotopic record of seasonality in Conus shells and its application to understanding late middle Eocene (38 Ma) climate, Paleontological Research, 7, 343-355. 

How to cite: Clark, A., Vellekoop, J., Keleman, Z., and Speijer, R.: Lutetian conid snails from the Paris and Hampshire Basins as seasonality archives of the middle Eocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5285, https://doi.org/10.5194/egusphere-egu2020-5285, 2020.

EGU2020-2842 | Displays | SSP1.5

Absolute temperature seasonality from skeletal carbonates—Techniques and limitations of oxygen- and clumped isotope analyses

Niels de Winter, Rob Witbaard, Clemens Ullmann, Anne Soerensen, Nicolas Thibault, Inigo Müller, Ilja Kocken, Philippe Claeys, and Martin Ziegler

The carbonate skeletons of marine organisms are unique archives for high-resolution climate reconstructions. Well-preserved specimens potentially allow for seasonal to even daily scale variability reconstructions of climate and environment  in deep time (pre-Quaternary), providing otherwise unavailable snapshots of climate variability during greenhouse periods (e.g. Steuber et al., 2005; Ivany et al., 2008; de Winter et al., 2017). However, uncertainties on past seawater compositions hamper use of the popular stable oxygen isotope ratio (δ18O) as proxy for paleotemperature reconstructions. The use of the independent carbonate clumped isotope (Δ47) paleothermometer, which is insensitive to changes in seawater composition, on these promising fossil archives is complicated because of sample size limitations (Fernandez et al., 2017; Bernasconi et al., 2018).

In an attempt to circumvent these issues and use the δ18O and Δ47 measurements jointly for accurate seasonal reconstructions of temperature and seawater isotope composition, we present a novel data reduction approach that combines Δ47 measurements of small (~100 µg) serially sampled aliquots to estimate summer and winter temperatures in mollusk shell records. When applied on Δ47 and δ18O measurements in the same specimens, combined with accurate shell chronologies, this approach reconstructs seasonal differences in temperature and seawater composition in a coastal site from the Campanian (Late Cretaceous) high-latitudes.

To test the robustness of these reconstructions, we apply different approaches of combining δ18O and Δ47 data on a wide range of simulated data representing various scenarios of variability in growth rate, temperature and sea water composition typical for the natural shallow marine environments of carbonate-producers. This approach tests how choices such as sampling resolution and the method of data collection and reduction influence the accuracy and reproducibility of (paleo)seasonality reconstructions in these scenarios.

Finally, we present preliminary data of δ18O and Δ47 analyses on bivalve specimens grown under controlled temperature conditions that allow us to calibrate the techniques above for temperature reconstructions. Together, these investigations pave the way for accurate, high-resolution climate reconstructions in deep time. These reconstructions provide valuable information on the dynamics of greenhouse climates, against which climate models can be compared to improve predictions of future climate.

References

Bernasconi, S. M., et al. Geochemistry, Geophysics, Geosystems, 19(9), 2895–2914, 2018.

Fernandez, A. et al. Geochemistry, Geophysics, Geosystems, 18(12), 4375–4386, 2017.

Ivany et al. Geological Society of America Bulletin, 120(5–6), 659–678, 2008.

Steuber, T. et al. Nature, 437(7063), 1341–1344, 2005.

de Winter, N. J. et al. Palaeogeography, Palaeoclimatology, Palaeoecology, 485, 740–760, 2017.

How to cite: de Winter, N., Witbaard, R., Ullmann, C., Soerensen, A., Thibault, N., Müller, I., Kocken, I., Claeys, P., and Ziegler, M.: Absolute temperature seasonality from skeletal carbonates—Techniques and limitations of oxygen- and clumped isotope analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2842, https://doi.org/10.5194/egusphere-egu2020-2842, 2020.

EGU2020-4506 | Displays | SSP1.5

A chemical investigation of microstructural changes in oyster (Magallana gigas) shells

Linda K. Dämmer, Niels J. de Winter, Michaela Falkenroth, Gert-Jan Reichart, Simone Moretti, Alfredo Martinez-García, Nils Höche, Katharina Rodiouchkina, Steven Goderis, Frank Vanhaecke, and Martin Ziegler

The shells of oysters (Family Ostreidae) are predominantly composed of two different calcite microstructures: A dense foliated structure consisting of sheet-like folia (“foliated” microstructure) and a more porous microstructure consisting of less well organized leaf-shaped crystals (“chalky” microstructure). These unique characteristics of oyster shells have been subject to a number of studies, with some authors hypothesizing that the chalky structures are mineralized by bacteria living in the shell (Vermeij, 2014). The formation of these microstructures is of great interest, because the phenomenon is unique in the mollusk phylum and because the shells of oysters are popular archives for paleoclimate and paleoenvironment reconstructions (e.g. Bougeois et al., 2018; de Winter et al., 2018). Previous authors have challenged the bacterially mediated mineralization hypothesis through microstructural observations of different parts of the oyster shell (Checa et al., 2018).

Here, we expand on this structural evidence by adding detailed observations of differences in chemical composition between the foliated and chalky microstructures. We combine information on trace element concentrations with stable carbon, oxygen, nitrogen and sulfur isotope ratios as well as carbonate clumped isotope analyses of samples from foliated and chalky structures in multiple modern specimens of Magallana gigas, the Pacific oyster. These analyses shed light on the chemical variability within the oyster shell and how it relates to the occurrence of various calcite microstructures. Given the unique isotopic signature of bacterially mediated calcite, our isotopic analysis results allow us to definitively conclude whether the chalky shell structure in modern oysters was precipitated via symbiotic microbes. Furthermore, the degree of intra-shell chemical variability has implications for paleoclimate and paleoenvirionmental reconstructions from fossil oyster shells, for which the applied trace element and isotope systems function as important proxies. The results of this study therefore yield important recommendations for sampling fossil oyster shells for reconstructions, and provide a baseline for the investigation of chemical variability between shell microstructures throughout the Ostreidae family and the mollusk phylum.

 

References

Bougeois, L., Dupont-Nivet, G., De Rafélis, M., Tindall, J. C., Proust, J.-N., Reichart, G.-J., de Nooijer, L. J., Guo, Z. and Ormukov, C.: Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters, Earth and Planetary Science Letters, 485, 99–110, 2018.

Checa, A. G., Harper, E. M. and González-Segura, A.: Structure and crystallography of foliated and chalk shell microstructures of the oyster Magallana: the same materials grown under different conditions, Scientific reports, 8(1), 7507, 2018.

Vermeij, G. J.: The oyster enigma variations: a hypothesis of microbial calcification, Paleobiology, 40(1), 1–13, 2014.

de Winter, N., Vellekoop, J., Vorsselmans, R., Golreihan, A., Soete, J., Petersen, S., Meyer, K., Casadio, S., Speijer, R. and Claeys, P.: An assessment of latest Cretaceous Pycnodonte vesicularis (Lamarck, 1806) shells as records for palaeoseasonality: a multi-proxy investigation, Climate of the Past, 14(6), 725–749, 2018.

How to cite: Dämmer, L. K., de Winter, N. J., Falkenroth, M., Reichart, G.-J., Moretti, S., Martinez-García, A., Höche, N., Rodiouchkina, K., Goderis, S., Vanhaecke, F., and Ziegler, M.: A chemical investigation of microstructural changes in oyster (Magallana gigas) shells, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4506, https://doi.org/10.5194/egusphere-egu2020-4506, 2020.

EGU2020-10873 | Displays | SSP1.5

Links between shell chemistry and microstructure – A case study using Arctica islandica

Ellen Schnabel, Kotaro Shirai, Naoko Murakami-Sugihara, Klaus Peter Jochum, Nils Höche, Kozue Nishida, and Bernd R. Schöne

Bivalves offer outstanding potential as environmental archives. However, vital effects exert a strong control on the incorporation of many trace and minor elements into the shell so that their use as environmental proxies is currently limited. Furthermore, Sr and Mg show a strong relationship to the micrometer-sized shell architecture (shell microstructure), i.e., near growth lines, which are typically dominated by irregular simple/spherulitic prismatic microstructures, the concentrations of these elements are significantly higher than in portions between growth lines (= growth increments, which are microstructurally more complex). In contrast, Ba is uncoupled from the prevailing shell microstructure. To shed more light on these issues, we conducted a combined element chemical (in-situ analysis by means of LA-ICP-MS) and microstructural analyses (using SEM) of shells of Arctica islandica collected alive in NE Iceland.

According to our findings, (1) contemporaneous shell portions in the hinge and ventral margin (both belonging to the outer shell layer) within individual specimens showed nearly identical Sr/Ca and Mg/Ca values, but Ba/Ca was 1.5 – 2.5 times higher in the ventral margin than in the hinge. (2) In agreement with previous studies, Sr and Mg were strongly elevated near annual growth lines. (3) Along an isochronous transect from the inner portion of the outer shell layer near the myostracum toward the outer shell surface (in the ventral margin), Si/Ca values increased, on average, by 75% ± 11%, whereas Na/Ca values decreased by 7% ± 1%. Along this transect, the shell microstructure gradually changed from crossed-acicular to homogeneous suggesting that Si and Na are linked to the prevailing nanometer-sized shell architecture or underlying physicochemical processes controlling their formation. (4) In the hinge, Ba/Ca, Sr/Ca, Mn/Ca and Mg/Ca attained highest values along the axis of maximum growth, but gradually decreased in slower growing (contemporaneous) shell portions away from that axis. (5) In contemporaneous shell portions (in either the hinge or the ventral margin), the concentration of some elements varied significantly among specimens, whereas others showed little variability. For example, in similar and contemporaneous shell portions of different specimens, Na/Ca values exhibited only little variation (17.4 – 23.7 mmol/mol), whereas Sr/Ca and B/Ca differed more severely (0.3 – 1.6 mmol/mol and 0.04 – 0.07 mmol/mol, respectively; both within growth increments). Despite these inter-specimen chemical differences, the shell microstructure remained largely invariant.

Our findings firstly suggest that the extrapallial fluid, if it exists at all, is chemically inhomogeneous. This could result from differences in the efficiency of transmembrane ion transport or to differences in shell formation rate along the growing margin (e.g., faster growth in the outer portion of the outer shell layer than in portions closer to the myostracum). Secondly, chemical differences among specimens may be attributed to physiological differences. Thirdly, some elements such as Ba are uncoupled to microstructural properties, but co-vary strongly among specimens suggesting an environmental control on the uptake and incorporation of this element into the shell.

How to cite: Schnabel, E., Shirai, K., Murakami-Sugihara, N., Jochum, K. P., Höche, N., Nishida, K., and Schöne, B. R.: Links between shell chemistry and microstructure – A case study using Arctica islandica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10873, https://doi.org/10.5194/egusphere-egu2020-10873, 2020.

EGU2020-21996 | Displays | SSP1.5 | Highlight

Nanostructure of biogenic aragonite: a study of otoliths and bivalve shells from a freshwater environment

Zsombor Molnár, Péter Pekker, Miklós Jakab, István Dódony, Zoltán Vitál, and Mihály Pósfai

There are numerous similarities between the otolith (an acellular calcium carbonate aggregate in the inner ears of fishes) and the shells of freshwater bivalves. Since both grow during a lifetime of the individuals, and show small increments or growth zones (in daily or subdaily periods), they are excellent time-keepers. By this capability they provide information about both the life history of the individuals and the geochemical evolution of their environments (Schulz-Mirbach et al., 2018; Cerrato, 2000). Changes of major and trace elements between the different growth zones have been studied thoroughly, but structural features, particularly those of otoliths, are not well known. We used scanning and scanning transmission electron microscopy (SEM and STEM) to study oriented ion-milled sections of an otolith and samples of Dreissena shells from Lake Balaton, a large, shallow lake in Hungary. SEM observations confirm that the growth zones within the otolith are built up of small increments, and they have a radially asymmetric appearance, whereas STEM images show that the small increments are terminated by tiny holes. Selected-area electron diffraction (SAED) patterns and HRTEM images show that the aragonite material of both samples is highly defective, with dense arrays of planar defects occurring in distinct areas, and grains joining along low-angle boundaries (around 1°). In addition, areas with multiple (double and triple) periodicities along the [110]* directions occur in both samples. Based on these preliminary observations, nanostructural features could provide important details about the growth of biogenic aragonite and the structural properties of distinct growth zones.



Cerrato R. M. (2000): What fish biologist should know about bivalve shells, Fisheries Research, 46, 39-49.

Schulz-Mirbach T., Ladich F., Plath M., Heß M. (2018): Enimgatic ear stones: what we know about the functional role and evolution of the fish otoliths, Biological Reviews, 94 (2), 457-482.

Acknowledgments: The research was supported by the ÚNKP-19-3 new national excellence program of the ministry for innovation and technology. 

How to cite: Molnár, Z., Pekker, P., Jakab, M., Dódony, I., Vitál, Z., and Pósfai, M.: Nanostructure of biogenic aragonite: a study of otoliths and bivalve shells from a freshwater environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21996, https://doi.org/10.5194/egusphere-egu2020-21996, 2020.

EGU2020-19006 | Displays | SSP1.5

Magnesium, calcium, strontium and radiocarbon in the shell of the brachiopod Pajaudina atlantica: implications for growth, biomineralisation and palaeo-proxy application

Volker Liebetrau, Hana Jurikova, Marcus Gutjahr, Daniela Henkel, Claas Hiebenthal, Stefan Krause, and Anton Eisenhauer

Brachiopods present a key taxon for Phanerozoic palaeo-climatic and palaeo-environmental reconstructions, owing to their good preservation and abundance in the geological record. Yet to date, only little is known on the mechanisms that control the incorporation of some key elements into their calcitic shells, as well as the mechanisms behind the biomineral formation itself, especially in thecideid brachiopods. To evaluate the distribution and controls on Mg, Ca, and Sr we examined the composition of natural Pajaudina atlantica Logan, 1988 (Thecideidae, Brachiopoda) originating from Canary Islands, Spain as well as specimens cultured experimentally under various pH-pCO2 and temperature conditions [1]. At a high-spatial resolution, electron microprobe analyses (EMP) revealed substantial intrashell and intraspecific Mg and Ca heterogeneities that seemed to be principally linked to growth features and different microstructures rather than changes in temperature. Strontium, on the other hand, appeared uniform across the shell and related to the culture medium or seawater Sr content. After almost two years of culturing, however, the new shell production was only minimal and cryptic, and difficult to evaluate by visual inspections. By combining culture-specific geochemical fingerprints with radiocarbon dating of natural samples, we estimated the growth rates to be on the order of several tens to few hundreds of µm per year, which may potentially suggest a large life span and slow growth of this species, and if true, would certainly make them a highly interesting archive for inferring past ocean variabilities.

[1] Jurikova H., et al. (2019) Geochim. Cosmochim. Acta 248, 370–386.

How to cite: Liebetrau, V., Jurikova, H., Gutjahr, M., Henkel, D., Hiebenthal, C., Krause, S., and Eisenhauer, A.: Magnesium, calcium, strontium and radiocarbon in the shell of the brachiopod Pajaudina atlantica: implications for growth, biomineralisation and palaeo-proxy application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19006, https://doi.org/10.5194/egusphere-egu2020-19006, 2020.

EGU2020-10590 | Displays | SSP1.5 | Highlight

Isotopic and elemental mapping of bamboo corals – reference to calcification mechanism and proxy applications

Sebastian Flöter, Jan Fietzke, Marcus Gutjahr, Jesse Farmer, Bärbel Hönisch, Gernot Nehrke, and Anton Eisenhauer

Bamboo corals are calcitic octocorals dwelling in a broad range of water depths and in all ocean basins. Their skeletons could give insight into the temporal variability of environmental parameters at their growth locations, in areas where long-time observations are often lacking. A thorough understanding of calcification mechanisms is essential to interpret the chemical composition of their high-magnesium calcite skeleton regarding environmental fluctuations of the deeper ocean. To address this issue, we employed electron microprobe analysis, confocal Raman spectroscopy, laser ablation-ICPMS and solution based multi collector-ICPMS that together provide insights into the fine-scale spatial heterogeneity of the coral chemical composition. We investigate the spatial distribution of Na, S, and Ca, as well as organic matter in skeletal sections of specimens of Keratoisis grayi (family Isididae) from the Atlantic Ocean. Two bamboo coral samples from the Atlantic and Pacific Ocean were further used to create laser ablation-based maps of δ11B and boron to carbon ratios (B/C) over the sample radii. These maps are compared with results obtained via solution based δ11B analyses on drilled samples.

An inverse correlation between Na and S is observed while S seems to be positively correlated with organic matter. We will discuss the ability of a qualitative physicochemical model to explain the observed Na and S distribution and the potential role of organic matter and amorphous calcium carbonate. Our results indicate that skeletal Na/Ca in bamboo corals is largely driven by physiological processes rather than environmental salinity variability. The spatial distribution of δ11B shows a positive correlation with B/C. The observed range of bulk δ11B - partly falling below the theoretical borate fractionation curve in seawater - is larger than the conventional measured δ11B of the calcite fraction alone. The latter cannot be explained with a spatial smoothing of the distribution during sample drilling but is rather associated with a loss of an isotopically highly variable B fraction during sample bleaching. Potential reasons for the observed differences in B isotopic range and their implications will be presented. We conclude that skeletal δ11B as a proxy for pHSW is dependent on the applied technique and investigated material fraction.

How to cite: Flöter, S., Fietzke, J., Gutjahr, M., Farmer, J., Hönisch, B., Nehrke, G., and Eisenhauer, A.: Isotopic and elemental mapping of bamboo corals – reference to calcification mechanism and proxy applications , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10590, https://doi.org/10.5194/egusphere-egu2020-10590, 2020.

EGU2020-17869 | Displays | SSP1.5

Palaeo cell size: A Novel Technique to Investigate the Coccosphere Fossil Record using Imaging Flow Cytometry

Beth Langley, Paul Halloran, Ann Power, Rosalind Rickaby, and John Love

Fossil coccospheres provide a wealth of information on cellular traits that can be compared directly to the living coccosphere such as cell size. Cell size is critical to ecosystem dynamics and particle sinking which has implications on the carbon cycle. However, cell size reconstruction is hindered by the poor preservation of coccospheres as coccospheres often disintegrate into individual coccoliths. Although palaeoecological information can be attained from individual coccoliths, assumptions must be made when correlating cell size to coccolith size. We demonstrate a novel technique using imaging flow cytometry to rapidly and reliably sort coccospheres from marine sediment by exploiting their unique optical and morphological properties. Imaging flow cytometry combines the functional insight of morphological information provided by microscopy with high sample numbers that are associated with flow cytometry. High throughput imaging overcomes the constraints of laborious manual microscopy enabling the analysis of sediments containing low concentrations of coccospheres that would simply not be feasible to manually hunt for coccospheres. By applying this technique to the fine fraction of sediments, hundreds of coccospheres can be isolated without the need for additional sample processing. Morphological information of individual coccospheres is obtained and graphical and statistical information can be extracted. This approach lends itself perfectly to rapid processing of down-core sediment samples or high spatial coverage from core-top samples and may prove valuable in investigating the interplay between a changing climate and coccolithophore response.

 

How to cite: Langley, B., Halloran, P., Power, A., Rickaby, R., and Love, J.: Palaeo cell size: A Novel Technique to Investigate the Coccosphere Fossil Record using Imaging Flow Cytometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17869, https://doi.org/10.5194/egusphere-egu2020-17869, 2020.

Despite their omnipresence in pelagic carbonate sediments, the coccoliths, the calcite biominerals produced by the coccolithophores, have historically been under-exploited in palaeoenvironmental studies. This is due, in part, to their small size (2-20 microns), which makes them difficult to isolate from other particles, and to the large differences in isotopic composition existing between coccolith calcite and equilibrium conditions. This so-called “vital effect” complicates the use of coccolith geochemistry to derive paleoclimatic signals with confidence. Recent studies from cultured and fossil coccoliths have shown that the oxygen and carbon isotopic compositions of the coccoliths are particularly sensitive to the availability of CO2 in the environment, upon which the coccolithophores rely for their photosynthetic activity. Therefore, our approach here is to test whether the coccolith geochemistry can be used as a novel proxy for surface ocean and atmospheric CO2 concentrations.

In this study, different size fractions of coccoliths were extracted from carbonate sediments of site MD95-2037 in the Northern Atlantic Ocean and run for isotopic analysis. Using calibrations between coccolith vital effects and seawater [CO2] from culture studies, we present a seawater [CO2] curve for site MD95-2037 across Termination II (130 kyrs). The curve was in turn translated into atmospheric pCO2 estimates taking into account changes in ancillary parameters (such as temperature). Coccolith-derived CO2 concentrations yield comparable values, both for the absolute numbers and trends, to the record from Vostok ice cores. This coherency is confirmed by a 80 ppm-shift in pCO2 concentrations in the North Atlantic between glacial and interglacial times reconstructed from the coccolith record.

Altogether, these datasets confirms that coccolith geochemistry can indeed be used to reconstruct past changes in [CO2]sw. Perspectives for this study include providing the scientific community with a new record of pCO2 for periods extending beyond the Vostok record, in particular the Mid-Pleistocene Transition, where a decrease in global pCO2 has been put forward to explain the shift from 41 kyr- to 100 kyr-cycles in glacial-interglacial cycles.

How to cite: Godbillot, C., Hermoso, M., and Minoletti, F.: Probing the use of coccolith geochemistry as a proxy for past carbon dioxide concentrations - Insights from Termination II in the Northern Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7471, https://doi.org/10.5194/egusphere-egu2020-7471, 2020.

EGU2020-19299 | Displays | SSP1.5

The interplay of glacial/interglacial climate-CO2 and productivity effects on coccolith calcification and vital effects across the MIS 12 to MIS 9 in the western tropical Atlantic

Alba González-Lanchas, Heather M. Stoll, José-Abel Flores, Francisco J. Sierro, Ivan Hernandez-Almeida, and Jose Guitian

Coccolithophores play an important dual role in ocean biogeochemistry: they use dissolved inorganic carbon (DIC) in the surface for both photosynthesis and coccolith calcification. Stable isotopes in coccoliths are the result of various effects, including different vital effects, allowing hypotheses about the varying active carbon acquisition strategies in response to changing environmental conditions. Understanding the physiological mechanisms that cause these changes remains challenging.

The MIS 12 to MIS 9 interval is a crucial climatic period encompassing changing glacial-interglacial cyclicity and pronounced variations in atmospheric CO2 concentration. Different paleorecords indicate that coccoliths were an important component of the carbonate fraction during this interval, with the outstanding worldwide dominance of the highly calcified coccolithophore species Gephyrocapsa caribbeanica.

The carbon isotopic fractionation during photosynthesis (εp) in alkenones, biomarkers produced by coccolithophores, is a proxy to reconstruct past aqueous CO2 concentration. Here we present a new εp reconstruction spanning this glacial/interglacial interval (460 to 330 kyr) at ODP Site 925 in the western tropical Atlantic. We aim to evaluate the interplay of CO2 and productivity effects on coccolith calcification and stable isotopes (δ18O and δ13C) in coccolith calcite integrating these data with the size and thickness of coccolith platelets and the geochemical Sr/Ca record.

The comparison of mean coccolith size with coeval samples from the deeper ODP Site 929 allows the evaluation of the degree of nannofossil dissolution across the interval.

How to cite: González-Lanchas, A., Stoll, H. M., Flores, J.-A., Sierro, F. J., Hernandez-Almeida, I., and Guitian, J.: The interplay of glacial/interglacial climate-CO2 and productivity effects on coccolith calcification and vital effects across the MIS 12 to MIS 9 in the western tropical Atlantic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19299, https://doi.org/10.5194/egusphere-egu2020-19299, 2020.

We cultured two species of Amphistegina under four pCO2 concentrations yielding variable pH (8.1 -7.6) and DIC (2340-2570 μM) at constant temperature (25 ºC) and alkalinity (~ 2500 μM). To mark the newly grown shells under the experimental conditions we spiked the culture seawater with 135Ba. The variability of trace elements within the foraminiferal shells was measured on three individuals of each species for each treatment using LA-ICPMS in the knob area. Sharp transition zones were observed between the natural and the ~tenfold increased 135Ba in the shells. The shape of the transition zone is best described by a logistic equation for population growth. We propose that this reflects the dynamics of seawater vacuoles population that serve the biomineralization process and provide Ca and DIC for calcification of Amphistegina as described in previous publications (e.g. Bentov et al., 2009). In individuals that showed significant growth (identified by 135Ba-enriched shell), B, Na and Sr showed a significant increase with DIC, while K and Mg were slightly lower or unchanged. LA-ICPMS profiles in the central knob (~70 µm depth) also revealed previously described cyclical changes in concentration of Mg, each apparently representing a growth of a new chamber. Additional elements such as K, Na and U showed similar cycles with the same frequency and phase as the Mg cycles. Sr showed variability with similar frequency but not in-phase with those of the Mg. These multi-element cycles were found both in the newly grown calcite (elevated-135Ba and pCO2) and in the natural skeleton regardless of the pCO2 treatments. These high Mg and multi-element cycles seem to be an essential part of the calcification process. They may originate from the interaction with the organic matrix resulting in elevated Mg and other elements in the primary calcite while secondary calcite of the lamination process shows lower concentrations. It is also possible that primary calcite is enriched in trace elements if an Amorphous CaCO3 (ACC) or vaterite precursors are involved. In addition, Rayleigh fractionation from a semi-closed reservoir, the presence of high Mg in the lattice or any combination of the previous causes may explain the trace elements enrichment. While changes in the pCO2 did change the average concentrations of B, Na, and Sr, they did not affect the banding of trace elements in these foraminifera, suggesting that these cycles are inherent to the biomineralization process.

Bentov, S., Brownlee, C., and Erez, J. (2009). The role of seawater endocytosis in the biomineralization process in calcareous foraminifera. Proc. Natl. Acad. Sci. U.S.A. 106, 21500–21504. doi: 10.1073/pnas.0906636106

How to cite: Levi, A., Müller, W., and Erez, J.: The effect of high pCO2 on trace elements and intrashell variability: A culture experiment with live benthic foraminifera., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13080, https://doi.org/10.5194/egusphere-egu2020-13080, 2020.

EGU2020-17249 | Displays | SSP1.5

The effect of salinity on Na/Ca in cultured shells of the foraminifer Operculina ammonoides

Hagar Hauzer, David Evans, Wolfgang Müller, Yair Rosenthal, and Jonathan Erez

Na is incorporated into marine carbonate minerals and was recently proposed as a proxy for paleo-salinity. However we demonstrated that Na/Ca ratio in foraminiferal shells (Na/Cashell) is actually a novel proxy for past ocean Ca concentrations (Casw) in benthic foraminifera (Hauzer et al., 2018). In the present study, we determined the extent to which foraminiferal Na/Ca (and other elements) change with salinity for the high-Mg large benthic foraminifer Operculina ammonoides. This laboratory culture experiment was conducted under four different salinities 32.9, 36.1, 40.65 and 43.0 PSU, at a constant temperature of 25 °C and pH of ~8.17. O. ammonoides specimens were labeled with the fluorescent dye Calcein (40 µM) for five days prior to the experiment. Experimental seawater was prepared from filtered Gulf of Eilat seawater (40.65 PSU) and the salinity was modified by the addition of deionized water or by the evaporation to the desired value at room temperature. All experimental seawater were spiked with 135Ba in order to unambiguously determine newly grown CaCO3 during spatially-resolved analysis of the shell. Six specimens of each treatment were selected according to the presence of non-fluorescent chambers past the Calcein mark. The CaCO3 shells were analyzed using the LA-ICPMS. Water chemistry was analyzed using ICP-OES and ICP-MS. Experimental foraminifera added 90-160% of their original weight, based on alkalinity-depletion measurements during the experiment. The elemental ratios of Na, Mg and Li to Ca in O. ammonoides shells increased linearly with increasing seawater salinity. In contrast, Sr/Cashell showed no resolvable change with salinity. Since Na/Cashell does correlate with salinity, it appears that it could be used as a paleosalinity proxy. However, when variations of Na/Cashell due to salinity are compared to variations due to Casw, it is clear that salinity has a minor effect compared to the Ca concentrations. Thus, when reconstructing paleosalinity, Na/Cashell will produce accurate results only for samples that are within the residence time of Casw (~1My). Furthermore, regional and global changes in ocean salinity over geological time can only slightly affect the use of Na/Cashell as a proxy for past changes in Casw.

Hauzer, H., Evans, D., Müller, W., Rosenthal, Y., & Erez, J. (2018). Calibration of Na partitioning in the calcitic foraminifer Operculina ammonoides under variable Ca concentration: Toward reconstructing past seawater composition. Earth and Planetary Science Letters, 497, 80-91.

How to cite: Hauzer, H., Evans, D., Müller, W., Rosenthal, Y., and Erez, J.: The effect of salinity on Na/Ca in cultured shells of the foraminifer Operculina ammonoides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17249, https://doi.org/10.5194/egusphere-egu2020-17249, 2020.

The calcite shells of planktonic foraminfera are a key archive for palaeoceanic reconstruction and represent one of the largest sinks of carbon from the surface ocean. Therefore, understanding the biomineralisation process of these organisms, and how responsive it is to ocean acidification, is an important part of accurately predicting the carbon cycle response to past and future climate change events. To date, the majority of the direct observational evidence on which foraminifera biomineralisation models are based comes from shallow-dwelling benthic species. Whilst this has provided a large amount of important information, it is not known how applicable these models are to the low-Mg planktonic foraminifera. In particular, key questions regarding the relative importance of seawater vacuolisation (SWV) versus calcium transmembrane transport (TMT) remain unresolved. We present the results of fluorescent labelling experiments on intact, decalcified planktonic foraminifera (Globigerinoides ruber and Globigerinella siphonifera) using the cell-impermeable dyes calcein, FITC-dextran, and SNARF-dextran, enabling direct observation of seawater vacuoles within the cell via confocal microscopy. Our results indicate that seawater endocytosis plays a dominant role in the calcification process. Seawater vacuoles can make up a large proportion of the intracellular volume, with a residence time on the order of hours. Moreover, we show that the skeleton is labelled with fluorescent dyes such that seawater derived from these vacuoles must be present at the calcification site. Along with inferences based on geochemical data [Evans et al., 2018], our results strongly argue that biomineralisation models centred on seawater endocytosis are applicable to the planktonic foraminifera.

Evans, D., Erez, J., Müller, W. [2018] Assessing foraminifera biomineralisation models through trace element data of cultures under variable seawater chemistry. GCA 236:198.

How to cite: Evans, D., Erez, J., and Müller, W.: Understanding the role of seawater vacuolisation in the biomineralisation of planktonic foraminifera using confocal microscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18090, https://doi.org/10.5194/egusphere-egu2020-18090, 2020.

EGU2020-19424 | Displays | SSP1.5

Latest Cretaceous foraminiferal ecology and palaeoceanographic inferences from chamber-specific LA-ICPMS analysis.

Michael Henehan, David Evans, Wolfgang Müller, and Pincelli Hull

Our understanding of how atmospheric pCO2 varied over the Cenozoic has been steadily improving, thanks in part to ever more numerous and more refined estimates from boron isotopes in foraminiferal calcite. However, the challenge of understanding how foraminiferal physiology and ecology might have influenced measured boron isotope-pH values becomes larger as we move towards older, extinct species that may be ever more different relative to well-studied modern descendants. For instance, shell morphology in itself may have effected differences in early Cenozoic foraminiferal carbon isotopes [1], while elsewhere some data suggest Eocene vital effects in boron isotopes may have been weaker than today [2]. To successfully extend boron isotope-derived pCO2 estimates further back into the Cretaceous, where most clades have no Cenozoic descendants, necessitates a thorough approach to understanding symbiont and depth ecology in these foraminifera. Some such information can be gleaned from trends in oxygen and carbon isotopes with size [e.g. 3], but this alone cannot fully elucidate differences in physiology and biomineralisation pathways.

Here we present new insights into the physiology and palaeoecology of several key late Cretaceous planktic foraminiferal species from element/Ca ratios, measured as depth-profiles by laser ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). While single-chamber Mg/Ca ratios support some depth migration patterns indicated from oxygen isotopes [3], our observed trends in boron incorporation with ontogeny often run counter to predictions based on carbon isotopes. Moreover, B/Ca ratios in Cretaceous foraminifera are strongly species-dependent, with studied trochospiral taxa recording far higher B/Ca ratios than co-habiting Heterohelicids, perhaps indicating fundamental differences in trace element incorporation mechanisms (and perhaps biomineralisation pathways) across different clades. We discuss the implications of these findings for proxy reconstructions in the Cretaceous, with a particular focus on expanding the horizons of palaeo-CO2 and palaeotemperature reconstruction. 

[1] Gaskell, D. E. and Hull, P. M. (2019) Symbiont arrangement and metabolism can explain high δ13C in Eocene planktonic foraminifera. Geology 47 (12): 1156–1160.

[2] Houston, R. M., Huber, B. T., and Spero, H. J. (1999) Size-related isotopic trends in some Maastrichtian planktic foraminifera: methodological comparisons, intraspecific variability, and evidence for photosymbiosis. Marine Micropaleontology 36: 169–188.

[3] Anagnostou, E., John, E., Edgar, K. M., Foster, G. L., Ridgwell, A. J., Inglis, G. N., Pancost, R. D., Lunt, D. J. & Pearson, P. N. (2016) Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate. Nature 533: 380-384.

How to cite: Henehan, M., Evans, D., Müller, W., and Hull, P.: Latest Cretaceous foraminiferal ecology and palaeoceanographic inferences from chamber-specific LA-ICPMS analysis., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19424, https://doi.org/10.5194/egusphere-egu2020-19424, 2020.

EGU2020-8966 | Displays | SSP1.5 | Highlight

Transformation of Amorphous Calcium Carbonate in Air - The Role of Additives and Humidity

Katja Goetschl, Tina Spirk, Bettina Purgstaller, and Martin Dietzel

Amorphous calcium carbonate (ACC) is one of the six well-known CaCO3.nH2O (0 ≤ n ≤ 6) solids and is of vast interest in the development of advanced materials. ACC offers enhanced performance compared to its crystalline equivalents due to its high solubility, specific surface and porosity. A large body of studies has been devoted to the applicability of ACC in pharmaceutical and industrial domains, pointing out material porosity to be a key property for its application. However, less is known about the material porosity evolution during ACC transformation into crystalline calcium carbonate (e.g. calcite or vaterite).

In this study we investigate the transformation of ACC in air and the effect of three additives (magnesium chloride, activated carbon and xanthan) at distinct humidities on the properties of the final crystalline product. ACC standard material was synthesized in either pure form or together with one of the above additives, stamped into a pellet, and exposed to 40 or 75 % RH. Mineralogical characterization of the crystalline products exhibits individual quantitative polymorph distribution induced by different additives and humidities. The most prominent result of the present study is the highly dissimilar pore size distribution when the ACC pellets were exposed to different humidities. Scanning electron microscopy combined with an image analysis software revealed 75 % RH to cause an increase of pore size of the final product by a factor of 10. These findings have significant implications to tailor and improve ACC nanomaterial designs and syntheses for pharmaceutical and industrial applications.

How to cite: Goetschl, K., Spirk, T., Purgstaller, B., and Dietzel, M.: Transformation of Amorphous Calcium Carbonate in Air - The Role of Additives and Humidity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8966, https://doi.org/10.5194/egusphere-egu2020-8966, 2020.

The crystallization pathways of amorphous into crystalline orthocalciumphosphate phases is a widely discussed topic, with processes not yet entirely understood. Current research focuses on medical applications as well as natural sedimentary systems, for example bone-tissue-engineering, bio-mineralization and phosphogenesis, with inorganic precipitation experiments under controlled ambient conditions being the first step to improve our understanding of the fundamental formation processes. By mixing of stock solutions with CaCl2/MgCl2 and NaHPO4 we created a supersaturated solution in respect to CaPO4-phases and varied the pH by adding different amounts of NaOH. Continuous sampling was performed over the period of 24 hours, with sampling intervals after 1 min, 10 min, 60 min and 24 h. In order to record temporal changes in mineralogical and chemical composition, samples (solids and fluids) were investigated by XRD, FTIR, SEM and ICP-OES, respectively. Our experiments yield considerable differences concerning the time of amorphous calcium phosphate (ACP) transformation into hydroxyapatite (HAP), heavily depending on the pH, Ca/P ratio and Mg content of the stock solution. Main results show that a higher pH stabilizes the ACP over a period of the first 60 min, whereas at lower pH the transformation of ACP into the crystalline phase already starts at 10 min after mixing. Increasing the Ca/P ratio of the stock solution results in ACP being less stable and the transformation into HAP occurs earlier. In contrast, the presence of Mg seems to delay the formation of HAP via ACP. After 24 hours the experiments showed nano-crystalline HAP and most likely some other phases as octacalcium phosphate.

How to cite: Hippler, D., Schnedlitz, T., and Purgstaller, B.: Investigating the reaction pathway of crystalline orthocalciumphosphate formation via amorphous precursors in respect to different pH, Ca/P ratios and Mg presence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20510, https://doi.org/10.5194/egusphere-egu2020-20510, 2020.

SSP1.8 – Automated image recognition in microscopic analysis for stratigraphical investigations

EGU2020-18865 | Displays | SSP1.8

Generating a pixel-wise annotated training dataset to train ML algorithms for mineral identification in rock thin sections

Jiaxin Yu, Joyce Schmatz, Marven von Domarus, Mingze Jiang, Simon Virgo, Bastian Leibe, and Florian Wellmann

Machine learning approaches and deep learning-based methods are efficient tools to address problems for which large amounts of observations and data are documented. They have proven excellent performance for many applications in the geosciences and remote sensing area. However, to one of the most fundamental data types in geoscientific studies, mineral thin sections, they have not yet been applied to its full potential. Mineral thin sections contain a treasure of information. It is anticipated that thin section samples can be systematically and quantitatively analyzed with a specifically designed system equipped with ML approaches or deep learning methods such as CNNs. The development of any artificial intelligence application that enables automated image analysis requires consistent and sufficiently large training datasets with ground truth labels. However, a dataset which serves for visual object detection in petrographic thin sections analysis is still missing. We wish to close this data gap by generating a large dataset of pixel-wise annotated microscopic images for thin sections.

The variation of optical features of certain minerals under different settings of a petrographic microscope is closely related to crystallographic characteristics that can be indicative for a mineral. In order to fully capture optical features into digital images, we generated raw data of microscopic images for different rock samples by using virtual petrographic microscopy (ViP), a cutting-edge methodology that is able to automatically scan entire thin sections in Gigapixel resolution under various polarization angle and illumination conditions. We proved that using ViP data will result in better segmentation result compared to single image acquisition.

Image annotation, especially pixel-wise annotation is always a time-consuming and inefficient process. Moreover, it would be particularly challenging when to manually create dense semantic labels for ViP data in view of its size and dimensionality. To address this problem, we proposed a human-computer collaborative annotation pipeline where computers extract image boundaries by splitting images into superpixels, while human-annotators subsequently associate each superpixel manually with a class label with a single mouse click or brush stroke. This frees the human annotator from the burden of painstakingly delineating the exact boundaries of grains by hand and it has the potential to significantly speed up the annotation process.

Instead of providing a discrete representation of images, superpixels are better aligned with region boundaries and largely reduce the image complexity. The use of superpixel segmentation in the annotation pipeline not only significantly reduce the manual workload for human annotators but also provides a significant dataset reduction by reducing the number of image primitives to operate on. In order to find the most suitable algorithms to generate superpixel segmentation, we evaluated state-of-art superpixel algorithms with regard to standard error metrics based on scanned ViP images and corresponding boundary maps traced by hand. We also proposed a novel adaption of the SLIC superpixel extraction algorithm that can cope with the multiple information layers of ViP data. We plan to use these superpixel algorithms in our pipeline to generate open data sets of several types of mineral thin sections for training of ML and DL algorithms.

How to cite: Yu, J., Schmatz, J., von Domarus, M., Jiang, M., Virgo, S., Leibe, B., and Wellmann, F.: Generating a pixel-wise annotated training dataset to train ML algorithms for mineral identification in rock thin sections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18865, https://doi.org/10.5194/egusphere-egu2020-18865, 2020.

The Mineral Liberation Analysis (MLA) setup is an automated measurement system to provide quantitative data of material features. Originally the MLA system was created and applied to mineralogical and metallurgical processing, however its usage turned out promising for extraction of quantitative data sets in other areas, including sedimentary geology, for example grain size and shape, digital textural maps, porosity, modal mineralogy or mineral associations.

The system is based on a scanning electron microscope (SEM) with an energy dispersive X-ray (EDX) spectrometer and a computer software:

(i)        backscattered electron (BSE) image analysis allows to determine grain boundaries and locations for X-ray spectral acquisition,

(ii)       X-ray spectra allow to classify mineralogical composition of samples by comparison to a library of reference spectra, and

(iii)     software automates microscope operations and data acquisition.

The application of the MLA is useful for collecting textural and mineralogical features of siliciclastic sediments, relevant for assessment of hydrodynamic properties of the flows that deposited them. Moreover, this approach seems to be crucial for analysis of the processes governing difficult to monitor submarine gravity flows, one of the most important sediment transport processes on Earth. Non-linear, non-uniform and unsteady dynamics of submarine gravity flows cause uncertainty in understanding of their nature. Usage of the MLA increases productivity, provides significant statistical representation, reduces human errors and bias as well as tedious manual analyses and is cost effective.

Research is the result of the project no. 2017/01/X/ST10/00048 funded by the Polish National Science Centre

How to cite: Pszonka, J.: Insight in hydrodynamic properties of submarine flows by the mineral liberation analysis system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-928, https://doi.org/10.5194/egusphere-egu2020-928, 2020.

EGU2020-4697 | Displays | SSP1.8

Machine learning to identify sandstone properties from thin sections

Benjamin Emmel, Ole-Andre Roli, and Anouar Romdhane

Sand volume and porosity measurements on sandstones are routine work in geoscientific applications, providing useful input to flow simulation in porous media-based analyses (e.g., in CO2 storage and/or hydrocarbon migration studies). The classic way to gain knowledge about these parameters is point counting on thin sections. This time-consuming, repetitive, and subjective work is usually done by an experienced petrographer. Attempts to automate and digitize this process are therefore promising. An example using image analysis has been discussed in Roduit, 2007. However, one step further is combining image analysis with machine learning.

In this work, we evaluate the use of a neural network learning algorithm to classify selected sandstone properties from thin section images. Our database consists of ca. 3500 thin section images from different sandstone types with known properties. The images are grouped into 8 different sand volume and 8 different porosity classes. We split the dataset into a training (85 %) and validation dataset (15 %). In the processing stage, we normalize and scale all the images to a reference number of 128 pixels. For both classifications, we trained a convolutional neural network consisting of 5 convolutional layers and 4 max pool layers. The batches are normalized after each pooling layer and a dropout layer used to reduce overfitting before flattening. A final soft max layer is added so that the recovered output can be interpreted as probability distributions. We perform the training phase with a varying number of epochs ranging between 20 and 200. A training and validation accuracy > ca. 90 % is obtained after 25 epochs. For both cases, we observe that initially high model loss for the validation data reaches low values after 50 epochs.

To further test the approach, we analyse in a second stage a holdout dataset of sandstones from the Norwegian Continental Shelf. Preliminary results show that the derived sand volumes classification reproduce the point counting results well (80 % accuracy of predicting classes or neighbouring classes). More problematic is the reproducibility of porosities. Here, models using different epochs show variable results and the ≥100 epochs models systematically underestimates the measured rock porosities. We observe that only porosity classes well represented in the initial population of training images are reproduced with high accuracy. We finally discuss strategies to overcome such limitations.

 

Roduit, N., 2007. JMicroVision: un logiciel d'analyse d'images pétrographiques polyvalent. PhD Thesis University of Geneva,116 pp. 

How to cite: Emmel, B., Roli, O.-A., and Romdhane, A.: Machine learning to identify sandstone properties from thin sections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4697, https://doi.org/10.5194/egusphere-egu2020-4697, 2020.

EGU2020-11879 | Displays | SSP1.8

The ICELEARNING project - Artificial Intelligence techniques for ice core analyses

Niccolò Maffezzoli, Giovanni Baccolo, Patrizia Ferretti, Barbara Delmonte, Kerim Nisancioglu, and Carlo Barbante

The detection of insoluble particles trapped in ice cores, like volcanic and dust particles, pollen grains, foraminifera and diatom assemblages, represents the experimental basis for multiple lines of environmental paleoresearch regarding the atmosphere, the biosphere and volcanology. To date, except for ice core dust, the detection of such particles is achieved through observations by manual microscopy. Artificial Intelligence predictive models are already applied to several research fields within geoscience, but up to date its implementation to ice core science is missing. The recently EU funded Marie Curie ICELEARNING project (2020-2022) aims to develop a two-phase routine for the automatic quantification of insoluble particles trapped in ice cores. The routine is based on a commercial Flow Imaging Microscope producing micro-scale images of insoluble particles from melted ice core samples. The image collection of mineral dust, tephra, pollen and marine foraminifera obtained from natural and/or ad-hoc prepared samples will constitute the training datasets. The images will be then analyzed by Pattern Recognition algorithms developed for automatic particle classification and counting. The routine will be specifically developed in order to be implemented in ice core Continuous Flow Analysis (CFA) systems, thus improving the more traditional methods and potentially providing continuous ice core insoluble particle records. The ICELEARNING methodology is suitable for melted ice core samples and any diluted aqueous sample, thus representing a ground-breaking analytical advancement for a wide range of research fields, from ice core science to marine geology. The innovative routine here presented is automatic and non-destructive, imperative prerequisites for future Antarctic ice core projects.

How to cite: Maffezzoli, N., Baccolo, G., Ferretti, P., Delmonte, B., Nisancioglu, K., and Barbante, C.: The ICELEARNING project - Artificial Intelligence techniques for ice core analyses , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11879, https://doi.org/10.5194/egusphere-egu2020-11879, 2020.

EGU2020-7858 | Displays | SSP1.8

Image recognition of microplastic particles in marine sediments – planned activities

Juho Junttila, Steffen Aagaard Sørensen, Thomas Haugland Johansen, and Geir Wing Gabrielsen

Information about the distribution microplastics is crucial in marine environmental research. At present, plastic pollution is an environmental threat to the oceans and more than 90 % of microplastic particles are assumed to be deposited in the sediments on the ocean floor. An efficient way of identifying microplastic particles in marine sediments would result in improved understanding of microplastic distribution, inception, accumulation areas, and impact on marine ecosystems. Today, manual classification of microplastic particles using a microscope is time consuming. The goal of this study is to identify microplastic particles in marine sediment samples with the help of image recognition and machine learning. The possibility of using artificial microplastic particles will also be tested as a means of constructing comprehensive training sets. Existing algorithms already have been successful in classification of microfossils, which could be further developed for recognition of microplastic particles. Furthermore, hyperspectral analysis will be tested to determine the origin of the microplastic particles. Our overall goal is to train classifiers that in the future successfully can recognize different plastic objects in marine sediment samples and thereby replace the time-consuming manual classification task. Comparison between human based and machine based identifications for a large number of data sets will be made to test these classifiers.

How to cite: Junttila, J., Aagaard Sørensen, S., Haugland Johansen, T., and Wing Gabrielsen, G.: Image recognition of microplastic particles in marine sediments – planned activities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7858, https://doi.org/10.5194/egusphere-egu2020-7858, 2020.

EGU2020-7606 | Displays | SSP1.8 | Highlight

First-order machine learning based detection and classification of foraminifera in marine sediments from Arctic environments

Steffen Aagaard-Sørensen, Thomas Haugland Johansen, and Juho Junttila

Foraminifera are microscopic single-celled organisms, ubiquitous to the marine realm, that construct shells during their life cycle. The shells, in general, fossilize well in the sediment and they are diagnosable due to inter-species morphology and ornamentation variability. Classifying and counting foraminiferal shells is an important tool in assessing and reconstructing past and present environmental, oceanographic and climatological conditions. However, the present day manual identification procedure, performed with a microscope and a needle/brush, is a very time consuming. Circumventing this manual procedure, using machine leaning, promises to dramatically lower the time consumption related to generating foraminiferal data records.

The first step towards that end is developing a deep learning model that can detect and classify microscopic foraminifera from 2D digital microscope pictures. The work is based on a VGG16 model implementation that has been pre trained on the ImageNet dataset and employing transfer learning techniques to adapt the model to the foraminifera task. The 2D photographic training data input was constructed by combining objects representative of and extracted from Arctic marine sediments (100µm-1mm size fraction) from the Barents Sea region. Four object groups, including 1) calcareous and 2) agglutinated benthic foraminifera, 3) planktic foraminifera and 4) sediments were used in the training data construction. With the initial set-up the algorithms were able to identify adherence to one of the four groups correctly ~90% of the time and with further fine-tuning and refinement reaching 98% correct identifications.

The second step is to use machine leaning for classification of individual benthic calcareous foraminiferal species within the sediment. The work will focus on the 20 most common species that comprise ca. ≥ 80% of the total benthic calcareous foraminiferal fauna in the Arctic. The training of the algorithms will be done using targeted species-specific 2D photographic and 3D CT scanning data in addition to potentially using hyperspectral imaging.

How to cite: Aagaard-Sørensen, S., Haugland Johansen, T., and Junttila, J.: First-order machine learning based detection and classification of foraminifera in marine sediments from Arctic environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7606, https://doi.org/10.5194/egusphere-egu2020-7606, 2020.

EGU2020-18067 | Displays | SSP1.8 | Highlight

Automated recognition and picking of foraminifera using the MiSo (microfossil sorter) prototype

Thibault de Garidel-Thoron, Ross Marchant, Martin Tetard, Michael Adebayo, and Yves Gally

Recent progresses in image processing, and image recognition have paved the way for automated procedures to classify natural objects such as foraminifera. Foraminifera are among the most useful tracers in biostratigraphy and paleoceanography. Yet, the protocol used to extract and recognize the foraminifera has not changed since the mid-18thcentury: manual picking using a brush with a stereomicroscope.

 

Here we present the results we achieve by developing the MiSo - Microfossil Sorter - automaton, to automatically pick microfossils from the sediment coarse fraction. This automated system, built with ATG Technologies, is fully operational and works 24/7 at CEREGE. In this study, we will detail the basic workflow of the automaton, processing ~8000 particles/day, and its ability to cope with the large morphological and structural variability of particles encountered in real, marginal to deep-sea sediments. We use convolutional neural networks adapted and trained on deep sea sediment samples to classify the coarse sediment particles, including planktonic and benthic foraminifera.

 

As a test case, we will compare paleoceanographic records generated by a micropaleontologist with the ones generated by our automaton: relative abundance, fragmentation rate, biometrical changes. We have studied two deep-sea cores from the equatorial Pacific to document past hydrographic changes in the late Quaternary, achieving millennial scale resolution through the last deglaciation. Using the automaton, we processed more than 500,000 foraminifera. The accuracy of recognition typically ranges around 85 to 95% depending of the morphoclasses and of the CNN used for the training. Morphoclass size probability density function and assemblages derived from the CNN will be compared to multi-proxy (micropaleontological and geochemical) records. We will discuss the ongoing applications of our workflow, from foraminifera to pteropods in deep sea sediments, and the recent updates of our system.

How to cite: de Garidel-Thoron, T., Marchant, R., Tetard, M., Adebayo, M., and Gally, Y.: Automated recognition and picking of foraminifera using the MiSo (microfossil sorter) prototype, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18067, https://doi.org/10.5194/egusphere-egu2020-18067, 2020.

EGU2020-5953 | Displays | SSP1.8 | Highlight

Foraminiferal sorting and identification: preliminary results of a test phase

Marit-Solveig Seidenkrantz, Claus Melvad, Kim Bjerge, Peter Ahrendt, Emiel J. Broeders, Anders O. B. Christensen, Mikkel Førrisdahl, Troels Poulsen, and Esben Skov

One of the best methods for studying past climate variability is the analyses of microfossils in sediment cores, especially foraminifera. However, this is highly laborious and time-consuming work. Consequently, several independent endeavors are currently underway with the aim of to automate this procedure, each testing different techniques. Here, we present preliminary results of one of these endeavors that focus on benthic foraminifera from arctic and temperate regions. The study is based on ongoing student projects carried out in collaboration between engineers and geologists. We combine robotics, imaging and machine learning.

The project is divided into three stages, with stage 1 and 2 currently ongoing: 1) Robotic separation of foraminiferal specimens from sediment particles, 2) Species classification algorithm based on Convolutional Neural Networks (CNN) including creation of training material. 3) System verification comparing analyses carried out by the automated system and a foraminiferal specialist on the same dataset. Phase 3 has not yet commenced, but initial results of 1 and 2 are available. In time, we hope to be able to build up a database of about 100 different foraminiferal species, which will cover the main assemblages of the coastal regions of the Arctic and Atlantic cold temperate regions.

For separating and picking of specimens (1) we have evaluated two different methods using a custom made xyz-platform or a robotic arm. Based on this, it seems that moving the specimens with a robotic arm will work well, but the price of such a robotic arm makes this solution less practical. In contrast, the combination of separating the specimens through shaking the sample in a tray and picking specimens for photographing and analyses using a suction system, with a custom made xyz-platform, is the best solution when considering quality, speed and price. Subsequently, the picked foraminifera/grains are delivered automatically to a digital microscopy system and photographed. So far focus on this part of the process has been developing a precise system for moving and picking, and in the future, we will work towards being able to handle particles of highly variable size in the same sample as well as increasing the speed of the picking and photographing process. 

For foraminiferal identification (2), parts of the labeling process have been automated using the Django (Python) framework and Amazon Web Services. Also, a number of imaging experiments have been investigated and several Convolutional Neural Network (CNN) algorithms are being developed and tested. In this first test, we include three different benthic foraminiferal species, with very distinct morphologies, as well as various types of clastic grains in approximately the same size fraction as the foraminiferal individuals. In this initial test case only relatively few specimens were included in the database (Ammonia batava - 168 specimens, Elphidium williamsoni - 168 specimens and Quinqueloculina seminulum specimens - 168 specimens as well as 449 clastic grains). Using a customized CNN algorithm, the separation of foraminifera from mineral grains and foraminiferal species identification could be carried out respectively with a precision, recall and F1-score of 94% and 91%.

How to cite: Seidenkrantz, M.-S., Melvad, C., Bjerge, K., Ahrendt, P., Broeders, E. J., Christensen, A. O. B., Førrisdahl, M., Poulsen, T., and Skov, E.: Foraminiferal sorting and identification: preliminary results of a test phase, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5953, https://doi.org/10.5194/egusphere-egu2020-5953, 2020.

The rich fossil record of planktonic foraminifera makes them an indispensable group for understanding interactions between climatic, oceanic, and biological dynamics through time and space. Over the past few years, we have been working to provide databases and informatics resources to standardize and speed up the generation of large datasets for community-scale analyses of planktonic foraminifera. Our public database Endless Forams Most Beautiful (www.endlessforams.org), which currently contains >34,000 unique images of individual planktonic foraminifera comprising 35 species, is an important new resource for taxonomic training and standardization, supervised machine learning, and large-scale analyses of community ecology and morphological evolution. Here, we present one such application using both the individuals in the Endless Forams database and an additional ~26,000 specimens from across the North Atlantic, identified using a supervised machine learning classifier trained using the Endless Foram data. We combine taxonomic information from these ~60,000 individuals with morphometric measurements extracted using our open source software AutoMorph to explore ecological and evolutionary drivers of modern planktonic foraminifera diversity and size.

How to cite: Hsiang, A. and Hull, P.: Next-generation community ecology: Exploring ecological and evolutionary drivers of planktonic foraminifera diversity using the Endless Forams database and a supervised machine learning classifier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9421, https://doi.org/10.5194/egusphere-egu2020-9421, 2020.

EGU2020-16034 | Displays | SSP1.8

A new automated radiolarian image acquisition, processing and identification workflow

Martin Tetard, Ross Marchant, Yves Gally, Thibault de Garidel-Thoron, and Luc Beaufort

Identification of microfossils is usually done by taxonomist experts and requires significant systematic knowledge and time, as about 300 specimens per sample are commonly identified for statistically reliable studies. Radiolaria are no exception, and their utility has been demonstrated for a long time in biostratigraphy using the presence / absence of some species, as well in palaeoceanographic reconstructions (past productivity, temperature, and water masses variability). Traditionally, these studies have required the manual identification of numerous species in a lot of samples under a transmitted light microscope, which is very time consuming. Furthermore, identification may differ between operators, biasing reproducibility. Recent technological advances in image acquisition, processing, and recognition now enable automated procedures for this process, from microscopic slide field-of-view acquisition to taxonomic identification.

 

A new workflow was developed for radiolarian acquisition, processing and identification. Firstly, a new protocol was developed as a proposed standard methodology for preparing radiolarian microscopic slides. We mount 8 samples per slide (using 12x12 mm cover slides) on which radiolarians were randomly and uniformly decanted using a new 3D-printed decanter that minimizes the loss of material. The slides are then automatically imaged using an automated transmitted light microscope. About 500 individual radiolarian specimens (excluding the broken and overlaying specimens) are recovered (about 4000 specimens per slide) from 3375 original fields of view (15 images z-stacked per FOV x 225 FOVs) per sample, after which automated image processing and segmentation is performed using a custom plugin developed for the ImageJ software. Each image is then classified using a convolutional neural network (CNN) trained on a database of radiolarian images.

 

To create the CNN classification stage, a dedicated software program, ParticleTrieur, was used to annotate a large dataset of radiolarian taxa (currently more than 27488 images, corresponding to 101 classes, from Neogene to recent). This software enables the visualisation and assignation of radiolarian pictures to defined taxa by progressively learning and suggesting taxa labels based on previous labelling. This database was then used to train a CNN (convolutional neural network) for the automated taxonomical identification stage. After fusing classes containing less than 10 images into a single “other” class, 69 classes were trained to be recognised with an overall accuracy of 93 %. This new workflow will now be used on a Miocene to Recent sedimentary record from the IODP expedition 363 (Core U1488A), recovered in the West Pacific Warm Pool.

How to cite: Tetard, M., Marchant, R., Gally, Y., de Garidel-Thoron, T., and Beaufort, L.: A new automated radiolarian image acquisition, processing and identification workflow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16034, https://doi.org/10.5194/egusphere-egu2020-16034, 2020.

EGU2020-17548 | Displays | SSP1.8

Automatic calcareous nannofossil biostratigraphy using the latest version of SYRACO

Luc Beaufort, Yves Gally, Thibault de Garidel-Thoron, Ross Marchant, and Martin Tetard

SYRACO (SYstème de Reconnaissance Automatique de COccolithes) is a software that pilots an automatic microscope and a digital camera in order to automatically recognize coccolith species and measure their morphological characteristic based on artificial neural networks. The first version was displayed in 1996 (Dollfus and Beaufort, 1996; 1999) and was scientifically used for the first time in 2001 (Beaufort et al., 2001). SYRACO evolved during the last 20 years in many aspects such as the architecture of the neural networks, the image scanning and pre-treatments. Twenty years ago, SYRACO was dedicated to quaternary paleoceanographic studies, because it was able to recognize morphological classes. With all the developments, it is now able to be used in biostratigraphy as it is able to determine coccolith species. The latest version of SYRACO will be described, and an example of application to a south Pacific core will be given.  

 

Beaufort, L., de Garidel Thoron , T., Mix, A. C., and Pisias, N. G.: ENSO-like forcing on Oceanic Primary Production during the late Pleistocene, Science, 293, 2440-2444, 2001.

Dollfus, D., and Beaufort, L.: Automatic pattern recognition of calcareous nannoplankton, Neural Network and their Applications : NEURAP 96, Marseille, France, 1996, 306-311, 

Dollfus, D., and Beaufort, L.: Fat neural network for recognition of position-normalised objects, Neural Networks, 12, 553-560, 1999.

How to cite: Beaufort, L., Gally, Y., de Garidel-Thoron, T., Marchant, R., and Tetard, M.: Automatic calcareous nannofossil biostratigraphy using the latest version of SYRACO, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17548, https://doi.org/10.5194/egusphere-egu2020-17548, 2020.

SSP1.9 – Integrating stratigraphy, sedimentology, paleoclimate and human evolution in- and out of Africa?

EGU2020-20138 | Displays | SSP1.9

The Dynamic History of the Saharan Desert revealed by 11 Million Years of Exported Dust

Anya Crocker, B. David Naafs, Thomas Westerhold, Rachael James, Matthew Cooper, Ursula Röhl, Richard Pancost, Colin Osborne, David Beerling, and Paul Wilson

The Sahara is the largest hot desert on Earth and the source of about half of the world’s atmospheric dust which acts to fertilize the Atlantic Ocean and Amazon Basin. The timing and cause of Saharan desert inception are vigorously debated, but northern Africa is widely suggested to have dried progressively with global cooling through the late Cenozoic, favoring both desert and C4-grassland savanna expansion. We present a wide range of data, encompassing sediment geochemistry and grain size distributions, plant wax isotopic signatures and lithogenic radiogenic isotopes to explore when and why desert conditions were established on North Africa. Our work on North Atlantic deep-sea sediments reveals persistent waxing and waning of Saharan dust input, with astronomically forced aridity in the interior of northern Africa more than three times earlier than the widely invoked date for the onset of desert conditions and no major changes in dust source regions over the last 11 Myr. This result strongly suggests that the Saharan desert is older and more dynamic than previously documented. Our data also challenge suggestions of a simple long-term escalation of northern African aridity driving an associated grassland expansion and provide a new framework from which to assess floral and faunal evolutionary outcomes on Africa, including the expansion of the C4-savanna ecosystem and the development of our hominid ancestors. 


How to cite: Crocker, A., Naafs, B. D., Westerhold, T., James, R., Cooper, M., Röhl, U., Pancost, R., Osborne, C., Beerling, D., and Wilson, P.: The Dynamic History of the Saharan Desert revealed by 11 Million Years of Exported Dust, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20138, https://doi.org/10.5194/egusphere-egu2020-20138, 2020.

EGU2020-10826 | Displays | SSP1.9

An ocean view of African climate change during the last 620,000 years

Stefanie Kaboth-Bahr, Asfawossen Asrat, Andrew S. Cohen, Walter Düsing, Verena Foerster-Indenhuck, Henry Lamb, Mark A. Maslin, Frank Schäbitz, and Martin H. Trauth

It has been a long-standing and passionately discussed hypothesis that important developments in human origins over the last 6-8 Ma coincided with environmental change, including cooling, drying, and wider climate fluctuations. However, testing these hypotheses is difficult as both high resolution climate records and fossil records of early human populations are often incomplete and poorly dated. Thus, to better understand the role that past African climate changes might have played in the evolution and dispersal of our ancestors, in particular Homo sapiens, we have developed a ~620,000 year record of humidity variability from the Chew Bahir basin situated in southern Ethiopia. This 293 m composite lacustrine sediment succession was compiled from two parallel cores HSPDP-CHB14-2A and 2B collected as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) in 2014. We utilized the log(K/Zr) ratio determined by micro X-ray fluorescence (μXRF) scanning to analyse past moisture changes in the Chew Bahir basin. By placing our results into the existing framework of marine and terrestrial proxy records from various parts of Africa and its surrounding oceans we document a close coupling between the spatio-temporal distribution of African rainfall and sea-surface temperature changes in the Indo-Pacific realm on orbital time scales. We argue that this coupling is facilitated by shifts in the Walker and Hadley circulations in response to insolation variability at the same time.

How to cite: Kaboth-Bahr, S., Asrat, A., Cohen, A. S., Düsing, W., Foerster-Indenhuck, V., Lamb, H., Maslin, M. A., Schäbitz, F., and Trauth, M. H.: An ocean view of African climate change during the last 620,000 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10826, https://doi.org/10.5194/egusphere-egu2020-10826, 2020.

EGU2020-19743 | Displays | SSP1.9

Palaeoenvironmental expression of humid phases in the western Nefud Desert over the past c. 500,000 years

Richard Clark-Wilson, Simon Armitage, and Ian Candy

Orbitally-driven humid phases in arid regions such as the Arabian and Saharan Deserts have played an important biogeographic role in ancient human dispersals, range expansions/contractions and population structure. The timing and regional climatic pattern of humid phases has been shown by multiple long-term continuous palaeoenvironmental records from both marine and terrestrial (speleothems and long palaeolake cores) archives. These attest to episodic humid phases across this region in line with peak interglacial periods over the Pleistocene. However, these records lack detailed information at the scale at which humans interact with the environment, meaning these interactions are poorly understood. To address this, we apply multi-proxy palaeoenvironmental analysis to interdunal carbonate/siliceous sediment beds that formed during episodic humid phases over the past c. 500,000 years in the western Nefud Desert, Saudi Arabia. While such deposits are short relative to many marine, speleothem and palaeolake records, they provide “snapshots” of the palaeoenvironmental conditions experienced by ancient humans. Importantly, these deposits are often directly associated with Lower and Middle Palaeolithic archaeology, demonstrating they were an important locus for ancient human activity during humid phases.

Our analysis demonstrates that humid intervals related to MIS 11, 9, 5e and 5a follow a simple environmental pattern where relatively stable interdunal lake bodies existed through a single humid phase. In contrast, MIS 7 is climatically complex as the sediment record demonstrates a dynamic hydrological system fluctuating between lacustrine and palustrine conditions within a single humid interval. Where available, diatom or invertebrate palaeoecology data consistently indicate predominantly fresh waters across multiple humid intervals, and this is supported by a lack of evaporitic minerals (i.e. gypsum and halite) through all sequences. We therefore argue that the western Nefud Desert has repeatedly provided vital freshwater resources for ancient humans and other fauna over the past c. 500,000 years.

How to cite: Clark-Wilson, R., Armitage, S., and Candy, I.: Palaeoenvironmental expression of humid phases in the western Nefud Desert over the past c. 500,000 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19743, https://doi.org/10.5194/egusphere-egu2020-19743, 2020.

EGU2020-7679 | Displays | SSP1.9

A 260 000-year reconstruction of diatom community dynamics and photosynthetic pigments in Lake Chala, a tropical crater lake

Heidi Tanttu, Christine Cocquyt, Dirk Verschuren, and Elie Verleyen

Lake Chala is a c. 90 m deep meromictic, oligotrophic crater lake near Mt. Kilimanjaro in equatorial East Africa. This sub-humid tropical region experiences two rainy seasons separated by a long dry season in June-August, when deep mixing fuels the epilimnion with nutrients resulting in increased phytoplankton primary production. Within the ICDP DeepCHALLA project, a 215-m long, continuous sediment sequence was obtained, which provides a unique opportunity to study long-term climate dynamics and aquatic ecosystem response during the past c. 260 000 years. Here we analyzed fossil pigments and diatom assemblages to reconstruct temporal dynamics in the lake’s phytoplankton community structure with millennial-scale resolution. Fossil pigments were analyzed using high-performance liquid chromatography, and a minimum of 400 valves were counted and identified with best-possible taxonomic discrimination from sediment samples taken at c. 800-yr intervals throughout the last glacial cycle (back to c. 160 kyr BP) and at c. 1600-yr intervals throughout earlier lake history. The most abundant pigments were zeaxanthin and lutein, reflecting the presence of cyanobacteria and green algae. Despite the high diatom content of the sediments, the diatom marker pigment fucoxanthin was almost absent, which we attribute to its labile nature. A small cyclotelloid diatom resembling the tychoplanktonic species Discostella stelligera at the base of the sequence probably reflects open-water conditions with the proximity of littoral habitats during the early filling stages of lake ontogeny. High proportions (20-50%) of an Encyonema species at c. 240-230 kyr BP indicate increased availability of benthic habitats, possibly because of a marked low-stand at the time of early sediment infilling when the central ash cone on the basin floor was still exposed. A phase of abundant needle-like Nitzschia and generally higher, yet fluctuating, pigment concentrations suggest a relatively moist environment with deep water and a stable stratification at c. 220-140 kyr BP. After c. 140 kyr BP, Afrocymbella barkeri appears for the first time, and from then onwards until the modern times the diatom community is composed of fluctuating abundances of Afrocymbella and needle-like Nitzschia taxa. The highest diatom biovolumes yet pronounced low carotenoid concentrations occur during the Afrocymbella-dominated (up to 100 %) intervals between c. 110 and 90 kyr BP and between c. 22 and 17 kyr BP, which broadly coincide with the MIS5 African megadrought and the Last Glacial Maximum, respectively. This suggests that during those time periods, the lake experienced pronounced dry and windy climate conditions, which triggered relatively deep mixing. This probably enhanced internal nutrient cycling and the injecting of oxygen to the bottom waters, which facilitated diatom growth in the epilimnion and resulted in pigment degradation in the hypolimnion. Superimposed on these long-term patterns, we found many short-term fluctuations in the appearance of different Nitzschia taxa, which may reflect stochastic colonization and extinction events, rather than actual climate-driven changes in the abiotic environment of Lake Chala.

How to cite: Tanttu, H., Cocquyt, C., Verschuren, D., and Verleyen, E.: A 260 000-year reconstruction of diatom community dynamics and photosynthetic pigments in Lake Chala, a tropical crater lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7679, https://doi.org/10.5194/egusphere-egu2020-7679, 2020.

EGU2020-11005 | Displays | SSP1.9

Tectonic and geochemical controls on soil edaphic variability in the southern Kenya Rift, implications for early hominin land use

Simon Kübler, Stephen Mathai Rucina, Maurice Obunga, Eileen Eckmeier, Donjá Aßbichler, and Geoffrey Charles Plume King

We have studied the importance of geological and soil edaphic factors for the location and duration of inhabitance of hominin sites in the southern Kenya Rift, East Africa. Using examples from the Lake Magadi-Olorgesailie region, we demonstrate that field mapping and analytical techniques derived from geology and soil science can provide important information for research in early hominin migration and land use.

The Lake Magadi-Olorgesailie region is located in the center of the ~60-km wide rift floor and characterized by a complex network of sub-parallel, nearly vertical, fault escarpments. The largest area of the rift floor is covered by trachyte flows, while other volcanic rocks including basalts, phonolites and carbonatites are located around Mt. Olorgesailie, Mt. Esayeti, Mt. Suswa and Singaraini. The Mid Pleistocene Olorgesailie site is famous for an unusual abundance of hominin artefacts, fossil mammals and palaeoenvironmental indicators, preserved in sediments spanning ~1.2 to <0.4 Ma and has been the subject of wide-ranging and intensive studies on hominins and their archeology. Other important hominin sites in the region are located in the Koora Graben, and in the vicinity of Lake Magadi. 

We have analyzed the chemical composition of a large number of geological and soil samples in the southern Kenya Rift, in order to understand the control of geochemical and tectonic processes on the release and distribution of vital soil nutrients.    

Results show that in the study region volcanic, tectonic and related pedogenic processes created a complex suite of landscape features potentially advantageous for human habitation. Analysis of soil samples from the main volcanic and metamorphic rocks as well as from sedimentary deposits shows that soil edaphic properties are closely correlated with the chemical composition of the parent materials and that deficiencies of soil nutrients are reflected in the mineralogy of the volcanic rocks. Particularly, deficient levels of calcium are sourced in the lack of calcium-bearing minerals in soils developed on trachytic rocks. Further, we show that soil nutrient distributions correlate with the relief created by tectonic faulting. We observed a significant increase of the concentrations of Ca, Mg, P in soils, with proximity to active normal faults.

 We suggest that the combination of complex terrain and patchy nutrient distributions created narrow migration corridors potentially exploited by animals and the humans who hunted them. Our study implies that tectonics, geology and related soil edaphics have been important drivers for human habitation and strategic land use. Knowledge of these processes and their impact on past human-landscape interactions contributes to a broader understanding of how landscapes influenced hominin behavior and subsistence strategies in prehistoric time.

How to cite: Kübler, S., Rucina, S. M., Obunga, M., Eckmeier, E., Aßbichler, D., and King, G. C. P.: Tectonic and geochemical controls on soil edaphic variability in the southern Kenya Rift, implications for early hominin land use, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11005, https://doi.org/10.5194/egusphere-egu2020-11005, 2020.

EGU2020-4855 | Displays | SSP1.9

Understanding modern kinetic isotope effect in Anjohibe cave, in Northwestern Madagascar: a key to calibrate speleothem δ18O and δ13C

Ny Riavo G. Voarintsoa, Antsa Lal’Aina J. Ratovonanahary, Zafitafika Miandrisoa Rakotovao, and Steven Bouillon

Madagascar, an island located ~300km off the eastern coast of Africa, is a natural laboratory to study paleoclimate and paleoenvironment. It holds a key position in the Indian Ocean and in Africa, as information from it has particularly helped fill gaps in paleoclimate reconstruction in the Southern Hemisphere, where such information is still scarce. Madagascar is seasonally visited by the Intertropical Convergence Zone (ITCZ) and experiences monsoon during austral summers. Furthermore, it hosts caves where speleothems can be found. Speleothems preserve a range of continuous geochemical records, mainly stable isotopes, that allow scientists to predict changes happening in the past.  In Madagascar, speleothem studies have revealed distinct early, mid, and late Holocene climatic regimes that were linked to the latitudinal migration of the ITCZ, and the monsoonal responses associated with the migration. Other speleothem studies revealed evidence of the African Humid Period, rapid climate changes, and most importantly the shift in δ13Cc starting ca. AD 800, that was attributed to anthropogenic activities. Although information from these speleothems is unquestionably significant, there are still gaps in isotopic proxies interpretation, mainly in linking modern environments where these speleothems grew and the signals they preserve. Such modern information is however fundamental to calibrate paleo-based climate and environmental reconstructions in Madagascar, which could be a key to refine their past interpretation. In this study, we performed an in-cave spatial test to understand kinetic isotope effect in Anjohibe Cave and to define oxygen isotopic fractionation between speleothem carbonate and its parent water and carbon isotopic fractionation between speleothem carbonate and the corresponding dissolved inorganic carbon (DIC). Results have been compared with modern calibration studies on speleothems from other locations worldwide, and we found that our data fit within the empirical relationship for cave-specific CaCO3-H2O isotope fractionation, grouping a range of monitored caves worldwide, 1000 ln α = 16.1 (103T-1(°K))–24.6 of Tremaine et al. (2011). Other physico-chemical parameters in Anjohibe Cave have also been measured, and they will be used to discuss potential linkages with the spatial variability in the  modern speleothem stable isotopic values and their corresponding parent water and DIC.

Tremaine, D.M., Froelich, P.N., Wang, Y., 2011. Speleothem calcite farmed in situ: Modern calibration of δ18O and δ13C paleoclimate proxies in a continuously-monitored natural cave system. Geochim Cosmochim Acta 75, 4929-4950.

How to cite: Voarintsoa, N. R. G., Ratovonanahary, A. L. J., Rakotovao, Z. M., and Bouillon, S.: Understanding modern kinetic isotope effect in Anjohibe cave, in Northwestern Madagascar: a key to calibrate speleothem δ18O and δ13C, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4855, https://doi.org/10.5194/egusphere-egu2020-4855, 2020.

Over the past 20 years a series of scientific drilling campaigns around Africa have yielded exciting new information about the evolutionary ecological history of that continent. Most of these records have come from highly resolved lacustrine deposits with rapid sedimentation rates, and primarily, though not exclusively, have come from the East African Rift Valley, spanning the last ~3.5Ma. Important insights about both lacustrine and terrestrial ecosystem evolution have emerged, including ones with implications for the ecological context of human evolution. During the transition from the Late Pliocene warm period into the Quaternary, phytoliths, charcoal, pollen and leaf wax records are reshaping our understanding of fine scale structure of landscape vegetation transformation, and the implications these changes had for resources and cover that mammals (including early hominins) relied upon.  Pleistocene drill core paleoecological records from Lake Malawi have provided evidence for transformations of that lake’s ecosystem, including water column mixing, transparency and nutrient recycling, that help explain the explosive phylogenetic radiation of that lake’s extraordinary endemic cichlid fish fauna. And high-resolution records from that same lake spanning the time of the ~75ka Toba super-eruption allow us to test and falsify hypotheses linking volcanic activity to wholesale transformation of the African ecosystem, including purported links to modern human population bottlenecks. These valuable archives will in the future be complemented by even longer records from Africa’s oldest lake, L. Tanganyika, allowing us to build a comprehensive picture of African ecosystem evolution extending back to the late Miocene.

How to cite: Cohen, A. S.: Continental scientific drilling: A game changer for understanding ecosystem evolution in Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1504, https://doi.org/10.5194/egusphere-egu2020-1504, 2020.

It still remains unclear what caused the disappearance of Neanderthals during the last glacial period. To determine whether their demise was mainly due to abrupt climate change, interbreeding or competition, I use a spatially resolved numerical hominin dispersal model that simulates the interaction of Anatomically Modern Humans and Neanderthals in the rapidly varying climatic environment of the last ice age. The numerical simulations, which are in good agreement with archeological and fossil data, document that rapid temperature and vegetation changes associated with Dansgaard-Oeschger events played no discernible role in Neanderthal extinction. Instead, the emerging resource competition in Eurasia between Homo sapiens and Neanderthals, along with low levels of interbreeding were the primary drivers for the demise of Neanderthals. 

How to cite: Timmermann, A.: Simulating Neanderthal extinction: the role of abrupt climate change, resource competition and interbreeding, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1724, https://doi.org/10.5194/egusphere-egu2020-1724, 2020.

EGU2020-5588 | Displays | SSP1.9

Palaeoenvironment of the earliest hominins in western Europe: the Guadix-Baza Basin

Hervé Bocherens, Hugues-Alexandre Blain, Mikael Fortelius, Juha Saarinen, Christian Sanchez Bandera, José Antonio García-Solano, Deborah Barsky, Carmen Luzón, and Juan Manuel Jiménez Arenas

The Guadix-Baza Basin (Granada Province, Southern Spain) is the richest area in Western Europe for the study of early hominin dispersal and evolution, having yielded the earliest localities with evidence of hominin occupation (a deciduous human molar, lithic industries and cutmarks) together with a rich large and small vertebrate assemblage dated to around 1.4 Ma. A key question is whether environmental changes were involved in the arrival of hominins in this region at this time. To answer this question, possible environmental differences between one older site lacking evidence for hominin occurrence (Venta Micena VM, ~1.6 Ma) and younger sites with undisputable evidence (Barranco León BL and Fuente Nueva-3 FN3, ~1.2-1.5 Ma) were investigated using various approaches, including carbon and oxygen isotopes in tooth enamel, tooth wear analysis, ecometrics and microvertebrates (amphibians, reptiles, mammals) as proxies for palaeoclimate.

Tooth enamel powders were collected from herbivorous mammal specimens from the three sites. For several specimens, enamel was sampled serially to document intra-annual dietary and/or habitat changes for the studied individuals. A large diversity of herbivorous taxa was sampled, including cervids, bovids, equids, rhinoceros, hippopotamus and mammoths. The analyses were conducted at the University of Tübingen (Senckenberg Centre for Human Evolution and Palaeoenvironment).

Carbon isotopic results from the three sites showed that the plants foraged by herbivores were essentially of C3 photosynthetic pathway (trees, shrubs and C3-grass adapted to mild growth season), which is consistent with the results of tooth wear analysis indicating browsing or mixed feeding with browsing preference for most taxa. The consumption of some C4 plants for some herbivores has been detected only in Barranco León, which is consistent with the results of palaeoclimatic investigations based on ecometrics and microvertebrate fauna, indicating a particularly wet and warm climate for this site compared to both others and colder conditions in Venta Micena, the site devoid of hominins. Oxygen isotopic results seem to be essentially related to browsing (high values) versus grazing (lower values) and to different habitats (lowest oxygen isotopic values for semi-aquatic hippos). The differences in isotopic results among taxa are in agreement with those of dietary preferences from mesowear tooth analysis. In addition, in a context of still Mediterranean climate with 4-months aridity during summer, isotopic variations within teeth suggest in some cases significant changes in foraging through a year, which could be related to local seasonal changes or mobility across areas with different vegetation types.

The first results of this multidisciplinary research project financed by the Leakey Foundation and a General Research Project from the Andalusian Regional Government help us to refine the palaeoenvironmental reconstruction around the time of the earliest arrival of hominins in Southern Spain. In combination with the climatic data provided by ecometrics and microvertebrate investigations, it allows us to develop a more detailed framework for the interpretation of the carbon and oxygen isotopic data from tooth enamel in a Mediterranean climate context, which corresponds to the type of climatic conditions where the earliest hominins occur in Europe in the Early Pleistocene.

How to cite: Bocherens, H., Blain, H.-A., Fortelius, M., Saarinen, J., Sanchez Bandera, C., García-Solano, J. A., Barsky, D., Luzón, C., and Jiménez Arenas, J. M.: Palaeoenvironment of the earliest hominins in western Europe: the Guadix-Baza Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5588, https://doi.org/10.5194/egusphere-egu2020-5588, 2020.

EGU2020-10806 | Displays | SSP1.9

Climate change and human lakeside adaptation in the Central Afar Region (Lake Abhe basin, Ethiopia & Djibouti) during the Later Stone Age - Neolithic transition: a multi-scalar and multi-proxy approach

Carlo Mologni, Lamya Khalidi, Marie Revel, Laurent Bruxelles, Jessie Cauliez, Fabien Arnaud, Emmanuel Malet, Eric Chaumillon, Thibault Colombier, Gourguen Davtian, Laure Schenini, Clément Ménard, and Isabelle Crevecoeur

Throughout the last 20 ka, tropical Africa was the site of significant hydrological changes related to variations in the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that gradual long-term monsoon humid oscillations (African Humid Period ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity (HS1, YD, 8.2 ka, 4.2 ka). These abrupt hydrological changes could have caused drastic transformations in landscape patterns, providing favourable ecosystems, but also produced arid environments that may have restricted human exploitation of the landscape.

The Abhe Lake basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater and terrigenous inputs from the Ethiopian Highlands, and is a hydro-sedimentary system sensitive to hydroclimatic change. Since 2014, in the context of the VAPOR-Afar and PSPCA programs (in Ethiopia and Djibouti respectively), we have intensified scientific investigations over this basin with the objective of exploring the evolution of Holocene hydroclimatic change, its impact on landscapes and on prehistoric human behaviour during one of the most forcible transitions in human history, that from a dominantly hunter-gathering way of life to the food production societies one.

We present the first results of this research that combines paleoclimatological, geomorphological and geoarchaeological studies based on a new set of 14C datations on two lacustrine cores, on several morpho-sedimentary outcrops and on 8 new archaeological sites spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the modalities of the African Humid Period and of the 8.2 and 4.2 ka hyperarid episodes, coupling paleolake-level reconstitution and lacustrine sediment analysis (paleolimnology, geochemistry); b) evaluate the impact of these hydroclimatic oscillations on perilacustrine sedimentary formation processes, especially for pedogenic formations; c) and better understand the relationship between environmental change and the development of one of the most important economic and cultural innovations, that of domestication.  

How to cite: Mologni, C., Khalidi, L., Revel, M., Bruxelles, L., Cauliez, J., Arnaud, F., Malet, E., Chaumillon, E., Colombier, T., Davtian, G., Schenini, L., Ménard, C., and Crevecoeur, I.: Climate change and human lakeside adaptation in the Central Afar Region (Lake Abhe basin, Ethiopia & Djibouti) during the Later Stone Age - Neolithic transition: a multi-scalar and multi-proxy approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10806, https://doi.org/10.5194/egusphere-egu2020-10806, 2020.

EGU2020-7055 | Displays | SSP1.9

Simulating multiple wave human dispersals out of Africa

Jiaoyang Ruan and Axel Timmermann

Human fossil and archeological findings indicate that Anatomically Modern Humans (AMHs) may have migrated from Africa into Eurasia multiple times during the last glacial period. However, mtDNA-based genetic data (haplogroup L3 & its daughters M, N) appear to be more consistent with a single wave dispersal ~ 70-60 ka, coinciding with one of the driest periods in northeastern Africa. 

To reconcile this discrepancy and better understand the migration routes and interactions of different groups of AMHs, we developed a new version of the Hominin Dispersal Model (HDM, version 2). The phenomenological reaction diffusion model simulates a realistic human dispersal in a spatio-temporally varying climatic environment.  In our configuration, we introduce a group which represents individuals which dispersed into Asia prior to 60 ka and a group which migrated into Eurasia post-60 ka. An ensemble of parameter sensitivity experiments suggests that their interaction caused a characteristic east-west gradient in admixture across Eurasia, which is consistent with latest genetic datasets, which reveal a faint signal of pre-60 ka dispersal waves in Southeast Asians and individuals from Papua New Guinea. Moreover, our simulations provide new insights into possible migration routes of AMHs. Based on this analysis we propose a new hypothesis to explain the increased Neanderthal DNA percentage in present-day Asians relative to Europeans.

How to cite: Ruan, J. and Timmermann, A.: Simulating multiple wave human dispersals out of Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7055, https://doi.org/10.5194/egusphere-egu2020-7055, 2020.

EGU2020-7304 | Displays | SSP1.9

Revisiting Lake Garba Guracha, high altitude lake in the Bale Mountains, Ethiopia: reconstructing Late Glacial – Holocene lake level history using δ2H/δ18O biomarker analyses

Lucas Bittner, Marcel Bliedtner, Dai Grady, Graciela Gil-Romera, Catherine Martin-Jones, Bruk Lemma, Henry F. Lamb, Cindy De Jonge, Hanno Meyer, Bruno Glaser, and Michael Zech

Our knowledge of East African paleoclimate is largely based on marine core and paleolimnological reconstructions. Accordingly, more humid climatic conditions such as the African Humid Period (AHP) are usually associated with summer insolation-driven increased monsoonal precipitation and the movement of the Congo Air Boundary.

In order to contribute to this discussion and to reconstruct the paleoclimate of the afro-alpine Bale Mountains, Ethiopia, within the DFG Research Unit 2358 ‘The Mountain Exile Hypothesis: How humans benefited from and re-shaped African high-altitude ecosystems during Quaternary climate changes’ we re-cored Lake Garba Guracha. This site represents one of the best dated Late Glacial - Holocene continuous, high altitude (3950 m asl) paleoenvironmental archives in East Africa.
We investigated sugar and lipid biomarkers and their compound-specific stable oxygen and hydrogen isotopic composition (δ18Osugar and δ2Hn-alkane) to infer past hydrological patterns. The δ18Osugar record reflects lake water and can thus be used to reconstruct lake evaporation history.

Our results suggest that a virtually permanent lake overflow existed from about 10 to 7 cal. ka BP, whereas the period from about 7 to 5 cal. ka BP is characterised by increased lake evaporation. We present initial results of δ18Odiatom analyses and organic geochemical and XRF data that document dominant minerogenic input during the Late Glacial and increased input of almost exclusively aquatic organic matter from 11 cal. ka BP on. Reconstructed mean annual temperatures (n=20, -2.2 to 2.5°C), inferred from brGDGT-based proxies, indicate that colder conditions prevailed in the high-altitude Bale Mountain ecosystem during the Younger Dryas.

How to cite: Bittner, L., Bliedtner, M., Grady, D., Gil-Romera, G., Martin-Jones, C., Lemma, B., Lamb, H. F., De Jonge, C., Meyer, H., Glaser, B., and Zech, M.: Revisiting Lake Garba Guracha, high altitude lake in the Bale Mountains, Ethiopia: reconstructing Late Glacial – Holocene lake level history using δ2H/δ18O biomarker analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7304, https://doi.org/10.5194/egusphere-egu2020-7304, 2020.

EGU2020-5600 | Displays | SSP1.9

Plio-Quaternary palaeoenvironments in West Turkana (East African Rift System; Kenya): palaeolake fluctuations, palaeolandscapes and controlling factors

Alexis Nutz, Mathieu Schuster, Doris Barboni, Ghislain Gassier, Jean-François Ghienne, and Jean-Loup Rubino

The Turkana Depression consists of several Oligocene to Pliocene North-South oriented half-grabens that connect the Ethiopian and Kenyan rift valleys within the eastern branch of the Cenozoic East African Rift System. In the northern portion of the Turkana Depression, exposed on the west side of modern Lake Turkana, is the Nachukui Formation that consists of a > 700 m pile of fluvial-deltaic-lacustrine sediments deposited between 4.2 and 0.7 Ma. The Nachukui Fm is a world-class fossil-bearing succession into which more than 500 hominin fossils were discovered, including major discoveries for the understanding of Human evolution and more than 100 archaeological sites. Most significant discoveries include Australopithecus anamensis, Kenyanthropus platyops, Paranthropus aethiopicus, Paranthropus boisei and specimens of Homo (i.e., H. rudolfensis and H. erectus) and early members of H. sapiens, as well as the earliest evidence of Acheulean stone tool technology and, more recently, the most primitive Lomekwian stone tool technology.

            Palaeoenvironmental changes may have had a strong influence on evolution, including that of the human lineage. However, in the Turkana Depression, palaeoenvironments are still very partially reconstructed and the respective role of climate and tectonism is still debated. Here, we used the interpretation of depositional environments, the delineation of depositional sequences and a record of d13C in pedogenic carbonates (i.e. paleovegetation proxy) to reconstruct 1) palaeolake Turkana fluctuations between ca. 4 and ca. 1.2 Ma and 2) the successive sedimentary palaeoenvironments and resulting landscapes that characterized the West Turkana area during the same time interval.

            Facies and sequence analyses reveal that palaeolake Turkana experienced eight low-frequency transgression-regression (T-R) cycles between ca. 4 and ca. 1.2 Ma; superimposed lower amplitude and shorter duration T-R cycles are also locally identified revealing subordinate-order fluctuations. In the same time, two different palaeolandscapes (labelled type-1 and type-2) alternated through times revealing variations in sediment supply coming from the western rift shoulder. A statistical treatment of the d13C record using a modified k-mean clustering allows us to confront a paleovegetation proxy and the sedimentological record. This combined approach reveals that the evolution of rainfall over the Ethiopian dome (i.e., drainage basin of the Omo river) controlled long-term palaeolake Turkana fluctuations during the Plio-Quaternary period while tectonism likely controlled the occurrence of different palaeolandscapes in West Turkana forced by changes in the rate of sediment supply.

            Finally, our study shows that traditional methods of basin geology (i.e., facies and sequence analysis) are key tools to provide large-scale paleolandscape reconstructions and palaeolake fluctuations needed for investigating the interactions between hominins and palaeoenvironments. Such a powerful procedure, however, is rare for hominins sites and has yet to be integrated in the workflow utilized by the paleontology and archeology communities.

This is a contribution of the Rift Lake Sedimentology project (RiLakS).

How to cite: Nutz, A., Schuster, M., Barboni, D., Gassier, G., Ghienne, J.-F., and Rubino, J.-L.: Plio-Quaternary palaeoenvironments in West Turkana (East African Rift System; Kenya): palaeolake fluctuations, palaeolandscapes and controlling factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5600, https://doi.org/10.5194/egusphere-egu2020-5600, 2020.

EGU2020-8481 | Displays | SSP1.9

Southern African hydroclimate during the Late Quaternary: integrating source to sink and multi-archive studies

Annette Hahn, Hayley Cawthra, Green Andrew, Humphries Marc, Schefuß Enno, and Zabel Matthias

Southern Africa is located at the interface of sub-tropical and temperate climate zones as well as between two major warm and cold ocean current systems (Agulhas and Benguela), respectively. This makes it a key region for understanding global climate dynamics and highly sensitive to future climatic change. A growing number of paleo-archives have revealed small-scale climatic dipoles in this region and the driving mechanisms of the complex climatic variability often in this region remain unclear. Several regional studies have suggested a synchronicity with the southern hemisphere and thus inferred a direct insolation forcing while others have observed a synchronicity with northern hemispheric climate and associated this with a teleconnection mechanism. In order to decipher the complex climatic processes affecting this region it is necessary to integrate on- and offshore paleo-archives as well as various paleo-environmental indicators (proxies). For the correct interpretation of the various proxies a source to sink approach is necessary determining the origin of the different terrestrial sedimentary components and their potential alterations during transport and deposition. With a focus on marine and lacustrine sedimentary archives along the west, south, and east coast of southern Africa we are now able to reconstruct Late Quaternary climate variability on regional scales. We propose a new conceptual model describing latitudinal shifts of rainfall zones as tropical and temperate climate systems shift over glacial and interglacial cycles. New insights allow us to resolve some of the apparent contradictions between paleoclimate records from the region. 

 

How to cite: Hahn, A., Cawthra, H., Andrew, G., Marc, H., Enno, S., and Matthias, Z.: Southern African hydroclimate during the Late Quaternary: integrating source to sink and multi-archive studies , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8481, https://doi.org/10.5194/egusphere-egu2020-8481, 2020.

EGU2020-9748 | Displays | SSP1.9

One Million Years of Human-Landscape Interaction in the Ethiopian and Kenyan Rift-System

Annett Junginger and Simon Kuebler

Landscapes form the basis for the development of human habitats. Studying human-landscape interactions thus requires an understanding of the character and evolution of landscapes on different temporal and spatial scales. In Africa, key anthropological sites are often associated with the tectonically active sectors of the East African Rift. But the landscapes inhabited by our ancestors have undergone massive changes over time, changes driven by climatic variability as well as long-term geomorphological and tectonic processes. River courses have changed, lakes expanded and then disappeared, and volcanic and tectonic activity formed steep fault scarps and barriers. Here we present a review of archaeological, paleo-climatological, paleo-limnological, tectonic and soil nutrients data sets of the southern Ethiopian and Kenyan Rift System in Eastern Africa of the past 1 Million years. Results suggest that tectonic processes and climatic change created a unique suite of landscape features potentially advantageous for human inhabitance. The combined analysis thus allows the quantification of styles and rates of surface modification, which in turn can be used for reconstructing ancient landscapes.

How to cite: Junginger, A. and Kuebler, S.: One Million Years of Human-Landscape Interaction in the Ethiopian and Kenyan Rift-System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9748, https://doi.org/10.5194/egusphere-egu2020-9748, 2020.

EGU2020-22010 | Displays | SSP1.9

The characteristics and drivers of climatological precipitation over the Serengeti-Mara region

Josephine Mahony, Ellen Dyer, and Richard Washington

The Serengeti National Park is famous for the biological phenomenon of the annual wildebeest migration. This migration is reliant on unique local precipitation conditions: a rainfall gradient stretching across the park, the strength and inclination of which alters from month to month. Given the ecological significance and the complexity of the regional precipitation, a detailed study of the region’s climatology is essential for understanding why these precipitation patterns exist, and whether they are likely to change.

Using multiple observational datasets, we studied the spatial distribution of annual and monthly climatological precipitation. We carried out harmonic analysis and cluster analysis to identify areas with similar annual cycles. We then examined regional wind, moisture and precipitation patterns on seasonal, monthly and diurnal timescales.

We found that the large-scale wind circulation patterns dictate the basic structure of the annual cycle over the region. However the shape of the annual cycle was distinctly different in 5 parts of the region, with varying peak rainfall months and dry season rainfall totals. Analysis of the diurnal wind patterns showed that the regional seasonality is strongly augmented by the lake and land breeze from Lake Victoria, and the interactions between this local source of moisture and the complex topography of the East African rift. This leads to a low-level convergence zone between the prevailing large-scale easterlies, and westerlies from Lake Victoria over the Serengeti in the afternoon. This in turn results in the rainfall gradient across the region, the orientation of which changes depending on the mid-tropospheric wind direction.

How to cite: Mahony, J., Dyer, E., and Washington, R.: The characteristics and drivers of climatological precipitation over the Serengeti-Mara region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22010, https://doi.org/10.5194/egusphere-egu2020-22010, 2020.

EGU2020-11488 | Displays | SSP1.9

Human responses to hydroclimate fluctuations over the last 200 kyr in Ethiopia

Frank Schäbitz, Verena Foerster, Asfawossen Asrat, Andrew S. Cohen, Melissa S. Chapot, Jonathan R. Dean, Alan Deino, Daniel M. Deocampo, Walter Duesing, Christina Günter, Annett Junginger, Stefanie Kaboth-Bahr, Henry F. Lamb, Christine Lane, Melanie J. Leng, Stefan Opitz, Rachel Lupien, Helen M. Roberts, Christopher Bronk Ramsey, and James Rusell and the HSPDP and CRC806 Science team

Humans have been adapting to more demanding habitats in the course of their evolutionary history. Nevertheless, environmental changes coupled with overpopulation naturally limit competition for resources. In order to find such limits, reconstructions of climate and population changes are increasingly used for the continent of our origin, Africa. However, continuous and high-resolution records of climate-human interactions are still scarce.

Using a 280 m sediment core from Chew Bahir*, a wide tectonic basin in southern Ethiopia, we reconstruct the paleoenvironmental conditions during the development of Homo sapiens. The complete multiproxy record of the composite core covers the last ~600 ka , allowing tests of hypotheses about the influence of climate change on human evolution and technological innovation from the Late Acheulean to the Middle/Late Stone Age, and on dispersal within and out of Africa.

Here we present results from the uppermost 100 meters of the Chew Bahir core, spanning the last 200 kiloyears (ka). The record shows two modes of environmental change that are associated with two types of human mobility. The first mode is a long-term trend towards a more arid climate, overlain by precession-driven wet-dry alternation. Through comparison with the archaeological record, humid episodes appear to have led to the opening of ‘green’ networks between favourable habitats and thus to increased human mobility on a regional scale. The second mode of environmental change resembles millennial-scale Dansgaard-Oeschger and Heinrich events, which seem to coincide with enhanced vertical mobility from the Ethiopian rift to the highlands, especially in the time frame between ~65–21 ka BP. The coincidence of climate change and human mobility patterns help to define the limiting conditions for early Homo sapiens in eastern Africa.

___________________

* cored in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Centre) 806 “Our way to Europe

How to cite: Schäbitz, F., Foerster, V., Asrat, A., Cohen, A. S., Chapot, M. S., Dean, J. R., Deino, A., Deocampo, D. M., Duesing, W., Günter, C., Junginger, A., Kaboth-Bahr, S., Lamb, H. F., Lane, C., Leng, M. J., Opitz, S., Lupien, R., Roberts, H. M., Bronk Ramsey, C., and Rusell, J. and the HSPDP and CRC806 Science team: Human responses to hydroclimate fluctuations over the last 200 kyr in Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11488, https://doi.org/10.5194/egusphere-egu2020-11488, 2020.

EGU2020-5233 | Displays | SSP1.9

Advanced hyperspectral analysis of sediment core samples from the Chew Bahir Basin, Ethiopian Rift in the spectral range from 0.25 to 17 µm: support for climate proxy information

Gabriele Arnold, Claudia Szczech, Asfawossen Asrat, Andrew S. Cohen, Verena Foerster, Frank Schäbitz, Henry Lamb, and Martin H. Trauth

This paper reports on the application of advanced hyperspectral analysis to support the non-destructive study of samples from long sediment cores (up to 280 m coring depth) collected under the Hominin Sites and Paleolake Drilling Program (HSPDP) in the Chew Bahir region of southern Ethiopia. For this purpose, the bidirectional reflectance of 35 core samples from different core depths in the wavelength range from 0.25 to 17 µm was measured. It can be directly compared with spectral remote sensing data of the corresponding land surface areas. We examined the relationship between the derived mineralogical and geochemical properties of the core samples to test for linkage to the hydroclimate history of the region. Using XRD and µXRD methods, it has been shown that an illitization of the smectites and an octahedral Al-to-Mg substitution occurs in the phyllosilicate materials present during phases that have been associated with increased salinity and alkalinity due to enhanced evaporation (Foerster et al., 2018). These processes are found to be accompanied by potassium fixation and they are associated with the increase of the layer charge due to the authigenic changes of the octahedral composition. Reflection spectroscopy is a suitable method for studying such mineralogical properties.

We investigated the spectral properties over a wide spectral range from UV to MIR. This enables detection of absorption bands of crystal field transitions of transition metal ions in the UV/VIS range and to detect the characteristic bands of OH, H2O, M-OH lattice vibrations in the NIR. It also allows the study of the fundamental vibration bands as well as other typical MIR features like the Christiansen band or transparency features of silicates and thus helps to reconstruct weathering paths.

The results show that the main mineralogical components are clays of the smectite group. The samples are rich in montmorillonite and show variable concentrations of calcite. The clays are composed of tetrahedral coordinated, corner-connected SiO4 for which Si is partially substituted by Al and of edge-linked Al (OH)6 octahedrons in which part of the Al is substituted by Mg and which are layered by OH and H2O groups. Thus all reflectance spectra show the characteristic absorption bands at 1.4 µm (OH), 1.9 µm (H2O), 2.2 µm (Al-OH), and 2.3 µm (Mg-OH). Their band depth ratios derived from continuum removed spectra have been used to characterize the clay structure within different climate periods. The results support the model of illitization and potassium fixation during dry climate intervals. In addition, the spectral indicators determined in the MIR can be used to specify the mineralogical properties of silicates and other materials in terms of their geochemical composition. In summary, the method is suitable for examining the main mineralogical components of Chew Bahir core samples and enables confirmation of climate-driven wet and dry weathering processes in the formation of phyllosilicates.


Foerster, V. et al., (2018) Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift. Palaeogeography, Palaeoclimatology, Palaeoecology, 501, 111-123.

How to cite: Arnold, G., Szczech, C., Asrat, A., Cohen, A. S., Foerster, V., Schäbitz, F., Lamb, H., and Trauth, M. H.: Advanced hyperspectral analysis of sediment core samples from the Chew Bahir Basin, Ethiopian Rift in the spectral range from 0.25 to 17 µm: support for climate proxy information, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5233, https://doi.org/10.5194/egusphere-egu2020-5233, 2020.

EGU2020-18292 | Displays | SSP1.9

Assessing the role of climate change in human evolution and dispersal: a 600,000-year record from Chew Bahir, southern Ethiopia

Verena E. Foerster, Asfawossen Asrat, Andrew S. Cohen, Melissa S. Chapot, Alan Deino, Daniel M. Deocampo, Walter Duesing, Christina Guenter, Annett Junginger, Stefanie Kaboth-Bahr, Henry F. Lamb, Christine Lane, Christopher Bronk Ramsey, Helen M. Roberts, Céline Vidal, Frank Schaebitz, and Martin H. Trauth

What role did climate dynamics play in the evolution and dispersal of Homo sapiens within and beyond Africa, and in key cultural innovations? Were gradual climatic changes, rapid shifts from wet to dry, or short-term climate flickers the main driver of human evolution and migration? As a contribution towards an enhanced understanding of those possible human-climate interactions the Chew Bahir Drilling Project, part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) and the Collaborative Research Center (CRC) 806 “Our way to Europe”, recovered two ~280 m-long sediment cores from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition from the Acheulean to the Middle Stone Age, and the origin and dispersal of Homo sapiens.

 

Here we present the results from our multi-proxy study of the Chew Bahir 280 m-long composite core, providing a detailed and high-resolution record of eastern Africa’s climate oscillations during the last ~600 ka. To determine sediment age we used a Bayesian model to combine ages derived from radiocarbon dating of ostracodes, optically-stimulated luminescence (OSL) dating of quartz, Argon-Argon (40Ar/39Ar) dating of feldspar grains from some key (micro)tephra layers, and correlation on the basis of geochemistry of a tephra unit in the core to a known and dated tephra in the outcrop. We used high-resolution geophysical and geochemical indicators, such as the established aridity proxy K, sediment colour and authigenic minerals to differentiate between climate fluctuations on different time scales and magnitudes.

 

Our results show that the full proxy record from Chew Bahir can be divided into three phases with similar trends in central tendency and dispersion. Phase I from ~600 to ~430 kyr BP shows a long-term shift from humid to arid conditions while slightly increasing the variability and ending with the most extreme oscillations between full humidity and extreme aridity. The transition into Phase II (~430 to ~200 kyr BP) is marked by a pronounced millennial-scale humidity increase. Phase II reflects generally more humid conditions and there is evidence of double humidity increase tendency. Firstly, between ~430 and ~315 kyr BP (Phase IIa), and again from ~280 to ~195 kyr BP (Phase IIb), with only slight changes in long-term variability. Since ~200 kyr BP (Phase III), a long-term aridification trend sets in, similar to Phase I, but with a distinct increase in variability and amplitudes. All of these changes would have had significant implications for shaping our ancestors’ living environments, both broadening and limiting their options in response to the different degrees and rates of climatic stress. The Chew Bahir record, one of the very few long terrestrial environmental records from continental eastern Africa, can contribute to testing the influence of low versus high latitude climate change in driving the expansion, contraction and fragmentation of early human habitats.

How to cite: Foerster, V. E., Asrat, A., Cohen, A. S., Chapot, M. S., Deino, A., Deocampo, D. M., Duesing, W., Guenter, C., Junginger, A., Kaboth-Bahr, S., Lamb, H. F., Lane, C., Bronk Ramsey, C., Roberts, H. M., Vidal, C., Schaebitz, F., and Trauth, M. H.: Assessing the role of climate change in human evolution and dispersal: a 600,000-year record from Chew Bahir, southern Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18292, https://doi.org/10.5194/egusphere-egu2020-18292, 2020.

EGU2020-13026 | Displays | SSP1.9

Climate beats from Africa: a statistical analysis of the 620 kyr Chew Bahir climate record, eastern Africa

Walter Duesing, Asfawossen Asrat, Andrew S. Cohen, Verena S. Foerster, Stefanie Kaboth-Bahr, Hauke Kraemer, Henry F. Lamb, Norbert Marwan, Helen M. Roberts, and Frank Schaebitz

The sediment cores of the Chew Bahir drilling project, part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), from southern Ethiopia, were used to reconstruct climatic changes by analyzing the sediment geochemistry with high-resolution XRF scanning. To interpret the multidimensional XRF dataset we computed a principal component analysis. We used the first principal component (PC1) to detect changes in variability by running a windowed standard deviation analysis and additionally a change point analysis to detect the exact timing of variability changes. 

 

Additionally we used the established Chew Bahir log(K/Zr) aridity proxy, representing clay mineral chemistry- detrital input ratio and compared it to a new Chew Bahir climate indicator, the log(Ca/Ti) proxy, an evaporation signal that is probably inversely related to lake level stands. We find that the log(Ca/Ti) record is also an exceptionally good climate indicator because, compared to the established log(K/Zr) proxy, it reacts with greater amplitude to insolation-controlled signals such as orbital precession. This is confirmed by the log (Ca/Ti) record showing a very clear signal during the African Humid Period, which is however less pronounced in the log(K/Zr) record.

 

To gain a deeper understanding of the climate cycles and their temporal evolution, we computed a continuous wavelet transformation (CWT) for each of the climate proxies, and studied temporal changes in their cyclicity. Our results indicate that in addition to the precession cycle (~ 20 kyr), the Chew Bahir climate record contains earth eccentricity cycles (~ 100 kyr), as well as half-precession cycles during high eccentricity. During low eccentricity (450-350 kyr ago), we find reduced variability, three of five changes in standard deviation, damped precession and half precession cycles, and an abrupt transition from dry to wet climate, possibly due to climatic change in high latitudes which may be related to the Mid-Bruhnes event (MBE). 

 

The results confirm that during high eccentricity the tropics are insolation controlled, largely independent of the high latitudes, whereas during low eccentricity the climate of tropical eastern Africa is sensitive to climatic drivers other than precession, possibly originating from high latitudes. Such a period occurring 450 to 350 kyr ago could have led to large regional differences in moisture availability and may have affected early humans by habitat separation, which by isolating populations, resulted in technological diversification. This possible scenario may help to explain the technological transition from Middle Stone Age (MSA) to Acheulean technology that was documented in the Olorgesailie basin during the same time period. 

 

How to cite: Duesing, W., Asrat, A., Cohen, A. S., Foerster, V. S., Kaboth-Bahr, S., Kraemer, H., Lamb, H. F., Marwan, N., Roberts, H. M., and Schaebitz, F.: Climate beats from Africa: a statistical analysis of the 620 kyr Chew Bahir climate record, eastern Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13026, https://doi.org/10.5194/egusphere-egu2020-13026, 2020.

EGU2020-4660 | Displays | SSP1.9

Recurrence quantification analysis of the ~620 kyr record of climate change from the Chew Bahir basin, southern Ethiopia

Martin H. Trauth, Asfawossen Asrat, Andrew S. Cohen, Walter Duesing, Verena Foerster, Stefanie Kaboth-Bahr, Hauke Kraemer, Henry Lamb, Norbert Marwan, Mark A. Maslin, and Frank Schaebitz

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that record Quaternary environmental changes in the Chew Bahir basin. In this statistical project we used recurrence plots (PRs) together with a recurrence quantification analysis (RQA) to distinguish two types of variability and transitions in Chew Bahir and compare them with the ODP 967 wetness index from the eastern Mediterranean. The first type of variability are slow variations with cycles of ~20 kyr and subharmonics of this cycle. In addition to the these cyclical wet-dry fluctuations in the area, extreme events often occur, i.e. short wet or dry episodes, lasting for several centuries or even millennia, with rapid transitions between wet and dry episodes. The second type of variability is characterized by relatively low variation on orbital time scales, but significant century-to-millennium-scale variations with increasing frequency in the course of an episode of type 2 variability. Within this type of variability there are extremely fast transitions between dry and wet, and vice versa, within a few decades or years, in contrast to those within type 1 which have transitions lasting several hundred years. Type 1 variability probably reflects the influence of precessional forcing in the lower latitudes at times of increased eccentricity, with the tendency towards extreme events, whereas type 2 variability seems to be linked with minimum values of the long (400 kyr) eccentricity cycle, and there does not seem to be a link with atmospheric CO2 levels. The different types of variability and transitions certainly had a completely different influence on the availability of water, food and shelter, and hence eastern Africa’s biotic environment, including the habitat of H. sapiens.

How to cite: Trauth, M. H., Asrat, A., Cohen, A. S., Duesing, W., Foerster, V., Kaboth-Bahr, S., Kraemer, H., Lamb, H., Marwan, N., Maslin, M. A., and Schaebitz, F.: Recurrence quantification analysis of the ~620 kyr record of climate change from the Chew Bahir basin, southern Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4660, https://doi.org/10.5194/egusphere-egu2020-4660, 2020.

EGU2020-18611 | Displays | SSP1.9

Insights into the African Humid Period from fossil stromatolites and Etheria elliptica shells from the Chew Bahir Basin, southern Ethiopia

Peter Nickolaus, Monika Markowska, Hubert Vonhof, Hervé Bocherens, Ashley Martin, Bahru Zinaye, Markus Fischer, Asfawossen Asrat, and Annett Junginger

In the context of human evolution and dispersal in Africa, it is important to understand past climate conditions and changes as possible drivers of these processes. One of the most recent climatic events was the end of the African Humid Period (AHP) at around 5 ka BP. This was marked by a decrease in precipitation following a long wet-phase in northern and eastern Africa, which caused many lakes to decrease in size or even desiccate. Although the termination of the AHP is well known, the timing and rate of the transition from wet to dry conditions is still heavily debated. To investigate the termination of the AHP at a high temporal resolution (subdecadal and subannual), fossil stromatolites and Etheria elliptica shells from paleo-shorelines in the Chew Bahir Basin, southern Ethiopia, were collected. Today, Lake Chew Bahir is a deltaic swamp, however in past pluvials a large lake was present that likely overflowed and connected to other basins similar to other amplifier lakes in the East African Rift System. Radiocarbon dating, oxygen and carbon stable isotope analyses, trace element analyses and petrographic mapping of stromatolite laminae structure were conducted. A strong correlation between δ18O and δ13C shows that paleo-lake Chew Bahir likely experienced highly evaporative conditions and indicate an endorheic state of the basin in times of stromatolite growth at 7.1, 5.8, 4.7 and 4.6 ka BP. Furthermore, our findings suggest highly fluctuating environmental conditions during these times and demonstrate that the transition to drier conditions was not a strictly linear trend. In summary, the stromatolites and Etheria elliptica shells are an excellent environmental archive due to their high temporal resolution, precise dating (± 30 yrs) and an indication of the paleo-lake water depth. These types of records provide insights to past changes in freshwater availability, the variability of which would have had large consequences for humans living in the region.

How to cite: Nickolaus, P., Markowska, M., Vonhof, H., Bocherens, H., Martin, A., Zinaye, B., Fischer, M., Asrat, A., and Junginger, A.: Insights into the African Humid Period from fossil stromatolites and Etheria elliptica shells from the Chew Bahir Basin, southern Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18611, https://doi.org/10.5194/egusphere-egu2020-18611, 2020.

EGU2020-2975 | Displays | SSP1.9

A 25-kyr record of East African monsoon variability: Insights from grain-size distributions and end-member modeling of siliciclastic sediments from Lake Chala

Inka Meyer, Maarten Van Daele, Niels Thange, Dirk Verschuren, and Marc De Batist

Terrigenous particles deposited in all kinds of sedimentary records (terrestrial, marine and lacustrine) have proven to yield valuable information for reconstruction of paleo-climate and paleo-environments. Natural sediments typically represent a mixture of deposits of diverse provenance, potentially supplied by different transport processes, expressed in a bi-or poly-modal grain-size distribution. Recently, complex mathematical-statistical end-member models have been developed to disentangle the different sub-populations within one grain-size distribution, which are then assumed to represent a distinct sediment fraction that has a single provenance and/or was transported by the same process to the site of deposition.

Here we present end-member modeling results of the terrigenous sediment fraction in a 25-kyr sediment sequence from Lake Chala (Kenya/Tanzania), revealing valuable information on climate and environmental change in equatorial East Africa since the Last Glacial Maximum (LGM). Calculated end members could be related to distinct source areas and transport processes, namely to fine aeolian dust, fine-grained soil runoff, coarser aeolian dust from proximal sources and coarse erosive material originating from the crater rim surrounding the lake. Variations in the occurrence of distal versus proximal dust is suggested to be a reliable indicator for changes in East African monsoon circulation. During Northern Hemisphere cold periods, such as the LGM and Younger Dryas (YD), wind systems associated with the Intertropical Convergence Zone (ITCZ) were pushed southward, causing a more intense influence of the NE monsoon at Lake Chala. This resulted in high amounts of fine dust originating from the Horn of Africa region. At the same time, SE monsoon circulation was diminished due to a reduced atmospheric pressure gradient between the Asian/Indian continent and the Indian Ocean. Influx of coarse dust from proximal sources, which are mostly located east of Lake Chala, was impossible due to the weaker SE monsoon circulation. After termination of the YD, rapid reestablishment of the SE monsoon in the Early Holocene is recorded by an abrupt increase in the influx of coarse dust.

Lake Chala sediments contain one of the few continuous and high-resolution climate records in East Africa spanning the past 25 kyr, providing detailed information on long-term climate variation in an area highly sensitive to hydrological variations. Subdividing the clastic sediment fraction into statistically robust end members produces multiple quantitative and independent proxies to help reconstruct this region’s climate and environmental history.

How to cite: Meyer, I., Van Daele, M., Thange, N., Verschuren, D., and De Batist, M.: A 25-kyr record of East African monsoon variability: Insights from grain-size distributions and end-member modeling of siliciclastic sediments from Lake Chala, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2975, https://doi.org/10.5194/egusphere-egu2020-2975, 2020.

Rock shelter and cave sites can be suitable archives for archaeological remains and environmental records if the right conditions are complied with. There are a few sediment stratigraphies in the Horn of Africa that preserved information about human occupation during the Upper Pleistocene and Holocene. Unfortunately, little is known about human settlement in Ethiopia during the period corresponding to MIS 2 due to discontinuous archaeological records. The project A1, within the framework of the Collaborative Research Centre 806 (CRC 806 – “Our Way to Europe”), focuses on Late Pleistocene stratigraphies and paleoenvironments of northeast African sites. In this context, during excavations at the Sodicho Rockshelter in the southwestern Ethiopian Highlands, a complex stratigraphy with evidence of several human occupation phases was exposed.

This poster presents the latest research results of the Sodicho Rockshelter. It displays first radiocarbon ages and the site formation processes according to a selection of sedimentological and geochemical methods to understand human settlement history in this tropical environment. A multi-proxy approach has been chosen to detect possible rapid or gradual changes in depositional conditions in the rock shelter. The sedimentological records suggest that the depositional and post-depositional processes varied significantly over time in response to external environmental changes and the use of the shelter by humans. For instance, lithic assemblages in anthropogenic influenced layers alternate with thick volcanic ash layers. In addition, a sterile, clayish horizon refers to a period of increased precipitation and could thus provide evidence for an African Humid Period. The Sodicho Rockshelter could validate the current state of research and possibly close the chronostratigraphic gap.

How to cite: Hensel, E. A., Vogelsang, R., Noack, T., and Bubenzer, O.: Geoarchaeology and chronology of Sodicho – insights into site formation processes and human activity in a volcanic rock shelter, SW Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12966, https://doi.org/10.5194/egusphere-egu2020-12966, 2020.

EGU2020-10635 | Displays | SSP1.9

Sedimentology, paleohydrology and geo-archaeology of southeastern Arabia during the Late Pleistocene and its implications for modern human dispersal Out of Africa

Mahmoud Abbas, Stephanie Neuhuber, Roman Garba, Denis Štefanisko Štefanisko, Dominik Chlachula, and Zhongping Lai

The paleohydrology and geomorphology of southeastern Arabia after 130 ka suggests complex climatic records in the area considered a potential route for human dispersal Out of Africa. Understanding the past hydrological systems is essential to relate the lithic assemblages at the surface to a habitable environment. Climatic records such as speleothems can in combination to sedimentological evidence provide crucial data on the potential formation and persistence of paleo-water bodies and human livelihood.  The transition of a more humid period in the past to the presently harsh environment of southeastern Arabia and its relationship with human occupation is one long-term focus of this project. The information on timing, permanency and depth of these paleo-water bodies in Central and Southern Oman are yet lacking.

An initial geo-archaeological investigation has been carried out in south-central Oman (al-Wusṭā Governorate) and southern Oman (Ẓufār Governorate) as part of TSMO (Trilith Stone Monuments of Oman) archaeological expedition During TSMO field campaign. The OSL samples were collected from fluvial, colluvial and valley sediments in the main study area of al-Duqm, south-central Oman, and the reference area of Mudayy, south of Oman in Ẓufār. At both locations we logged several sediment profiles that mainly consist of well-rounded boulders, imbricated gravels and coarse-grained sediments intercalated with sporadic sand lenses. The sediments suggest fluvial transport in a perennial river and differ significantly from today’s ubiquitous angular Wadi-sediments. At both locations we found reddish sediment that might originate from fluvially reworked soil and would indicate not only the presence of water but also enough moisture to facilitate soil forming processes. Preliminary XRD scans from samples in Ẓufār identified calcite, quartz, feldspar and the sheet silicates illite and kaolinite. The clay fraction of this material has been separated and analyzed to determine the exact minerals that might be typical for soil formation in the B-horizon. Sediments in the Mudayy area are – similarly to al-Duqm - composed of river sediments with well-rounded imbricated gravels but in contrast to further north, they are covered by aeolian (loess) sediments. This captures the transition of fluvial deposition to aeolian deposition and thus a transition of the environmental setting during the time of formation. The Mudayy area in southern Oman is associated with Middle Paleolithic lithic tools of Levallios/Nubian complex technology as well as early-middle Holocene stone tools. The main research area of al-Duqm revealed several new Middle Palaeolithic sites with preferential Levallois facie with some influence of Nubian complex suggesting the landscape with favorable local environmental conditions, forming a possible human refugium between the harsh northern and southern borderlands. The understanding of Quaternary geomorphic, sediment and erosion processes, paleoclimate reconstruction, techno-typological analysis of lithic tools and cosmogenic nuclide dating of the raw material procurement sites in al-Duqm can shed more light on occupation and movement of human population on Arabian Peninsula during the Late Pleistocene.

How to cite: Abbas, M., Neuhuber, S., Garba, R., Štefanisko, D. Š., Chlachula, D., and Lai, Z.: Sedimentology, paleohydrology and geo-archaeology of southeastern Arabia during the Late Pleistocene and its implications for modern human dispersal Out of Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10635, https://doi.org/10.5194/egusphere-egu2020-10635, 2020.

It has long been hypothesized that long and short term climate changes influenced early human evolution and dispersal. With the use of paleoclimate, archeological, genetic, and climate model data, we can infer climate factors that influenced dispersal and possible migration routes. Recent research has shown that with the use of data from these different disciplines, we can model human dispersal and interactions with the environment at a group level. However, decision-based questions such as push vs. pull scenarios and what is the optimal time to move are challenging to answer using classical differential-equation based models. With the use of individual-based modeling (IBM), we can connect archeological research with paleoclimate (modeling) data and build possible dispersal scenarios.

IBM has long been used in ecology to research the overall behavior of a group based on decisions made by individuals. In IBMs, each individual is modeled as a discrete agent who decides its action based on the environment and relation to other agents, thereby allowing for more individual variation and adaptation than is possible with classical differential-equation and difference-equation models.

Here we present some preliminary results from our climate forced IBM. Climate variables such as net primary production, temperature, and rainfall were obtained from a transient simulation of the LOVECLIM intermediate climate model. These climate factors were used for movement decisions and influence the birthrate and life span of the agents. We show the most likely dispersal routes for different climate scenarios and the role of dispersal strategies (push vs. pull).

How to cite: Zeller, E. and Timmermann, A.: Possible dispersal routes based on individual-based modeling forced with past climate conditions., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1756, https://doi.org/10.5194/egusphere-egu2020-1756, 2020.

Archaeological records indicate that human population experienced frequent decline and growth as humans were on their way to populate the whole planet. Our hypothesis is that climate and environment were the main drivers for human existence and dispersal. Based on this hypothesis, we develop a Lagrangian Constraint Random Walk Model (CRW) to simulate the dispersal of hunter-gatherers. Human existence potential (HEP) is estimated using climate/environment model data, supported by archaeological evidence. The CRW simulates the movement of individual humans with a stochastic differential equation. While the movement of the individuals has a random component, it is constrained by a drift term which depends on the HEP. Population growth and decline are represented using a birth and a death term. Sociological elements of hunter-gatherers, such as population pressure, conflicts, and cooperation, are considered in the model. With the CRW, we estimate human mobility and dispersal based on the statistical behavior of a large ensemble of individuals. Furthermore, by varying the external factors and hence the HEP, we evaluate the response of hunter-gatherer societies to climate change. We will present the model and a case study on the mobility of hunter-gatherers on the Iberian Peninsula during the Last Glacial Maximum.

How to cite: Klein, K., Shao, Y., and Rostami, M.: Simulating human mobility with a Lagrangian Constraint Random Walk Model based on climatic and environmental conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15470, https://doi.org/10.5194/egusphere-egu2020-15470, 2020.

How climatic and environmental conditions contributed to early human migration between mainland and island Southeast Asia during the Pleistocene is one of the most hotly debated topics in paleoanthropological communities today. As Peninsular or Southern Thailand is regarded as an obligatory pathway for humans and mammals during their dispersal between these two terrestrial areas, the understanding of paleoenvironments and vegetation covers in this region is highly relevant. The hypothesis of a “savanna corridor” or a band of open vegetation (seasonal forests and grasslands) stretching from Central Thailand to Java during several periods of lowering sea level and exposed land bridges though the Pleistocene has been suggested for explaining the facilitated route of early humans and associated large mammals in migrating out of mainland Southeast Asia towards Sundaland southwards. However, the existence of savanna grasslands in Peninsular Thailand during the Pleistocene has rarely been demonstrated due to the scarcity of available proxies.

Here we reconstructed the Pleistocene vegetation and environments of the region using stable isotope analyses of mammalian tooth enamel from the channel cave deposits of Tham Phadan (Nakhon Si Thammarat Province in Peninsular Thailand) where diversified large mammal fossils were collected. The mammal fauna is tentatively attributed to a late Middle to early Late Pleistocene age according to the presence of an extirpated spotted hyaena Crocuta crocuta ultima. The stable carbon isotope results, ranging from -13.9‰VPDB to +4.3‰VPDB, reveal that an open vegetation/forest-grassland mosaic was dominant in this region, unlike the present-day landscapes that are mostly covered by rainforests, thus confirming the existence of a savanna corridor in Peninsular Thailand during that time. The extreme southward distribution of some grassland-related taxa (such as spotted hyaenas and Himalayan gorals), which were common in mainland Southeast Asia during the Pleistocene, reflects the habitat continuity from north to south of Thailand. However, the lack of fossil records of these two taxa in Peninsular Malaysia and the islands of Indonesia suggests that the open vegetation band did not extend far beyond the transequatorial region. Further investigations of the Pleistocene mammal faunas in the Thai-Malay Peninsula will be helpful to identify such a corridor and to examine the paleobiogeographic affinities of Southeast Asian large mammals in the future, providing empirical data for understanding the timing and pathways of human migrations into island South-East Asia.

How to cite: Suraprasit, K. and Bocherens, H.: Peninsular Thailand as a part of the Pleistocene savanna corridor: isotopic evidence of mammalian tooth enamel from the cave of Tham Phedan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3401, https://doi.org/10.5194/egusphere-egu2020-3401, 2020.

EGU2020-20692 | Displays | SSP1.9

Exploring the climate signal in tree-ring density of Clanwilliam cedar, South Africa

Valerie Trouet, Tom De Mil, Matthew Meko, and Jan Van den Bulcke

High-resolution annual precipitation and temperature proxies are largely lacking in Southern Africa, partly due to the scarcely available tree species that are suitable for dendrochronology. Clanwilliam cedar (Widdringtonia cedarbergensis) from Cape Province, South Africa, is a long-lived conifer with distinct tree rings and thus a strong dendroclimatic potential. However, the climatic signal in its tree-ring width (TRW) is weak and other tree-ring parameters such as density need to be explored to extract climatic information from this proxy. Here we investigate the climatic signal of density parameters in 17 Clanwilliam cedar samples (9 trees) collected in 1978 (Dunwiddie & LaMarche, 1980). We use a non-destructive X-ray Computed Tomography facility to develop minimum density (MIND) and maximum density (MXD) chronologies from 1900 until 1977. EPS for both density series exceeded 0.85. For the period 1930-1977 (reliable instrumental records), MIND correlates negatively with early-growing season precipitation (Oct-Nov), whereas MXD correlates negatively with end-of-season (March) temperature. The spatial correlation between MIND and spring precipitation spans the winter rainfall zone of South Africa. Clanwilliam cedar can live to be 356 years old and the current TRW chronology extends to 1564 CE. Full-length density chronologies for this long-lived species could provide a precipitation reconstruction for southern Africa, a region where historical climate observations are limited and where societal vulnerability to future climate change is high.

References:

Dunwiddie, P. W., & LaMarche, V. C. (1980). A climatically responsive tree-ring record from Widdringtonia cedarbergensis, Cape Province, South Africa. Nature, 286(5775), 796–797.

How to cite: Trouet, V., De Mil, T., Meko, M., and Van den Bulcke, J.: Exploring the climate signal in tree-ring density of Clanwilliam cedar, South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20692, https://doi.org/10.5194/egusphere-egu2020-20692, 2020.

EGU2020-2944 | Displays | SSP1.9

Calibration of δ2Hn-alkane and δ18Osugar for paleoclimate reconstructions in South Africa and its first application to peat sediments from Vankervelsvlei

Paul Strobel, Roland Zech, Marcel Bliedtner, Julian Struck, Bruno Glaser, Michael Zech, Michael E. Meadows, and Torsten Haberzettl

Hydrogen isotope analyses of leaf wax n-alkanes (δ2Hwax) are widely applied to reconstruct paleoclimate changes. To date, it has proved difficult to disentangle past changes in the isotopic signal of precipitation (δ2Hp) and other fractionation factors, e.g. evapo-transpirative enrichment. Oxygen isotopes from hemicellulose sugars (δ18Osugar) have been proposed to complement δ2Hwax and enable more robust paleohydrological reconstructions by coupling both isotopes. However, up to now, there is a lack of studies analysing both water isotopes in South Africa.

Therefore, we analysed δ2Hwax and δ18Osugar from topsoils from South Africa to evaluate the coupled isotope approach on modern reference material as an initial step towards more robust paleohydrological reconstructions. The results indicate that δ2Hwax significantly correlates with δ2Hp values for growing season precipitation. However, no correlation exists between δ18Osugar and growing season δ18Op. While the apparent fractionation εapp 2H, i.e. the difference between δ2Hwax and δ2Hp, is relatively constant and not affected by climate, εapp 18O correlates significantly with both potential evapotranspiration and the aridity index, indicating a strong influence of evapo-transpirative enrichment on δ18Osugar. Coupling δ18Osugar and δ2Hwax facilitates the reconstruction of δ2Hp and δ18Op in South Africa with a 1σ accuracy of ± ~27‰ and ± ~3.7‰, respectively, and relative humidity (RH) with a 1σ accuracy of ± ~17%.

In a second step, we applied the coupled isotope approach to a 14.6 m long sediment core to complement geochemical and sedimentological analyses. The core is from Vankervelsvlei, a fen near the southern Cape coast located 152 m above mean sea level within the year‑round rainfall zone of South Africa. Our results show relatively high values for δ2Hwax between 7,020 +200/‑270 and 4,770 +280/‑230 cal BP. Conventionally, this would be interpreted to indicate more arid conditions (referring to the ‘amount effect’ or enhanced evapo-transpirative enrichment). However, corresponding reconstructed RH values are high and point to more humid conditions. Thus, we interpret the higher δ2Hwax (as well as the isotopically positive reconstructed precipitation) to reflect changing moisture sources, i.e. more summer precipitation related to greater prominence of the Easterlies. Enhanced RH as well as increased wind speed inferred from high wind driven allochthonous input (Al, Sr, Ti), is associated with a maximum in obliquity during that time. Drier and less windy conditions are indicated between 4,770 +280/‑230 and 2,820 +350/‑330 cal BP, as suggested by lower δ2Hwax and reconstructed precipitation, low RH and reduced wind driven allochthonous input. Moister conditions persisted between 2,820 +350/‑330 and 1,620 +430/‑280 cal BP and are followed by a ~1 kyr dry period. Moisture levels have been increasing since 640 +90/‑100 cal BP.

How to cite: Strobel, P., Zech, R., Bliedtner, M., Struck, J., Glaser, B., Zech, M., Meadows, M. E., and Haberzettl, T.: Calibration of δ2Hn-alkane and δ18Osugar for paleoclimate reconstructions in South Africa and its first application to peat sediments from Vankervelsvlei, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2944, https://doi.org/10.5194/egusphere-egu2020-2944, 2020.

EGU2020-11782 | Displays | SSP1.9

Modern environment characterization of interdunal lakes in Inhambane province (SE Mozambique) as an analogue to understand past environmental changes

Ana Gomes, Simon Connor, Maria João Martins, Brandon Zinsious, Célia Gonçalves, Delminda Moura, Elena Skosey-LaLonde, João Cascalheira, Jonathan Haws, Judite Nhanombe, Mussa Raja, Paulo Fernandes, Reginelinda Mauelele, Roxane Matias, Sónia Oliveira, Susana Costas, and Nuno Bicho

To better understand Quaternary environmental changes in Southeastern Mozambique and their role in human evolution, it is first necessary to characterized the modern environment of this area and the environmental drivers on their evolution. For this reason, an international and interdisciplinary team interpreted the Inhambane Province’s geology, hydrographic and tectonic maps and open-access satellite imagery and derived products (for morphometric analysis and landscape interpretation). Inhambane province is in a coastal plain composed of a Pleistocene dune system, within which many lakes can be found. Additionally, a comprehensive review of the existing research for the region was conducted, to choose the most suitable lakes from which to collect sediment records for paleoenvironmental reconstructions. The team carried out fieldwork during the summer of 2019 in four of the selected interdunal lakes (Muangue, Nyalonzelwe, Nhambutse and Chivanene). During fieldwork the vegetation cover and the land uses were carefully described, and the lakes water column parameters were measured. Additionally, in the two lakes that presented the longest sedimentological records (Muangue and Nyalonzelwe), an unmanned aerial vehicle (UAV) survey was carried out to create high resolution maps and elevation models of the lakes and their surroundings. UAV flights were carried out at 25 and 60 m height, with a front and side overlap between 60 to 70 %, using georeferenced Ground control points (GCPs). The lakes’ areas vary between 0.4 (Muangue) to 0.8 km2 (Chivanene). The longest sedimentological records were found in lakes with a water level 5 m above the Mean Sea Level (MSL) and surrounded by higher dunes (between 31 and 121 m elevation in relation to MSL). Most of the lake margins are used for agriculture, livestock and housing and some have fish farming. Regarding vegetation, between 16 families and 27 species were identified around Nhambutse and 27 families and 43 species around Muangue. The lakes’ maximum depths vary between 1 (Nhambutse) and 4.6 meters (Muangue). All lakes are freshwater except Nyalonzelwe, which is brackish. On average, surface water pH varies between 7.2 (Chivanene) and 9.12 (Nyalonzelwe). Surface water temperature varies between 25.03 (Nhambutse) and 26.6 ° C (Chivanene). All the collected data highlight the diversity of interdunal lake environments in the Inhambane Province, and how these environments may impact the sedimentological record. This work was supported by project PTDC/HAR-ARQ/28148/2017, funded by the Portuguese Foundation for Science and Technology.

How to cite: Gomes, A., Connor, S., Martins, M. J., Zinsious, B., Gonçalves, C., Moura, D., Skosey-LaLonde, E., Cascalheira, J., Haws, J., Nhanombe, J., Raja, M., Fernandes, P., Mauelele, R., Matias, R., Oliveira, S., Costas, S., and Bicho, N.: Modern environment characterization of interdunal lakes in Inhambane province (SE Mozambique) as an analogue to understand past environmental changes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11782, https://doi.org/10.5194/egusphere-egu2020-11782, 2020.

EGU2020-11485 | Displays | SSP1.9

Biogeochemical analysis of newly dated lacustrine cores: a first look at Quaternary paleoenvironment in coastal Mozambique

Elena Skosey-LaLonde, Ana Gomes, Maria João Martins, Simon Connor, Mussa Raja, Brandon Zinsious, Roxane Matias, Reginelinda Mauelele, Jonathan Haws, Delminda Moura, Gideon Hartman, Célia Gonçlaves, João Cascalheira, Sónia Oliveira, Paulo Fernandes, Susana Costas, and Nuno Bicho

In order to better quantify the role of climate variability in southeastern Africa, and its impact on the evolution and spread of anatomically modern humans, our international and interdisciplinary team cored a series of coastal lakes during the summer of 2019. Here, we present data from lake Nyalonzelwe, one of many interdunal lakes present along the coast in the Inhambane region of southeastern Mozambique. Nyalonzelwe sits 5m above MSL and is bounded by a Pleistocene dune system, reaching between 29-121m in elevation, protecting the lake from the Indian Ocean. The sedimentological record of Nyalonzelwe presents over 6m of stratigraphic variability, including a varve sequence spanning the basal 2m, making it an incredibly rare record of seasonal resolution climate variability and the first record of its kind in Mozambique. Two cores, C1 and C4, with depths of 6.12m and 6.22m respectively, were collected for multiproxy biogeochemical analyses and C14 dating using a Livingstone corer. This work seeks to present the results of Carbon, Hydrogen, Nitrogen (CHN) elemental analysis for core C1, sampled at 10 cm intervals and aragonite/calcite ratios for gastropod assemblages across C4, sampled at 1 cm resolution in preparation for stable isotope analysis.

CHN analysis was conducted using an Elementar model Vario EL III at the University of Algarve CCMAR for both organic and inorganic carbon present in sediment samples from C1. Aragonite/calcite ratios for identified gastropod species, namely Melanoides tuberculata, were collected from individual representatives in samples from C4 with more than 8 individuals present and determined using Fourier Transform Infrared Spectroscopy at the University of Connecticut. Nyalonzelwe cores C1 and C4 are stratigraphically correlated. Together these data represent the first look at Quaternary paleoenvironmental evolution in southeastern coastal Mozambique and the importance of climate (in)stability in the region and its impact on early modern human populations. This work was supported by the project PTDC/HAR-ARQ/28148/2017, funded by the Portuguese Foundation for Science and Technology.

How to cite: Skosey-LaLonde, E., Gomes, A., Martins, M. J., Connor, S., Raja, M., Zinsious, B., Matias, R., Mauelele, R., Haws, J., Moura, D., Hartman, G., Gonçlaves, C., Cascalheira, J., Oliveira, S., Fernandes, P., Costas, S., and Bicho, N.: Biogeochemical analysis of newly dated lacustrine cores: a first look at Quaternary paleoenvironment in coastal Mozambique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11485, https://doi.org/10.5194/egusphere-egu2020-11485, 2020.

EGU2020-21437 | Displays | SSP1.9

Lake level changes and their paleo-climatic implications at the middle Pleistocene excavation of MAR-1, southern Greece

Ines Bludau, Max Weiss, Ellen Schnabel, Nicholas Thompson, Vangelis Tourloukis, Panagiotis Karkanas, Eleni Panagopoulou, Katarina Harvati, and Annett Junginger

In the fossil-rich sediments of the Megalopolis Basin, southern Greece, the remains of an ancient paleo-lake alternate between detrital units and lignite seams deposited during the Middle Pleistocene. The detrital sediments of MAR-1 (480-420 kyr) between two lignite seams are where lithics and elephant bones with cut-marks have been systematically excavated indicating hominin activity along a paleo-shoreline circa 440 kyr. Based on current knowledge, lignite seams formed during interglacials, while the silty-clay-rich deposits in between were deposited under glacial conditions. However, the paleoenvironmental and paleoclimatic conditions on shorter times-scales, leading to the preservation of hominin activity in the area, remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and thus sedimentation patterns and their governing paleo-climatic factors, we analyzed a high resolution 5-meter long sediment sequence from the archaeological site MAR-1. For the reconstruction, a multiproxy approach was applied using microfossils, grain-size, and geochemical analysis such as total organic carbon, total inorganic carbon, X-ray diffraction, and conventional X-ray fluorescence. Diatoms were often too corroded to be of use, most likely due to a combination of alkaline water conditions and the influence of silicate sponges. The results of the analyses revealed that MAR-1, located between lignite unit II and III, experienced multiple lake level oscillations mostly following insolation changes suggesting that several short-term wet-dry-wet cycles occurred during the investigated period, which must have impacted flora and fauna, including hominins, in the area. This research was conducted under the auspices of the Ephoreia of Paleoanthropology and Speleology, Greek Ministry of Culture, and was supported by the European Research Council (PaGE, CROSSROADS).

How to cite: Bludau, I., Weiss, M., Schnabel, E., Thompson, N., Tourloukis, V., Karkanas, P., Panagopoulou, E., Harvati, K., and Junginger, A.: Lake level changes and their paleo-climatic implications at the middle Pleistocene excavation of MAR-1, southern Greece , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21437, https://doi.org/10.5194/egusphere-egu2020-21437, 2020.

EGU2020-8414 | Displays | SSP1.9

The diatom flora of Lake Lisan (Israel): a preliminary investigation

Hannah Hartung, Jane M. Reed, and Thomas Litt

The Eastern Mediterranean, and the southern Levant in particular, is a key region for palaeoclimatological and palaeoenvironmental research due to its highly complex topography and climatic variability. Our understanding of environmental variability and its possible drivers, and the interaction with migration processes of modern Homo sapiens from a source area in Africa to Europe, is still limited. This is partly because continuous sediment records of sufficient age are rare across the Mediterranean Basin. The deposits of the Dead Sea represent an ideal archive to investigate palaeoenvironmental conditions during human migration phases in the Last Glacial period (MIS 4-2). 

Diatoms (single-celled siliceous algae, Bacillariophyceae) have well-recognised potential to generate high-quality palaeolimnological data, especially in closed-basin saline lakes, but they remain one of the least-exploited proxies in Eastern Mediterranean palaeoclimate research. Here, we present preliminary results of a low-resolution diatom study derived from analysis of sediment deposits of Lake Lisan, the last glacial precursor of the Dead Sea. Sediment cores were recovered during an ICDP campaign in 2010/2011 from the centre of the modern Dead Sea. 18 sediment samples were analysed to investigate (a) the preservation of diatom valves in various evaporitic deposits (b) possible shifts in diatom species composition of Lake Lisan during the Last Glacial period, and (c) if diatoms can be used as proxy indicator for lake-level and, thus, palaeoclimate reconstruction. We focus on a prominent lake-level high stand of Lake Lisan at around 28-22 ka BP, which resulted in the merging Lake Lisan and freshwater Lake Kinneret.

First results show that the diatom preservation is exceptionally good in evaporitic deposits of the sediment cores from Lake Lisan, which is contradictory to the available literature. In contrast to Holocene deposits from the Dead Sea, diatoms are abundant in all analysed samples from laminated deposits from Lake Lisan: the diatom flora is dominated by halophilous benthic diatoms, such as Amphora spp., Halamphora spp. and Nitzschia spp. In phases of lake-level high stands of Lake Lisan, the diatom flora shifts towards a more plankton-dominated freshwater flora containing Aulacoseira spp. and taxa from the Cyclotella-ocellata-species complex.

How to cite: Hartung, H., Reed, J. M., and Litt, T.: The diatom flora of Lake Lisan (Israel): a preliminary investigation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8414, https://doi.org/10.5194/egusphere-egu2020-8414, 2020.

EGU2020-7706 | Displays | SSP1.9

Human environmental interactions during the Neolithization of the Ammer Valley: first results integrating paleo-ecological and bio-archaeological evidence

Shaddai Heidgen, Elena Marinova, Raiko Krauß, Oliver Nelle, Martin Ebner, Stefan Klingler, Tatiana Miranda, Jörg Böfinger, Elisabeth Stephan, and Annett Junginger

The Upper Neckar and Ammer river valleys in southwestern Germany correspond to the southwestern limit of the overall distribution of the oldest Linear Bandkeramik (LBK) culture. More than 200 Neolithic sites are known from this region with one of the oldest sites located in the vicinity of the village Ammerbuch-Pfäffingen, around 10 km west of Tübingen, Germany. The archaeological record suggests that settlement activities occurred here between 7260 and 7110 cal BP (or 5310-5160 cal BC). Despite the various activities at the settling site itself, little is known about the environmental impact of the first settlers on the area, ranging from the introduction of farming and animal husbandry with impacts to the forests due to pasture and collection of wood, as well as possible control of water bodies. We here present the first results of a palynological study of two parallel, overlapping 8 m long sediment cores that were retrieved in 2018 from a shallow paleo-lake only a few hundred meters distant from the excavation site. The composite core allows environmental reconstruction of the area between 11540 and 7000 cal BP, based on six radiocarbon dates. Pollen analysis indicates mixed oak forests and an increase of light-demanding vegetation (i.e. Quercus, Corylus, Betula). Current analyses on micro- and macro-charcoal are going to reveal the natural or anthropogenic induced causes of paleo-fire events and Non-Pollen-Palynomorphs (NPP), including dung spores, unravel the possible presence of herbivores (including domestic ones) in the area. The results of the current study and its integration into the bioarchaeological record are relevant even beyond the region providing the usually rarely available paleoecological records from close proximity of an LBK site and thus deliver valuable insights on the environmental settings at the beginning of farming in central Europe.

 

How to cite: Heidgen, S., Marinova, E., Krauß, R., Nelle, O., Ebner, M., Klingler, S., Miranda, T., Böfinger, J., Stephan, E., and Junginger, A.: Human environmental interactions during the Neolithization of the Ammer Valley: first results integrating paleo-ecological and bio-archaeological evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7706, https://doi.org/10.5194/egusphere-egu2020-7706, 2020.

EGU2020-22297 | Displays | SSP1.9

Geological and geomorphological investigations in the Early Pleistocene paleontological multi-site of Olteț River Valley, Romania

Alexandru Petculescu, Virgil Drăgușin, Anca Avram, Sabrina Curran, Luchiana Faur, Radu Irimia, Ionuț Mirea, Chris Robinson, Marius Robu, Ionuț Şandric, Barbara Soare, Claire E. Terhune, Alida Timar-Gabor, and John Woodhead

The Olteț River Valley in southern Romania hosts a large number of fossiliferous sites, the richest of which is Valea Grăunceanului. Based on biochronological estimations, these sites were assigned to the Late Villafranchian (MN17/MNQ1), at ~2.0-1.8 Ma. As yet, no other dating methods were employed and our present study aims to provide the geological and geomorphological background for radiometric and trapped charge dating, as well as for the stratigraphic correlation of these sites. These deposits are represented by fluvial-lacustrine sediments belonging to the Dacian Basin, a part of the Eastern Paratethys domain.

Our approach is to create a regional stratigraphic column onto which to place the fossil sites. We first created a high-resolution 3D model of the surface using UAV technology. Further, we sampled sediments from several sections and determined their grain size and mineralogy. We also sampled pedogenic carbonates and fossil teeth for preliminary geochemical analysis, in preparation for uranium series dating.

Although no human fossils have been found so far in the Olteț River Valley, the site is important for understanding the environment used by early humans to migrate out of Africa. These sites are close both in time and space to important anthropological sites such as Dmanisi, Khapry or Kozarnika, while being part of an area dominated by large water bodies that included the Pannonian, Dacian and Euxinic lakes.

How to cite: Petculescu, A., Drăgușin, V., Avram, A., Curran, S., Faur, L., Irimia, R., Mirea, I., Robinson, C., Robu, M., Şandric, I., Soare, B., Terhune, C. E., Timar-Gabor, A., and Woodhead, J.: Geological and geomorphological investigations in the Early Pleistocene paleontological multi-site of Olteț River Valley, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22297, https://doi.org/10.5194/egusphere-egu2020-22297, 2020.

EGU2020-2925 | Displays | SSP1.9

Luminescence dating challenges: about hiati and methodological considerations in the Urluia and Vlasca loess-paleosol sequences, Romania

Janina Bösken, Nicole Klasen, Daniela Constantin, Ulrich Hambach, Daniel Veres, Christoph Schmidt, Stephan Pötter, Christian Zeeden, Frank Lehmkuhl, and Alida Timar-Gabor

Loess-paleosol sequences are in the focus of paleoenvironmental research because they offer potentially quasi-continuous terrestrial records of environmental change. For the research on paleoenvironments, paleoclimates, and human evolution studies reliable dating approaches are essential. Age models can be based on different methods, e.g. proxy data correlation and chronometric dating approaches. For the Urluia loess-paleosol sequence, which provides a high-resolution record covering the Last Glacial Cycle in the Lower Danube-Black Sea area (Romania), correlative and luminescence age models do not agree with each other (Bösken et al., 2018). While the results of internal quality checks of the luminescence data speaks for a reliable chronology, the radiometric ages of samples assigned to the MIS 4-5 interval based on stratigraphic evidence are significantly overestimated. As ages in the lower half of the section do not increase with depth, field saturation has been suggested, while new measurements indicate that laboratory saturation has not been reached. This contribution presents a detailed luminescence dating approach using OSL and pIRIR protocols for fine-grain quartz and polymineral samples. Furthermore, the geochronology of the Vlasca loess-paleosol sequence that is located at the bank of the Danube ~40 km north of Urluia is presented. The section was chosen because it contains a vast accumulation of loess with one prominent paleosol at the bottom (total height ~27 m), presumably covering a similar time-interval as the Urluia sequence. The dating approach includes fine-grain quartz, coarse-grain quartz, polymineral pIRIR225, and portable OSL measurements. The question whether the observed discrepancy between the dating results and the stratigraphy at Urluia represents a regional pattern and/or possibly intrinsic luminescence properties are responsible will be discussed.

References

Bösken, J., Zeeden, C., Hambach, U., Veres, D., Klasen, N., Brill, D., Burow, C., Obreht, I. and Lehmkuhl, F. (2018). Consistency challenges between correlative and luminescence age models for the last ~150 ka in the Lower Danube Basin loess-paleosol sequences. Geophysical Research Abstracts 20, EGU2018-7986, EGU General Assembly 2018.

How to cite: Bösken, J., Klasen, N., Constantin, D., Hambach, U., Veres, D., Schmidt, C., Pötter, S., Zeeden, C., Lehmkuhl, F., and Timar-Gabor, A.: Luminescence dating challenges: about hiati and methodological considerations in the Urluia and Vlasca loess-paleosol sequences, Romania , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2925, https://doi.org/10.5194/egusphere-egu2020-2925, 2020.

EGU2020-4723 | Displays | SSP1.9

Lower Danube loess - a crucial palaeoclimatic archive for the last glacial cycle in Southeast Europe

Stephan Pötter, Janina Bösken, Igor Obreht, Philipp Schulte, Daniel Veres, Ulrich Hambach, Christian Zeeden, Slobodan Marković, and Frank Lehmkuhl

The vast Pleistocene aeolian sediments of the Lower Danube Basin are an important archive of Quaternary palaeoclimate dynamics in Southeast Europe. The intercalation of loess layers and fossil soils, so called loess-palaeosol sequences (LPS) are interpreted as the results of oscillating climate phases in the past. However, the characteristics of these LPS vary quite strongly, since they are influenced by various factors. Those factors are mainly the (palaeo-) climate, the (palaeo-) relief and the availability of source material, which differ notably, even at a regional scale. Taken that into account, it is crucial to consider local characteristics while comparing data from different LPS.

Against this backdrop, we compare two LPS from the dry Bărăgan steppe area in southeast Romania: Vlasca (VLA) and Balta Alba Kurgan (BAK). The two sections are approx. 100 km afar and developed under different geomorphic and climatic situations, resulting in varying accumulation rates and post-depositional alterations. Vlasca is a natural exposure on the left bank of the Danube River, whereas BAK is situated in a road cut, approx. 15 km south of the Carpathian bending. The two sites show remarkable differences concerning accumulation rates, grain size, colour, geochemical characteristics as well as magnetic properties, which are interpreted as the results of sediment availability, depositional milieu and especially post-depositional alterations. The variations and the commonalities are used, together with the chronological framework, to better understand the palaeoclimatic evolution of the Lower Danube Basin within the last glacial cycle and to gauge possible ramifications of palaeoclimatic variations on the migration of modern humans.

How to cite: Pötter, S., Bösken, J., Obreht, I., Schulte, P., Veres, D., Hambach, U., Zeeden, C., Marković, S., and Lehmkuhl, F.: Lower Danube loess - a crucial palaeoclimatic archive for the last glacial cycle in Southeast Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4723, https://doi.org/10.5194/egusphere-egu2020-4723, 2020.

EGU2020-18353 | Displays | SSP1.9

European Standard Loess as baseline for paleoenvironmental interpretations of loess granulometric variations

Philipp Schulte, Tobias Sprafke, and Frank Lehmkuhl

Loess-paleosol sequences are sensitive terrestrial archives of Quaternary aeolian dynamics and paleoclimatic changes. Loess is predominantly formed during glacial periods, whereas soils form during interglacials and interstadials, when dust sedimentation is reduced or absent. Common grain size (GS) based proxies used in loess research mainly reconstruct past sedimentation dynamics. However, the GS distribution of a loess sample is not solely a function of aeolian dynamics; rather complex polygenetic depositional and post-depositional processes must be taken into account.

Here we integrate GS data of primary loess samples from 14 profiles in Europe as baseline to identify and quantify the imprint of local paleoenvironments on GS distribution along vertical loess sections. Our GS data are measured by the same laser diffraction device (Beckmann Coulter LS13320) and available in the database of the Physical Geography laboratory at the RWTH Aachen University. Based on a catalogue of criteria, samples with least signs of weathering and reworking (e.g. low GS mean and good sorting, low magnetic susceptibility, low geochemical weathering proxies) are defined as primary loess of the studied loess sections. GS distributions of these loess samples show little variation, both within individual profiles (temporal) and in a supra-regional comparison (spatial). We calculate an averaged loess sample and interpret it as baseline loess or European Standard Loess. We discuss the significance of deviations from this standard loess related to different geomorphological conditions during deposition and later pedogenetic processes.

How to cite: Schulte, P., Sprafke, T., and Lehmkuhl, F.: European Standard Loess as baseline for paleoenvironmental interpretations of loess granulometric variations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18353, https://doi.org/10.5194/egusphere-egu2020-18353, 2020.

EGU2020-681 | Displays | SSP1.9

Combined rock-magnetic and colorimetric stratigraphy for a 430 ka- covering loess-palaeosol sequence in the vicinity of Belgrade, Northern Serbia

Christian Laag, Ulrich Hambach, Christian Zeeden, Mladjen Jovanović, and Slobodan Marković

Quaternary palaeoenvironmental recorders are particularly in the Northern Hemisphere provided by loess-palaeosol sequences (LPSs). In the Middle Danube basin, these terrestrial archives cover the last million years (Markovic et al., 2015) of the climate history as well as archaeological horizons from occupations by early humans. The Zemun loess site (ZLS, located in the Vojvodina, Northern Serbia) was declared as a protected site, based on artefacts of previous settlements found on the river bench. For providing a stratigraphy for this site and to set the archaeological findings into an environmental and temporal context, the ZLS was investigated by means of environmental magnetic and colorimetric properties. This requires not only to creation of a stratigraphy to be compared to already investigated sites of northern Serbia, but also provides independent age control, carried out by tephrochronology. Therefore, the ZLS contains two important chronological anchor-points, namely the L2-tephra (correlated to Vico Ignimbrite B and dated to 160.6 ± 4 ka, (Mannella et al., 2019)) and the Bag-Tephra (correlated to the Villa Senni eruption and dated to 351-357 ka (Fu et al., 2019)). This tephrochronological timeframe, in combination with the colorimetric and environmental magnetic parameters, witnesses an accumulation of mineral dust, providing insights from glacial to interglacial conditions ranging from marine oxygen isotope stage (MIS) 11 to MIS 4.

 

References

Fu et al. (2019): Chances and challenges in tephrochronology of loess: A case study from the Bag tephra in Serbia. Poster at the XX. INQUA International Quaternary Association Conference 25 – 31 July, Dublin, Ireland.

Mannella et al. (2019): Palaeoenvironmental and palaeohydrological variability of mointain areas in the central Mediterranean region: A 190 ka-long chronicle from the independently dated Fucino palaeolake record (central Italy). Qua. Sci Rev., 210, pp. 190-210.

Markovic et al. (2015): Danube loess stratigraphy – Towards a pan-European loess stratigraphic model. Earth-Sci. Rev., 148, pp. 228-258.

How to cite: Laag, C., Hambach, U., Zeeden, C., Jovanović, M., and Marković, S.: Combined rock-magnetic and colorimetric stratigraphy for a 430 ka- covering loess-palaeosol sequence in the vicinity of Belgrade, Northern Serbia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-681, https://doi.org/10.5194/egusphere-egu2020-681, 2020.

EGU2020-13340 | Displays | SSP1.9

Evolution and stratigraphy of the Nakdong River valley deposits in response to late Quaternary sea-level change

Dong-Geun Yoo, Seok-Hwi Hong, Gwang-Soo Lee, Jin-Cheul Kim, Gil-Young Kim, and Yun-Soo Choi

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley reveals that the Nakdong River valley deposits, approximately 60 - 70 m thick, consist of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuary, coastal/shoreface, and delta. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed approximately before 12 ka. The transgressive systems tract (TST) can be divided into two depositional systems (Unit II and III). The river-derived sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 6 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the recent deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 6 ka.

How to cite: Yoo, D.-G., Hong, S.-H., Lee, G.-S., Kim, J.-C., Kim, G.-Y., and Choi, Y.-S.: Evolution and stratigraphy of the Nakdong River valley deposits in response to late Quaternary sea-level change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13340, https://doi.org/10.5194/egusphere-egu2020-13340, 2020.

SSP1.14 – Salt Giants: formation, deformation, and resource potential

EGU2020-4040 | Displays | SSP1.14

Levant Basin as a key for Understanding the Messinian Salinity Crisis: Challenging the Desiccation Paradigm

Zohar Gvirtzman, Vinicio Manzi, Ran Calvo, Ittai Gavrieli, Rocco Gennari, Stefano Lugli, Matteo Reghizzi, Davide Persico, B. Charlotte Schreiber, and Marco Roveri

The Messinian salinity crisis (MSC) is an extreme event in Earth history during which a salt giant (>1×106 km3) accumulated on the Mediterranean seafloor within ~640 kyrs. The Messinian salt giant was formed about 6 million years ago when the restriction of water exchanges between the Atlantic Ocean and the Mediterranean Sea turned the Mediterranean into an enormous saline basin. After more than 40 years of research, the timing and the depositional environments of shallow (<200 m) and intermediate (200-1000 m) water-depth Messinian basins are known quite well from onshore outcrops. But what happened in the deepest portions of the Mediterranean Sea is still unclear, because the information about offshore successions is mainly based on geophysical data with no rock samples that can be dated.

The Levant Basin is the only deep Mediterranean basin where the entire Messinian section has been penetrated by wells tied to high resolution 3D seismic surveys. Here we present two studies challenging the desiccation paradigm dominating the MSC scientific literature for more than 40 years.

The first study focuses on the nearly flat top erosion surface (TES) that truncates a basinward-tilted Messinian evaporitic succession. This truncation is commonly interpreted to be the result of subaerial erosion at the end of the MSC. However, based on high resolution seismic surveys and wireline logs, we show that (1) the TES is actually an intra-Messinian truncation surface (IMTS) located ~100 m below the Messinian-Zanclean boundary; (2) the topmost, post-truncation, Messinian unit is very different from the underlying salt deposits and consists mostly of shale, sand, and anhydrite showing typical 87Sr/86Sr values and fauna assemblages from stage 3; and (3) the flat IMTS is a dissolution surface related to significant dilution and stratification of the water column during the transition from stage 2 to stage 3. We suggest that dissolution occurred upslope where salt rocks at the seabed were exposed to the upper diluted brine, while downslope the salt rocks were preserved because submerged in the deeper halite-saturated layer. The model, which requires a stratified water column, is inconsistent with a complete desiccation of the eastern Mediterranean Sea.

The second study focuses on the onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin. Biostratigraphy and astronomical tuning of the Messinian pre-salt succession in the Levant Basin allows for the first time the reconstruction of a detailed chronology of the MSC events in deep setting and their correlation with marginal records that supports the CIESM (2008) 3-stage model. Our main conclusions are (1) MSC events were synchronous across marginal and deep basins, (2) MSC onset in deep basins occurred at 5.97 Ma, (3) only foraminifera-barren, evaporite-free shales accumulated in deep settings between 5.97 and 5.60 Ma, (4) deep evaporites (sulfate and halite) deposition started later, at 5.60 Ma. The wide synchrony of events implies inter-sub-basin connection during the whole salinity crisis and is not compatible with large sea-level fall that would have separated the eastern and western basins producing diachronic processes.

How to cite: Gvirtzman, Z., Manzi, V., Calvo, R., Gavrieli, I., Gennari, R., Lugli, S., Reghizzi, M., Persico, D., Schreiber, B. C., and Roveri, M.: Levant Basin as a key for Understanding the Messinian Salinity Crisis: Challenging the Desiccation Paradigm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4040, https://doi.org/10.5194/egusphere-egu2020-4040, 2020.

In August of 1970, during Mediterranean Sea Leg 13, when the Glomar challenger ventured Mediterranean waters, nobody was expecting to run into one of the most exiting scientific discoveries regarding the Mediterranean Sea evolution. Cores and seismic surveys made possible the discovery of a basin-wide Messinian evaporitic deposit buried beneath the deep-sea Pliocene sediments which was attributed to the Messinian Salinity Crises (MSC) already known and studied in onshore outcrops in the Apennines. Now, 50 years later the debate regarding the conditions and timing of the deposition of this salt giant is still ongoing as many theories are still open and in search for validating proof.

One of the main open questions certainly regards the base level drop during the MSC and the location, efficiency and dynamics of the Mediterranean – Atlantic connectivity. The Mediterranean level is thought to have dropped somewhere between a moderate 200 m up to an extreme high amplitude oscillation of 1500 m while according to different schools of thought the watergate to the Atlantic is considered as completely closed, intermittently open or to have been always open during the MSC. Gibraltar strait is the main candidate for a possible gateway during this time interval (5.96-5.33 Ma) as well as the leading cause of the re-establishment of open marine conditions in the Mediterranean. Consequently, understanding its evolution and opening is fundamental to endorse any of the MSC theories and a thorough investigation of the Messinian and early Pliocene sedimentological record of basins in its proximity is highly needed.

In this optic, the Alboran Sea is the place where many of those answers lie and its worth of further exploration. In the hope of a new oceanographic expedition in the near future, an effort should be made towards gathering and re-interpreting all the available data. We propose a refined planktonic foraminifer chronology of the Alboran DSDP and ODP sites 976B, 121 and 978A with a careful characterization of the main MSC facies that will clarify to a certain extent the MSC expression and the degree of Atlantic water influence in the Alboran basin.

 

How to cite: Bulian, F. and Sierro, F. J.: Revision of the Alboran sea Tortonian-Pliocene record: possible new insights on Mediterranean-Atlantic connectivity during the Messinian Salinity Crises, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4845, https://doi.org/10.5194/egusphere-egu2020-4845, 2020.

EGU2020-21743 | Displays | SSP1.14

Calcareous nannofossil size as a proxy for the Messinian Salinity Crisis dynamics

Alan Maria Mancini, Patrizia Ziveri, Michael Grelaud, and Francesca Lozar

Dwarfism is a common feature affecting organism during and after extreme events that characterized the geological history. The organism size reductions are frequently referred as the result of “stressed condition”. Such changes occurred for instance during Oceanic Anoxic Events and are well recorded in the fossil assemblage of calcareous marine organisms. To date, no study addressed the morphological and biometric changes during the Messinian Salinity Crisis (MSC), one of the most recent and impacting event occurred in the Mediterranean Sea.

Here we focus on morphometric changes affecting calcareous nannofossils at the MSC onset in order to better constrain the paleoenvironmental changes and the “stressed conditions” that characterized this interval. Samples were collected in the Perales section (Sorbas Basin, West Mediterranean) in which size characterization of 50 specimens of 4 different calcareous nannofossil taxa (Helicosphaera carteri, Sphenolithus abies, Umbilicosphaera rotula and Coccolithus pelagicus) was performed in each sample, along with their absolute abundances (number of nannofossils over gram of dry sediment).  In order to test the reliability of the obtained data and demonstrate that the size change recorded at the MSC onset was a basin-scale event, 2 sections in the Piedmont Basin (Banengo and Pollenzo), encompassing the same time period were also analysed. In addition, size changes and cyclicity related to orbital forces were addressed in a high temporal resolution size and calcite mass analysis performed on Reticulofenestra minuta, using an automated image analyses system of calcareous nannofossils recognition (SYRACO) on several cycles encompassing the MSC onset.

A significant size reduction affected the calcareous nannofossil taxa involved in the MSC onset biostratrigraphic event in both the North and West Mediterranean sections. These morphometric changes were related to the restriction of the Mediterranean Basin, resulting in an increase in both productivity and environmental variability, stimulating  calcareous nannofossils growth rate and decreasing their cell and sizes. The R. minuta size and calcite mass correlate with the change in the orbital variability, governed mostly by precession, with minimum values recorded during the cyclical diatomite deposition in the Sorbas Basin. In this case, the size reduction was triggered by the precession-induced enhanced environmental variability that characterized the diatomitic deposition.

Our findings highlight the relevance of calcareous nannofossil morphometry and mass to trace the dynamics of extreme events, such as the MSC. Size and mass changes of selected calcareous nannofossils taxa at the MSC onset suggest that “stressed conditions” characterizing this event likely coincide with the instauration of a highly variable environment, linked to the restriction of the paleo Gibraltar strait. 

How to cite: Mancini, A. M., Ziveri, P., Grelaud, M., and Lozar, F.: Calcareous nannofossil size as a proxy for the Messinian Salinity Crisis dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21743, https://doi.org/10.5194/egusphere-egu2020-21743, 2020.

EGU2020-7533 | Displays | SSP1.14

The Role of Restricted Basins in Global Biogeochemical Cycles

Alexandra Turchyn

The formation of restricted basins isolates seawater from the global ocean and allows the formation of salt deposits, often because restricted basins can have minor connectivity to the global ocean and thus can fill and evaporate many times over. The formation of salts removes ions from the global ocean, potentially decreasing their concentration elsewhere and leading to an alteration of their biogeochemical cycle.  The subsequent exposure and chemical weathering of these salt deposits changes the source of these elements back into the global ocean and can influence their biogeochemical cycles for a long time after the formation of the restricted basin.   Sediment biogeochemistry in restricted basins also differs from most global continental shelf, slope, and deep-sea sediments. The formation of sedimentary minerals and their subsequent diagenesis means that the amount and isotopic composition of deposited minerals in restricted basins can differ greatly from those in the global ocean. In this talk I am going to explore how the formation of restricted basins, including epicontinental seas and isolated seas, has influenced the biogeochemical cycle of carbon and sulfur over the course of the last 65 million years.  I am going to use a combination of new measurements on the carbon and sulfur isotopic composition of the ocean over this time to explore how different types of restricted basins influence global biogeochemical cycles in the rest of the ocean. I will argue that the formation of restricted basins has been important in driving changes in the carbon and sulfur isotopic composition of the ocean over time, linking changes in ocean chemistry to tectonics.

How to cite: Turchyn, A.: The Role of Restricted Basins in Global Biogeochemical Cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7533, https://doi.org/10.5194/egusphere-egu2020-7533, 2020.

EGU2020-4996 | Displays | SSP1.14

The Zanclean megaflood of the Mediterranean. Searching for independent evidence

Daniel Garcia-Castellanos, Aaron Micallef, Angelo Camerlenghi, Ferran Estrada, Gemma Ercilla, Raúl Periañez, José María Abril, José David del Moral-Erencia, and Patricio Bohorquez

The Mediterranean Sea underwent restriction from the ocean and widespread salt deposition during the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km3 of Miocene sediment and bedrock.

How to cite: Garcia-Castellanos, D., Micallef, A., Camerlenghi, A., Estrada, F., Ercilla, G., Periañez, R., Abril, J. M., del Moral-Erencia, J. D., and Bohorquez, P.: The Zanclean megaflood of the Mediterranean. Searching for independent evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4996, https://doi.org/10.5194/egusphere-egu2020-4996, 2020.

EGU2020-8772 | Displays | SSP1.14

Unraveling temperature and hydrological conditions of salt deposits by measuring the speed of sound in halite fluid inclusions: the case of the Last Interglacial Dead Sea

Emmanuel Guillerm, Véronique Gardien, Niels Brall, Markus J. Schwab, Adeline Lach, Ina Neugebauer, Daniel Ariztegui, and Frédéric Caupin

Salt deposits found throughout the geological record and across the globe are witnesses of extreme paleoclimatic and paleoenvironmental conditions. However, little is known about the hydrological conditions that gave rise to these deposits, and the role of temperatures is even less constrained. Here we have used a new technique, Brillouin spectroscopy,  to investigate the paleoenvironmental and paleoclimatic conditions that led to the deposit of a thick salt sequence in the Dead Sea during the Last Interglacial (LIG, ~135,000 to 115,000 years before present). Through measuring the speed of sound inside halite fluid inclusions (FIs), this method provides the parent brine temperature and salinity at the moment of crystal growth. We applied it to several tens of halite intervals from the 450-meters-long core 5017-1 drilled in 2010-2011 in the deepest part of the Dead Sea in Palestine within the framework of the Dead Sea Deep Drilling Project (DSDDP). The application of Brillouin spectroscopy to this record provides a unique quantification of temperature and hydrological changes in this area during the LIG and outlines a radically new narrative for the climate of the region during this period. The example of the Dead Sea shows that Brillouin spectroscopy on halite FIs is in position to provide valuable data to test the efficiency of climate models and to better understand the processes that lead to the deposition of salt giants.

How to cite: Guillerm, E., Gardien, V., Brall, N., Schwab, M. J., Lach, A., Neugebauer, I., Ariztegui, D., and Caupin, F.: Unraveling temperature and hydrological conditions of salt deposits by measuring the speed of sound in halite fluid inclusions: the case of the Last Interglacial Dead Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8772, https://doi.org/10.5194/egusphere-egu2020-8772, 2020.

EGU2020-18963 | Displays | SSP1.14

Trapped Sea-Lakes, the anomalous water bodies that herald the birth and demise of the oceans

Dan Valentin Palcu and Wout Krijgsman

The tectonic opening and closure of oceans presents windows of opportunity for the formation of anomalous waterbodies which we term “trapped-sea-lakes” (TSL); poorly connected or isolated water basins characterized by anomalohaline (brackish, hyperhaline, mixohaline or limnetic according to the Venice system) conditions that change over time, reflecting the fluctuating connectivity with the global ocean and the climatic history of their watershed. TSLs contain elements typical for a sea (basin bathymetry, marine chemistry, faunistic elements), but also reflect lacustrine aspects like endemism and major environmental fluctuations over geological time. They are characterized by unusual large dimensions, long life-span (compared with classic lakes), anomalous environments with salinity and chemistry controlled by the limited connectivity with the global ocean and by climate forcing.

Here we present a classification of TSLs, supported by key studies, showing that Anoxic Giants, Salt Giants and brackish mega-basins are all related forms of TSLs and that transition between them is possible. We showcase several key TSLs that occurred over the last 100 Million years: the East African rift basins and the early South Atlantic basins providing a reference for the lacustrine - evaporitic transitions that characterize the opening of oceans and similarly the key moments in the closure of the Tethys ocean, presented to showcase the post-oceanic restriction episodes of the Paratethys waterworld in Central Eurasia, with its particular evaporite-brackish environment transitions.

The transition from marine basins to TSL is reversible and our model predicts that TSLs that lie in the proximity of the global ocean are likely to trigger cataclysmic floods during the partial or full reconnection with the global ocean if the reconnected water bodies have different water levels. These floods can be either in the form of marine flooding events, such as the Zanclean deluge of the Mediterranean, when TSL’s water level is below the global sea-level or in the form of “lake burst-floods”, if the isolated TSL evolves to a mega-lake with water levels above the global ocean. We present a first example of such lake burst-floods that scarred the Aegean Sea and likely turned the Mediterranean-Paratethys realm into a unique system of double-locked TSLs, in the eve of the Messinian Salinity Crisis.

How to cite: Palcu, D. V. and Krijgsman, W.: Trapped Sea-Lakes, the anomalous water bodies that herald the birth and demise of the oceans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18963, https://doi.org/10.5194/egusphere-egu2020-18963, 2020.

Syntectonic growth strata in extensional settings are characterized by gross divergent geometries towards the master normal faults. Similar depositional patterns might be expected for evaporitic successions deposited during active extension although for salt-rich systems it might be very difficult to discern initial syn-tectonic depositional thickness variations from those caused by syn-depositional or early post-depositional halokinetic flow. Evaporites can be also passively infilling accommodation space that was created before their deposition either by tectonics or by erosion. Re-evaluation of regional coverage of seismic data from the Polish Basin provided evidences that, contrary to previous views, formation of Zechstein (Wuchiapingian – Changshingian) evaporites was significantly controlled by active extension. This sedimentary basin was located within the eastern periphery of the large epicontinental Permian-Mesozoic Central European Basin System and was filled with several kilometers of siliciclastics and carbonates, and thick Zechstein evaporites. Its axial part, the Mid-Polish Trough, characterized by the thickest Permo-Mesozoic sedimentary cover and developed partly above the Teisseyre–Tornquist Zone, underwent substantial Late Cretaceous–Paleogene inversion and currently forms a large regional anticlinal structure referred to as the Mid-Polish Swell. Some previous models of deposition of Zechstein evaporites assumed that evaporation started after catastrophic flooding of vast paleo-topographic depression (“hole in the ground” model). Regional coverage of seismic data was used to map major sub-Zechstein fault network that were responsible for crustal extension during development of the Polish Basin and were reactivated as reverse fault zones during its regional Late Cretaceous – Paleogene inversion. Those sub-Zechstein fault zones are often associated with locally increased thickness of Zechstein evaporites (salt pillows). It could be shown that such thickness increase could be in turn associated with gradual thickness increase of particular Zechstein cyclothems towards sub-Zechstein fault zones. All those observations were used to construct regional model of the Zechstein basin that was controlled by regional extension. As a consequence, Zechstein evaporites deposited within the axial part of the basin have been partly reinterpreted as growth strata related to active basement extensional tectonics.

How to cite: Krzywiec, P., Peryt, T. M., and Kiersnowski, H.: Was Zechstein basin in Poland just large “hole in the ground”? – new extensional model based on reinterpreted regional seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10756, https://doi.org/10.5194/egusphere-egu2020-10756, 2020.

EGU2020-13577 | Displays | SSP1.14

A warmer Mediterranean region at the Miocene to Pliocene transition

Iuliana Vasiliev, Daniela Boehn, Darja Volkovskaja, Clemens Schmitt, Konstantina Agiadi, Federico Andreetto, and Andreas Mulch

Between 5.97-5.33 Ma several kilometre-thick evaporite units were deposited in the Mediterranean Basin during the Messinian Salinity Crisis (MSC). The MSC reflects a period featured by a negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. The contemporary changes in continental and marine circum-Mediterranean temperature are, however, poorly constrained. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (GDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma). Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using isoprenoidal GDGTs based TEX86 proxy. The excellently preserved organic biomarkers were extracted from outcrops and DSDP cores spread over a large part of the onland (Malaga, Sicily, Cyprus) and offshore (holes 124 and 134 from the Balearic abyssal plane and hole 374 from the Ionian Basin) Mediterranean Basin domain. The calculated MATs for the 5.55 to 5.33 Ma interval show values around 16 to 18 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A hole 374 are lower, around 11 to 13 ºC.

For samples where the branched and isoprenoid tetraether (BIT) index was lower than the 0.4 we could calculate TEX86 derived SSTs averaging around 27 ºC for all sampled locations. Where available (i.e. Sicily), we compared the TEX86 derived SSTs with alkenone based, Uk37 derived SST estimates from the same samples. The TEX86 derived SST values are slightly higher than the Uk37 derived SST of 20 to 28 ºC. For the Mediterranean region, values between 19 and 27 ºC of the Uk37 derived SSTs were calculated for the interval between the 8.0 and 6.4 Ma (Tzanova et al., 2015), close to our calculations for Sicily section (20 to 28 ºC). Independent of common pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase (Stage 3) of the MSC. These elevated temperatures coincide with higher δD values measured on alkenones and long chain n-alkanes (both records indicating for more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We therefore conclude that the climate between 5.55 to 5.33 Ma was warmer than present-day conditions, recorded both in the Mediterranean Sea and the land surrounding it.

How to cite: Vasiliev, I., Boehn, D., Volkovskaja, D., Schmitt, C., Agiadi, K., Andreetto, F., and Mulch, A.: A warmer Mediterranean region at the Miocene to Pliocene transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13577, https://doi.org/10.5194/egusphere-egu2020-13577, 2020.

EGU2020-3852 | Displays | SSP1.14

Environmental changes across the onset of the Messinian salinity crisis: insights from the Piedmont Basin (NW Italy).

Mathia Sabino, Daniel Birgel, Francesco Dela Pierre, Marcello Natalicchio, and Jörn Peckmann

Since the discovery of the late Miocene (Messinian) Mediterranean Salt Giant more than 50 years ago, the environmental conditions that caused its formation have been debated. Such reconstruction suffers from the absence of modern analogues, the lack or scarcity of fossils (calcareous plankton and benthos, but also pollens), and the inaccessibility of the evaporites buried beneath the present-day Mediterranean seafloor. We investigate the palaeoenvironmental changes, which drove the formation of the Mediterranean Salt Giant at the onset of the Messinian salinity crisis (MSC) through high resolution sedimentological, petrographical, and geochemical (lipid biomarkers, major and trace elements) analyses of sedimentary successions of the Piedmont Basin (NW Italy). Shale/marl couplets deposited in intermediate to deep-water settings (200 – 1000 m) are targeted, representing the lateral equivalent of primary sulphate evaporites from shallow-water settings that accumulated between 5.97 and 5.60 Ma. We suggest that climate and hydrological changes affected the northern Mediterranean in the earliest stage of the MSC event, leading to an intensification of water column stratification. An upper water layer of marine water influenced by freshwater input was separated through a pycnocline from more evaporated, denser and oxygen-depleted bottom waters. The water column structure and pycnocline oscillation exerted pivotal control over the sedimentary products pertaining to the first stage of the MSC.

How to cite: Sabino, M., Birgel, D., Dela Pierre, F., Natalicchio, M., and Peckmann, J.: Environmental changes across the onset of the Messinian salinity crisis: insights from the Piedmont Basin (NW Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3852, https://doi.org/10.5194/egusphere-egu2020-3852, 2020.

The thick saline series deposited in the deep Mediterranean during the latest Messinian (between 5.97 and 5.3 Ma) is among the youngest of salt giants in Earth history. During this Messinian Salinity Crisis (MSC) voluminous evaporites precipitated in the abyssal basins when the main inflow of saline water from the Atlantic through the Gibraltar Straits was severely restricted. Considerable volumes of sediments were also interbedded with evaporites, eroded from the shelves or mass-transported downslope during the oceanic drawdowns and thus this event was also a major erosional crisis.  Geochronologic advances and better understanding of the geodynamic history of various basins have led to insights about the timing of the salinity crisis and the tectonics and role of Gibraltar passage and other western narrows from the Atlantic to the Mediterranean. However, much of the new understanding comes from the Mediterranean’s shallow peripheral basins whereas knowledge of the nature of evaporites from the deep basins remains sketchy due to lack of deep drilling through the salt, and many controversies remain unresolved. An invaluable collaboration between academia and industry permitted access to most of the available seismic and core data from the Mediterranean allowing the total amount of salt (thicknesses and volumes) and associated interbedded sediment from all abyssal basins to be calculated. These new estimates are based on seismic facies analysis, which reveal that there is between 821 ± 50 and 927 ± 50 thousand cubic km of late Messinian salt, and a total of up to 1.2 ± 0.1 million cubic km of salt plus associated sediment tied up in the deep Mediterranean basins. First isochron maps of the MSC deposits (evaporites + sediment) in all the basins have been produced. These volumetrics suggests that after the initial restriction, the Mediterranean had to be either continuously supplied with brine, or partially to completely refilled several times to produce the total salt edifice. The amount of Atlantic saline water needed to amass this evaporite giant is between 7 and 8 times the modern-day Mediterranean's equivalent of saline water. The volumetric data have implications for the MSC sequestration and desiccation scenarios and should lead to more meaningful geodynamic models and provide constraints for many of the controversies that still surround this major event in geological history. Maps of salt distribution in various basins also have important implications for sub-salt exploration geoscience.

 

How to cite: Haq, B. and Gorini, C.: Mapping the abyssal Mediterranean's Messinian Evaporite Giant: Salt volumetrics from all deep basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5990, https://doi.org/10.5194/egusphere-egu2020-5990, 2020.

EGU2020-15585 | Displays | SSP1.14

Morphology of the Messinian Salinity Crisis surfaces and its related deposits in the Alboran Sea: a continuous Mediterranean-Atlantic connection?

Damien Do Couto, Ferran Estrada, Christian Gorini, Gemma Ercilla, and Jean-Pierre Suc

The Messinian Salinity Crisis (MSC), which affected the Mediterranean region during the latest Miocene, is mainly characterized by the deposition of thick evaporites in central basins and strong fluvial erosion of margins. The subaerial fluvial erosion, known as the Messinian Erosional Surface (MES), is for instance continuously followed from the Gulf of Lions up to 360 km from the present-day shoreline upstream the Rhône Valley. Short drainage systems limited by high coastal mountain ranges, must have been significantly affected by the Messinian erosion.

The Alboran Sea is similarly characterized by a geographic context and was the first Mediterranean area concerned by connection-disconnection to the Atlantic Ocean during the last millions years. A recent study suggested that the Alboran Sea remained always connected to the Atlantic Ocean during the MSC, being the marine refuge for the Mediterranean taxa.

In this work, we have performed an extensive research of the MES and MSC-related deposits in the Alboran region, both onshore and offshore, integrating outcrop descriptions, supported by new biostratigraphic data and seismic profile analyses. This study leads to an up-to-date geological and morphological map displaying the actual contours and morphology of the MES in the whole Alboran domain. The MES has a subaerial origin and is continuously followed from land to the offshore domain, sealed by post-MSC marine sediments. Both Spanish and Morrocan sides show three different erosive morphologies: downslope trending paleocanyons cut by a large reflooding channel crossing the entire Alboran basin from the Strait of Gibraltar to Algerian Basin, and alongslope   terraces. The occurrence of all these striking erosive features with basinal extension  questions the hypothesis of the permanent connection with the Atlantic Ocean.

How to cite: Do Couto, D., Estrada, F., Gorini, C., Ercilla, G., and Suc, J.-P.: Morphology of the Messinian Salinity Crisis surfaces and its related deposits in the Alboran Sea: a continuous Mediterranean-Atlantic connection?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15585, https://doi.org/10.5194/egusphere-egu2020-15585, 2020.

EGU2020-18341 | Displays | SSP1.14

The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension

Leonardo Muniz Pichel and Christopher Jackson

The Albian Gap is an enigmatic salt-related feature in the Santos Basin, offshore Brazil. It is a uniquely large, up to 65 km wide and >450 km long structure, located in the updip portion of the basin and trending NE (i.e. sub-parallel to the coast). The gap is characterized by the near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, post-Albian seaward-dipping rollover that is up to 9 km thick. Due to its unique geometry, size, and counter-regional aspect, the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models for its origin and evolution; i.e. did it form due to thin-skinned extension, or progradation loading and expulsion? The extension-driven model invokes that the rollover and the Albian Gap formed due to post-Albian gravity-driven extension associated with a large, counter-regional, listric normal fault, the Cabo Frio Fault. Conversely, the expulsion-driven hypothesis suggests that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence, and basinward salt expulsion without significant lateral extension. This study utilizes a large (c. 76,000 km2) and dense depth-migrated, 2D seismic dataset that covers and which thus permit a detailed, 3D structural analysis of the entire Albian Gap, focusing on i) base-salt relief and original salt thickness variations and ii) the geometry of the post-Albian rollover, and its related faults and salt structures. We also apply novel structural restoration workflows incorporating flexural isostasy, along with a detailed sequential reconstruction of the rollover sequences, to constrain the kinematics of the Albian Gap, and how this relates to base-salt relief. Our results show that the geometry and kinematics of the Albian Gap vary along-strike and that both post-Albian extension and expulsion play a significant role on its evolution. Seaward-dipping growth wedges, salt rollers and normal listric faults evidence extension, whereas sigmoidal wedges, halokinetic sequences, and upturned near-diapir flaps, the latter two associated with inflated diapirs bounding the downdip edge of the gap, indicate basinward salt expulsion and inflation. Where the Albian gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the observed amount of basinward translation further downdip within ramp basins in the Sao Paulo Plateau and seemingly reconciles one of the longest-running debates in salt tectonics. Our results have implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular, the controls on the development of large, salt-detached, counter-regional faults.

How to cite: Muniz Pichel, L. and Jackson, C.: The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18341, https://doi.org/10.5194/egusphere-egu2020-18341, 2020.

EGU2020-4533 | Displays | SSP1.14

The geochemical riddle of Mediterranean low-salinity gypsum deposits

Giovanni Aloisi, Marcello Natalicchio, Laetitia Guibourdenche, Antonio Caruso, and Francesco Dela Pierre

Large deposits of gypsum accumulated in the marginal basins of the Mediterranean Sea during the Messinian Salinity Crisis. These form the marginal portions of the Mediterranean Salt Giant (MSG) that also occupies the deep, central Mediterranean basins. Although the marine, evaporitic origin of the MSG is undisputed, the analysis of gypsum fluid inclusions and of gypsum-bound water (d18OH2O and dDH2O) suggest that marginal basin gypsum formed from low- to moderate-salinity water masses (5 - 60 ‰), rather than from high-salinity brines (130 - 320 ‰), as expected during the evaporation of seawater.  The formation of low-salinity gypsum poses a fundamental geochemical problem: how can gypsum saturation conditions be met in marginal basins if evaporation does not concentrate marine water to high salinity? In other words, can gypsum saturation be attained by adding Ca2+ and/or SO42- ions rather than by extracting water? We are exploring two geochemical scenarios to explain this phenomenon: (1) the addition of Ca2+ and SO42- to marginal basins by continental runoff, and (2) the non-steady state addition of SO42- to marginal basins via the biogeochemical oxidation of reduced sulfur. Both scenarios may lead - at least theoretically - to the decoupling of saturation state from salinity that is suggested by gypsum geochemical signatures.

How to cite: Aloisi, G., Natalicchio, M., Guibourdenche, L., Caruso, A., and Dela Pierre, F.: The geochemical riddle of Mediterranean low-salinity gypsum deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4533, https://doi.org/10.5194/egusphere-egu2020-4533, 2020.

EGU2020-11563 | Displays | SSP1.14

Paratethys pacing of the Messinian Salinity Crisis: low salinity waters contributing to gypsum precipitation?

Wout Krijgsman, Arjen Grothe, Federico Andreetto, Gert-Jan Reichart, Mariette Wolthers, Christiaan van Baak, Iuliana Vasiliev, Marius Stoica, Francesca Sangiorgi, Jack Middelburg, and Gareth Davies

During the so-called Messinian Salinity Crisis (MSC: 5.97-5.33 Myr ago), reduced exchange with the Atlantic Ocean caused the Mediterranean to develop into a “saline giant” wherein ~1 million km3 of evaporites (gypsum and halite) were deposited. Despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed. Gypsum formation commonly requires enhanced dry conditions (evaporation exceeding precipitation), but recent studies also suggested major freshwater inputs into the Mediterranean during MSC-gypsum formation. Here we use strontium isotope ratios of ostracods to show that low-saline water from the Paratethys Seas actually contributed to the precipitation of Mediterranean evaporites. This apparent paradox urges for an alternative mechanism underlying gypsum precipitation. We propose that Paratethys inflow would enhance stratification in the Mediterranean and result in a low-salinity surface-water layer with high Ca/Cl and SO4/Cl ratios. We show that evaporation of this surface water can become saturated in gypsum at a salinity of ~40, in line with salinities reported from fluid inclusions in MSC evaporites.

How to cite: Krijgsman, W., Grothe, A., Andreetto, F., Reichart, G.-J., Wolthers, M., van Baak, C., Vasiliev, I., Stoica, M., Sangiorgi, F., Middelburg, J., and Davies, G.: Paratethys pacing of the Messinian Salinity Crisis: low salinity waters contributing to gypsum precipitation?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11563, https://doi.org/10.5194/egusphere-egu2020-11563, 2020.

EGU2020-19087 | Displays | SSP1.14

The biogeochemical sulfur cycle during the formation of the Mediterranean Salt Giant

Laetitia Guibourdenche, Pierre Cartigny, Francesco Dela Pierre, Marcello Natalicchio, Antonio Caruso, and Giovanni Aloisi

Sulfur is a key element to understand ocean biogeochemical processes. Since decades, numerous studies have explained sulfur isotopic variations registred in the geological record as reflecting changes in continental sulfur inputs, biogeochemical recycling of sulfur and the relative proportion of oxidized (gypsum) vs reduced (e.g. pyrite) sulfur burial fluxes. Geochemical and petrographic studies have showed that these processes were active during the formation of the Mediterranean Salt Giant (MSG), a giant salt deposit formed at the end of the Messinian period (5.9-5.33 Ma) following the restriction of hydrological exchanges between the Mediterranean Sea and the Atlantic Ocean. To date, the biogeochemical sulfur cycle during the formation of the MSG has been investigated by analyzing the sulfur and oxygen isotope composition (δ34S and δ18O, respectively) of the sulfate ion in gypsum accumulated in the deep and marginal Mediterranean basins. In the uppermost gypsum layers (Upper Gypsum unit), significantly higher δ18O isotopic ratios (averaging at 12,7‰) than Messinian marine values suggest implications of microbial sulfate reduction activity followed by complete re-oxidation of sulfide back to sulfate in evaporated marine waters.

 Nevertheless, these different microbial processes can overprint each other δ34S and δ18O isotopic signatures and could have been provoked by various type of microbial metabolisms, involving different hydrological and environmental conditions. Here we present for the first time a multiple sulfur isotope (δ34S, Δ33S, Δ36S) investigation of samples from the well-known sections of Vena del Gesso (Apennines) and Pollenzo (Piedmont basin) in order to identify and understand how microbial mechanisms were coupled during the MSG formation. We designed a simple steady-state, three-box model representing the analysed S-bearing fractions (SO42-, S0, FeS2) and the different hydrological and biogeochemical S fluxes involved in marginal basin S-cycling. This system of 18 equations allows us to explain the strong isotopic variations we measured (-40.2 to 25.4‰ in δ34S, -0.001 to 0.160‰ in Δ33S and -1.79 to 0.001 in Δ36S‰) as produced by a huge variability in sulfate reduction activity reflecting fluctuations in the availability of organic matter. Moreover, our results, with relatively high λ33net (0.513 to 0.516) suggest than more than 90% of the hydrogen sulfide produced was re-oxidized by disproportionation reactions. Large, cyclic fluctuations of the Mediterranean hydrological cycle, and the presence of easily accessible S-compounds with a variety of oxidation states, makes the MSG a key system to understand the dynamics of the S biogeochemical cycle in the geological past.

How to cite: Guibourdenche, L., Cartigny, P., Dela Pierre, F., Natalicchio, M., Caruso, A., and Aloisi, G.: The biogeochemical sulfur cycle during the formation of the Mediterranean Salt Giant, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19087, https://doi.org/10.5194/egusphere-egu2020-19087, 2020.

EGU2020-22621 | Displays | SSP1.14

Drainage systems and their relations to the Messinian Salinity Crisis in the Levant Basin

Jimmy Moneron and Zohar Gvirtzman

New high-resolution imaging of recently acquired data in the Levant basin shed light on very dense channel systems. The processes behind their origin, timing and direction - during the different stages of the Messinian Salinity Crisis (MSC) - is still unresolved and partly understood. Discoveries of such drainage systems raise questions on a past topography and mechanisms responsible for the channel morphologies, the understanding of these channel patterns is thus essential for a meaningful assessment of such mechanisms involved in the context of the MSC and its aftermath. Our results show that the drainage direction was undergoing extreme changes during short time intervals in the Levant Basin. Indeed, new maps presented here indicate different past drainage orientations, which is in contrast to the current-day turbidite channels - draining the Sinai-Levant continental margin northward towards the Cyprus Arc. We hypothesize from these results that drainage change, from southwest to north, expresses northward tilting of the basin towards the Cyprus subduction zone, however, when exactly did this tilting occur? Deciphering the timing of such events is important in order to get a better understanding of tectonostratigraphic settings, controlling depocenter locations in the Levant basin in the MSC. We also suggest that the unique pattern of channels over the Intra-Messinian Truncation Surface (IMTS), expresses a complex seafloor relief which was mainly controlled by salt tectonics induced thrusts faults.

Keywords: Messinian Salinity Crisis, Channel systems, Evaporites, Seismic Reflection Profiles

How to cite: Moneron, J. and Gvirtzman, Z.: Drainage systems and their relations to the Messinian Salinity Crisis in the Levant Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22621, https://doi.org/10.5194/egusphere-egu2020-22621, 2020.

EGU2020-1201 | Displays | SSP1.14

Isotopic analyses of the Middle Miocene evaporite assemblage and its fluid inclusions (Praid, Transylvanian Basin, Romania)

Orsolya Gelencsér, László Palcsu, István Futó, and Csaba Szabó

The objective of this study is to constrain the formation conditions of deposition of the Middle Miocene marine evaporite in the Transylvanian Basin (TB).  The salt rock, formed during the Badenian Salinity Crisis (BSC), consists principally of halite (> 90%).  Representative samples were collected from Praid salt diapir.

Detailed petrographic study was carried out in order to distinguish primary features of the salt rock and to exclude secondary movements and their impacts.  Two types of salt rock can be distinguished: 1/ massive grey salt with large, elongated halite crystals, containing primary fluid inclusions (FIp), surrounded by submicrometer size halite grains and clay matrix, and 2/ layered salt building up greyish (clay rich) and white (clear halite) layers.  This type has quasi mosaic structure and contains very rarely FIps.

The primary fluid inclusions in halite, containing aqueous solutes, are expected to record compositions and isotopic characters of paleo-seawater during the BSC of the Paratethys.  Beside halite, authigenic anhydrite and dolomite are also present, which precipitated in marine environment and their compositions also reflect the geochemical conditions of the seawater.

Microthermometry of FIp in both types of halite shows low homogenization temperature (10-24 °C) which is typical for marine environment.  Isotopic characteristics of FIp are -15.55 – -7.07 ‰ for δ18O and -87,9 – -74.17 ‰ for δ2H.  Sulfate isotope values measured in anhydrite are ranging δ34S 20.4 – 22.4 ‰ and δ18O 12.9 – 14.5 ‰ that coincide with the Middle Miocene Outer Carpathians salt deposits (Halas & Krouse, 1981) and support evaporated seawater origin.  The geochemical signatures (Fe-zonation) and isotopic characters (δ18O -7.07 – -4.55 ‰ and δ13C -9.03 – -8.31 ‰) of the rombohedral translucent dolomite suggest mainly meteoric origin.  They possibly precipitated from an upper level of the seawater.  All of these isotopic and geochemical characters of the evaporite reveal a complex restricted hydrogeologic evolution environment.

How to cite: Gelencsér, O., Palcsu, L., Futó, I., and Szabó, C.: Isotopic analyses of the Middle Miocene evaporite assemblage and its fluid inclusions (Praid, Transylvanian Basin, Romania), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1201, https://doi.org/10.5194/egusphere-egu2020-1201, 2020.

EGU2020-3097 | Displays | SSP1.14

Flexural-isostatic reconstruction of the Western Mediterranean vertical motions after the Messinian Salinity Crisis: implications for sea level and basin connectivity

Hanneke Heida, Daniel Garcia-Castellanos, Ivone Jiménez-Munt, Fadl Raad, Agnès Maillard, and Johanna Lofi

The Messinian Salinity Crisis was a period of rapid and extreme environmental change in the Mediterranean occurring from 5.96 to 5.33 Ma, leading to deposition of a huge amount of evaporites in the deep basins and erosion on the margins. Erosional surfaces located deep below current sea level suggest a kilometric drop in sea level commonly associated with the deposition of massive halite deposits during the crisis. However, the timing and magnitude of this sea level drawdown are not well constrained in spite of its important implications for the conditions under which the different MSC sedimentary units were deposited and the connectivity of various sub-basins during the crisis. A 2D (planform) flexural backstripping allows us to restore the Messinian topography in tectonically quiescent areas, constraining the isostatic subsidence due to the (post)Messinian sediment, and the potential effect of falling sea level during the crisis. In this way we restore the elevation of paleoshorelines and the original depth of erosional surfaces and other stratigraphic markers. We apply this method to the area spanning the Valencia Basin, Balearic Promontory and the Algero-Provençal Basin, to restore the Messinian Erosion Surfaces which formed subaerially during the drawdown to their original depth, constraining the minimum base level drop required to erode the margins at these locations. We reconstruct three key moments in the basin history: the pre-crisis basin, the end of halite deposition, and the end of the crisis. We consider multiple scenarios in terms of timing of sea level fall. Preliminary results indicate that over 1 km of sea level drop is required at the end of the Messinian, and over 2 km at the crisis acme to reproduce the observed location of the paleoshorelines, with only small sensitivity to crustal strength. This is in good agreement with estimates from previous backstripping investigations, and provides constraints on the progression of the MSC in the Western Mediterranean.

How to cite: Heida, H., Garcia-Castellanos, D., Jiménez-Munt, I., Raad, F., Maillard, A., and Lofi, J.: Flexural-isostatic reconstruction of the Western Mediterranean vertical motions after the Messinian Salinity Crisis: implications for sea level and basin connectivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3097, https://doi.org/10.5194/egusphere-egu2020-3097, 2020.

Although the Mediterranean is known for its equable climate, this does not apply on geological timescales. At the end of the Miocene, salinity of the Mediterranean Sea exceeded gypsum and halite saturation, leading to the youngest known salt giant to form in a relatively short time span. This event is called the Messinian Salinity Crisis. Insight into the exact circumstances leading to this extreme situation would increase our understanding of today’s system and how it would react to climatic changes. Some of the theories rely on a drastic change in circulation, leading to a stably stratified water column at high salinities. It is yet to be determined how realistic these ideas are.

Conceptual box models can help to find answers to this. In a previous study it was already shown that a decrease in the rate of deep water formation in the margins can lead to a stratified water column. Here we used a predefined value for the overturning. In contrast, in the present study, the circulation, including the exchange through the strait of Gibraltar, is dynamically driven by density differences. By modelling stratification for various assumptions regarding the efficiency of the strait of Gibraltar, evaporation and the connectivity of the margins, this set-up ables us to get in-depth insights regarding the system in general, and the influence of climate and bathymetry on the circulation, specifically.

This model brings us one step closer to an understanding of the circumstances of this extreme state of the Mediterranean Sea

How to cite: Ebner, R. and Meijer, P.: Slowing down the overturning – Insights from conceptual modelling on a stably stratified Mediterranean Sea during the Messinian Salinity Crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10338, https://doi.org/10.5194/egusphere-egu2020-10338, 2020.

EGU2020-13769 | Displays | SSP1.14

Image improvement of Late Miocene (Messinian) to Plio-Quaternary units in the Algero-Balearic basin

Simon Blondel, Fadl Raad, Angelo Camerlenghi, Johanna Lofi, and Anna Del Ben

This study intends to contribute to the understanding of the Mediterranean Salt Giant in the Western Mediterranean, formed about 6 Ma ago during the Messinian Salinity Crisis. It provides reprocessed multichannel seismic reflection data that aim at improving our knowledge of the stratigraphy in the Algero-Balearic deepwater basin and its continental margins, in the absence of lithological information from wells.

We investigate the seismic expression of the Messinian salinity crisis from the south-east of the Balearic promontory to the central Algero-Balearic abyssal basin and the salt tectonic processes associated to these facies. Here the segmentation of salt structures has been previously described using shallow chirp sonar data, low-resolution vintage multichannel seismic data and high-resolution multi-channel seismic data post-stack migrated with a constant velocity field. The structure of the northern Algero-Balearic basin is controlled by two abrupt fault scarps oriented SW–NE (mainly the Emile Baudot Escarpment transform fault) and WSW-ENE (mainly the Mazarron Escarpment transform fault) emplaced during the basin extension, and later intruded by steep and narrow volcanic ridges of Pleistocene age. It is a good analogue to early stage salt tectonic for older and more complex salt giants in the North Sea or the Gulf of Mexico.

We reprocessed 2D Kirchhoff PSTM multichannel seismic data acquired by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (SBALDEEP Cruise of 2005 and SALTFLU cruise of 2012; the latter within a Eurofleet cruise) spanning the South-East continental margin of the Balearic islands and the Algero-Balearic basin. The reprocessing was designed for improving the continuity of the reflectors by applying Kirchhoff PSTM using a detailed velocity model, while preserving amplitude information. The objectives are to better apprehend the structural complexity of the area and to retrieve the amplitude variation within the Messinian units, in an attempt to derive the composition of the salt and the pressure regime.

We present preliminary results where we delineate four different domains based on i) the seismic facies, ii) the amount of salt deformation, iii) the thickness of the overburden and iv) the pre-salt configuration. We try to assess the presence of the Messinian trilogy in the south-eastern continental slope. We attempt to reconstitute the paleo-depositionnal environment of the various depositional units, and the effect of crustal structures and salt tectonic gravity spreading and gliding on their syn to post-depositional evolution. Finally, we search for evidence of fluid circulation within the Messinian and the Plio-Quaternary deposits over the study area.

How to cite: Blondel, S., Raad, F., Camerlenghi, A., Lofi, J., and Del Ben, A.: Image improvement of Late Miocene (Messinian) to Plio-Quaternary units in the Algero-Balearic basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13769, https://doi.org/10.5194/egusphere-egu2020-13769, 2020.

EGU2020-15813 | Displays | SSP1.14

Microbial carbonate and native sulphur formation associated with gypsum lithologies of the Lorca Basin, Spain

Simon Rouwendaal, Daniel Birgel, Vincent Grossi, Giovanni Aloisi, and Jörn Peckmann

EGU2020-15647 | Displays | SSP1.14

A new molluscan assemblage from the pre-evaporitic Messinian of Crete (Greece)

Efterpi Koskeridou and Danae Thivaiou

The Messinian Salinity Crisis (MSC) was an environmental perturbation with dramatic environmental consequences that greatly affected marine organisms. Messinian deposits are found in several locations around the Mediterranean, but few offer marine faunas rich in molluscs. A section near Heraklion, central Crete, has provided new material that contains a well preserved and rich molluscan fauna that includes many micromorphic species. The section is of early Messinian age, belongs to Agios Miron Formation, and bears several layers of fossiliferous marly sands.

Molluscs from a fossiliferous bed of the section are presented here for the first time. Gastropods and bivalves are most common, but scaphopods and chitons are not infrequent. The assemblage seems to be composed of transported elements from nearby environments and the most frequent species are present in comparable abundances for gastropods and bivalves. The gastropod fauna is represented by Bittium sp. and Gibbula sp., accompanied by Diodora cf. graeca, Turritella sp., Jujubinus sp., species of Pyramidellidae and rarer Homalopoma sp. and Haliotis sp. The presence of Bittium sp. together with Jujubinus sp. suggests vegetated environments. Bivalves are represented by species dwelling mostly in sandy environments such as Glycymeris cf. inflata (also occurring in larger specimens), Spisula sp., Timoclea sp. and various cardiids. Exceptionally well-preserved chitons indicate the presence of hard substrates such as rocks, pebbles or roots of seagrass beds. This is confirmed by the presence of the gastropods Diodora cf. graeca and Haliotis sp.

The assemblage points towards normal salinity shallow marine conditions of sandy bottoms with patches of seagrass-type vegetation before the onset of the MSC.

How to cite: Koskeridou, E. and Thivaiou, D.: A new molluscan assemblage from the pre-evaporitic Messinian of Crete (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15647, https://doi.org/10.5194/egusphere-egu2020-15647, 2020.

EGU2020-19545 | Displays | SSP1.14

New onshore/offshore evidence of the Messinian Erosion Surface from key areas: the Ibiza-Balearic Promontory and the Orosei-Eastern Sardinian margin

Agnès Maillard, Virginie Gaullier, Carine Lézin, Frank Chanier, Francis Odonne, and Johanna Lofi

As the Messinian sea-level drawdown associated with the Messinian Salinity Crisis is still questioned, we propose to show that the widely spread erosion surface affecting the Mediterranean margins is indeed linked to an exondation demonstrated from offshore and onshore data.

Our study presents for the first time a comprehensive onshore to offshore correlation of the Messinian erosional surface, and it is focused on small drainage systems or interfluve areas, outside of evaporite basins or incised canyons, where the Messinian erosion had not yet been studied previously: around Ibiza on the Balearic Promontory and around Orosei on the Eastern Sardinian margin, Tyrrhenian Basin, both areas where new offshore data were recently acquired. We show that the late Messinian erosion formed in subaerial settings, as testified by evidence of continentalization events, and attests for a regression phase that was correlated from the offshore continental slopes to the onshore paleo-platforms in both areas. Characteristics of this erosion in both study areas strengthen the scenario with at least one important low-stand sea-level for the Messinian Salinity Crisis with evaporites subbasins lying at different depths and possibly disconnected.

How to cite: Maillard, A., Gaullier, V., Lézin, C., Chanier, F., Odonne, F., and Lofi, J.: New onshore/offshore evidence of the Messinian Erosion Surface from key areas: the Ibiza-Balearic Promontory and the Orosei-Eastern Sardinian margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19545, https://doi.org/10.5194/egusphere-egu2020-19545, 2020.

EGU2020-3903 | Displays | SSP1.14

Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

Angelo Camerlenghi, Anna Del Ben, Christian Hübscher, Edy Forlin, Riccardo Geletti, Giuseppe Brancatelli, Aaron Micallef, Marco Saule, and Lorenzo Facchin

We conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the “salinity crisis” between 5.97 and 5.33 Ma, a basin‐wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end‐members, one of which is the typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – MU) and upper anhydrite and marl layers (Upper Unit – UU) traced in the Western Mediterranean Basins. The other end‐member is a single MU unit subdivided in seven sub‐units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end‐members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km3 Å} 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V‐shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite‐free pre‐ Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post‐Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments.

How to cite: Camerlenghi, A., Del Ben, A., Hübscher, C., Forlin, E., Geletti, R., Brancatelli, G., Micallef, A., Saule, M., and Facchin, L.: Seismic markers of the Messinian salinity crisis in the deep Ionian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3903, https://doi.org/10.5194/egusphere-egu2020-3903, 2020.

EGU2020-4823 | Displays | SSP1.14

Mapping of the Gessoso-Solfifera layer and Messinian Erosional Surface in the Northern and Central Adriatic Sea

Alessandra Lanzoni, Anna Del Ben, Forlin Edy, and Busetti Martina

Since the discovery of widespread Salt and Gypsum deposits of the Mediterranean Sea in the early ’50s, a large number of scientists tried to unravel the mystery related to this huge deposition of evaporites. Evidence of the later so-called “Messinian Salinity Crisis” (MSC) are largely distributed all around the Mediterranean Basin and widely studied. Although gypsum deposits were recognized in some peripheral or marginal basins (e.g. Sorbas Basin in Spain, Northern Apennines in Italy), mechanism of their deposition and formation are still uncertain. Particularly, the so-called Gessoso-Solfifera formation (GS Fm) was recognized in the ’50s by Selli in several outcrops in Northern Apennines and it is nowadays well known and mapped in the on-shore outcrops.  A regional analysis in the Adriatic Sea is still incomplete, even though a large amount of data is available (2D multichannel seismic lines, boreholes, exploration reports). In the Adriatic Sea, the MSC event can be recognized in the 2D seismic lines as actual thin deposit (maximum GS Fm thickness of about 120 ms TWT) or Messinian erosional surface (MES). In both cases, a strong and clear reflector at the Pliocene base is picked and calibrated by the boreholes reaching its depth. Along the main part of the available seismic profiles it is sometimes very hard to ascribe this strong reflector to the MES or to the presence of a thin gypsum layer.
Calibration of 2D seismic lines with boreholes, also integrated by physical properties derived from geophysical well logs and core data) of the Plio-Quaternary sediments, allowed a detailed seismic facies analysis useful for this purpose. A structural map of the Plio-Quaternary base describes the Plio-Quaternary deformation that affected the study area mainly as Apennine foreland. The thickness map of the GS Fm describes the subsidence and the erosional effect occurred during the MSC. Both these maps are here presented as a first result of a regional study, that intends cover the whole Adria offshore.

How to cite: Lanzoni, A., Del Ben, A., Edy, F., and Martina, B.: Mapping of the Gessoso-Solfifera layer and Messinian Erosional Surface in the Northern and Central Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4823, https://doi.org/10.5194/egusphere-egu2020-4823, 2020.

EGU2020-7690 | Displays | SSP1.14

The Messinian Salinity Crisis (MSC) deposits in the Balearic Promontory: An undeformed analog of the MSC Sicilian basins??

Fadl Raad, Johanna Lofi, Agnes Maillard, Antonio Caruso, and Athina Tzevahirtzian

The Messinian Salinity Crisis (MSC) is a prominent and still misunderstood event that influenced the Mediterranean basin in the late Miocene leaving behind a Salt Giant (SG) widespread all over the Mediterranean basin. More than 90% of the Messinian Evaporitic deposits are located offshore with reduced access via boreholes, and thus has been studied mainly by seismic imaging. Onshore-Offshore should be considered a key for a better understanding and answering some of the controversies on the MSC.

The Balearic Promontory (BP) contains a series of small perched basins presently lying at different water depths, stepped from the present-day coastline down to the deep basin. These topographic lows trapped sedimentary series up to 500m thick, interpreted as MSC in age.
The reduced tectonic movements in the BP since the late Miocene (Messinian) till recent days, favored the conservation of the MSC records in this area. Moreover, recent studies revealed the presence of a Salt layer in the Central Mallorca Depression (CMD).

Considering: 1- the bathymetry of the BP, classified as an intermediate perched basin; 2- the distribution of the MSC records accumulated in a series of sub-basins more or less connected between each other; 3- the geometries of the evaporitic formations, provided by how these records appear on the seismic data; this might recall similarities between the BP records (especially the ones in the CMD) and the MSC reference records outcropping in Sicily (especially in the Caltanissetta Basin).

We perform seismic interpretation of a wide seismic reflection dataset in the study area with the aim of refining the mapping of the Messinian evaporites covering the study area. Four seismic units were identified in the BP based on their seismic facies and their seismo-stratigraphic position. We try to match up these units to the consensus Messinian 3-stages chrono-stratigraphic model proposed during the CIESM in 2008.
We also attempt to find similarities in geometries, facies and distribution of the MSC between the sub-basins of the BP and those described in the Sicilian sub-basins.

How to cite: Raad, F., Lofi, J., Maillard, A., Caruso, A., and Tzevahirtzian, A.: The Messinian Salinity Crisis (MSC) deposits in the Balearic Promontory: An undeformed analog of the MSC Sicilian basins??, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7690, https://doi.org/10.5194/egusphere-egu2020-7690, 2020.

The Calcare di Base Formation (CdB) mostly (but not exclusively) represents a microbial-mediated carbonate body formed during Messinian and extending for more than 500 km across the Southern Italy, along the accretionary wedges of Calabria and Sicily Apennine chain. In these areas, the microbial carbonates, frequently associated with evaporites, are stratigraphically positioned at the onset of the Messinian Salinity Crisis, pre-dating the massive basinal sulphates and halite deposition in the Mediterranean Circum.

The CdB highlights a wide spectrum of different facies positioned along a prograding carbonate platform to slope system. The inner platform environments are characterized by sabkhas, flood-influenced salinas and peritidal mudflats, rich of planar to domal laminated microbial boundstones associated with evaporites, solution breccias and local cross-laminated detrital carbonates. Megabreccias with plarform-derived clasts and a local siliciclastic input prevail in the upper slope, whereas debris flows and high-density turbidity currents occurred in the lower slope. Basinward, thinly laminated clay and marlstones associated to low-density turbidites characterize the outer-platform.

In a newly-proposed general sequential stratigraphic model of the Messinian Salinity Crisis, the carbonate platform systems represent a high-stand phase of at least two depositional cycles that follow one another. Each cycle begins with a relative sea-level fall responsible for the emplacement of prograding wedges composed of terrigenous and evaporitic deposits that, subsequently, evolve in the deposition of huge deposits of primary basin-fill evaporites. This latter phase is followed by open marine transgression due to relative sea-level rise that predates the development of another carbonate platform.

Despite the intense syn-sedimentary tectonic activity, responsible for huge basinward sediments exportation and fast decreasing in the accommodation space, the defined systems tracts succession has been mainly controlled by eustatic sea-level variations.

How to cite: Borrelli, M. and Perri, E.: PRE-SALT CARBONATES DEFINE A NEW STRATIGRAPHIC MODEL FOR THE MESSINIAN SALINITY CRISIS IN THE CENTRAL MEDITERRANEAN (CALCARE DI BASE Fm, SOUTHERN ITALY), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8141, https://doi.org/10.5194/egusphere-egu2020-8141, 2020.

While the Mediterranean Sea is, since the Middle Miocene, a nearly completely land-locked basin indeed, it is itself comprised of several smaller semi-enclosed seas. What the Mediterranean Sea as a whole is to the Atlantic Ocean, are the Adriatic Sea or Aegean Sea to the Ionian-Levantine basin, for example. In the discussions regarding the Messinian salinity crisis the marginal basins of the Mediterranean play a prominent role because it is from these parts that the sedimentary record has been uplifted and become exposed.

In view of this and with an aim to contribute insight from the field of modelling, we focus on the basic element: a single marginal basin, subject to atmospheric forcing and exchanging water through a seaway with an adjacent larger basin. The equations are derived in dimensionless form and a universal, scale-independent, solution for basin salinity obtained. The analysis yields two dimensionless ratios which control basin behaviour in terms of salinity and response time. 

Application of the theoretical model to the Messinian salinity crisis sheds new light on the formation of gypsum in marginal basins that were separated from the main Mediterranean by a sill, gives insight about the role of atmospheric heat exchange, and underlines the previous finding that, at elevated salinity, marginal basins respond to periodic climate variation (e.g. due to precession) with a significant lag.

How to cite: Meijer, P.: A scale-independent model for land-locked seas with application to the Messinian salinity crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10494, https://doi.org/10.5194/egusphere-egu2020-10494, 2020.

The discovery in the 70’s of the km-thick Mediterranean salt giant alongside the seismic observance of Pliocene-filled engravings along its shelf-slope systems concurred together to postulate that the Mediterranean-Atlantic seaway terminated during the late Messinian. The resulting changes in paleogeographic, paleohydrological and biological conditions, acknowledged as Messinian Salinity Crisis (MSC, 5.97-5.33 Ma), find their expression in the marginal sedimentary record in fauna-depleted gypsum and halite-bearing successions (5.97-5.42 Ma). During the Lago-Mare phase (5.42-5.33) that terminates the MSC the evaporitic deposition endures in the intermediate basins (e.g. Caltanissetta Basin, Sicily), whilst all the marginal basins fill with fluvio-lacustrine terrigenous sediments. Up to five conglomerate to sandstone-laminated pelite alternations thought to be precession controlled are counted underneath the Zanclean marine deposits featuring the restoration of a marine environment. Finer hemicycles tuned to insolation maxima period stand out above all for the occurrence of faunal assemblages consisting of brackish water ostracods, mollusks and dinoflagellate cysts. The affinity of these faunal elements with the coeval inhabitants of the Eastern Paratethys region, fragmented in isolated, long-lived brackish lakes (i.e. Euxinic and Caspian Basin), led to the primordial hypothesis of a similar paleoenvironment in force during the Lago-Mare phase for the Mediterranean, coherent with the paleoenvironment subsisting immediately prior to it. However, the progress of scientific research provided additional evidence arguing against the desiccation theory and supporting a basin filled even during the Lago-Mare phase. Within the full Mediterranean model controversial views exist on the hydrochemistry of the water mass, disputed between marine, brackish and density-stratified. To elucidate Mediterranean base level and hydrology just preceding the restoration of open marine conditions we merge together new and published ostracod biostratigraphic data and radiogenic strontium isotope ratios (87Sr/86Sr) from locations (SE Spain, Piedmont, Sicily and Cyprus) covering the whole extent of the Mediterranean Basin. Ostracod faunal assemblages share approximately the same species and the same distribution pattern. Within a single pelitic bed, richness varies from oligotypic assemblages dominated by Cyprideis torosa to heterotypic assemblages with up to 17 Black Sea-derived species. Consequently, we conclude that it is most likely that the Mediterranean water level during the final phase of the MSC was high enough to let the Paratethyan fauna to reach and spread throughout the shallow Mediterranean depositional environments. 87Sr/86Sr ratios measured on ostracod valves range between 0.709131-0.708715. The generally lower and higher Sr isotopic composition than contemporary seawater (∼0.709024) alongside the data spreading are considered as a further proof of the presence of multiple lakes acquiring their own isotopic composition. We demonstrate that, when taken individually, none of the marginal basins yields an isotopic signature that matches that of the local rivers. If anything, these 87Sr/86Sr values arise from the mixing of local river water with Mediterranean water and we show that the discrepancies among each basin are consistent with variations in the lithologies of the contributing catchments. Lastly, we show that multiple, isotopically different water sources of both internal (major peri-Mediterranean rivers) and external (Atlantic and Eastern Paratethys) contributed to building up the Mediterranean water mass.

 

How to cite: Andreetto, F., Flecker, R., and Stoica, M.: Crunching of the primordial interpretation of the Lago-Mare phase: new insights from integrated ostracod biostratigraphy and Sr isotope ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18814, https://doi.org/10.5194/egusphere-egu2020-18814, 2020.

EGU2020-18964 | Displays | SSP1.14

Seismic Mapping of Massive Dolomite Deposit Associated with Demise of MSC Salt Giant in Ionian Basin

Judith A. McKenzie, Christian Huebscher, and Angelo Camerlenghi

The origin of massive dolomite deposits has been an enduring and challenging problem for carbonate sedimentologists since the initial recognition of dolomite as a discrete carbonate mineral [CaMg(CO3)2]. The dolomite problem or enigma involves the fact that the mineral is very abundant in the geologic record, but it is rarely found forming in modern environments.  However, when modern dolomite is observed, it is generally, but not exclusively, found forming in hypersaline environments and in minor amounts.  Although the geologic record indicates that many ancient massive dolomite deposits formed in association with evaporites, modern examples of extensive amounts of dolomite being deposited under hypersaline conditions have not, or only rarely, been reported.   

One example of a massive hypersaline dolomite deposit of relatively recent origin may be the dolomite units associated with the end phase, at approximately 5.33 Ma, of the Messinian Salinity Crisis (MSC) in the Ionian Basin, Central Mediterranean (Hsü, Montadert, et al., 1978, Initial Reports of DSDP, Vol. 42, Part 1).  Drill core and interstitial waters obtained at DSDP Leg 42A, Site 374 in the Ionian abyssal plain revealed the presence of approximately 25 m of latest Miocene dolomitic mudstone (Lithologic Unit IIIa) capped by 8.5 m of earliest Pliocene dolomite (Lithologic Unit II).  Significantly, the pore-water geochemical data indicate that the dolomitization of the overlying earliest Pliocene nannofossil ooze may be an ongoing process.  Deeper drilling below the two dolomite units (Lithologic Unit II and IIIa) to the bottom of Site 374 recovered a further 29.5 m of gypsum/dolomitic mudstone cycles (Lithologic Unit IIIb) followed by 21 m of anhydrite and salts (Lithologic Unit IIIc).  Hence, the latest Miocene/earliest Pliocene dolomite sequence recovered at DSDP Site 374 is directly associated with the Messinian Salt Giant and potentially represents a massive dolomite deposit of an undetermined horizontal extent.

In order to measure the lateral dimensions of the combined dolomite/evaporite lithologic units in the central Ionian Sea, the University of Hamburg, using the facilities of the RV Meteor, conducted a multi-channel reflection seismic survey centered at DSDP Leg 42A, Site 374.  A powerful 6 kJoule sparker created the seismic signals, while a digital 144-channel streamer with an active length of 600 m recorded the data. The lowermost Pliocene reveals high lateral continuity and low reflection amplitudes, which is typical for the entire Pan-Mediterranean realm. The uppermost Messinian unit is characterized by a package of strong and positive reflection amplitudes (High Amplitude Reflection Package, HARP). The lateral continuity of the corresponding reflections is very low and the upper boundary is quite irregular. It is unlikely that the reflection configuration results from depositional processes, but it rather suggests diagenetic processes. We correlate the HARP with the dolomite- and gypsum-bearing sediments cored at DSDP Site 374 (Lithologic Unit IIIa, IIIb, IIIc), which is also consistent with the calculated depth. Based on preliminary estimates derived from the seismic survey, the areal extent of the dolomite deposit beneath the Ionian abyssal plain corresponds to a few 10’000 Km2, potentially representing a massive hypersaline dolomite deposit.

How to cite: McKenzie, J. A., Huebscher, C., and Camerlenghi, A.: Seismic Mapping of Massive Dolomite Deposit Associated with Demise of MSC Salt Giant in Ionian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18964, https://doi.org/10.5194/egusphere-egu2020-18964, 2020.

EGU2020-19209 | Displays | SSP1.14

eastern and western med Messinian salinity crisis : comparison scenarii and propositions

Christian Gorini, Romain Pellen, jean-loup Rubino, Benoit Didier, Lucien Montader, and Damien do Couto

The partial sequestration of the Mediterranean Sea from adjacent oceans at the end of the Miocene caused an evaporation surfeit that increased the water salinity above the seafloor of the deep basins and peripheral basins. As a result, an up to 2-3 km-thick sequence of evaporites was deposited in the center of the deep basins. This coincided with the concomitantly intense subaerial erosion of the adjacent margins and important Mass transport deposit events all around the peri- Mediterranean slopes. The volume of evaporites deposited in the deep basins implies a periodic connection with the world oceans concomitant with a huge evaporation during all the MSC. “Deep basins” refers to their position in the deep central parts of the extant Messinian basins in the western basin, the central basins (Ionian) and the eastern basins. The configuration of these basins and the distribution and thickness of the evaporites were very different 6 Myr ago due to the Africa Europe convergence. Evaporites deposition at the edge of the evaporites basins was affected by the geodynamic nature of the margins: Tertiary or Mesozoic passive or transform margins (North Africa), strike slip margins (northern and eastern Levant), convergent margins in the North of the East Mediterranean with evaporites subducted or stacked in a fore arc position. We propose a kinematic reconstruction of the central Mediterranean sea to discuss the connections between the Atlantic waters and the eastern Mediterranean Sea. In this presentation, we show that: (1) There is no opposition between the deposition of the first deep water evaporites and a sea level fall of more than 1000 m. (2) by a threshold effect the eastern Mediterranean could have been more restricted than the western Mediterranean during the phase 1 of the MSC, which could explain the two major incisions observed in the Nile delta (3). At the end of the MSC, this threshold effect could have been maximal with an accommodation space almost filled up and a bathymetry probably not exceeding 50 m in the western Mediterranean and in the Central Mediterranean with deposition of K and Mg evaporates, and almost zero in the Eastern Mediterranean as shown by the fluvial network developed on a wide-spread erosional surface on top of the Levant basin salt. (4) The Messinian salinity crisis (MSC) ended with the rapid re-flooding of the Mediterranean sea. A two-step flooding in the western Mediterranean could find its origin in this threshold effect.

How to cite: Gorini, C., Pellen, R., Rubino, J., Didier, B., Montader, L., and do Couto, D.: eastern and western med Messinian salinity crisis : comparison scenarii and propositions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19209, https://doi.org/10.5194/egusphere-egu2020-19209, 2020.

A detailed biostratigraphical and cyclostratigraphical study provided the opportunity of cycle-by-cycle correlations between sections from the marginal and deep areas of the Caltanissetta Basin (Sicily), and the northern Calabrian Rossano Basin. All the sections were compared with the Falconara-Gibliscemi composite section. We present new mineralogical and geochemical data on the transition from Tripoli to Calcare di Base (CdB), based on the study of several field sections. The outcrops display good record of the paleoceanographical changes that affected the Mediterranean Sea during the transition from slightly restricted conditions to the onset of the Mediterranean Salinity Crisis (MSC). This approach permitted to better constrain depositional conditions and highlighted a new palaeogeographical pattern characterized by separated sub-basins. The sedimentological and geochemical parameters of these basins introduced a different and diachronous response to the global constraints of the MSC. Our preliminary results display already evidences of paleoenvironmental changes: (1) a lithological transition passing from the Tripoli’s triplet (grey marls, reddish laminites and diatomites) to the complex carbonates of CdB; (2) the appearance of evaporite pseudomorphs implying early stage diagenesis; (3) the presence of sulphur-rich deposits involving process of bacterial sulphate reduction. The local transition from the uppermost part of the Tripoli cycles to the CdB reflects the worsening of the marine connections, leading to the individualisation of semi-closed settings where the marine inputs were not great enough to balance the effects of the climate fluctuations and especially of the evaporation/precipitation budget.

How to cite: Tzevahirtzian, A., Blanc-Valleron, M.-M., Rouchy, J.-M., and Caruso, A.: New insights of Tripoli and “Calcare di Base” Formations from Caltanissetta (Sicily) and Rossano (Calabria) Basins: a detailed geochemical, sedimentological and bio-cyclostratigraphical study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19511, https://doi.org/10.5194/egusphere-egu2020-19511, 2020.

EGU2020-20640 | Displays | SSP1.14

Precession-paced climate oscillations in Messinian sulphate evaporites recorded by carbon stable isotopes of leaf wax derived n-alkanes

Dave Stolwijk, Marcello Natalicchio, Francesco Dela Pierre, Daniel Birgel, and Jörn Peckmann

During the Messinian salinity crisis (MSC), the Mediterranean Sea was gradually isolated from the Atlantic Ocean due to tectonics, ultimately resulting in the deposition of enormous volumes of evaporites on the Mediterranean seafloor. In marginal Mediterranean sub-basins, the first phase of the MSC is represented by a cyclic succession of gypsum and shales (Primary Lower Gypsum unit; PLG), changing laterally into an alternation of shales, marls and carbonates towards the deeper parts of the basins. The current consensus is that the lithological cyclicity is the expression of precession-paced climate oscillations, with shales deposited during insolation maxima (precession minima) and gypsum deposited during insolation minima (precession maxima). However, this hypothesis has yet to be validated, because this assumption is primarily based on the continuation of sedimentary cyclicity from the open marine pre-MSC sediments into the Primary Lower Gypsum unit. To assess the possible role of orbitally-driven paleoclimate change on the deposition of the PLG unit, we have analysed molecular fossils (lipid biomarkers) preserved in shales and gypsum of the Pollenzo section (Piedmont basin, NW Italy).

Long-chain n-alkanes are reliable biomarkers that are used to track the input of terrestrial organic matter and allow to reconstruct paleovegetation. By using the distribution of higher plant-derived long chain n-alkanes and their compound specific carbon isotope signature (δ13C), we show that the sedimentary cyclicity in the PLG unit is indeed controlled by precession. Our high-resolution paleoclimatic proxy records cover approximately 300 Ka (6.003 Ma – 5.721 Ma) and comprise the onset of the MSC (5.971 Ma) and the first 12 cycles of the PLG unit. Cyclic fluctuation of δ13C values is observed, with higher δ13C values typifying long-chain n-alkanes extracted for gypsum, while lower values correspond to shales.

Our results, which represent the first paleoclimatic proxy data derived from Messinian gypsum, show that riverine flux of organic matter to the basin varied significantly during the first phase of the MSC. In agreement with a precessional control on paleoclimate, lower n-alkane abundance in gypsum reflects drier conditions, while higher n-alkane abundance in shales indicates more humid climate and increased input of terrestrial organic matter to the basin.

How to cite: Stolwijk, D., Natalicchio, M., Dela Pierre, F., Birgel, D., and Peckmann, J.: Precession-paced climate oscillations in Messinian sulphate evaporites recorded by carbon stable isotopes of leaf wax derived n-alkanes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20640, https://doi.org/10.5194/egusphere-egu2020-20640, 2020.

SSP2.1 – Phanerozoic Stratigraphy, Paleoenvironments, Eustasy and Paleoclimate

EGU2020-11136 | Displays | SSP2.1

A mechanism to explain the timing of glaciations related to orogenic episodes

Manoj Joshi and Benjamin Mills

Over very long timescales, mountain building or orogenesis is associated with increased weathering, the drawdown of atmospheric CO2, and global cooling. Considering the Phanerozoic glaciation in particular, a multimillion‐year delay appears to exist between peaks in low‐latitude mountain uplift and the maximum extent of glaciation, implying a complex causal relationship between them. We show, using a combination of physical climate/circulation modelling and geochemical modelling approaches, that global silicate weathering can be modulated by orogeny in three distinct phases. High, young mountain ranges experience preferential precipitation and the highest erosion. As mountain ranges denude, precipitation decreases, but runoff temperature rises, sharply increasing chemical weathering potential and CO2 drawdown. In the final phase, erosion and weathering are throttled by flatter topography. We hypothesise that orogeny acts as a capacitor in the climate system, granting the potential for intense transient CO2 drawdown when mountain ranges are denuded. Intriguingly, depending on the future evolution of the Tibetan Plateau, the mechanism suggests such a scenario potentially happening 10–50 × 106 years in the future.

How to cite: Joshi, M. and Mills, B.: A mechanism to explain the timing of glaciations related to orogenic episodes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11136, https://doi.org/10.5194/egusphere-egu2020-11136, 2020.

EGU2020-14059 | Displays | SSP2.1

Exhumed fjords of Namibia: A glimpse of the Late Paleozoic Ice Age in the Karoo Supergroup of the Kaokoland basin

Pierre Dietrich, Neil Griffis, Christoph Kettler, Daniel Le Heron, and Isabel Montañez

The Late Paleozoic Ice Age (LPIA) is the longest-lived and most extreme glacial period (from ca 360 to 260 Ma) of the Phanerozoic. Over this time span, ice masses are thought to have covered most of Gondwana, from South America to Australia. In southern Africa, the sedimentary, stratigraphic and geomorphic evidence of this glaciation is recorded in the Karoo Supergroup. The Kaokoland region of northern Namibia is characterized by a dense network of deep (200-700 m), large (5-15 km) and U-shaped incised valleys formed during the LPIA (Martin, 1981). A recent reappraisal of the morphology and sedimentary infill of these outstanding geomorphic features attests of their glacial origin. Valley flanks are spectacularly striated and scratched while valley floors are characterized by extensive whalebacks and roches moutonnées. Moreover, the sedimentary infill at the base of these valleys is mainly composed of coarse deposits (conglomerates, diamictites, erratics, striated clasts) interpreted as glaciogenic in origin. Of particular interest, however, is the presence of coarse (ranging from sand to boulders) glaciogenic sediments plastered on the sub-vertical and striated valley sides. Vitally, the elevation of these deposits in the valleys appears to correspond to a linear bench-like level, which may reflect a marginal moraine allowing for the maximum thickness of the LPIA glaciers to be derived, an unprecedented advance. For the first time in the characterization of a pre-Pleistocene glacial epoch, an ice thickness has been inferred. Collectively, these features prove that the valleys were carved and occupied by ice masses during the LPIA from which ice volume, and in turn their contribution to global eustasy, can directly be inferred. In addition, postglacial sedimentary succession abutting on valley flanks and showcasing marine, deltaic and estuarine affinities clearly indicate that these glacial valleys formed fjords in the immediate aftermath of the LPIA, after the retreat of the ice margins. Sealed by the Karoo Supergroup sediments through Carboniferous to early Cretaceous times, these major glaciogenic morphologic features have subsequently been exhumed during the Cenozoic. Thus, some desertic landscapes of northern Namibia correspond to a glacial relief inherited from the LPIA at ca ~ 300 Myr ago.

 

Martin, H., 1981, The Late Paleozoic Dwyka Group of the South Kalahari Basin in Namibia and Botswana and the subglacial valleys of the Kaokoveld in Namibia, in Hambrey, M.J., and Harland, W.B. (eds.) Earth’s Pre-Pleistocene Glacial Record: New York, Cambridge University Press, 61–66

How to cite: Dietrich, P., Griffis, N., Kettler, C., Le Heron, D., and Montañez, I.: Exhumed fjords of Namibia: A glimpse of the Late Paleozoic Ice Age in the Karoo Supergroup of the Kaokoland basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14059, https://doi.org/10.5194/egusphere-egu2020-14059, 2020.

EGU2020-14346 | Displays | SSP2.1

Contribution of sedimentology, organic geochemistry and clay mineralogy to reconstruct the palaeoenvironments of late Carboniferous to Permian of the northeastern Massif central, France.

Mathilde Mercuzot, Sylvie Bourquin, Pierre Pellenard, Christophe Thomazo, Laurent Beccaletto, Johann Schnyder, François Baudin, Céline Ducassou Ducassou, and Anne-Catherine Pierson-Wickmann

Late Carboniferous to Permian French intracontinental basins have been studied during the 20th century, mainly for industrial applications due to their carbonaceous resources. This period is also of great interest for its palaeogeographical, palaeoenvironmental and palaeoclimatic evolution associated with large geodynamic modifications, such as the transition from the Variscan orogeny to the breakup of Pangaea, and with the change from an icehouse to a greenhouse climate.

The end-Carboniferous (i.e. late Pennsylvanian) to Permian Autun and Lucenay-lès-Aix basins, studied here, are located south of the Paris Basin (France). The Autun Basin crops out in the Morvan area and lies on a Devonian and Carboniferous magmatic substratum. The Lucenay-lès-Aix area is a subsurface basin, under a ca. 250 m-thick Meso-Cenozoic cover, located in the southern termination of the outcropping Decize-La Machine Basin.

The study is based on subsurface data, using cored boreholes, well-log and seismic profiles. Our investigations have been achieved through a sedimentological approach including facies associations analysis and sequence stratigraphy, mineralogy and petrography, supplemented by a geochemistry approach to characterise the deposition and preservation mechanisms of organic matter (OM).

In the Autun Basin, three cores encompass a part of the lower Autunian, near the Gzelian/Asselian boundary. Sedimentological observations indicate lacustrine-dominated environments, with black shales and intercalated turbidites, interrupted by more proximal facies (microbial deposits and coarse river-mouth sediments). Palynofacies and Rock-Eval analyses show a dominant Type I OM, i.e. lacustrine algae, in the laminated fine-grained deposits. The geochemical results indicate periods of both high primary productivity and sedimentary OM storage, reflected in high total organic carbon and total nitrogen contents in sediments (TOC and TN, up to 21.5 wt.% and 0.76 wt.%, respectively), and very low δ13Corg values (down to -29.1‰, σ = 0.07‰).

In the Lucenay-lès-Aix Basin, the sedimentation dated from the late Gzhelian to the late Sakmarian is mostly characterised by alluvial, deltaic, lacustrine and floodplain deposits (coal), with a great volcaniclastic component. The geochemical proxies in coal deposits show high TOC and TN contents (up to 71 wt.% and 1.6 wt.%, respectively), with δ13Corg values averaging -23.7‰ (σ = 0.03‰), indicating a Type III OM, as already reported for these deposits at that time.

In both basins, the main clay assemblage, slightly affected by burial diagenesis and mostly detrital, is dominated by kaolinite, illite, R1 type illite/smectite and chlorite/vermiculite mixed-layers. Kaolinite/illite ratio (K/I) is used as a proxy of the continental runoff, considering that kaolinite was formed in soils under more humid climate, although reworked kaolinite from previous deposits under high runoff conditions is possible. Moderate K/I values in black shales indicate low continental runoff conditions, while a substantial runoff indicated by high K/I ratio is associated with the more proximal coarse detrital sediments (river-mouth/delta). These interpretations are consistent with the mixture of both lacustrine and terrestrial OM (i.e. C3 vascular plants, Type III).

How to cite: Mercuzot, M., Bourquin, S., Pellenard, P., Thomazo, C., Beccaletto, L., Schnyder, J., Baudin, F., Ducassou, C. D., and Pierson-Wickmann, A.-C.: Contribution of sedimentology, organic geochemistry and clay mineralogy to reconstruct the palaeoenvironments of late Carboniferous to Permian of the northeastern Massif central, France., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14346, https://doi.org/10.5194/egusphere-egu2020-14346, 2020.

EGU2020-19788 | Displays | SSP2.1

Re-calibrating the Late Palaeozoic palynostratigraphy in the basins of the southern domain of the Variscan Belt (southwestern Europe).

Manuel A. Juncal, José B. Diez, Joan Lloret, Raúl de la Horra, Nicola Gretter, Ausonio Ronchi, José F. Barrenechea, Violeta Borruel-Abadía, and José López-Gómez

The Late Carboniferous - early Permian was a time-interval of major geological and climatological changes, mostly due to the transition to greenhouse conditions from the maximum glacial coverage (Late Palaeozoic Ice Age or LPIA). This climatic change produced an increase of the extinction rates on land plants and a variation on the constitution and distribution of palaeofloras during this time. The restructuring of ecosystems during Late Pennsylvanian is interpreted as the "collapse of the rainforests". A replacement of hygrophytic (“Stephanian flora”) by mesophytic and meso-xerophytic flora (“Autunian flora”) that tolerate seasonally dry climate is described.

In the Euramerican Province, the continental vegetation during the Pennsylvanian was a hygrophilous flora comprising pteridosperms, marattialean ferns, lycopsids, Calamites and Cordaites trees. At the Late Pennsylvanian-early Permian, the “Carboniferous hygrophilous flora” proliferated in the wet depressions (lowlands) and the mesophilic or even meso-xerophytic flora, grew on the heights (uplands) in the dewatered habitats. Later, this xerophytic flora will be dominant in the landscapes during the middle and late Permian.

There are detailed palynostratigraphic studies that allow precise palynological datings for the Carboniferous period in the Euramerica Province. However, few palynological works have been published relative to the early Permian sedimentary record in this province. In a broad sense, these latter studies only differentiate the early Permian flora (“Autunian flora”) due to the presence of sporomorph taxa as Potonieisporites novicus and Vittatina costabilis, and the middle-late Permian (“Thuringian flora”) mainly characterised by Lueckisporites virkkiae and Nuskoisporites dulhuntyi. This lack of precision was probably due to the different sedimentation rates in the intramontane basins and the “border effect” (as a phytogeographic barrier) caused by the Variscan Belt.

The number of works and the wrong use of non-chronostratigraphic terms like “Autunian” and “Thuringian”, making it necessary to re-calibrate the palynological assemblages in the Euramerica Province. A detailed biostratigraphic study allows us to show here, for the first time, a new palynostratigraphic chart derived from palynological studies from some of the best known low-latitude basins radiometrically dated (Pyrenees, Autun, Lodève, Collio and Tregiovo basins) and from basins with well-known internal lithostratigraphic correlation (e.g., the Cantabrian Mountains and the Iberian Ranges).

Based on the results obtained here, the microflora evolution in the early-middle Permian has been described at low latitudes of the Euramerican Province. Furthermore, this study provides a solid base for stabilising the palynozones for the Permian in the southern domain of the Variscan Belt.

How to cite: Juncal, M. A., Diez, J. B., Lloret, J., de la Horra, R., Gretter, N., Ronchi, A., Barrenechea, J. F., Borruel-Abadía, V., and López-Gómez, J.: Re-calibrating the Late Palaeozoic palynostratigraphy in the basins of the southern domain of the Variscan Belt (southwestern Europe)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19788, https://doi.org/10.5194/egusphere-egu2020-19788, 2020.

Developed on the North China Craton, the intra-cratonic Ordos basin contains a complete Paleozoic to Cenozoic sediment record allowing long-term paleo-environmental and climate change investigation. During the Carboniferous-the early Permian period, convergence between the North China block and the paleo-Yangtze plate to the south lead to a general marine regression characterised by a series of second-order transgression/regression cycles diachronous along the eastern margin of the Ordos. However, the detailed mechanisms that induced these cycles, as well as the associated paleoecological changes, are still unknown. In this study, we integrated the description of numerous core samples with electric-log data and 2-D seismic data to reconstruct the sediment facies associations across the first-order regression from the Carboniferous tidal flat depositional system to the early Permian prograding fluvial delta system. δ18O, δ13C and clay content (w(Illite + Kaolinite)/w(smectite) ratio) stratigraphic variations were then used to reconstruct the paleo-sea level from the late Carboniferous to the early Permian. We conclude that the direction of second-order transgression/regression mainly stroke to the east during the late Carboniferous and switched clockwise towards the north during the early Permian. We suggest that the variability of the second-order cycles, diachronous in space and time was mainly linked to local variations in sediment supply and regional uplift.  Using detrital zircon U-Pb data, major and trace elements content and heavy minerals assemblages (HMA), we estimated the sediment provenance area. The sediment volumes deposited in the basin through time were obtained using 3Dseismic data. During the Carboniferous, the coarse-grained sediments deposited in the eastern Ordos were derived from the uplifting Helan Mountain. By the early Permian, the detrital material became multi-sourced issuing from both the Yinshan range to the north and the Qinling range to the south. During the first stage, regression was controlled by regional uplift, while the sediment supply controlled the second stage. Indeed, based on sediment dispersal volume calculation, we can infer that the sediment supply during the early Permian was more extensive than during the Late Carboniferous – early Permian. We correlate this observation to a more humid climate during the early Permian: multi- paleoecological indexes, including the sporopollenin content and microsomal type assemblage, suggest that glaciation prevailed during the Late Carboniferous – early Permian shallow-marine stage. In contrast, the early Permian alluvial and deltaic series were deposited under a warmer, interglacial climate (Sakmarian). Finally, the typical interglacial coal accumulation pattern occurs earlier than the Pennsylvanian–Permian transition it characterises around the world (Artinskian).

How to cite: Fu, C., Yu, X., Jolivet, M., Li, S., Peng, Z., and Shi, S.: Mechanism of Carboniferous-Permian transgression/regression in the east Ordos basin and associated paleoecological variability: Insight from detrital geochronology and palaeontology data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2573, https://doi.org/10.5194/egusphere-egu2020-2573, 2020.

EGU2020-21820 | Displays | SSP2.1

Permian inheritance : post-orogenic extension and metamorphic core complex formation (Western Pyrenees)

Nicolas Saspiturry, Bryan Cochelin, Philippe Razin, Sophie Leleu, Benoit Issautier, Olivier Serrano, Thierry Baudin, and Cécile Allanic

This study documents the sedimentary and structural response of continental crust in relatively hot lithosphere that is subjected to extension. We focus on the Permian rift system in the Western Pyrenees, where the narrow, post-orogenic intracontinental extensional Bidarray Basin is in contact with late Variscan granulites of the Ursuya massif. The western margin of the N-S trending Bidarray Basin preserves alluvial fans dominated by hyperconcentrated flows and interdigitating eastward into a N-S trending fluvial system. Structural analysis of the Ursuya granulites shows that they underwent orogen-parallel mid-crustal flow and were exhumed owing to strain localization during retrogressive metamorphism within an extensional shear zone flanking an E-W elongated domal structure. We show that the Bidarray Basin formed during Permian time on the hanging wall of a south-vergent detachment system that developed in response to the formation of an immature “a-type” metamorphic core complex (the Ursuya massif) under regional E-W extension, resulting in homogeneous thinning of the hot crust. This core complex was later exposed by denudation during Cenomanian time. The preservation of the Permian and Triassic paleogeography and structure indicates that there has been no lateral motion between Iberia and Europe in the study area. The Cretaceous Pamplona transfer zone, responsible for the shift of the Mesozoic rift axis, reactivated a N-S trending Permian crustal heterogeneity.

How to cite: Saspiturry, N., Cochelin, B., Razin, P., Leleu, S., Issautier, B., Serrano, O., Baudin, T., and Allanic, C.: Permian inheritance : post-orogenic extension and metamorphic core complex formation (Western Pyrenees), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21820, https://doi.org/10.5194/egusphere-egu2020-21820, 2020.

EGU2020-8499 | Displays | SSP2.1

Latest Pliensbachian–Toarcian eustatic calibration using shallow-marine sedimentological record coupled with basinal geochemical analyzes

François-Nicolas Krencker, Alicia Fantasia, Mohamed El Ouali, Lahcen Kabiri, and Stéphane Bodin

Sea-level fluctuation is an important parameter controlling the sedimentation in deep-marine environments and influenced also the expansion of oxygen-depleted conditions in neritic settings during oceanic anoxic events (OAEs). Despite this fundamental role, sea-level fluctuation remains on a short timescale (<1 Myr) one of the least constrained parameters for numerous OAEs. Here we refine the sequence stratigraphic framework for the uppermost Pliensbachian–Toarcian with a special focus on the Toarcian OAE interval. This study is based on sedimentological and total organic carbon isotope data used to correlate 16 sections located in the central High Atlas (Morocco). Palinspastically, those sections formed a 50-kilometer proximal–distal transect along the northern Gondwana continental shelf, which allow reconstructing the shoreline migration through time and space. Our sequence stratigraphic interpretation is then compared to the geochemical signals (e.g. detrital index, chemical index of alteration) measured on samples collected in deep-environment settings from numerous basins distributed worldwide. Our study shows that the relative sea-level changes recorded in Morocco can be correlated over large distances across those basins, indicating that the relative sea-level changes were driven by eustatic fluctuations. This study gives insights into the relationship between relative sea-level fluctuations and the geochemical record.

How to cite: Krencker, F.-N., Fantasia, A., El Ouali, M., Kabiri, L., and Bodin, S.: Latest Pliensbachian–Toarcian eustatic calibration using shallow-marine sedimentological record coupled with basinal geochemical analyzes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8499, https://doi.org/10.5194/egusphere-egu2020-8499, 2020.

EGU2020-9527 | Displays | SSP2.1

Evidence for repeated and global palaeoenvironmental perturbations during the Aalenian

Alicia Fantasia, Thierry Adatte, Jorge E. Spangenberg, Nicolas Thibault, Emanuela Mattioli, Enrique Bernárdez, François-Nicolas Krencker, and Stéphane Bodin

Over the last decades, studies on Jurassic palaeoenvironments have been mostly focussed on the early Toarcian as this latter was marked by the Toarcian Oceanic Anoxic Event (T-OAE; ca. 183 Ma), which was one of the most extreme hyperthermal of the Phanerozoic. Hence, little is know about palaeoclimatic and palaeoenvironmental changes during the Aalenian time interval, although it is likely marked by an abrupt cooling in the aftermath of the Toarcian warm mode. Available palaeontological and geochemical datasets suggest that the Aalenian is also characterized by faunal turnovers and potential carbon-cycle perturbations. Despite those evidence, there is still no consensus about the modality of Aalenian palaeoenvironmental and palaeoclimatic changes as well as their potential triggering mechanisms. In addition, data from outside Europe are absent, leading to large uncertainties whether the observed changes are of gobal significance. In this study, we focus on the upper Toarcian–lower Bajocian interval of two marl/limestone alternation successions, namely Le Brusquet (Vocontian Basin, SE France) and El Peñon (Andean Basin, N Chile). Palaeoenvironmental and palaeoclimatic conditions are inferred based on high-resolution mineralogical (whole-rock and clay fraction) and geochemical (carbon isotopes, Rock-Eval pyrolysis, phosphorus, mercury) analyses. Additionaly, we provide a cyclostratigraphic framework for the Aalenian based on high-resolution magnetic susceptibility spectral analysis. The carbon isotope composition of bulk organic matter reveals evident correlatable fluctuations between sites from both hemispheres, providing the first evidence that the carbon cycle was globally and repeatedely disturbed during the Aalenian. The Toarcian–Aalenian transition is associated with a decrease in detrital and nutrient input (phosphorus), which is likely related to the shift towards the Aalenian cool mode. Interestingly, the middle–upper Aalenian transition is characterized by a sharp increase in terrigenous and nutrient influxes suggesting a more humid and warmer episode. The concomitance between strongly expressed precession cycles and palaeoenvironmental changes suggests moreover the influence of orbital parameters on the Aalenian sedimentary record.

How to cite: Fantasia, A., Adatte, T., Spangenberg, J. E., Thibault, N., Mattioli, E., Bernárdez, E., Krencker, F.-N., and Bodin, S.: Evidence for repeated and global palaeoenvironmental perturbations during the Aalenian , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9527, https://doi.org/10.5194/egusphere-egu2020-9527, 2020.

EGU2020-13124 | Displays | SSP2.1

Ample and recurrent sea-level fluctuations during the Bajocian: A hint towards middle Jurassic glacio-eustatism

Stéphane Bodin, Jan Danisch, Malte Mau, Francois-Nicolas Krencker, Alexis Nutz, and Lahcen Kabiri

Mesozoic sea-level fluctuations have been a matter of debate for several decades, especially the extend and origin of sea-level cycles that have a periodicity of about 1 Myr or less. The debate lies in the main driving mechanism for sequence development (global sea-level or sediment flux variations) as well as the reason behind water exchanges between the continents and the oceans (glacio- or aquifer-eustatism). In this study, we focus on the carbonate-dominated sedimentary record of the Bajocian (Middle Jurassic) in the Central High Atlas Basin of Morocco. Several aspects make this basin an appropriate location for discussing Middle Jurassic sea-level changes. Firstly, the outstanding exposures of the High Atlas Mountains, with continuous exposures for 10s of kilometres, allow to describe and track sedimentary packages and their bounding surfaces from proximal to distal settings. Moreover, a combination of ammonite and brachiopod biostratigraphy with carbon-isotopes chemostratigraphy allows to temporarily constrain their development, which permits to correlate and compare the Central High Atlas sedimentary record to other basins. Finally, due to high-subsidence rates, thick Bajocian sedimentary sequences have accumulated, minimizing condensation and hiatus that might prevail in other basins due to a lack of accommodation space creation. Two Bajocian long-term transgressive-regressive (T-R) packages are observed throughout the basin. They are modulated by several medium-term T-R packages, that have each an approximate duration of 1 Myr. These sequences can also be correlated on a basinwide scale. Combined with sedimentological and facies analyses, architectural evidence along proximal-to-distal transect illustrates that several of the medium-term sequences are characterized by the presence of a falling stage and lowstand systems tracts, demonstrating that medium-term T-R stacking patterns are not solely linked to fluctuation in sediment supply, but also to episodes of relative sea-level fall of at least 30m of amplitude. This is confirmed by backstripping analysis performed in a composite section from the center of the Basin. Comparison with Bajocian deposits from France and Scotland, where good biostratigraphic dating is also available, shows that similar contemporaneous sea-level fall can be observed, highlighting their potential global character. The two long-term Bajocian sequences are more difficult to correlate on a global scale, suggesting that they are rather primarily linked to fluctuation in regional sediment supply or dynamic topography processes. The exact cause of the Bajocian medium-term sea-level falls is currently unknown, but it is here interesting to note that a relatively cool globate climate has been postulated for the Middle Jurassic, suggesting that glacio-eustasy was their most likely driver.

How to cite: Bodin, S., Danisch, J., Mau, M., Krencker, F.-N., Nutz, A., and Kabiri, L.: Ample and recurrent sea-level fluctuations during the Bajocian: A hint towards middle Jurassic glacio-eustatism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13124, https://doi.org/10.5194/egusphere-egu2020-13124, 2020.

EGU2020-3088 | Displays | SSP2.1

Timing, Magnitude, Rate, and Drivers of Eustasy: A Review of the Cretaceous Period

Andrew Davies, Mike Simmons, David Ray, Benjamin Gréselle, Frans van Buchem, and Chris Robson

Isolating the eustatic signal from the sedimentary record remains challenging, yet much progress is being made toward understanding the timing, magnitude, and rate of eustasy on both long-term (107-108 yr) and short-term (105-106 yr) scales throughout the Phanerozoic. Knowledge of timing, magnitude, and rate, in turn, provides insights into driving mechanisms (tectono-eustasy vs. climatically mediated eustasy; e.g., glacio- or aquifer-eustasy). As an example, we review the current state of knowledge of Cretaceous eustasy. A literature-based review of sea-level change estimates has been conducted, and the results were evaluated against the different driving mechanisms. A further evaluation of driving mechanisms has been derived from a global geodynamic and associated paleoclimate model.

An analysis of short-term sea-level cycles reveals four broad episodes of magnitude change. Three of these episodes reflect trends of increasing sea-level change magnitudes from the Berriasian to early Hauterivian, late Hauterivian to Aptian, and Santonian to Maastrichtian. The fourth episode reflects a decreasing magnitude trend from the Albian to Coniacian. In addition, the maximum magnitude of sea-level change, at an approximate stage level, has been identified and categorised as slight (less than 10 m), modest (10 to 40 m), or significant (41 to 65 m). Significant magnitudes are inferred for the Valanginian, Aptian, Albian, and Maastrichtian; exclusively slight magnitudes are restricted to the Berriasian.

Because climatically driven eustasy is the likely cause of short-term sea-level change, an assessment of the characteristic maximum magnitude limits of the principal climatic drivers (thermo‑, aquifer-, and glacio-eustasy) has been made. Such a comparison argues for glacio-eustasy as the driver of significant short-term sea-level change and is supported by climate proxy data demonstrating that the Valanginian, Aptian, Albian, and Maastrichtian are intervals of cooling.

While the mechanisms, frequency, and magnitude short-term sea-level cycles linked to thermo- and glacio-eustasy are understood, the likely contribution of aquifer-eustasy remains enigmatic and, for the most part, untested. To better understand the role of aquifer-eustasy, paleoclimate simulations aimed at assessing the spatio-temporal pattern of aridity and humidity under differing CO2 forcing have been undertaken during time slices considered reflective of the differing Cretaceous climates and paleogeographic configurations (Valanginian, Turonian, and Maastrichtian). Only modest changes in the spatial extent of arid and humid zones are observed in response to large changes in CO2 forcing. The simulations also demonstrate that the greatest aquifer charge is more likely during lower CO2/cooler intervals, indicating that aquifer-eustasy works in phase with both glacio- and thermo-eustasy in contrast to the aquifer-eustasy paradigm. Additionally, using information on modern water table depths, we estimate that aquifer eustasy would be unable to contribute significantly to Cretaceous sea-level change. Indeed, even in the most optimistic case, the largest possible total aquifer-eustasy response remains smaller than 7 m. Our results indicate that glacio-eustasy is the most likely driver of Cretaceous short-term eustatic cycles because aquifer-eustasy is unable to account for the estimated Cretaceous magnitudes.

How to cite: Davies, A., Simmons, M., Ray, D., Gréselle, B., van Buchem, F., and Robson, C.: Timing, Magnitude, Rate, and Drivers of Eustasy: A Review of the Cretaceous Period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3088, https://doi.org/10.5194/egusphere-egu2020-3088, 2020.

EGU2020-19580 | Displays | SSP2.1

Oceanography of the Western Interior Seaway during OAE 2 using Nd isotopes

Sietske Batenburg, Hugh Jenkyns, Raquel Bryant, Mark Leckie, Alexander Dickson, Stuart Robinson, Micha Ruhl, and James Eldrett

During the greenhouse climate of the mid-Cretaceous, the Western Interior Seaway (WIS) experienced semi-restricted conditions with poor water-column ventilation, leading to the accumulation of black organic-rich shales. In the Maverick Basin, the southernmost extent of the WIS, the main phase of organic-matter deposition occurred in the early to late Cenomanian, before Oceanic Anoxic Event 2 (OAE 2). A sea-level rise prior to the event may have caused the basin to become better ventilated during the Cenomanian–Turonian transition, and ocean circulation likely played a major role on productivity and the preservation of organic matter. Widely different regimes of ocean circulation are suggested to have operated, with alternating incursions of water masses from both the north and the south. Foraminiferal assemblages suggest that during the early phase of OAE 2, Tethyan waters were drawn northward into the WIS (Elderbak & Leckie, 2016), whereas dinocyst occurrences indicate an influx of boreal surface waters into the Maverick Basin at that time (Eldrett et al., 2014; 2017). This cooler episode correlates with the so-called Plenus Cold Event, recognized in northern Europe by southward invasion of boreal faunas.

Here we present neodymium-isotope records (εNd) of fish teeth and detrital fractions from the Eagle Ford Formation that record the presence of distinct water masses at depth and allow testing of suggested mechanisms of ocean circulation. Mid- to late Cenomanian values of εNd around -3 (this study) are unusually radiogenic compared to coeval open ocean εNd records from the North Atlantic, where values typically lie between -4 and -10 (Martin et al., 2012, Robinson & Vance, 2012) and may reflect a strong influence of regional volcanism close to the WIS and/or weathering of mafic volcanic rocks in the water-mass source area. An excursion to positive εNd values in the WIS during OAE 2 may reflect changes in local weathering, or alternatively, the incursion of water masses carrying a signature of volcanic activity. The coeval emplacement of several Large Igneous Provinces (LIP), including the High Arctic LIP (Estrada et al., 2015) and the Caribbean LIP, may have influenced the seawater chemistry of the WIS, as reflected in Os and Cr concentrations and isotope ratios from the USGS Portland core (Du Vivier et al., 2014; Holmden et al., 2016).  Comparison of seawater and detrital εNd signatures with records north and south of the Maverick Basin will elucidate the direction and degree of deep-water exchange in the southern WIS.

 

References:

Du Vivier, A.D.C. et al., 2014, EPSL, 389, 23-33

Elderbak, K. & Leckie, R.M., 2016. Cret. Res., 60, pp.52-77.

Eldrett, J.S., et al., 2014. Geology, 42(7), pp.567-570.

Eldrett, J.S., et al., 2017. Climate of the Past (13), pp.855–878.

Estrada, 2015. Int. J. Earth Sci. (104), pp.1981–2005.

Holmden et al., 2016. Geochim. Cosmochim. Acta 186 (2016) 277–295

Martin, E.E., et al., 2012. EPSL, 327, pp.111-120.

Robinson, S.A. & Vance, D., 2012. Paleoceanography, 27(1).

How to cite: Batenburg, S., Jenkyns, H., Bryant, R., Leckie, M., Dickson, A., Robinson, S., Ruhl, M., and Eldrett, J.: Oceanography of the Western Interior Seaway during OAE 2 using Nd isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19580, https://doi.org/10.5194/egusphere-egu2020-19580, 2020.

EGU2020-260 | Displays | SSP2.1

Belemnites, clumped isotopes and oxygen fractionation

Madeleine Vickers, Stefano Bernasconi, Clemens Ullmann, Stephen Hesselbo, Gregory Price, and Christoph Korte

Belemnite calcite has been used extensively for Jurassic and Cretaceous stable oxygen isotope temperature reconstructions since the 1950s. However, with the advent of clumped isotope thermometry, a consistent offset between reconstructed δ18O temperatures vs Δ47 temperatures from the same belemnites has been observed. We investigate the causes of this offset by analyzing samples from the aragonitic phragmacone and calcitic rostrum from the same Cylindroteuthis belemnites, along with other aragonitic benthos, from the Callovian-aged Christian Malford Lagerstätte, U.K. Our new clumped isotope data suggest that the water-calcite 18O-fractionation factor in belemnite calcite was larger than that of the commonly used δ18O thermometry equations (e.g. Kim and O’Neil, 1997), and which is currently observed in other marine calcifiers. Our reconstructions suggest that the oxygen isotope fractionation is compatible with that observed in slow-forming abiotic calcites (e.g. Coplen, 2007) and in rapidly precipitating Travertines (Kele et al. 2015). The application of more established δ18O thermometry equations (Kim and O’Neil, 1997) to belemnite calcite for temperature reconstructions has resulted in a consistent underestimation of belemnite calcification temperatures, which has led to erroneous conclusions about belemnite life habits, and underestimation of global temperatures during these greenhouse times. We therefore advocate the use of calcite equations based on low precipitation rate experiments (e.g. Coplen, 2007; Kele et al., 2015) for belemnite rostra temperature reconstructions.

How to cite: Vickers, M., Bernasconi, S., Ullmann, C., Hesselbo, S., Price, G., and Korte, C.: Belemnites, clumped isotopes and oxygen fractionation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-260, https://doi.org/10.5194/egusphere-egu2020-260, 2020.

EGU2020-82 | Displays | SSP2.1 | Highlight

Latest Miocene Mediterranean-Atlantic gateway restriction: The Atlantic's side of the story

Zhi Lin Ng, Francisco Javier Hernández-Molina, Débora Duarte, Francisco Javier Sierro, Santiago Ledesma, Estefanía Llave, Cristina Roque, and Mike Rogerson

The closure of Late Miocene Mediterranean-Atlantic gateways and the restriction of Mediterranean Outflow Water (MOW) led to the Messinian Salinity Crisis (MSC), the dynamics of which is not well understood. However, restriction of the Mediterranean-Atlantic exchange and the Mediterranean Outflow Water (MOW) is one of the prerequisites to generate hypersaline conditions for evaporitic deposition. During the Late Miocene, MOW circulation was active through a Mediterranean-Atlantic exchange of the Betic, Riffian, and possibly Gibraltar gateways. This connection is thought to have ceased or reduced with the onset of the MSC, before re-establishing through the Gibraltar gateway since the Pliocene to the present. In this study, we define the sedimentary evolution of the Neogene Basins of the Gulf of Cádiz to investigate MOW evolution during the latest Miocene. Seismic interpretation shows an Upper Messinian sedimentary unit of transparent seismic facies. It could also be found in the lower Guadalquivir and Gharb basins, and towards the West Portuguese margin. Biostratigraphic dating indicate an onset of deposition predating the MSC. Distribution of this transparent unit implicates the dominant deposition of hemipelagic/pelagic deposits during a period of quiescence in the Atlantic margins, subsequent to MOW disconnection. This suggests that weakening or cut-off of the intermediate bottom currents of the Mediterranean-Atlantic exchange through the Betic-Gibraltar-Riffian paleo-gateways precedes the onset of MSC evaporites. This work is crucial for the understanding of sedimentary, paleoceanographic and climatic implications of the Latest Miocene Mediterranean isolation in the Atlantic margins.

How to cite: Ng, Z. L., Hernández-Molina, F. J., Duarte, D., Sierro, F. J., Ledesma, S., Llave, E., Roque, C., and Rogerson, M.: Latest Miocene Mediterranean-Atlantic gateway restriction: The Atlantic's side of the story, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-82, https://doi.org/10.5194/egusphere-egu2020-82, 2020.

EGU2020-10017 | Displays | SSP2.1 | Highlight

Cenozoic sea-level and cryospheric evolution from deep-sea geochemical and continental margin records

Kenneth Miller, James Browning, W. John Schmelz, Robert Kopp, Gregory Mountain, and James Wright

Cenozoic (past ~66 Myr) sea-level history reflects temperature changes and cryospheric evolution of the Earth from essentially ice-free conditions in the Early Eocene to bipolar ice sheets in the Quaternary. We derived a global mean sea level (GMSL) estimate for the Cenozoic using a new astronomically calibrated Pacific benthic foraminiferal δ18O splice from published records and a 2 Myr-smoothed Pacific bottom water temperature record based on published benthic foraminiferal Mg/Ca data. Our GMSL estimates are similar to sea-level estimates derived from “backstripping” (progressively accounting for compaction, loading and thermal subsidence) of cores from the mid-Atlantic U.S. continental margin. Peak global warmth, elevated GMSL, high CO2, and largely ice-free conditions occurred during the Early Eocene “Hothouse.” During the Middle-Late Eocene “Cool Greenhouse,” small ice sheets associated with lower atmospheric CO2 drove sea-level changes. Continental-scale ice sheets began in the Oligocene “Icehouse” (ca. 34 Ma), a permanent East Antarctic ice sheet began in the middle Middle Miocene (ca. 12.8 Ma), and full, bipolar glaciation began in the Quaternary (ca. 2.55 Ma). The Last Glacial Maximum (20-27 ka) was the largest lowering of GMSL (~130 m) of the Mesozoic-Cenozoic and GMSL rise during last deglaciation (ca. 19-10 ka) exceeded 40-45 mm/yr.  Sea-level rise progressively slowed from 10 ka to 2 ka and was then at stillstand until late 19th to early 20th century when rates began to rise. Despite large uncertainties in proxies, our study reaffirms that throughout the Cenozoic, high long-term (107-year scale) CO2 was associated with warm climates and high sea levels.  However, sea level-change was dominated by periodic, astronomically controlled (10’s kyr-Myr scale) Milankovitch variations superimposed upon longer-term changes driven by CO2.

How to cite: Miller, K., Browning, J., Schmelz, W. J., Kopp, R., Mountain, G., and Wright, J.: Cenozoic sea-level and cryospheric evolution from deep-sea geochemical and continental margin records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10017, https://doi.org/10.5194/egusphere-egu2020-10017, 2020.

The Ediacaran–Cambrian (E–C) transition witnessed profound biological and oceanic changes, among which the appearance of explosive radiation of skeletonized animals is considered as the most remarkable one. Although the prominent rise of oxygen concentration in atmosphere and ocean is believed to be the major trigger of the “Cambrian Explosion”, it is still an open question about the persistence of anoxic/ferruginous deep waters. In this study, the δ15Nbulk, δ13Corg values, TOC and TN contents, as well as trace elements concentrations of Well ZK4411 fresh core samples are analyzed to explore redox conditions of deep ocean, the nitrogen cycle and their relationships with biological evolution. The Mo concentrations, Mo–U covariations and Th/U ratios of studied samples indicate the oxic water condition of the mid-depth ocean during the late Ediacaran and Cambrian Fortunian stage, widespread anoxic/euxinic water conditions with temporarily sulfidic water condition during Cambrian Stage 2 and early Stage 3, and oxic water condition during the middle and late Stage 3. Based on a combination of δ15Nbulk values from this study and other published data, the low δ15Nbulk values (4+ assimilation in the photic zone, and the extinction of Ediacaran-type and small shelly-type animals during widespread anoxic event of Cambrian Stage 2 and early Stage 3. However, the high δ15Nbulk values, close to those of modern ocean sediments, imply that an established large NO3 reservoir and the existence of the well-oxygenated mid-depth ocean during the middle to late Stage 3, which is coincident with the appearance of larger, diversified skeletonized animals as exemplified by the Chengjiang Biota. All these results indicate a stepwise oxygenation of the early Cambrian deep ocean and an increasing supply of nitrogen nutrient, which leads to the Cambrian diversification and ecological radiation.

 

How to cite: Tian, H., Gai, H., and Wu, Y.: Nitrogen isotope evidence for the stepwise oxygenation of the mid-deep ocean across the Yangtze Block during the Ediacaran-Cambrian transition in South China , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13097, https://doi.org/10.5194/egusphere-egu2020-13097, 2020.

EGU2020-14482 | Displays | SSP2.1

Late diagenetic versus near-primary isotopic compositions in Ordovician carbonate rocks and fossils: A Baltoscandian example

Oluwaseun Edward, Christoph Korte, Clemens Vinzenz Ullmann, and Christian Mac Ørum Rasmussen

The Ordovician was an important interval in Earth’s history, characterized by major sea level fluctuations, carbon cycle and climatic perturbations, as well as a profound increase in marine biodiversity – the Great Ordovician Biodiversification Event (GOBE) (1-4){Sepkoski, 1981 #6}. Recently, direct links between Ordovician climatic evolution and biotic turnover have been proposed, based on geochemical data obtained from the East Baltic (5). However, the potential impact of late diagenetic modification of the geochemical compositions remains to be evaluated. Based on calcitic fossil brachiopods and bulk rock carbonates, this study documents the Early (Floian) to Late Ordovician (Sandbian) carbon (C) and oxygen (O) isotope evolution on the Swedish island of Öland, which was situated in the central part of the Ordovician Palaeobasin on the palaeocontinent of Baltica. The near-primary nature of the carbon and oxygen isotopic trends and its potential palaeoenvironmental significance is evaluated using optical, chemical and statistical methods. The results suggest that diagenetic alteration may have shifted both C and O isotope compositions to higher values, in contrast to classical interpretations. Nevertheless, both long-term and shorter-duration C and O isotope trends of palaeoenvironmental significance are discernible. Carbon isotope compositions suggests that despite the influence of late diagenesis, prominent C isotope perturbations are robust enough to be recorded in both bulk carbonates and calcitic brachiopods. Our Baltic oxygen isotope record reveals a long-term increase in carbonate oxygen isotopic composition during the Ordovician – consistent with the general O isotope Phanerozoic trend (1, 2, 6), which is most pronounced in the Darriwilian (Middle Ordovician). Therefore, the Ordovician brachiopod fossils, although partially altered, preserve a record of Middle Ordovician climate amelioration; supporting recent suggestions of Middle Ordovician climatic cooling (5, 7).

 

 

REFERENCES

  1. J. Veizer et al., 87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater. Chemical geology 161, 59-88 (1999).
  2. H. Qing, J. Veizer, Oxygen and carbon isotopic composition of Ordovician brachiopods: Implications for coeval seawater. Geochimica et Cosmochimica Acta 58, 4429-4442 (1994).
  3. A. Munnecke, M. Calner, D. A. Harper, T. Servais, Ordovician and Silurian sea–water chemistry, sea level, and climate: a synopsis. Palaeogeography, Palaeoclimatology, Palaeoecology 296, 389-413 (2010).
  4. J. J. Sepkoski, Jr., A factor analytic description of the Phanerozoic marine fossil record. Paleobiology 7, 36-53 (1981).
  5. C. M. Ø. Rasmussen et al., Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse. Scientific Reports 6, (2016).
  6. J. Veizer et al., Oxygen isotope evolution of Phanerozoic seawater. Palaeogeography, Palaeoclimatology, Palaeoecology 132, 159-172 (1997).
  7. S. Stouge, G. Bagnoli, J. A. Rasmussen, Late Cambrian (Furongian) to mid-Ordovician euconodont events on Baltica: Invasions and immigrations. Palaeogeography, Palaeoclimatology, Palaeoecology, (2019).

 

How to cite: Edward, O., Korte, C., Ullmann, C. V., and Rasmussen, C. M. Ø.: Late diagenetic versus near-primary isotopic compositions in Ordovician carbonate rocks and fossils: A Baltoscandian example, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14482, https://doi.org/10.5194/egusphere-egu2020-14482, 2020.

Metazoan reef builders receded globally during the Carboniferous, after the Late Devonian extinction event, with only few exceptions of coral-bearing bioconstructions reported worldwide. Among the latter, two exceptional extended coral reefs, dated as Late Viséan–Serpukhovian and Kasimovian-Gzhelian in age, respectively, were recently reported from southern China. The scarcity of coral buildups worldwide suggests global unfavorable conditions, with specific settings considered to represent refugia. To constrain these environmental conditions, seawater composition is reconstructed using carbon and oxygen isotopes originating from five measured sections located in southern China.

The resulting δ13C data reveals several environmental changes throughout the Carboniferous attributed to climate changes, ocean current variations, and proliferation of terrestrial plants. During the Late Viséan-earliest Serpukhovian, the high δ13C values (˜3‰) are interpreted as recording short-lived glacial events, with the expansion of ice-sheets in South America and eastern Australia. The scarcity of coral reef growth suggests that the cooling acted as an inhibiting factor during this period. Conversely, the development of the exceptional coral reefs in southern China could be explained by the persistence of warm oceanic currents in the epicontinental sea, located in equatorial position. During the Kasimovian-Gzhelian, the gradual δ13C positive shift from -0.7 to +4.7‰ coincides with a short-lived warming, which should be suitable for the recovery of coral communities. However, in spite of the mild climate, the scarcity of Pennsylvanian coral reef leads to consider other inhibiting factors (e.g. biological competition and aragonite seas). Interestingly, the disappearance of coral reefs in southern China correlates with negative δ13C shifts (e.g. Mid-Viséan, Late Gzhelian), interpreted as related to intensified upwellings.

The reconstitution of the Carboniferous environmental conditions documents several factors contributing to the metazoan reef demise and recovery subsequent to the Late Devonian extinction events, and adds to our current knowledge of the longest reef recovery in the Phanerozoic.

 

 

How to cite: Maillet, M. and Samankassou, E.: Oceanic δ13C, environmental changes and Carboniferous coral reef development: Records from Tianlin and Ziyun (southern China), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5054, https://doi.org/10.5194/egusphere-egu2020-5054, 2020.

Large-scale studies of Carboniferous–Permian trilobites by Russian paleontologists were completed about 80 years ago. As a result, the systematic and stratigraphic distributions of the previously described taxa require revision in accordance with modern data. In addition, in recent decades, a fairly large number of new, not yet described fossil materials have accumulated.

The author conducted a revision of all localities of the trilobites of the Carboniferous and Permian of the former USSR. Most of localities received accurate geographic location and age in accordance with modern data, which allowed us to review the stratigraphic distribution of many species and some genera. So, e. g., the endemic genus Anujaspis (North-East of Russia), widely known in the literature, which was long considered as Artinskian, is actually not younger than the Bashkirian.

In the process of research, the author established 6 new species: Brachymetopus (Conimetopus) alekseevi Mychko, 2019 (Asselian of the Urals), Ditomopyge (Carniphillipsia) mosquensis Mychko et Alekseev, 2018 (Gzhelian of the Moscow Region), Pseudophillipsia (Pseudophillipsia) darvazica (Lower Permian of the Darwaz; unpublished), D. (D.) arctica (Kasimovian of the Novaya Zemlya; unpublished), D. (D.) zhirnovskiensis (Kasimovian of the Volgograd Region; unpublished), Paraphillipsia urushtensis (Upper Permian of the Northern Caucasus; unpublished).

The other interesting group is Cyclida – enigmatic the Late Paleozoic–Mesozoic arthropods. Their taxonomic position is still open. Now 55 species and 17 genera have been described. Cyclids on the territory of Russia are extremely rare: until now only 6–7 forms from Carboniferous and Permian were known. Since 2016, the author has been searching for new material and revising all previously known cyclids of this territory.

Based on the new material, the author (with co-authors) established 2 new genera (Skuinocyclus and Prolatcyclus) and 2 new species: Skuinocyclus juliae Mychko & Alekseev, 2018 and Prolatcyclus kindzadza Mychko et. al., 2019. According to the results of the revision of previously known forms, it was found that Cyclus spinosus and C. tuberosus are synonyms and represent a new undescribed genus; C. miloradovitchi is a typical species for the new genus Uralocyclus Mychko & Alekseev, 2018. A new species of cyclids from the Carboniferous of Urals is currently under description.

Some researchers include cyclids in the subclass Branchiura along with modern parasitic carp lice. However, in the structure of cyclids there are features that contradict this: Skuinocyclus juliae has small lugs on the ventral side of the carapaces, which significantly complicated the ectoparasitic lifestyle. New taxa expand our knowledge of the biodiversity of this extinct animal group.

The study was funded by Russian Foundation for Basic Research (RFBR), project No. 18-35-00165.

How to cite: Mychko, E.: New rare Arthropods (Trilobites and Cyclids) from Carboniferous and Permian of Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-105, https://doi.org/10.5194/egusphere-egu2020-105, 2020.

Several characteristics and properties of Jurassic carbonates have received great attention as they have economic significance and was attractive for several researchers. Micro-fauna was studied for various purposes such as biostratigraphy and paleo-environment. Stable isotope composition analysis of ancient successions of carbonates is one of the strongest and powerful tools for the purpose of reconstructing paleoclimate and paleo-environment. This study aims to refine the stratigraphic signatures on the Carbon and Oxygen isotope composition through picking different timeline surfaces during middle Jurassic Tuwaiq Limestone Formation and related sequences. Field observations were carried out and samples were collected. Several laboratory analyses were performed including thin section petrography, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). Powder samples were prepared to analyze isotopic composition.

Tuwaiq Mountains Formation consists of skeletal, oolitic, intraclasts, fossiliferous planar laminated limestones and trough crossbedded limestone in the most upper part of the studied section. The cherty and bioturbated limestone is predominated also as well as large reef bioherm within the thick massive beds. The studied section consists of several types of foraminiferal assemblage species including Trocholina elongata, Redmondoides lugeoni, Kurnubia palastiniensis, Cladocoropsis, and minor amounts of Lenticulina and Nautiloculina oolithica. Other non-foraminiferal species also exist including noncostate gastropods, brachiopods fragments, bivalve, echinoderm, and coral fragments. Based on previous studies and the results of fossil associations that are found in the studied section, the  Tuwaiq MountainsLimestone Formation varies from fore-bank into lagoonal and intertidal sub-environments. Due to the absence of sponge spicules species, deep marine intra-shelf basin was excluded. Tuwaiq Mountain Limestone Formation is composed of shallowing upward outer lagoon (T1) graded upward into a back reef (T2) and reef (T3) Members.   This is reflected in the vertical signatures of both Oxygen and Carbon isotopes. Both of them are enriched upward because of the change  to more shallow marine lithofacies (low temperature and higher organic productivity). Two breakthroughs were observed in the upper part of Tuwaiq Formation where strong depletion for both Carbon and Oxygen isotopes is found, this is thought to be a result of a nearby continental source of negative lighter carbon and oxygen isotopes (δ12C and δ16O). Chert nodules and stratified chert might have an impact on isotope curves and thought to be associated with the overlying intensive occurrences of sponge spicules that are rich in silica in the lower parts Hanifa Formation. The overall enrichment in Oxygen isotopes is probably associated with the predominant Callovian-Oxfordian polar glaciation.

How to cite: Abdlmutalib, A. and Abdullatif, O.: Integration of lithofacies, biofacies, and stable isotope analysis of Middle Callovian Tuwaiq Formation: Implications for paleoenvironments and paleoclimate, Central Saudi Arabia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1481, https://doi.org/10.5194/egusphere-egu2020-1481, 2020.

EGU2020-9192 | Displays | SSP2.1

New insight on the paleoclimatic evolution in the Boreal Realm at the onset of the Early Cretaceous chalk sea

Carlette Blok, Alicia Fantasia, Kresten Anderskouv, Jon Ineson, Niklas Edvardsen, Thierry Adatte, and Stéphane Bodin

During the Albian, the open marine carbonate production underwent a profound revolution with the onset of the dominance of planktonic production in the total carbonate budget. This led to the deposition of vast amounts of chalk across the world’s Oceans as a result of the accumulation of large amounts of nannoplankton. The worldwide Upper Cretaceous white chalks are however not the first true chalks (i.e. deposits dominated by calcareous nannofossils) to be recorded in Earth’s History. Already during the Barremian, chalks were deposited in the North Sea Central Graben. These chalks did not extend until the Albian, since a ‘nannoconid crisis’ occurred at the onset of the early Aptian OAE-1a, with the deposition of an organic-rich marlstone layer named the Fischschiefer. To better understand if climatic changes have governed the occurrence of the Barremian true chalks and the switch to organic-rich marlstones during OAE-1a, we have reconstructed the evolution of climate in the North Sea Basin based on clay mineral assemblages. Clay mineral composition and distribution are proven indicators of paleo­climate and evolution of a basin as the formation of clay minerals in soils depends on the climate under which it develops. Hence, based on high-resolution clay mineral data from various cores from the North Sea, a paleoclimatic reconstruction of the late Hauterivian to early Aptian stratigraphic interval is proposed. Based on a long-term decrease of kaolinite content, a trend toward aridification is observed during the late Barremian, concordant with the development of the first true chalks. A sharp increase in kaolinite content is recorded at the onset of OAE-1a, with its highest peak occurring towards the end of the event. This suggest that a significant increase in humidity accompanies the unfolding of OAE-1a in the North Sea Basin. Further investigation is needed to confirm the hypothesis that paleoclimatic changes in the Boreal Realm are responsible for the onset of chalk deposition and the change in clay mineral assemblages.

How to cite: Blok, C., Fantasia, A., Anderskouv, K., Ineson, J., Edvardsen, N., Adatte, T., and Bodin, S.: New insight on the paleoclimatic evolution in the Boreal Realm at the onset of the Early Cretaceous chalk sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9192, https://doi.org/10.5194/egusphere-egu2020-9192, 2020.

EGU2020-13304 | Displays | SSP2.1

Links between temperature changes and oceanic-plateau emplacement during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2)

Lawrence Percival, Niels van Helmond, David Selby, Steven Goderis, and Phillipe Claeys

The Cenomanian–Turonian boundary interval (~94 Ma) was marked by a period of climatic turbulence, and featured the widespread expansion of strongly oxygen-depleted conditions across a large part of the global ocean; collectively these environmental degradations are referred to as an oceanic anoxic event or OAE (specifically OAE 2 for this time interval). Extremely high sea-surface temperatures are documented for several regions during OAE 2, likely beginning at the onset of the event, but a shift towards colder conditions during the early stages of the OAE (the Plenus Cold Event or PCE) is also recorded in several locales, before a return to a very warm climate during the latter part of the crisis. The overarching high temperatures are thought to have resulted from major volcanic activity during the emplacement of one or more oceanic plateaus, as evidenced by a globally documented shift in osmium-isotope ratios to very unradiogenic values just below the base of OAE strata that indicates a very large flux of mantle-like osmium to the open ocean at that time. Intriguingly, the PCE cooling has been shown as likely non-synchronous globally, suggesting a local control in addition to/instead of global forcing; whilst the high temperatures associated with OAE 2 appear to have continued long after the OAE itself ceased.

 

This study presents new osmium-isotope data from the New Jersey shelf of the proto-North Atlantic (ODP Leg 174AX: Bass River), correlating the results with a previously generated sea-surface temperature dataset from the same site. These results are then compared with other temperature archives and osmium records of oceanic-plateau activity for OAE 2. The new data indicate intense oceanic-plateau activity prior to and in the earliest stages of the OAE, with a decline in mantle-osmium output before the end of the event, consistent with previous findings. However, when the osmium data are directly correlated with temperature records, both at Bass River and other sites, they clearly show that not only were high sea-surface temperatures maintained after the OAE, but also after oceanic-plateau activity (and presumably associated volcanism and COemissions) fell. Thus, a reduction in mantle carbon output did not manifestly result in an immediate reduction of atmospheric CO2. Moreover, the beginning of the osmium recovery broadly correlates with the end of the PCE cooling at all locations where both osmium and temperature trends have been studied. Consequently, although the PCE cooling was not globally synchronous and its precise timing at individual locations was likely controlled by local processes, some feature of the oceanic-plateau development allowed the cooling spells to occur when plateau activity was most intense, before a reduction in that intensity stymied the spread of cold conditions and resulted in the restoration of high temperatures in the latter stages of the OAE and beyond. These data highlight the need for further work to understand the complexity of and nuances in the relationships between large-scale volcanism and major climate/environment perturbations, both for OAE 2 and for other events.

How to cite: Percival, L., van Helmond, N., Selby, D., Goderis, S., and Claeys, P.: Links between temperature changes and oceanic-plateau emplacement during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13304, https://doi.org/10.5194/egusphere-egu2020-13304, 2020.

EGU2020-8319 | Displays | SSP2.1

The Cenomanian–Turonian boundary mass extinction (Late Cretaceous): Ammonoid biodiversity in the Eastern Desert, Egypt

Ahmed Hefny, Gamal M. El Qot, Abd El Moneim El Araby, and Mohamed F. Aly

The Cenomanian-Turonian (C-T) mass extinction occurred during a peak global greenhouse interval, with eustatic sea-level elevated nearly 300 m above present stand. The time period spanning the Cenomanian–Turonian boundary was characterized by profound paleoenvironmental changes at global scale. World-wide consequences of these events have been the focus of new reports and their influence on local to regional depositional systems. A faunal turnover is recorded in the uppermost Cenomanian, marked by the disappearance of most of the Cenomanian taxa. The macrofossil contents of two Upper Cretaceous sections from Wadi Qena, central Eastern Desert, Egypt have been collected and studied in detail. These fossils, ranging in age from Late Cenomanian to middle Turonian. The Cenomanian- Turonian sequence of centeral Eastern Desert is represented by the fossiliferous Galala formation (about 90 meter) at base and Umm Omeiyid formation (about 40 meter) at top. The Galala Formation is characterized by shale, fossiliferous marl, marly limestone, sandstone and siltstone interbeds. The Umm Omeiyid Formation overlies the Galala Formation unconformably. It consists of unfossiliferous siltstone with fine, medium-grained hummocky cross-stratified sandstone intercalations with a few fossiliferous limestone beds and marl intercalations. The Cenomanian-Turonian boundary cuts within the upper part of the Galala Formation at the last occurrence (LO) of Vascoceras cauvini and the first occurrence (FO) of Vascoceras proprium. There is rapid faunal change across the Cenomanian-Turonian boundary in all the studied sections. Most benthic fauna become extinct at the Upper Cenomanian and new taxa appeared at the Lower Turonian. All Upper Cenomanian cephalopod taxa become extinct at the same level and new taxa appeared at the Lower Turonian. The faunal diversity decreased from the Upper Cenomanian to the Lower Turonian. The ammonite ranges are used for a biostratigraphic zonation of the Cenomanian- Turonian succession in the northern and central parts of Wadi Qena. five ammonite zones have been distinguished (Neolobites vibrayeanus Zone , Vascoceras cauvini Zone , Vascoceras proprium Zone , Choffaticeras (Choffaticeras) segne Zone  and Coilopoceras requienianum Zone).

How to cite: Hefny, A., El Qot, G. M., El Araby, A. E. M., and Aly, M. F.: The Cenomanian–Turonian boundary mass extinction (Late Cretaceous): Ammonoid biodiversity in the Eastern Desert, Egypt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8319, https://doi.org/10.5194/egusphere-egu2020-8319, 2020.

EGU2020-13036 | Displays | SSP2.1

Changes in carbon cycling across the OAE 1b cluster (Aptian-Albian transition): New insights from the Vocontian Basin

Mickaël Charpentier, Clemens V. Ullmann, Arka Rudra, Hamed Sanei, and Stéphane Bodin

The Aptian-Albian transition is marked by the unfolding of the Oceanic Anoxic Event (OAE) 1b, a protracted environmental perturbation characterized by occurrence of several sub-events out of which the Kilian and Paquier events are the most well-known ones. So far, the conditions leading to the unfolding of the OAE 1b cluster and its sub-events, as well as their consequences, remain elusive as most of the studies have focussed on the Paquier level, thereby precluding a broader perspective on this event. In this study, we focus on an extended stratigraphic interval from the Brier section (Vocontian Basin, SE France) spaning the Kilian to Paquier levels interval. Our goal is to better understand the processes having led to organic matter (OM) accumulation across this stratigraphic interval as well as to constrain the exogenic carbon cycle framework in which these changes are inscribed. For this purpose, we have performed high-resolution bulk-rock pyrolysis analyses, paired stable carbon isotope measurements on both bulk carbonate and organic matter, and handheld XRF analyses.

Measured total organic contents (TOC) average 1.5% with peaks reaching 3% in the Paquier level. Apart for the Kilian, Paquier and HN 12 levels, which are characterized by the dominance of marine organic matter, the remainder of the studied interval is characterized by the accumulation of continental organic matter. Moreover, there is a good correlation between changes in the long-term TOC content and detrital input as inferred from changes in element concentration such as aluminium and thorium. A preservation model therefore best explains the long-term OM accumulation across the studied interval. Sporadic episodes of enhanced marine OM productivity account only for the deposition of the Kilian, Paquier and HN 12 levels.

Carbon isotope analyses shows that the Kilian and Paquier levels are both associated with a 0.5 – 1‰ negative excursion in the bulk carbonate record. In the bulk OM record, the C-isotope signal is however different. The Kilian level is hence characterized by a 3‰ negative excursion whereas the Paquier level is characterized by a 4‰ positive excursion. This discrepancy is due to the fact that the bulk OM C-isotope record is strongly influenced by the mixing of different types of organic matter. By applying a correction factor tacking into account the type of organic matter, as characterized by the pyrolysis analyses, both OM and carbonate C-isotope records can be reconciled.

Importantly, our paired C-isotope record shows that in between the Kilian and Paquier levels, two others episodes of similar negative C-isotope excursion occur, with an abrupt onset and a total amplitude of 1‰. These episodes likely correspond to the Monte Nerone level observed in Italy.  The unfolding of OAE 1b cluster is thus thightly tied to a very dynamic exogenic carbon cycling, characterized by repeated injections into the oceans-atmosphere of light isotopic carbon, potentially similar to the Early Eocene scenario.

How to cite: Charpentier, M., Ullmann, C. V., Rudra, A., Sanei, H., and Bodin, S.: Changes in carbon cycling across the OAE 1b cluster (Aptian-Albian transition): New insights from the Vocontian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13036, https://doi.org/10.5194/egusphere-egu2020-13036, 2020.

EGU2020-2258 | Displays | SSP2.1

Paleoceanographic reconstruction of Maastrichtian from the hemipelagic sediments of Pakistan, Eastern Tethys

Bilal Wadood, Suleman Khan, Hong Li, and Yiqun Liu

The evolution of planktonic foraminifera in Cretaceous is forced by the paleo-oceanographic changes associated with Oceanic Anoxic Events (OAEs). The paleo-oceanographic conditions including global sea level rise, loss of ocean stratifications and subsequent loss of niche partitioning, ocean acidification and warming were common during early-middle Cretaceous. The evolution of planktonic foraminifera is associated globally with such changes in oceans. The global warming of early to middle Cretaceous was replaced by a period of cooling during early Maastrichtian. The stratification in global oceans resumed and the diversity of planktonic foraminifera increased. This study deals with signals of paleo-oceanographic conditions of Maastrichtian time preserved in Mughal Kot Section, Eastern Tethys.

A thick succession of hemipelagic sediments of Maastrichtian age is exposed in Mughal Kot Formation, Indus Basin, Pakistan. The studied section revealed abundant taxa of Globotruncana, Globotruncanita and Heterohelix. Based on these taxa a local assemblage biozone of Maastrichtian (~76-~69 Ma) age is erected. The overall species richness in the studied section is very low. This significantly low richness is thought to be associated with high sedimentation rate as 1100 meter thick strata is deposited during Maastrichtian. Presence of turbidite beds supports such high sedimentation rates. However, a consistent decrease in species richness from base (early Maastrichtian) to the top (late Maastrichtian) is recorded in the section. This decrease is associated with the dominance of opportunistic taxa of Heterohelix. The proliferation of opportunistic taxa at the expense of specialized taxa during late Maastrichtian gives a strong clue that the global cooling of early Maastrichtian was replaced by warming during late Maastrichtian. Such warming may have resulted in the melting of polar ice, uniformity in the physical properties of water masses in global oceans and hence destruction of habitat for the dwelling of specialized foraminifera. 

How to cite: Wadood, B., Khan, S., Li, H., and Liu, Y.: Paleoceanographic reconstruction of Maastrichtian from the hemipelagic sediments of Pakistan, Eastern Tethys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2258, https://doi.org/10.5194/egusphere-egu2020-2258, 2020.

The rifting and the amalgamation of earth landmass is a continuous process. The assembly of the Gondwana lasted from ~730 Ma to 500 Ma, and most of the mass is covered by glaciation at the southern hemisphere. Afterthought experienced multiple episodes of rifting and collision of small ribbon shape microcontinents. The extra-peninsular Gondwana sequence is discontinuous in the Himalayan orogenic belt while peninsular Gondwana sequence is broadly distributed in numerous intracratonic basins of peninsular India. The detrital zircon U-Pb ages from Permo-Carboniferous sequence peak at ~1164 with a subordinate peak at ~1305 Ma. This result emphasised that the sediments were mainly sourced from the Stenian magmatism in Albany-Fraser orogeny or the East Africa-Nibua and eastern coast of India, and southwest Australia. Also, the unit also contains sporadic volcanic unit (Baraha Volcanics). The Saptakoshi Formation, uncomfortably overlain the Khokha Diamictite, yield the peaks at ~522 Ma and 941 Ma with a younger peak at ~113 Ma with some older peaks at ~1811 and 1917 Ma. This younger detritus possibly sourced from the Rajhmahal basalt ~~115-120 Ma) while the remaining grains show a similar trend to the underlying Diamictite and overlying Tamrang Formation. Additionally, the Tamrang Formation have peaks at ~976 Ma, and 1716 Ma, identically identical to the Greater Himalayan sequence. The U-Pb age distribution of these three units coincide with the Tethys Himalaya further brings the possibility that either they share the same provenance or recycled from the Tethys Himalaya till Permian and onwards there was input from the Lhasa terrane, South Qiangtang terrane, and Indo China blocks.

How to cite: Baral, U. and Lin, D.: The break-up of the Indian subcontinent from Gondwana: constrain by detrital zircon U-Pb dating of mid- Paleozoic-early Cenozoic strata in eastern Nepal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-66, https://doi.org/10.5194/egusphere-egu2020-66, 2020.

EGU2020-3629 | Displays | SSP2.1

Late Carboniferous-early Permian tectono-sedimentary cycles and climate proxies in the Pyrenean and Basque-Cantabrian basins, N Spain.

José F. Barrenechea, Joan Lloret, Raúl de la Horra, Nicola Gretter, Violeta Borruel-Abadía, Ausonio Ronchi, José López-Gómez, Manuel Juncal, and José Bienvenido Díez

The late Carboniferous to early Permian interval was a time of major global changes on Earth. It encompassed the final consolidation of the Pangaea supercontinent and the subsequent development and infill of continental basins. This interval also witnessed a climate transition towards warmer conditions, including the substantial retreat of the extensive continental ice sheets developed during the Late Palaeozoic Ice Age (LPIA). The end of this climate transition represented an evolution form an icehouse to a greenhouse period at the early to middle Cisuralian, which in turn was a time of important tectonic changes in Pangaea. However, our understanding of this whole chain of processes still has many gaps and many of its features still generate debate, especially those concerning the origin and the end of this transition period. This study focuses the late Carboniferous to early Permian interval by means of a multidisciplinary study in the Pyrenean (P) and Basque-Cantabrian (BC) basins, that constitute a near equatorial complex extensional structure located in the middle of the late-Variscan fold belt. The present-day Pyrenean Ranges, extending E-W along almost 1000 Km, from the Mediterranean coast to the Basque-Cantabrian Cordillera, is the result of intense inversion of previous Permian to Cretaceous extensional to transtensional rift basins. In those basins, the time-interval has been traditionally studied in two separated structural units: Basque-Cantabrian Pyrenees and Aragonese-Catalan Pyrenees. However, this multidisciplinary study, proposes the existence of a lateral tectono-sedimentary connection for the entire basin.  Nine late Carboniferous - early Permian sub-basins have been studied in the Basque-Cantabrian and Pyrenean domain. From west to east they are: Frieres, Sotres, Carmona, Anayet, Aragorn-Bearn, Castejón-Sas, Erill Castell, Gramós and Camprodón. Three lithological units, separated by unconformities and dated by means of pollen associations and radiometric data, represent the Permian record of these basins. They constitute three cycles of sedimentation of similar age (Gzhelian-Asselian, Asselian-Sakmarian, and Sakmarian-Kungurian) related to the same post-Variscan geodynamic stages of evolution affecting the whole Pyrenean and Basque-Cantabrian basins. The two younger cycles broadly coincide with other similar cycles defined in SE France and Sardinia, thus pointing to a common tectono-sedimentary evolution for the westernmost continental Peri-Tethys domain during this time-interval. In addition, the middle cycle (Asselian-Sakmarian) mostly represents a calc-alkaline volcano-sedimentary event in most of the sub-basins, related to a post-Variscan extensional phase. Detailed studies of paleosols, sedimentology, and mineralogy indicate a progressive evolution towards warmer conditions that were accelerated during the Artinskian, probably related to the end of the global icehouse period associated to the LPIA in the equatorial late-Variscan fold belt domain.

How to cite: Barrenechea, J. F., Lloret, J., de la Horra, R., Gretter, N., Borruel-Abadía, V., Ronchi, A., López-Gómez, J., Juncal, M., and Díez, J. B.: Late Carboniferous-early Permian tectono-sedimentary cycles and climate proxies in the Pyrenean and Basque-Cantabrian basins, N Spain., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3629, https://doi.org/10.5194/egusphere-egu2020-3629, 2020.

EGU2020-22505 | Displays | SSP2.1

Jurassic-Cretaceous paleogeography of Central-West Parnaiba Basin, NE Brazil - stratigraphy and sedimentary provenance of detrital zircons

André Pereira de Assis, Kelly Aparecida Caldas da Cruz, Renata da Silvia Schmitt, and Silvia Regina de Medeiros

The Phanerozoic Parnaíba Basin occupies 600.000km² in northeast Brazil, covering cratons and Neoproterozoic belts. Its Central-West region is mostly represented by the Jurassic-Cretaceous Sequence (Mosquito, Corda Grajaú, Codó and Itapecuru formations) recording magmatic events from the Central Atlantic Magmatic Province, with depocenters migrations and shifts on depositional environments related to Pangea breakup.  This work discusses the Jurassic-Cretaceous siliciclastic units testing possible sedimentary source areas with U-Pb and combined Lu-Hf data on detrital zircons, using LA-ICP-MS. The basalts from Mosquito Formation are dated at +/- 198Ma and the Codó Formation present accurate Aptian fossil data. This formation records a hypersaline lake system, succeeded by a transgression that represents pioneer marine ingression within an intracontinental rift. The other units (Corda, Grajaú and Itapecuru) are constituted by siliciclastic sediments involved in intracontinental sub-environments. The Corda Formation consists of aeolian system, sand sheets and wadis deposited in a desertic setting. The contact between the subsequent Grajaú Formation is abrupt, represented, at the base, by thick coarse braided river facies grading laterally and upwards to ephemeral channels in association with low amplitude Aeolian dunes, evidencing still arid conditions. Interlayered beds of fluvial and aeolian sandstones within lacustrine deposits, indicates that Codó and Grajaú formations consists the same seasonal fluvial-lacustrine system. The last Itapecuru Formation, is represented by a thick red sandstone succession deposited in a deltaic system. Paleocurrents measurements below Codó Formation (i.e. Corda and lower Grajaú) points a W-NW sense of direction, whereas paleocurrents above Codó Formation (i.e. upper Grajaú and Itapecuru) presents a regional sense to E-NE. Detrital zircons geochronology analysis helped to identify the source area of sediments through the comparison of the main ages of possible uplifted tectonic terranes. The preliminary results revealed that sandstones below Codó Formation shows a major Neoproterozoic population (56, 41% to 40%) with age peaks at 583 and 628 Ma; and also Paleoproterozoic (43, 48% to 35,05%); Archean (4,35%) and Paleozoic (2,61%) populations. Sandstones above Codó Formation, also show a Neoproterozoic major detrital zircon population (40% to 37,12%) with 625, 665 and 783 Ma age peaks. Two other populations are present: Paleoproterozoic (22.68% to 20%) with peaks at 1749 and 1881 Ma, and Archean (24,45% to 15,47%). This last source has a greater contribution than in the formations below the Codó maker. We envisaged that the shift from W-NW to E-NE sandstones paleocurrent is coherent with the rise on Archean contribution, possibly related to the Amazon Craton to the West. In addition, the youngest Phanerozoic detrital zircons obtained in all samples are minor (6,66% to 6,18%). The integration of field stratigraphic analysis, paleocurrents and detrital zircon provenance studies corroborate to the hypothesis that Codó Formation must represent a Cretaceous stratigraphic datum for the transition of a rift and post-rift phase, thus the change of source areas is consistent.

The authors acknowledge support from Shell Brasil Petroleo Ltda. and ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation (Technichal Cooperation #20.219-2).

How to cite: de Assis, A. P., da Cruz, K. A. C., da Silvia Schmitt, R., and de Medeiros, S. R.: Jurassic-Cretaceous paleogeography of Central-West Parnaiba Basin, NE Brazil - stratigraphy and sedimentary provenance of detrital zircons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22505, https://doi.org/10.5194/egusphere-egu2020-22505, 2020.

EGU2020-3702 | Displays | SSP2.1

Tectono-stratigraphic evolution of the Aptian Pre-Salt of the onshore Espírito Santo Basin, SE Brazil, an example of proximal passive margin sag basin

Francyne Bochi do Amarante, André Basso Schilling, Juliano Kuchle, David Iacopini, Claiton Marlon dos Santos Scherer, Renata dos Santos Alvarenga, and Patrycia Leipnitz Ene

The Espírito Santo Basin is part of the Brazilian rift system basins, formed by the break-up of the Supercontinent Gondwana and subsequent opening of the South Atlantic Ocean. The Aptian sedimentary succession of the basin is named Mucuri Member, lower unit of Mariricu Formation, and is contemporary to the pre-salt main carbonate reservoirs. Proximal deposition consists mostly of clastic sediments, interpreted as fluvial and coastal systems in the margins of a wide lake, which synchronously accumulated carbonates to the distal portions. The economic interest for oil is centered on the distal carbonates, thus the proximal sections lack detailed studies. The main objective of this study is the tectono-stratigraphic analysis of the marginal Mucuri Member. Leading methodology is seismic stratigraphy based on 220 2D lines and 1 3D volume, coupled with petrophysical and lithological analysis of 103 well log data and 5 cored wells. The combined analysis of seismic and lithological parameters resulted in the individualization of four seismic facies, which correspond to the predominance of one or two amongst five facies associations interpreted in cored wells. Seismic facies (SF) 1 is predominantly composed of offshore and lower shoreface successions; SF 2 is characterized by a dominance of poorly confined fluvial channels facies association; SF 3 records the interaction between fluvial and coastal successions composing mound-like structures, and is interpreted as wave-dominated deltaic facies association; SF 4 corresponds to sandspits structures and is restricted to regions where the coastal waves interact with basement highs. Four seismostratigraphic units were identified (named, from the base upwards: MUC1, MUC2, MUC3 and MUC4), delimited by three subparallel horizons. Unit-bounding reflectors coincide with gamma ray maxima or minima representing shales or anhydrites, respectively, deposited in deep water environments. The Mucuri Member records an enlargement in depositional area from the base upwards witnessing an overall lacustrine base level rise during deposition. The geometry of the depositional area during MUC1 and MUC2 was conditioned by the paleorelief of the preceding rift basins. MUC3 and MUC4 seismic units record a decrease in thickness as remnant topography was gradually filled; both units transcended and draped the half-grabens. The Early Cretaceous Mucuri Member composes the beginning of the post-rift sequence of Espírito Santo Basin, marked by the onset of thermal subsidence and cessation of mechanical subsidence.

How to cite: Amarante, F. B. D., Schilling, A. B., Kuchle, J., Iacopini, D., Scherer, C. M. D. S., Alvarenga, R. D. S., and Ene, P. L.: Tectono-stratigraphic evolution of the Aptian Pre-Salt of the onshore Espírito Santo Basin, SE Brazil, an example of proximal passive margin sag basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3702, https://doi.org/10.5194/egusphere-egu2020-3702, 2020.

EGU2020-20037 | Displays | SSP2.1

Proposed depositional scenarios of the Nise Formation on the Mid-Norwegian Continental Shelf, with focus on the Halten Terrace.

Maren Hope Blå, Maarten Felix, Jeremy Watt, and Arve Næss

The Late Cretaceous Nise Formation is located on the Mid-Norwegian Continental Shelf. On the Halten Terrace, the formation is generally described as a mudstone interbedded with thin sandstones and carbonate stringers. The spatial distribution, connectivity, sediment source and depositional processes of the sandstones are uncertain. 

Six cores and associated thin sections of the Nise Formation on the Mid-Norwegian Continental Shelf have been described. Three of the cores are from the Halten Terrace area, and one core each are from the Vestfjorden Basin, Nyk High and the Møre/Vøring Basin transition respectively. The main focus has been on the Halten Terrace while the cores from the other areas (tens to hundreds of kilometres away from Halten) are included to compare facies, depositional environment, source of sediment, grade of bioturbation and other characteristics with those of the Halten Terrace.

An isochore map of the Nise Formation in the central part of the Halten Terrace has been constructed based on interpretation of wireline logs from approximately 280 well penetrations. The map reveals a distinct thickness increase in the central parts of the Halten Terrace, suggesting the infilling of a former sub-basin. Additionally, the map supports an eastern and/or northern sediment source, which might exclude the Greenlandic landmasses as a provenance area. The cores from the Halten Terrace, supported by additional wireline well logs, indicate that the upper parts of the formation contain a greater amount of sandstone facies compared to the lower parts. These sandstones are interpreted as densely bioturbated distal turbidites. The comparison of facies development in the cores from the different areas indicates variability in depositional systems between the areas at the time of deposition.

Different depositional scenarios of the Nise Formation on the Mid-Norwegian Continental Shelf are being developed in order to increase the understanding of the Nise Formation on the Halten Terrace. The proposed scenarios include various sediment input models and alternative depositional environments in the different areas. The scenarios mainly display marine, isolated systems. 

How to cite: Hope Blå, M., Felix, M., Watt, J., and Næss, A.: Proposed depositional scenarios of the Nise Formation on the Mid-Norwegian Continental Shelf, with focus on the Halten Terrace., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20037, https://doi.org/10.5194/egusphere-egu2020-20037, 2020.

EGU2020-21218 | Displays | SSP2.1

Mixed siliciclastic-carbonate sequence stratigraphy, Miocene Dam Formation, Saudi Arabia

Mazin Bashri, Osman Abdullatif, Moaz Salih, Michael Kaminski, Lamidi Babalola, and Ammar Adam

Sequence stratigraphy of the mixed siliciclastic-carbonate successions is considered to be more complex than their counterparts of pure siliciclastic or carbonate systems. This is due to the higher number of controlling factors in the depositional environment. Consequently, the reservoir and source rock characterization within these systems is relatively more difficult in term of the spatial distribution of the lithologic unit and its petrophysical properties heterogeneity.

Following Scharland et al., 2001, the Miocene Dam Formation is regarded as a third-order sequence which consists of both siliciclastic and carbonate sediments, with the dominance of carbonates. Three fourth-order sequences are well exposed in the Lidam area, Eastern Saudi Arabia. Sequence boundaries are delineated using the existing Rhizolith and desiccation cracks in the most upper part of the high stand systems tract, where it is dominated by shallow marine carbonate deposits. The early low stand systems tract is of dolomitic mudstone interbedded with dissolved chicken-wire anhydrite. Fine sandstone of estuarine origin, in addition to intertidal mudstone-sandstone succession, represent the late low stand systems tract. Transgressive surfaces are either sharp erosional surfaces or ravinement surfaces with intraformational lag deposits. Subtidal quartz skeletal wackestone with pieces of evidence of storm events represent the transgressive systems tract. Going toward the end of the vertical succession of the Dam Formation, shallow marine siliciclastics dominate. A set of incised channels filled with intraformational boulders of calcareous sandstone lies over the shallow marine siliciclastics succession, indicating a great drop in the sea level. Finally, a fluvial system of high energy braided stream origin, composed of medium to coarse ferruginous sandstone within a fining upward succession and high abundance of plant remains, represent the Hufouf Formation base and the start of a new third-order sequence. The heterogeneity of the lithofacies is intense, but the sequence stratigraphic framework helps in their rearrangement vertically into packages, which helps in the prediction of their spatial distribution.   

 

 

How to cite: Bashri, M., Abdullatif, O., Salih, M., Kaminski, M., Babalola, L., and Adam, A.: Mixed siliciclastic-carbonate sequence stratigraphy, Miocene Dam Formation, Saudi Arabia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21218, https://doi.org/10.5194/egusphere-egu2020-21218, 2020.

EGU2020-12238 | Displays | SSP2.1

Rock physics modelling of siliciclastic shallow-marine clinoforms on the New Jersey continental shelf using 3D seismic data and well logs

Masoud Aali, Mladen R. Nedimovic, Craig S. Fulthorpe, Gregory S. Mountain, Bill Richards, and James A. Austin

Heterogeneities within clinoforms, which can be in the form of variations in internal geometry and/or change in sediment distribution, may act as fluid flow barriers or conduits for hydrocarbon or freshwater reservoirs. These heterogeneities can lead to considerable uncertainty in estimating pore-fluid recovery factors by up to 35%. And yet, variations in sediment petrophysical characteristics within clinoforms have been poorly documented. Understanding the rock physics of clinoform heterogeneities along continental margins is a key to reducing the uncertainties in predicting the dynamics and the volume of recoverable pore fluids within these structures.

The Miocene sedimentary record of the New Jersey continental margin is a prime candidate for studying continental-margin clinoform structures and the variation in their petrophysical properties. The margin has experienced a stable tectonic history, smooth and gradual thermal subsidence, and continuous sediment loading in the Miocene, resulting in deposition of well-developed siliciclastic clinoformal sequences. We use data from three IODP Expedition 313 boreholes and an encompassing high-resolution 3D multichannel seismic volume, collected in 2015 by the R/V M.G. Langseth on the New Jersey continental shelf, to predict shallow-marine sedimentological properties of the Miocene clinoforms at a significantly higher resolution (~5 m laterally) than previously achieved (~100s of m). We identify 76 system tracts and 22 sequences spanning ~8 m.y. of the Miocene. The results of our 3D stratigraphic analysis provide a detailed structural framework for analyses of the Miocene deposits to: 1) define the sedimentary structure in terms of stratal packages and 2) estimate the internal clinoform heterogeneity associated with phases of known mid-Cenozoic sea-level change.

Our statistical analysis of the estimated elastic properties, including P-wave velocity (Vp), density and clay volume, reveals repeating spatial patterns in the internal rock physics properties of the Miocene clinoforms. We show that diagenesis and sediment compaction within the dipping parts of clinoforms cause a continuous increase of Vp in the seaward direction, with a magnitude that decreases from top to bottom. Our results also suggest that lithofacies change in clinoforms imposes a stronger influence on density, as lateral changes in lithofacies are more pronounced in sediment density than in Vp. In the Miocene sedimentary record, the transgressive system tracts show a seaward coarsening trend in grain size and a 3%-5% increase in density from clinoform topsets to bottomsets. Highstand and lowstand system tracts show a fining trend basinward, with a ~8% and 5% reduction in density, respectively. We further demonstrate that the identified trends can provide a standard model allowing incorporation of clinoforms in reservoir characterization techniques, such as model-based seismic inversion, and enable setting of guidelines on how the petrophysical properties change regionally in shallow-marine siliciclastic environments of continental margins.

How to cite: Aali, M., Nedimovic, M. R., Fulthorpe, C. S., Mountain, G. S., Richards, B., and Austin, J. A.: Rock physics modelling of siliciclastic shallow-marine clinoforms on the New Jersey continental shelf using 3D seismic data and well logs , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12238, https://doi.org/10.5194/egusphere-egu2020-12238, 2020.

EGU2020-11830 | Displays | SSP2.1

DeepDust - A Proposed Drilling Project to Probe Continental Climate of the Late Paleozoic Icehouse-Greenhouse Transition

Gerilyn Soreghan, Laurent Beccaletto, Kathleen Benison, Sylvie Bourquin, Natsuko Hamamura, Michael Hamilton, Nicholas Heavens, Linda Hinnov, Cindy Looy, Lily Pfeifer, and Stephane Pochat

The climatic, biotic, and tectonic events of the Permian are amongst the most profound in Earth history. Global orogeny leading to Pangaean assembly culminated by middle Permian time, and included multiple orogenic belts in the equatorial Central Pangaean Mountains, from the Variscan-Hercynian system (east) to the Ancestral Rocky Mountains (west). Earth’s penultimate global icehouse peaked in early Permian time, transitioning to full greenhouse conditions by late Permian time, thus archiving the only example of icehouse collapse on a fully vegetated Earth. The Late Paleozoic Icehouse was the longest and most intense glaciation of the Phanerozoic, with hypothesized low-elevation glaciation posited for both eastern and western tropical Pangaea during early Permian time. Reconstructions of atmospheric composition record the lowest CO2 and highest O2 levels of the Phanerozoic, with average CO2 levels comparable to the Quaternary, rapidly warming climate. Fundamental shifts occurred in atmospheric circulation: a global megamonsoon developed and the tropics became anomalously arid with time. Extreme environments are well documented in the form of voluminous dust deposits, acid-saline lakes and groundwaters, extreme continental temperatures and aridity, and major extinctions/extirpations, ultimately culminating at the Permo-Triassic boundary with the largest extinction of Earth history.

We seek to elucidate paleoclimatic conditions and forcings through the Permian at temporal scales ranging from the millennial to the Milankovitch  and beyond by acquiring continuous core in continental lowlands known to harbor stratigraphically complete records dominated by loess and lacustrine strata. We have identified sites in the western U.S. and Europe as the key sites globally to achieve our objectives, as these represent the western and eastern limits, respectively of the Pangaean tropics. Identified sites harbor arguably the most complete continental Permian sections in the paleoequatorial region, with adjacent paleo-uplands hypothesized to have hosted glaciation. We will also address the nature and character of the modern and fossil microbial biosphere, Mars-analog conditions, and exhumation histories of source regions.

How to cite: Soreghan, G., Beccaletto, L., Benison, K., Bourquin, S., Hamamura, N., Hamilton, M., Heavens, N., Hinnov, L., Looy, C., Pfeifer, L., and Pochat, S.: DeepDust - A Proposed Drilling Project to Probe Continental Climate of the Late Paleozoic Icehouse-Greenhouse Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11830, https://doi.org/10.5194/egusphere-egu2020-11830, 2020.

EGU2020-8856 | Displays | SSP2.1

Complex development of a 300-million-year old subglacial unconformity in southern Namibia

Daniel Paul Le Heron, Christoph Kettler, Neil Griffis, Pierre Dietrich, and Isabel Montañez

The expansion of ice masses across southern Africa during the Late Palaeozoic Ice Age (LPIA) at about 300 Ma has been recognised in the literature for over a century, including the distribution of upland areas in controlling the configuration of ice masses (Davis, 1908). In Namibia, increasing attention has focussed on long and deep palaeovalley networks in the north, but comparatively little work has been attempted in the topographically subdued plains of the south. The desert terrain of the Mariental area exposes diamictites of the Dwyka Formation discontinuously over about 300 km, extending further south to the Noordoewer area at the Namibian-South African border along the Orange River. Whilst examined at a stratigraphic level, the nature of the contact between the Dwyka glacial rocks and underlying lithologies has not been systematically investigated. This paper presents some preliminary results from fieldwork in austral winter 2019, in which we describe a highly varying basal contact that records the processes of growth, flow and expansion of ice masses across this part of Gondwana. Subglacially-produced unconformities may exhibit classic glacially-striated pavements at basin margins, which substitute for soft-sediment striated surfaces in comparatively more “basinal” areas. Where these features are absent, additional criteria may be sought. In Mariental, spectacular soft-sediment shear zones exhibit a combination of brittle and ductile end products are recognised, overprinted by shear bands. This type of subglacial unconformity developed over well differentiated, unconsolidated, siliciclastic materials. Where ice advanced over more poorly sorted material or cannibalised pre-existing diamictites, “boulder-pavements” formed in which in single clast-thick boulder-dominated intervals were facetted and striated in situ by overriding ice. By integrating measurements of striation orientations, fold vergence and palaeocurrent information, former ice flow pathways can potentially be reconstructed over a wide area, which is suspected to have been dominated by Piedmont glaciers.

How to cite: Le Heron, D. P., Kettler, C., Griffis, N., Dietrich, P., and Montañez, I.: Complex development of a 300-million-year old subglacial unconformity in southern Namibia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8856, https://doi.org/10.5194/egusphere-egu2020-8856, 2020.

EGU2020-19962 | Displays | SSP2.1

Long-term lacustrine paleo-productivity and/or paleo-anoxia trends controlled by eccentricity cycles in the continental Autun Basin (France) at the Carboniferous/Permian boundary

Johann Schnyder, Mathieu Martinez, François Baudin, Mathilde Mercuzot, Pierre Pellenard, Christophe Thomazo, Sylvie Bourquin, and Laurent Beccaletto

The organic-rich lacustrine beds of the Autun Basin (France) were deposited from the late Gzhelian (late Carboniferous) to the Sakmarian (early Permian), encompassing the Carboniferous-Permian boundary (∼299 Ma). Those deposits reach up to 1500 m thick, and correspond to a tropical, intra-mountainous late-orogenic basin infilling associated with the Variscan orogeny (Marteau, 1983; Schneider et al., 2006). Organic-rich and laminated facies are attributed to distal lacustrine environments which sometimes alternate with silty to sandy rich deltaic depositional environments (Mercuzot et al., 2019). The four successive formations (respectively the Igornay, Muse, Surmoulin and Millery fms) yield series of oil-shale beds (successively the Moloy, Igornay, Lally Muse, Surmoulin and Les Télots beds) (Marteau, 1983; Garel et al., 2017). The oil-shale beds are at least several m thick in the basin, except for the “Margenne” boghead bed which is only 0.3 m thick (Marteau, 1983; Garel et al., 2017). Recently, accurate U-Pb ages obtained on zircons from volcanic layers of the Autun Basin have placed the Carboniferous-Permian boundary within the Lally oil-shale beds (Pellenard et al., 2017).

In this work, we present a detailed study of the 364-m thick Chevrey 1 core, based on a Rock-Eval pyrolysis survey. The Chevrey 1 core encompasses the successive Igornay and Muse fms., including the Lally oil shale bed and the C/P boundary. TOC varies from 0.2 to 21 wt%, whereas HI values range from 22 to 421 mgHC/gTOC. The Lally oil-shale bed seems to correspond to a 2.5-m thick interval of maximum organic preservation between -145.02 m and -142.55 m, with TOC peaks reaching 12-21 wt%. However, the broad organic-rich interval seems much larger, with TOC around 6.1 wt% on average and HI values of 282 mgHC/gTOC on average between -157.3 m and -126.1 m. Moreover, a long-term progressive increase of TOC accumulation, highlighted by several organic pulses is obvious, starting at -282.4 m and pre-dating the Lally oil shale bed occurrence. We thus evidence for the first time that the Lally oil shale bed corresponds to the short-lived apex of a long-term lacustrine organic rich sequence of increasing paleo-productivity and/or paleo-anoxia that is ∼ 200m in thickness and therefore, is not only limited to a thin, (pluri)-meter-thick organic rich interval associated with short-lived anoxia and/or primary productivity pulse, as previously admitted. These findings rise the question of the paleoenvironmental mechanism(s) behind the occurrence of oil-shale intervals within the Autun Basin. Although further works are needed to fully understand those mechanisms, a preliminary cyclostratigraphy study using the Chevrey 1 TOC record suggests that the organic accumulation was likely controlled by climatic cycles in the Milankovitch frequency bands, and that the ∼ 200 m long-term organic trend may be linked to ~2 Myrs eccentricity.

How to cite: Schnyder, J., Martinez, M., Baudin, F., Mercuzot, M., Pellenard, P., Thomazo, C., Bourquin, S., and Beccaletto, L.: Long-term lacustrine paleo-productivity and/or paleo-anoxia trends controlled by eccentricity cycles in the continental Autun Basin (France) at the Carboniferous/Permian boundary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19962, https://doi.org/10.5194/egusphere-egu2020-19962, 2020.

SSP2.2 – Integrated Stratigraphy - Recent advances in stratigraphic systems and geochronology

EGU2020-16771 | Displays | SSP2.2 | Highlight | SSP Division Outstanding ECS Lecture

Constraints on late Miocene ice volume variability from a global benthic δ18O compilation (8.0-5.0 Ma)

Anna Joy Drury, Thomas Westerhold, David Hodell, Sarah White, Ana Christina Ravelo, and Roy Wilkens

Accurate stable isotope stratigraphies are essential for understanding how past climates are influenced by orbital forcing. Deep-sea benthic foraminiferal δ18O and δ13C stratigraphies can provide precise astronomical age control and record changes in past deep-sea ocean temperatures, global ice volume and the carbon cycle. Our understanding of Plio-Pleistocene climate dynamics has improved through the development of global (LR04; Lisiecki & Raymo, 2005) and regional stacks (Ceara Rise; Wilkens et al., 2017). However, the late Miocene climate system remains poorly understood, in part because the late Miocene benthic foraminiferal δ18O stratigraphy is notoriously low amplitude.

Here, we present the first global late Miocene global benthic foraminiferal δ18O compilation spanning 8.00-5.33 Ma. We formed a “Base Stack” using six continuous benthic stratigraphies from the Atlantic (ODP Sites 982 (N), 926 (E) and 1264 (S)) and Pacific Oceans (IODP Sites U1337 and U1338 (E), ODP Site 1146 (W)). To avoid misidentification of individual excursions between sites, we verified existing splices, generated isotope data where necessary and established independent astrochronologies. To accompany the “Base Stack”, we compiled a “Comprehensive Stack”, which incorporates single-hole benthic δ18O stratigraphies to optimise global coverage.

The new global late Miocene benthic foraminiferal δ18O stack represents a stratigraphic reference section back to 8.00 Ma. The stack is accurately tied to the Geomagnetic Polarity Time Scale between Chrons C3r and C4n.2n using the magnetostratigraphy from IODP Site U1337. We recognise 68 new δ18O Marine Isotope Stages (MIS) between 7.7 and 6.5 Ma. An exceptional global response is imprinted on the dispersed sites between 7.7-6.9 & 6.4-5.4 Ma, when a strong 40 kyr heartbeat dominates the climate system. The origin of these cycles remains unclear. The influence of deep-sea temperature on the benthic δ18O stack is explored at IODP Site U1337 using Mg/Ca data. The dominant 40-kyr δ18O cycles are asymmetric, suggesting at least a partial ice volume imprint and raising the possibility that these cycles relate to early signs of northern hemisphere glaciation.

How to cite: Drury, A. J., Westerhold, T., Hodell, D., White, S., Ravelo, A. C., and Wilkens, R.: Constraints on late Miocene ice volume variability from a global benthic δ18O compilation (8.0-5.0 Ma), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16771, https://doi.org/10.5194/egusphere-egu2020-16771, 2020.

EGU2020-13410 | Displays | SSP2.2

Biostratigraphic correlation of Miocene drillings in the Vienna Basin (Austria) - Integrated Neogene stratigraphy of the largest onshore petroleum province in Central Europe (Vienna Basin, Austria)

Matthias Kranner, Mathias Harzhauser, Oleg Mandic, Werner E. Piller, Stjepan Ćorić, Philipp Strauss, and Wolfgang Siedl

Numerous boreholes of the OMV oil company penetrate the northern Vienna Basin (VB) and several detailed analyses have been conducted on these drilling for years. Despite the effort of decades, the distribution and correlation of Neogene sediments throughout the basin remained ambiguous, due to the complex fault system of the VB. To resolve remaining issues of the Neogene deposits of the area OMV initiated detailed integrative stratigraphic analyses, combining biostratigraphical, lithological, modern 3D seismic- and geophysical data.

Paleontological analysis with main focus on micropaleontology, especially foraminifers, of 46 wells (more than 650 samples) of the northern Vienna Basin have been conducted and help to create a well resolved stratigraphic north – south cross-section of the Neogene units. Of particular interest were lower and middle Miocene (Ottnangian, Karpatian, Badenian and Sarmatian) units. Hardly known and described were the patchy lower Badenian deposits and the much more complex, than previously expected, middle Badenian units. Foraminiferal analysis revealed about 50.000 specimens belonging to 228 species and an allocation to local ecozones, biostratigraphic zonations and ecological reconstructions were established.

Additionally, 50 samples have been analyzed for calcareous nannoplankton which showed extreme reworking throughout all successions.

Some samples displayed the underlying Mesozoic limestones and cutting samples of one well brought insights into the Cenozoic underling Rhenodanubian Flysch units of the Vienna Basin This huge and stratigraphic long ranging set of data did not just reveal major sedimentation gaps during the formation of the modern pull-apart basin, but also provided the opportunity to create a framework for a modern sequence stratigraphy re-assessment of the Vienna Basin.

Furthermore, a formalization of widely used formations in literature will be established in later steps of this project.

This project was financed by the OMV-AG.

How to cite: Kranner, M., Harzhauser, M., Mandic, O., Piller, W. E., Ćorić, S., Strauss, P., and Siedl, W.: Biostratigraphic correlation of Miocene drillings in the Vienna Basin (Austria) - Integrated Neogene stratigraphy of the largest onshore petroleum province in Central Europe (Vienna Basin, Austria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13410, https://doi.org/10.5194/egusphere-egu2020-13410, 2020.

The Cretaceous Normal Polarity Superchron (CNPS, chron C34n, Aptian–Santonian, ~83–118 Ma in CK95 GPTS) is followed in the Campanian by two relatively long chrons (chron C33r, 3.925 My duration and then the normal chron C33n, 5.456 My duration) straddling most of the Campanian stage. The analysis of the geomagnetic reversal history has classically determined two nearly linear segments for the late Cretaceous–Cenozoic interval divided at chron C12r. The length of chrons in the younger interval has no systematic trend and henceforth is considered stationary for statistical analysis with a mean chron length of 0.248–0.219 My while the older segment has 0.749 My mean chron length. The stationarity for this latter interval is attained, however, when the two long polarity chrons C33r and C33n adjacent to the CNPS are omitted. Studies in the weakly magnetized southern England chalk succession and marine Bearpaw Shale in the Canadian Rockies from Alberta have argued about the presence of a number of reversals within C33r and C33n (and C34n). However, all these remain ambiguously established and not incorporated in the standard GPTS despite their significance for theories of geodynamo behavior and potentiality for high-resolution stratigraphic correlations that could notably impact, for instance, the chronostratigraphy of dinosaur-bearing terrestrial Upper Cretaceous of the Western Interior of North America. In any case, no polarity subchrons within C33r or C33n have been reported in any deep-sea record or in the landmark pelagic “scaglia” sections from the Gubbio area in the central Italian Apennines, for which a good integrated biostratigraphy and a thorough paleomagnetic record exists.

Here, we report on a new reverse subchron in the lower part of C33n, informally named the Postalm Fall Subchron (PFS), retrieved in the Postalm section (Gosau Group, Northern Calcareous Alps of Austria). The Postalm section shows a deepening trend from upper Santonian conglomerates and grey shelf marls to pelagic bathyal red marly limestones of Campanian age. The section has previously been studied in the frame of an integrated multi-proxy stratigraphic study that includes high-resolution calcareous plankton biostratigraphy, magnetostratigraphy, stable isotopes, strontium stratigraphy and Fe content. Robust paleomagnetic data has pinpointed the top of C34n that defines the Santonian-Campanian boundary together with key biostratigraphic markers in the lower part of the red unit. The integrated study extents upwards for about 170 m up to calcareous nannofossil zone UC16 in chron C32 in the late Campanian. The cyclic nature of the pelagic sequence has been studied by means of spectral analysis on the limestone/marl couplet thickness data and geochemical proxies that allows identifying the short and long eccentricity cycles and to establish a cyclostratigraphic framework. From 33 new tightly collected samples in this study, 23 display unambiguous reverse polarity and conform the PFS subchron that straddles 3–4 precession cycles (~70 ky duration) within the UC15b calcareous nannofossil biozone. The average sediment accumulation rate at Postalm (~2 cm/ky compared to ~0.6–1 cm/ky at Gubbio) and the high-quality paleomagnetic signal have favored this discovery. The absolute age calibration and related geomagnetic and chronostratigraphic implications would be discussed.

How to cite: Dinarès-Turell, J., Wolfgring, E., and Wagreich, M.: A new reverse subchron (C33n.1r) in the Campanian: astronomical duration estimate and geomagnetic/chronostratigraphic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1677, https://doi.org/10.5194/egusphere-egu2020-1677, 2020.

EGU2020-10299 | Displays | SSP2.2

Chemostratigraphy of Triassic successions on the southern Barents Sea Shelf – preliminary results from XRF Core Scanning.

Sigrun Maret Kvendbø Hegstad, Juha Ahokas, Matthias Forwick, and Sten-Andreas Grundvåg

The Barents Sea Shelf on the north-western corner of the Eurasian plate has a complex geological history, comprising large-scale processes controlled by plate movements, climatic variations and changing depositional environments. During the last decades, as the search for hydrocarbons within the area gained increased interest, Triassic sequences have been the target of comprehensive investigations. In our project, we test the potential of improving the correlation of Triassic strata using X-ray fluorescence (XRF) core scanning of siliciclastic drill cores.

XRF core scanning is a frequently used method on soft sediment cores, e.g. within marine geology and palaeo-climate studies. However, the applicability of this method on drill cores from exploration wells from the hydrocarbon industry has not been tested so far. We use this method to establish geochemical stratigraphic parameters, as well as to contribute to the identification of provenances, reconstruct palaeo-envrionments, and support the correlation of drill cores. This provides a novel, fast, inexpensive, and non-destructive method to be applied in hydrocarbon exploration, as well as in studies of lithified siliciclastic sediments in general.

Triassic intervals from 24 shallow drill cores from the southern Barents Sea (Finnmark Platform, Nordkapp Basin, Svalis Dome, Maud Basin and Bjarmeland Platform) provide the basis for this study. The cores have previously been comprehensively studied and described by IKU (the Norwegian Continental Shelf Institute; today SINTEF Petroleum Research), and studies of provenance and palaeo-environment have also been performed (e.g. Vigran et al., 1986). This data makes it possible to compare the geochemical units established in this study with other stratigraphic information.

We present preliminary results of establishing geochemical units from XRF core scanning, and the use of these for correlation within known stratigraphic frameworks and between geographic areas, as well as to increase the understanding of changes in provenance and palaeo-environments within these successions in the Barents Sea.

References:
Vigran, J.O., G. Elvebakk, T.L. Leith, T. Bugge, V. Fjerdingstad, R.M. Goll, R. Konieczny, and A. Mørk. 1986. 'Dia-Structure Shallow Drilling 1986. Main data report. IKU Rep. No. 21.3420.00/04/86, 242 pp'.

 

How to cite: Kvendbø Hegstad, S. M., Ahokas, J., Forwick, M., and Grundvåg, S.-A.: Chemostratigraphy of Triassic successions on the southern Barents Sea Shelf – preliminary results from XRF Core Scanning., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10299, https://doi.org/10.5194/egusphere-egu2020-10299, 2020.

EGU2020-10839 | Displays | SSP2.2

Geochronologic constraints on the Shuram excursion in Oman

Marjorie Cantine, Alan Rooney, Ulf Linneman, Mandy Hofmann, Richard Albert, Irene Gomez Perez, Badar Baloushi, Axel Gerdes, and Kristin Bergmann

            The rise of animals occurred during an interval of Earth history that witnessed highly dynamic atmosphere-ocean redox conditions; regional, transient glaciations; extraordinarily low magnetic field intensities potentially related to inner core formation; and perturbations to the global carbon cycle of a size not seen before or since. The largest of these, the Shuram carbon isotope excursion, has been invoked as a driving mechanism for, or consequence of, various biological and geological events during the Ediacaran Period. However, there are a number of major controversies regarding the Shuram, including its timing. Without age constraints on its onset or duration, it is impossible to confidently connect the Shuram Event with any biological or geological upheavals.

Here, we apply multiple methods, including Re-Os on black shales and U-Pb LA-ICP-MS dating on carbonates, to well-preserved Ediacaran stratigraphy from Oman, deriving new age controls in previously undated parts of the stratigraphy. Our new data show that paired Re-Os shale and U-Pb carbonate analyses constrain the onset and duration of the Shuram excursion in Oman. The results—which are consistent with recent age constraints on Shuram-bearing stratigraphy from Northwest Canada (Rooney et al. 2019, Goldschmidt)—demonstrate the utility of leveraging multiple geochronological techniques within a single basin to constrain deposition in deep to shallow depositional environments. The results also provide key absolute age constraints on the onset of the Shuram excursion in the stratigraphy where it was first defined, critical for testing global correlation schemes, constructing a temporal framework for the Ediacaran period, and identifying causal mechanisms during this interval of geobiological and geodynamic dynamism.

 

How to cite: Cantine, M., Rooney, A., Linneman, U., Hofmann, M., Albert, R., Gomez Perez, I., Baloushi, B., Gerdes, A., and Bergmann, K.: Geochronologic constraints on the Shuram excursion in Oman, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10839, https://doi.org/10.5194/egusphere-egu2020-10839, 2020.

EGU2020-10874 | Displays | SSP2.2

A posteriori verification methodology for astrochronology: a step further to improve the falsifiability of cyclostratigraphy

Sébastien Wouters, Michel Crucifix, Matthias Sinnesael, Anne-Christine Da Silva, Christian Zeeden, Miroslav Zivanovic, Frédéric Boulvain, and Xavier Devleeschouwer

Cyclostratigraphy is increasingly used to improve the Geologic Time Scale and our understanding of past climatic systems. However, except in a few existing methodologies, the quality of the results is often not evaluated.

We propose a new methodology to document this quality, through a decomposition of a signal into a set of narrow band components from which instantaneous frequency and amplitude can be computed, using the Hilbert transform. The components can be obtained by Empirical Mode Decomposition (EMD), but also by filtering a signal (be it tuned or not) in any relevant way, and by subsequently performing EMD on the signal minus its filtered parts.

From that decomposition, verification is performed to estimate the pertinence of the results, based on different concepts that we introduce:

  •  Integrity quantifies to what extent the sum of the components is equal to the signal. It is defined as the cumulated difference between (1) the signal, and (2) the summed components of the decomposition. EMD fulfils integrity by design, except for errors caused by floating-decimal arithmetic. Ensemble Empirical Mode Decomposition (EEMD) may fail to satisfy integrity unless noisy realisations are carefully chosen in the algorithm to cancel each other when averaging the realisations. We present such an algorithm implemented in R: “extricate”, which performs EEMD in a few seconds.
  •  Parsimony checks that the decomposition does not generate components that heavily cancel out. We propose to quantify it as the ratio between (1) the cumulated absolute values of each component (except the trend), and (2) the cumulated absolute values of the signal (minus the trend). The trend should be ignored in the calculation, because an added trend decreases the parsimony estimation of a similar decomposition.
  •  IMF departure (IMFD) quantifies the departure of each component to the definition of intrinsic mode functions (IMF), from which instantaneous frequency can reliably be computed. We define it as the mean of the absolute differences of the base 2 logarithms of frequencies obtained using (1) a robust generalized zero-crossing method (GZC, which simplifies the components into extrema separated by zero-crossings) and (2) a more local method such as the Hilbert Transform.
  •  Reversibility is the concept that all initial data points are preserved, even after linear interpolation and tuning. This allows to revert back to the original signal and discuss the significance of each data point. To facilitate reversibility we introduce the concept of quanta (smallest depth or time interval having significance for a given sampling) and an algorithm computing the highest rational common divisor of given values in R: “divisor”.

This new methodology allows to check the final result of cyclostratigraphic analysis independently of how it was performed (i.e. a posteriori). Once the above-mentioned concepts are taken into account, the instantaneous frequencies, ratios of frequencies and amplitudes of the components can be computed and used to interpret the pertinence of the analysis in a geologically meaningful way. The instantaneity and independence of frequency and amplitude so obtained open a new way of performing time-series analysis.

How to cite: Wouters, S., Crucifix, M., Sinnesael, M., Da Silva, A.-C., Zeeden, C., Zivanovic, M., Boulvain, F., and Devleeschouwer, X.: A posteriori verification methodology for astrochronology: a step further to improve the falsifiability of cyclostratigraphy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10874, https://doi.org/10.5194/egusphere-egu2020-10874, 2020.

EGU2020-1531 | Displays | SSP2.2

Detecting original variations in calcite and aragonite input in limestone-marl alternations

Theresa Nohl, Manuel Steinbauer, Matthias Sinnesael, and Emilia Jarochowska

The origin of carbonatic rhythmically alternating lithologies, called limestone-marl alternations (LMA), is a lively debated topic. LMA are commonly used as high-resolution cyclostratigraphic record, but diagenetic studies indicate that not all LMA reflect genuine differences in the original composition driven by environmental changes. LMA with a clear difference between limestones and marls in their ratios of diagenetically inert elements such as Al2O3/TiO2 can be identified as the product of primary sedimentary differences, i.e. variation affecting the terrigenous compound of the precursor sediment. In contrast, LMA without these differences could be the product of (1) variations in the carbonate compounds of the precursor sediment, i.e. aragonite and calcite input, or of (2) the distortion of the latter by diagenetic carbonate redistribution, or of (3) diagenetic carbonate redistribution in a homogenous precursor sediment. The problem of differentiating these three cases is known as the diagenetic dilemma. The question is, how can the composition in the original CaCO3 compound (aragonite, calcite) of the precursor sediment be reconstructed? This study provides a new approach to tackle the diagenetic dilemma. According to the model of differential diagenesis, the concentration of trace elements is inversely proportional to the amount of diagenetically redistributed carbonate. Consequently, the difference between the ratios of diagenetically inert elements from two adjacent beds is a measure for carbonate redistribution between them. This is quantifiable by calculating the vector length between these ratios for two adjacent beds. The new approach is illustrated here by evaluating 75 contiguous limestone and marl beds from the Högklint Formation (Silurian) on Gotland, Sweden. To test the new method, trace elements in these beds were compared according to their relative solubility during diagenesis. All elements which are either bound to clay minerals or fit into the calcite lattice show the same pattern of vector lengths (

How to cite: Nohl, T., Steinbauer, M., Sinnesael, M., and Jarochowska, E.: Detecting original variations in calcite and aragonite input in limestone-marl alternations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1531, https://doi.org/10.5194/egusphere-egu2020-1531, 2020.

EGU2020-141 | Displays | SSP2.2

Assessing the rift to sag evolution of Parnaiba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance

Rodrigo Irineu Cerri, Lucas Verissimo Warren, and Mario Luis Assine

Assessing the rift to sag evolution of Parnaíba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance

Rodrigo I. Cerri1; Lucas V. Warren1; Mario L. Assine1
1 São Paulo State University (UNESP), Institute of Geosciences and Exact Sciences, Rio Claro, Brazil.

Nowadays one of the most prolific topics in the geological sciences is the origin of intracratonic basins. Despite many Paleozoic examples in which rift systems occur under these basins, there is no consensus about how these mechanical subsidence basins influenced the origin of continental-scale intracratonic basins. Due to its inherent complexity, the understanding of this problem only comes from integrated studies based in multi-proxy analysis, placing it on the frontier of modern science. In the northeast part of Brazil, the Late-Precambrian to Early-Cambrian Jaibaras Basin is interpreted as the precursor rift of the Parnaíba intracratonic Basin, following a simple model of mechanical-to-thermal subsidence evolution. In order to assess the provenance patterns and maximum depositional ages (MDA) between the rift and cratonic phases of these basins, we present a novel detrital zircon U-Pb ages of rocks from the Aprazível and Ipu formations. The main goals of this approach is to identify provenance changes (or similarities) between the last rift related sedimentary unit of the Jaibaras Basin and the first intracratonic related sedimentary unit form the Parnaíba Basin, thus allowing to test the rift-to-sag hypothesis. The MDA for the Aprazível Formation (ca. 499 ± 5 Ma, Furongian to Miaolingian) indicates a Late Cambrian age for the upper part of the Jaibaras Basin. The Ipu Formation records a MDA of ca. 528 ± 11 Ma (Terreneuvian to Series 2, Early Cambrian). However, due to its stratigraphic position relative to the lower Aprazível (499 ± 5 Ma) and upper Tianguá (Early Silurian, Llandovery) formations, the depositional age of this unit is probably younger (Late-Cambrian to Early-Ordovician). Thus, the successions deposited in the end of the rift and the beginning of the sag phase are clearly separated by a regional unconformity (10 to 30 Ma). We also identify the complete absence of Cambrian zircons followed by a significant increase in Paleoproterozoic ones in the Ipu Formation. Although these units were significantly sourced by Neoproterozoic terrains (especially Ediacaran), this modification indicates an interesting change in provenance between the rift to sag basins. The detrital zircon provenance, helped by a consistent paleocurrent analysis, reveal local source areas for the Aprazível Formation and a consistent distal sedimentary transport towards NW for the Ipu Formation. This suggests that the primary sources for the first cratonic unit of Parnaíba Basin were located at the orogenic areas related with the Neoproterozoic Brasiliano/Pan-African Orogeny at the south/southern of Borborema Province (e.g. Rio Preto, Riacho do Pontal and Rio Grande do Norte metamorphic belts). Unlike the alluvial-related Aprazível Formation, the Ipu Formation characterizes a huge fluvial system that flowed towards NW, probably following a homoclinal ramp-like tilted and opened to the paleomargins of Gondwana.

How to cite: Cerri, R. I., Warren, L. V., and Assine, M. L.: Assessing the rift to sag evolution of Parnaiba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-141, https://doi.org/10.5194/egusphere-egu2020-141, 2020.

EGU2020-12101 | Displays | SSP2.2

U-Pb CA-IDTIMS geochronology of the Late Paleozoic glacial and post-glacial deposits in southern Paraná Basin

Joice Cagliari, Mark D. Schmitz, Ernesto L. C. Lavina, and Renata G. Netto

The Late Paleozoic Ice Age (LPIA), one of the best known and prolonged glaciation events in Earth's history, resulted in the deposition of glacial sediments over Gondwana. The terminal deglaciation, a diachronic event starting earlier at the western and later in the eastern part of the continent, caused sea level rise and the widespread deposition of transgressive sedimentary successions. The Paraná Basin is one of these basins recording both glacial influenced (Itararé Group) and post-glacial (Guatá Group) deposits. However, the absence of Carboniferous and Permian guide fossils has motivated a chronostratigraphic approach based on plants and palynomorphs, which associated with sparse radioisotopic ages have suggested that transition between the glacial-influenced and the post-glacial succession would have occurred in the Sakmarian, early Permian (Holz et al., 2010).  These results are in conflict with recent studies that indicate LPIA glacial deposits are constrained to the Carboniferous (Cagliari et al., 2016; Griffis et al., 2019). Therefore, in this study we present new high-precision single-crystal CA-ID-TIMS U-Pb radioisotopic ages for the glacial influenced (one samples) and post-glacial (six samples) deposits in the southern Paraná Basin. Along with these new radioisotopic ages, a Bayesian age-depth model was applied to constrain the age of the LPIA demise in the southern Paraná Basin, which also represents the icehouse-greenhouse transition. The resulting age for the Rio do Sul Formation, topmost unit of the Itararé Group, is Ghzelian (Carboniferous). For the Rio Bonito Formation, basal Guatá Group, all samples are Asselian (Permian). The results reinforce that glacial-influenced deposits in the southern Paraná Basin are constrained to the Carboniferous. Based upon the depth-age model, the icehouse to greenhouse transition likely occurred in the Late Carboníferous. The integration between our results and recent published high-resolution U-Pb ages allowed us to detail the Carboniferous-Permian chronostratigraphic framework of the southern Paraná Basin.

 

References:

Holz, M., França, A.B., Souza, P.A., Iannuzzi, R., Rohn, R. (2010). A stratigraphic chart of the Late Carboniferous/Permian succession of the eastern border of the Paraná Basin, Brazil, South America. Journal of South American Earth Sciences 29, 381–399.

Cagliari, J., Philipp, R.P., Buso, V.V., Netto, R.G., Hillebrand, P.K., Lopes, R.C.L., Basei, M.A.S., Faccini, U.F. (2016). Age constraints of the glaciation in the Paraná basin: Evidence from new U–Pb dates. Journal of the Geological Society 173, 871–874.

Griffis, N.P., Montañez, I.P., Mundil, R., Richey, J., Isbell, J., Fedorchuk, N., Linol, B., Iannuzzi, R., Vesely, F., Mottin, T., Rosa, E., Keller, B., Yin, Q. (2019). Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana. Geology 47, 1146–1150.

How to cite: Cagliari, J., Schmitz, M. D., C. Lavina, E. L., and G. Netto, R.: U-Pb CA-IDTIMS geochronology of the Late Paleozoic glacial and post-glacial deposits in southern Paraná Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12101, https://doi.org/10.5194/egusphere-egu2020-12101, 2020.

The Ladinian/Carnian boundary (LCB) is defined at Prati di Stuores (GSSP of the Carnian Stage) with the First Appearance Datum (FAD) of ammonoid Daxatina canadensis and approximated by the FAD of conodont Paragondolella polygnathiformis. The age of the Carnian is currently estimated at ca. 237 Ma using the composite magnetostratigraphy of the main late Ladinian basinal sequences from literature, calibrated with a U-Pb radiometric age of 237.77±0.14 Ma from the Rio Nigra section in Alpe di Siusi (Dolomites, NE Italy). In the attempt to improve the precision of the Geomagnetic Polarity Time Scale (GPTS) around the LCB we investigated for magnetostratigraphy the Punta Grohmann section in the Dolomites. The Punta Grohmann section is calibrated with ammonoids (the FAD of Zestoceras cf. lorigae is considered a proxy of the LCB) and is chronologically constrained by two U-Pb radiometric ages from zircons (237.58±0.04 Ma; 237.68±0.05 Ma). The magnetostratigraphy of the Punta Grohmann section has been successfully correlated to other Ladinian-Carnian magnetostratigraphic sections (Prati di Stuores, Mayerling, Rio Nigra) and compared to the most recent version of the Triassic Geomagnetic Polarity Time Scale (GPTS). The LCB at Prati di Stuores is calibrated through magnetostratigraphy with the U-Pb radiometric datings of Punta Grohmann, obtaining an age of the LCB of ca. 237.4 Ma. Therefore, the Ladinian should be ca. 4 Myr long and the Carnian ca. 10.4 Myr long.

How to cite: Maron, M., Muttoni, G., Ghezzi, M., Rigo, M., and Gianolla, P.: New magnetostratigraphy from the Punta Grohmann section (Dolomites, NE Italy): an improvement of the Geomagnetic Polarity Time Scale around the Ladinian/Carnian boundary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11836, https://doi.org/10.5194/egusphere-egu2020-11836, 2020.

EGU2020-10406 | Displays | SSP2.2

Environmental controls on the magnetic properties of Upper Jurassic black shales on the Norwegian shelf

Jonas Kristensen Kimerud and Maarten Felix

This project examines organic rich black shales from the Upper Jurassic on the Norwegian shelf. The aim is to investigate the relationship between the depositional environment as determined from facies descriptions and the magnetic properties of the black shale. An additional aim is to relate cyclicity in the magnetic measurements to the Milankovitch cycles using time series analysis techniques. Cores from four different location on the Norwegian shelf were investigated using sedimentological description, facies analysis, and measuring of bulk magnetic susceptibility. The cores were drilled in the Skagerrak Region in the North Sea (core 13/01-U-01), Møre-Trøndelag Region of the Norwegian Sea (core 6307/07-U-03 A), Lofoten Region of the Norwegian Sea (core 6814/04-U-02), and the Nordkapp Basin in the NE Barents Sea (core 7230/05-U-02).

Based on preliminary results from the sedimentological description and facies analysis, the sediments were separated into facies: (1) massive black mudstone, (2) siderite cemented mudstone, (3) lenticular laminated sandy mudstone, (4) flaser laminated muddy sandstone with silt clasts, (5) heavily bioturbated silty sandstone, and (6) sandstone. Deposits like high-density turbidites, debrites and slump deposits, as well as post depositional processes like bioturbation, pyrite- and siderite-cementation were found in the cores. Deposits from mass movements can be thick, but they are deposited over a short time interval. It is therefore important to remove the mass movement deposits in the cyclostratigraphic analysis. The high iron content in the siderite and pyrite cemented deposits must be taken into account in regard to the magnetic susceptibility measurements. The magnetic susceptibility data will be used to correlate the cores in the homogeneous black shale sections.

How to cite: Kimerud, J. K. and Felix, M.: Environmental controls on the magnetic properties of Upper Jurassic black shales on the Norwegian shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10406, https://doi.org/10.5194/egusphere-egu2020-10406, 2020.

A new δ13C reference curve for the Mesozoic is presented. This has been constructed using in excess of 10,000 published analyses of bulk carbonate sediments extracted from published literature.  Available data from sections world-wide were compiled for each stage and the stratigraphic trends visually compared.  Data sets used to construct the composite reference curve were those offering patterns that are consistent with other sections and offer the highest stratigraphic resolution (close sample spacing), constrained by biostratigraphic first appearance (FAD) and last appearance datum (LAD) levels, magnetostratigraphy, radiometric dates and cyclostratigraphy.  Preference was given to time series that showed the least scatter.  Pelagic carbonates proved most suitable for these purposes but data from hemipelagic and shallow-water carbonate sections were included where necessary. 

Age calibration was achieved using stage boundary ages, biostratigraphic FAD and LAD datums levels, and chron boundary ages derived from the new GTS2020 timescale.  Where possible, data from multiple authors and/or multiple stratigraphic sections were age-calibrated and interleaved to generate composite profiles for each time interval.  Data from individual stages were spliced together with offsets being avoided wherever possible; minor offsets in values were corrected where necessary to generate a continuous smooth time series.  The uneven geographical spread of published data and suitable lithofacies has resulted in source information being derived from different regions for different time intervals.  For example, the Early – Middle Triassic curve is constructed from eastern Paleotethys sections (South China), the Jurassic and Early Cretaceous curves principally from Tethyan areas of Europe and North Africa (Morocco, Portugal, southern France, Switzerland, northern Italy), and the Late Cretaceous curve from the Boreal Sea of northern Europe (England, Denmark).  The global significance of the resulting curves requires further testing.

The stratigraphic positions and recalibrated ages of positive and negative δ13C excursions that define carbon isotope events (CIEs) are presented.  These reflect major perturbation in the global carbon cycle.  Changes in the production and burial of organic matter on land and in the oceans, plus the balance between carbonate versus organic carbon deposition, are the principal mechanisms driving the observed long-term stratigraphic trends and short-term excursions.  These are linked to palaeogeographic and palaeoceanographic change, with climate and sea-level fluctuations driven by orbital forcing, tectonics, and volcanic events.  The emplacement of large igneous plateaus (LIPs) and associated volcanism likely played a major role in driving many of the palaeoenvironmental perturbations reflected in the carbon isotope stratigraphy. 

The most prominent CIEs characterise the Early Triassic with amplitudes exceeding 5‰ δ13Ccarb (VPDB), with other notable excursions in the mid-Carnian, mid-Norian and Rhaetian.  The Toarcian negative CIEs are the stand-out feature of the Jurassic, but multiple lower amplitude CIEs occur throughout, notably in the Hettangian, Bajocian Callovian and Oxfordian.  The most prominent Cretaceous CIEs in the Valanginian, Aptian and at the Cenomanian/Turonian boundary are linked to Oceanic Anoxic Events.

How to cite: Jarvis, I.: Secular variation in the global carbon cycle during the Mesozoic: a new composite carbonate δ13C reference curve calibrated to GTS2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13553, https://doi.org/10.5194/egusphere-egu2020-13553, 2020.

EGU2020-4462 | Displays | SSP2.2

A new Berriasian to Turonian carbon isotope stratigraphy for the Boreal Realm

André Bornemann, Jochen Erbacher, and Martin Blumenberg

EGU2020-13863 | Displays | SSP2.2 | Highlight

A chemostratigraphic framework for the type-Maastrichtian

Johan Vellekoop, Pim Kaskes, Sinnesael Matthias, John W. M. Jagt, Robert P. Speijer, and Philippe Claeys

The youngest time interval of the Cretaceous Period is known as the Maastrichtian, a reference to the marine strata exposed in the area surrounding the city of Maastricht, in the Netherlands-Belgium border region. The stratigraphic succession at the original type-locality of the Maastrichtian (ENCI quarry, NL) only covers the upper part of the Maastrichtian Stage as it is nowadays defined. However, in combination with similar rock sequences in several other quarries (e.g. Hallembaye, Curfs) in the region, a substantial part of the Maastrichtian Stage is represented.

While the type-Maastrichtian strata have provided a wealth of paleontological data, comparatively little geochemical work has been carried out on this succession. So far, the age assessment of, and stratigraphic correlation with, the type-Maastrichtian has been largely based on biostratigraphy and preliminary attempts at cyclostratigraphy, techniques that are hampered by bioprovincialism and the presence of stratigraphic gaps in the succession. In recent years, stable carbon isotope stratigraphy has been proven to be a powerful tool for correlating Upper Cretaceous strata on a global scale. When calibrated with biostratigraphic events, carbon isotope stratigraphy can be used to test the synchroneity of bio-events and reconcile inter-regional biostratigraphic schemes. Therefore, we have generated the first high-resolution stable carbon isotope stratigraphy for the type-Maastrichtian, using the extensive sample set acquired in the context of the Maastrichtian Geoheritage Project. In combination with elemental data generated using µXRF (e.g. Ca, Si, Al, Ti, Fe wt%), our record presents the first high-resolution chemostratigraphy for the type-Maastrichtian. This new chemostratigraphic framework enables us to refine the age-model for studied strata, and allows a better regional and global correlation with the type-Maastrichtian successions, placing the paleontological records from the type-Maastrichtian in a global context.  

How to cite: Vellekoop, J., Kaskes, P., Matthias, S., Jagt, J. W. M., Speijer, R. P., and Claeys, P.: A chemostratigraphic framework for the type-Maastrichtian, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13863, https://doi.org/10.5194/egusphere-egu2020-13863, 2020.

EGU2020-5033 | Displays | SSP2.2

Upper Cretaceous and Eocene litho- and biostratigraphy of the Istria Basin (NW Black Sea)

Madalina Eliza Anton, Ioan Munteanu, Corneliu Dinu, and Mihaela C. Melinte-Dobrinescu

The Istria basin, situated in the NW Black Sea, is composed of Mesozoic to Cenozoic successions. The opening of the Western Black Sea, including the Istria basin, initiated in the late Early Cretaceous. Rifting and expansion continued in the Late Cretaceous, while in the Late Paleogene a compressional regime settled. In the Middle Eocene, the Western Black Sea basin margin inverted, due to the collision of Pontides and Taurides belts (Okay and Tüysüz, 1999; Dinu et al., 2005). The continuing compression shaped this basin until the Middle Miocene (Ionescu et al., 2002).

 

Tens of wells for hydrocarbon exploration were drilled in the Istria basin (Romanian offshore) since the 70’s. In this study, we have interpreted the acquired core reports containing litho- and biostratigraphic data. Based on identified calcareous nannofossil biozones, a continuous deposition was found in the Cenomanian-Maastrichtian interval. Lithologically, the Upper Cretaceous is composed of carbonatic rocks, such as limestones and marlstones, with intercalations of calcareous sandstones. The Eocene deposits are unconformably lying on Upper Cretaceous ones. Lithologically, the Eocene is characterized by alternating calcareous and siliciclastic sandstones. Biostratigraphy on planktonic and benthic foraminifers, as well as calcareous nannofossils, indicate a late Early Eocene to Middle Eocene age (i.e., late Ypresian to Bartonian).

 

The observed large thickness variation, from W towards E in the Istria Basin, is a consequence of various tectonic settings. The western part (i.e., the Sinoe area) is situated in the hanging-wall of an inverted normal fault filled with Early Eocene deposits and was inverted by high angle thrust fault during the Late Eocene-Oligocene interval. In the E (i.e., the Lebǎda area), there is an uplifted normal fault foot-wall, showing a reduced thickness in comparison with the W (Munteanu et al., 2011). The erosion level increased eastward, removing the entire Upper Eocene and the top of the Middle Eocene. This feature may be linked to a large sea level drop towards the Eocene top, with subaerial erosion and development of large-scale canyons system at the self to slope transition, like the Plio-Quaternary Viteaz Canyon of the NW Black Sea.

 

The financial support for this paper was provided by the Romanian Ministry of Research and Innovation, through the Programme Development of the National System of Research – Institutional Performance, Project of Excellence for Rivers-Deltas-Sea Systems No. 8PFE/2018.

 

References

Dinu, C., Wong, H.K., Țambrea, D., Mațenco, L., 2005. Stratigraphic and structural characteristics of the Romanian Black Sea shelf. Tectonophysics, 410, 417-435.

Ionescu, G., Sisman, M., Cataraiani, R., 2002. Source and reservoir rocks and trapping mechanism on the Romanian Black Sea shelf. In: Dinu, C., Mocanu, V. (Eds.) Geology and Tectonics of the Romanian Black Sea Shelf and its Hydrocarbon Potential. BGF Special Volume, 2, 67–83.

Munteanu, I., Maţenco, L., Dinu, C., Cloetingh, S., 2011. Kinematics of back-arc inversion of the western Black Sea basin. Tectonics, 30, TC5004.

Okay, A.I., Tüysüz, O., 1999. Tethyan sutures of northern Turkey. Geological Society, London, Special Publications, 156, 475-515.

How to cite: Anton, M. E., Munteanu, I., Dinu, C., and Melinte-Dobrinescu, M. C.: Upper Cretaceous and Eocene litho- and biostratigraphy of the Istria Basin (NW Black Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5033, https://doi.org/10.5194/egusphere-egu2020-5033, 2020.

EGU2020-22410 | Displays | SSP2.2

Timing and pacing of middle to late Miocene intensification of the Indian Ocean-Atmospheric circulation system

Gerald Auer, Beth Christensen, Or Bialik, Nanako Ogawa, Ryo Yamaoka, Mary-Elizabeth Antoulas, David De Vleeschouwer, Dick Kroon, Naohiko Ohkouchi, and Werner Piller

A recent biostratigraphic re-evaluation of Ocean Drilling Program (ODP) Site 722 (Bialik et al., accepted, Paleoceanogr. and Paleocl.) provides new insights into the history of monsoon driven upwelling in the Arabian Sea between 15 and 8.5 Ma. They suggest the modern monsoon was only established after tectonic preconditioning, linked to the uplift of the Himalayas, closure of the Tethyan Seaway, and the inception of Indonesian Throughflow restriction. But the requisite topography for the Indian monsoon was already in place by at least the late early Miocene which suggests another driver. However, as northern hemisphere latitudinal heat gradients continued to be shallower than modern throughout the Miocene, steepening southern hemisphere gradients during the middle Miocene glaciation of Antarctica ~14.8 Ma (Pound et al., 2012, Earth-Sci. Rev., 112) may have played an important role in pacing the monsoon system during the middle to late Miocene.

Here we further explore these findings by using recently acquired X-ray fluorescence (XRF) core scanning data from two additional ODP sites located in the central (Site 707) and southern (Site 752) Indian Ocean. We trace the timing and pacing of these environmental changes along a cross hemispheric transect within key areas of the larger Indian Ocean-Atmospheric system: (1) the monsoonal upwelling regions along the Oman Margin (Site 722); (2) the Somali/Findlater jets (Site 707); and (3) the high-pressure zone in the southern horse latitudes (Site 752).

Using updated age constraints at all sites, we show that the intensification of upwelling at Site 722 is tightly linked to climatic and oceanographic changes in the southern high latitudes (e.g., Groeneveld et al., 2017; Sci. Adv.). This close co-evolution of southern hemisphere climatic shifts and monsoon dynamics hints at a strong contribution of increasing southern hemisphere thermal gradients on the middle to late Miocene evolution of the Indian Ocean circulation system and Indian monsoon dynamics. Our findings thus re-emphasize the Indian summer monsoon as the result of a complex cross-hemispheric ocean-atmospheric system spanning the Indo-Pacific (e.g., Gadgil, 2018, J. Earth Syst. Sci., 127). We postulate that the Indian Ocean-Atmospheric system experienced a gradual intensification that began after the Middle Miocene Climatic Optimum with Antarctic Ice Sheet expansion. These changes then culminated in a synchronous shift ~11 Ma during the Ser4/Tor1 sea level lowstand (Haq et al., 1987; Science, 235). Future chrono-, chemo- and cyclostratigraphic work at ODP Sites 707 and 752 will further help to constrain the timing of these events, and fully place them in the context of the global climatic evolution during the Miocene.

How to cite: Auer, G., Christensen, B., Bialik, O., Ogawa, N., Yamaoka, R., Antoulas, M.-E., De Vleeschouwer, D., Kroon, D., Ohkouchi, N., and Piller, W.: Timing and pacing of middle to late Miocene intensification of the Indian Ocean-Atmospheric circulation system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22410, https://doi.org/10.5194/egusphere-egu2020-22410, 2020.

EGU2020-4700 | Displays | SSP2.2

StratigrapheR: making and using lithologs in R

Xavier Devleeschouwer, Anne-Christine Da Silva, Frédéric Boulvain, and Sébastien Wouters

StratigrapheR is an open-source integrated stratigraphy package. It is available in the free software environment R (https://CRAN.R-project.org/package=StratigrapheR) and is designed to generate lithologs in a semi-automated way, to process stratigraphical information, and to visualize any plot along the lithologs in the R environment.

The basic graphical principle behind StratigrapheR is the incremental addition of elements to a drawing: a plot is opened, and graphical elements are successively added. This allows compartmentalisation of the drawing process, as well as the superposition of different plots for comparison. For instance a litholog of a single section can be written as a single function including all the drawing sub-functions, and be integrated in a larger plot, for instance to be correlated to other sections or to show proxy data.

The StratigrapheR package is designed for efficient work, and minimum coding, while still allowing versatility. The lithological information of beds (upper and lower boundary, hardness, lithology, etc.) is converted into polygons. All polygons are drawn together using a single function, and each polygon can have its personalised symbology allowing to distinguish lithologies. A similar workflow can be used for plotting proxies while distinguishing each sample by their lithology. Vector graphics can be imported as SVG files, and precisely drawn with the lithologs to serve as symbols or complex elements. Every type of symbol is plotted by calling one single function which repeats the drawing for each occurrence of the represented feature. This illustrates that the amount of work invested to make lithologs using StratigrapheR is related to their complexity rather than their length: a long but monotonous litholog (e.g. of marl-limestone alternations) only takes a few lines of code to generate.

The StratigrapheR package also provides a set of functions to deal with selected stratigraphic intervals (for instance in the [0,1[ form): they allow simplification, merging, inversion and visualisation of intervals, as well as identifying the samples included in the given intervals, and characterising the relation of the intervals with each other (overlap, neighbouring, etc.). StratigrapheR includes PDF and SVG generation of plots, of any dimension. The generated PDF can even store multiple plots in a single file (each plot on a different page) to document data processing comprehensively.

How to cite: Devleeschouwer, X., Da Silva, A.-C., Boulvain, F., and Wouters, S.: StratigrapheR: making and using lithologs in R, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4700, https://doi.org/10.5194/egusphere-egu2020-4700, 2020.

EGU2020-20017 | Displays | SSP2.2

U-Pb dating of carbonate-fluorapatite: a potential chronological tool for ancient marine sediments

Gary O'Sullivan, Rory Mortimore, David Chew, and Stephen Daly

Carbonate-fluorapatite (CFA) is a common early diagenetic component of marine sedimentary sequences. Nodules, laminae and shell overgrowths or infills composed of CFA are relatively common features in phosphorites, carbonates and other marine sediments (e.g., Datillo et al., 2016). CFA U-Pb dating thus has potential application as a chronometer in a wide variety of ancient marine sediments, particularly in those marine sections lacking diagnostic faunal and/or floral assemblages, or well-dated volcanogenic horizons.

In order to test empirically whether accurate and precise U-Pb ages can be obtained from CFA using LA-ICPMS we have analysed CFA from a several marine sediment samples. These include samples of Cretaceous phosphatic chalk from southern England, phosphatic nodules from the Cretaceous of northern Ireland and western Scotland, and a sample from a laterally extensive Carboniferous phosphorite in western Ireland. Ages obtained from CFA in these rocks can be precise (as low as c. 0.55% 2SE error in one sample), and are all unimodal. U-Pb ages of CFA, however, range from stratigraphically-consistent ages to ages that record much younger events than their host rock stratigraphic ages.

While ‘ages’ obtained from CFA may be precise, what each of these ages represents geologically requires further study. The genetic relationship between phosphate and its host rock must be petrographically studied to understand the correspondence between the phosphatic and other components of these rocks in terms of their depositional and diagenetic histories. It is apparent that in some cases CFA will record deposition or early diagenesis, but that the U-Pb system in CFA can be overprinted by later tectonic events in other cases. In addition, whilst LA-ICPMS U-Pb dating of apatite (i.e. fluorapatite and chlorapatite) in crystalline rocks is now routine, the crystal structure and composition of CFA differs from apatite derived from igneous and metamorphic rocks, including the established fluorapatite U-Pb standards (e.g. Madagascar apatite, Thomson et al., 2012). Thus, assessment of matrix-matching effects will have to be undertaken to fully establish the CFA U-Pb chronometer.

Dattilo, B.F., Freeman, R.L., Peters, W.S., Heimbrock, W.P., Deline, B., Martin, A.J., Kallmeyer, J.W., Reeder, J. and Argast, A., 2016. Giants among micromorphs: were Cincinnatian (Ordovician, Katian) small shelly phosphatic faunas dwarfed?. Palaios, 31(3), pp.55-70.

Thomson, S.N., Gehrels, G.E., Ruiz, J., Buchwaldt, R., 2012. Routine low-damage apatite U-Pb dating using laser ablation-multicollector- ICPMS. Geochemistry, Geophys. Geosystems 13, 1–23. doi:10.1029/2011GC003928

How to cite: O'Sullivan, G., Mortimore, R., Chew, D., and Daly, S.: U-Pb dating of carbonate-fluorapatite: a potential chronological tool for ancient marine sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20017, https://doi.org/10.5194/egusphere-egu2020-20017, 2020.

EGU2020-10627 | Displays | SSP2.2

Towards data interchangeability in paleomagnetism

Christian Zeeden, Christian Laag, Pierre Camps, Yohan Guyodo, Ulrich Hambach, Janna Just, Pontus Lurcock, Christian Rolf, Sara Satolli, Stephanie Scheidt, and Sebastien Wouters

Paleomagnetic data are used in different data formats, adapted to data output of a variety of devices and specific analysis software. This includes widely used openly available software, e.g. PMag.py/MagIC, AGICO/.jr6 & .ged, and PuffinPlot/.ppl. Besides these, individual software and data formats have been established by individual laboratories.

Here we compare different data formats, identify similarities and create a common and interchangeable data basis. We introduce the idea of a paleomagnetic object (pmob), a simple data table that can include any and all data that would be relevant to the user. We propose a basic nomenclature of abbreviations for the most common paleomagnetic data to merge different data formats. For this purpose, we introduce a set of automatization routines for paleomagnetic data conversion. Our routines bring several data formats into a common data format (pmob), and also allow reversion into selected formats. We propose creating similar routines for all existing paleomagnetic data formats; our suite of computation tools will provide the basis to facilitate the inclusion of further data formats. Furthermore, automatized data processing allows quality assessment of data.

How to cite: Zeeden, C., Laag, C., Camps, P., Guyodo, Y., Hambach, U., Just, J., Lurcock, P., Rolf, C., Satolli, S., Scheidt, S., and Wouters, S.: Towards data interchangeability in paleomagnetism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10627, https://doi.org/10.5194/egusphere-egu2020-10627, 2020.

SSP2.8 – Cenozoic evolution of the Indo-Pacific Warm Pool and its role in global climate teleconnections

EGU2020-597 | Displays | SSP2.8

Persistent high latitude amplification over the past 10 million years

Xiaoqing Liu, Matthew Huber, Gavin L Foster, R Mark Leckie, and Yi Ge Zhang

When the Earth warms, the high latitudes often warm more than the low latitudes, a phenomenon commonly known as high latitude amplification. Although high latitude amplification has been observed by both climate data and models, the trajectory of high latitude amplification in our future changing climate is uncertain. Pacific-wide reconstructions of sea surface temperature variability from past climates are important for establishing the historical records of high latitude amplification. Multiple extratropical temperature records have been established for the past 10 million years (Myr). However, it is debated whether the warmest end member, the Western Pacific Warm Pool (WPWP), warmed during the late Miocene (~12 to 5 million years ago, Ma) and Pliocene (5 to 3 Ma). Here we present new multi-proxy, multi-site paleotemperature records from the WPWP. These results, based on lipid biomarkers and foraminiferal Mg/Ca, unequivocally show warmer temperatures in the past, and a secular cooling over the last 10 Myr. We combine these new data, along with the previously established paleotemperature records, to reveal a persistent pattern of change in the Pacific described by a high latitude amplification factor of ~1.7, which does not seem to be affected by the major climate changes over the past 10 Myr. The evolution of spatial temperature gradients in the Pacific is also evident in climate model output and instrumental observations covering the last 160 years, and thus appears to be a robust and predictable feature of the climate system. These results therefore confirm that climate models can capture the major features of past climate change, providing increased confidence in their predictions of future patterns that are likely to be similar to those reconstructed here.

How to cite: Liu, X., Huber, M., Foster, G. L., Leckie, R. M., and Zhang, Y. G.: Persistent high latitude amplification over the past 10 million years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-597, https://doi.org/10.5194/egusphere-egu2020-597, 2020.

The morphological evolution was investigated in the tropical Neogene planktonic foraminiferal lineage Globorotalia menardii, G. limbata and G. multicamerata during the past 8 million years at ODP Hole 806C (Ontong-Java Plateau). This research is an extension of previous studies from the Caribbean Sea, the tropical Atlantic and the Eastern Equatorial Pacific.

The peripheral influence of Agulhas Current faunal leakage of Indian Ocean or even Pacific menardiforms into the South Atlantic is suspected to be responsible for a transgressive, transatlantic expansion of large menardiforms from 2.3-2.06 Ma to 2.58-1.7 Ma, which installed after a Northern Hemisphere Glaciation (NHG) size incursion of menardiforms around 2.6 Ma (Knappertsbusch, 2007 and 2016; Knappertsbusch & Friesenhagen 2018). The investigation from Western Pacific Warm Pool (WPWP) ODP Hole 806C, i.e. from an area outside reach of Agulhas Current, serves as a blind test for this szenario. Here, stable warm environments prevailed back to Pliocene times, and influences of NHG are expected to bear less severely on shell size evolution than in the Atlantic Ocean.

For this study >5250 specimens comprising G. menardii, G. limbata and G. multicamerata from 33 stratigraphic levels were morphometrically investigated using imaging- and microfossil orientation robot AMOR. Attention was given to trends of spiral height (δX) versus axial length (δY) in keel view, for which bivariate contour- and volume density diagrams were constructed for visualization of evolutionary patterns.

In WPWP Hole 806C G. menardii evolved in a more gradual manner than in the Atlantic. Plots of δX versus δY reveal bimodality between 3.18 Ma – 2.55 Ma with a dominant mode of smaller G. menardii (δX<~300 μm) persisting until the Late Quaternary, and a weak mode of larger G. menardii (δX>~300 μm) until 2.63 Ma. Up-section, bimodality vanished but G. menardii populations shifted towards extra large shells between 2.19-1.95 Ma supporting the possibility of long-distance diversal in this group. Morphological evolution of G. limbata and its evolutionary successor G. multicamerata in the WPWP are also different from those in the tropical Atlantic, but analyses need still further investigation.

In summary, Pacific menardiform globorotalid patterns contrast those in the Atlantic realm. There is inter-oceanic morphological asymmetry with considerable regional environmental control over shell evolution and indication of long-distance dispersal of G. menardii, both with implications for biostratigraphic applications.

 

References

Knappertsbusch, M. and Friesenhagen, T. (2018). Prospecting patterns of morphological evolution in menardiform globorotalids along Agulhas‘ trackway: Review and research in progress. Abstract. FORAMS 2018 Symposium, 17-22 June 2018, Edinburgh, UK., Session IX, temporary abstracts, 331.

Knappertsbusch, M. (2016). Evolutionary prospection in the Neogene planktic foraminifer Globorotalia menardii and related forms from ODP Hole 925B (Ceara Rise, western tropical Atlantic): evidence for gradual evolution superimposed by long distance dispersal ? Swiss Journal of Palaeontology, 135, 205-248.

Knappertsbusch, M. (2007). Morphological variability of Globorotalia menardii (planktonic foraminifera) in two DSDP cores from the Caribbean Sea and the Eastern Equatorial Pacific. Carnets de Géologie / Notebooks on Geology, Brest, Article 2007/04. http://paleopolis.rediris.es/cg/CG2007_A04/index.html.

More info: https://micropal-basel.unibas.ch/

How to cite: Knappertsbusch, M.: Morphological evolution of menardiform globorotalids at ODP Hole 806C (Ontong-Java Plateau), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2396, https://doi.org/10.5194/egusphere-egu2020-2396, 2020.

EGU2020-5309 | Displays | SSP2.8

Oligocene-Miocene benthos biogeography of the Indian Ocean

Mathias Harzhauser, Markus Reuter, and Werner E. Piller

With the final closure of the Tethys Seaway during the early Miocene the Indian Ocean came into existence as geographic entity. The total breakdown of faunistic interrelations between the proto-Mediterranean Sea and Indian Ocean during the Aquitanian suggests a major biogeographic separation around ~22 Ma somewhere between Mesopotamia, Arabia, and NW-India. This event predates the development of the so-called Gomphotherium landbridge in the Burdigalian by 4-5 Ma and provides an example for biogeographic separation in the marine realm without formation of a continental barrier. The benthic mollusk fauna of the Miocene Indian Ocean was far from uniform. Data on Oligocene and Miocene mollusks from southern Iran (Qom Basin, Makran), the Sultanate of Oman, Tanzania, northern India (Kutch), southern India (Kerala) and Sri Lanka document a complex pattern of faunistic relations between these areas with high rates of endemism. Thus, a strong early Miocene bioprovincialism can be postulated for the Proto-Indo-West Pacific Region with a Central East African Province, a East African-Arabian Province, a Western Indian Province and a Proto-Indo-Polynesian Province in the east. This pattern differs fundamentally from the modern biogeography in the Indian Ocean. Similarly, fossil reef coral faunas from Eastern Africa (Tanzania, Somalia) show a low relation with southern Iran and no relationship with Indonesia during the Oligocene and early Miocene, but a strong faunistic affinity with Indonesia during the late Miocene and Recent.

We postulate that three main factors explain the strong difference between the Oligocene-Miocene and modern biogeographic patterns: the absence of the Miocene Indian Ocean Equatorial Jet, which did not arise before the middle Miocene, the absence of the Indonesian Throughflow due to the completely different paleogeography, and finally the devasting effect of Pleistocene sea-level fluctuations and subsequent recolonizations of the Indian Ocean from the east.

 

This project was funded by the Austrian Science Fund (FWF, Grants P 18189-N10 and P 29158-

N29).

How to cite: Harzhauser, M., Reuter, M., and Piller, W. E.: Oligocene-Miocene benthos biogeography of the Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5309, https://doi.org/10.5194/egusphere-egu2020-5309, 2020.

EGU2020-8387 | Displays | SSP2.8

Benthic Foraminifera as indicative of Austral Summer monsoon precipitation and winter monsoon wind-driven upwelling

Patricia Eichler, Katharina Billups, Ana Christina Ravelo, and Helenice Vital

During IODP Expedition 363, a hemipelagic sediment succession was retrieved for the first time off NW Australia (Site U1483: 13°5.24ʹS, 121°48.25ʹE, water depth: 1733 m, sedimentation rate: ~10 cm/kyr). This carbonate- and clay-rich sequence provides an ideal archive to monitor intensity and variability of the Australian Monsoon (AM) and to better constrain monsoon sensitivity to changes in radiative forcing. Due to the location at the southern edge of the largest amplitude seasonal swing of the Intertropical Convergence Zone (ITCZ) within the large-scale Asian-Australian monsoon system, the AM subsystem is sensitive to tropical hydroclimate variability. However, this sensitivity to changing climate boundary conditions such as ice volume and greenhouse gas concentrations remain poorly understood across the Calabrian, in the Pleistocene Epoch (add ages?). Here we report on benthic foraminiferal assemblages as a tracer for terrigenous runoff (Austral Summer monsoon precipitation). We find shallow, fresh water-tolerant to transitional environments species Bolivina striatula, Buliminella elegantissima, Dentalina spp., Oolina sp., and paleo productivity indicator Melonis spp (winter monsoon wind-driven upwelling) from 1.34 Ma. through 1.61Ma. Principl component analysis (PCA) indicates that Melonis is present in 4 out of 5 PCA axes. It prefers organic matter in a more altered form, and migrates in the sediment depending on the quality of the organic matter supply and remineralization, which indicates surface upwelling during this time. The genera Stilostomella spp. is present in 3 out of 5 axes, and it is indicative of intermediate water temperature. These records will be compared to C org wt (%), TN wt (%) and a benthic foraminiferal stable isotope record to related faunal patterns to carbon cycling and global climate.

 

 

How to cite: Eichler, P., Billups, K., Ravelo, A. C., and Vital, H.: Benthic Foraminifera as indicative of Austral Summer monsoon precipitation and winter monsoon wind-driven upwelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8387, https://doi.org/10.5194/egusphere-egu2020-8387, 2020.

EGU2020-9060 | Displays | SSP2.8 | Highlight

Beyond Sea Surface Temperatures: a Holistic Approach to Addressing Pliocene Tropical Conditions

Heather L. Ford, Natalie Burls, Deepak Chandan, Jonathan LaRiviere, Alexey Fedorov, and A. Christina Ravelo

The tropical Pacific thermocline structure is critical to tropical sea surface temperatures (SSTs) and variability. During the mid-Pliocene warm period (~3 Ma), the zonal SST gradient was reduced due to relatively warm SST in the Eastern Equatorial Pacific; we call this mean state “El Padre.” How did the equatorial thermocline contribute to this reduced zonal SST gradient? Here we summarize published Mg/Ca (surface and subsurface dwelling foraminifera) and alkenone records and generate new SST estimates from Mg/Ca and alkenones. The subsurface dwelling Globorotalia tumida Mg/Ca-based temperature records from the eastern and western equatorial Pacific show mid-Pliocene warm period subsurface temperatures warmer than today; El Padre included a basin-wide thermocline that was relatively warm, deep, and weakly tilted. We compare the published and newly generated SST and subsurface temperature records to the Pliocene Modeling Intercomparison Project (PlioMIP1) and show that few models capture the magnitude and spatial pattern suggested by the temperature records. Those models that do corroborate the temperature records have warm subsurface temperatures in the Eastern Equatorial Pacific that dynamically link to warm SSTs in the cold tongue. This highlights the need to accurately model thermocline dynamics and mid-latitude conditions, where equatorial thermocline waters originate, in order to gain an understanding of the underlying processes that explain the mid-Pliocene warm period.

How to cite: Ford, H. L., Burls, N., Chandan, D., LaRiviere, J., Fedorov, A., and Ravelo, A. C.: Beyond Sea Surface Temperatures: a Holistic Approach to Addressing Pliocene Tropical Conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9060, https://doi.org/10.5194/egusphere-egu2020-9060, 2020.

EGU2020-11494 | Displays | SSP2.8 | Highlight

Past and future changes in tropical climate amplified by the Indian Ocean

Pedro DiNezio

Presently, the Indian Ocean exhibits a unique climate state with subtle east-west contrasts and weak year-to-year variability. Whether these features could change in response to external forcings remains highly debated, an issue that is critical to predict future climate changes in highly populated neighboring countries. We explored this question combining climate reconstructions and numerical simulations and of the Last Glacial Maximum – the interval ca. 21,000 years ago when the Earth experienced the largest, most recent climate change. We found that the Indian Ocean exhibited radically altered rainfall patterns and oceanographic conditions across the basin, changes that according to our simulations, can only be explained by the amplifying effect of coupled ocean-atmosphere feedbacks. We also find that these changes favored the emergence of an El Niño mode driving significantly stronger climate variability. Despite different triggers in the past and the future, our results show that Indian Ocean climate could also be highly sensitive to future greenhouse forcing.

How to cite: DiNezio, P.: Past and future changes in tropical climate amplified by the Indian Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11494, https://doi.org/10.5194/egusphere-egu2020-11494, 2020.

EGU2020-11701 | Displays | SSP2.8

Geochemical and Geophysical Evidence for Late Miocene Onset of Tasman Leakage

Beth Christensen, David DeVleeschouwer, Jeroen Groeneveld, Jorijntje Henderiks, Gerald Auer, Christian Beztler, Gregor Eberli, Anna Joy Drury, and Dirk Kroon

The recent documentation of the southern hemisphere “supergyre”, the coupled subtropical southern hemisphere gyres spanning the 3 ocean basins, leads to questions about its impact on Indian Ocean circulation. The Indonesian Throughflow (ITF) acts as a switchboard directing warm surface waters towards the Agulhas Current (AC) and return flow to the North Atlantic, but Tasman Leakage (TL) is another source of return flow, however, at intermediate water depths. Fed by a complex mixture of South Pacific (SP) western boundary current surface and intermediate waters, and Antarctic Intermediate Water (AAIW), today the topography forces it to flow in a westerly direction. The TL flows over the Broken Ridge towards Madagascar, joining the AC and ultimately Atlantic Meridional Circulation (AMOC).

Stable isotope data from 4 DSPD/ ODP Indian Ocean sites define the history of TL and constrain the timing of its onset to ~7 Ma.  A simple nannofossil- biostratigraphy age model applied to previously published benthic foraminiferal carbon isotope data ensures the 4 time-series (~11 – 2 Ma) are consistent. All 4 records (Sites 752 Broken Ridge, 590 Tasman Sea, 757 90 East Ridge, 751 Kerguelen Plateau) are similar from ~11 Ma to ~7 Ma, indicating the Tasman Sea intermediate water was sourced from the Southern Ocean (SO). A coeval shift at ~7 Ma at Sites 590 and 752 signals a SP contribution and the onset of TL. We do not observe TL at Sites 757 and 751 and so interpret the post-7 Ma divergence between the TL pair and the KP / 90E Ridge sites as a reflection of different intermediate water masses. The KP / 90E Ridge sites record a more fully SO signal, and these waters are constrained to the region west of the 90 East ridge.

The isotopic record of TL onset suggests important tectonic changes ~ 7 Ma: 1) opening of the Tasman Sea to the north and 2) Australia’s northward motion allowing westward flow around Tasmania. The former is supported by a change in sedimentation style on the Marion Plateau (ODP Site 1197). The latter is supported by unconformities on the South Australian Bight margin (Leg 182 Sites 1126 (784 m), 1134 (701 m), 1130 (488m) and coeval decreases in mud- sized sediments at the Broken Ridge sites, indicating winnowing associated with the onset of the TL. A divergence is also apparent between Broken Ridge and Mascarene Plateau Site 707 records at this time. These events, coupled with the temporal relationship between the onset of the TL and a change in the character of deposition in the Maldives indicate enhanced Indian Ocean circulation at intermediate depths coincident with the late Miocene global cooling. Combined, these observations suggest the Indian Ocean in general plays a larger role in the global ocean system than previously recognized, and intermediate waters in particular are a critical yet poorly understood component of AMOC.

How to cite: Christensen, B., DeVleeschouwer, D., Groeneveld, J., Henderiks, J., Auer, G., Beztler, C., Eberli, G., Drury, A. J., and Kroon, D.: Geochemical and Geophysical Evidence for Late Miocene Onset of Tasman Leakage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11701, https://doi.org/10.5194/egusphere-egu2020-11701, 2020.

The Western Pacific Warm Pool (WPWP) as a major source of heat and water vapor has a crucial influence on climate dynamics both in the tropics and globally. Yet, there is conflicting proxy evidence regarding the evolution of WPWP temperatures since the Miocene. On the one hand TEX86 data suggest a gradual cooling by ~2℃ (O’Brian et al., 2014, Zhang et al., 2014) from the Pliocene to today, while faunal (planktonic foraminifera) sea surface temperature estimates (Dowsett, 2007) and Mg/Ca data measured in planktonic foraminifera (Wara et al., 2005) on the other hand indicate the absence of any long-term temperature trends. It has been suggested that Mg/Ca temperatures could on these time scales be biased by long-term changes of the Mg/Ca ratio of seawater (Evans et al., 2016). To test the influence of the proposed seawater changes on Mg/Ca we combined data from two independent temperature proxies, Mg/Ca and clumped isotopes, measured on two species of planktonic foraminifera from IODP Site U1488 in the central WPWP. Our study finds good agreement between both proxies thereby verifying the validity of Mg/Ca records from the WPWP and confirming the absence of a Plio-Pleistocene cooling trend for the WPWP. This finding suggests that the persistent disagreement between foraminifer-based proxies such as Mg/Ca and biomarker data might be caused by different environmental parameters being recorded in the two archives.

 

References:

O’Brien CL, Foster GL, Martínez-Botí MA, Abell R, Rae JWB, Pancost RD. High sea surface temperatures in tropical warm pools during the Pliocene. Nature Geoscience. 2014;7(8):606-11.

Zhang YG, Pagani M, Liu Z. A 12-million-year temperature history of the tropical Pacific Ocean. Science. 2014;344(6179):84-7.

Dowsett H. Faunal re-evaluation of Mid-Pliocene conditions in the western equatorial Pacific. Micropaleontology. 2007;53(6):447-56.

Wara MW, Ravelo AC, Delaney ML. Permanent El Nino-like conditions during the Pliocene warm period. Science. 2005;309(5735):758-61.

Evans D, Brierley C, Raymo ME, Erez J, Müller W. Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene–Pleistocene seawater Mg/Ca, temperature and sea level change. Earth and Planetary Science Letters. 2016;438:139-48.

How to cite: Meinicke, N., Reimi, M., Ravelo, C., and Meckler, N.: Coupled Mg/Ca and clumped isotope measurements at IODP Site U1488 confirm absence of Plio-Pleistocene sea surface temperature cooling in the Western Pacific Warm Pool, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16364, https://doi.org/10.5194/egusphere-egu2020-16364, 2020.

EGU2020-17079 | Displays | SSP2.8

Late Neogene carbonate productivity and terrigenous input in the central Western Pacific Warm Pool (IODP Site U1488)

Anna Joy Drury, Thomas Westerhold, Ana Christina Ravelo, Ivano Aiello, Roy Wilkens, Ursula Röhl, and Denise Kulhanek

As the largest modern reservoir of oceanic heat, the Western Pacific Warm Pool (WPWP) plays an important role in atmospheric and oceanic circulation patterns. Little is known about how regional deposition patterns have changed over the past 10 Ma. To understand the interplay between regional processes and global climate evolution in the WPWP, we explore the late Neogene evolution of biogenic (carbonate/siliceous) versus terrigenous deposition.

We collected high-resolution (2 cm/~0.5 kyr) X-Ray fluorescence (XRF) core scanning data at IODP Site U1488 (Exp. 363) in the central WPWP. These data were especially useful for estimating the carbonate, siliceous and terrigenous components below 65 m CCSF, where the shipboard track data were less robust. The shipboard splice was verified and revised using the Ba/Sr ratio to ensure a continuous composite section down to ~330 m revised CCSF-A at Site U1488. Fe and Si likely reflect terrigenous and partially biogenic silica components. We calibrated the high-resolution ln(Ca/K) record to %CaCO3 using discrete shipboard %CaCO3 measurements.

Fe and Si decrease, whilst ln(Ca/K) increases downcore, in agreement with shipboard data showing increasing %CaCO3 and decreasing terrigenous/siliceous input­. During the late Pleistocene, the site shows high amplitude %CaCO3, Fe and Si cycles superimposed on low carbonate. The amplitude decreases during the early Pleistocene-mid Pliocene, although clear variability remains. The early Pliocene-late Miocene is dominated by high CaCO3 (80-90%). The %CaCO3, Fe and Si variability is considerably reduced, although clear obliquity-precession interference patterns are visible, in addition to longer-term ~400 kyr eccentricity modulation. The high-carbonate interval at IODP Site U1488 likely reflects the early Pliocene to late Miocene Biogenic Bloom (LMBB). The expression of the LMBB in the WPWP is distinctly different to the Atlantic and eastern equatorial Pacific. This indicates that although productivity was enhanced during the late Miocene-early Pliocene, regional processes determined the exact expression and timing of the LMBB in different areas.

How to cite: Drury, A. J., Westerhold, T., Ravelo, A. C., Aiello, I., Wilkens, R., Röhl, U., and Kulhanek, D.: Late Neogene carbonate productivity and terrigenous input in the central Western Pacific Warm Pool (IODP Site U1488), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17079, https://doi.org/10.5194/egusphere-egu2020-17079, 2020.

EGU2020-19624 | Displays | SSP2.8

Invigoration of Indian Ocean zonal circulation drove Pleistocene eastern African aridification

Jeroen van der Lubbe, Ian Hall, Steven Barker, Sidney Hemming, Janna Just, Tim Baars, Josephine Joordens, Aidan Starr, and Expedition 361 Scientists

The coupled ocean-atmosphere circulation of the Indian Ocean Dipole (IOD) controls monsoon rainfall in eastern Africa and southeast Asia at seasonal to decadal time-scale. In years when the dipole is particularly active, it can lead to catastrophic floods and droughts. A growing body of evidence suggests that IOD variability influenced the continental hydroclimate also at longer timescales in the past and thus may have affected human evolution.  However, long-term continuous high-resolution well-dated records have so far been unavailable to test this hypothesis. In 2016, long-term continuous deep-sea sediment cores have been recovered from the Davie Ridge in the Mozambique Channel during Expedition 361 ‘Southern African Climates’ as part of the International Ocean Discovery Program (IODP).

Here, we present a more than seven million-year-long multi-proxy record of Mozambique Channel Throughflow (MCT), which is tightly coupled to IOD variability; defined here as the zonal sea surface temperature gradient (ΔSST) between the Indo-Pacific warm pool (IPWP) and the Arabian Sea. We show that the MCT was relatively weak and steady until 2.1 million years ago (Ma), when it started to significantly accelerate with progressively increasing glacial-interglacial amplitude, culminating in high flow speeds from 0.8 Ma onwards. The invigoration of MCT activity coincided with increasing zonal ΔSST, which fuels the atmospheric Walker Cell circulation along the tropical Indian Ocean.  Our results demonstrate that the overall intensification of the Indian Ocean Walker Cell amplified the coupled ocean-atmosphere Indian Ocean zonal circulation at orbital time-scales, which agrees with the heightened glacial continental aridity recorded in other eastern African climate proxy records. We argue that the corresponding progressively drier glacials alternated with relative humid interglacials, providing the climatic-environmental setting –varying at seasonal to orbital timescales- for speciation and global expansion of our genus Homo after 2.1 Ma.

How to cite: van der Lubbe, J., Hall, I., Barker, S., Hemming, S., Just, J., Baars, T., Joordens, J., Starr, A., and 361 Scientists, E.: Invigoration of Indian Ocean zonal circulation drove Pleistocene eastern African aridification , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19624, https://doi.org/10.5194/egusphere-egu2020-19624, 2020.

SSP2.13 – Asian Climate and Tectonics

EGU2020-7711 | Displays | SSP2.13 | Highlight

Modelling the Interaction between Tibet and Climate and Biosphere during the Cenozoic.

Paul Valdes, Alex Farnsworth, Tao Su, Robert Spicer, Lin Ding, Shufeng Li, Zhekun Zhou, and Shihu Li

The Cenozoic uplift history of Tibet and its impact on the Asian monsoon and vegetation is complex. The building of the Tibetan Plateau is not a simple story of the rise of a single geological entity driven by the relentless northward passage of India as depicted in numerous modelling exercises, but was a complex process involving a succession of collisions of several Gondwanan terranes with Asia. The talk will review our current understanding of the uplift history of Tibet and show new climate model simulations of how Tibet has influenced climate, vegetation and biodiversity in the region. We make use of isotope-enabled Earth System models, as well as high resolution models to show that the complex history of Tibet has important consequences for understanding the evolution of both the summer and winter Asian monsoon. We show that post-Oligocene growth of north and north-eastern Tibet is crucial for the evolution of vegetation and biodiversity in the region by altering the strength of the winter monsoon system over Asia.

How to cite: Valdes, P., Farnsworth, A., Su, T., Spicer, R., Ding, L., Li, S., Zhou, Z., and Li, S.: Modelling the Interaction between Tibet and Climate and Biosphere during the Cenozoic., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7711, https://doi.org/10.5194/egusphere-egu2020-7711, 2020.

EGU2020-1523 | Displays | SSP2.13

India-Asia collision paleogeography constrained by Burma Terrane (Myanmar) Late Cretaceous to Miocene paleomagnetic data

Jan Westerweel, Pierrick Roperch, Alexis Licht, Guillaume Dupont-Nivet, Zaw Win, Fernando Poblete, Nathan Cogné, Gilles Ruffet, Huasheng Huang, Hnin Hnin Swe, Myat Kai Thi, Carina Hoorn, and Day Wa Aung

The paleogeographic evolution of the India-Asia collision and the resulting formation of the Himalayan orogen remain an intensely debated topic. A variety of disputed models propose different collision ages for the numerous terranes incorporated into the collision with variable paleolatitudes and tectonic rotations that can be constrained using paleomagnetism. Recent plate tectonic reconstructions have shown that the Burma Terrane (BT), a microplate at the eastern edge of the Himalayan orogen, is a key element to solve the India-Asia collision puzzle. Here we provide new paleomagnetic and geochronological data of Paleocene, Eocene, Oligocene and Miocene age, in addition to our previously published Late Cretaceous and late Eocene results. We present a robust plate tectonic reconstruction for the BT with GPlates software, and show that the BT moved towards southern hemisphere latitudes between the Late Cretaceous and Paleocene without significant rotation. Starting in the Paleocene, the BT and India coevally moved northwards and the BT started to undergo a major clockwise rotation of ~60 ̊. By the late Eocene, most of this rotation was completed and the BT was translated ~2000 km northward from near-equatorial latitudes without significant rotation. This northward translation culminated with the early Miocene indentation of the BT into the eastern Himalayan collision zone, leading to the setup of the modern Eastern Himalayan Syntaxis. These first order constraints are used to infer a Trans-Tethyan arc collision model including timing of rollback, extrusion and initiation of strike-slip systems. Our model has important implications for Asian biotic and climatic evolution.

How to cite: Westerweel, J., Roperch, P., Licht, A., Dupont-Nivet, G., Win, Z., Poblete, F., Cogné, N., Ruffet, G., Huang, H., Swe, H. H., Thi, M. K., Hoorn, C., and Aung, D. W.: India-Asia collision paleogeography constrained by Burma Terrane (Myanmar) Late Cretaceous to Miocene paleomagnetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1523, https://doi.org/10.5194/egusphere-egu2020-1523, 2020.

EGU2020-5992 | Displays | SSP2.13 | Highlight

Low-latitude arc–continent collision as a driver for global cooling

Oliver Jagoutz, Leigh Royden, and Francis Macdonald

New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90–70 Ma and at ∼50–40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2. Based on these results, we suggest that the low-latitude closure ofoceanbasins alongeast–west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean.

How to cite: Jagoutz, O., Royden, L., and Macdonald, F.: Low-latitude arc–continent collision as a driver for global cooling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5992, https://doi.org/10.5194/egusphere-egu2020-5992, 2020.

EGU2020-4042 | Displays | SSP2.13

A new negative feedback mechanism for balancing Tibet uplift-driven CO2 drop: Evidence from Paleogene chemical weathering records in the northern Tibetan Plateau

Xiaomin Fang, Albert Galy, Yibo Yang, Weilin Zhang, Chengcheng Ye, and Chunhui Song

The CO2 degassing by plate tectonic process has long been thought to be balanced by weathering of silicate rocks on continents, keeping the Earth a relative stable global carbon cycle and temperature suitable for life creation, survival and evolution. The uplift of the Tibetan Plateau (TP) is hypothesized to enhance erosion and silicate weathering and organic carbon burial, thus cool the global temperature. However, the imbalance resulting from accelerated CO2 consumption by uplift of the TP and a relatively stable CO2 input from volcanic degassing during the Cenozoic should have depleted atmospheric CO2 within a few million years; therefore, a negative feedback mechanism must have stabilised the carbon cycle. Here, we present the first almost complete Paleogene silicate weathering intensity (SWI) records from continental rocks in the northern TP, based on detailed volcanic ash and paleomagnetic dating of two continuous Cenozoic sections in the Xining and Qaidam Basin in NW China. They show that the Paleogene silicate weathering in this tectonically inactive area was modulated by global temperature. These findings suggest that Paleogene global cooling was also strongly influenced by the temperature feedback mechanism that regulated silicate weathering rates and hydrological cycles and maintained a nearly stable carbon cycle. It acted as a negative feedback through decreasing CO2 consumption resulting from the lower SWI and the kinetic limitations in tectonically inactive areas that followed the global cooling. This means that the enhanced erosion and silicate weathering by the uplift of the south and central Tibetan Plateau, thus accelerated CO2 consumption, must be compensated by reducing CO2 consumption of the rest vast continents through their reduced silicate weathering from cooling.

How to cite: Fang, X., Galy, A., Yang, Y., Zhang, W., Ye, C., and Song, C.: A new negative feedback mechanism for balancing Tibet uplift-driven CO2 drop: Evidence from Paleogene chemical weathering records in the northern Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4042, https://doi.org/10.5194/egusphere-egu2020-4042, 2020.

EGU2020-10034 | Displays | SSP2.13 | Highlight

Temperature decrease through the Eocene-Oligocene transition controls eco-hydrologic shifts in Central Asia

Alexander Rohrmann, Guillaume Dupont-Nivet, Michael Hren, Dirk Sachse, Niels Meijer, Natasha Barbolini, and Delphine Tardif

At ca. 34 Ma the Eocene-Oligocene transition (EOT) marks the shift from greenhouse conditions during the Eocene to the icehouse of the Oligocene and was the most pronounced cooling event during the Cenozoic. This event is well documented in marine records with a significant increase in benthic foraminifera δ18O values suggesting a 5°C cooling in air temperature through the EOT. Instead, the few but growing number of terrestrial records suggest a much larger cooling of 4-9°C. Yet, details regarding the exact timing of cooling and ensuing terrestrial changes in climate, hydrology, and ecology are sparse. Here, we investigate the impact of the EOT cooling event and associated climatic changes on the hydrology and vegetation in central China. We use stable isotopes of hydrogen (δDwax) and carbon (δ13Cwax) from leaf-waxes, a paleo-hydrology proxy obtained from organic material in sedimentary rocks, in combination with pollen data from a continuous well-dated, high-resolution sedimentary section from the Xining Basin in NE Tibet (36°42' N, 101°43' E). We then compare our results to a fully-coupled, global climate model (GCM) simulating the pre- and post-EOT conditions in central Asia.

The obtained δDwax record ranges between -160 to -190‰ and shows a complex two-step transition through the EOT with a rapid initial drop of -30‰ from 33.9 to 33.7 Ma, a recovery to pre-EOT values between 33.7 to 33.4 Ma and a second drop similar in magnitude as the first one. In contrast, δ13Cwax values remain unchanged at -29 to -28‰ through the EOT. The GCM indicates a difference in temperature throughout the year between pre- and post-EOT runs of 8-9°C at the Xining Basin with change in seasonality due to the collapse of the pre-EOT wet spring season, yielding mainly autumn precipitation after the transition. The overall precipitation amount remained in both simulations dry with < 500 mm/yr. The combined results show that the region experienced: (a) a significant temperature drop of 8-9°C through the EOT being the first-order control on the records decrease in δDwax  (1-2 ‰ per 1°C in mid-latitudes and up-to 5 ‰ per 1°C in higher latitudes) through the EOT; (b) constant bioproductivity and/or similar water-use efficiency within plants displayed by unchanged δ13Cwax values; (c) a changeover from a “warm-wet” desert abundant in Nitraria and Ephedra shrubs to a “temperate” desert with an expansion of conifers and broad-leaf trees in the higher-elevation hinterlands. We interpret that this change in seasonality and cooler EOT temperatures reduced the plant’s overall transpirational pressure, contributing to the spread of conifers and broad-leaf trees after the EOT under regionally new hydrologic conditions.

How to cite: Rohrmann, A., Dupont-Nivet, G., Hren, M., Sachse, D., Meijer, N., Barbolini, N., and Tardif, D.: Temperature decrease through the Eocene-Oligocene transition controls eco-hydrologic shifts in Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10034, https://doi.org/10.5194/egusphere-egu2020-10034, 2020.

The Siwalik deposits of Himalayan foreland basin (HFB) preserved the Miocene records of the Himalayan tectonics, monsoonal variation and evolution of C4 plants. Previous vegetation reconstructions emphasized   the Late Miocene expansion of C4 plants (ca. 7 Ma) with an implicit assumption that the vegetation thrived in the floodplain of lowland rivers. The coarsening-upward sequence of the Siwalik Group suggests deposition  in an alluvial fan setting in which the Middle and Lower Siwaliks are deposits of distal area whereas the Upper Siwaliks represent proximal areas of the fan. The modern alluvial fans forming in the Himalayan foothills show a significant difference in elevation and vegetational composition between proximal and distal areas. In the HFB, the elevation difference between the proximal and distal areas is expected to be more pronounced due to surface exhumation of the Siwalik deposits. The increased elevation would have had affected the vegetation distribution in the Upper Siwaliks which implies that vegetation  inproximal part of the fan might not represent lowland floodplain. However, the vegetation composition is less understood from the Upper Siwaliks region as conventional proxies are scanty in these younger foreland deposits.

In the present study, the impact of elevation on vegetation distribution in the HFB is examined from comparatively higher exhumed Late Plio-Pleistocene Siwalik deposits at SuraiKhola (Nepal). The δ13C values of bulk soil organic matter (SOM), n-alkane and n-alkanoicacid from the SuraiKholapaleosols suggest most commonly observed expansion of the C4 plants at ca. 7 Ma, and a unique second phase of expansion of C3 plants after ca. 3 Ma. The higher δD values in n-alkane and n-alkanoicacid suggest that the climate was drier in last 4 Myr; most likely driven by the onset of the Northern Hemisphere Glaciation (NHG). The growth of C3 plants was favored due to cool climatic condition induced by higher elevation in the proximal part of the fan. The water-bearing conglomerate units in the Upper Siwaliks helped the C3 plants to thrive in a relatively drier climate. Therefore, the higher abundance of C3 plants in the Upper Siwaliks suggests morpho-tectonic control on vegetation with the possible influence of NHG.

 

How to cite: Sanyal, P., Roy, B., and Ghosh, S.: Morpho-tectonic control on the distribution of C3-C4 plants during Late Plio-Pleistocene in the central Himalayan Siwaliks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-550, https://doi.org/10.5194/egusphere-egu2020-550, 2020.

EGU2020-14895 | Displays | SSP2.13 | Highlight

Quantifying the contribution of Tibetan Plateau (TP) uplift and CO2 decrease for late Eocene and present day climate with emphasis on Meridional Ocean Circulation.

Gilles Ramstein, Baohuang Su, Dabang Jiang, Ran Zhang, and Pierre Sepulchre

Since late Eocene (40 Ma), atmospheric CO2 drastically decreased from 4 to 1 PAL.  During this period, two major geological events occurred over Asia: the India/Asia collision producing the uplift of large mountain ranges and the shrinkage of the Paratethys (G. Ramstein et al., Nature, 1997; F. Fluteau et la., JGR, 1999). Most modeling studies focused first on the sensitivity of AGCMs to the Tibetan plateau elevation through simple experiments; then new simulations accounting for more realistic description of paleogeographic reconstructions have been published. Indeed, progress has been done concerning both: paratethys evolution (Z. Zhang et al., PAL PAL PAL, 2007), chronology of uplifts of different mountain ranges (R. Zhang et al., JGR, 2017) and large TP northern shift (R. Zhang et al., EPSL, 2018), but again these experiments focused mostly on atmosphere circulation and hydrologic pattern (monsoon evolution) not specifically on their impacts on ocean dynamics.

Therefore, this study aims to investigate the role of TP uplift on Northern hemisphere ocean circulation through long runs of coupled ocean atmosphere model to analyze its impact not only on atmosphere but also on ocean dynamics. We provided a series of sensitivity simulations disentangling the two different factors, pCO2 decrease and TP uplift. These simulations allow analyzing the response to TP uplift in a warm high CO2 world as Eocene and in a cold low CO2 world as Quaternary (B. Su et al., CP, 2018).

We describe how the TP uplift through changes of atmosphere (surface winds and planetary waves) and hydrology (runoff and precipitation/evaporation patterns) modified the meridional circulation in the North Atlantic and Pacific basins with emphasize on the causes of the two different basins sensitivity to this major mountain range uplift in both contexts.

How to cite: Ramstein, G., Su, B., Jiang, D., Zhang, R., and Sepulchre, P.: Quantifying the contribution of Tibetan Plateau (TP) uplift and CO2 decrease for late Eocene and present day climate with emphasis on Meridional Ocean Circulation., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14895, https://doi.org/10.5194/egusphere-egu2020-14895, 2020.

Constraining spatial and temporal patterns of topography and exhumation along the Himalayan orogen is a starting point for studies aimed at understanding the development of Asian climate and tectonic evolution. Starting from the pioneering work of Cerveny et al. (1988), many scientists have applied a detrital thermochronologic approach to reveal the Cenozoic exhumation history of the Himalayas. Thermochronologic studies involve analyses of modern river sediments and sedimentary successions either accreted on the southern side of the orogen or accumulated in the Indus and Bengal fans. As datasets have grown and techniques evolved, the available interpretations are often contradictory.

In this contribution, we analyse previously published detrital-thermochronology datasets in the Himalayan region using the interpretive keys illustrated in Malusà and Fitzgerald (2020). These keys reinforce existing approaches and provide new perspectives for the application of detrital thermochronology to tectonic settings where the geologic evolution is often still debated. Different thermochronologic systems applied to proximal and distal sedimentary successions derived from Himalayan erosion yield a complex exhumation and tectonic history, but a relatively consistent picture for the Cenozoic evolution of India-Eurasia collision emerges. Detrital thermochronology data are supportive of a progressive southward thrust propagation towards the Himalayan foreland, progressively involving new eroding sources. The onset of fast exhumation in the Lesser Himalaya is constrained by different thermochronologic methods and datasets, indicative of onset at ~10 Ma, in line with independent geologic evidence. Coeval fast exhumation is also recorded in detritus derived from the Greater Himalaya. These findings are supportive of a major morphogenic phase of mountain building in the Himalayas at ~10 Ma, prior to the onset of fast exhumation in the Namche Barwa syntaxis.

Cerveny PF et al (1988). History of uplift and relief of the Himalaya during the past 18 million years: Evidence from fission-track ages of detrital zircons from sandstones of the Siwalik Group. In: New perspectives in basin analysis, Springer.

Malusà MG, Fitzgerald PG (2020). The geologic interpretation of the detrital thermochronology record within a stratigraphic framework, with examples from the European Alps, Taiwan and the Himalayas. Earth-Science Reviews, https://doi.org/10.1016/j.earscirev.2019.103074

How to cite: Malusa', M. G. and Fitzgerald, P. G.: Detrital thermochronology evidence of a major morphogenic phase of mountain building in the Himalayas at 10 Ma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3398, https://doi.org/10.5194/egusphere-egu2020-3398, 2020.

EGU2020-4206 | Displays | SSP2.13

Climate controlled catchment erosion in the Himalaya during the late Quaternary

Mohd Amir, Mohd Tarique, Waliur Rahaman, and Debajyoti Paul

The alluvial sediments deposited in the Indo-Gangetic Plains originated as a result of tectonic and climatic factors controlling the exhumation and erosion of the Hinterland Himalaya. However, erosion distribution over the Himalaya and sediment delivery to the plains, on a shorter millennial time scale, are primarily controlled by the climatic factors such as glacial cover over the Himalaya and intensity of Indian summer monsoon (ISM) precipitation. Therefore, these alluvial sediment archives record important information about the past climatic changes. Here, we report the geochemical record of 87Sr/86Sr, 143Nd/144Nd (εNd), and δ13C of sediment organic matter (δ13CSOM) in a ~45 m long drill-sediment core collected from a buried channel of the paleo-Yamuna River in the northwest Indo-Gangetic Plains, Haryana to infer variations in provenance, paleoclimate, and paleovegetation during the late Quaternary. The Sr–Nd isotopic compositions (87Sr/86Sr: 0.75144–0.79241, εNd: –15.9 to –19.7) of the core sediments suggest their derivation from isotopically distinct Higher Himalaya and Lesser Himalaya end-member sources in the catchment. Down-core variability in the isotopic compositions show increased contribution from the Higher Himalaya during marine isotope stage (MIS) 1 and late MIS 3 interglacial periods due to receding glacial cover and intense ISM. The δ13CSOM values (−21.6‰ to −27.0‰, average: −25.6‰) in the core samples imply a C3 dominant paleovegetation in the catchment. Down-core variability in the δ13CSOM exhibits significant correlation with the ISM precipitation intensity, implying an increased abundance of C4 plant in response to the ISM intensification during MIS 1, and early and late MIS 3.

How to cite: Amir, M., Tarique, M., Rahaman, W., and Paul, D.: Climate controlled catchment erosion in the Himalaya during the late Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4206, https://doi.org/10.5194/egusphere-egu2020-4206, 2020.

EGU2020-20362 | Displays | SSP2.13

"Terra Antiqua" : a paleogeographic reconstruction plugin for QGIS

Diego Ruiz, Guillaume Dupont-Nivet, Jovid Aminov, Fernando Poblete, Thomas van der Linden, and Douwe van Hinsbergen

Paleogeographic reconstructions are essential across disciplines in Earth and Environmental Science from geodynamics to climate, as well as related fields of biology and ecology. They are at the foundation of many academic as well as industrial applications. As for geologic maps, paleogeographic reconstructions integrate a vast amount of multidisciplinary data and interpretations. Building such reconstructions thus requires a large set of sequential procedures to position around the globe various oceanic and continental features and to modify their topographies, bathymetries and shorelines according to the considered dataset included.

We present here a tool that enables to perform simply these operations. It is under development as a plugin for QGIS. With a graphical user interface, preset options can be readily applied to generate quickly multiple reconstructions with varying parameters. This makes project data management and treatment considerably easier, more intuitive and user-friendly. As most tools in GIS do, Terra Antiqua includes help texts incorporated to its interface to guide the user through each module.  The Plugin is divided into modules and this format allows a high degree of flexibility in the order of the reconstruction steps. These are: the compilation of topography and bathymetry, the definition of the paleoshorelines, the topography modification and the interpolation. Resulting paleogeography digital elevation model (DEM) can be visualized and exported in any GIS-supported format – NetCDF, GeoTIFF, Grid (.grd) or as PDF, JPEG, SVG etc. for publication. The tool is tested to make global reconstructions at 50 and 30 Ma.

How to cite: Ruiz, D., Dupont-Nivet, G., Aminov, J., Poblete, F., van der Linden, T., and van Hinsbergen, D.: "Terra Antiqua" : a paleogeographic reconstruction plugin for QGIS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20362, https://doi.org/10.5194/egusphere-egu2020-20362, 2020.

The Tibetan Plateau (TP) has undoubtedly played an essential role in the evolution and strengthening of the coupled climate system of the Asian monsoon and inland arid climate since the Cenozoic. However, a growing number of studies have found that regional and relatively smaller scale topography also has significant impact on Asian climate.
By using high resolution atmospheric circulation model, we analyzed the effect of the main body of the TP and its surrounding topography on the evolution of Asian climate. The surrounding topography includes the Yunnan-Guizhou Plateau (YG) at the southeastern margin of the Tibetan Plateau, the Pamir Plateau (Pr) and Tian Shan mountains (TS) at the northern margin and the Mongolian Plateau (MP) further north. The results show that different from the strengthening effect of the main TP, the YG significantly weakens the Indian monsoon. With the uplift of the YG, an anomalous anticyclonic circulation appeared in the lower troposphere over the southwest, resulting in the weakening of monsoon circulation from the Bay of Bengal to the Indian subcontinent and the Arabian sea. The decline in Indian monsoon precipitation caused by the YG accounts for one-third of the total increase in precipitation caused by the entire TP.
For the arid interior Asia, the main TP, YG, Pr and TS, as well as the MP all have reduced the annual precipitation in some extent. However, different from the consistent inhibiting effect of the main TP on the precipitation over the arid interior Asia throughout the year, the decreasing effect of the YG and the MP is mainly effective in boreal winter, which is closely related to the mechanical blocking effect. In addition, the Pr and TS play a key role in the temporal and spatial differentiation of precipitation in the arid interior Asia. Before the appearance of the Pr and TS, the precipitation seasonality over the eastern sub-region was characterized with maximum rainfall in spring and winter and minimum rainfall in summer. With the uplift of Pr and TS, the precipitation over the eastern part decreases in winter and significantly increases in summer, which leads to the change of precipitation seasonality to summer dominated.
The above results indicate that different part of the extensive-third pole have different influences on the Asian monsoon and inland aridity. It suggests that the Asian monsoon-inland arid climate may have undergone complex evolutionary processes on tectonic scale.

How to cite: Sha, Y. and Shi, Z.: Complex Role of the Tibetan Plateau and its Surrounding Topography in the Formation of Asian Climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13623, https://doi.org/10.5194/egusphere-egu2020-13623, 2020.

EGU2020-5171 | Displays | SSP2.13

Vegetation and ocean feedbacks on the Asian climate response to the uplift of the Tibetan Plateau

Ran Zhang, Dabang Jiang, and Zhongshi Zhang

The growth of the Tibetan Plateau (TP) is one of the important forcings acting on the evolution of the Asian climate during the Cenozoic. However, whether vegetation and ocean feedbacks play a specific role in the Asian climate response to TP uplift remains unclear. Here we investigate this issue through a set of numerical experiments with the Community Earth System Model. The results indicate that vegetation and ocean feedbacks have important but different effects on the Asian climate change in association with TP uplift, which are intrinsically related to the adjustment of thermal structure. The vegetation feedback leads to excess annual precipitation in East China and South Asia and a weakening of the Asian winter monsoon winds. By comparison, the ocean feedback induces a deficit of annual precipitation particularly in most areas of the Bay of Bengal and the South China Sea and a weakening of the Asian summer and winter monsoon winds. These results highlight the importance of vegetation and ocean feedbacks and further facilitate a better understanding of the paleoclimatic response to the uplift of the TP.

How to cite: Zhang, R., Jiang, D., and Zhang, Z.: Vegetation and ocean feedbacks on the Asian climate response to the uplift of the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5171, https://doi.org/10.5194/egusphere-egu2020-5171, 2020.

EGU2020-6692 | Displays | SSP2.13

Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis

Yingying Jia, Christoph Glotzbach, Todd Ehlers, and Lixing Lü

The Pamir is an along-strike continuation of the Tibet-Himalaya orogen and penetrated ~300 km into the Tarim and Tajik basins in Cenozoic times. This northward indentation led to regional paleoenvironmental changes and facilitated northward transport of the far-field stress from the India-Asia plate boundary. Due to the compressional stress from the India-Asia boundary and Cenozoic lithosphere delamination, the Pamir underwent intense exhumations, which well recorded its Late Cenozoic mountain building processes. However, the very rapid Late Cenozoic exhumation also erased earlier cooling records and hinders a clear understanding of the Early Cenozoic tectonic evolution of Pamir. Thus, the onset and magnitude of the northward movement of Pamir are loosely constrained (Eocene-Late Oligocene) and long debated. In particular, the Early Cenozoic tectonic evolution of Pamir is unclear.

Provenance study of sediments in the adjacent sediment basins is a widely used method to reconstruct the tectonic-geomorphologic evolution of a mountain range. We carried out paleocurrent measurements and detrital zircon analysis of the Cretaceous-Pliocene sediments in the northern Pamir-Tian Shan convergence zone. Our study area, the Tierekesazi section, is located immediately south to the southern Tian Shan and is evolved in the present foreland basin of the southwestern Tian Shan. The provenance data show that the Tian Shan was the primary source area of the northwestern Tarim basin in the Cretaceous. The appearance of the Triassic-Jurassic detrital zircon grains and northward paleo-flow directions in the Eocene (~41 Ma) to Middle Miocene sediments suggest the Pamir became an important source area of the northwestern Tarim basin. Combining with the regional crustal shortening and paleoclimate data, we speculate that the northward indentation of the Pamir initiated before ~41 Ma. In contrast with the northward movement and Middle-Late Miocene accelerated exhumation of the Pamir, the source area of the studied section shifted back to the Tian Shan after the Middle Miocene. It consists with the Middle-Late Miocene uplift of the southwestern Tian Shan. Simultaneously, the crustal shortening of Pamir propagated to its northern foreland. Newly formed fold-and-thrust zones probably blocked the sediment transport from Pamir to the Tierekesazi section, and the present-day east flowing drainage system in the Pamir-Tian Shan convergence zone was established. We infer, in this period, the Pamir likely reached its present position, which is consistent with the appearance of an extreme arid climate in the Tarim basin.

How to cite: Jia, Y., Glotzbach, C., Ehlers, T., and Lü, L.: Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6692, https://doi.org/10.5194/egusphere-egu2020-6692, 2020.

EGU2020-12681 | Displays | SSP2.13

Late Cretaceous – early Paleogene tectonic evolution of the Central Pamir inferred from the geochemical features of the Bartang volcanics

Jovid Aminov, Guillaume Dupont-Nivet, Lin Ding, Stephane Guillot, Johannes Glodny, Carole Cordier, Pierrick Roperch, Yunus Mamadjanov, and Mamurjon Mirvaisov

The Pamir orogen in Central Asia has formed by the amalgamation of several Gondwana-derived terranes and their accretion to the southern Eurasian margin in the Mesozoic. Later on, the crust of the Pamir orogen was strongly deformed and uplifted as a result of the Cenozoic India-Asia collision. The deformation of the Pamir orogen, which resulted in shortening, crustal thickening and exhumation of deep crustal rocks within the gneiss domes of the Central and Southern Pamir makes the area an ideal site for studying the India-Asia collision and its paleogeographic and climatic effects. To account for today’s 70-km-thick crust of the Pamir orogen and more than 400 km of convergence accommodated in the Pamir, pre- and syn-collisional processes have been proposed including, continental subduction, delamination, extrusion and oroclinal bending of the Pamir arc. However, testing these models requires constraints on the pre-collisional state of the Pamir lithosphere and its tectono-magmatic evolution. During most of the Cretaceous, the southern Pamir terrane was a site of a widespread arc-related magmatism, which resulted in the formation of many plutons and a volcanic suite of intermediate to acidic composition, whereas the central Pamir terrane lacked any sign of magmatic activity. However, in the late Cretaceous to early Paleogene (78 – 61 Ma) a less widespread magmatic activity in the western part of the Central Pamir resulted in the formation of the Bartang mafic to intermediate volcanic and volcaniclastic rocks. We report here the geochemical and Sr-Nd isotopic features of the late Cretaceous – early Paleogene Bartang volcanics. This volcanic suite bears geochemical and radiogenic isotope features that differ from the arc-related southern Pamir igneous rocks. Mafic basalts that comprise the lowest portion of the section exhibit MORB-like pattern with slightly depleted light rare earth elements (LREE) and large ion lithophile elements (LILE). Further up in the section this pattern shifts towards an arc-related pattern with enriched LREE and LILE. The 87Sr/86Sri isotope ratios are lower (0.705335 – 0.706693) than those from the southern Pamir igneous rocks (0.706915 – 0.711105) and epsilon Nd values exhibit ratios close to mantle domain, ranging between -0.7 and -2.7, with the lower part of the section showing less negative values then the upper. In contrast to the Bartang volcanics, the southern Pamir igneous rocks exhibit more negative epsilon Nd values (from -4.7 to -13). The relatively low initial 87Sr/86Sr isotope ratios and slightly negative epsilon Nd values of the Bartang volcanic rocks together with the trace elements pattern that shifts from MORB-like to arc-related indicate mixing of two magmas derived from depleted and enriched mantle sources, with the latter inheriting the arc-related pattern from the subduction stage. Alternatively, the arc-related pattern could be derived through contamination of the primary magma by the crustal material. These features, compared to the southern Pamir arc-related igneous rocks, also indicate that the tectonic setting in the Pamir changed during the late Cretaceous from a continental arc to a within-plate extensional setting.

How to cite: Aminov, J., Dupont-Nivet, G., Ding, L., Guillot, S., Glodny, J., Cordier, C., Roperch, P., Mamadjanov, Y., and Mirvaisov, M.: Late Cretaceous – early Paleogene tectonic evolution of the Central Pamir inferred from the geochemical features of the Bartang volcanics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12681, https://doi.org/10.5194/egusphere-egu2020-12681, 2020.

EGU2020-6105 | Displays | SSP2.13

Late Miocene deformation and surface uplift of the North Pamir

Lin Li, Guillaume Dupont-Nivet, Pierrick Roperch, Yani Najman, Mustafa Kaya, Niels Meijer, and Jovid Aminov

The Pamir Plateau, as the west extension of the Tibetan Plateau, forms a prominent salient into central Asia. Previous studies have suggested that the Pamir indented northward, causing retreat of the proto-Paratethys Sea and aridification of Central Asia. However, its indentation and surface uplift history are poorly constrained, with existing studies focusing mainly on the eastern side of the Pamir salient. This study presents new multi-proxy data from the southeast Tajik Basin, located on the western side of the salient, to explore the tectonic evolution of the Pamir Plateau. In the southeast Tajik Basin, our magnetostratigraphic study indicates that the fluvial and alluvial strata were deposited between ~20-8 Ma, with thick conglomerates starting at ~15 Ma. Provenance data from sandstone detrital zircon U-Pb ages and mudstone eNd values indicate a pronounced shift in sediment source from the Central Pamir to the North Pamir around 12 Ma. This provenance change is corroborated by carbonate stable oxygen isotopes showing a gradual decreasing trend between 12-8 Ma, which most likely reflects surface uplift of the North Pamir. Collectively, our results indicate that the North Pamir was originally part of the broad Tarim-Tajik Basin, and has been gradually uplifted since ~12 Ma.

How to cite: Li, L., Dupont-Nivet, G., Roperch, P., Najman, Y., Kaya, M., Meijer, N., and Aminov, J.: Late Miocene deformation and surface uplift of the North Pamir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6105, https://doi.org/10.5194/egusphere-egu2020-6105, 2020.

EGU2020-18291 | Displays | SSP2.13

Asian paleoenvironments, paleogeography and paleobiodiversity interactions during the Greenhouse-Icehouse transition

Guillaume Dupont-Nivet, Niels Meijer, Mustafa Kaya, Jan Westerweel, Delphine Tardif, Natasha Barbolini, Alexander Rohrmann, Jovid Aminov, Diego Ruiz, Amber Woutersen, Huansheng Huang, Fernando Poblete, Alexis Licht, Pierrick Roperch, Carina Hoorn, Jean-Noël Proust, Frederic Fluteau, Yannick Donnadieu, and Stéphane Guillot

The ongoing surge of international research on Asian Climate and Tectonics enables to better assess interactions between forcing mechanisms (global climate, India-Asia collision, Tibetan Plateau growth) and paleoenvironmental changes (monsoons, aridification), land-sea distribution, surface processes, paleobiogeographic evolution and the global carbon cycle. We review here the progress of the ERC MAGIC project (Monsoons in Asia caused Greenhouse to Icehouse Change?) integrating regional geodynamic constraints, well-dated environmental / biodiversity records and climate modeling. MAGIC focuses on the Paleogene period that includes the global Greenhouse to Icehouse cooling, the early collision and plateau growth and associated regional development of monsoons and westerlies over the Proto-Paratethys sea. Our work focuses on three areas constraining Asian paleoenvironments. (1) In Myanmar, paleomagnetic results, new dating of magmatic rocks and sediments along with additional detrital geochronology and basin analysis of the Burmese subduction margin and implications for the history of India-Asia convergence. (2) Along the Northeastern Tibetan Plateau margin, the combination of multiple proxies (leaf wax stable isotope, pollen, grain size, etc…)  applied to an extended lacustrine Paleogene record enables to identify precisely Asian climate changes and their consequences on ecosystems. (3) In westernmost China and Tajikistan, the proto-Paratethys sea fluctuations and the sedimentary records of Pamir tectonic evolution are now precisely dated enabling to constrain driving mechanisms and paleoenvironmental consequences. Together these results are used to constrain climate modeling experiments which permit validation of hypotheses on interactions between paleogeography, paleoenvironments and paleobiodiversity at Asian and global scales in response to long-term and short-term events.

How to cite: Dupont-Nivet, G., Meijer, N., Kaya, M., Westerweel, J., Tardif, D., Barbolini, N., Rohrmann, A., Aminov, J., Ruiz, D., Woutersen, A., Huang, H., Poblete, F., Licht, A., Roperch, P., Hoorn, C., Proust, J.-N., Fluteau, F., Donnadieu, Y., and Guillot, S.: Asian paleoenvironments, paleogeography and paleobiodiversity interactions during the Greenhouse-Icehouse transition , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18291, https://doi.org/10.5194/egusphere-egu2020-18291, 2020.

EGU2020-8570 | Displays | SSP2.13

Epicontinental seas as efficient carbon sinks: proto-Paratethys & West Siberian seas during the PETM

Mustafa Kaya, Guillaume Dupont-Nivet, Joost Frieling, Chiara Fioroni, Alexander Rohrmann, Sevinç Özkan Altıner, Ezgi Vardar, Birgit Plessen, Mehmut Mamtimin, and Guo Zhaojie

Removal of carbon on geological timescales is generally assumed to be governed by the relative strength of silicate weathering and organic carbon burial. For past transient warming phases organic carbon burial has been considered as a relevant negative feedback, but it remains uncertain how this compares to present-day anthropogenic emissions. The ocean is very effective at organic carbon remineralization and, only certain regions bury significant amounts of organic carbon. Organic carbon burial hotspots include shallow water regions along active continental margins and permanently oxygen-deficient zones.

Shallow inland seas covering continents bear depositional settings with broad low-energy facies and delivery of low-reactivity, fossil (ancient) and terrestrial (both contemporary and aged, i.e., soil) organic carbon and lithogenic particles when they are associated with an active margin. These epicontinental seas might be hydrographically and geographically restricted resulting in oxygen-depleted environments. As such, epicontinental seas might serve as significant carbon sinks for all types of organic carbon components (i.e. marine, fossil, contemporary and aged terrestrial) with a high organic carbon preservation efficiency. However, oxygen deficient environments associated with epicontinental seas are currently rare and, as a consequence, organic carbon burial may be overestimated in importance as a negative feedback to anthropogenic emissions compared to the past.

As part of the ERC “MAGIC” project, we study the mechanics, relative contribution and preservation efficiency of ancient epicontinental seas as carbon sinks, using organic rich deposits dated to the Paleocene – Eocene Thermal Maximum (PETM) from the proto-Paratethys and West Siberian seas. We then calculate and compare the amount of organic carbon sequestered in these basins, relative to modeled estimates of global organic carbon burial. Our data corroborates the view that the sequestration of organic carbon arises due to enhanced recycling of phosphorus from sediments under anoxic conditions and coupled increase in biological productivity. We estimate ca. 1380 Gt C burial, plausibly more than half of the estimated global total excess burial across the PETM is focused in the proto-Paratethys and West Siberian seas. This supports the hypothesis that alongside the organic carbon burial on other continental margins, the proto-Paratethys and West Siberian basins acted as significant carbon sinks, leading to the termination of the PETM. An important implication of this is that, for the present-day and other periods in the geological past with small epicontinental seas, the effectiveness of this negative carbon cycle feedback is likely greatly diminished.

How to cite: Kaya, M., Dupont-Nivet, G., Frieling, J., Fioroni, C., Rohrmann, A., Özkan Altıner, S., Vardar, E., Plessen, B., Mamtimin, M., and Zhaojie, G.: Epicontinental seas as efficient carbon sinks: proto-Paratethys & West Siberian seas during the PETM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8570, https://doi.org/10.5194/egusphere-egu2020-8570, 2020.

EGU2020-8597 | Displays | SSP2.13

Intensified hydrological cycle during the Early Eocene Climatic Optimum (EECO) recorded in the Xining Basin, NE Tibet

Niels Meijer, Guillaume Dupont-Nivet, Alexis Licht, Pierrick Roperch, Alexander Rohrmann, Amber Woutersen, Carina Hoorn, Natasha Barbolini, Aijun Sun, Hemmo Abels, Hanno Meyer, and Norbert Nowaczyk

The evolution of Asian climate during the Cenozoic is traditionally linked to shifts in paleogeography such as the proto-Paratethys Sea incursions and uplift of the Tibetan Plateau driving monsoonal circulation and affecting the mid-latitude westerlies in Central Asia. In contrast, the role of global climate in the Asian hydrological cycle remains unclear. Here, we present a new stratigraphic record from the terrestrial Xining Basin in central China, which covers the Early Eocene Climatic Optimum (EECO), a period characterized by long-term global warmth and elevated atmospheric CO2 levels. The record is dated using magnetostratigraphy and extends the previously studied Paleogene strata down to 50.9 Ma (chron C23n). We use a variety of paleoclimate proxies, to derive the hydroclimatic evolution of the basin at this time. The lithostratigraphy is characterized by organic-rich mudrocks and gypsum beds (reaching TOC contents of up to 1.7%) interpreted as an alluvial mudflat to saline lake. The higher organic content of the strata indicates either increased organic productivity or preservation, both of which suggest a wetter depositional environment during the EECO. This is corroborated by palynological records showing a large increase in the abundance and diversity of trilete spores, indicating a wetter biome at this time. In addition, the d13C values of the bulk organic matter and leaf waxes (both C29 and C31), suggest a reduction in water stress on plants and a wetter environment as well. These observations are in stark contrast to the arid red beds, evaporites and xerophytic pollen observed in the underlying Cretaceous-Paleocene strata and overlying middle-late Eocene deposits. The peak global warmth of the EECO is thus clearly linked to an intensified Asian hydrological cycle suggesting a major driving role for global climate.

 

How to cite: Meijer, N., Dupont-Nivet, G., Licht, A., Roperch, P., Rohrmann, A., Woutersen, A., Hoorn, C., Barbolini, N., Sun, A., Abels, H., Meyer, H., and Nowaczyk, N.: Intensified hydrological cycle during the Early Eocene Climatic Optimum (EECO) recorded in the Xining Basin, NE Tibet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8597, https://doi.org/10.5194/egusphere-egu2020-8597, 2020.

EGU2020-12228 | Displays | SSP2.13

Cenozoic Nd isotopic variation of Asian dust in the northern Tibetan Plateau and the North Pacific Ocean

Yibo Yang, Xiaomin Fang, Albert Galy, Rongsheng Yang, Bowen Song, and Yudong Liu

Cenozoic changes in climate, erosion, and atmospheric circulation in Asian interior continents can be reconstructed from records of eolian dust deposition from sediments of the North Pacific Ocean (NPO). Through a careful investigation of Nd isotope as eolian dust source tracer, the well-known core GPC3 in the central NPO has provided so far the most complete Asian dust records since ~40 Ma. Nd isotope in the GPC3 eolian dust thus documented an integrated history of Nd isotopic change of very fine eolian dust contributed from various geological terranes in Asian dust source areas. Unraveling this ~40 Myr-long Nd isotopic change in the NPO provides a first order constraint on the provenance change of the Asian dust source areas as a whole. However, this work cannot be done without an explicit Nd isotopic history for each geological terrane within the broad Asian dust source areas, since the Asian dust source area can be at least divided isotopically into two regions with distinct Nd isotopic values, e.g., the northern Tibetan Plateau (NTP) and the Central Asian Orogen (CAO). In this work, we present new data of river sediment Nd isotopic data around the entire Qaidam and Xining Basins to yield a more comprehensive Nd isotopic regimes at the NTP with compiling previously reported data. We have established an integrated Cenozoic Nd isotopic records of finer dust in the NTP based on previous records and our new Nd isotopic records in the Xining Basin from 52 to 17 Ma and Linxia basin from 23 to 5 Ma using both bulk sediments and clay fractions (<2 μm). After comparison of the reconstructed Nd isotopic variation in fine dust at the NTP with that in the NPO, we have further assessed the relative contributions of NTP and CAO to the Asian dust preserved in the NPO during the last 40 Myr, which indicates a dominant late Oligocene-Neogene uplift and growth of the mountains at the NTP and the CAO regions.

How to cite: Yang, Y., Fang, X., Galy, A., Yang, R., Song, B., and Liu, Y.: Cenozoic Nd isotopic variation of Asian dust in the northern Tibetan Plateau and the North Pacific Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12228, https://doi.org/10.5194/egusphere-egu2020-12228, 2020.

EGU2020-13422 | Displays | SSP2.13

Magnetostratigraphy of the Eocene Jianchuan Basin in southeast Tibet: A preliminary result

Cairong Luo, Ping Wang, Yongxiang Li, Shanying Li, Xiaochun Wei, and Yongjie Huang

Early Cenozoic continental sediments deposited contemporaneously or soon after the onset of India-Asian collision provide an obvious target for gaining insight into the early stages of the growth of the Tibetan plateau. These continental sequences are generally found in an arcuate belt that extends from the central plateau into the western Yunnan province (e.g. Nangqian-yushu Basin, Gongjo Basin and Jianchuan Basin). With limited exposure and elusive datable horizons except for a few dikes cross-cutting stratigraphy and interbedded lava flows, there were few constraints on absolute time of these Cenozoic sediments, limiting further studies of the tectonic, topographic and environmental evolution in southeast Tibet. Here, we focus on the Jianchuan basin, the age of which was mapped from the Paleocene up to the Pliocene but recently reassigned to the Paleocene/Eocene as a whole. The Xinsong section with 1547 meters in thickness was measured at the meter scale to determine vertical changes through the depositional facies. The lower part of the section consists of 1027 m thick red-colored, massive siltstone with many fine sandstone interlayers, while the upper part of the section is composed by a series of basal-scoured, upward-fining and stacked sand bodies with the thickness of 520 m. A total of 981 standard paleomagnetic oriented samples were collected. Samples were subjected to stepwise thermal demagnetization that revealed either two or three component magnetizations with the high temperature component (HTC) unblocked at ∼660-680 °C. Our preliminary results show multiple polarity reversals that can be well correlated with the Geomagnetic Polarity Time Scale (GPTS) between ca. 50 and ca. 40 Ma. We interpret that these sediments were deposited in a restricted, narrow basin in the footwalls of thrust fault where the depositional environments were highly related to the compressional deformation. Our new result may be of great significance for understanding the kinematic and dynamic models of the deformation and evolution of the Tibetan plateau.

How to cite: Luo, C., Wang, P., Li, Y., Li, S., Wei, X., and Huang, Y.: Magnetostratigraphy of the Eocene Jianchuan Basin in southeast Tibet: A preliminary result, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13422, https://doi.org/10.5194/egusphere-egu2020-13422, 2020.

EGU2020-13156 | Displays | SSP2.13

Lower Yangtze drainage reorganization response to western Pacific Subduction

Ping Wang, Hongbo Zheng, Yongdong Wang, Xiaochun Wei, Lingyu Tang, Fred Jourdan, Jun Chen, and Xiangtong Huang

The evolution of the longest river in Asia, Yangtze, provides a spectacular example to understand the Cenozoic interaction between tectonic, climate and surface processes. The oldest Yangtze deposits in southeast China, characterized by thick sequence of unconsolidated gravel, sand and silty clay, referred as “Yangtze Gravel”, has been recently found in its lower reach and dated back to > 23 Ma, indicating a pre-Miocene establishment of a through-going river. However, the link between river reorganization and tectonic evolution has never been well understood. Far-field effects of the Indian–Eurasia collision are often invoked to explain the widespread East Asia lithospheric deformations and the opening of the marginal, as well as the through-going of the large rivers. However,  some geological and geophysical investigations challenge this model and suggest that the Pacific Plate subduction beneath Eurasia plays an much more active role in East Asia lithospheric deformation during the Cenozoic. Here, we study the sedimentology, chronology and provenance of the Yangtze Gravel based on 17 stratigraphic sections exposed along the Lower Yangtze River. Our results indicate a braided alluvial system (Paleo-Lower Yangtze) established since early Miocene across the Jianghan Basin, North Jiangsu Basin and East China Sea Shelf Basin. Compared with the Early Cenozoic red-colored, halite-bearing lacustrine deposits, our results indicate a larger tectonically controlled shift from rifting to post-rift down-warping across these basins. During Early Cenozoic, the initial subduction of Pacific Plate may contribute to the back-arc extension and affect the continental deep interior of East Asia many thousands of kilometers from the subduction margin. During Oligocene to Miocene, the ongoing subduction of the Pacific plate produced a stagnant slab that may have significantly triggered the post-rift subsidence and the connection of these basins. The deposition of the “Yangtze Gravel” reflect the dynamic response of surface processes to western Pacific subduction in East Asia.

How to cite: Wang, P., Zheng, H., Wang, Y., Wei, X., Tang, L., Jourdan, F., Chen, J., and Huang, X.: Lower Yangtze drainage reorganization response to western Pacific Subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13156, https://doi.org/10.5194/egusphere-egu2020-13156, 2020.

EGU2020-11882 | Displays | SSP2.13

Cenozoic affinity of the Gondwanan rocks of eastern Timor: evidence from geo-thermochronometry

Brendan Duffy, Brian Lew, Kevin Boland, Barry Kohn, Erin Matchan, Roland Maas, David Dixon, Lourenço Pedro, Paulo de Carvalho, and Mike Sandiford

EGU2020-20827 | Displays | SSP2.13

Monster polar shift, shifts back: paleoclimate and CA-ID-TIMS evidence from northern China

Paul Olsen, Jingeng Sha, Scott Maclennan, Sean Kinney, Yanan Fang, Clara Chang, Theo Kuhn, Roger Fu, Dennis Kent, and Blair Schone

The two great lacustrine fossil Konservat-Lagerstätten of northeastern China producing feathered dinosaurs, the Jurassic Yanliao Biota and the Jehol Biota, were deposited during relatively humid times and are separated by a major redbed interval, typified by the Tuchengzi Formation deposited under a much more arid climate (1). We present new zircon CA-TIMS U-Pb ages for the peaks of the Yanliao [~160 Ma] and the Jehol biotas [Yixian Fm ~125 Ma] constraining a shift in that region from a higher-latitude temperate zone to a lower-latitude semiarid zone consistent with a ~30° arc distance shift true polar wander shift (1, 2, 3). The Yanliao Biota and the Jehol Biota are preserved in remarkably similar facies almost lacking signs of desiccation, while the Tuchengzi Formation has abundant evidence for desiccation and even eolian dune sands. This suggests, under a simple zonal climate model, a rapid shift to the south from Jurassic times and a shift back into Early Cretaceous times. A very similar and even more dramatic shift is seen in northwest China in the Junggar Basin where Triassic-Middle Jurassic coal bearing sequences with evidence of seasonal freezing (4) is replaced by a Late Jurassic [~150 Ma (5)] redbed sequence [including the famous dinosaur- and crocodiliomorph-bearing Shishugou Formation], and again replaced by coal-bearing strata in the Early Cretaceous, suggesting a similar magnitude shift south and back north of the region. The hypothesis that the monster polar shift is transient, swinging south and then north in ~35 million years necessitates rigorous testing by inclination-error-corrected paleomagnetic data to cleanly separate rapid latitudinal effect from rapid global climate change or regional orographic effects.

  1. Olsen P E et al. (2015) Geological Society of America, Abstracts with Programs 47, 378.
  2. Muttoni G, Kent D V (2019)Journal of Geophysical Research. Solid Earth 124, 3288-3306.
  3. Yi Z, Liu J, Meert, G (2019) Geology 47, 1112-1116.
  4. Olsen P E et al. (2018) Geological Society of America Abstracts with Programs 50, doi: 10.1130/abs/2018AM-325061 (2018).
  5. Fang Y et al. (2019) Topographic evolution of the Tianshan Mountains and their relation to the Junggar and Turpan Basins, Central Asia, from the Permian to the Neogene. Gondwana Research 75, 47-67 (2019).

How to cite: Olsen, P., Sha, J., Maclennan, S., Kinney, S., Fang, Y., Chang, C., Kuhn, T., Fu, R., Kent, D., and Schone, B.: Monster polar shift, shifts back: paleoclimate and CA-ID-TIMS evidence from northern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20827, https://doi.org/10.5194/egusphere-egu2020-20827, 2020.

EGU2020-3865 | Displays | SSP2.13

Trend analysis of extreme climate indices during winter wheat growth period in China

Hanjiang Nie, Tianling Qin, Zhenyu Lv, and Jianwei Wang

In this study, the major winter wheat planting area of China is selected as the study area, with the time scale of the growth period of winter wheat (a total of 56 growth periods during 1961/10-2016/5). The significance, stability, magnitude of the trend and the average trend of the study area with 8 temperature indices and 7 precipitation indices of 453 meteorological stations are tested by Mann–Kendall method and Sen's nonparametric method. The following observation can be made: (1) the cold extreme indices show strong and stable downward trend in most of the stations in the study area, while the hot extreme indices show strong and stable upward trend, especially in the northern winter wheat planting area and the north of the southern winter wheat planting area. (2) The trends of extreme precipitation indices in most of the sites in the study area are insignificant and unstable. Only in R20mm, a significant and stable decreasing trend is showed in some stations, which mainly located in the northern winter wheat planting area and part of the central and western regions in study area. The results in some ways could enrich the references for understanding the climate change in the growth period of winter wheat in the region and help to formulate a better agronomic management practice of winter wheat.

How to cite: Nie, H., Qin, T., Lv, Z., and Wang, J.: Trend analysis of extreme climate indices during winter wheat growth period in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3865, https://doi.org/10.5194/egusphere-egu2020-3865, 2020.

SSP2.14 – Volcanism, impacts, and extinctions: links between deep time and the Anthropocene

EGU2020-6727 | Displays | SSP2.14 | Highlight

Constraining North Atlantic Igneous Province (NAIP) activity during the late Paleocene and early Eocene

Morgan Jones, Ella Stokke, Lars Augland, Philip Pogge von Strandmann, Emma Liu, Tamsin Mather, Alan Rooney, Jessica Tierney, Jessica Whiteside, Christian Tegner, Bo Schultz, Sverre Planke, and Henrik Svensen

The close temporal correlation between the emplacement of large igneous provinces and environmental crises in the geological record suggests a causal relationship. One such example is the emplacement of the North Atlantic Igneous Province (NAIP) and the Paleocene-Eocene Thermal Maximum (PETM), an extreme climate change event that occurred ~56 Ma. The main pulse of activity from the NAIP is around this time, but current radioisotopic ages are too low-resolution to constrain whether this activity was before, during and/or after the PETM. An ideal locality for understanding the initiation and development of the PETM is the island of Fur, northwest Denmark. The sedimentary sequence consists of clays and diatomites deposited in an epicontinental, shallow marine sea. The high sedimentation rates and close proximity to the NAIP means there are numerous volcanic and climatic proxies in the strata that can be used to provide high-resolution records constraining the relative and absolute timings of these events.

Here we present the findings of the project ‘Ashlantic’, which focuses on pre- to post-PETM strata. We adopt a multiproxy approach using volcanic tracers, including tephra horizons, Hg anomalies, and Os isotopes, to infer the intensity and timing of NAIP activity. Volcanic glass morphology and chemistry suggests a hydromagmatic origin for key tephra intervals, while U-Pb dating of magmatic zircon constrains the timing of NAIP activity and the development of the PETM. Detailed chemostratigraphic logs and datasets (e.g. δ13C analyses) define the onset and duration of the PETM, while clay chemistry, Li isotopes, total organic carbon (TOC), and the paleothermometer TEX86 are used to assess the climate response to global warming during the PETM. In concert, our results suggest that the NAIP was active just before, during, and after the PETM, but the relationship between the NAIP and the marine and terrestrial environments is complex. These findings call for further work, such as ICDP and/or IODP drilling of North Sea sediments.

How to cite: Jones, M., Stokke, E., Augland, L., Pogge von Strandmann, P., Liu, E., Mather, T., Rooney, A., Tierney, J., Whiteside, J., Tegner, C., Schultz, B., Planke, S., and Svensen, H.: Constraining North Atlantic Igneous Province (NAIP) activity during the late Paleocene and early Eocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6727, https://doi.org/10.5194/egusphere-egu2020-6727, 2020.

EGU2020-8025 | Displays | SSP2.14

Severe perturbations of the marine biosphere following the Chicxulub impact

Georg Feulner, Julia Brugger, Matthias Hofmann, and Stefan Petri

Among the "big five" mass-extinction events during the Phanerozoic, the end-Cretaceous extinction 66 million years ago is particularly well known because it marks the demise of the non-avian dinosaurs. Evidence for the Chicxulub impact as the primary cause of this mass extinction has been accumulating over the past four decades, but there are still many open questions regarding the detailed course of events.

Building on our earlier modelling results demonstrating strong global cooling due to sulfate aerosols formed in the wake of the Chicxulub impact (Brugger, Feulner & Petri 2017, Geophys. Res. Lett., 44:419-427), we here explore the response of the ocean in more detail. Specifically, we added a marine biogeochemistry module to a coupled atmosphere-ocean model to investigate the effects of the impact on ocean geochemistry and primary productivity.

We find that the formation of stratospheric sulfate aerosols leads to a marked decrease in annual global mean surface air temperatures by at least 26°C in the coldest year after the impact, returning to pre-impact temperatures after about one century. The strong surface cooling induces vigorous ocean mixing that leads to changes in oxygen distributions and nutrient availability. Due to the darkness, marine net primary productivity essentially shuts down in the first years after the impact. Once the light returns, however, we find a significant increase in primary productivity caused by a surge in nutrient availability, both due to upwelling in the ocean and delivery by the impactor. These strong perturbations of the marine biosphere further support the notion that the impact played a decisive role in the end-Cretaceous mass extinction.

How to cite: Feulner, G., Brugger, J., Hofmann, M., and Petri, S.: Severe perturbations of the marine biosphere following the Chicxulub impact, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8025, https://doi.org/10.5194/egusphere-egu2020-8025, 2020.

EGU2020-22414 | Displays | SSP2.14 | Highlight

Deccan Volcanism or the Chicxulub Impact: The Chicken or Egg Question

Gerta Keller

The Cretaceous–Paleogene boundary (KTB or KPB) mass extinction is primarily known for the
demise of the dinosaurs, the Chicxulub impact, and the rancorous forty-year-old controversy
over the cause of this mass extinction. For the first 30 years, the controversy primarily revolved
around the age of the impact claimed as precisely KTB based on the assumption that it caused
the mass extinction. The iridium (Ir) anomaly at the KTB was claimed proof of the asteroid
impact, but no Ir was ever associated with impact evidence and recent findings reveal no
extraterrestrial component in PGEs or the KTB Ir anomaly. Impact melt rock glass spherules are
also claimed as indisputable evidence of the KTB age impact, but such spherule layers are
commonly reworked from the primary (oldest) layer in late Maastrichtian, KTB and Danian
sediments; thus only the oldest impact spherule layer documented near the base of zone CF1
~200 ky below the KTB can approximate the impact’s age. Similarly, the impact breccia in the
Chicxulub impact crater predates the KTB. The best age derived from Ar/Ar dating of impact
glass spherules is within 200 ky of the KTB and thus no evidence for the KTB age. All evidence
strongly suggests the Chicxulub impact most likely predates the mass extinction ~ 200 ky and
played no role in it.
Deccan volcanism (LIP) was dismissed as potential cause or even contributor to the KTB mass
extinction despite the fact that all other mass extinctions are associated with Large Igneous
Province (LIP) volcanism but none with an asteroid impact. During the last decade, Deccan
volcanism gained credence based on a succession of discoveries: 1) the mass extinction in
between the longest Deccan lava flows across India; 2) high-precision dating of the entire
sequence of Deccan volcanism based on UPb zircon dating; 3) recognition of four distinct
eruption pulses all related to global climate warming with the largest pulse beginning 20 ky prior
to and ending at the KTB; 4) Identifying the climate link to Deccan volcanism based on age
dating and mercury from Deccan eruptions in marine sediments; and 5) Identifying the KTB
mass extinction directly related to the major Deccan eruption pulse, hyperthermal warming and
ocean acidification all linked to global mercury fallout from Deccan eruptions in marine
sediments. Despite this remarkable culmination of evidence, the controversy continues with
impact proponents arguing that Deccan volcanism didn’t exist at the KTB – the impact was the
sole cause.

How to cite: Keller, G.: Deccan Volcanism or the Chicxulub Impact: The Chicken or Egg Question, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22414, https://doi.org/10.5194/egusphere-egu2020-22414, 2020.

EGU2020-14578 | Displays | SSP2.14

Voluminous crustal degassing and immiscible sulfide genesis caused by magma-shale interaction in Large Igneous Provinces

Frances Deegan, Jean Bédard, Valentin Troll, Keith Dewing, Harri Geiger, Steve Grasby, Valeria Misiti, and Carmela Freda

Large Igneous Province (LIP) activity is hypothesized to impact global volatile cycles causing climate changes and environmental crises deleterious to the biosphere. Recent work suggests that the potential of LIPs to impact climate is magnified where they intrude organic-rich (i.e. shale-bearing) sedimentary basins. However, the chemical and degassing dynamics of magma-shale interaction are not well understood. Here we present the first experimental simulations of disequilibrium interaction between LIP magma and carbonaceous shale during upper crustal sill intrusions in the Canadian High Arctic LIP (HALIP), the latter of which were co-eval with oceanic anoxic event 1a. Experiments show that magma-shale interaction results in intense syn-magmatic degassing and simultaneous precipitation of sulfide droplets at the ablation interface. Magma-shale interaction on a basin-scale can thus generate substantial amounts of climate-active H-C-S volatiles, while the presence of strongly reducing volatiles may also increase the likelihood of magma to segregate a sulfide melt. These findings have fundamental consequences for our understanding of both large-scale Earth outgassing and metal prospectivity in sediment-hosted LIPs.

How to cite: Deegan, F., Bédard, J., Troll, V., Dewing, K., Geiger, H., Grasby, S., Misiti, V., and Freda, C.: Voluminous crustal degassing and immiscible sulfide genesis caused by magma-shale interaction in Large Igneous Provinces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14578, https://doi.org/10.5194/egusphere-egu2020-14578, 2020.

EGU2020-2141 | Displays | SSP2.14 | Highlight

Refining the temporal relation between Large Igneous Provinces and carbon cycle perturbations: not every LIP triggers environmental crises, not every crisis is due to a LIP!

Urs Schaltegger, Philipp Widmann, Nicolas D. Greber, Luis Lena, Sean P. Gaynor, Torsten Vennemann, and Hugo Bucher

The connection between volcanic activity of large igneous provinces and the respective feedback from environment and biosphere contributing to the carbon cycle has been investigated at the present temporal resolution of high-precision U/Pb dating. Uncertainties of 0.05 % on the 206Pb/238U age from zircon dating allow a resolution of 30-50 ka pulses of magmatic activity; simultaneously, the duration of carbon isotope excursions (CIE) can be determined, the geological boundaries dated, or global sedimentary gaps can be quantified at the same level of precision. This contribution demonstrates with two case studies that we can refine the contemporaneity and start to reliably infer causality of consecutive events at the 104 year level.

Until the Anisian the aftermath of the Permo-Triassic Boundary Mass extinction (PTBME; ~251.94 Ma, Baresel et al., 2017) is characterized by profound fluctuations of the global carbon cycle with amplitudes of up to 8 ‰ in d13Ccarb values. These represent large variations in the global climate and biological crises, in particular during the end-Smithian extinction event (~249.1 Ma). A precise chronology from the southern Nanpanjiang basin (China) allows for a quantification of these fluctuations of Earth climate. Following the volcanic pulse causing the PTBME, several discontinuous episodes of volcanism of the Siberian Large Igneous Province (S-LIP) were generally assumed to have caused the subsequent Early Triassic carbon cycle fluctuations. This is, however, in disagreement with the geochronological database of precise zircon U/Pb dates that put an end to the volcanic activity at 250.6 Ma (Burgess & Bowring, 2015; Augland et al., 2019). Therefore, recurrent S-LIP volcanism is an unlikely explanation for the Early Triassic unstable carbon cycle.

The initial intrusive pulse of the Karoo Large Igneous Province (K-LIP) formed the sill/dyke complex of the Karoo basin, South Africa. New, precise U/Pb geochronology confirms its very short duration at around 183.2-182.8 Ma (Burgess et al., 2015; Corfu et al., 2016), as well as its synchronicity with the lower Toarcian oceanic anoxic event (T-OAE), and a carbon cycle disturbance of presumable global importance. Repeated excursions in d13Corg of up to 3 ‰ in the late Pliensbachian (~185.5 Ma) as well as at the Pliensbachian-Toarcian boundary (~183.5 Ma) are therefore at least partly older than any known magmatic activity of the K-LIP (Lena et al., 2019). We therefore, again, must invoke non-volcanic drivers in order to explain the instability of the carbon cycle.

These two case histories demonstrate that in order to invoke causality and global importance to carbon cycle instability, as well as for the testing of its correlation with volcanic episodes, we need to rely on geochronology of both sedimentary and volcanic records at the 104 years level of precision.

References: Augland et al. (2019) Scientific Reports, 9:18723 ; Baresel et al. (2017) Solid Earth, 8, 361–378, 2017; Burgess & Bowring (2015) Science Advances, 1(7), e1500470–e1500470; Burgess et al. (2015) Earth and Planetary Science Letters, 415(C), 90–99; Corfu, F. et al. (2016) Earth and Planetary Science Letters, 434(C), 349–352; Lena et al. (2019) Scientific Reports, 9:18430.

How to cite: Schaltegger, U., Widmann, P., Greber, N. D., Lena, L., Gaynor, S. P., Vennemann, T., and Bucher, H.: Refining the temporal relation between Large Igneous Provinces and carbon cycle perturbations: not every LIP triggers environmental crises, not every crisis is due to a LIP!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2141, https://doi.org/10.5194/egusphere-egu2020-2141, 2020.

EGU2020-4145 | Displays | SSP2.14

Sills Sautéing Shales: Did Karoo Intrusions into the Ecca Formation cause the Toarcian Ocean Anoxic Event?

Sean P. Gaynor, Urs Schaltegger, and Henrik Svensen

Eruptions of Large Igneous Provinces (LIP) are commonly correlated with global climate change, and environmental, as well as biological, crises. However, establishing a causative link via chemical and physical proxies for global change is more complicated and often ambiguous. As technical improvements have allowed for increasingly higher precision dates especially in U/Pb dating, it is possible to better assess hypotheses connecting LIP’s and environmental impact via their contemporaneity. Here, we focus on the early Jurassic period, which includes a period of global change known as the Toarcian oceanic anoxic event (TOAE), as well as emplacement of the Karoo Large Igneous Province (K-LIP). Previous work has tied these two events together due to overlapping chronology and observed metamorphism and degassing (e.g., Svensen et al., 2012; Sell et al., 2014), and excellent exposure allows for extensive sampling of both the intrusive and extrusive components of the K-LIP. Therefore it is possible to directly study the influence of intrusive LIP magmatism on potential climate forcing.

The K-LIP is comprised of a suite of basaltic lava flows, sills, dike swarms, centered in southern Africa. Approximately 340,000 km3 of sills are interlaid within the Karoo Basin, and therefore served as significant heat source to the basin upon emplacement. While much of the sedimentary rocks of the basin are siliciclastic, the Ecca Group contains organic-rich facies and hosts 160,000 km3 of basaltic sills (Svensen et al., 2012). This unit is therefore uniquely capable of generating large volumes of thermogenic gas through thermal metamorphism of the organic matter of the shale. Previous mass balance calculations indicate that between 7,000 and 27,000 Gt of CO2 equivalents was released through metamorphic reactions in contact aureoles within the Ecca Group (Svensen et al. 2007). If intrusive magmatism was short lived within this formation, causing rapid volatilization and degassing from the shales, than this event could represent a mechanism to drive a short pulse of global climate change. Previous studies have shown that intrusions are coeval with the TOAE (Svensen et al., 2012; Corfu et al. 2016), however higher-precision geochronology data from the sills is necessary to determine if the flux and timing of thermogenic gases from the basin was sufficiently high to destabilize Earth’s climate. In order to test the hypothesis, we present single crystal U-Pb zircon dates from sills across the Ecca Group. These data will be used (i) to quantify the duration and flux rate of carbon gas during the intrusive event, and (ii) to better understand how and to what extent K-LIP intrusive activity and associated thermogenic gas release of Ecca wall rocks were able to drive global climate change.

 

Corfu, F., et al., (2016) EPSL, 434, 349-352.

Sell, B., et al., (2014) EPSL, 408, 48-56.

Svensen, H., et al., (2007) EPSL, 3-4, 554-566.

Svensen, H., et al., (2012) EPSL, 325-326, 1–9.

How to cite: Gaynor, S. P., Schaltegger, U., and Svensen, H.: Sills Sautéing Shales: Did Karoo Intrusions into the Ecca Formation cause the Toarcian Ocean Anoxic Event?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4145, https://doi.org/10.5194/egusphere-egu2020-4145, 2020.

EGU2020-10473 | Displays | SSP2.14

Rapid and intense CO2 emissions into the atmosphere: Examples from the end-Triassic extinction

Manfredo Capriolo, Benjamin Mills, Robert Newton, Jacopo Dal Corso, Alexander Dunhill, and Andrea Marzoli

The coincidence between mass extinction events and the emplacement of Large Igneous Provinces (LIPs) in the Phanerozoic geological record points to the magmatic CO2 degassing as the potential trigger of rapid global-scale climatic and environmental changes. The Central Atlantic Magmatic Province (CAMP) is one of the Earth’s hugest LIPs, and is coincident with the end-Triassic extinction, at ca. 201.5 Ma. Such LIPs emplacement and associated magmatic CO2 degassing have traditionally been interpreted as occurring over periods much longer than those of anthropogenic CO2 emissions, however our improving understanding of LIPs activity is reducing these timescales, with the latest estimates indicating CAMP magmatic pulses lasting approximately a few centuries each and characterized by high eruption rates [1; 2]. We employed a biogeochemical model to investigate the effects on ocean-atmosphere system and climate of these CAMP magmatic pulses, and to test whether such rapid and intense magmatic CO2 degassing is consistent with the climatic, geochemical and palaeontological record of the end-Triassic. Hence, we compared the modern anthropogenic emissions (since the Industrial Revolution) with the pulsed magmatic degassing during CAMP emplacement, in order to evaluate the impact of rapid and intense events on climate and environment changes.

 

[1] Knight et al. (2004), Earth Planet. Sci. Lett. 228, 143-160. [2] Marzoli et al. (2019), J. Petrol. 60, 945-996.

How to cite: Capriolo, M., Mills, B., Newton, R., Dal Corso, J., Dunhill, A., and Marzoli, A.: Rapid and intense CO2 emissions into the atmosphere: Examples from the end-Triassic extinction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10473, https://doi.org/10.5194/egusphere-egu2020-10473, 2020.

EGU2020-9792 | Displays | SSP2.14 | Highlight

Mercury anomalies in Palaeocene-Eocene Thermal Maximum (PETM) successions of Pyrenean peripheral basins: new evidence of a plausible link between volcanic emissions from the North Atlantic large igneous province and the PETM

Maxime Tremblin, Hassan Khozyem, Jorge E. Spangenberg, Charlotte Fillon, Eric Lasseur, Olivier Serrano, Jean-Yves Roig, Sylvain Calassou, Francois Guillocheau, Thierry Adatte, and Sébastien Castelltort

The Palaeogene represents the last “greenhouse” period characterized by high atmospheric CO2 concentrations and warm surface temperatures. This long-term climatic state was punctuated by several transient hyperthermal events. These events are recorded primarily by prominent negative carbon isotope excursions (NCIE) in both carbonates and organic matter of sedimentary successions. The largest hyperthermal of the Palaeogene, the Palaeocene-Eocene Thermal Maximum (PETM), is associated with a 5-8° rise in global temperature, ocean acidification and a global biotic perturbation. The PETM is thus often seen as a geological analogue for future greenhouse-gas-driven global warming. The source of the 13C-depleted carbon for the NCIE and whether it was released in one or numerous events however remains controversial. Numerous carbon sources have been suggested, either in concert or individually to explain the onset and the duration of the NCIE. These include magmatic as well as thermogenic release of CO2 associated with large scale magmatism. Over the last decade, mercury (Hg) found in marine and continental sedimentary succession has emerged as a potential proxy of past volcanic emissions, allowing to trace the relationship between the emplacement of Large Igneous Provinces (LIP) and periods of warming, mass extinctions, and biotic disruptions.

Although the PETM is widely recorded in pelagic and hemipelagic settings, its record in shallow-water and continental successions remains scarce due to frequent hiatuses and unconformities in such environments and a lack of enough biostratigraphic constraints. However, the high sedimentation rate, which may characterize shallow water settings, compared to deeper marine environments, may potentially preserve expanded NCIE successions to better understand the nature and causes of the PETM

In this study, we present the first synthetic high-resolution mercury and stable isotopic records of three shallow-water and continental successions from highly subsident peripheral basins North (Lussagnet) and South (Serraduy and Esplugrafreda) of the Pyrenean orogen across the PETM. In those sections, our results show two important negative carbon isotope excursions in the bulk-rock carbonates. Based on biostratigraphy and similarity of shape and amplitude of the isotopic excursions with global records, the largest NCIE is interpreted as the NCIE associated with the PETM. This excursion is immediately preceded by another NCIE, second largest in amplitude in our record, and that we interpret as the Pre-Onset Excursion (POE), found in few other profiles worldwide. The occurrence of the POE suggests a first episode of 13C-depleted carbon release before the onset of the PETM. These various NCIE are associated with important mercury anomalies, even when normalized to total organic content. This suggests that pulses of magmatism, probably associated to the emplacement of the North Atlantic Igneous Province (NAIP), contributed to the onset and to the long duration of the PETM.

Our work confirms that hyperthermal events of the Palaeogene can be well recorded in shallow water and continental successions and can be used as powerful stratigraphic tools for these depositional environments, in addition to providing information on the climatic perturbations associated with the PETM.

 

This work is founded and carried out in the framework of the BRGM-TOTAL project Source-to-Sink.

How to cite: Tremblin, M., Khozyem, H., Spangenberg, J. E., Fillon, C., Lasseur, E., Serrano, O., Roig, J.-Y., Calassou, S., Guillocheau, F., Adatte, T., and Castelltort, S.: Mercury anomalies in Palaeocene-Eocene Thermal Maximum (PETM) successions of Pyrenean peripheral basins: new evidence of a plausible link between volcanic emissions from the North Atlantic large igneous province and the PETM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9792, https://doi.org/10.5194/egusphere-egu2020-9792, 2020.

EGU2020-19252 | Displays | SSP2.14

Timing environmental perturbations across the Cretaceous – Paleogene boundary in the Boreal Realm (N. Denmark)

Sarah D. Møller, Thierry Adatte, Christian J. Bjerrum, and Nicolas Thibault

The Cretaceous-Paleogene boundary (K-PgB) interval of Denmark has been the subject of numerous contributions for understanding this mass extinction, focusing essentially on the famous coastal exposures of Stevns Klint (Sjælland). Although less popular, exposures of the K-PgB are also known in northern Jutland (NW Denmark) and have been the subject of a few contributions on their macro- and microfaunal content. Through an integrated study of the section of Nye Kløv (biostratigraphy and high-resolution stable isotope stratigraphy), we show here that the KPgB interval in northern Jutland presents the double advantage of (1) being continuous across the latest Maastrichtian to early Paleogene (contrary to Stevns Klint sections that bear several discontinuities such as prominent hardgrounds) and (2) bearing well-preserved macro- and microfossil assemblages, and isotopic trends in carbon and oxygen. Bulk carbonate oxygen isotopes delineate with great precision temperatures trends across the KPgB interval with cyclic oscillations that faithfully reproduce trends of the La2010b astronomical solution, hence allowing for an astronomical calibration of the section. The orbital calibration of the KPgB in Nye Kløv points to an age of 66.01 Ma. Our study delineates a Deccan warming optimum at 66.25 Ma corresponding to the deposition of the Kjølby Gaard marl, a distinct marly layer that can be traced throughout the North Sea. A clear shift toward the end-Maastrichtian cooling follows the Deccan warming at 66.1 Ma and precedes a last pulse of warming immediately below the boundary at 66.02 Ma. The earliest Danian is characterized by lower temperatures up until 65.88 Ma, after which temperatures resume to the same range as those of the Deccan warming, albeit with strong oscillations that reflect pacing by the short-eccentricity. This shift toward much warmer temperatures is associated with a first negative excursion in carbon isotopes. A second marked negative excursion in carbon isotopes occurs at 65.65 Ma and taken all-together, the overall warm interval comprising these two carbon isotope excursions reflects the local expression of the Dan-C2 hyperthermal event. Orbital calibration of the Nye Kløv section also allowed us to determine the timing of the recovery in the benthic community in the Boreal Chalk Sea, marked by an increase in skeletal fragments and brachiopod diversity, which occurred at 65.8 Ma, hence in conjunction with the Dan-C2 event.

How to cite: Møller, S. D., Adatte, T., Bjerrum, C. J., and Thibault, N.: Timing environmental perturbations across the Cretaceous – Paleogene boundary in the Boreal Realm (N. Denmark), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19252, https://doi.org/10.5194/egusphere-egu2020-19252, 2020.

EGU2020-20315 | Displays | SSP2.14 | Highlight

New insights about the processes leading to marine extinction at the K-Pg boundary using a coupled biogeochemical-ecosystem model

Le Hir Guillaume, fluteau fréderic, Hennequin Salome, and Goddéris Yves

If most experts agree that the Cretaceous-Paleogene (K-Pg) extinction (66 Ma) resulted from a combination of the Chicxulub impact and of Deccan volcanism, the chain of reactions (Bond and Wignall, 2014) leading to the extinction is not well constrained. 
 
 In the present study, we use the GEOCLIM model to explore extreme perturbations induced by the two events and to investigate processes leading to the marine extinction. This state-of-the-art numerical tool (geoclimmodel.wordpress.com) includes in particular a marine ecological model in which food webs are simulated and marine organisms are sensitive to abiotic factors of their environment. The characteristics of each “species” of marine organisms, such as the tolerance to pH or temperature changes or the efficiency of predation, are randomly fixed to avoid any determinism in the response to the environmental perturbations. 

  The response of the Earth system to the onset of Deccan traps and to the Chicxulub impact is explored by forcing the model with the most recent “eruptive sequences”  (Schoene et al., 2019, Sprain et al. 2019) and with the assumption of a pulse-like degassing (Chenet et al. 2009) sequence over 500 kyrs that includes CO2 and SO2. This new approach allows us to take into account the interplays between the sulfur and carbon cycles on multiple time scales (from year to 105  yrs) and to capture the model sensitivity to the uncertainties in atmospheric emissions (duration, timing, nature of gases, intensity of pulses, intensity of the impact).

  The coupled evolution of the Earth’s climate and oceanic geochemistry during the K-Pg boundary crisis will be presented. Without considering evolution processes, the biotic response (biomass and biodiversity) will be discussed with respect to the ecosystem structure existing before the perturbations. 

How to cite: Guillaume, L. H., fréderic, F., Salome, H., and Yves, G.: New insights about the processes leading to marine extinction at the K-Pg boundary using a coupled biogeochemical-ecosystem model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20315, https://doi.org/10.5194/egusphere-egu2020-20315, 2020.

EGU2020-2002 | Displays | SSP2.14

Faunal and environmental changes through the Cretaceous-Paleogene boundary (K-Pg) linked with Deccan Volcanism: evidence from the Neo-Tethys, Turkey

Ali Uygar Karabeyoglu, Thierry Adatte, Valentin Lorenzo, Jorge Spangenberg, Sevinç Özkan Altıner, and Demir Altıner

Recent multi-disciplinary efforts demonstrate a correlation between continental flood basalt (CFB) volcanism and major environmental catastrophes associated with four out of the five largest Phanerozoic mass extinctions. Unique among these is the end-Cretaceous mass extinction, which is potentially coincident with both the Chicxulub bolide impact and the Deccan volcanism. Among these two drivers, the role of the Deccan volcanism is crucial in order to decipher if there is a causal relationship between volcanism and environmental stress, and if so, how stressed the environment was during the latest Maastrichtian. To assess the cause-and-effect relationship between Deccan volcanism and climate change and mass extinctions, high-resolution biostratigraphy, quantitative species analysis coupled with geochemical measurements have been performed on complete sections of Mudurnu-Göynük and Haymana basins (Turkey).

In both basins Maastrichtian sedimentation is characterized by monotonous mudstones, which sharply in turn to marl-calcareous mudstone alternations in the earliest Danian. Detailed quantitative study on planktonic foraminifera of the Haymana Basin revealed that planktonic foraminiferal community in the latest Maastrichtian is dominated by ecological generalists with small, simple morphologies (e.g., Heterohelix, Globigerinelloides, Guembelitria). Among them low oxygen tolerant Heterohelix globulosa is the most dominant taxa and their abundance changing with the presence of stress marker Guembelitria cretacea. In all sections, the K/Pg boundary itself is characterized by 2-3 mm thick reddish oxidized layer which corresponds to sudden annihilation of large, ornamented ecological specialists (e.g., Globotruncana, Rugoglobigerina, Racemiguembelina). Right after the boundary, there is an acme of calcareous dinoflagellate cysts (Thoracosphaera) and a surge of Guembelitria cretacea indicate ecosystem collapse in post-K/Pg environment.

On the other hand, detailed quantitative analysis shows a systematic reduction in the species richness throughout the Plummerita hantkeninoides Zone corresponding to the final 150 kyr of the Cretaceous. Proliferations of the Guembelitria cretacea through late Maastrichtian is known as an indicator of high terrigenous influx; therefore, enhanced food resources. The high sedimentation rates observed in all the studied sections might be linked to increased greenhouse conditions due to Deccan volcanism leading to enhanced weathering. Overall, our multiproxy approach including quantitative biostratigraphy and geochemical analyses highlights the influence of the Deccan volcanism by releasing high amounts of atmospheric CO2 and SO2, leading to the climatic changes and associated biotic stress, which predisposed faunas to eventual extinction at the K/Pg boundary.

How to cite: Karabeyoglu, A. U., Adatte, T., Lorenzo, V., Spangenberg, J., Özkan Altıner, S., and Altıner, D.: Faunal and environmental changes through the Cretaceous-Paleogene boundary (K-Pg) linked with Deccan Volcanism: evidence from the Neo-Tethys, Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2002, https://doi.org/10.5194/egusphere-egu2020-2002, 2020.

Major events like global anoxic episodes and mass extinctions are often associated with the eruption of Large Igneous Provinces (LIPs) in the geological past. The Deccan Trap eruption in the end-Cretaceous period in India forms the second-largest LIP and has often been causally linked to the Cretaceous-Paleogene Boundary (K/PgB) mass extinction event. To date, however, environmental reconstructions from pre- and post-volcanic sequences (infra- and inter-trappean, respectively) have mostly been qualitative and fragmentary and as a result, the effects of volcanism on the adjacent environmental conditions are still not well understood. Here, we present evidence of bottom water anoxia as a direct consequence of the Deccan volcanism. For this work, we analyzed major and trace element abundance, total organic carbon (TOC), bulk carbon isotope composition (δ13Corg), and molecular characterization of organic matter (OM) from shallow marine trappean sediments in Rajahmundry, SE India, where the main volcanic episodes separating the infra- and inter-trappean sediments also encompass the K/PgB. The infra-trappean shows overall low TOC (<0.1%) and δ13Corg (–26.3±0.4‰) values, with relatively higher concentrations of longer-chained n-alkane homologues and detrital elements (Al, Ti, Th, K) suggesting a larger contribution from terrestrial derived OM. Across volcanism, however, there is considerable decrease in terrigenous influx, as well as lowering in Pristane/Phytane ratios (<0.6) and enrichment in redox-sensitive elements like Mo, U, V and Co. This is also accompanied by contemporaneous increases in TOC (~0.6%) and δ13Corg values (~3.9‰), suggesting that the change from oxic to sub-oxic or anoxic condition after the main volcanic episode led to increased OM burial and perturbations in the shallow marine carbon reservoir. Higher supply of micro-nutrient during this interval, as evidenced from enrichment in Ba, Fe, Ni and Zn possibly suggest that hydrothermal recycling and initial phases of eutrophication led to depletion in the bottom-water oxygen levels. Temperature increases due to CO2 degassing from volcanism may have further decreased the solubility of oxygen in the sea-waters; however, further studies from the volcanic province are required to ascertain the underlying causes and extent of perturbations and ultimately, to better constrain the complex environmental feedbacks associated with the Deccan volcanism.

How to cite: Roy, S. and Sanyal, P.: Anoxic bottom water condition during the Deccan volcanism: Multi-proxy evidences from a shallow marine sequence in Rajahmundry, SE India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1037, https://doi.org/10.5194/egusphere-egu2020-1037, 2020.

EGU2020-4201 | Displays | SSP2.14 | Highlight

Late Maastrichtian global warming triggered by Deccan dykes and sills, evidence from Malwa and Mandla regions, Central India.

Thierry Adatte, Michael Eddy, Blair Schoene, Gerta Keller, and Syed Khadri

Recent studies indicate that the bulk (80%) of Deccan trap eruptions occurred over a relatively short time interval in magnetic polarity C29r. U-Pb zircon geochronology shows that the main phase began 250 ky before the Cretaceous-Paleogene (KPg) mass extinction and continued into the early Danian suggesting a cause-and-effect relationship. But the potential causal relationship between paleo-environmental change and Deccan volcanism remains debated. New U-Pb zircon geochronology from the Malwa Plateau (~7% of the inferred total volume of the Deccan LIP) located on the northern margin of the Deccan Traps allows  to correlate basalts from the periphery of the province with the volcanic stratigraphy of the Western Ghats as well as to global paleoenvironmental records and precise the Deccan eruption rates at larger scale. Main part of the basalts released in northern Deccan area appears to be of latest Maestrichtian age.  Moreover recent geophysical and field observations show that the Malwa and Mandla basalt plateaus erupted in the Narmada-Tapti rift, made up of 2-3.5 km of Carboniferous to Cretaceous sedimentary rocks, including  up to 60m thick Lower Permian coal interval. Numerous dolerite dykes and sills intersecting these coal beds have been observed in open and underground mines from the Satpura area. The interaction between these dykes  and the coal seams may have significantly contributed to the latest Maastrichtian warming  by releasing high amounts of CO2, SO2 and halogens into the atmosphere. These observations indicate that Deccan volcanism played a key role in increasing atmospheric CO2 levels that resulted in global warming and enhanced greenhouse effect during the latest Maastritchtian, which coupled with high SO2 emissions, increased biotic stress and predisposed faunas to eventual extinction at the KTB.

How to cite: Adatte, T., Eddy, M., Schoene, B., Keller, G., and Khadri, S.: Late Maastrichtian global warming triggered by Deccan dykes and sills, evidence from Malwa and Mandla regions, Central India., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4201, https://doi.org/10.5194/egusphere-egu2020-4201, 2020.

EGU2020-18005 | Displays | SSP2.14

Toarcian Ocean Anoxic Event (TOAE) recording in shallow environment : example from Central Atlas, Morocco

Arnaud Ruchat, Thierry Adatte, and Jorge Spangenberg

The Toarcian Ocean Anoxic Event (TOAE) took place in the early Jurassic (­ ∼183 My) and is characterised by the widespread deposition of organic matter-rich black shales in deep basins, and by a negative carbon isotope excursion reflecting profound environmental changes. This event is well documented in the sedimentary record of deeper marine settings, in which the TOAE is marked by the presence of organic-rich shales. However, the recording of the TOAE in shallower environments is less common, due to incomplete sediment records, to sea-level fluctuations and the lack of good biostratigraphy markers.

Here we present data gathered from a new extremely shallow section in Morocco (Dadès Gorges, Central Atlas), which was located along the northern Gondwana margin. This section consists of alternating dolomitic limestones and paleosols, associated with the presence of several dinosaur tracks and other sedimentary features such as stromatolites, ripple marks, mud cracks and fossil roots. This section shows a significant increase in mercury (Hg) located just below a negative excursion in 13C carbonate isotopes (-3 ) that we attributed to the TOAE NCIE, which coincides with several cyclical episodes of emersion. Bulk rock and clay mineralogy indicate an increase in weathering intensity in the upper part of the section marked by higher phyllosilicates quartz and kaolinite contents.

The upper part of the section shows a gradual decrease in the number of carbonate banks coinciding with an increase of clay-rich intervals. The carbonate banks interbedded with the clay levels are almost entirely composed of an accumulation of stromatolites reflecting even more extreme conditions, which coincide with the TOA-NCIE.

These results confirm the presence of the TOAE-NCIE even in the most shallow environments of the Tethys. The observed Hg anomalies have been globally recorded and are probably linked with the volcanic activity from the Karoo Ferrar province. This marker combined with stable isotopes is therefore a very promising correlative tool.

How to cite: Ruchat, A., Adatte, T., and Spangenberg, J.: Toarcian Ocean Anoxic Event (TOAE) recording in shallow environment : example from Central Atlas, Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18005, https://doi.org/10.5194/egusphere-egu2020-18005, 2020.

EGU2020-8692 | Displays | SSP2.14

Traces of the Rochechouart Asteroid Impact in the uppermost Triassic sediments of the NE Paris-, Aquitanian- and Lodève Basin

Natascha Kuhlmann, Jean Thein, Thorsten Nagel, and Robert Colbach

The end-Triassic extinction event just below the Triassic/Jurassic boundary and its dramatic paleoenvironmental and paleogeographical variations are well documented by rapid changes in the sedimentological and geochemical composition of the uppermost Triassic and lowest Jurassic sequence in the NE Paris Basin. 

An outstanding horizon in the Middle Rhaetian of the Paris Basin is the result of the effects generated by the asteroid impact of Rochechouart (~50 km large crater, ~201 Ma old). The asteroid hit the variscan basement at the southern margin of the Paris Basin, near the town of Limoges (France). This horizon starts at its base with seismically deformed alternation of siltstones and quartzites (seismite), which represent the result of a mega earthquake, generated during the initial impact phase. The seismite is overlain by a completely unsorted conglomerate, fining upwards into a strongly folded and sheared silt/clay with numerous vertebrate bones and ends at the top with a thick red clay formation of the Upper Rhaetian.

The horizon above the seismite obviously represents the deposits of a large tsunami (called tsunamite), triggered when the enormous ejecta masses of the impact entered the waterbody of the southern Paris Basin. Indicators for this event are not only the remains of the reworked vertebrates and exotic sedimentological structures. Additionally the enrichment of platinum group elements which was found in the sequence, clearly points to an impact with cosmic material being involved. The layer can be observed from the Eifel (Germany) over Luxembourg to Lorraine (France). Thickness, sedimentological structures and the lithological composition differ locally, mainly depending on the former geomorphological situation.

Here we present similar impact horizons in two other sites from France: in the northern Aquitanian Basin near Brive-la-Gaillarde (which is in a close distance to the crater) and in the southern Lodève Basin (at a larger distance and in carbonatic rocks). Intensive research in these areas is still in progress.  

The excellently conserved Rochechouart impactite in the Rhaetian of the Paris Basin and surrounding regions offers a unique chance to study in all detail the processes of a large impact with their effects on the adjacent marine sedimentation areas and to compare the results to similar events  worldwide.

 

How to cite: Kuhlmann, N., Thein, J., Nagel, T., and Colbach, R.: Traces of the Rochechouart Asteroid Impact in the uppermost Triassic sediments of the NE Paris-, Aquitanian- and Lodève Basin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8692, https://doi.org/10.5194/egusphere-egu2020-8692, 2020.

EGU2020-18885 | Displays | SSP2.14

Hyaloclastite formation during the effusion of the first lava flows of Siberian traps into a shallow freshwater basin

Alexander G. Polozov, Sverre Planke, John A. Millett, Dmitrii A. Zastrozhnov, Dougal A. Jerram, and Henrik H. Svensen

Hyaloclastites have long been described within numerous volcaniclastic sequences in the Siberian Traps Large Igneous Province. They are typical for the southern and central parts of the Tunguska basin, and we inspected them in 2004-2010. In recent years, we have focused our attention on the northwestern region of the Tunguska basin (Norilsk area) with a volumetric manifestation of basaltic lava flows. We have completed fieldwork in this region from 2006 to 2019, with a recent focus on the understanding of the emplacement environments for the lowermost lava flow erupted directly on the end-Permian boggy surface. We studied pillow basalt at the basal part of the lowermost lava flow in the Norilsk region (Ivakinskaya Formation). In the upper part of this pillow basalt horizon, hyaloclastite is very common, and at the basal part, several tree trunks occur. The hyaloclastite includes black equant angular clasts and rusty red matrix and easily recognize at any outcrops. We studied hyaloclastite with optical microscopy and SEM-EDS. Black clasts composed of sideromelane cracked and altered to palagonite. Sideromelane fragments include crystals of olivine (Fo70), plagioclase (An63-70), and likely OPx altered to chlorite. Sideromelane glass has a basalt composition with elevated P2O5, CaO, and decreased amount of MgO and minor halogens (F, Cl). Some sideromelane clasts bear round inclusions (blobs) entirely infill with dolomite, siderite, and calcite. Every single carbonate inclusion has a specific structure and minerals infill.

We interpret these hyaloclastite rocks formations with carbonate inclusions as a result of lava flow effusion onto the shallow freshwater basin or boggy surface. Water and organic-rich sediments transferred with an explosion to steam and carbon dioxide gas, and this gas mixture was formed a hyaloclastite horizon at the basal part of a lava flow. We suppose that these sideromelane clasts with carbonate blobs are additional evidence of greenhouse gas generation during the early stage of the Siberian Traps lavas eruption.

How to cite: Polozov, A. G., Planke, S., Millett, J. A., Zastrozhnov, D. A., Jerram, D. A., and Svensen, H. H.: Hyaloclastite formation during the effusion of the first lava flows of Siberian traps into a shallow freshwater basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18885, https://doi.org/10.5194/egusphere-egu2020-18885, 2020.

EGU2020-21766 | Displays | SSP2.14

The Siberian Traps magma emplacement dynamics links to environmental changes across the Permian-Triassic boundary in Svalbard

Sverre Planke, Alexander Polozov, John Millett, Dougal Jerram, Dmitrii Zastrozhnov, Henrik Svensen, Lars Augland, Morgan Jones, Valentin Zuchuat, Arve Sleveland, Ivar Midtkandal, Richard Twitchett, and Jan Inge Faleide

The end-Permian Siberian Traps large igneous province (LIP) is temporally associated with the major extinction event at the Paleozoic-Mesozoic boundary. The extinction was likely triggered by massive eruption of carbon and halocarbon gases released from metamorphic aureoles around sill complexes in the Tunguska Basin. Additional environmental pollution was likely associated with magma degassing, forest fires, and extensive tuff formation during magma-water interaction. We have conducted detailed field work in the Norilsk area since 2006 to study the environment during the initial lava eruptions in the Siberian Traps. The field work included mapping, photogrammetric drone surveying, sampling, and subsequent inorganic geochemical and petrographic analyzes. The sediment-lava transition is particularly well exposed in the Norilsk area. In the Kajerkan quarry, shallow basaltic igneous intrusions were emplacement into the coal-rich upper part of the Tunguska Group of Late Carboniferous and Permian age. In the Ore Brook and Red Rocks localities, more than ten sub-vertical tree trunks have been mapped and sampled in the lowermost lava flow. The tree trunks are petrified wood of end-Permian age. Pillow basalts are found at the same levels, showing that the lava flow was emplaced in a wet environment. Ropy pahoehoe structures are found at the top of this flow, which suggests that the uppermost part of the lava flow was emplaced in a subaerial environment. Further south, in the Bratsk area, extensive sill intrusions and magnetite-rich hydrothermal vent complexes are abundant, documenting extensive eruptions of metamorphic gases and tuffs to the atmosphere. We have been drilling two 100-m long stratigraphic boreholes across the Permian-Triassic boundary in Svalbard, arctic Norway, to study the effect of the Siberian Traps magmatism on the sedimentary basin development some 2000-km away from the main eruption sites. The near complete core recovery, complemented by material collected in a river section ca. 1 km north-east of the drill site, allowed high-resolution analyses of the Permian-Triassic boundary interval. The cores have been logged and analyzed in detail, including organic and inorganic geochemistry, isotope geochemistry, petrography, and biostratigraphy. The Permian-Triassic boundary (PTB) is identified in the cores and lies within the Reduviasporonites chalastus Assemblage Zone, 2.50 m above the lithological change from bioturbated to dark grey, laminated mudstones. This corresponds to the local position of the Late-Permian Mass Extinction event (LPME) and its associated sharp negative δ13Corg excursion. High-resolution environmental proxies indicate a dramatic change in provenance across the PTB, and a transition towards a more arid climate in the earliest Triassic. This transition was contemporaneous with prolonged bottom-water dysoxic or anoxic conditions, following a Late Permian increase in volcanic activity, probably linked to the emplacement of the Siberian Traps LIP. Zircons have been separated from numerous basaltic ash layers in this sequence, and a few have been successfully dated with the U-Pb TIMS method and overlap in age with the Siberian Traps magmatism. This study shows that the Siberian Traps LIP had a major impact of both the basin development and life in the arctic Barents Sea region.

How to cite: Planke, S., Polozov, A., Millett, J., Jerram, D., Zastrozhnov, D., Svensen, H., Augland, L., Jones, M., Zuchuat, V., Sleveland, A., Midtkandal, I., Twitchett, R., and Faleide, J. I.: The Siberian Traps magma emplacement dynamics links to environmental changes across the Permian-Triassic boundary in Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21766, https://doi.org/10.5194/egusphere-egu2020-21766, 2020.

SSP3.1 – Limnogeology - reading the geological record of lakes

EGU2020-11490 | Displays | SSP3.1

Ecological effects of sudden drainage of large karst lakes in the Lacandon Maya region, southern Mexico

Liseth Perez and the Selva Lacandona science team

Water levels in Lakes Metzabok and Tzibaná, two large karst lakes in the Lacandon Forest of southern Mexico, declined dramatically within a two-week period in July 2019. Lake Metzabok (0.83 km2; zmax = 25 m) dried completely, whereas in Lake Tzibaná (1.24 km2; zmax = 70 m) it fell by ~30 m. Analysis of satellite images in Lake Metzabok suggested a combined reduction in surface area of ~0.86 km2 and water volume loss of ~11.7 million m3. The sudden loss of such a large volume of water had negative impacts on local Lacandon Maya inhabitants, and profound ecological and environmental effects, in that it caused biodiversity loss.

We combined limnological and paleolimnological analyses to evaluate the ecological effects of the sudden loss of water from Lakes Metzabok and Tzibaná. We collected and analyzed remnant waters, surface sediments and short sediment cores from what remained of the water bodies to evaluate whether evidence for such drainage events is preserved in lake sediments. In situ water-column measurements yielded values similar to those from the previous six years when the lakes were filled, suggesting that evaporation was not the process responsible for lake level lowering, but rather that the lakes drained through fractures in the underlying karst bedrock. We collected phytoplankton and zooplankton samples from the remnant waters and found abundant diatoms, green algae, testate amoebae, crustaceans (copepods, cladocerans, ostracodes), insects (chironomids, trichopterans), collembolans, rotifers, tardigrades and nematodes. Environmental conditions in such small remnant ponds are probably stressful and unstable, but because many fish, the main predators in these ecosystems, did not survive the desiccation event, the aquatic environment is ideal for survival or recolonization by many invertebrate groups. Understanding the dynamics of this modern scenario with low lake levels is key for making paleolimnological inferences that use these aquatic bioindicators. We also investigated the commencing transition from an aquatic to a terrestrial habitat in Lake Metzabok. Abundant spiders colonized cracks in the dry sediment. Small, deep holes in surface mud were probably created by aquatic organisms when water levels decreased rapidly. Some cracks held rain water and were inhabited by tadpoles of the Gulf Coast toad (Incilius valliceps). The first plants to colonize the exposed lake beds belonged to the families Poaceae (grasses), Amaranthaceae (amaranths/chenopods) and Fabaceae (legumes), among others.

The sediment record from Lakes Metzabok and Tzibaná as well as testimonies of local Lacandon Maya inhabitants suggest that similar lake level lowering events occurred in the past. The hydrology of karst lakes is complex and unpredictable because multiple geological and hydrological factors control the water balance. The cause of this recent lake level lowering event remains unknown, but may be revealed by interdisciplinary studies of the limnology, paleolimnology, structural geology, geophysics, hydrology, geochemistry, genomics and geodesy of lakes and rivers in the region, as well as traditional environmental knowledge of the Lacandon Maya.

How to cite: Perez, L. and the Selva Lacandona science team: Ecological effects of sudden drainage of large karst lakes in the Lacandon Maya region, southern Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11490, https://doi.org/10.5194/egusphere-egu2020-11490, 2020.

EGU2020-20176 | Displays | SSP3.1

Eemian environmental changes recorded in the north located lakes (N Poland and Germany) - subfossil Cladocera data

Monika Niska, Anna Hrynowiecka, Joanna Mirosław-Grabowska, Andreas Borner, and Robert Sokołowski

In the current study the result of subfossil Cladocera analysis of the lake sediments from tree sites: Hinterste Mühle (H-M) (NE Germany), Rzecino (NW Poland) and Łęczyce (N Poland) of the Eemian Interglacial and the inferred environmental alterations are presented. The aim of the study was to reconstruct and compare the development of Eemian lakes located within the north of Poland and Germany as determined on the basis of the changes in subfossil Cladocera composition in the context of local conditions, climate change and natural evolutionary processes.

The studied reservoirs, fully developed during the Eemian Interglacial, were formed at the end of Late Saalian (MIS 6) and Early Eemian. The Hinterste Mühle profile is located in Mecklenburg-Western Pomerania. The site lies in the southeastern edge of the gravel pit, at about 48 m a.s.l. The Rzecino paleolake is located in the West Pomerania Lakeland (NW Poland), at an elevation of 104.5 m a.s.l. The Łęczyce palaeolake is located in northern Poland, on the northern slope of the Łeba river valley.

The subfossil Cladocera fauna from the H-M palaeolake is represented by 14 species belonging to three families. Three of them belong to a benthic group inhabiting mainly the bottom sediments, one to the open water zone, while the remaining species the dominant group occur among aquatic plants. Such a species composition marks a shallow water body or the littoral, macrophyte zone of a deeper lake. The Cladoceran fauna of deposits from the Rzecino paleolake are represented by 22 species that belong to four families. The majority of the remains consist of Chydoridae and Bosminidae. In the deposits, the ephippial eggs of the Daphnia longispina group, Ceriodaphnia spp., Chydorus spp., and Bosmina spp. are also identified. The subfossil cladoceran fauna of sediments in the Łęczyce profile is represented by 18 species that belong to four families. Most of the remains belong to the family of Chydoridae (13). Such species composition points to a deeper reservoir with a developed littoral zone with macrophytes.

Summing up, a similar pattern was observed in the research paleolakes related to the beginning of the existing of the lakes, their full development and ending time, different from the paleolakes found in the south, related to the location and more intense contact with cool air masses from Northern Europe.

How to cite: Niska, M., Hrynowiecka, A., Mirosław-Grabowska, J., Borner, A., and Sokołowski, R.: Eemian environmental changes recorded in the north located lakes (N Poland and Germany) - subfossil Cladocera data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20176, https://doi.org/10.5194/egusphere-egu2020-20176, 2020.

EGU2020-5849 | Displays | SSP3.1

Basin- and global-scale environment alternately drive diatom community structure in ancient Lake Ohrid

Aleksandra Cvetkoska, Dedmer B. Van de Waal, Timme H. Donders, Elena Jovanovska, Zlatko Levkov, Torsten Hauffe, Jane M. Reed, Alexander Francke, Hendrik Vogel, Thomas Wilke, Bernd Wagner, and Friederike Wagner-Cremer

Evidence for global environmental and climate change-related loss of biodiversity is accumulating. Understanding the causes of species community change is thus essential for effective management and conservation policies. Nonetheless, disentangling the relative influence of the individual or multiple drivers determining the species communities is challenging, as ecosystems are simultaneously affected by variable drivers acting on different spatial and temporal scales. To this end, paleolimnological data may provide critical information on long-term community changes, species dominance shifts, and their underlying drivers. Natural forced changes in the aquatic environments can be used to study the response of biota to repeated fluctuations in essential key variables. In this study, we investigated the planktonic diatom communities in a continuous, 1.36 Ma sedimentary succession from ancient Lake Ohrid (North Macedonia/Albania). This is the oldest, continuously existing freshwater lake in Europe, acknowledged as a site of exceptional biodiversity and endemic species richness. An extended biogeochemical dataset from the DEEP site sedimentary record and previously-published variables representing global climate variability was used to: i) quantify the relative influence of individual environmental variables in governing species communities, and ii) disentangle the contribution of basin-scale environmental processes and global-scale climate variability in driving community patterns over time. The results show that the structure of planktonic communities was primarily determined by the basin-scale environment, particularly, nutrient availability, water temperature and water column mixing, but also local tectonic processes, since lake ontogeny. However, since the onset of the penultimate glacial period 0.185 Ma ago, global-scale climate variability became the principal drivers of the diatom community structure. Our proxy time-series illustrates how various factors at different spatial scales may determine the freshwater planktonic communities over geological time-scales. Extended periods of stable communities can be terminated by changes in climate, environmental conditions and/or lake ontogeny, leading to species extinctions and community turnovers. Thereby lake ecosystem structure and functioning are affected and effective management and conservation policies are required to minimize additional anthropogenic change-related loss of biodiversity. 

How to cite: Cvetkoska, A., B. Van de Waal, D., H. Donders, T., Jovanovska, E., Levkov, Z., Hauffe, T., M. Reed, J., Francke, A., Vogel, H., Wilke, T., Wagner, B., and Wagner-Cremer, F.: Basin- and global-scale environment alternately drive diatom community structure in ancient Lake Ohrid, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5849, https://doi.org/10.5194/egusphere-egu2020-5849, 2020.

EGU2020-15070 | Displays | SSP3.1

Traces of sunlight in carbon biochemistry of shallow subarctic lakes

Marttiina Rantala, Henriikka Kivilä, Carsten Meyer-Jacob, Maxime Wauthy, Milla Rautio, Andrea Lami, Tomi Luoto, and Liisa Nevalainen

Sunlight fuels the drawdown and evasion of carbon in shallow northern lakes. Amplified polar warming is altering the sunlit transport and transformation of aquatic carbon at an alarming rate entailing potential for climate feedbacks. We combined experimental and retrospective approaches to explore the synoptic interlinks between underwater light, aquatic carbon biochemistry, landscape carbon cycling and climate change in two shallow subarctic lakes with divergent light and carbon regime (a clear lake low in organic carbon and a dark organic rich lake). In situ enclosures (treatments under full sunlight, sunlight without the ultraviolet [UV] spectrum, no light) were first deployed on the lakes to decipher the effect of photochemical alteration on the spectral, elemental and isotopic properties of lake water organic carbon pools under short term (four weeks) exposure. We then focused on elemental, isotopic and spectral fingerprints archived in the sediments of the lakes to trace coeval variability in aquatic primary production, terrestrial carbon transport, and underwater light under centennial climate fluctuations. We observed distinct differences in carbon biochemistry between the experimental treatments illustrating the importance of sunlight, and particularly the UV spectrum, in shaping the carbon pools of the lakes already over short time scales. Over the past centennia, sediment biogeochemical composition carried signatures of change in carbon origins (algal vs terrestrial) and shifting underwater light regime. The results shed light on how climate change and sunlight shape carbon flows in shallow northern lakes over short and long time scales.

How to cite: Rantala, M., Kivilä, H., Meyer-Jacob, C., Wauthy, M., Rautio, M., Lami, A., Luoto, T., and Nevalainen, L.: Traces of sunlight in carbon biochemistry of shallow subarctic lakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15070, https://doi.org/10.5194/egusphere-egu2020-15070, 2020.

EGU2020-5995 | Displays | SSP3.1

Factors Leading to Increased Algal Production in Mountain Lakes: A Paleolimnological Perspective from the Uinta Mountains, Utah, USA

Katrina A. Moser, Elizabeth J Hundey, Maria E. Sia, Rebecca M. Doyle, Holly Dunne, and Fred J. Longstaffe

Mountain lakes are often remote, located in environments that experience cold temperatures, high incident solar and ultraviolet radiation, and prolonged ice and snow cover. They are, therefore, frequently dilute and oligotrophic. Together these factors can affect mountain lake ecosystem structure, diversity, and productivity. However, distant human activities resulting in atmospheric pollution, as well as more local disturbances, such as fish stocking, potentially increase nutrient inputs and alter mountain lake ecosystems. Our research addresses how these human activities have altered algal production in Uinta Mountain (Utah, USA) lakes. Sedimentary chlorophyll a and its derivatives were measured using visible reflectance spectroscopy in short sediment cores from a total of 12 lakes, including both alpine and subalpine lakes, to determine trends in algal production. All sediment cores were dated using 210Pb and 14C dating, and the records were shown to extend back 300 to 500 years. Our results show that regardless of whether lakes were stocked or not, algal production remained virtually unchanged until 1950 when it increased dramatically in most lakes. The widespread distribution of the sites points to a regional stressor, such as atmospheric deposition of nutrients, as being the main cause for increased algal production. Additional analyses, including diatoms and C and N isotopes, measured in sediments from some lakes support this finding. The few lakes where algal production trends differed showed either that algal production had changed little overtime or that it was variable throughout the record. Although speculative, the lake that showed unchanged algal production is surrounded by a wetland that may have contributed nitrogen to the lake throughout the record meaning that additional nitrogen had little effect on algal production. Lakes with more variable algal production were subalpine lakes. The variable trend may point to more complex pathways and transport of nitrogen from the catchment to the lakes at lower elevation sites. Our findings show that remote mountain lakes, which typically are important water resources and biodiversity hotspots, are rapidly changing as a result of human activities, but not all of these lakes are responding in the same way. To effectively protect mountain lakes it will be important to identify and quantify influential factors affecting lake response to anthropogenic stressors.  

How to cite: Moser, K. A., Hundey, E. J., Sia, M. E., Doyle, R. M., Dunne, H., and Longstaffe, F. J.: Factors Leading to Increased Algal Production in Mountain Lakes: A Paleolimnological Perspective from the Uinta Mountains, Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5995, https://doi.org/10.5194/egusphere-egu2020-5995, 2020.

EGU2020-9772 | Displays | SSP3.1

Lake trophic states shape microbial community structure in sediments

Xingguo Han, Carsten Schubert, Annika Fiskal, Nathalie Dubois, and Mark Lever

Lake sediments are globally important carbon sinks, and play a critical role in the global carbon cycle. Although the fate of organic carbon in lake sediments depends mostly on sedimentary microorganisms, the environmental controls on the microbial community structure in lake sediments are still poorly understood.

Here we investigate the relationships of lake trophic state, sediment redox chemistry, sediment organic matter (OM) sources and microbial community structure in sediment records across five lakes with different eutrophication histories and trophic states in central Switzerland. Our results show that, across all five lakes, bacterial and archaeal communities based on 16S rRNA gene sequencing analyses show similar sediment depth-dependent zonations at the phylum- and class-level, which appears to be primarily driven by vertical distributions of electron acceptors and secondarily by differences in the contributions of aquatic and terrestrial OM revealed by biomarkers. Yet, there are clear differences in microbial communities between lakes, most notably the higher abundances of putatively aerobic nitrifying Bacteria (Nitrospirae) and Archaea (Marine Group I, Thaumarchaeota) in anoxic sediments of oligotrophic Lake Lucerne. Furthermore, at the level of Zero-radius Operational Taxonomic Unit (ZOTU), eutrophication-related trends are more pronounced, in which microbial communities in the sediments of eutrophic lakes are more similar and share more ZOTUs with each other than with the oligotrophic lake. Notably, deep sediment layers of presently eutrophic lakes that were deposited prior to the era of eutrophication show high similarities in bacterial communities to equivalent depths in the oligotrophic lake. By contrast, archaeal communities are clearly differentiated according to trophic state only in recently deposited sediment layers, and independent of trophic state converge toward high similarities over time.

Our study indicates a significant role of trophic status in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of bacterial and archaeal communities to anthropogenic eutrophication.

How to cite: Han, X., Schubert, C., Fiskal, A., Dubois, N., and Lever, M.: Lake trophic states shape microbial community structure in sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9772, https://doi.org/10.5194/egusphere-egu2020-9772, 2020.

Many lakes in industrialised areas have undergone anthropogenically driven eutrophication and increases in pollution leading to decreased water and sediment quality. In some cases, these effects are enhanced by seasonally changing lake redox conditions that may act to concentrate potentially toxic elements sufficiently to exceed internationally recognised Sediment Quality Standards, impacting key species and jeopardizing water supply.  A combined, geochemical and sediment microfabric analysis is applied to reconstruct the history of cultural eutrophication and pollution in the North and South Basins of Windermere, England’s largest natural lake. We also document a record of seismicity and link increased sedimentation rates and sediment instability. The onset and development of eutrophication in Windermere occurred from the mid-19th to the early 20th centuries.  Raised lake productivity is indicated by an increase in sedimentary δ13C, and increased pollution by elevated sedimentary trace metals (Pb, Zn, Cu, Hg, and As), likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin of the lake, contemporaneous increasing sediment δ15N values also occur in step with increasing Zn, Hg, Cu from this time, linking metal enrichment to the input of isotopically heavy nitrate (N) from anthropogenic sources including sewage. From around 1930, a decrease in Mn and Fe-rich laminae indicate reduced deep water ventilation, and increased incidence of sediment anoxia, being most intense in the deeper North Basin where benthic activity intermittently ceased. Strongly reducing conditions in the sediment promoted Fe and Mn reduction and the formation of unusual Pb-bearing barite, hitherto only described from toxic mine wastes and contaminated soils. In the North Basin cores a clay rich laminae dated 1979-1980 is shown to be a mass transport deposit linked to large scale slope failure likely caused by the 4.7 ML 1979 Carlisle earthquake. Slope failure was exacerbated by preconditioning principally by increased sedimentation as a result of anthropogenic activities. From 1980 there was a partial recovery in oxygenation with Mn and Fe rich laminae returning in some parts. But in the South Basin, the continued impacts of sewage discharge is indicated by elevated δ15N of organic matter. Imaging and X-ray microanalysis using scanning electron microscopy has enabled the identification of seasonal-scale redox mineralisation of Mn, Fe and Ba related to intermittent sediment anoxia. Elevated concentrations of Mn, Fe, Ba, and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements that may be released to the lake waters. Concentrations of As, in particular, exceed international Sediment Quality Standards. These surface enrichments in As and other toxic elements may become more prevalent in the future with climate change driving lengthened summer stratification in the lake.

How to cite: Fielding, J., Kemp, A., Croudace, I., Langdon, P., Pearce, R., Cotterill, C., and Avery, R.: High resolution sediment microfabric and geochemical analysis reveals seasonal scale redox mineralisation, anthropogenic environmental change and pollution in England's largest natural lake - Windermere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-523, https://doi.org/10.5194/egusphere-egu2020-523, 2020.

EGU2020-12343 | Displays | SSP3.1

Differences in calcite varve formation discerned by a dual lake monitoring approach in the southern Baltic lowlands

Patricia Roeser, Nadine Dräger, Dariusz Brykała, Florian Ott, Sylvia Pinkerneil, Piotr Gierszewski, Christin Lindemann, Birgit Plessen, Brian Brademann, Michał Kaszubski, Michał Fojutowski, Markus J. Schwab, Michał Słowiński, Mirosław Błaszkiewicz, and Achim Brauer

Varved lake sediments are valuable archives for reconstructing climate and environmental change in the human habitat at seasonal resolution. However, it is still not fully understood which factors control varve thickness and, consequently, varve proxy records are differently interpreted with respect to their climatic significance. Here we present, for the first time, a dual lake monitoring in two lakes forming calcite varves to provide new insights into the seasonal depositional processes forming these varves. The study lakes, Tiefer See (TSK) in NE Germany and Czechowskie (JC) in N Poland, are located a few hundred km away from each other in the southern Baltic lowlands. This is an ideal test region for this investigation because it holds the major known geographical cluster of calcite varve producing lakes. The lake basins are different in morphology and bathymetry and, therefore, are ideal to investigate common processes and local differences of seasonal deposition. The monitoring setup in both lakes is largely identical and included instrumental observation of (1) meteorological parameters, (2) chemical profiling of the lake water column including water sampling and analyses, and, (3) sediment trapping at both bi-weekly and monthly intervals. Finally, we compared our six-year monitoring time series with varve micro-facies of sediments deposited during this time at the lake bottom. Based on this robust data-set, we present and discuss new findings with respect to the seasonal deposition of endogenic calcite varves, as well as their limnologic control factors.

How to cite: Roeser, P., Dräger, N., Brykała, D., Ott, F., Pinkerneil, S., Gierszewski, P., Lindemann, C., Plessen, B., Brademann, B., Kaszubski, M., Fojutowski, M., Schwab, M. J., Słowiński, M., Błaszkiewicz, M., and Brauer, A.: Differences in calcite varve formation discerned by a dual lake monitoring approach in the southern Baltic lowlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12343, https://doi.org/10.5194/egusphere-egu2020-12343, 2020.

EGU2020-12774 | Displays | SSP3.1

Weihe Basin Drilling Project (WBDP): Cenozoic tectonic-monsoon interactions

Zhisheng An, Peter Molnar, Peizhen Zhang, Hendrik Vogel, Mark Level, Carmala Garzione, John Dodson, Youhong Sun, Thomas Wiersberg, Hailiang Dong, Xijie Feng, Yougui Song, Hong Chang, Xiaoke Qiang, Xulong Wang, Huayu Lu, Xingxing Liu, Li Ai, and Youbin Sun

Earth’s climate underwent dramatic cooling throughout much of the Cenozoic, which has been linked to continental drift, mountain building, and the formation and expansion of ice-sheets in Antarctica and the Arctic. In particular, the India-Asia collision and uplift of the Tibetan Plateau (TP) have been posited as critical events responsible for increasing the rates of physical and chemical weathering on land, thereby decreasing the CO2 concentration of the atmosphere. The uplift of the TP ultimately led to the onset of the complexly coupled monsoon-arid environmental system in East Asia. Global-scale studies of Cenozoic deep-sea sediments and Quaternary ice cores indicate that, superimposed to the long-term cooling trend, climate variability at orbital-to-centennial time-scales is primarily induced by changing solar insolation and irradiance, and strongly modulated by complex internal land-air-ocean interactions. From the continental perspective, however, both the dynamics and impacts of long-term climate evolution and short-term climate variability remain poorly constrained due to the paucity of continuous terrestrial sequences spanning the entire Cenozoic.
The Weihe Basin is located in the monsoon-sensitive region to the north of the Qinling Mountains, a landform that constitutes the geographic and climatic boundary between northern and southern China. In the depocentre of this basin, a predominantly lacustrine sedimentary sequence with a thickness of >7 km, provides an unprecedented opportunity for: (1) reconstructing tectonic-to-millennial-scale climate changes from the Eocene to the present; (2) elucidating basin-mountain coupling processes; (3) assessing the effects of Cenozoic tectonic-climate interactions on the onset and evolution of the Asian paleomonsoon; and (4) investigating climatic/environmental impacts on the evolution of microbial communities. Importantly also, (5) sedimentary filling of the Weihe Basin can potentially yield unique high-resolution records of continental climate variability during high atmospheric CO2 periods of the Eocene, mid-Miocene, and Late Pliocene, and thus serve an analog for Earth’s near future climate.
The Weihe Basin Drilling Project (WBDP) proposes a two-phase drilling strategy to recover a complete as possible Cenozoic terrestrial sedimentary record from the eastern Weihe Basin depocenter. In the first phase (applied for here) we aim at producing a 3-km-long pilot sedimentary record (WBDP-1) to test the best suitable analytical approach and to reconstruct orbital-to-millennial-scale climate variability since the Late Miocene. In the second phase our aim is to produce a 7.5-km-long sedimentary record (WBDP-2) spanning the entire Cenozoic sedimentary infill of the Weihe Basin. The regional geological framework is well characterized through numerous exploration boreholes and detailed multichannel seismic reflection surveys. Scientific drilling operations will be accompanied by downhole logging, as well as on- and off-site analyses of the retrieved cores. The WBDP-1 borehole is expected to yield a world-class paleoclimate record for the last ~10 Ma and lead to fundamental advances in our understanding of multi-timescale climate variability and tectonic-climate monsoon linkages. The project will also enhance public awareness of human adaptation to Earth’s changing environment.

How to cite: An, Z., Molnar, P., Zhang, P., Vogel, H., Level, M., Garzione, C., Dodson, J., Sun, Y., Wiersberg, T., Dong, H., Feng, X., Song, Y., Chang, H., Qiang, X., Wang, X., Lu, H., Liu, X., Ai, L., and Sun, Y.: Weihe Basin Drilling Project (WBDP): Cenozoic tectonic-monsoon interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12774, https://doi.org/10.5194/egusphere-egu2020-12774, 2020.

Before the onset of the modern Amazon river system, north-western South America was shaped by an extensive wetland during the Miocene. This ‘Pebas mega-wetland’ kept a well renowned endemic mollusk and ostracod fauna, which initiated a persisting debate about marine ingressions reaching the center of Amazonia at that time. Due to high endemism, uniformitarian principles are hardly applicable to this biota but also other paleontological, sedimentological and geochemical information led to ambiguous paleoenvironmental interpretations. These results are based on ostracod and foraminiferal assemblages and the oxygen and carbon stable isotopy of their biogenic calcite from an outcrop at the cutbank of the Amazon river (NE-Peru, ~55 km S of Iquitos). While ostracods (e.g., Cyprideis) are able to calcify their carapaces along the entire salinity range, at least low saline conditions are a prerequisite for the biomineralization of calcareous foraminiferan tests. Hence, the finding of calcareous foraminifers (Ammonia, Elphidium), associated mainly with brackish water ostracods, indicates the presence of saline waters. In contrast, δ18O- and δ13C-analyses performed on co-occurring ostracod valves and foraminiferan tests yielded constantly very light ratios. Such values refer to a pure freshwater environment and are incompatible with the interference of isotopically heavier, marine waters or an evaporative stable isotope enrichment. Based on these opposing data, we hypothesize that the Pebas mega-wetland was episodically influenced by mineralized but isotopically light groundwater discharge. Possibly, the resulting specific hydrochemistry contributed not only to the evolution of the endemic Pebasian fauna but also facilitated the sporadic settlement of euryhaline foraminifers, which mimics short-lived marine incursions.

How to cite: Piller, W. and Gross, M.: Aquatic ecosystems in Miocene western Amazonia – marine ingressions vs. salt leaching, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5483, https://doi.org/10.5194/egusphere-egu2020-5483, 2020.

EGU2020-5126 | Displays | SSP3.1

Tephrostratigraphy and tephrochronology of a 430 ka sediment record from the Fucino Basin, central Italy

Niklas Leicher, Biagio Giaccio, Bernd Wagner, Giorgio Mannella, Lorenzo Monaco, Giovanni Zanchetta, Stephanie Scheidt, Eleonora Regattieri, Sebastién Nomade, Alison Pereira, Danilo M. Palladino, Elizabeth M. Niespolo, and Paul R. Renne

The Fucino Basin is the largest and probably the only Central Apennine basin hosting a thick, continuous lacustrine sediment succession documenting the environmental history from the Early Pleistocene to recent historical times. The basin is located downwind of the Italian volcanic districts (< 150 km), which makes it the best candidate available in the central Mediterranean to construct a long and continuous tephrostratigraphic and tephrochronological record. Tephrostratigraphic investigations conducted on a first core (F1-F3) revealed 21 tephra layers of different Italian volcaoes. Among them several widespread and well-dated key Mediterranean marker tephra layers (e.g., Neapolitan Yellow Tuff, Y-1, Campanian Ignimbrite, Y-7, X-5, X-6, and Taurano Ignimbrite) were recognized and allowed to date, together with 40Ar/39Ar ages directly obtained from the Fucino tephra layers, the record back to 190 ka.

Based on these promising results, a new drilling site with a lower sedimentation rate was targeted, bringing forth the ~98 m long F4-F5 record. In addition to the already recognised tephra layers occurring in the section that overlaps with core F1-F3, ~110 additional tephra and cryptotephra horizons were identified in the composite sediment succession of the F4-F5 record, providing new insights into the Italian volcanic history for the poorly explored interval beyond 200 ka.

Here we present the first tephrostratigraphic and tephrochronological results for this interval, which is dominated by eruptions from the Sabatini, Vulsini, Vico, and Colli Albani volcanoes. Several important known eruptions were identified and dated for the first time in distal settings: e.g., Canino (256.8 ± 1.1 ka), Tufo Giallo di Sacrofano (288.0 ± 2.0 ka), Magliano Romano Plinian Fall (315.0 ± 2.0 ka), Orvieto-Bagnoregio Ignimbrite (335.8 ± 1.4 ka), Villa Senni (367.5 ± 1.6 ka), Pozzolane Nere and its precursor (408.5 ± 1.3 ka, and 407.1 ± 4.2 ka, respectively). Finally, a tephra located at the base of the succession was directly dated by 40Ar/39Ar at 424.3 ± 3.2 ka, thus extending the record back to the MIS 12/11 transition (~430 ka).

Ongoing geochemical analysis, including trace elements, Sr and Nd isotopes, and 40Ar/39Ar dating of both Fucino tephra layers and potential proximal counterparts will help to reveal their volcanic sources and enable further tephrostratigraphic correlations supported by independent age determinations. These results will contribute towards an improved MIS 11-MIS 7 Mediterranean tephrostratigraphy, which is still poorly characterized and exploited.

The recognition and dating of the numerous tephra layers from the F4-F5 record can be directly combined to construct a comprehensive age-depth series of biogeochemical proxies and geomagnetic excursions derived from the lacustrine sediments, forming the backbone for an independent, radioisotopically anchored chronology for the F4-F5 multi-proxy record. Through paleoclimatic alignments and geomagnetic excursion synchronizations, the independent Fucino chronology can be propagated to the North Atlantic records, and possibly on a global scale, setting the framework for a better understanding of the spatio-temporal variability, magnitude, and different expressions of Quaternary orbital and millennial-scale paleoclimatic changes.

How to cite: Leicher, N., Giaccio, B., Wagner, B., Mannella, G., Monaco, L., Zanchetta, G., Scheidt, S., Regattieri, E., Nomade, S., Pereira, A., Palladino, D. M., Niespolo, E. M., and Renne, P. R.: Tephrostratigraphy and tephrochronology of a 430 ka sediment record from the Fucino Basin, central Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5126, https://doi.org/10.5194/egusphere-egu2020-5126, 2020.

EGU2020-5782 | Displays | SSP3.1

Etablishing the first continuous Holocene tephrostratigraphy on Kerguelen Archipelago, subantarctic Indian Oean

Fabien Arnaud, Pierre Sabatier, Anouk Leloup, Aymerick Servettaz, Bertrand Moine, Anne-Lise Develle, Stéphane Guédron, Vincent Perrot, Jérôme Poulenard, Bernard Fanget, Emmanuel Malet, Eivind Støren, Jean-Louis Reyss, Nicolas Le Viavan, Katrien Heirman, Marc De Batist, Elisabeth Michel, Jacques-Louis de Beaulieu, Nathalie Vanderputten, and Jostein Bakke

Here we present the first Holocene-long continuous chronology of volcanic eruptions on Kerguelen archipelago, where no evidence of Holocene volcanic activity has been published so far. Our chronicle is based upon sedimentological, chronological and geochemical data form two sediment cores, taken in two different depocenters of a large lake, Lake Armor, located ca. 70 km away from the archipelago’s potentially active volcanic area. This allowed us to confidently attribute the origin of pumice-rich or ash-rich layers to contemporaneous volcanic eruptions. Altogther eight main eruptions, as well as three secondary ones, were here documented and dated, among which the youngest occurred during the Middle Age, between 890 and 980 AD. The oldest eruption is also by far the strongest one and deposited more  than 1.2m of up-to 3cm large pumices, 70 km away from the volcanic edifice. It occurred at the very beginnning of the Holocene (11 ka cal. BP), suggesting a climatic control after glacial retreat upon volcanic activity. Additionnal evidences from lake sediment and geological outcrops, both close to Lake Armor and in remote areas over Kerguelen mainland, open the future possibility of a better reconstruction of major eruptions deposit spreading and thus an assessment of their intensity. This established chronostratigraphy will be useful to synchronise paleoenvironment record at least at the scale of the archipelago as well as in surrounding marine areas where Holocene climate reconstructions are particularly sparse.

How to cite: Arnaud, F., Sabatier, P., Leloup, A., Servettaz, A., Moine, B., Develle, A.-L., Guédron, S., Perrot, V., Poulenard, J., Fanget, B., Malet, E., Støren, E., Reyss, J.-L., Le Viavan, N., Heirman, K., De Batist, M., Michel, E., de Beaulieu, J.-L., Vanderputten, N., and Bakke, J.: Etablishing the first continuous Holocene tephrostratigraphy on Kerguelen Archipelago, subantarctic Indian Oean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5782, https://doi.org/10.5194/egusphere-egu2020-5782, 2020.

EGU2020-14955 | Displays | SSP3.1

Jura glacial lakes: a paleoclimatic and paleoenvironmental evolution since the Late Glacial Period.

Brahimsamba Bomou, Damien Zappa, Anne-Marie Rachoud-Schneider, Jean-Nicolas Haas, Marina Gärtner, Jorge Spangenberg, Vincent Bichet, and Thierry Adatte

During the retreat of a Würm ice sheet, numerous glacial paleolakes took place in the Swiss and French Jura. Two sites were investigated: the Amburnex Valley site (Switzerland), which evolved in well-developed peatland and the Lake Val (France), which is still persisted as a lacustrine system. During the Late Glacial period, both sites were glacial lakes characterized by a significant accumulation of lacustrine sediments.

Using a multiproxy approach, this project aims to reconstruct the paleoclimatic and the paleoenvironmental evolution recorded in lacustrine sediments and peatbog deposits since the last 13’000 years.

The Amburnex core (7m) exhibit a basal morainic deposit from the Würm period, overlain by three meters of lacustrine deposits and four meters of peatland deposits. The Lake Val core (4.5m) consists of the same lithological succession.

A multiproxy approach based on palynological analyses, grain-size analyses, mineralogical analyses (XRD) and geochemical analyses (TOC, Nitrogen, Phosphorus and Mercury contents; major and trace elements; organic carbon isotopes) have been used to characterize the hydrological and climatic fluctuations, the trophic level and the origin of organic matter in order to reconstruct the paleoenvironmental and paleoclimatic evolution of this area.

In the Amburnex site, the Bølling-Allerød, the Younger Dryas and the beginning of the Preboreal period have been recognized by palynological analyses and confirmed by carbon 14 dating. During the Oldest Dryas, oligotrophic conditions took place as suggested by the very low concentrations in nitrogen and organic matter. Then, during the warmer Bølling period, an enrichment in total organic carbon (TOC) associated with a decrease in phosphorus content are observed, implying the development of eutrophic conditions and maybe phosphorus recycling. Later in the Allerød period, low TOC and phosphorus contents, associated with varved carbonate deposits, indicate a return to more oligotrophic conditions. New organic matter enrichments are observed in the interval corresponding to the colder Younger Dryas period. These trends are quite consistent with those observed in the Lake Val and reflect significant changes in runoff and nutrient inputs at least at regional scale.

How to cite: Bomou, B., Zappa, D., Rachoud-Schneider, A.-M., Haas, J.-N., Gärtner, M., Spangenberg, J., Bichet, V., and Adatte, T.: Jura glacial lakes: a paleoclimatic and paleoenvironmental evolution since the Late Glacial Period., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14955, https://doi.org/10.5194/egusphere-egu2020-14955, 2020.

EGU2020-17438 | Displays | SSP3.1

Climate and tectonic modulation of sand delivery to deep water lakes in rift basins. Late Pliocene, Corinth Rift, Greece

Martin Muravchik, Gauti T. Eliassen, Gijs A. Henstra, Rob L. Gawthorpe, Gunn Mangerud, Katerina Kouli, Haralambos Kranis, Emmanuel Skoutsos, Mike Leeder, Julian Andrews, and Darren F. Mark

The sedimentary record of deep-water lakes is often used to investigate past climate and environmental change. Correct identification however, of the main controls driving the production and transport of sediment to the deepest parts of tectonically active basins is often challenging, especially when trying to differentiate autogenic from allogenic factors. This study focuses on the changes observed in a deep-water sedimentary system that evolved from mudstone-dominated to the development of a lacustrine sand-dominated channel-lobe distributary fan and back to mudstone deposition during the Pliocene climatic optimum in the Corinth Rift, Greece. This is a multidisciplinary study that involves the integration of sedimentology and structural geology with digital outcrop modelling, palynology, palaeomagnetology and geochronology.

The studied sedimentary system consisted of a coarse-grained delta (Mavro delta) that fed the deep-water Rethi Dendro Formation (RDF) in the Amphithea fault block during the Pliocene and Early Pleistocene. These syn-rift deposits were sourced from a major hinterland catchment, the Olvios catchment, draining the southern, fault-controlled margin of the rift. The depocentre was located at the exit of a structurally controlled sediment fairway, ~15 km from the source of sediment and ~12 km basinwards from the basin margin coastline. The stratigraphy of the RDF in the study area is well constrained due to the combination of detailed surface mapping and logging with LiDAR, photogrammetry and UAV surveys of large-scale exposures in the Sythas river valley. These were integrated with the information obtained from the analysis of rock cores obtained through wells drilled immediately behind the cliffs where the RDF is exposed. The Amphithea fault block has a half-graben configuration and tilting of the hangingwall was one of the main tectonic controls on the evolution of the depocenter fill. The stratigraphic interval considered in this study is ~130 m thick. It was deposited above a ~6° angular unconformity and it is composed predominantly of fine-grained hemipelagic dominated units, interrupted by the development of an ~30 m thick sandstone-dominated channelized lobe unit. Detailed palynological analysis of this interval shows significant changes in pollen and spore assemblages that are used to interpret the palaeoflora developed in the drainage catchments. The palynoflora in fine-grained hemipelagic intervals is dominated by temperate forests mixed with subtropical elements, whereas the channelized lobe unit is dominated by palynofloras typical of open herbaceous vegetation including steppic taxa, suggesting a dryer and cooler climate. The shift from forest- to herbaceous-dominated palynological assemblages is gradual, recorded from 5 m below the facies change marking the base of the channelized lobe unit.  In contrast, the top of the channelized lobe unit coincides with the abrupt change back to the forest-dominated pollen assemblage. The correlation between the establishment of a sand-dominated channel-lobe distributary fan in the basin floor with the predominance of open herbaceous vegetation is interpreted to reflect the highly erodible condition of land covered in this type of vegetation. In contrast, during periods when forests are dominant, erodibility decreases.

How to cite: Muravchik, M., Eliassen, G. T., Henstra, G. A., Gawthorpe, R. L., Mangerud, G., Kouli, K., Kranis, H., Skoutsos, E., Leeder, M., Andrews, J., and Mark, D. F.: Climate and tectonic modulation of sand delivery to deep water lakes in rift basins. Late Pliocene, Corinth Rift, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17438, https://doi.org/10.5194/egusphere-egu2020-17438, 2020.

The Crimean Peninsula has around 50 saline lakes, which formed during the Holocene marine transgression. These lakes are valuable archives of the Holocene sea-level changes in the Black Sea, but their chronologies and evolution remain largely unknown. This study presents reconstructions of evolution of the Lake Chokrak basin and its depositional environment during the last 8000 years. At present, the lake is hypersaline and separated from the Sea of Azov by a narrow sandbar. The environmental reconstructions are based on multi-proxy data including shell content, organic geochemical and x-ray fluorescence analyses and radiocarbon dating of an 11-m sediment core. The aim of the study is to provide new insights into the evolution history of the lake in the region where such data are limited. Based on the interpretation, the following succession of stages was recognized in the lake evolution. Around 8000 cal yr BP, an open relatively shallow marine embayment existed in the study area, which is evidenced by high contents of Mn, indicating well-oxygenated waters, and presence of shells of Cerastoderma edule, which is favoured by shallow calm waters. Lamination of the sediments during this stage indicates relatively stable marine conditions. A deeper transgressive stage is observed from 7000 to 6500 cal yr BP when waters became less oxygenated, the grain size decreased and laminations disappeared. Precipitation of carbonates at the end of this stage indicates seawater evaporation. A dry stage from 6500 to 6200 cal yr BP is characterized by further decrease in water level and precipitation of gypsum. Starting from 6200 cal yr BP, a renewed transgressive stage is observed with increased water oxygenation, accumulation of fine sediments and precipitation of carbonates. From 5400 to 5000 cal yr BP higher erosion is demonstrated by an increase in Zr, Ti, Rb and Si contents and occurrence of sand layers in the sediment core. After 5000 cal yr BP starts a dry stage of the basin, which is connected to the slower rate of the Holocene sea transgression. Precipitation of evaporites (carbonates, halite, gypsum) increased at this time and fine-grained clays accumulated in the basin. This stage is also characterized by virtually continuous presence of C. edule shells. Relatively high organic carbon content and C/N ratios imply increased input of terrestrial organic material throughout this stage. The infilling of the basin and formation of the sandbar started around 3000 cal yr BP when clay sediments intermixed with sand layers. A transitional stage from semi-open to closed basin lasted from 1400 to 800 cal yr BP and it is characterized by precipitation of evaporites and disappearance of shells. The current stage (from 800 cal yr BP to present) of the closed lake basin is characterized by sediment lamination, high precipitation of gypsum and potassium salts, and complete absence of molluscs due to high salinity of the brine. The obtained results show that hydrological regime and geochemical composition of the lake were influenced by complex interaction of climatic, local tectonic and eustatic factors throughout its history.

How to cite: Rohozin, Y. and Ljung, K.: Mid- and Late Holocene hydrological and geochemical changes in Lake Chokrak (NE Crimea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-602, https://doi.org/10.5194/egusphere-egu2020-602, 2020.

EGU2020-20024 | Displays | SSP3.1

Complex investigation of Lake Bannoe sediments (South Ural, Russia)

Diliara Kuzina, Yusupova Anastasia, Nurgaliev Danis, Krylov Pavel, Antonenko Vadim, Gareev Bulat, and Batalin Georgii

In paper presented results of complex investigations of Lake Bannoe (53°34'40.5"N 58°38'05.0"E) and its sediments. The origin of the Lake is tectonic. Seismoacoustic investigations were carried out for choose the best places for coring with continuous sedimentation and avoid gas saturated sediments. 4 long cores of sediments (up to 5.5 meters) were collected with using special hydraulic corer.

To study the sediments, a set of methods was used including petromagnetic and paleomagnetic studies, the study of mineralogical and elemental composition. According radiocarbon dating the maximum age of samples is 12.5 thousand. The age of samples increases with depth naturally, which means we have continuous sedimentation without hiatus.

Measurements of magnetic susceptibility (MS), hysteresis parameters and thermomagnetic analysis were carried out to determine changes in magnetic mineralogy and sedimentation conditions. Thermomagnetic curves measured on Curie express balance, coercitive parameters on J-coercivity spectrometer and magnetic susceptibility on multi-function kappabridge MFK1-FA (AGICO). The elemental composition was studied on an S8 Tiger X-ray fluorescence wave dispersion spectrometer. X-ray diffraction was performed on a Bruker D2 Phaser for studying mineralogical composition.

Changes in the magnetic susceptibility along the section are not significant, which indicates the constancy of sedimentation conditions. Only lower part, below 4.7 meters, MS increasing which corresponds to big input of terrigenous material. Most common magnetic minerals of sediments are pyrite and magnetite. Main minerals are quartz, albite, mica, from 1.3 meters and below in sediments detected calcite and dolomite.

Obtained data from all methods (magnetic properties, minerology, elemental composition) used for preliminary paleoclimatic and paleoenvironmental reconstructions of South Ural region for last 12.5 kyr. According petromagnetic data there is no big changes in sedimentation conditions. Also elemental composition shows the same, no big changes. Bottom part of sediments core are consist of more coarse material this is reflected both in magnetic properties and in elemental composition.

This work was funded by the Russian Science Foundation under grant № 18-17-00251.

How to cite: Kuzina, D., Anastasia, Y., Danis, N., Pavel, K., Vadim, A., Bulat, G., and Georgii, B.: Complex investigation of Lake Bannoe sediments (South Ural, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20024, https://doi.org/10.5194/egusphere-egu2020-20024, 2020.

EGU2020-20977 | Displays | SSP3.1

The Khuray deep-water fan: a beautifully complex lacustrine depositional system of Lake Baikal

Marina Solovyeva, Grigorii Akhmanov, Oleg Khlystov, and Adriano Mazzini

Lake Baikal (Russia) is the World’s oldest and deepest lake, which has been formed within a recently active rift zone at the edge of Siberian platform. Active tectonics influences all subaqueous geological processes in the Lake area with sedimentation, in particular. Selenga River is the largest river flowing into Lake Baikal. The river carries a large amount of terrigenous material sourced from Siberian-Mongolian drainage basin. Selenga River forms a large delta and several deep-water fans in the Central and South Baikal basins. Large amount of supplied terrigenous material, high sedimentation rates, steep slopes of the Baikal basins and active tectonic are favorable factors for the development of gravity-driven sediment transport processes.

A new large depositional system, named the Khuray deep-water fan, was discovered and studied since 2014 in the deep part of Lake Baikal during six Class@Baikal Project expeditions. It is located at the south-west of the Central basin of Lake Baikal, where it occupies a narrow, SW-NE extended area of about 1500 square km. Several 2D seismic surveys and bottom sampling campaigns were run during the expeditions in this area ranging in water depth from 800 to 1580 meters. A comprehensive set of collected geophysical and geological data provided important insights on the architecture of the Khuray lacustrine deep-water depositional system.

The system is fed by the Kukuy canyon, which is incised into the north part of the Selenga delta-front. In its upper reaches, immediately beyond the mouth of the Kukuy canyon, the Khuray system is represented by a set of meandering channels forming typical deep-water channel-levee complexes, which are well-expressed in bottom topography. The central part of the system develops over a large uplifted fault block, which is separated from of the rest of the Central basin by a well-expressed tectonic escarpment up to 80 m high. Within the block the system of the meandering channels is gradually replaced by a system of less distinct channels, which form a large braided channel complex less commonly observed in deep-water fan systems. At the distal part of the system, the channels become better expressed in bottom relief again and begin merging with each other forming, eventually, a single main channel. Another very interesting feature, a secondary canyon, is also observed at the distal part of the Khuray system. Once the small channels converge into the single one, it reaches a tectonic escarpment and forms a distinct erosional incision named the Khuray canyon. Several depositional lobes forming the lower reaches of the Khuray fan are found beyond the mouth of this secondary canyon, which is associated with a base of an active tectonic fault.

Active tectonic processes are believed to be the key factors responsible for the development of such complex architecture of the Khuray lacustrine deep-water depositional system comprising typical slope meandering channels, braided channel complex and several cascading canyons.

The reported study was funded by RFBR according to the research project № 18-35-00363.

How to cite: Solovyeva, M., Akhmanov, G., Khlystov, O., and Mazzini, A.: The Khuray deep-water fan: a beautifully complex lacustrine depositional system of Lake Baikal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20977, https://doi.org/10.5194/egusphere-egu2020-20977, 2020.

EGU2020-1104 | Displays | SSP3.1

Fine laminated clastic deposits revealing the delay of the deglaciation timing in the High Tatras Mts. (Central Europe) to Early Holocene

Dhavamani Ramachandran, Radovan Pipík, Timea Chamutiová, Lucia Žatková, Marina Vidhya, Rastislav Milovský, Stanislava Milovská, Dušan Starek, Juraj Šurka, Peter Uhlík, Peter Bitušík, Ladislav Hamerlík, and Adrian Biroň

The Tatra moraine relief and cosmogenic nuclide dating show glacier stabilizationand the maximum glacier extent in two phases,at26 – 21 ka and at 18 ka followed by a gradual retreat and  a termination of the glaciation during the Bølling/Allerød warming at 14.64 –12.9 ka (Makos etal., 2014). A renewed glaciation within the Younger Dryas (12.9 – 11.5 ka) formed smaller rock glaciers. This retreat was connected with the formation of the morainic, trough and cirque lakes and the beginning of light-grey silt sedimentation dated from 10ka to 16ka cal BP on the northern slopes of the Tatra Mountains and before 10ka cal BP on its southern slopes (Klapyta et al., 2016).

A new paleolimnic research led to a discovery of a cyclic fine laminated deposit in the four Tatra Mts. lakes. The laminae of thickness from 1 to 3 mm are built of couplets of light-coloured coarse detrital and fine dark-coloured laminae. Thicker light coloured laminae occasionally show a gradation ending in dark-coloured laminae. Laminae consist occasionally of low spherical angular grains of sand and gravel fractions, rarely up to size 10 mm which deformed underlying laminae. Light-coloured laminae are predominantly composed of quartz, followed by K-feldspar, plagioclase, mica, and clay-like particles. Dark-coloured laminae consist of clay-size clastic particles. These laminae were formed in cold, oxygen-rich, ultra-oligotrophic, slightly acid conditions in which the chironomids Pseudodiamesa nivosa and Micropsectra radialis-type dominated. We interpret these lamination as varves related to annual glacial melting. Once the valleys were ice-free, varve production stopped and a short deposition period of homogenous silt was replaced by gyttja. The radiometric C14 age dating shows the deglaciation in the Tatra Mts terminated at the beginning of the Early Holocene, around 10ka cal BP – 9ka cal BP.

 

The research was funded by APVV-15-0292 and the project Centre of Excellence for Integrated Research of the Earth's Geosphere, ITMS 26220120064.

 

Klapyta P., Zasadni J., Pociask-Karteczka J., Gajda A., Franczak P., 2016. Late Glacial and Holocene Paleoenvironmental records in the Tatra Mountains, East-Central Europe, based on lake, peat bog and colluvial sedimentary data: A summary review. Quaternary International 415: 126-144.

 

Makos M., Dzierzek J., Nitychoruk J., Zreda M., 2014. Timing of glacier advances and climate in the Tatra Mountains (Western Carpathians) during the Last Glacial Maximum. Quaternary Research 82: 1-13.

How to cite: Ramachandran, D., Pipík, R., Chamutiová, T., Žatková, L., Vidhya, M., Milovský, R., Milovská, S., Starek, D., Šurka, J., Uhlík, P., Bitušík, P., Hamerlík, L., and Biroň, A.: Fine laminated clastic deposits revealing the delay of the deglaciation timing in the High Tatras Mts. (Central Europe) to Early Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1104, https://doi.org/10.5194/egusphere-egu2020-1104, 2020.

EGU2020-7726 | Displays | SSP3.1

Holocene paleoclimate and environmental reconstruction from Urmia Lake sediments in southwest Asia

Negar Haghipour, Daniela Hunziker, Javad Darvishi, Ali Mohammadi, and Tim Ian Eglinton

Lake Urmia, in northwest Iran, is the largest saline lake in the Middle East with surface area of 5000 km2. Despite its potential as an archive of paleoclimate and paleoenvironmental information for Southwest Asia there has been no molecular organic geochemical investigation or precise dating of these sediments, especially for the Holocene. This study used multi-proxy analysis combining sedimentological, bulk and stable organic geochemical and compound specific stable isotopes along with high-resolution radiocarbon dating on organic and carbonate material to understand the Holocene climate and environmental variability in SW Asia.

The age model based on sixty calibrated radiocarbon dates shows variation of sedimentation rates between early and middle Holocene and a sudden increase in late Holocene. The most prominent change, at 4.3 Ka, closely corresponds to the well-documented 4.2 ka event (Medieval Optimum) in the Mediterranean and Middle East.

We used compound-specific hydrogen isotope ratios (δD) in long chain n-alkanes and n-alkonic acids as paleohydrological proxy. The fact that Urmia Lake is large and little affected by in-situ production of iso-GDGTs from methanogenic Euryarchaeota makes the measured TEX86 proxy reliable. Therefore, we used this proxy to reconstruct the Holocene paleotemprature.  The analyzed record reveals multi-decadal to centennial pacing of paleoclimate and paleoenviromental changes, with most prominent events recorded at 8.1, 4.3 and 2.5 ka BP.

 

How to cite: Haghipour, N., Hunziker, D., Darvishi, J., Mohammadi, A., and Eglinton, T. I.: Holocene paleoclimate and environmental reconstruction from Urmia Lake sediments in southwest Asia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7726, https://doi.org/10.5194/egusphere-egu2020-7726, 2020.

EGU2020-9608 | Displays | SSP3.1

Human-induced soil erosion and landscape changes in the Mongolian Altai – a biogeochemical multi-proxy approach from Lake Khar Nuur

Marcel Bliedtner, Paul Strobel, Julian Struck, Brigitta Enyedi, Tobias Bromm, Bruno Glaser, Gary Salazar, Sönke Szidat, Ronald Lloren, Nathalie Dubois, and Roland Zech

During the “Paleoanthropocene”, humans have become one of the major factors affecting Earth surface processes, with intensified soil erosion being one of the most notable human-induced process. Especially semi-arid regions are vulnerable to human-induced soil erosion and landscape changes, which is particularly true for the Mongolian Altai, where extensive pastoralism and the rise of nomadic empires strongly influenced landscape changes. So far, only little is known about the impact of humans in the Mongolian Altai and whether landscape changes are naturally or human-driven. Therefore, our study investigates a 5 ka sediment core from Lake Khar Nuur, which is located at ~2500 m a.s.l. in the Mongolian Altai. More specifically, we carried out a biogeochemical multi-proxy approach to disentangle between natural and anthropogenic signals in the Khar Nuur sediments, which includes extensive 14C-dating, XRF analyses, CNS analyses and their stable isotopes, and fecal sterols.

For the 5 ka sediments from Khar Nuur, XRF, Corg and bulk δ13C results show alternating phases of in-situ produced aquatic sediments/organic material versus increased terrestrial input from the catchment. Since no hardwater effect is observed for Khar Nuur sediments, phases of dominated in-situ aquatic production (i.e. high Ca/Ti ratios, higher Corg and positive bulk δ13C values) gave 14C-ages close to the timing of sediment deposition/biomass formation. In contrast, during phases of increased terrestrial input (i.e. low Ca/Ti ratios, low Corg and negative bulk δ13C values), 14C-ages become successively older and show larger age offsets compared to their timing of deposition in the lake. Thus, clear evidence is given that old organic carbon became mobilized from the catchment soils by increased soil erosion during three terrestrial phases from ~4.3 to 3.7 cal. ka BP, ~3.2 to 2.8 cal. ka BP and ~2.0 to 0.7 cal. ka BP. Abundances of fecal sterols start to increase at ~2 cal. ka BP, and human and herbivore feces strongly increase until ~1 cal. ka BP. This increase in fecal sterols falls directly into the last erosive phase between ~2.0 to 0.7 cal. ka BP and indicate that soil erosion during that time was mainly human-induced by increased pastoralism. Moreover, beginning human presence at ~2 cal. ka BP corresponds to the Xiongnu (the Huns), whereas the strongly increased anthropogenic activity in the region at ~1 cal. ka BP falls into a period where Turks, Uighurs and Mongols are present in western Mongolia and the Altai. Thus, soil erosion and landscape changes in the Mongolian Altai are strongly driven by the rise of pastoralism and nomadic empires during the late Holocene.

How to cite: Bliedtner, M., Strobel, P., Struck, J., Enyedi, B., Bromm, T., Glaser, B., Salazar, G., Szidat, S., Lloren, R., Dubois, N., and Zech, R.: Human-induced soil erosion and landscape changes in the Mongolian Altai – a biogeochemical multi-proxy approach from Lake Khar Nuur, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9608, https://doi.org/10.5194/egusphere-egu2020-9608, 2020.

EGU2020-5669 | Displays | SSP3.1

Lake level changes in the Dead Sea during the late Pleistocene recorded by fossil lake shorelines

Julius Jara-Muñoz, Amotz Agnon, Jens Fohlmeister, Jürgen Mey, Norbert Frank, Birgit Plessen, Andrea Schroeder-Ritzrau, Yannick Garcin, Yaniv Darvasi, Daniel Melnick, and Manfred Strecker

High-resolution records of lake-level changes are crucial to elucidate the impact of local and global climatic changes in lacustrine basins. The Late Quaternary evolution of the Dead Sea has been characterized by substantial variability apparently linked with global climatic changes, beign subject of many research efforts since decades. Previous studies have defined two main lake phases, the Lake Lisan and the Dead Sea, the earlier was a highstand period that lasted between ~70 and ~15 ka, the  latter was the lowstand period that persisted until the present. Here we focus on the switch between Lake Lisan and Dead Sea studying fossil lake shorelines, a sequence that comprises dozens of levels exposed along the rims of the Dead Sea, containing abundant fossil stromatolites that we dated by mean of radiocarbon and U-decay series. We determined 90 radiocarbon and 35 U-Th ages from stromatolites from almost every shoreline level. We compared U-Th and radiocarbon ages to estimating a radiocarbon reservoir between 0.2 and 0.8 ka, used to correct the remaining radiocarbon ages before calibration. The resulting ages range between ~45  and ~20 ka. Dating was complemented with analysis of stable oxygen and carbon isotopes. Furthermore, we applied a distributed hydrological balance model to constrain past precipitation and temperature conditions. Our results suggest that the duration of the last Lake Lisan highstand was shorter than previously estimated. Taking this at face value, the switch between Lake Lisan and Dead Sea occurred at ~28 ka, ~10 ka earlier than previously suggested. Oxygen and carbon isotopes show a consistent pattern, displaying a switch between wet and dry conditions at ~28 ka. Preliminary results from the hydrological model indicate a much stronger sensitivity of the lake level to precipitation amounts than to air temperature. From our results we can’t observe a clear link between global temperature variations and lake-level changes in the Lisan/Dead Sea lakes. Similar non-linear response to northern hemisphere climatic changes have been also documented in Holocene Dead Sea paleoclimatic records, suggesting that global climatic variations may led to variable lake-level responses. The results of this study adds further complexity to the understanding of factors controlling climate variability in the Dead Sea.

How to cite: Jara-Muñoz, J., Agnon, A., Fohlmeister, J., Mey, J., Frank, N., Plessen, B., Schroeder-Ritzrau, A., Garcin, Y., Darvasi, Y., Melnick, D., and Strecker, M.: Lake level changes in the Dead Sea during the late Pleistocene recorded by fossil lake shorelines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5669, https://doi.org/10.5194/egusphere-egu2020-5669, 2020.

EGU2020-20276 | Displays | SSP3.1

New insights on sediment provenance in the Dead Sea since the last glacial maximum using grain-size distribution

Cecile Blanchet, Hana Jurikova, Julia Fusco, Rik Tjallingii, Markus Schwab, Christoff Andermann, and Achim Brauer

Sedimentary records from the Dead Sea constitute unique paleoclimatic archives that enable investigating the response of environments to climatic changes. Large lake-level fluctuations (>100 m) occurred during the past glacial-interglacial cycles due to reorganizations of the hydroclimatic regime and drastically modified the morphology of the drainage area. We aim here to reconstruct past sedimentary dynamics at times of varying lake level to gain insights into paleoclimate and landscape evolution.

For this study, we have compared present-day surface sediments (fluvial and soil sediments) retrieved on both the eastern Jordanian and western shores of the present Dead Sea with downcore sediment archives including the ICDP Dead Sea Deep Drilling Program Site 5017-1. Streams originating from various parts of the watershed can be distinguished by their grain-size distribution, with northern and south-western streams having generally finer grain-size modes when compared with streams from the eastern side. We find that all modes identified in the fluvial sediments were present in the ICDP downcore samples from the last deglaciation, when lake levels were up to 250m higher than today. This suggests that the whole watershed contributed to the sediment input at that time. In contrast, Holocene sediments from the deep core and shore deposits are enriched in fluvial particles showing similar grain-size modes as the northern and south-western streams. This suggests that these regions were prime sediment sources during lower lake-level stands. An additional mode, tentatively related to aeolian particles, was also identified in the Holocene samples, pointing to the remobilization of deposited dust in the watershed or to a more arid regional climate.

Our results provide a first synoptic view on sedimentary dynamics in the Dead Sea watershed and help to relate sediment provenance to the drainage morphology and paleo-hydrological regimes. They constitute a solid basis for further assessment of sedimentary provenance using geochemical indicators.

How to cite: Blanchet, C., Jurikova, H., Fusco, J., Tjallingii, R., Schwab, M., Andermann, C., and Brauer, A.: New insights on sediment provenance in the Dead Sea since the last glacial maximum using grain-size distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20276, https://doi.org/10.5194/egusphere-egu2020-20276, 2020.

EGU2020-6544 | Displays | SSP3.1

A 45 kyr laminae record from the Dead Sea: Implications for basin erosion and floods recurrence

Nicolas Waldmann, Yin Lu, Revital Bookman, and Shmulik Marco

Recording and analyzing how climate change impacts flood recurrence, basin erosion, and sedimentation can improve our understanding of these systems. The aragonite-detritus laminae couplets comprising the lacustrine formations that were deposited in the Dead Sea Basin are considered as faithful monitors of the freshwater supply to the lakes. We count a total of ~5600 laminae couplets deposited in the last 45 kyr (MIS3-MIS1) at the Dead Sea depocenter, which encompass the upper 141.6 m of the ICDP Core 5017-1. The present study shows that aragonite and detritus laminae are thinner and occur at high frequency during MIS 3-2, while they are much thicker and less frequent during MIS 1. By analyzing multiple climate-connected factors, we propose that significant lake-level drops, enhanced dust input, and low vegetative cover in the drainage basin during the last deglaciation (22-11.6 ka) have considerably increased erodible materials in the Dead Sea watershed. We find a decoupling existed between the significant lake-level drop/lake size reduction and lamina thickness change during the last deglaciation. We argue that during the last glacial and the Holocene, the variation of lamina thickness at the multiple-millennium scale was not controlled directly by the lake-level/size change. We interpret this decoupling implying the transport capacity of flash-floods is low and might be saturated by the oversupply of erodible materials, and indicating a transport-limited regime during the time period. We suggest that the observed thickness and frequency distribution of aragonite-detritus laminae points to the high frequency of small-magnitude floods during the last glacial period, in contrast to low frequency, but large-magnitude floods during the Holocene.

How to cite: Waldmann, N., Lu, Y., Bookman, R., and Marco, S.: A 45 kyr laminae record from the Dead Sea: Implications for basin erosion and floods recurrence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6544, https://doi.org/10.5194/egusphere-egu2020-6544, 2020.

EGU2020-7372 | Displays | SSP3.1

Changes in hydroclimate during last deglaciation lake-level fall in the Dead Sea sediment record

Markus J. Schwab, Daniela Müller, Ina Neugebauer, Rik Tjallingii, Yoav Ben Dor, Yehouda Enzel, and Achim Brauer

The drainage basin of the Dead Sea is the largest hydrological system in the Levant and spans across the boundary between the sub-humid to semi-arid Mediterranean and the arid to hyper-arid Saharo-Arabian climate zones. As a terminal lake, precipitation changes due to climatic variations result in extensive fluctuations of lake level and sediment deposition.

A unique sediment record from the deepest part of the Dead Sea Basin was obtained as part of the ICDP Dead Sea Deep Drilling Project. Here we analyze the partially annually laminated sediments of Core 5017-1-A between 88.5-99.2 m core depth, which comprise the period between ~16.5 and ~11 ka and document a lake level drop of ca 160 m. In the sediments of Core 5017-1-A, this marks the transition from MIS2 aad (alternating aragonite and detritus) sediments to MIS1 halite deposits and ld (laminated detrital marl) sediments, coinciding with increased drying in the Dead Sea watershed.

Microfacies analyses show the occurrence of several lithological facies that accumulated during MIS2: aad, gd (massive gypsum deposit within marl), native sulfur concretions (associated with greenish colored aad), mtd (mass-transport deposits, typically graded) and homogenites consisting of clay and silt. Further, flood layers have been identified, potentially indicating rainstorms associated with specific eastern Mediterranean synoptic systems. To complement the microfacies analyses, XRF scanning provides continuous Ti/Ca and S/Ca records to reconstruct relative detrital input and gypsum occurrence, respectively. Additionally, to study potential early signs of hydroclimatic change, the deep lake sediments are correlated to the Lisan Formation of the marginal Masada outcrop using distinct gypsum marker layers, indicative of pronounced lake level drops. However, due to a significant lake level decline, the Masada outcrop sediments terminate at around 14.5 ka and the subsequent lake level lowering is solely recorded in the deep lake sediments.

This study was funded by the German Science Foundation (DFG Grant BR 2208/13-1/-2). Further, it is a contribution to the Helmholtz Association (HFG) climate initiative REKLIM Topic 8 “Abrupt climate change derived from proxy data”.

How to cite: Schwab, M. J., Müller, D., Neugebauer, I., Tjallingii, R., Ben Dor, Y., Enzel, Y., and Brauer, A.: Changes in hydroclimate during last deglaciation lake-level fall in the Dead Sea sediment record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7372, https://doi.org/10.5194/egusphere-egu2020-7372, 2020.

EGU2020-10897 | Displays | SSP3.1

A 500-year record of paleoclimate and paleoenvironment from the Lacandon Forest, southern Mexico

Karla Zurisadai Rubio Sandoval, Alexander Correa-Metrio, Juan Felipe Franco-Gaviria, Antje Schwalb, Philipp Hoelzmann, Mark Brenner, Maarten Blaauw, William Kenney, Jason Curtis, and Liseth Pérez

Tropical karst Lakes Metzabok (550 masl, surface area = ~77 ha, zmax = 25 m) and Nahá (832 masl, surface area = ~57 ha, zmax = 36 m) are located in the Lacandon Forest, in the state of Chiapas, southern Mexico. The region is characterized by high aquatic and terrestrial biodiversity. We generated high-resolution paleoclimate and paleoenvironmental records that span the last ~500 years, using invertebrate remains (ostracodes and gastropods) and geochemical variables (elemental and mineralogical contents) in sediment cores from the two water bodies. We collected a short sediment core from each lake (Metzabok = 46 cm, Nahá = 60 cm) and analyses were carried out at 1-cm intervals. Uppermost sediments in the cores were dated using 210Pb and 137Cs, and deeper deposits were dated by 14C. Ostracodes and snails were identified to species level and their abundances were quantified. Concentrations of Ti and Fe were determined by portable XRF. The geochemical record reveals information about past climate variability, human-mediated erosion and transport of terrigenous elements. Changes in ostracode and gastropod assemblages mainly reflect past lake level fluctuations and changes in water conductivity. The dominant ostracode species was Cytheridella ilosvayi and the most common gastropod is Aroapyrgus sp., indicative of water depths ≤40 m and low water conductivity, respectively. Analysis of the ecological distances between samples suggests that Lake Metzabok is unstable, with frequent ecological changes equal to or greater than 50% of the community. These changes may have resulted from dramatic environmental differences associated with hydrological dynamics during dry and rainy seasons. The Nahá record presents two environmental conditions, i.e. periods of high stability and periods of change, when the system was in transition from a dry period to a wetter one, or vice versa. Despite differences between the two lakes with respect to elevation, size, depth, and seasonal dynamics, both records contain evidence of droughts ca. 300 and 200 yr BP, during the Little Ice Age. Whereas both records show a long-term tendency towards higher moisture conditions, the high-resolution of our study enabled us to detect fluctuations between dry and wet periods over the last 500 years that previous studies failed to recognize.

How to cite: Rubio Sandoval, K. Z., Correa-Metrio, A., Franco-Gaviria, J. F., Schwalb, A., Hoelzmann, P., Brenner, M., Blaauw, M., Kenney, W., Curtis, J., and Pérez, L.: A 500-year record of paleoclimate and paleoenvironment from the Lacandon Forest, southern Mexico , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10897, https://doi.org/10.5194/egusphere-egu2020-10897, 2020.

EGU2020-8943 | Displays | SSP3.1

Comparison of varve preservation and characteristics between remote and urban lakes in Finland

Sarianna Salminen, Mikko Uotinen, and Saija Saarni

Comparison of varve preservation and characteristics between remote and urban lakes in Finland

 

Sarianna Salminen1, Mikko Uotinen1, and Saija Saarni2

1Department of Geography and Geology, University of Turku, Finland

2Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Finland

 

The occurrence of varved sediments in Finnish lakes is known to be dependent on certain features, such as morphometry of the lake and its catchment. However, varve preservation triggered by recent hypoxia has been observed in Finnish lakes of which sediments are not naturally laminated. In these lakes human-induced eutrophication and hypoxia might have been the major factor triggering varve preservation.

Here we compare varve preservation, varve characteristics, and varve qualities between one remote and naturally laminated (Lake Lehmilampi in Eastern Finland) and two lakes close to urban areas (Lake Vesijärvi in Southern Finland and Lake Kallavesi in Eastern Finland) with recent start of varve preservation.

Surplus of organic matter leading to hypoxia seems to have triggered the start of varve preservation in Lake Vesijärvi and possibly in Lake Kallavesi in the 20th century. In these two lakes several varve microfacieses were identified representing human-induced changes in the catchment. In the remote Lake Lehmilampi sedimentation rate is lower compared to the two urban lakes and the number of identified microfacieses is lower. The results suggest that in these three lakes varve characteristics, varve quality, and the cause of varve preservation as well as the continuity of varve preservation differ between lakes as a result of regional and local factors. In Lake Lehmilampi varve preservation seems to be dependent on lake and catchment morphometry as well as climate, whereas in Lake Vesijärvi and Lake Kallavesi varve preservation mainly seems to be dependent on anthropogenic factors. For instance, in Lake Vesijärvi rehabilitation actions seem to have affected varve preservation turning the sediment non-laminated. Furthermore, varve characteristics and quality seem to be sensitive to climate in Lake Lehmilampi, whereas in Lake Vesijärvi and Lake Kallavesi they correspond to anthropogenic changes.

How to cite: Salminen, S., Uotinen, M., and Saarni, S.: Comparison of varve preservation and characteristics between remote and urban lakes in Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8943, https://doi.org/10.5194/egusphere-egu2020-8943, 2020.

Inland waters are sites of active carbon (C) processing and transport along the land to ocean aquatic continuum (LOAC) that need to be accounted for closing the global C budget1,2. However, monitoring data are lacking and do not extend back as far as few decades, limiting our comprehension of the LOAC C cycle for the last centuries. Lake sediments provide a key archive for assessing C transport and transformation that occurs in lake catchments. Here, the analysis of large numbers of samples was performed on 420 lakes sediment records of the world to assess C burial rates and sources during the last 300 years. C and N (organic and mineral forms) on discrete samples were analyzed using a Variomax elemental analyzer to assess total C sequestration by lakes, C sources, and long-term changes in the contribution of allochtonous vs autochtonous sources to C transfers in lake-watersheds. Continuous sediment records were generated using core scanners (i.e. micro-XRF) and computed tomography to provide near-annual trends on terrigenous elements, here used as proxies of allochtonous sources (e.g. Al, Ti, K, Fe), and Mn:Fe ratio to infer past oxygen conditions3. Our results suggest that establishing a morphology-relevant lake typology that better characterises the types and distribution of oxygen conditions and terrigenous supplies across our sites is therefore the first step in providing a more robust evidence base for explaining the spatial-temporal variation in lake C burial rates.

How to cite: Jenny, J.-P., Niemman, C., Francus, P., Noren, A., and Carvalhais, N.: A meta-analysis of paleolimnological records reveals the sensitivity of lacustrine carbon burial rates to carbon sources and preservation conditions during the Anthropocene , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11679, https://doi.org/10.5194/egusphere-egu2020-11679, 2020.

EGU2020-8560 | Displays | SSP3.1

Variability of fine-grained basin floor turbidites and evaluation of controls on their development: Late Pleistocene, Gulf of Corinth, Greece

Natacha Fabregas, Robert Gawthorpe, Mary Ford, Martin Muravchik, Sofia Pechlivanidou, and Ursula Röhl

The Gulf of Corinth is one of the World’s fastest extending continental rift basins. During the Late Pleistocene, it alternated between marine and lacustrine conditions due to climate-driven sea-level fluctuations connecting or isolating/semi-isolating it from the open ocean. Core from IODP Expedition 381 (Corinth Active Rift Development) provide a continuous record of depositional processes operating within this deep-water rift and the interaction of tectonic and climate drivers controlling deep-water deposition over the Middle to Late Pleistocene. Subaqueous sediment density flows affect the Gulf of Corinth and are classified either by physical flow properties and grain support mechanisms or by depositional processes. Existing classifications mainly describe deposits from decimetre to 10’s of meter scale with an emphasis on sandy beds. Thinner (millimetre to centimetre scale) and finer (muddy to sandy) subaqueous sedimentary density flows beds are understudied. Low energy flows and tail of flow processes need a better understanding and are the target of this work. The aim of this study is to characterise the variability of fine-grained subaqueous sedimentary gravity flow deposits and the controls on their development based on core data from Site M0079 (IODP Expedition 381).  This site is located in the deepest part of the Gulf of Corinth (857 m water depth), in the most distal part of the sediment routing system. Analyses were performed within a 100 m interval covering Marine Isotope Stages 6 and 7 (from ~130 to ~250 ka). Detailed, sub-centimetre visual logging recorded over 2 000 beds classified according to (1) the presence/absence of a coarse base, (2) the grain-size (silty or sandy) of the base (if any), (3) the presence/absence of laminations within the muddy intervals, (4) sedimentary structures. The bed types reflect the diversity of the sedimentary processes and the subaqueous sediment density flows are thus organised within the depositional model. Bed frequency analysis provides insight into the variability between marine and lacustrine conditions. Relative chemical composition obtained from high resolution (2 mm) X-ray fluorescence scanning is used: (1) to examine the interactions between tail of the flow and background sedimentation in the basin and (2) to assess the provenance of the sediments.

How to cite: Fabregas, N., Gawthorpe, R., Ford, M., Muravchik, M., Pechlivanidou, S., and Röhl, U.: Variability of fine-grained basin floor turbidites and evaluation of controls on their development: Late Pleistocene, Gulf of Corinth, Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8560, https://doi.org/10.5194/egusphere-egu2020-8560, 2020.

EGU2020-16826 | Displays | SSP3.1

Lagoa de Santo André - The Holocene evolution of a coastal lake at the Atlantic coast of Portugal

Sebastian Frank, Hannes Laermanns, Anna Pint, Barbara Wagner, Piero Bellanova, Lisa Feist, Margret Mathes-Schmidt, Klaus Reicherter, and Helmut Brückner

The Lagoa de Santo André is a coastal lake located ca. 80 km south of Lisbon at the Atlantic coast of Portugal. The region is highly vulnerable to earthquake-triggered tsunami events due to its exposure to the very active tectonic boundary between the Eurasian and the African plates. Despite several natural and artificial breaches of beach barrier in the past, the lagoon still represents an appropriate geo-bio-archive for reconstructing the Holocene palaeoenvironmental evolution. For this purpose, a 10-m-long sediment core was taken from the centre of the lake by using a floating platform. Sedimentological, geochemical and micropalaeontological analyses were performed in order to unravel the former geological and climatic conditions, and to identify short-term events like tsunamis or storm surges that might have crossed or breached the shielding barrier, leaving their footprint in the sedimentary record of the lagoon.

The sediment core covers the palaeoenvironmental evolution of Lagoa de Santo André for at least the last eight millennia. The sandy deposits of the lowermost part of the core most likely represent the littoral phase of a palaeo-beach that had developed when the postglacial marine transgression had reached the area. Above alternating layers indicate varying environmental conditions that are characterised by peat growth, stagnant-water areas and intercalating sand layers that deposited during disconnections from and reconnections with the open sea. Since 3000 BC at the latest, the longshore transport had formed a beach barrier that separated the coastal lake from the open sea. As yet no deposits of an extreme wave event have been detected. However, the ongoing microfaunal analysis will clarify, if sudden changes of the salinity have occurred due to significant saltwater intrusions, which would hint at potential extreme wave events.

How to cite: Frank, S., Laermanns, H., Pint, A., Wagner, B., Bellanova, P., Feist, L., Mathes-Schmidt, M., Reicherter, K., and Brückner, H.: Lagoa de Santo André - The Holocene evolution of a coastal lake at the Atlantic coast of Portugal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16826, https://doi.org/10.5194/egusphere-egu2020-16826, 2020.

SSP3.2 – Carbonates!

EGU2020-8 | Displays | SSP3.2

Sedimentary Cyclicity in the Upper Paleocene- Eocene Successions of the Haymana Basin (Ankara, Turkey): Responses of Fossils to Cyclicity

Nilya Bengül

EGU2020-2721 | Displays | SSP3.2

Application of Clumped Isotope Palaeothermometry to reconstruct thermal evolution of recrystallised calcite in fine-grained micrites

Alexandra Sarah Robinson, Dr Cédric M John, Dr Annabel Dale, and Dr Mark Osborne

Previous studies have shown that within fine-grained dolomites, recrystallisation that occurs at shallow burial depths (<1 km) and low temperatures (<40 °C) can alter the carbonate clumped isotope signature of the minerals. Dolomites are, therefore, no longer representative of the environment of deposition, but rather capture temperatures present during burial. Currently, we do not understand isotopic re-setting of carbonate clumped isotopes during calcite recrystallisation during burial within micritic formations and whether the temperatures measured are representative of maximum burial temperatures reached. This study thus aims to determine if recrystallisation in fine-grained calcitic micrites show similar degrees of isotopic alteration to early dolomites; this is important as temperatures measured could be representative of temperatures reached during burial and serve as a proxy to reconstruct the thermal evolution of a formation and burial diagenetic processes. We have combined carbonate clumped isotope palaeothermometry with SEM/EDS imaging to study calcite recrystallisation under moderate burial (<1.8 km).

We analysed 17 samples collected from outcrops located on the West of the Eagle Ford Shale outcrop belt, Texas. The Eagle Ford is an ideal study location as it contains abundant fine-grained carbonate mixed with clastic material. The burial depth and temperature reached are understood through previous studies using organic proxies, giving this study a reasonable calibration for temperatures obtained through clumped isotope palaeothermometry. Results confirm that the Eagle Ford Shale is mixed formation, with nearly all samples showing 50:50 carbonate to clastic material. Clumped isotope analysis show variability in both measured clumped isotope temperatures (T(Δ47 calcite), 35 to 105 °C) and calculated water oxygen isotope composition (δ18Ovsmow, -1.93 to 6.96 ‰). The results show higher temperatures than reconstruction based on organic matter matutuation index. This indicates that thermal evolution of calcite recrystallisation can differ from that of organic matter transformation, probably because different kinetics exist for the two reactions. Organic matter transformation depends on both temperature and time, whereas carbonate recrystallisation can occur instantaneously and depends on temperature and the fluid present. A correlation also exists between T(Δ47 calcite) and δ18Ovsmow; the higher T(Δ47 calcite), the higher δ18Ovsmow. This correlation is interpreted to be evidence of burial recrystallisation via dissolution/re-precipitation within a closed system, therefore with minimal to no change in the δ18Ocalcite. We suggest that even with the large range of measured T(Δ47 calcite), these variations could be a result of recrystallisation via dissolution/re-precipitation during burial and therefore representative of maximum burial temperatures, which are not recorded by the organic temperature proxies.

How to cite: Robinson, A. S., John, D. C. M., Dale, D. A., and Osborne, D. M.: Application of Clumped Isotope Palaeothermometry to reconstruct thermal evolution of recrystallised calcite in fine-grained micrites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2721, https://doi.org/10.5194/egusphere-egu2020-2721, 2020.

EGU2020-4041 | Displays | SSP3.2

Multi-proxy study of cannon-ball concretions with glendonites from Paleogene-Neogene sediments of Sakhalin Island: implication for concretion growth and ikaite-calcite trans-formation

Kseniia Vasileva, Victoria Ershova, Oleg Vereshchagin, Mikhail Rogov, Marianna Tuchkova, Yuriy Kostrov, Eduard Khmarin, and Boris Pokrovsky

The objects of the current study are glendonite pseudomorphs forming the central part of cannon-ball carbonate concretions found within Miocene terrigeneous sediments of Sakhalin island (easternmost part of Russia). Twelve samples of glendonites and host carbonate concretions were examined using optical and cathodoluminescence microscopy, EDX analysis, powder X-ray diffraction and isotopic analysis. The aim of the study is to determine the origin of the concretions and the relationships between the concretion and glendonite occurrence.

Glendonites and host cannon-ball concretions were found within terrigeneous sediments of Bora (Lower Miocene) and Vengeri (Upper Miocene) formations. These formations are composed of laminated sandstones, siltstones, argillites and siliceous rocks. Dropstones are often found within these sediments as well as cannon-ball carbonate concretions, some of them with glendonites in central part. 60-90% of the cannon-ball concretion is occupied by sandy limestone (with high-magnesium calcite) and occasionally contains dolomite and pyrite. Central part of the cannon-ball concretion is occupied by glendonite (single crystal-like or star-like cluster of crystals). Glendonites are composed of several calcite generations. Rosette-like calcite crystals (“ikaite-derived calcite”) are composed of low-magnesium calcite, they are non-luminescent. Needle-like calcite cement is composed of high-magnesium calcite or dolomite and show bright-yellow cathodoluminescence. The rest of the glendonite is occupied with low-magnesium radiaxial fibrous or sparry calcite with dark-red cathodoluminescence.

Isotopic ratios of glendonites are close to those of host concretions. For host concretions δ13С varies from -20.3 to -14.9 ‰PDB, δ18О varies from +1.7 to +2.7 ‰PDB; for glendonites δ13С varies from -18.1 to -1.9 ‰PDB, while δ18О varies from +0.7 to +3.4 ‰PDB.

Close mineralogical and isotopic composition of the studied glendonites and host cannon-ball concretions suggest they were formed in similar geochemical environment. Association of glendonite occurrence along with dropstones is an indicator of cold conditions, which is well-corresponding with view on glendonites as a proxy for cooling events. Cementation of surrounding sediment (formation of the cannon-ball concretions) and glendonite formation was simultaneous and occurred during early diagenesis in the sulfate-reduction zone. The source of calcium and magnesium ions was seawater (δ18О values are characteristic for seawater). Ikaite was replaced with low-magnesium calcite; the replacement was favored by organic matter decay (δ13C values are characteristic for organic matter). Cementation of the cannon-ball concretion with high-magnesium calcite occurred together with needle-like high-magnesium calcite growth in the glendonite with increasing concentration of magnesium due to calcite extraction from the pore water. The remaining pore space was subsequently filled with radiaxial fibrous or blocky sparry calcite during burial diagenesis.

The study is supported by RFBR, project number 20-35-70012.

How to cite: Vasileva, K., Ershova, V., Vereshchagin, O., Rogov, M., Tuchkova, M., Kostrov, Y., Khmarin, E., and Pokrovsky, B.: Multi-proxy study of cannon-ball concretions with glendonites from Paleogene-Neogene sediments of Sakhalin Island: implication for concretion growth and ikaite-calcite trans-formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4041, https://doi.org/10.5194/egusphere-egu2020-4041, 2020.

The "black chimney" type of hydrothermal vents in the modern deep sea have become a popular research topic in many disciplines. Due to the actual conditions, the research on palaeo-thermal vents in geological history is relatively low. Fortunately, the discovery of hydrothermal vents and bio-fossils from the Chang 7 source rocks of the Yanchang Formation of the Triassic in the Ordos Basin, China, provides the best evidence for deciphering hydrothermal activity during geological history. Here, we report a case study. Through ordinary sheet observation, scanning electron microscopy and electron probe observation, layered grained siliceous rocks, dolomites, and hydrothermal mineral combinations, such as pyrite + dolomite + gypsum and calcite + barite, are found. Their unique petrological characteristics, mineral composition, and structure confirm the existence of palaeo-thermal fluid vents. We further analysed the geochemical characteristics and in situ isotope characteristics. The study found that Cs, U, Th, Pb, Ba and other trace elements of the sample showed positive abnormalities, in which values of U/Th were high; in addition, the enrichment of major elements such as Sr, Mn, and the in situ sulphur isotopes of pyrite reached 7.89%-10.88%. This study of hydrothermal vents over geological history is expected to provide new insights on the life forms of various extreme microorganisms in hydrothermal environments and on their formation of high-quality source rocks.

How to cite: You, J., Liu, Y., and Zhou, D.: Discovery and geological significance of the Magma-hydrothermal micro-jets at the bottom of a lake: A case from the Chang 7 section of the Yanchang Formation of the Triassic in the Ordos Basin, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6331, https://doi.org/10.5194/egusphere-egu2020-6331, 2020.

EGU2020-6963 | Displays | SSP3.2

Depositional environment control on the geochemical signal of ancient shallow-water carbonates (Upper Jurassic, French Jura)

Simon Courgeon, Yasin Makhloufi, Lucas Vimpere, Michel Meyer, and Elias Samankassou

Chemostratigraphy has become a key tool to study shallow-water carbonate systems and propose insightful time correlations where biostratigraphic markers are limited. However, the bulk geochemical signal of shallow-water carbonate deposits commonly results from the superposition of local and global trends. Additionally, the shallow-water carbonate deposits frequently undergo intense diagenetic alteration obliterating the original seawater signature.

Based on three well-constrained Upper Jurassic sections of the French Jura, this study aims at discussing the control of the original depositional environment on the bulk geochemical signature of ancient shallow-water carbonates. Using isotope ratios (δ13C, δ18O, 87Sr/86Sr), elemental concentrations (Ca, Mg, Fe, Mn, Sr, Al, U) and statistical methods, this paper shows that two main processes, closely linked to the depositional environments and associated conditions, control the overall signature of bulk samples of the studied deposits: the detrital input and the diagenetic effects. The detrital input, identified by increase in Fe, Al, Mn and U concentrations, is the highest in very proximal areas (supra- and intertidal domains) affected by terrestrial organic matter and pedogenetic material influx, and in distal realms (open sea) characterized by fine terrigenous fraction deriving from continental landmass erosion. The diagenetic effects can be subdivided into two processes: the dolomitization and the diagenetic imprint. The dolomitization, associated to increase in Mg and δ18O, mostly concerns supra- and intertidal deposits affected by refluxing evaporitic-derived brines. The diagenetic imprint, mainly associated to decrease of δ13C, δ18O and increase in 87Sr/86Sr, is the most important in platform margin deposits associated to high primary porosities enhancing fluid-rock interactions during burial and/or meteoric diagenesis. Because of these processes, time correlations are overall very difficult to establish between the studied sections.

The combined analyses of depositional environments and geochemical signal finally led to the conclusion that the concept of “geochemical facies” might represent an interesting tool to discuss depositional conditions and diagenetic effects along specific depositional models. This integrated study provides (1) relevant results to step back on challenging chemostratigraphic interpretations in shallow-water carbonate settings and (2) new insights into the complex sedimentological, diagenetic and geochemical interactions in shallow-water carbonate depositional systems.



How to cite: Courgeon, S., Makhloufi, Y., Vimpere, L., Meyer, M., and Samankassou, E.: Depositional environment control on the geochemical signal of ancient shallow-water carbonates (Upper Jurassic, French Jura), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6963, https://doi.org/10.5194/egusphere-egu2020-6963, 2020.

EGU2020-7074 | Displays | SSP3.2

First Record of Conodonts from the Permo-Triassic Khartam Member, Khuff Formation in Central Saudi Arabia

Jarrah Babiker, John Humphrey, Khalid Al-Ramadan, and Michael Kaminski

EGU2020-11397 | Displays | SSP3.2

Preservation potential assessment of central Atlantic biogenic carbonate deposits using X-ray micro-computed tomography (XMCT)

Stergios Zarkogiannis, George Kontakiotis, and Assimina Antonarakou

Dissolution of foraminiferal calcite above the lysocline can occur within the water column, at the sediment-water interface, and/or within the sediment column as a result of low in-situ carbonate ion concentrations. The dissolution of foraminiferal shells, which are widely used for paleoceanographic studies, has the potential to influence the weight and the chemical composition of the whole test. Their partial dissolution has been suggested to significantly bias their δ18O and δ13C signals, while the trace element ratios decrease as dissolution progresses. Despite the significant Atlantic importance on the climate system, and that of the carbonate system on atmospheric CO2 concentration, there have been only a few studies examining carbonate preservation along depth transects in the North and South Atlantic, and mostly by indirect means.

In order to assess the preservation potential of the central Atlantic basins, a set of 16 Atlantic surface sediment (core-top) samples along the mid-Atlantic Ridge was deployed. The samples span from approximately 30°N to 30°S and are situated along the mid-Atlantic Ridge from an average water depth of 3700 m, well above the 4200 m modern lysocline, with roughly equal bottom water ΔCO32− values (23 ±4 μmol/kg). Typically 15 pre-weighed shells of three different planktonic foraminifera species, widely used in paleoceanographic research, were picked from each sample (300-355 μm) and scanned using a GE vtomex s high-resolution micro-CT scanner. The species under consideration, namely Globigerinoides ruber s.s. (white), Trilobatus trilobus and Globorotalia truncatulinoides, inhabit different water depths and are known to have different geochemistries and thus preservation potentials. The preliminary analysis of the tomographs suggests that although carbonate sediments from the eastern basins below from the south equatorial upwelling zone are more corroded their initial geochemistry is not greatly altered by dissolution.

How to cite: Zarkogiannis, S., Kontakiotis, G., and Antonarakou, A.: Preservation potential assessment of central Atlantic biogenic carbonate deposits using X-ray micro-computed tomography (XMCT), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11397, https://doi.org/10.5194/egusphere-egu2020-11397, 2020.

EGU2020-21365 | Displays | SSP3.2

Carbonate Diagenesis in a Sequence Stratigraphic Framework; Case study from Miocene Dam Formation, Eastern Saudi Arabia

Moaz Salih, Osman Abdullatif, Khalid Al-Ramadan, and Mazin Bashri

The Miocene Dam Formation in the Al-Lidam area of Eastern Saudi Arabia consists of a succession 

of mixed siliciclastic-carbonate sequences that were deposited during Miocene (Burdigalian) 

times. Stratigraphic equivalents of the Dam Formation occur as hydrocarbon reservoir intervals in 

the Arabian Plate. Reservoir quality of carbonate rocks is controlled by a combination of 

depositional setting and post-depositional diagenetic factors. 

In this study, fifteen lithofacies were identified as they were deposited on a low angle dipping 

carbonate ramp, under supratidal, beach, intertidal and shallow subtidal conditions. Carbonate 

diagenesis has been examined using: thin-section petrography, SEM, XRD and 

cathodoluminescence. These analytical tools have shown that the intertidal lithofacies are 

influenced by extensive meteoric dissolution and minor cementation. Marine diagenesis was 

restricted to beach grainstone and subtidal lithofacies, in the form of aragonite and high magnesium 

calcite cement. Shallow burial conditions were inferred by grain contacts represented by point, 

suture and concavo-convex contacts. Mimetic dolomitization for the whole succession was also 

observed. Three fourth - order, shallowing upward sequences were identified in the study area, and 

they are separated by two sequence boundaries. A clear relation between sequence surfaces and 

diagenetic processes was observed; meteoric diagenesis and dolomitization increases upwards in 

each sequence. Porosity and permeability measurements have shown that the highest values are 

associated with the HST of each sequence, followed by the TST and the LST. The results of this 

study can help in understanding of diagenetic processes, and consequently in developing better 

and more accurate predictions of the porosity and permeability distribution within hydrocarbon 

reservoirs.

 

How to cite: Salih, M., Abdullatif, O., Al-Ramadan, K., and Bashri, M.: Carbonate Diagenesis in a Sequence Stratigraphic Framework; Case study from Miocene Dam Formation, Eastern Saudi Arabia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21365, https://doi.org/10.5194/egusphere-egu2020-21365, 2020.

EGU2020-21627 | Displays | SSP3.2

Basin subsidence and Miocene/Pliocene sedimentary change in the Browse Basin, NW Australia

Sebastian Thronberens, Stefan Back, Lars Reuning, and Julien Bourget

The upper Miocene to Pliocene interval of the Browse Basin on the Australian North West Shelf (NWS) records a significant paleo-environmental change in its sedimentary record concerning the decay of middle to late Miocene tropical reefs. Seismic observations towards the Pliocene show a clear landward migration of carbonate build-ups in the eastern part of the basin, and very high subsidence rates seem to have outpaced most reef growth in distal shelf-edge positions. Nevertheless, the Scott Reef and the Seringapatam Reef were able to withstand shelf-edge drowning, which indicates a significant contribution of inversion-related uplift for reef survival. The contribution of basin subsidence as a driving factor for this reef decay and survival is still discussed and has not been studied in detail. This study provides an estimate for the laterally and through time changing late Miocene/Pliocene subsidence pattern. A 3D paleo-environmental reconstruction was generated by 3D quantitative backstripping, integrating 3D paleo-waterdepth information derived from seismic-based depositional system interpretation. The base of this analysis is a giant 2D and 3D seismic-reflection data set (>130.000 km²) integrated with borehole data (logs, cores, cuttings), new Sr-isotope dating, X-ray diffractometry (XRD) and microfacies analyses, supporting paleo-bathymetric correction and ties to global sea-level data. The seismic-reflection data is covering a study area extending over 130.000 km² and is supported by industry borehole data (logs, cores, and cuttings), SR-Isotope dating, X-Ray diffractometry (XRD) and microfacies analysis.

How to cite: Thronberens, S., Back, S., Reuning, L., and Bourget, J.: Basin subsidence and Miocene/Pliocene sedimentary change in the Browse Basin, NW Australia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21627, https://doi.org/10.5194/egusphere-egu2020-21627, 2020.

EGU2020-21797 | Displays | SSP3.2

3D identification and quantification of multi-phase diagenetic carbonate mineralogy using µ-computed tomography: roadmap to original isotope geochemistry of altered archives

Stefan Krause, Volker Liebetrau, Karolin Engelkes, Sebastian Büsse, Hana Jurikova, Gernot Nehrke, Stanislav Gorb, and Anton Eisenhauer

Marine biogenic carbonate deposits are important climate archives as environmental conditions during mineral genesis are recorded chemically in the crystal lattice. When exposed to diagenetic alteration metastable carbonate phases as aragonite are prone to transform into more stable calcite, Mg-calcite or dolomite resulting in the loss of the original geochemical information. As diagenetic alteration is often heterogeneous, numerous carbonate archives are characterized by multi-phase compositions, including potentially unaltered remains of primary formation. Consequently, high-spatial-resolution identification of adjacent carbonate mineral phases is of key interest to constrain diagenetic fronts, as well as the degree and pattern of a carbonate archive alteration, and the deciphering of relevant geochemical proxy information.

The aim of the present study is to contribute to the localization of potentially unaltered localities within heterogeneous carbonate samples, enhancing the retrieval of original geochronological and proxy information. Using natural tropical fossil coral samples as an example, we present an approach for the 3D-identification of multiple carbonate phases using µ-computed tomography scans with a resolution on a µm scale. The straightforward discrimination of aragonite, calcite, and dolomite from CT-imaging is principally hampered by the similar X-ray densities of these carbonate phases. To overcome this problem, reference material blocks for each of the three carbonate minerals were scanned together with the carbonate sample. Using the AVIZO 2019 software package in combination with a self-developed Tool command language (Tcl) script each of the carbonate reference blocks within the scanned volume was systematically subsampled for its voxel grey values. The obtained data set was statistically analysed and a robust mean voxel grey-value was calculated for each reference mineral. Subsequently, these mean grey values were used for the automated selection of seed points for subsequent image segmentation throughout the entire scanned volume based on a self-developed Tcl script. After seed point definition mineral identification was carried out throughout the volume using the watershed algorithm as a region-based image segmentation method. The final result yielded an approximation of the 3D-distribution of identified carbonate phases throughout the sample on a µm scale, which represents an excellent starting point for subsampling strategy development. 

How to cite: Krause, S., Liebetrau, V., Engelkes, K., Büsse, S., Jurikova, H., Nehrke, G., Gorb, S., and Eisenhauer, A.: 3D identification and quantification of multi-phase diagenetic carbonate mineralogy using µ-computed tomography: roadmap to original isotope geochemistry of altered archives , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21797, https://doi.org/10.5194/egusphere-egu2020-21797, 2020.

EGU2020-22663 | Displays | SSP3.2

The complexity of carbonate porosity distribution in the Upper Marrat Formation, Central Saudi Arabia

Saleh Ahmed, Luis González, Johannes Jozef Gerardus Reijmer, and Ammar ElHusseiny

In terms of reservoir properties distribution carbonate rocks are very heterogeneous. Moreover, the types of porosity in carbonate rocks is very diverse. In our study of the Upper Marrat Formation near Khasm-adh-Dhibi (central Saudi Arabia) we have documented the pore system complexity and are deconvolving the impact of various post-depositional processes on porosity and permeability evolution of the formation. The Upper Marrat Formation is exposed in the central part of the Arabian plate in a north-south elongated mountain belt. It forms the lower part of the thick Jurassic petroleum-rich succession. The sediments forming the Upper Marrat Formation were deposited during the Early Jurassic time, the Toarcian. The Upper Marrat Formation shows fossiliferous biomicrite to sparse biomicrite carbonates with an evaporite deposit at the top. It is bounded by clayey units at both the top and the base. In general, because of the muddy matrix of the Upper Marrat, sediments are very tight and show low permeability. During the last 175 My, the Upper Marrat has been subjected to a series of diagenetic and tectonic processes. The initial micro- and intergranular porosity was reduced due to early compaction and cementation, however, during later diagenesis and tectonism, porosity and permeability were enhanced. The dominant diagenetic porosity in the Upper Marrat sediments is vuggy porosity, followed by fabric selective intragranular porosity. Many of the horizons in the Upper Marrat are heavily burrowed and mostly filled with sand-sized grains showing a higher porosity than the matrix. Dolomite is limited to evaporite strata and contain extensive inter-crystalline porosity produced during dolomite formation. Tectonism has enhanced porosity through the development of micro- and macro-fractures.  The different sized and orientated micro-fractures are important while they enhance permeability by connecting different pore types. Then extensive macro-fracture network has a major impact on the reservoir qualities, both porosity and permeability. The heavily fractured formation shows numerous fractures sets with NNE to SSW and ENE to WNW orientations. Fractures are mostly vertical to near-vertical; they are nearly all open, and often crosscut beds, or end at bedding planes. These fractures are the most abundant porosity type and their connectivity results in a very high permeability. In conclusion, initial porosity and permeability, and subsequent diagenetic and tectonic processes reduced and enhanced the porosity and permeability development of the sediments of the Early Jurassic Upper Marrat Formation.

How to cite: Ahmed, S., González, L., Reijmer, J. J. G., and ElHusseiny, A.: The complexity of carbonate porosity distribution in the Upper Marrat Formation, Central Saudi Arabia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22663, https://doi.org/10.5194/egusphere-egu2020-22663, 2020.

SSP3.5 – Flow and bedform dynamics on Earth and Mars: current understanding of a complex interplay

Desert (sandland) margin is the transition region from inner aeolian landforms  to other landforms outside, while it remains as an ambiguous conception in previous researches. Accurately delineating its boundary line and realizing the characteristics of the particle size distribution of surface aeolian sands in margin area can help us understand the formation of modern boundary of desert (sandland). In this research, the criteria of identification of the boundary were proposed and the boundary line was extracted quantitative. Then systematic analyses of grain size of aeolian sand in margin were conducted. Together with the morphologic type, activity and the geomorphological location of collected dunes, the factors controlled the particle-size distributions had also been analyzed. The results reveal the following: (1) There is notable difference in grain size characteristics of aeolian sand between inside and outside of Mu Us sandland. The outside samples are finer than inside. Additionally, the aeolian sand covering on loess is always more poorly sorted and with different grain size fraction composition. (2) The controlling factors on particle size distribution are different in different downwind margins. In southwest margin, the grain size characteristics of aeolian sand are influenced by time and degree of stabilization of sampled dune and locally topographic relief; From the estuary of Lu River to Yuxi River, sediment transport by wind is affected by topographic obstacles including both valley and loess gully. Meanwhile, the small dunefields in Loess Plateau outside of Mu Us sandland may originate from a local alluvial source; In northeast downwind margin, the grain size characteristics of aeolian sand covering on loess are determined by regional gully erosion after its deposition.

How to cite: Wang, Z. and Wu, Y.: Grain size characteristics of surface aeolian sands in the downwind margin of modern Mu Us Sandland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6583, https://doi.org/10.5194/egusphere-egu2020-6583, 2020.

EGU2020-9998 | Displays | SSP3.5

River dunes under extreme high and low flows: outline of a research project

Lieke Lokin, Jord Warmink, and Suzanne Hulscher

In the near future river discharges are expected to become more extreme due to climate change. Both high discharges and low discharges will occur more frequently and become more extreme (Klijn et al., 2015). While during high discharges bedforms grow and result in increased bed roughness resulting in higher flood levels. During extreme low discharges bed material may become immobile. Remaining bedforms are obstacles for waterborne transport, reducing the maximum load each vessel can transport.

Current dune models can describe the growth of the dunes and representative bedform related roughness under high flows and flood waves (Paarlberg et al., 2009). Also steps have been made to implement the processes leading to upper stage plane bed by adding suspended load transport (Naqshband et al., 2016). However, a model resolving the dune evolution though a full flood wave, including a falling stage towards extreme low flows with partly immobile bed, are not available yet.

The evolution of dunes during the falling stage of a flood wave, towards extremely low discharges, is not well understood and therefore cannot be properly predicted. Predictions of dune heights during periods of extreme low discharge can help fairway managers to maintain sufficient depth. To obtain this understanding first a fast dataset of bed level measurements, made by COVADEM on the Rhine river, will be analyzed with special focus on the growth and decrease of bedforms. This analysis will produce a set of parameters, valid for circumstances where immobile bed can occur and will lead to immobile bedforms. This new understanding of bedform development will be combined with the current knowledge on bedform development into an integrated model which can predict dune development from lower stage immobile dunes or flat-bed toward upper stage flat bed and vice versa.

References

Klijn, F, Hegnauer, M., Beersma, J. and Sperna-Weiland, F. (2015). Wat betekenen de nieuwe klimaatscenario’s voor de rivierafvoeren van Rijn en Maas? Samenvatting van onderzoek met GRADE naar implicaties van nieuwe klimaatprojecties voor rivierafvoeren. Deltares, KNMI, Ministerie van Infrastructuur en Milieuw (In Dutch)

Naqshband, S., van Duin, O., Ribberink, J., and Hulscher, S. (2016). Modeling river dune development and dune transition to upper stage plane bed. Earth Surf. Process. Landforms, 41: 323– 335. doi: 10.1002/esp.3789.

Paarlberg, A.J., Dohmen-Janssen, C.M., Hulscher, S.J.M.H. and Termes, A.P.P. (2009). Modeling river dune development using a parameterization of flow separation. Journal of Geophysical Research 114: F01014. DOI:2002JB001785/2007JF000910

How to cite: Lokin, L., Warmink, J., and Hulscher, S.: River dunes under extreme high and low flows: outline of a research project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9998, https://doi.org/10.5194/egusphere-egu2020-9998, 2020.

EGU2020-10561 | Displays | SSP3.5

Active and fossil aeolian bedforms in Arabia Terra (Mars): climate and sedimentological implications

Simone Silvestro, Francesco Salese, David Vaz, Joel Davis, Hezi yizhaq, Gabriele Franzese, and Francesca Esposito

Aeolian bed forms such as dark dunes and ripples are abundant and widespread on Mars and can be used to constrain present-day wind conditions at the surface. Fossils aeolian bed forms are usually fractured, cemented and useful to constrain paleo wind conditions. Here we describe active dark dunes and fossil megaripples from an area in Arabia Terra and we discuss theirs climate implications. This area shows dark-toned domes and barchans dunes 1.5 – 10.5 m in height. Dunes slip faces, dipping SW, suggest NE dominant winds. Dunes were targeted in 2006 and 2016 (ΔT = 9.37 Earth years) by the HiRISE camera onboard of the NASA Mars Reconnaissance Orbiter (MRO). By tracking the position of the dunes in the 2006 and 2016 images, we measured an average SW displacement of 1.1 m (0.12 m yr-1). This translates to an average flux of 0.82 m3 m-1 yr-1 (median 0.78 m3 m-1 yr-1), which is almost three times the median dune flux in the MSL Curiosity landing site but ¼ of the flux measured in McLaughlin and Nili Fossae, areas where active megaripple migration were measured for the first time. Flux distribution (dune by dune) in the study area provides insights on the topographic effect, with the dunes located in depressed areas showing the lower fluxes. The dunes monitored over the 9.37 Earth years’ time-span migrated on the top of light toned layered deposit, which show a stair-stepped pattern of bright and dark layers showing different resistance to erosion. The different albedo and erosional pattern may represent different cementation/lithology, chemical composition and/or different grain sizes (bimodal). Eroded mounds 50 – 400 m-large, are the remnants of the widespread-layered unit in the studied area and are surrounded by a set of NW-SE trending linear ridges 10 – 20 m spaced. The morphology and regular spacing of the ridges suggest they are aeolian in origin. The ridges show a clear sinuous morphology that is typical of terrestrial megaripples. Megaripples are a particular type of ripples forming in bimodal sand which have coarse grains (> 1 mm) accumulating over the crest. In this scenario, the light-toned unit erosion could result in the production of bimodal sediment then re-organized in megaripples by the blowing winds and finally fossilized as suggested by the presence of fractures cutting through the megaripple crestlines. The capability of the winds to move coarse grains give hints on the transport capacity of the flows blowing in the past. The trend of the sinuous megaripples, matching the orientation of the dunes, suggests that the wind regime was consistent through time. The results reported here show how different aeolian features both active and fossils can be used to better constrain Martian climate and sedimentology.

How to cite: Silvestro, S., Salese, F., Vaz, D., Davis, J., yizhaq, H., Franzese, G., and Esposito, F.: Active and fossil aeolian bedforms in Arabia Terra (Mars): climate and sedimentological implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10561, https://doi.org/10.5194/egusphere-egu2020-10561, 2020.

Dunes and dune-fields, being indicators and recorders of environmental conditions, have attracted extensive attentions and are massively studied on the individual behaviors and dune-dune interactions. However, the processes of field-field interaction are still elusive. Here, using the latest bathymetric datasets, we presented the new-found dune fields developing under reversing tidal currents on a shallow shelf, northwest South China Sea. The dune fields separately had dunes with opposite inclination and were head-to head colliding with a coarse-coarse pattern and a coarse-fine pattern in term of the sediment character. The dune-field fronts defined by the transition of dune asymmetry were outlined, where convergent bed load transports coexisted with divergent suspended load transports. The dunes had apparent spatial variability in their scale and morphology across the dune fields. Dunes obtained steeper shapes towards the dune-field fronts due to the different responses of height and length when dune-fields met together, which were benefited from the bidirectional sand supply and the comparable reversing current speed. Dune scale also exhibited distinct variations towards the dune-field fronts, suggesting the past dominant southward migration of the north fields and the resistance of the south fields. From 2014 to 2016, dunes inside the dune fields mostly moved to their inclining direction while some dunes in the dune-field fronts migrated to oppositely. The dune-field fronts shifted oppositely in various regions because of the rebalance of sand transports, which are inferred to essentially result from the regional flow changes. The migrating rates of the fronts are also influenced by the magnitude of grain size, water depth, dune height, and current speed. The behaviors of dune-field fronts can possibly record the interactions between dune-field and local environmental changes. More studies are still required on the internal structures of dunes near dune-field fronts and the modelling of local effects of regional environment modification.

How to cite: Ma, X., Gan, Y., and Yan, J.: Head-to-head encountering dune-fields under reversing flows in the Beibu Gulf, South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6371, https://doi.org/10.5194/egusphere-egu2020-6371, 2020.

EGU2020-10439 | Displays | SSP3.5

Turbidity current signature on consecutive turbidity current: analysis through numerical simulations of multiple consecutive submarine flows

Maria Azpiroz-Zabala, Joep Storms, Joris T. Eggenhuissen, Helena van der Vegt, Bert Jagers, Dirk-Jan Walstra, Arnau Obradors-Latre, and Anna Pontén

Turbidity currents are powerful submarine density flows that travel towards the deep-sea carrying huge amounts of suspended sediment. The flow capacity of keeping sediment suspended in turbidity currents controls the flow duration, which can last from minutes to days. Sediment in turbidity currents is entrained when the flows are triggered, or when the flows erode the seafloor and suspend additional sediment in their downslope path. Eventually, suspended sediment settles to form deposits on the seafloor. Therefore, the composition of the seafloor after the passage of turbidity current depends on the initial composition of the seafloor and the erosion, reworking of the bed and deposition of the flow-entrained sediment. Can the comparison of seafloor before and after turbidity currents provide information about the initial flow and seafloor parameters? Can the seafloor composition after a turbidity current passage modify next flow behaviour and to what extent?

We set up numerical models of multiple consecutive turbidity currents in Delft3D4 to study the evolution of both the flows themselves as well as their interaction with the seafloor. Some simulated flows run into clear water while other simulated flows run into the tail of the previous turbidity current. We analyse the influence of the initial flow sediment grain size composition on the flow behaviour and on the bed sediment composition. We investigate the influence on the flow structure of the sediment kept in suspension between consecutive flows. We analyse the evolution of the stratigraphy in the deposit formed by multiple consecutive turbidity currents. The aim of this work is enhancing the knowledge on the evolution of both flows and seafloor. The combination of the findings of these numerical models with field and experimental measurements and interpretations add to the prediction of the characteristics of turbidity currents and the distribution of the flow sediment.

How to cite: Azpiroz-Zabala, M., Storms, J., Eggenhuissen, J. T., van der Vegt, H., Jagers, B., Walstra, D.-J., Obradors-Latre, A., and Pontén, A.: Turbidity current signature on consecutive turbidity current: analysis through numerical simulations of multiple consecutive submarine flows, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10439, https://doi.org/10.5194/egusphere-egu2020-10439, 2020.

EGU2020-8948 | Displays | SSP3.5

The influence of gravel mixed with sand on the formation and development of ripples.

Katrien Van Landeghem, Irinios Yiannoukos, Connor McCarron, Jacob Morgan, and Barney Clayton-Smith

Coarse and bimodal sediment mixtures like sand and gravel are common in palaeo-glaciated shelf seas and in coastal environments. Their presence leads to more complex sediment transport and morphodynamic processes, depending on the ratio of sand to gravel in the bed. With increased pressure on our near-and offshore sea beds, there is a growing need to more accurately model sediment transport and bedform dynamics with an increasing focus on bimodal sand-gravel sediment mixtures. Revisiting the quantification of the hiding-exposure (HE) effect highlighted how differently sized grains in a bimodal mixture modify each other’s threshold of motion. The critical shear stress needed to mobilise the sand and gravel fractions increased by up to 75% and decreased by up to 64% respectively, compared to that needed to mobilise well-sorted sediment of similar size. Implementation of this newly quantified HE correction in current-and wave-driven models illustrated that its influence on bedload transport rates and bed morphodynamics was greatest for mixtures where gravel percentage ranges between 10 and 20 %. Laboratory experiments were therefore conducted to investigate ripple formation and bed dynamics in mixtures with gravel percentage between 0 and 25%. The development of initial bedforms was quicker in sand-gravel mixtures compared to those developed in pure sand, whilst final heights and migration rates of the developed ripples decreased with increasing fraction of gravel in the bed. During this presentation, a full comparison will be made of the morphology and “down-core” sedimentary properties of ripples formed at different flow speeds. If we want to use our seabeds cost-effectively and sustainably, we need a better understanding on the influence of a decreased mobilisation of the finer fractions and an increased mobilisation of the coarser fraction on the dynamics of beds with a bimodal sediment composition.

How to cite: Van Landeghem, K., Yiannoukos, I., McCarron, C., Morgan, J., and Clayton-Smith, B.: The influence of gravel mixed with sand on the formation and development of ripples., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8948, https://doi.org/10.5194/egusphere-egu2020-8948, 2020.

Braided rivers are highly dynamical systems characterized by varying network-like structures even under quasi-steady conditions. Understanding their dynamics is crucial in geomorphology and river engineering (e.g., river restoration in Alpine and piedmond streams). Open questions about these dynamics include the definition and quantitative description of bed equilibrium. Here we propose to tackle this problem using a new method based on graph theory. This algorithm, called low-path allows one to extract the network structure of a braided river from its Digital Elevation Model (DEM). It is then possible to quantify and analyse the dynamics of the braided system, and not just the bed evolution, as has been done in earlier studies. To assess the dynamics and equilibrium of a braided river, we study two runs representing two distinct phases of the same braided river: the transition from a single channel to a braided river (run 1) and the equilibrium state of this river (run 2). A set of control parameters was used to characterise both runs and supplement the low-path method. We find that although a clear distinction can be made between straight channel and braided channel for both methods, it is more difficult to distinguish between transitional braided and equilibrium braided rivers. Finally we propose a set of dimensionless numbers that specify the braided network and can be used with numerical or stochastic simulations of a braided network. To illustrate their utility, we apply the Low Path method to a real Alpine braided river (the River Navisence, Wallis, Switzerland) and compare the results to our experimental data.

How to cite: Papa, D. and Ancey, C.: Braided rivers networks dynamics: analyzing topographic data from a large flume experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17914, https://doi.org/10.5194/egusphere-egu2020-17914, 2020.

EGU2020-7802 | Displays | SSP3.5

Initiation and flow conditions of contemporary flows in Martian gullies

Tjalling de Haas, Brian McArdell, Susan Conway, Jim McElwaine, Maarten Kleinhans, Francesco Salese, and Peter Grindrod

Understanding the initial and flow conditions of contemporary flows in Martian gullies, generally believed to be triggered and fluidized by CO2 sublimation, is crucial for deciphering climate conditions needed to trigger and sustain them. We employ the RAMMS (RApid Mass Movement Simulation) debris flow and avalanche model to back-calculate initial and flow conditions of recent flows in three gullies in Hale crater. We infer minimum release depths of 1.0–1.5 m and initial release volumes of 100–200 m3. Entrainment leads to final flow volumes that are 2.5–5.5 times larger than initially released, and entrainment is found necessary to match the observed flow deposits. Simulated mean cross-channel flow velocities decrease from 3–4 m s-1 to ~1 m s-1 from release area to flow terminus, while flow depths generally decrease from 0.5–1 m to 0.1–0.2 m. The mean cross-channel erosion depth and deposition thicknesses are _0.1–0.3 m. Back-calculated dry-Coulomb friction ranges from 0.1 to 0.25 and viscous turbulent friction between 100–200 m s-2, which are values similar to those of granular debris flows on Earth. These results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on Earth. Using a novel model for mass-flow fluidization by CO2 sublimation we are able to show that under Martian atmospheric conditions very small volumetric fractions of CO2 of ~1% within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility.

How to cite: de Haas, T., McArdell, B., Conway, S., McElwaine, J., Kleinhans, M., Salese, F., and Grindrod, P.: Initiation and flow conditions of contemporary flows in Martian gullies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7802, https://doi.org/10.5194/egusphere-egu2020-7802, 2020.

EGU2020-7920 | Displays | SSP3.5

The effects of bedform-related roughness on hydrodynamics and sediment transport patterns in Delft3D

Laura Brakenhoff, Reinier Schrijvershof, Bart Grasmeijer, Jebbe van der Werf, Gerben Ruessink, and Maarten van der Vegt

To contribute to solving scientific and practice-inspired questions, the morphological development of coastal systems is predicted using numerical morphodynamic models like Delft3D. In such models, many of the processes are parameterized, for which various assumptions have to be made. One of the estimated variables is the bedform-related hydraulic roughness, which affects the magnitude and vertical structure of the flow and consequently also the magnitude of the sediment transport. A comparison is missing between model-predicted and observed hydraulic roughness values and it is unknown how this affects the hydrodynamics and sediment transport. Furthermore, the roughness is often used as a calibration parameter. The calibrated value might be very different from observed values and models might possibly do a good job for the wrong reasons.

The aim of this study is to determine the effect of the roughness caused by small-scale ripples (length ≈ 10 cm, height ≈ 1.5 cm) on hydrodynamics and sediment transport computed by a high-resolution, fully-coupled Delft3D model that is forced by waves, tides, wind, and atmospheric pressure. The study site is the wave-current dominated environment of the Ameland ebb-tidal delta in the north of the Netherlands. In 2017, a six-week field campaign was executed here, in which bedform heights and lengths, water levels, wave orbital velocity and direction, and current velocity and direction were measured.

The model was run for the duration of the field campaign with various bedform roughness scenarios, in which the roughness was either coupled to the hydrodynamics (thus varying over space and time), or it was set to a constant and spatially uniform value based on the observed mean ripple heights. Of all scenarios, we compared the predicted ripple heights, wave orbital velocities, depth-averaged current velocities and sediment transport magnitudes and directions. In addition, we compared the modelled and observed ripple heights, wave heights and flow velocities.

A previous study focused on the field campaign showed that observed ripple heights were much more constant than the ones computed by the default ripple predictor in Delft3D. Ripple heights were found to be related to orbital velocity and no other relations between ripple characteristics and hydrodynamics were found. However, first results of the present study indicate that the predicted roughness used to calibrate Delft3D to the water levels and currents is quite similar to the measured roughness. The main difference is that the predicted roughness is highly variable through time, which is not observed in the field. The simulations also show that the ripple-related roughness especially affects the magnitude of the depth-averaged current velocity, while its effect on the wave-orbital velocity is negligible. This also affects the sediment transport magnitude, while its direction is not affected. The cumulative suspended load transport magnitude can increase with more than 50% when a constant roughness is used instead of a spatio-temporally variable roughness.

How to cite: Brakenhoff, L., Schrijvershof, R., Grasmeijer, B., van der Werf, J., Ruessink, G., and van der Vegt, M.: The effects of bedform-related roughness on hydrodynamics and sediment transport patterns in Delft3D, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7920, https://doi.org/10.5194/egusphere-egu2020-7920, 2020.

EGU2020-19118 | Displays | SSP3.5

Aggradational Channels on Mars

Joshua Ahmed, Jeffrey Peakall, Anne W. Baar, Na Yan, Daniel R. Parsons, and Matthew R. Balme

Sedimentary deposits and geomorphic landforms preserved on the surface of Mars afford scientists a possible insight into the formative conditions of these features and of the planetary climate in the deep past. We use a high-resolution digital elevation model (~1 m/pixel) created from imagery captured using the High Resolution Imaging Science Experiment (HiRISE) camera on board the Mars Reconnaissance Orbiter to examine the characteristics of 17 meanders from a channel in the Aeolis Dorsa region of Mars. We extracted the topographic signatures from 17 meanders that reveal a characteristic vertically stacked sequence of preserved point bars. These bars increase in elevation by up to 10 m and exhibit incline angles of between one and eight degrees. Each of the meanders is observed to grow vertically while contemporaneously undergoing lateral migration, creating sedimentary architecture not characteristic of fluvial meandering rivers. These landforms are commonly described as inverted channels; however, the preserved architecture differs from other so-called inverted channel topography on Mars, which fail to display such prevalent preserved bar topography. On Earth, vertically stacked deposits are observed in aggradational environments such as in tidally-affected backwater river sections, coastal wetlands, submarine settings, and sediment-rich fluvial systems. Given the pronounced vertical aggradation, and observed in-channel topography, we propose that this channel was fed with an exceptional sediment load – potentially comprised of a high concentration of fine-grained sediment – confined within strong cohesive banks that limited lateral migration and promoted vertical bedform growth. The channel may have also experienced base level controls from a downstream water body. These findings suggest that liquid water must have been persistent over a considerable timescale in Mars’ history.

How to cite: Ahmed, J., Peakall, J., Baar, A. W., Yan, N., Parsons, D. R., and Balme, M. R.: Aggradational Channels on Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19118, https://doi.org/10.5194/egusphere-egu2020-19118, 2020.

EGU2020-1554 | Displays | SSP3.5

The main types of river channel bedforms movement

Olga Borisova and Alexei Sidorchuk

There are two main types of movement of bedforms in the river channel. Active bedforms are three-dimensional, symmetrical, with gentle slopes. They move without significant change in shape, since all parts of their surface move at the same celerity. Passive bedforms are two-dimensional, asymmetric, with steep leeward slope. Bedform top moves faster than hollow and bedform deform, skew.

Bedforms are usually organised into hierarchical complexes in the river channels, where smaller bedforms move along the surface of larger ones. With active movement, the morphology and dynamics of bedforms of different orders in the hierarchy are relatively independent. The relationships between bedforms of different orders is increasing in the case of passive movement.

Bed load transport in the river channel depends on the type of bedforms movement. In the case of active bedforms, bedload transport rate, computed with their morphology and celerity, is different for different bedform orders. The total bedload transport rate is equal then to the sum of bedload transportation by bedforms of different orders, plus sediments transit. In the case of passive movement, the total bedload transport rate is equal to bedload transportation by bedforms with steep leeward slopes and complete deposition there of all incoming sediments. Then it is possible to use Exner’s equation of deformation for estimating of bedload transport rate.

This study was carried out under the project: “Evolution and Transformation of Erosion-Channel Systems under Changing Environment and Human Impact”

How to cite: Borisova, O. and Sidorchuk, A.: The main types of river channel bedforms movement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1554, https://doi.org/10.5194/egusphere-egu2020-1554, 2020.

Intertidal dune morphodynamics is closely tied to bedload transport that is variable in time and space due to the interplay between tide, wave and runoff discharge. Surprisingly the control of intertidal channel morphology on the dune morphodynamics and related bedload transport is scarcely documented. Actively migrating dunes are widely developed in the lower intertidal zone of Yeochari tidal flat in the northern Gyeonggi Bay, west coast of Korea. High-resolution aerial images, high-precision transect profiles, and hydrodynamic dataset were repeatedly obtained and analyzed to quantify the intertidal dune morphodynamics and associated bedload transport, and to address the role of channel morphodynamics. During the research period, the intertidal channel became more sinuous and an ebb barb arose concurrently at the upstream of the channel point bar. The ebb barb exerted a key role in the downstream delivery of fine-grained sediments onto the areas covered by dunes and the intertidal channel by reinforcing ebb currents with a pronounced time-velocity asymmetry. The presence of the ebb barb resulted in a rapid decrease of the width/depth ratio of the channel that had migrated laterally 130 m in six years. After the ebb-barb development, the heights and steepness (height/wavelength) of dunes on the point bar and near the ebb barb decreased notably. Simultaneously dune migration rate had increased from 0.5 m/day to 2.5 m/day, which decreases away from the channel. Bedload transport estimated by using Meyer-Peter and Muller (MPM) equation and Dune-Tracking Method (DTM) also decreases away from the channel. Bedload transport calculated by DTM (qbDTM, 0.03-0.38 m2/day) is much smaller than that estimated by MPM (qbMPM, 0.10-4.17 m2/day) by a factor of 1.5 to 62. The discrepancy ratio between the two bedload estimates (qbMPM/qbDTM) increases toward the channel and the ebb barb. Downslope flow toward the channel during the late stage of ebb tide may account for the underestimation of qbDTM by facilitating downslope sediment transport that reduced the dune steepness with the infilling of dune trough. The present study showcased a dynamic response of the dune morphodynamics and associated bedload transport in the open-coast tidal flats to the changes in the channel morphodynamics that is controlled by seasonal runoff discharge as well as tidal currents.

How to cite: Jo, J., Kim, D., and Choi, K.: Controls of channel morphodynamics on the intertidal dune morphodynamics and associated bedload transport in the open-coast macrotidal flats, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16500, https://doi.org/10.5194/egusphere-egu2020-16500, 2020.

EGU2020-2600 | Displays | SSP3.5

Validation of process-based sand wave models: applying a linear and nonlinear sand wave model to the Netherlands Continental Shelf

Geert Campmans, Pieter Roos, Thaiënne Van Dijk, and Suzanne Hulscher

Tidal sand waves are dynamic large-scale bed forms occurring in tide-dominated, sandy shelf seas such as the North Sea. Since they may interfere with various activities, understanding sand wave dynamics is important from a practical point of view. Recently, two process-based model studies were carried out to investigate the influence of storm processes on sand wave dynamics (Campmans et al., CSR2017; JGR2018). While this type of model gives insight in the morphodynamic mechanisms, quantitative comparison with field observations remains a challenge.

 

Here we present a systematic validation of the afore mentioned linear and nonlinear models, against a wide range of sand wave observations from the entire Netherlands Continental Shelf (Damen et al., JGR2018). Specifically, from the available locations with sand wave observations and environmental characteristics, we have chosen a grid for calibration and, staggered to that, a grid for validation. For the so-called calibration locations, we tuned the linear model (using local environmental conditions) in order to minimize the difference between observed and modelled wavelengths. Next, on the validation locations, we used the thus obtained parameter settings (location-independent values of slip parameter and effective wave period) to test our model performance, both in the linear and nonlinear regime. First results demonstrate fair agreement for the wavelengths from the linear model and indicate a systematic overestimation of sand wave heights by the nonlinear model.

 

References

Campmans, G.H.P., Roos, P.C., De Vriend, H.J., Hulscher, S.J.M.H., 2017.  Modeling the influence of storms on sand wave formation: A linear stability approach. Continental Shelf Research 137, 103–116.

Campmans, G.H.P., Roos, P.C., De Vriend, H.J., Hulscher, S.J.M.H., 2018. The influence of storms on sand wave evolution: a nonlinear idealized modeling approach. Journal of Geophysical Research: Earth Surface 123, 2070-2086.

Damen, J.M., Van Dijk, T.A.G.P., Hulscher, S.J.M.H., 2018. Spatially varying environmental properties controlling observed sand wave morphology. Journal of Geophysical Research: Earth Surface 123, 262-280.

How to cite: Campmans, G., Roos, P., Van Dijk, T., and Hulscher, S.: Validation of process-based sand wave models: applying a linear and nonlinear sand wave model to the Netherlands Continental Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2600, https://doi.org/10.5194/egusphere-egu2020-2600, 2020.

EGU2020-5281 | Displays | SSP3.5

Modeling the influence of the gravitational circulation on estuarine sand dunes

Wessel M. van der Sande, Pieter C. Roos, and Suzanne J.M.H. Hulscher

Estuaries are hydrodynamically complex regions where a river meets saline water. In many estuaries, sand dunes can be found; these are large-scale rhythmic bedforms. Observational studies have revealed several estuarine processes that affect sand dune dimensions and dynamics. These are for instance sand-mud interactions and tidal amplification. Here, we build upon an observational study in the Gironde Estuary, France, which indicated that the gravitational circulation – present in many estuaries due to the interaction between (heavy) seawater and (light) freshwater – is significant enough to affect sand dunes (Berne et al., 1993). Our aim is to understand the effect of this circulation on bedform dimensions and dynamics, and to explain the underlying mechanisms.

To this end, we develop an idealized process-based model which contains descriptions for the motion of water and non-cohesive sediment transport within a local section of a generic estuary. On this geometry, we impose a steady river discharge, superimposed on an oscillatory tidal flow. Furthermore, we include the effect of salinity-induced density differences by following the model as presented by MacCready (2004). In here, we adopt a diagnostic approach, meaning that the along-estuarine salinity gradient is imposed on the domain instead of being an unknown which interacts with the flow. The alternative, a so-called prognostic approach, is also explored.

This model is analyzed using a so-called linear stability analysis, as applied earlier to e.g. marine sand waves (Hulscher, 1996) but not yet to estuarine dunes. Within this analysis, the reference state with a flat bed is slightly perturbed, and the model shows whether these perturbations decay (the flat bed is stable) or grow (it is unstable). The model results provide a generic insight into the role of the gravitational circulation on bedform dimensions and dynamics, particularly growth and migration; the latter possibly directed opposite to the river discharge. To test our model, it is then applied to the specific settings of the Gironde. Furthermore, a systematic sensitivity analysis shows the effect of environmental parameters on bedform development when subject to the gravitational circulation. Including this estuarine-specific process is a novel and first step in obtaining a solid understanding of the behavior of estuarine sand dunes.

 

References

Berne, S., Castaing, P., le Drezen, E., & Lericolais, G. (1993). Morphology, Internal Structure, and Reversal of Asymmetry of Large Subtidal Dunes in the Entrance to Gironde Estuary (France). Journal of Sedimentary Petrology, 63(5), 780–793. https://doi.org/10.1306/d4267c03-2b26-11d7-8648000102c1865d

Hulscher, S. J. M. H. (1996). Tidal-induced large-scale regular bed form patterns in a three-dimensional shallow water model. Journal of Geophysical Research, 101(C9), 727–744. https://doi.org/10.1029/96JC01662

MacCready, P. (2004). Toward a unified theory of tidally-averaged estuarine salinity structure. Estuaries, 27(4), 561–570. https://doi.org/10.1007/BF02907644

 

How to cite: van der Sande, W. M., Roos, P. C., and Hulscher, S. J. M. H.: Modeling the influence of the gravitational circulation on estuarine sand dunes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5281, https://doi.org/10.5194/egusphere-egu2020-5281, 2020.

EGU2020-9261 | Displays | SSP3.5

New insights into the internal structure of Turbidite deposits from physical modelling of relevant erosional and depositional processes

Jonathan Wilkin, Alan Cuthbertson, Sue Dawson, Dorrik Stow, Karl Stephen, Uisdean Nicholson, and Nadia Penna

Results are presented from the current experimental campaign which aims to observe the character of supercritical turbidity currents and other supercritical sediment gravity flows (SGFs) as they respond to morphological transition zones, e.g. slope breaks and losses of lateral confinement. This experimental setup aims to reproduce lower slope, channel-lobe transition zone, and, proximal lobe conditions, in order to be analogous to conditions found within deep-marine sedimentary environments such as those found within foreland basins, and on passive margins. Of particular interest is the sedimentological expression of these systems, how sedimentological variability arises in the form of sediment waves and scour fields, and how does an understanding of current dynamics help in the prediction of the internal structures of these features. Thus, this study will yield new data on how turbidity currents impact multi-layered sedimentary beds and determine parametric controls on erosion, deposition and bed restructuring processes. Turbidity currents are scaled via dimensionless parameters representing prevalent flow (e.g. Reynolds, Densimetric Froude Number, and Shields Numbers) and sedimentary (e.g. Rouse and Reynolds Particle Numbers) conditions, following the scaling techniques of de Leeuw et al., (2016) which have now been tested in numerous experimental studies e.g. Pohl et al., 2019.

 

Investigating how varying experimental conditions such as current parameters, severity of breaks in-slope, and, losses of lateral confinement impact the resulting depositional signature of lower slope, and channel-lobe transition zones. Of particular interest is the impact of previously developed bedforms upon current dynamics which will be studied via UVP and ADV measurements, as well as through the application of digital elevation models (DEM), which will be used to understand how systems evolve over multiple runs. DEM models will be generated using a photogrammetry technique capable of producing a high-resolution model (±2mm). The results of which will then be linked to synchronous sedimentological packages – both on the modern seafloor and preserved within ancient geological outcrops – with the aim of enhancing the predictive sedimentological concepts applied to these systems when being interpreted within the subsurface.

 

A seafloor study will focus upon supercritical bedforms generated by SGFs upon a deep-water slope and terrace located offshore of Senegal, West Africa. Combining seafloor seismic images, high-resolution sparker data, and drop cores taken from deep water channels, and overbanks. Through the interpretation of this dataset, it will be possible to understand the sedimentological variability of bedforms present on this slope system and allude to the flow conditions that led to their formation.

 

References

de Leeuw, J., Eggenhuisen, J.T., Cartigny, M.J.B., 2016. Morphodynamics of submarine channel inception revealed by new experimental approach. Nat. Commun. 7. https://doi.org/10.1038/ncomms10886

Pohl, F., Eggenhuisen, J.T., Cartigny, M.J.B., Tilston, M., de Leeuw, J. & Hermidas, N. (in review). The influence of a slope break on turbidite deposits: an experimental investigation. Marine Geology.

How to cite: Wilkin, J., Cuthbertson, A., Dawson, S., Stow, D., Stephen, K., Nicholson, U., and Penna, N.: New insights into the internal structure of Turbidite deposits from physical modelling of relevant erosional and depositional processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9261, https://doi.org/10.5194/egusphere-egu2020-9261, 2020.

EGU2020-20538 | Displays | SSP3.5

The internal sedimentary architecture of Terrestrial sinuous ridges: clues to understanding sinuous ridges on Mars

Kartikeya S. Sangwan, Sanjeev Gupta, Robert Barnes, and Steven G. Banham

Noachian-Hesperian terrains on Mars host multiple geomorphic and stratigraphic signatures of ancient water flow on early Mars. Sinuous, branching systems of ridges are one such geomorphic landform and have been interpreted as topographically-inverted ancient river channel systems. Characterising the internal sedimentary architecture of such systems is important to constraining the evolution and duration of ancient fluvial flows on early Mars. For example, such ridges are present at the Western delta at Jezero crater, the landing site for the NASA Mars 2020 rover mission. Some studies have used these ridges as time-frozen snapshots of ancient channels and focused on the distribution and geometries of these ridges. However, recent works have characterised these ridges as exhumed channel-belt deposits, composed of multiple channel deposits based on comparisons with similar deposits on Earth. Detailed sedimentary architectural analysis of Terrestrial ridges is needed to provide models for interpreting the earliest fluvial flows on Mars.

Here we present a fine-scale sedimentological analysis of sinuous ridges from the Caspe Formation, Ebro Basin, Spain as potential Terrestrial analogues for sinuous ridge networks on Mars. The Caspe Formation comprises of Oligo-Miocene fluvial deposits of the Guadalope-Matarranya fan system deposited within the endorheic Ebro Basin. The sandstone ridges of the formation are dissected by a number of roads and recent road cuts present a unique opportunity to analyse the fluvial stratigraphy in cross-section. We used traditional field methods and photo-panel interpretations to identify the internal architecture of the ridges and the analysis was complemented with observations from sections parallel to the ridge axes and Unmanned Aerial Vehicles.

Our results provide identification of complete suite of elements preserved within an exhumed channel belt deposits such as channel scour surfaces, channel deposits in the form of lateral and downstream accreting bedforms and barforms, coarser gravel lags and finer-grained deposits from overbank and splay deposits. The ridges preserve a complex continuum of these elements suggesting deposition in an amalgamated channel-fill complex. We also record multi-storey depositional structures with stacked channel elements suggesting an aggrading fluvial system that experienced frequent local avulsion and reoccupation of previous channel positions. The internal architecture of these ridges suggests that Martian sinuous ridges are likely to comprise multiple stacked channel units. If correct this would indicate long lived fluvial activity on early Mars as opposed to short episodes of water flow.

How to cite: Sangwan, K. S., Gupta, S., Barnes, R., and Banham, S. G.: The internal sedimentary architecture of Terrestrial sinuous ridges: clues to understanding sinuous ridges on Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20538, https://doi.org/10.5194/egusphere-egu2020-20538, 2020.

The Loshui Sandstone, a Miocene turbidite succession accumulated in the northern slope of the rifted continental margin of the South China Sea, is exposed in the Hengchun Peninsula, Taiwan. We conduct lithofacies analysis to understand the depositional processes and mechanisms of the gigantic-thick turbidite succession.

Several features can be recognized from outcrops: (1) the Loshui Sandstone is of around 1,000 m thick with turbidite units stacked vertically; (2) high net-to-gross ratio (> 0.9) with dominant fine-to-medium grained sandstones, amalgamated beds are commonly found in the very thickly-bedded turbidites; (3) thick individual turbidite beds with a nominal thickness of 70 cm, which is thicker than classical Bouma sequence; and (4) limited deep scouring surfaces and thick mud are found. Two end-member lithofacies of high-density turbidites and low-density turbidites, respectively, are identified. High-density turbidites are thicker (more than 1 m thick) and coarser in grain size (mostly medium sands) with abundant massive intervals, dewatering structures and/or climbing ripples. Low-density turbidites tend to be thinner in thickness and finer in grain size (mostly fine sands) with parallel bedding and/or normal ripples. In addition to the above two lithofacies, chaotic deposits of mass transport deposits (MTDs) are also widespread within the studied succession.

Sand-rich, vertically aggrading succession, but lack of deep-scouring surfaces and levee deposits, indicates that turbidites are laid down by unconfined turbidity currents in a sand-rich deepwater lobe. In addition, gigantic thick turbidite unit stacked continuously up to 1,000 m, implying that the lobe is confined within a rapidly subsiding basin. We interpreted that the Loshui Sandstone is vertically stacked and accumulated within a fault-bounded trough in the deepwater area of the rifted continental margin of the South China Sea.

 

How to cite: Li, J. and Lin, A. T.-S.: Gigantic-thick turbidite succession in a Miocene fault-bounded trough of the South China Sea rifted continental margin: Examples from Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9753, https://doi.org/10.5194/egusphere-egu2020-9753, 2020.

EGU2020-6423 | Displays | SSP3.5

A new hypothesis that contributes to the formation of cold sludge volcanoes and fluid outlets in tectonic seabed & terrestrial regions; with its helpful interpretation for time fracture sequence of fault segments.

Dursun Acar, M. Sinan Ozeren, Nazmi Postacioglu, Sebnem Onder, Ulku Ulusoy, K. Kadir Eris, Serdar Akyuz, Namık Cagatay, and Bedri Alpar

During the co-seismic development of a fault in lithological environments, regions containing cavities may form momentarily or permanently. In the tectonic shift zones, these pressure gaps lead to the formation of irregular new intermediate sediment zones, as infiltrate in to the gap, if the pressure perturbations are large. The semi-fluid sediment material and sea water enter through opening fault sector's surrounding sediments at the far place from dispersing fault energy burst. But pore water infiltration is independent about place of vomited energy burst. In some cases hard material which detached from fault wall or top sediment material, provide isolation lids, as obstacling on 'cell type empty interlaying gaps' at tectonic line. They can collapse again or stay as gap form for a long time with suction force after seismic activities by effects of gravitation or pressure perturbations. For durable gaps, pore water is capable to infiltrate in to the gap with long lasting suction forces.  In these regions, in contrast to gravitational folding or collapse structures, the partial sediment sequence may be drawn and folded into the area of the material with different or close lithological density value. Deformational variety of the displaced materials are related with physical properties of seismic event at opening sector such as friction, displacement parameters (velocity, time), dimensional parameters of gap, and water depth.  The main objective of the paper is to figure out all interference mechanisms about these zones (created by pressure perturbations), which develop rapidly during earthquake fractures (or in some cases fractures generated by impulsive pressure changes such as those created by volcanoes). Fracture of fault segments forms a complex mechanical system associated with bedrock, upper sedimentary sequence, and aquatic environment, depending on the location where they occur, even the atmosphere. Therefore, the displacement may be bi-directional to the lower slit or upward from the seabed during the opening or closing stages of the cavity, depending on the nature with variations of the atmosphere & water-sediment mixture. The strong (pulling or impulsive) pressure perturbation effect associated with permanent cavities caused by rapid breakage pulls the material that may form a sludge volcano or water outlet under deformation and brings the environment to near pressure equilibrium. This simple explanation can help to find real additional effective reason for the different formations of assumed collapse or folding structures created by gravitational movements in geology. The hypothesis after main objective at above mentioned in this article is based on the fact that the emergence of  escapes as squeezed fluid form  of water & sediment from compacted secondary irregularities in the previously broken fault segment will help to understand the next seismic mobility in other tectonic segments by identifying source depth cues through physical and chemical analysis. Geophysical instrumentation and applications are still need further developments of compact reflection line information, because the vertical thin anomalies mentioned in this paper are the most difficult structures for detection.

How to cite: Acar, D., Ozeren, M. S., Postacioglu, N., Onder, S., Ulusoy, U., Eris, K. K., Akyuz, S., Cagatay, N., and Alpar, B.: A new hypothesis that contributes to the formation of cold sludge volcanoes and fluid outlets in tectonic seabed & terrestrial regions; with its helpful interpretation for time fracture sequence of fault segments., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6423, https://doi.org/10.5194/egusphere-egu2020-6423, 2020.

EGU2020-4577 | Displays | SSP3.5

“In situ” characterization of the sedimentary record and structures using Virtual Reality: new insights from the Kimberley outcrop (Gale Crater, Mars)

Gwénaël Caravaca, Nicolas Mangold, Stéphane Le Mouélic, Laetitia Le Deit, and Marion Massé

Since 2012, the Mars Science Laboratory Curiosity rover has studied the sedimentary deposits within the Gale Crater, leading to the description of varying lacustrine to fluviatile and fluvio-deltaic environments. Here, we focus on the sedimentary record of the Kimberley outcrop traversed by Curiosity between sols 603 and 630. This section presents siliciclastic rocks with an unusually high potassic content (Le Deit et al., 2016, JGR-Planets). However, poorly constrained architecture and stratigraphic relations between the series of the Kimberley Formation and their local to regional surroundings still prevent further understanding of the exact extent of these accumulations and their significance within the broader Gale Crater paleoenvironmental scheme.
Such questions highlight the need for a new finer mapping of the area to characterize the contacts observed on the outcrop itself and in its immediate vicinity, but also for a new assessment of the precise nature and morphology of the sedimentary structures and their spatio-temporal distribution throughout the outcrop and beyond.
We therefore propose to use a true color highly resolved Digital Outcrop Model (DOM) of the Kimberley outcrop, obtained using Mars Science Laboratory imagery, integrated into a Virtual Reality (VR) environment (Caravaca et al., in press, PSS). Taking advantage of this “in situ” geological analysis of the DOM, we were able to observe and characterize such sedimentary structures and contacts, as well as their spatial extension throughout the reconstructed area of Kimberley with an unprecedented precision. We notably observe and describe both conformable and unconformable contacts over the entire outcrop, but also several sets of varying scale cross-stratifications (from cm- to pluri-meter scale). These results are in accordance with a fluviatile hydrodynamically active system. They tend to corroborate the idea of a complex yet diachroneous evolution of the area, with the possibility of laterally evolving depositional settings, spanning a significant amount of time.

How to cite: Caravaca, G., Mangold, N., Le Mouélic, S., Le Deit, L., and Massé, M.: “In situ” characterization of the sedimentary record and structures using Virtual Reality: new insights from the Kimberley outcrop (Gale Crater, Mars), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4577, https://doi.org/10.5194/egusphere-egu2020-4577, 2020.

EGU2020-13679 | Displays | SSP3.5

Sediment sorting in tidal sand waves fields: the internal structure revealed?

Johan Damveld, Bas Borsje, Pieter Roos, and Suzanne Hulscher

Tidal sand waves are rhythmic bed forms found on coastal shelves all around the world. An important property of sand waves is their mobility, as they display migration rates of several meters per year. Insight in these dynamics is of practical relevance, as this behaviour may interfere with offshore engineering activities. State-of-the-art morphodynamic models are used to predict sand wave dynamics, but they still overestimate dimensions such as their height (Van Gerwen et al, 2018). Moreover, these models often assume a uniform grain size distribution, whereas field observations indicate a clear sorting of sediments along sand waves. Previous modelling studies found that a combination of sediment mobility effects and tidal current strength may explain these sorting patterns (e.g. van Oyen and Blondeaux, 2009). However, as these models were limited to the early stage of sand wave formation, they did not account for the nonlinear effects of increasing sand wave amplitudes. Our goal is to include these nonlinear effects in order to further unravel sorting processes, in particular the internal sand wave structure.

Hereto we extend the work by van Gerwen et al (2018), allowing for an arbitrary number of sediment fractions, and we adopt the active layer approach of Hirano (1971) to account for bed stratigraphy. To investigate the role of asymmetry in hydrodynamic forcing, we include a residual current superimposed on the dominant tidal component.

Results show that in general the crests of sand waves are coarser than the troughs. In the case of an asymmetrical forcing, larger sediments are found on the upper lee slope, whereas the smaller grains are deposited on the lower lee slope. Due to migration, also the internal structure of the sand wave is revealed over time, showing the same pattern as found on the lee slope surface. Many field studies have shown that these model results qualitatively agree with observations on surficial sorting patterns (e.g. Cheng et al, 2018). However, as field data on the internal sediment structure is scarce, it is difficult to validate this model output.

Hence, the question remains whether the results on the internal sorting are a true representation of the substrate of sand waves. Nonetheless, the model results give insight in the processes governing grain size sorting over and in sand waves, which could be a valuable element in developing future coastal management strategies, such as sand extraction.

Cheng, C.H., Soetaert, K., & Borsje, B.W. (2018). Small-scale variations in sediment characteristics over the different morphological units of tidal sand waves offshore of Texel. NCK Days 2018.
Hirano, M. (1971). River bed degradation with armouring. Trans. Jpn. Soc. Civ. Eng, 3, 194-195.
Van Gerwen, W., Borsje, B.W., Damveld, J.H., & Hulscher, S.J.M.H. (2018). Modelling the effect of suspended load transport and tidal asymmetry on the equilibrium tidal sand wave height. Coastal Engineering, 136, 56-64.
Van Oyen, T., & Blondeaux, P. (2009). Tidal sand wave formation: Influence of graded suspended sediment transport. Journal of Geophysical Research: Oceans, 114(C7).

How to cite: Damveld, J., Borsje, B., Roos, P., and Hulscher, S.: Sediment sorting in tidal sand waves fields: the internal structure revealed?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13679, https://doi.org/10.5194/egusphere-egu2020-13679, 2020.

EGU2020-13499 | Displays | SSP3.5

Tidal bedforms dynamics, Weser River, Germany

Alice Lefebvre, Gerald Herrling, Anna Zorndt, Knut Krämer, Marius Becker, and Christian Winter

The distribution, morphology and dynamics of tidal bedforms in the Weser estuary, Germany, between the tidal limit (river-km 0 at the tidal weir in Bremen) and the open North Sea (river-km 111 in the Outer Weser) has been analysed for a five-year period based on monthly bathymetric surveys carried out along the main waterway. For the years 2009 to 2014, bedforms were detected from gridded bathymetry data (2x2 m) and their geometric properties described. In particular, the presence and position of a slip face, here defined as the portion of the lee side steeper than 15°, was traced. This was shown to be a practical criterion for the presence of permanent flow separation and turbulent wake in the lee of bedforms. Here it is used as a simplified indicator of bedform roughness: if a bedform does feature a slip face, it is assumed to be an active roughness element. The results were related to river discharge, water levels, and flow velocities.

Bedforms were present along most of the river channel, apart from a large section between river-km 55 and 75. There, muddy cohesive sediment in the estuarine turbidity maximum zone hindered the formation of bedforms. Along the channel and throughout the years, bedform lengths varied between 20 and 60 m and heights between 0.3 and 1.6 m.

During times of high fluvial discharge, in winter and spring, ebb velocities were stronger than flood velocities. The bedforms then were small, long and ebb-oriented (i.e. the ebb lee side was shorter than the flood lee side) and many bedforms featured an ebb slip face but no flood slip face. This suggests that throughout the survey area, bedforms were active roughness elements during the ebb phase only.

In summer and autumn, when the discharge was low, bedforms in the upper reach (ca. river-km 15 to 30) gradually became flood-oriented and many bedforms there developed a flood slip face, implying that these bedforms were active roughness elements during the flood. Between km 30 and 55, bedforms were predominantly ebb-oriented, and many bedforms had an ebb slip face but only few had a flood slip face, so most bedforms were only active during the ebb phase.

The annual variations of bedform dimensions and shapes reveal an intricate feedback between river and tidal flows, channel morphology, sediment dynamics and bedforms. The results have implications for bedform research, river management and numerical modelling.

How to cite: Lefebvre, A., Herrling, G., Zorndt, A., Krämer, K., Becker, M., and Winter, C.: Tidal bedforms dynamics, Weser River, Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13499, https://doi.org/10.5194/egusphere-egu2020-13499, 2020.

In northwestern Taiwan, Cholan Formation in Dahan river is about 1400 m thick that contains high-frequency sequence stratigraphy (6th-order) and detail of facies architecture which indicates evolution of the foreland basin. In late Miocene (6 Ma), the Taiwan orogeny belt is formed by the arc-continental collision (the Luzon Volcanic Arc and the Eurasian plate). During Pliocene-Pleistocene, uplift of the Hsueshan Range and the Western Foothill created by a series of the fold-thrust belt formed the foreland basin. Most importantly, high subsidence rate and high sedimentation rate are critical that glacio-eustasy (6th-order) could be correlated to parasequences in Cholan Formation. It provides a precise age model to discuss different stages of foreland basin.

Parasequences in Cholan Formation could be divided into three types of depositional systems including siliciclastic shallow marine (Type 1), margin marine (Type 2) and nonmarine (Type 3) that are a typical sequence of foreland basins. Type 1, which is tidal-dominated open coast, shows 10-30 m coarsening-upward succession. Type 2, which is tidal-dominated delta, shows two different parts. The lower part is 10-50 m coarsening-upward succession which unconformity contact with Type 1. The upper part changes to 20-50 m fining-upward succession. Type 3, which is alluvial system, shows 30-70 m fining-upward succession that is conformable with Type 2. From shallow marine to nonmarine, the thickness of parasequence is growing thicker that indicates long-term tectonic subsidence rate is getting higher with more sediment deposits in the basin. In more detail, in marine setting, sea level change is the main considered factor to identify sequence boundary (SB) and maximum flooding surface (MFS), while in nonmarine setting, precipitation change in glacial and inter-glacial may be a critical factor to impact the formation of SB. However, MFS is complicated to define because some parasequences show tidal signal, but some don’t. It could be influenced by degree of sea level uplift or paleotopography. In Cholan Formation, the signal of sea level, tectonic and climate is sensitive to reflect in stratigraphy architecture.

Keywords: Foreland basin, High-order sequence stratigraphy, Marine to nonmarine facies architecture

How to cite: Zhu, X.-C. and Chen, W.-S.: High-frequency Sequence stratigraphy and facies architecture in Cholan Formation (Pleistocene), northwestern Taiwan: the evolution of a foreland basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3321, https://doi.org/10.5194/egusphere-egu2020-3321, 2020.

EGU2020-20680 | Displays | SSP3.5

The growth process of river dunes

Suleyman Naqshband and Ton Hoitink

Dunes dominate the bed of sandy rivers and they are of central importance in predicting sediment transport and flow resistance. Using a novel acoustic instrument over migrating dunes in a laboratory setting, we quantify a number of dynamical properties that are crucial in our understanding and modeling of dune response to changes in flow and sediment transport. Measured sediment transport distribution during the initial stage of dune growth reveals a negative spatial lag between dune crest and maximum sediment transport rate. In absence of this spatial lag, the dune field is observed to grow by merging of smaller, faster migrating dunes.

How to cite: Naqshband, S. and Hoitink, T.: The growth process of river dunes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20680, https://doi.org/10.5194/egusphere-egu2020-20680, 2020.

EGU2020-19409 | Displays | SSP3.5

Observations of sediment sorting over rapidly developed marine bedforms, using multibeam backscatter

Timo C. Gaida, Thaiënne A.G.P. Van Dijk, Mirjam Snellen, and Dick G. Simons

Grain-size sorting in bedforms is well known in river dunes. On continental shelves, however, datasets aimed at grain-size sorting over bedforms, are limited. More extensive observations of sediment sorting over bedforms may help to understand their morphodynamic processes, and are key in habitat mapping, since grain-size is a main control on the composition of benthic fauna. A time series of seven multibeam (MBES) bathymetry and backscatter measurements and box cores were collected for the monitoring of a coastal nourishment in a tidal inlet at Ameland, Netherlands. Prior to the nourishment (April 2017), 10-15 m long and 1.5 m high megaripples occurred. The time series shows the rapid development of high and steep megaripples in the newly replenished sediment, with a wavelength of 40 m and height of 2.5 m within three months (during-nourishment; October 2017), which then grew into 120 m long and 3 m high sand waves in relatively shallow water (10 - 14 m) within 5 months (post-nourishment; March 2018). 
Relative backscatter (BS) strengths, which are corrected for, among others, transmission losses and bed morphology, represent seabed sediment characteristics. Bed classification of BS strengths, using an unsupervised Bayesian method, resulted in a high-resolution map of 5 acoustic classes (ACs), to which sediment types were assigned using the box cores as ground truthing. These box cores, however, were not taken at the detailed level of sand wave crests and troughs. 
The acoustic sediment classes (ASCs) exhibit a repetitive pattern, indicating horizontal sediment sorting over bedforms, that shifted and intensified during the growth of the megaripples into sand waves. The ASC megaripple pattern is less consistent, but generally comprises finer sediments (ASC2-3: sand) on the stoss sides and coarser sediments on the lee sides (ASC3-4: sand to slightly gravelly sand). The sand wave pattern is very consistent and comprises coarse sediments on the stoss sides (ASC5: gravel- and shell-containing sands), finer sediments towards the crests (ASC2-3: sand) and even finer sediments (ASC1: sandy mud) in the troughs. In the course of one year, both the morphological and sorting patterns seem to repeat itself. A similar sorting evolution was observed during the growth of megaripples just farther offshore. 
In a different data set, farther offshore on the Netherlands Continental Shelf and built up over several years, grab samples were collected in transects, specifically at crests and troughs of sand waves and long bed waves, and were analysed for grain size, organic matter and CaCO3 contents. Median grain sizes in the troughs of bedforms are consistently finer than at the crests, and reveal significant signatures between sand wave fields, with crest-trough differences among sites ranging between 10 and 85 micrometer. Unfortunately, MBES-BS data are not available for establishing large-scaled, spatial sorting patterns.
This evolution of horizontal sediment-sorting patterns during the growth of marine bedforms may support modelling studies of hydrodynamic responses of flow over undulating beds and may explain the morphodynamic evolution of marine bedforms, as relevant in marine ecology. However, coherent empirical datasets are required. 

How to cite: Gaida, T. C., Van Dijk, T. A. G. P., Snellen, M., and Simons, D. G.: Observations of sediment sorting over rapidly developed marine bedforms, using multibeam backscatter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19409, https://doi.org/10.5194/egusphere-egu2020-19409, 2020.

EGU2020-6486 | Displays | SSP3.5

Early and late Holocene paleoenvironmental reconstruction of the Pearl River estuary, South China Sea

Huixian Chen, Jianhua Wang, Nicole S. Khan, Jiaxue Wu, and Benjamin P. Horton

Proxy reconstructions of estuarine evolution provide perspectives on regional to global environmental changes, including relative sea-level changes, climatic changes, and agricultural developments. Although there are studies of the Holocene sedimentary processes in the Pearl River estuary, the understanding of early Holocene sedimentation in unknown due to limited preservation.

Here, we present a new record of lithological, benthic foraminiferal, and geochemical (δ13C and C/N) change from a sediment core in the west shoal of the modern Lingding Bay along a paleo-valley. The lithologic and foraminiferal record reveal the transgressive evolution from fluvial, inner estuary to middle estuary in the early Holocene between 11300 and 8100 cal a BP in response to rapid sea-level rise. δ13C and C/N data indicate high freshwater discharge from 10500 to 8100 cal a BP driven by a strong Asian monsoon. The middle Holocene (8100 - 3300 cal a BP) sediment is absent in this core and others in the northward of the Lingding Bay. Seismic profiles reveal a tidal ravinement surface across Lingding Bay, which contributed to subaqueous erosion on the mid-Holocene sedimentation hiatus, might be resulted from unique geomorphology of the Pearl River Delta. In the late Holocene (3300 cal a BP to the present), the lithology and foraminiferal assemblages suggest further regressive evolution from outer estuary, middle estuary channel, to middle estuary shoal due to deltaic progradation under stable relative sea levels. In the last 2000 years, δ13C and C/N values reveal the intensive development of agriculture coupled with the reduction of freshwater input derived from a weakening Asian monsoon. Our study illustrates the interaction of Asian monsoon and sea-level changes within the Pearl River estuary landform and their impact on Holocene sedimentary processes.

How to cite: Chen, H., Wang, J., Khan, N. S., Wu, J., and Horton, B. P.: Early and late Holocene paleoenvironmental reconstruction of the Pearl River estuary, South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6486, https://doi.org/10.5194/egusphere-egu2020-6486, 2020.

SSP3.21 – Glacial Overdeepenings: Preserving the sedimentary record through ice ages

EGU2020-3124 | Displays | SSP3.21

Micromorphology as a tool to interpret glacial depositional environments from late Paleozoic glacial rocks in the Paraná Basin, Brazil

Aurora Machado Garcia, Bárbara Trzaskos, Fernando Farias Vesely, Eduardo Menozzo Rosa, Emrys R. Phillips, and John L. Isbell

The Itararé Group and time equivalent Aquidauana Formation represent the Late Paleozoic Ice Age in the Paraná Basin. These sedimentary rocks provide an extensive glacial record which contains deformed intervals interpreted as glaciotectonites, with features such as folds, thrusts and subhorizontal shear zones, which could be produced sub- or proglacially. In addition, similar deformation structures have been recognised reflecting different depositional processes in glacial related environments, such as subaqueous mass flows, iceberg keel marks and ice-rafting. Micromorphological analysis of glacially-related soft-sediment structures have been widely applied to Quaternary deposits as a tool to aid in the interpretation of paleoenvironments. However, few studies have approached microscale deformation in glacial and glacially-related deposits from the Paleozoic or even older periods, in which the distinction between subglacial, proglacial and non-glacial products is crucial for deep-time paleoclimatic reconstructions. 

Our work aims to address this issue and correlate the range of microstructures present in thin section to different depositional settings interpreted on the basis on macroscale sedimentary facies analysis. The results are used to critically evaluate the applicability of micromorphology in distinguishing paleoenvironments in the pre-Pleistocene glacial record and how those structures can be modified over time in response to lithification and diagenesis. The study combines field data with detailed micromorphological and microstructural analysis of 40 thin sections from the Itararé Group and the Aquidauana Formation. Samples were collected from a range of lithotypes from different depositional settings including: diamictites, sandstones and mudstones from rain-out, mass transport, subglacial overriding and ice-marginal glaciotectonism. The microstructures present include unistrial plasmic fabrics, glaciotectonic laminations, rotational structures (turbates), microshear zones, sheared clasts, faults, folds, boudins and intraclasts. However, in some well-sorted facies, which contain very little or no matrix, also contain features typically associated with compaction and diagenesis, such as grain crushing, reduction of primary porosity, sutured grain contacts and stylolites. 

Preliminary results show that sediments from a range of different depositional facies may contain a similar assemblage of microstructures. This suggests that microstructures on their own cannot fully characterize the original sedimentary depositional environment in older glacigenic sequences. Furthermore, diagenesis plays a major role when it comes to the preservation of primary sedimentary and soft-sediment deformation features and can lead to the overprinting of these structures.

How to cite: Garcia, A. M., Trzaskos, B., Vesely, F. F., Rosa, E. M., Phillips, E. R., and Isbell, J. L.: Micromorphology as a tool to interpret glacial depositional environments from late Paleozoic glacial rocks in the Paraná Basin, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3124, https://doi.org/10.5194/egusphere-egu2020-3124, 2020.

EGU2020-21432 | Displays | SSP3.21

Overdeepened glacial basins as archives for Pleistocene glaciation history and subglacial processes: Results from scientific drilling in the Northern Alpine Foreland

Marius W. Buechi, Gaudenz Deplazes, Lukas Gegg, Herfried Madritsch, and Flavio S. Anselmetti

Overdeepened glacial basins are excellent archives for the Quaternary glaciation history and the landscape evolution of the Alps. While they are common large-scale glacial features in many inner-Alpine and foreland settings, most of these basins remain underexplored as challenging drilling operations into 10s to 100s of meters of unconsolidated sediment are required to access the sedimentary record.

We currently investigate some of the most prominent overdeepened glacial basins between the Aare and Rhine Rivers in Northern Switzerland with a multi-method approach –  including geophysical methods and scientific drilling – to characterise the geometry, sedimentary infill and age of these glacial basins. The focus of this research is on 1) extracting and refining the Middle to Late Pleistocene glaciation history of Northern Switzerland, and 2) identifying the mechanisms and controls of overdeepening subglacial erosion by characterizing former ice-contacts in the basin fills using micro- to macroscale sedimentological tools.

How to cite: Buechi, M. W., Deplazes, G., Gegg, L., Madritsch, H., and Anselmetti, F. S.: Overdeepened glacial basins as archives for Pleistocene glaciation history and subglacial processes: Results from scientific drilling in the Northern Alpine Foreland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21432, https://doi.org/10.5194/egusphere-egu2020-21432, 2020.

EGU2020-5214 | Displays | SSP3.21

Drilling into mid-Pleistocene sediments in the overdeepened Aare Valley, CH

Michael A. Schwenk, Dimitri Bandou, Patrick Schläfli, Guilhem A. Douillett, and Fritz Schlunegger

Overdeepenings are common bedrock features that were formed within the Alps and their forelands during repeated glaciations. Here, we present a total of 208.5 m of sediment core recovered during a scientific drilling campaign in spring 2019. The drilling is located on the Swiss Plateau (CH) close to the terminus of the overdeepening that was formed by the Alpine Aare glacier. The drilling reached the Molasse bedrock at an elevation of 362.5 m a.s.l. This is the first time in the middle Aare Valley that a scientific drilling fully recovered the sedimentary fill of the overdeepening.

The retrieved material comprises an alternation of silt- and sandbeds, and massive as well as cross-bedded gravel layers. We divide the suite into two packages reflecting sedimentation within a fluvio-glacial environment. The first package starts with a glacial till, c. 15 m thick, which is overlain by an 89 m-thick succession of cross-bedded sandy and gravelly layers and mud interbeds reflecting deposition at the toe of a prograding delta. At c. 104 m depth, the succession is interrupted by a till sequence, c. 20 m thick, which forms the base of the second package. This package records a fining-upward trend, starting with massive sand beds at the base and ends with massive silt layers at the top. Mapping has shown that the core section is overlain by a sand layer with soft-sediment deformation structures reflecting the occurrence of a mouth bar environment. The sequence ends with fluvial gravels. The entire sediment core thus records a shallowing-up sequence that is interrupted by a glacial till.

Optical stimulated luminescence dating (IRSL; Buylaert et al., 2009) yielded a minimum age of c. 200 ka for the mouth bar deposits, which is in accordance with reported Late-Middle Pleistocene ages of corresponding sequences in the region (Preusser et al., 2005). We therefore assign the upper package in our drilling to the MIS 7/8 glacial-interglacial cycle, and to the MIS 9/10 for the basal package. The sediments in our drilling thus record a crucial time interval when glacial erosion in the Alps (Haeuselmann et al., 2007) and in the northern foreland (Schlüchter, 2004) occurred at the highest rates.

Buylaert, J.P., Murray, A.S., Thomsen, K.J., Jain, M., 2009. Testing the potential of an elevated temperature IRSL signal from K-feldspar. Radiat. Meas. 44, 560–565.

Haeuselmann, P., Granger, D.E., Jeannin, P.Y., Lauritzen, S.E., 2007. Abrupt glacial valley incision at 0.8 Ma dated from cave deposits in Switzerland. Geology 35, 143–146.

Preusser, F., Drescher-Schneider, R., Fiebig, M., Schlüchter, C., 2005. Re-interpretation of the Meikirch pollen record, Swiss Alpine Foreland, and implications for Middle Pleistocene chronostratigraphy. J. Quat. Sci. 20, 607–620.

Schlüchter, C., 2004. The Swiss glacial record - a schematic summary. Dev. Quat. Sci. 2, 413–418.

How to cite: Schwenk, M. A., Bandou, D., Schläfli, P., Douillett, G. A., and Schlunegger, F.: Drilling into mid-Pleistocene sediments in the overdeepened Aare Valley, CH, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5214, https://doi.org/10.5194/egusphere-egu2020-5214, 2020.

Glaciers are major agents of landscape erosion. By their erosive power, glaciers are also considered as a sediment production “factory”. During glacial cycles, glacially-conditioned sediment is either transported by the flowing ice and the meltwaters towards terminal distal sinks (e.g. oceans), or stored for shorter or longer periods of time inland. In terms of the long-term disposal of radioactive waste (at timescales of 1 Ma) in areas affected by glaciations, scenarios for the potential of excavation of repositories by glaciers have to be calculated, so as the chance for dispersion of contaminated sediment into the environment. The question as to whether glacially-conditioned sediment contaminated by radioactive waste will be stored inland or dispersed across larger scales towards terminal sinks is therefore of great importance, and glacial overdeepenings are considered as one of the best candidates to store sediment through multiple glacial cycles.

This question of persistence of glacially-conditioned sediment within glacial overdeepenings through multiple phases of glacier advance and retreat has been investigated through a literature review. The study focuses on the Plateau of Northern Switzerland, an area that has been subject to glaciations and which is characterized by many glacial overdeepenings. Results of the literature review show that under some circumstances, glacially-conditioned sediment could persist within glacial overdeepenings across the Plateau of Northern Switzerland during multiple glacial cycles. In the meantime, the conditions required for persistence, as well as the proportions of sediment stored as compared to the sediment transferred to terminal sinks, are much less clear.

How to cite: Antoniazza, G. and Lane, S. N.: Chance for glacially-conditioned sediment to persist within glacial overdeepenings through multiple glacial cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13149, https://doi.org/10.5194/egusphere-egu2020-13149, 2020.

EGU2020-7445 | Displays | SSP3.21

Environmental changes in the Wehntal Valley in Northern Switzerland

Johannes Miocic, Ruth Drescher-Schneider, Hans Rudolf Graf, Marlu Kühn, Frank Preusser, Werner H. Schoch, Nigel Thew, Lucia Wick, and Heinz Furrer

Quaternary deposits within the glacially overdeepened trough of the Wehntal Valley in Northern Switzerland, record glacial and interglacial conditions from the Beringen Glaciation (MIS 6) through to the Holocene. The area is well known for the Niederweningen site, with its rich Late Pleistocene mammal remains found in a buried peat deposit. In addition to this famous “mammoth peat”, more deeply buried peat layers, part of which have previously been attributed to the final part of the Last Interglacial, also include a wealth of environmental data.

Here, we present the first results of an investigation, including sedimentology, geochemistry, palaeobotany (pollen, wood and plant macroremains), malacology, and luminescence dating, of two 16 meter drill cores taken close to the Niederweningen site. The analysed sedimentary successions in both cores show a transition from a series of laminated silts typical of a lake environment to a several meter-thick succession of well-developed organic silts, tufaceous silts and peat layers characteristic of near shore and shore conditions. The presence of dropstones and a lack of organic material in the lower part of the lake sediments indicate glacial conditions, while the peat-rich succession formed during a relatively warm period followed by a time of fluctuating climate. Preliminary results indicate that the organic-rich units represent the Last Interglacial, followed by warm interstadials during the early part of the Last Glacial period. The "mammoth peat" appears to be missing from the studied cores. Erosive surfaces within the peaty succession impede a straightforward interpretation.

How to cite: Miocic, J., Drescher-Schneider, R., Graf, H. R., Kühn, M., Preusser, F., Schoch, W. H., Thew, N., Wick, L., and Furrer, H.: Environmental changes in the Wehntal Valley in Northern Switzerland , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7445, https://doi.org/10.5194/egusphere-egu2020-7445, 2020.

EGU2020-8287 | Displays | SSP3.21

Biostratigraphic dating of palaeolake deposits from an overdeepening in the Swiss Northern Alpine Foreland by numerical assessments of vegetation composition and the role of species dynamics

Patrick Schläfli, Erika Gobet, Willy Tinner, Jacqueline van Leeuwen, Elisa Vescovi, Guilhem Douillet, Michael Schwenk, Dimitri Bandou, and Fritz Schlunegger

Pollen analysis has shown that at regional to subcontinental scales interglacial vegetation successions usually follow similar patterns throughout the Middle and Late Quaternary. Yet, relevant compositional and species-specific differences among interglacials exist and contribute to their characteristic biostratigraphic fingerprint. We use these divergences to indirectly date palaeolake deposits from Spiezberg (SW margin of overdeepened lake Thun, Switzerland), which have been assigned to either MIS 5e (last interglacial) or MIS 7a (penultimate interglacial) according to the average IRSL age of 164 ± 16 ka. For this purpose, we analyzed the fossil pollen record of the Spiezberg palaeolake deposits and applied optimal partitioning and the broken stick model for zonation. Furthermore, we re-assessed local pollen assemblage zones (LPAZ) of two physically dated reference records (Beerenmösli: MIS 5e; Meikirch: MIS 7a) from the study area by using the same zonation approaches. LPAZ of all three records were then compared optically and numerically (PCA and significance tests) to test which of the two reference records is more similar to Spiezberg. Pollen data show that the major part of the Spiezberg record was sedimented during full interglacial conditions. The irrelevance of Fagus points towards an MIS 5e age for the sediments. This is supported by PCA axis 2, which shows a statistically significant similarity of the Spiezberg record to the MIS 5e reference. This outcome is explained by Fagus playing an important role in the PCA axis 2 gradient, which is probably determined by competition for light. PCA axis 1 is not taken into consideration for the correlation since it represents a climate gradient (e.g. from boreal to temperate forests) and explains most of the intra-locality but less of the inter-locality variance. We thus assign the Spiezberg record to the last interglacial and show that climate-driven compositional differences between MIS 5e and MIS 7a are not diagnostic. In contrast, distinct differences in single-species abundances (e.g. Fagus) are strong enough to significantly distinguish between MIS 5e and MIS 7a records. We conclude that variability across various interglacial vegetation successions (e.g. MIS 5e vs. 7a, PCA axis 2) is smaller than local vegetation variability within a full interglacial succession at the same site (PCA axis 1). This implies a very high vegetation resilience to glacial-interglacial climatic variability, the biotic properties involved might be migration capacity, survival in refugia and adjustments to rapidly changing Quaternary environments.

How to cite: Schläfli, P., Gobet, E., Tinner, W., van Leeuwen, J., Vescovi, E., Douillet, G., Schwenk, M., Bandou, D., and Schlunegger, F.: Biostratigraphic dating of palaeolake deposits from an overdeepening in the Swiss Northern Alpine Foreland by numerical assessments of vegetation composition and the role of species dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8287, https://doi.org/10.5194/egusphere-egu2020-8287, 2020.

EGU2020-15807 | Displays | SSP3.21

Overdeepenings modelled with gravimetry-based data

Dimitri Bandou, Patrick Schläfli, Michael Schwenk, Guilhem Douillet, Edi Kissling, and Fritz Schlunegger

The processes and mechanisms resulting in overdeepenings, valleys carved deeper than today’s rivers base level during glaciations, are still a matter of debate. Whether or not these valleys formation is due to glacial or fluvio-glacial processes or through fluvial down cutting in the geological past is difficult to affirm, as the depressions are filled with sediment or host lakes (Cook and Swift, 2012). In order to bypass this limitation, we use precise gravimetric data, GNSS data and borehole data, which we combine within a 3D forward modelling code, Gravi3D. We particularly aim at reconstructing the geometry of overdeepened valleys’ walls, which bear information on the erosional mechanism leading to the formation of these troughs. We proceed through the building of models for a given geometry to reproduce the Bouguer gravity that we measured in the field along sections and on a grid of stations. We constrain our models by using precise density values, determined by gravimetry, along with borehole data.

We apply this technique to overdeepenings located in the Alpine foreland (Belpberg area, Central Switzerland) because this area hosts multiple overdeepenings from the past glaciations. The region is characterized by three hill ranges made up of Molasse bedrock with c. 300 m-deep and c. 1 km-wide valleys in-between, where overdeepenings with a Quaternary infill are expected. The results of gravity data collection, accomplished over a section with stations spaced between 100 and 300 m and after standard corrections yield a Bouguer anomaly for the Belpberg region that ranges from c. -99 to -106 mgal. We infer this large range to the regional trend (c. 2 mgal over 8 km) and to the effect of the overdeepening infill (2-4 mgal over 1 km), disclosing a sharp anomaly pattern over the inferred overdeeping. The subsequent three steps include: (i) the removal of the regional trend, (ii) the use of the Nettleton method for the quantification of an accurate density contrast between the Molasse bedrock and the Quaternary infill, and (iii) the configuration of Gravi3D for the Belpberg situation, will yield further information on the morphology of the overdeeping. We thus conclude that Gravi3D, within this framework, is a useful tool to determine the geometry of overdeepings in particular, and shallow subsurface bodies and structures in general.

Reference:

Cook, S.J., Swift, D.A., 2012. Subglacial basins: Their origin and importance in glacial systems and landscapes. Earth-Science Reviews 115, 332–372.

How to cite: Bandou, D., Schläfli, P., Schwenk, M., Douillet, G., Kissling, E., and Schlunegger, F.: Overdeepenings modelled with gravimetry-based data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15807, https://doi.org/10.5194/egusphere-egu2020-15807, 2020.

EGU2020-7501 | Displays | SSP3.21

Geological controls on the morphology of an overdeepened canyon investigated by seismic surface waves (Lower Aare Valley, Switzerland)

Lukas Gegg, Lorenz Keller, Marius W. Buechi, Thomas Spillmann, Gaudenz Deplazes, Herfried Madritsch, and Flavio S. Anselmetti

Subglacial overdeepenings are common features of past and presently glaciated landscapes. In the Northern Alpine Foreland, these troughs occur mostly within the rather soft, poorly lithified sandstones of the Molasse basin. An exceptional setting is the Lower Aare Valley in Northern Switzerland, where a narrow, finger-like overdeepening (Gebenstorf-Stilli Trough) has been incised more than 100 m below the present surface into the fold-and-thrust belt of the Jura Mountains with its diverse Mesozoic lithologies including competent limestone units. Consequently, the morphology of this overdeepening can provide valuable information on lithological and structural controls on subglacial overdeepening erosion.

We investigate the Gebenstorf-Stilli Trough with three scientific boreholes located along the South-North oriented trough axis. In addition, a set of seismic cross-sections has been acquired by a combination of active and passive seismic approaches analysing surface waves, namely passive horizontal-to-vertical spectral ratio (HVSR) measurements, active measurements applying multiple filter analysis of group velocity (MFA), and extended spatial auto correlation of ambient vibration array data (ESAC).

Preliminary results show that the base of the overdeepening can be well imaged using our methodology. In combination with borehole information, surface elevation data and 3D models of the subsurface geology, we see great potential to better constrain the morphology of the Gebenstorf-Stilli Trough, and to assess how different bedrock lithologies and structures influence subglacial overdeepening erosion – an underexplored and poorly understood issue.

How to cite: Gegg, L., Keller, L., Buechi, M. W., Spillmann, T., Deplazes, G., Madritsch, H., and Anselmetti, F. S.: Geological controls on the morphology of an overdeepened canyon investigated by seismic surface waves (Lower Aare Valley, Switzerland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7501, https://doi.org/10.5194/egusphere-egu2020-7501, 2020.

EGU2020-8386 | Displays | SSP3.21

Seismic response of three glacially overdeepened valleys – a comparison

Thomas Burschil, Hermann Buness, Anna-Catharina Brandt, David C. Tanner, and Gerald Gabriel

Seismic imaging is a spiffing tool to explore the shape and stratigraphy of Quaternary structures such as glacially overdeepened valleys. Recent seismic investigations have unlocked some of the secrets of three of such valleys in the European Alps. Their locations range from distal Quaternary overdeepened basins in the Alpine foreland, i.e. Tannwald Basin (TB) in Germany and the Basadingen Valley (BV) in Switzerland, to the proximal, intra-mountainous Lienz Basin (LB) in Austria. All of them are also primary investigation sites of the project Drilling Overdeepened Valleys (DOVE), funded by the International Continental Scientific Drilling Program (ICDP).

Seismic reflections map the shape and the internal structure of the infill of these basins in detail. The LB shows a classical sedimentary succession of only one glacial cycle, i.e. (from bottom to top) tills, lacustrine sediments, and fluvial deposits. Reflections in the bedrock are not visible. This is in contrast to the distal foreland basins that incise Tertiary sediments and possess sediments of more than one glacial cycle. The reflection patterns of the substrata of the TB and BV basins consist of deeper, continuous horizons and a thick sedimentary package that was incised by glacial erosion. However, the internal reflections differ significantly. In the TB, we discriminate (from bottom to top) plucked molasses units, till of an older glacial cycle, lacustrine sediments, younger till and till sequences, as well as fluvial deposits on top. The preliminary result of the BV illustrates several unconformities and a spatial highly variable setting. The latter is supported by trackable horizons that show several laterally-shifted troughs within the basin fill.

The comparison of the seismic results thus reveals the difference of the sedimentary infill of all three glacially overdeepened valleys. Especially, the internal structure of both basins in the foreland shows unexpected variability.

How to cite: Burschil, T., Buness, H., Brandt, A.-C., Tanner, D. C., and Gabriel, G.: Seismic response of three glacially overdeepened valleys – a comparison, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8386, https://doi.org/10.5194/egusphere-egu2020-8386, 2020.

SSP4.3 – Palaeontology, Palaeoecology and Evolution of Life

EGU2020-9733 | Displays | SSP4.3

Global patterns of plant diversity and their evolutionary drivers

Melanie Tietje, William J. Baker, Rafaël Govaerts, Stephen A. Smith, Miao Sun, and Wolf L. Eiserhardt

Spatial patterns of plant diversity follow the well-known global latitudinal biodiversity gradient, however there is little consensus about the underlying causes for this pattern. Here we present a spatial analysis of a complete checklist of the world’s seed plants, integrated with a comprehensive plant Tree of Life. This combination allows insights into the evolutionary drivers of plant species richness patterns, specifically current plant biodiversity patterns, and the diversification processes that shaped them. Our study provides a comprehensive global species richness map and relates the observed species richness pattern to speciation rates derived from phylogeny, and with environmental variables, which are hypothesized to impact speciation rates. Initial results show that tropical rain forest regions, although being areas that contain among the highest numbers of species, are regions with comparatively low speciation rates, contradicting the widespread notion that rainforests are “cradles” of biodiversity. This finding seems further supported by contrasting association of environmental variables, like precipitation and temperature, with speciation rates and species richness.

How to cite: Tietje, M., Baker, W. J., Govaerts, R., Smith, S. A., Sun, M., and Eiserhardt, W. L.: Global patterns of plant diversity and their evolutionary drivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9733, https://doi.org/10.5194/egusphere-egu2020-9733, 2020.

EGU2020-8146 | Displays | SSP4.3

CO2 driven changes in leaf biochemistry may have influenced fire behaviour at the Triassic-Jurassic boundary

Sarah Baker, Rebecca Dewhirst, Jennifer McElwain, Matthew Haworth, and Claire Belcher

EGU2020-21187 | Displays | SSP4.3

Major palaeoenvironmental upheavals in both marine and terrestrial realms during the Toarcian oceanic anoxic event: a multi-proxy approach

Francesca Galasso, Susanne Feist­Burkhardt, Annette Schmid- Röhl, Stefano Benasconi, and Elke Schneebeli-Hermann

EGU2020-15431 | Displays | SSP4.3 | Highlight

Perturbation and recovery of shelf ecosystems during the PETM

Monika Doubrawa, Peter Stassen, Marci M. Robinson, Tali L. Babila, James C. Zachos, and Robert P. Speijer

During the early Paleogene, a long-term warming trend of Earth’s climate was punctuated by a major global warming event, known as the Paleocene-Eocene Thermal Maximum (PETM) and marked by a carbon isotope excursion (CIE) and an acidification episode. The associated worldwide environmental perturbations are best studied in open marine settings, and resulted in a major extinction event in deep-sea benthic foraminifera, followed by migration and diversification. Yet, the evolutionary impact on shelf foraminiferal faunas is still poorly constrained due the inherent stratigraphic complexities in these environments. In order to understand the prelude and aftermath of peak warming during the PETM, we study the South Dover Bridge core (SDB), drilled in the US Atlantic Coastal Plain in Maryland. Here, the Paleocene-Eocene transition is stratigraphically well constrained by calcareous nannoplankton and stable isotope records. Additionally, the PETM is regionally characterized by the appearance of fine-grained sediments, known as the Marlboro Clay, contrasting with the late Paleocene glauconitic sands. Our newly generated high-resolution foraminiferal stable isotope, biotic and grain size data enable an assessment of the stratigraphic completeness of this site, and the disentanglement of the successive recovery-phases, by correlation across the paleoshelf.

The mid-shelf benthic foraminiferal assemblage we recorded in the upper Paleocene indicates well-oxygenated, continuously oligo- to mesotrophic bottom water conditions. These conditions were temporarily interrupted during a pre-PETM CIE, which initiated minor, but prominent, changes in foraminiferal assemblage. The relationship with the PETM is still unclear, but it may indicate that the latest Paleocene climate was not as stable as previously assumed and instead exhibited a more gradual change towards the PETM. At the onset of the PETM diversity decreases, as more stress-resistant benthic taxa become predominant and planktic abundances increase. This probably points to periodically dysoxic bottom waters due to river-induced stratification, resulting from enhanced regional river outflow, as well as to a shift to episodic food fluxes to the sea floor.

The studied expanded SDB sequence also presents an excellent and nearly complete record of the PETM isotope recovery phase. Throughout this recovery phase a third, more diverse foraminiferal assemblage starts to prevail, indicating a gradual return to sustained high food levels and increasing oxygen levels, related to a decrease of river influence. Species, dominant during the core phase of the PETM, like Anomalinoides acutus or Pseudouvigerina wilcoxensis, show strongly declining numbers in the recovery phase. Other taxa, like Cibicidoides alleni, returned to the shelf ecosystem, after disappearing nearly completely from the sediments during the initial PETM CIE interval. This coincides with reduced planktic foraminiferal abundances and a tendency towards more silty and less clayey sediments, linked to renewed bottom current activities and winnowing.

The lack of severe benthic extinction among shelf-dwelling benthic foraminifera and the observed lateral variability in environmental conditions, demonstrate how foraminiferal shelf communities can adapt to massive global carbon perturbations. As more regional data will become available, these will enable more constraints on environmental parameters and variations along the Atlantic Coastal Plain prior and during the PETM.

How to cite: Doubrawa, M., Stassen, P., Robinson, M. M., Babila, T. L., Zachos, J. C., and Speijer, R. P.: Perturbation and recovery of shelf ecosystems during the PETM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15431, https://doi.org/10.5194/egusphere-egu2020-15431, 2020.

EGU2020-1053 | Displays | SSP4.3

Shelf ecosystem response to the Eocene-Oligocene Transition

Laura Cotton, David Evans, and Daniela Schmidt

The Eocene-Oligocene transition (EOT) is one of the most dramatic climate shifts of the Cenozoic with severe consequences for reef ecosystems. The onset of continental Antarctic glaciation is associated with widespread environmental change, resulting in a global peak in biotic turnover. Whilst numerous studies of the biotic response to the changes at the EOT have been carried out, most high-resolution studies consist of open ocean records of marine plankton and predominantly single groups of organisms. However, this is not representative of the ocean system as a whole and does not provide a holistic view of mechanism of restructuring of the marine ecosystems. The shelf seas and reefs are some of the most diverse and fundamentally important ecosystems of the oceans. Long-term diversity loss across the EOT has been shown in several macrofossil studies, but mainly at low resolution, and recovery is not well understood.  Many shelf species are ecosystem engineers whose loss and recovery have profound implications for the entire ecosystem. Understanding these interactions will provide insights into shallow marine ecosystems and their response to major climate perturbations.

The Tanzanian Drilling Project EOT record (TDP 11, 12, 17) is recognised globally for its completeness and exceptionally preserved calcareous microfossils. It is most importantly, though, a rare record of both shallow water organisms and open ocean plankton. The latter are fundamentally important for reconstructions of the environment and a globally calibrated timescale. Here we draw together a unique dataset of high-resolution mollusc, Dasycladaceae, bryozoan, larger benthic foraminifers, coral, smaller benthic foraminifera, trace element and isotope records from the EOT. The response and recovery of these species is compared with known, modern physiology of each group to provide a complete picture of the shallow marine ecosystem response.

Following rapid extinctions within the larger foraminifera during the transition, molluscs, Dasycladaceae and bryozoans all show increases in abundance, indicating a major shift in shelf ecosystem composition. These assemblage changes are coincident with a period of more positive values in d13C of both benthic and planktonic foraminifera and changes in trace element values. Comparison with the open ocean record of planktonic foraminiferal, pteropod, and nannofossils confirm these assemblage changes are a biological, rather than sedimentological response and additionally support a that a transition to more eutrophic conditions took place. an environmental framework of traditional and novel geochemistry, indicate that increased nutrient fluxes played a pivotal role in restructuring shelf ecosystem dynamics and therefore offers new insight into mechanisms of reorganisation under ecosystem loss and environmental change.

How to cite: Cotton, L., Evans, D., and Schmidt, D.: Shelf ecosystem response to the Eocene-Oligocene Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1053, https://doi.org/10.5194/egusphere-egu2020-1053, 2020.

Impact craters are formed when an asteroid strikes the surface with the hyper-velocity (usually higher than ~1km/s). The kinetic energy of the impactor is released as an explosion, a crater is formed, and target material is deposited outside, forming a proximal and later distal ejecta blanket. This consists of rocks, the surface soil layer and numerous plants remains (Cassidy et al. 1965, Khryanina 1981, Herd et al. 2008), including remains of trees directly killed by the asteroid (Losiak et al. 2016, Losiak et. Al. 2020). We have found a number of charcoals that we suggest are related to the formation of the following confirmed impact craters: Kaali Main, Kaali 2/8 (Estonia, Losiak et al. 2016), Morasko (Poland, Szokaluk et al. 2019), Whitecourt (Canada, Herd et al. 2008) and Ries crater (Buchner and Schmieder 2009). Three of these locations represent small (30-100 m in diameter) impact craters developed primarily in unconsolidated materials such as glacial tills and fluvioglacial sands. Whereas, Ries is a much larger and older crater: it is 24 km in diameter and 14.5 Ma old.

Here we present the results from a set of experiments that reproduce the process of formation of charcoals within the proximal ejecta blankets of small impacts. Firstly, charring experiments were achieved using the iCone Calorimeter that recreated a range of heating possibilities that might results from small impact cratering processes. The iCone allows samples to be heated, with or without ignition at a range of radiant heat fluxes for given durations; these heat fluxes can be static or transient, both of which may be relevant to different impact formation mechanisms. Secondly, we buried leaves and fragments of different woods in heated sand over a range of temperatures durations and cooling regimes to assess the potential for relatively cool ejecta to cause transformations of organic material to char in situ. All the chars created in the experiments were analysed via reflectance microscopy and compared with the charcoal that have been produced by modern wildfires. Our aim being to better understand the environmental effects of differently sized impact craters, but also to study the mode of preservation of plants killed during such extraterrestrial impact events.

Buchner & Schmieder 2009. MAPS44:1051–1060.

Cassidy et al. 1965. Science149:1055-1064.

Herd et al. 2008. Geology36:955–958.

Hudspith et al. 2010. PPP291:40–51.

Khryanina 1981Int. Geology Rev.23:1-10.

Losiak et al. 2016. MAPS51:681–695.

Losiak et al. 2020. MAPSaccepted.

Scott 2010 PPP291:11–39.

Sztokaluk et al. MAPS54:1478-1494. 

How to cite: Losiak, A., Belcher, C., and Buchner, E.: Fossil plant remains preserved as charcoal within proximal ejecta blankets of impact craters reveal the influence of asteroid collisions with the Earth’s surface , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11609, https://doi.org/10.5194/egusphere-egu2020-11609, 2020.

EGU2020-8566 | Displays | SSP4.3

Quaternary molluscan assemblages of cold-water coral mounds: a new perspective on deep-sea ecosystem dynamics in the western Mediterranean

Chelsea Korpanty, Leon Hoffman, Jürgen Titschack, Claudia Wienberg, and Dierk Hebbeln

Cold-water corals (CWC) act as ecosystem engineers and thus contribute to biodiversity on continental margins worldwide. CWC mounds – built over geologic time by the interplay of biological, sedimentological, and oceanographic processes – create ecological niches for a variety of macrobenthic marine taxa (e.g. molluscs, sponges, bryozoans). The growth of CWC mounds is discontinuous over time due to changes in environmental and ecological conditions, such as food supply, water temperature, and dissolved oxygen concentration. While surficial distribution patterns of living and recently-dead mound macrobenthic communities have been described, their temporal ecological relationship with coral growth and mound formation is yet largely unexplored. Therefore, this project aims to determine what effects stagnations in CWC growth (i.e. repeated periods of ecosystem “turn off”) have on the local biodiversity and community structure of other CWC mound taxa, and thus what influences CWC mound development may have on regional biodiversity and biogeography in the deep sea over geologic time. Focusing on a single taxonomic group with high preservation potential, this study 1) quantitatively assesses temporal ecological trends of coral mound molluscan assemblages (bivalves and gastropods), and 2) statistically correlates those data with coral growth and palaeoceanographic records. Preliminary results from two CWC mound gravity cores through Brittlestar Ridge I in the Alboran Sea, western Mediterranean (~13.2 – 2.9 ka) indicate that throughout both cores the molluscan assemblages are typically quantitatively dominated by sessile benthic filter-feeding bivalves, particularly Heteranomia squamula and Hiatella arctica. Although bivalves are more abundant and diverse than gastropods in both cores, these taxonomic groups yield generally similar downcore dynamics in abundance and diversity. Comparisons of total molluscan assemblages (bivalves and gastropods combined) suggest that the older assemblages – those associated with the Bølling-Allerød interstadial (13.5-12.8 ka) and Early Holocene (11.3-9.8 ka) – are more similar to one another than to younger assemblages in the cores. Rotational vector fitting analyses indicate that these older assemblages are significantly related to higher productivity and different hydrodynamics (and sediment input), which are factors that have also been linked to CWC growth in the region. Altogether, our paleoecological reconstructions so far reaffirms the connectivity of benthic communities with local oceanographic conditions and adjacent taxa. Additional ecological assessments will further refine our understanding of the relationships between CWC growth and benthic communities, and in turn the temporal drivers and dynamics of CWC mound biodiversity.

How to cite: Korpanty, C., Hoffman, L., Titschack, J., Wienberg, C., and Hebbeln, D.: Quaternary molluscan assemblages of cold-water coral mounds: a new perspective on deep-sea ecosystem dynamics in the western Mediterranean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8566, https://doi.org/10.5194/egusphere-egu2020-8566, 2020.

EGU2020-20597 | Displays | SSP4.3

Multi-millennial legacy of climate change in marine plankton communities

Anne Strack, Lukas Jonkers, Marina C. Rillo, Helmut Hillebrand, and Michal Kucera

Understanding the response of marine ecosystems to climate change requires knowledge of processes that operate over long time scales. Over the last decades, abundant data have been generated on the change in the composition of marine microplankton assemblages across the last deglaciation. These data were used to reconstruct various aspects of the ocean and climate system during this climatic upheaval; however, their potential to evaluate biotic response to climatic forcing has been rarely explored. Here, we compiled records of plankton response to the last deglaciation covering the entire North Atlantic Ocean. The records comprise assemblage composition data of marine zooplankton (planktonic foraminifera) and phytoplankton (coccolithophores, diatoms and dinoflagellates) covering the last 24 ka with a resolution of at least 1 ka. The comparability of the data is ensured by using either published age models or a combination of radiocarbon ages and correlated oxygen isotope data. We use these records to first determine the shape of the major compositional change in each record by principle components analyses and quantification of compositional turnover. The mean global response of the plankton to the deglaciation was then evaluated by an Empirical Orthogonal Function analysis of the main biotic trends across all sites. A preliminary analysis was run solely on the zooplankton data set as the phytoplankton data set is still work in progress. We find that the dominant response of the zooplankton consists of synchronous unidirectional shifts initiated between 16-17 ka BP, and progressing into the Holocene. When regressed on the global ocean temperature and CO2 trends, we can see a proportionate response to the forcing during the last glacial maximum, the deglaciation and the early Holocene. In contrast, the late Holocene is characterised by continued compositional change, which does not appear related to environmental forcing. We speculate that this decoupling indicates the existence of a multi-millennial delay in community change following the climatic forcing, likely due to biotic interactions acting on communities that have been newly assembled or geographically displaced due to abiotic forcing. We will present a similar analysis for marine phytoplankton and discuss the consequences of the observations for the understanding of community variability on millennial time scales.

How to cite: Strack, A., Jonkers, L., Rillo, M. C., Hillebrand, H., and Kucera, M.: Multi-millennial legacy of climate change in marine plankton communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20597, https://doi.org/10.5194/egusphere-egu2020-20597, 2020.

EGU2020-8053 | Displays | SSP4.3

Benthic foraminifera as tracers in one of Africa's most polluted water bodies: The Lagos Lagoon (Nigeria)

Nisan Sariaslan, Olugbenga T. Fajemila, and Martin Langer

The Lagos Lagoon is among Africa’s largest estuarine ecosystems. It is bordered by one of the fastest growing megacities in the world (Lagos) and the ultimate repository of contaminants carried in industrial, municipal and agricultural wastes. The high levels of pollutants have progressively deteriorated the water quality, adversely affected marine ecosystems, impacted the livelihood of the coastal population and pose serious risks to human health. Benthic foraminifera are excellent proxies and sensitive bioindicators of environmental disturbances but comprehensive studies on the structure, distribution, diversity and impact of pollution upon foraminiferal communities have not yet been conducted. In order to demonstrate the potential of foraminifera as proxies of environmental perturbations, benthic foraminifera were investigated on a lagoon-wide basis.

Lagos Lagoon has areas that range from low levels of direct impact to severely affected by various forms of anthropogenic disturbance. The goal of this study was to elucidate foraminiferal community structure, to analyze patterns of distribution and species richness and to identify taxa that track documented records of pollution in Lagos Lagoon sediments. The sediments were analyzed for a range of physicochemical properties via a multi-parameter sensor probe-device including temperature, pH, depth and total dissolved solids (TDS) measurements. Quantitative analysis of 24 sediment samples yielded a total 3872 individuals of benthic foraminifera that belong to 42 species and 25 genera. They comprise 10 porcelaneous, 22 hyaline perforate and 10 agglutinated species. Ammobaculites aff. A. exiguus, Ammotium salsum, Ammonia tepida, Ammonia parkinsoniana and Trochammina sp. have been found to be the most abundant species.

Heat maps were generated from abundance records for selected species to illustrate environmental preferences and relative resistance levels to individual forms of anthropogenic disturbance. The features recorded allow to delineate the spatial effects of hydrocarbon and heavy metal pollutants, urban sewages, and sand dredging activities. The data generated may ultimately form the basis to assess the progressive deterioration of Lagos Lagoon environments from cores by using benthic foraminifera as bioindicators of environmental perturbation.

How to cite: Sariaslan, N., Fajemila, O. T., and Langer, M.: Benthic foraminifera as tracers in one of Africa's most polluted water bodies: The Lagos Lagoon (Nigeria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8053, https://doi.org/10.5194/egusphere-egu2020-8053, 2020.

EGU2020-8249 | Displays | SSP4.3

Recent environmental change in a marine protected area as reflected by sediment proxy data.

Irina Polovodova Asteman, Thorbjørn Joest Andersen, Torsten Linders, Kjell Nordberg, and Nicolas Van Nieuwenhove

The Koster Trench is the deepest part of the Kosterfjord (Skagerrak, North Sea), which stretches southward along the west coast of Sweden. Since 2009 Kosterfjord has been included in the Marine Protected Area Kosterhavet National Park due to the presence of cold-water coral reefs. In this study we present multiproxy data from the sediment core KSK12-01D taken in the southern part of the Koster Trench. The core has been dated by 137Cs and was subject to bulk geochemistry (TOC, C/N and heavy metals: Ni, Cu, Zn, As, Cd and Pb) and micropaleontological (benthic foraminifera, dinocysts and selected palynomorphs) analyses. Results show that the core is an archive for the environmental changes that took place between ~1988 and 2012. Both TOC and heavy metals indicate high/good to moderate ecological quality status, as defined by the Swedish Environmental Protection Agency. Dinocysts suggest a major change occurring in the upper water column around 2002. The cysts of Pentapharsodinium dalei peak around 1992 and shows overall slightly higher relative abundances between 1988 and 2002. Increased abundance of cysts produced by Protoceratium reticulatum (i.e. Operculodinium centrocarpum sensu Wall and Dale 1966), cysts produced by Biecheleria baltica and heterotrophic dinoflagellates, oligotrichids, pollen and spores characterise the upper core part deposited from 2002 to 2012. Furthermore, there is a clear increase of calcareous Alexandrium cysts in the top of the core (~2008-2012). Benthic foraminifera show a major faunal change reflected in a drastic increase of agglutinated species (mainly Textularia earlandi) from 2007 towards present day, while the lower part of the core (1988-2007) is dominated by calcareous species (Stainforthia fusiformis, Epistominella exigua, Cassidulina laevigata, Bulimina marginata andHyalinea balthica). Overall, the changes in the dataset suggest an increased freshwater input or a higher river/land runoff, as supported by a local climate and hydrography data showing increasing precipitation and particulate organic carbon in the surface waters over the time period covered by our record.

How to cite: Polovodova Asteman, I., Andersen, T. J., Linders, T., Nordberg, K., and Van Nieuwenhove, N.: Recent environmental change in a marine protected area as reflected by sediment proxy data. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8249, https://doi.org/10.5194/egusphere-egu2020-8249, 2020.

EGU2020-9500 | Displays | SSP4.3 | Highlight

Oxygen-fire-vegetation feedbacks and the distribution of Earth’s biomes

Rayanne Vitali, Claire Belcher, Jed Kaplan, Stephen Sitch, and Andrew Watson

Oxygen has varied in its abundance in the atmosphere throughout Earth’s long –term evolutionary history. Laboratory experiments have shown that fire responds rapidly to oxygen changes. Therefore it has been suggested that increases and decreases in atmospheric oxygen levels have influenced fire frequency, fire behaviour and plant evolutionary adaptations to fire.

Recent research has indicated that periods with high atmospheric oxygen, such as the Cretaceous period, which also saw the evolution of new plant groups had the coupled effect of altering fire behaviour. Such modelled fire behaviour has been able to estimate that fires during this period would have been more intense and spread more rapidly which likely fed back to changes in ecosystem dominance. However, we are lacking understanding of how oxygen driven changes in fire might feedback to influence the dominance and distribution of land-surface vegetation cover across Earth’s surface throughout Earth history.

Here I will present, a series of oxygen-fire-land cover simulations using the LPJ-LMfire Dynamic Global Vegetation Model that considers how oxygen-mediated changes in fire frequency and behaviour lead to changes in dominance of selected plant functional types within Earth’s biomes and influence the total land area covered by forest.

Our aim being to explore the coupled influence of oxygen and a climate on vegetation distributions mediated by fire throughout Earth’s past such that we can work towards understanding the balance of natural fire feedbacks to the Earth system versus human interrupted fire feedbacks in our modern day.

How to cite: Vitali, R., Belcher, C., Kaplan, J., Sitch, S., and Watson, A.: Oxygen-fire-vegetation feedbacks and the distribution of Earth’s biomes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9500, https://doi.org/10.5194/egusphere-egu2020-9500, 2020.

The Meridional Overturning Circulation is crucial in regulating Earth‘s climate and is composed of various ocean currents, playing an important role in heat exchange and the distribution of water masses. The transfer of water masses also affects regional carbon storage, nutrient contents, temperature, evaporation and precipitation balances in the oceans. The advancement in our understanding of the interaction between these water masses can contribute to our current knowledge on the state of the oceans. The use of foraminiferal isotope geochemistry and faunal analyses has greatly contributed to understanding the changes our oceans have undergone in the Quaternary. The purposes of this study are to determine what the timescales were at which the bottom water masses were changing and to determine at which periods the influence of these water masses were the strongest. A combination of neodymium and δ13C isotopes, as well as faunal abundance records in this study, were derived from foraminifera in cores recovered at 3522 m and 3631 m water depths along the western margin of South Africa to investigate deep water mass variability in the southeast Atlantic Ocean during the last two glacial terminations. The neodymium isotope composition (143Nd/144Nd), expressed as εNd, were measured in planktic foraminifera from the western continental slope of South Africa. This isotopic tracer is useful in tracking deep water masses on the sub-millennial scale owing to the short residence time of Nd in seawater. Foraminifera (single-celled protists) microfossils acquire the bottom water Nd signature upon burial that can be useful in providing insight into the variability of deep water masses. In addition to the εNd records, the foraminiferal δ¹³C results also support the results of the neodymium isotopes. These records in this study are largely correlative with the abundances of benthic species Cibicidoides wuellerstorfi, reflecting shifts between the southern-sourced Antarctic Bottom Water (AABW) and the northern-sourced North Atlantic Deep Water (NADW) during the last two glacial terminations at ~130 ka and ~18 ka. The εNd, δ¹³C results and C. wuellerstorfi relative abundances indicate an intensified inflow of southern-sourced water masses and weakened NADW inflow along the margin during peak glacial periods MIS 6 and MIS 2. The terminations of these peak glacials were more beneficial to stronger penetration of NADW into the southeast Atlantic.

How to cite: Bergh, E., Compton, J., and Zabel, M.: A combined approach in determining late Quaternary fluctuations in deep water masses derived from neodymium isotopes, faunal variations and d13C in foraminifera along the western continental slope of South Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-85, https://doi.org/10.5194/egusphere-egu2020-85, 2020.

EGU2020-2668 | Displays | SSP4.3 | Highlight

Basin-wide homogenization of soft-bottom benthic communities in the wake of anthropogenic habitat degradation in the northern Adriatic Sea

Martin Zuschin, Alexandra Haselmair, Ivo Gallmetzer, Anna Wieser, and Adam Tomasovych

We studied the origin and collapse of Holocene benthic baseline communities in the northern Adriatic Sea from sediment cores and surface grab samples at eight widely spaced sites. They cover areas with sedimentation rates spanning two orders of magnitude, with different nutrient input and with different degrees of time-averaging, ranging from decadal to millennial temporal resolution. Data from sediment cores indicate that during the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. Live-dead data from grab samples give deeper insight into the degree of anthropogenic impact in historical times. At all sites the living assemblages differ strongly from the death assemblages. At some sites from oligotrophic settings with low sedimentation rates, a total overturn in the community composition is obvious: formerly abundant species have disappeared completely, while the living assemblage is numerically dominated by species that were not present before. Even at sites, which are characterized by physically stressful conditions (i.e., high sedimentation rates in the Po delta), some species that were abundant in the death assemblage have totally disappeared from the living assemblage. Comparison with the dataset from sediment cores documents the recent establishment of an impoverished community, which has no analogue in the Holocene history of the northern Adriatic Sea.

How to cite: Zuschin, M., Haselmair, A., Gallmetzer, I., Wieser, A., and Tomasovych, A.: Basin-wide homogenization of soft-bottom benthic communities in the wake of anthropogenic habitat degradation in the northern Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2668, https://doi.org/10.5194/egusphere-egu2020-2668, 2020.

EGU2020-13783 | Displays | SSP4.3 | Highlight

Climate change driven massive extirpation of native species from the Israeli Mediterranean shelf

Paolo G. Albano, Jan Steger, Marija Bošnjak, Beata Dunne, Zara Guifarro, Elina Turapova, Bella Galil, Gil Rilov, and Martin Zuschin

We quantify a large-scale extirpation of native species from the Israeli Mediterranean shelf, a region strongly affected by rapidly changing environmental conditions and the introduction of non-indigenous species, based on an extensive sampling programme of mollusks on intertidal to subtidal soft and hard substrata. We reconstruct historical species richness from shelly death assemblages, quantify the time range they cover with radiocarbon dating, and compare their richness with today’s living assemblage diversity. The median native richness is 50% of the historical richness for the intertidal, but only 8% for the subtidal down to 40 m. Samples from the mesophotic zone show a much higher median of 42%, which is likely an underestimation due to sampling constraints. In contrast, non-indigenous species show assemblages matching the historical richness. Seasonality is very strong: autumn samples, after the summer heat peak, are highly impoverished in native species but enriched in non-indigenous ones. Additionally, a comparison between today’s and historical native species maximum size shows that shallow subtidal native populations are mostly non-reproductive. In contrast, non-indigenous species reach reproductive size. These results suggest that a recent large-scale change in environmental conditions is strongly favoring non-indigenous species and is the main cause behind the shallow subtidal native species decline. Such an environmental factor is likely seawater temperature that plays a greater role in the shallow subtidal than in the cooler mesophotic zone, and affects subtidal species more than intertidal ones, pre-adapted to a climatically extreme environment.

How to cite: Albano, P. G., Steger, J., Bošnjak, M., Dunne, B., Guifarro, Z., Turapova, E., Galil, B., Rilov, G., and Zuschin, M.: Climate change driven massive extirpation of native species from the Israeli Mediterranean shelf , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13783, https://doi.org/10.5194/egusphere-egu2020-13783, 2020.

EGU2020-2095 | Displays | SSP4.3 | Highlight

Forms of life on Early Earth as model for Exoplanets?

Karin Moelling

The recent discovery of exoplanets with putative habitable zones which may be as frequent as 1025 stimulate the interest in the origin of life on the exoplanets but also on the Earl Earth (EE). Meteorites and missions to Mars or Moon teach us about their composition, and make us think about the origin of life in general. Prebiotic molecules such as amino acids, nucleosides, and fullerenes arrived from extraterrestric space and cyanobacteria and archaea are inhabitants of the EE. They exhibit properties such as protein synthesis, which requires advanced machineries adapted to our Earth. What could be early precursors of such mechanisms. What kind of life can we envision in its simplest form? Molecules which can replicate, mutate, and evolve are signatures of life.

The simplest such biomolecules on Earth may be non-protein-coding (nc)RNA catalytic RNA, the ribozymes and viroids, which can fulfill many protein functions, including replication, evolution, and are a prerequisite for peptide synthesis. Ribozymes/viroids can evolve to higher complexity. Archaea and bacteria resemble giant viruses suggesting a continuous transition from dead to living matter. Archaea are extremophiles which revolutionalized our view on what life can be like in respect to environmental conditions and specialized metabolic pathways. Some exotic spots on Earth can teach us about other habitable zones. Meteorites help to understand chemical compositions on other planets and the consequences for life. During evolution loss and gain of of genetic information are important evolutionary driving forces. Viroids  are discussed as models for potentially other forms of life. Simulators of Mars environment are under study to determine possible effects on biological sepcimens.

Ref: Broecker and Moelling Geosciences (2019), Annals NY Acad Sci. (2019), Frontiers Microbiol (2019). Book: Moelling:Viruses more friends than foes World Scientific Press ( 2017)

 

 

How to cite: Moelling, K.: Forms of life on Early Earth as model for Exoplanets?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2095, https://doi.org/10.5194/egusphere-egu2020-2095, 2020.

EGU2020-2558 | Displays | SSP4.3

The Devonian plant revolution and its role in multiple marine extinction crises

David Bond and Charlotte Stephenson

The Devonian was one of the most dynamic periods in Earth history, with major changes on land and in the oceans that experienced at least two of the ten most severe biotic crises of the Phanerozoic. The Period saw the first extensive global floral record; prior to the Devonian, plant assemblages were low in diversity and abundance, and were restricted to areas close to water sources with little competition from co-existing taxa. By the end, plants were geographically widespread in diverse environments. Their colonisation of the land surface has been implicated in the Frasnian/Famennian marine crisis, but little is known of the effects of plants on the global biosphere during the rest of the Devonian. Synthesis of 389 publications reporting 294 Devonian plant genera has resulted in a database that we analyse at generic and stage level for trends in Devonian plant evolution and extinction. Our analysis reveals several key events within this dynamic phase of terrestrialisation: 1) an early Euramerican presence for all plant groups, suggesting this region may have been the site of origination for several higher taxa; 2) the origination of lycopsids in equatorial settings was followed by latitudinal migration northward and southward; 3) a major turnover in plants between the Late Givetian and Middle Frasnian, when significant diversity losses occurred in every palaeo-region in every extant plant group – this may be a hitherto unidentified terrestrial extinction event that coincided with one or both of the Taghanic and Frasne minor marine crises; 4) several Devonian marine black shale events coincide with major steps in terrestrialisation suggestive of a causal link and supporting the notion that plant evolution played a significant role in the Frasnian/Famennian mass extinction nexus.

How to cite: Bond, D. and Stephenson, C.: The Devonian plant revolution and its role in multiple marine extinction crises, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2558, https://doi.org/10.5194/egusphere-egu2020-2558, 2020.

EGU2020-8044 | Displays | SSP4.3

The clams before the storms: the fate of bivalve diversity during times of crisis

Katie Collins, Stewart Edie, and David Jablonski

Of all the macrofossil groups, bivalves (clams, scallops, oysters and mussels) have perhaps the best global record. Known from the Cambrian, bivalves have survived every mass extinction and climate perturbation the planet has suffered. Many of the ~90 living families of bivalves with a fossil record have roots that stretch back to the Paleozoic.

This lineage longevity makes bivalves an ideal model group for studying biodiversity responses to changing climate – families have been separate for a long time, and their varied ecological roles and habitats means that the effects of climate on different biogeographic regions and ways of making a living can be teased apart. The abundance of bivalves in marine and freshwater deposits provides large specimen-level datasets for analysing survivorship across climate-event boundaries, such as the Paleocene-Eocene Thermal Maximum, a major warming event, or the end-Pliocene cooling. Bivalves have been shown to be a good proxy for much of marine benthic biodiversity, and they can give us insights into questions such as: is biodiversity response to climate perturbation predictable? What species and lineages are at risk, and can we identify them?

Not only can bivalves help us track effects of climate changes of the past thanks to their rich fossil record; they may also be a major player in human efforts towards our own future climate resilience. Bivalves today provide food for many millions of people worldwide, both in artisanal and commercial fisheries, and perform vital ecosystems services, such as water filtration, sequestration of carbon, and as both food and habitat for many other animals of all sizes. Increased aquaculture of molluscs has been postulated as a way to take more of the burden of feeding the world’s population off the terrestrial realm, and without the adverse effects of finfish farming.

This talk will discuss patterns and fluctuations of bivalve diversity through time, focusing on predictive models for survivorship across major climate transitions in the Cenozoic, and using the past behaviour of species and clades to look ahead to potential marine diversity responses to projected climate scenarios.

How to cite: Collins, K., Edie, S., and Jablonski, D.: The clams before the storms: the fate of bivalve diversity during times of crisis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8044, https://doi.org/10.5194/egusphere-egu2020-8044, 2020.

EGU2020-1318 | Displays | SSP4.3 | Jean Baptiste Lamarck Medal Lecture

The early origin of feathers

Michael Benton

Feathers are a diagnostic character of birds, and yet new fossils show they likely originated more than 100 million years before the first birds. In fact, feathers probably occurred in all dinosaur groups, and in their cousins, the pterosaurs, as we showed in 2019. This finding confirms current knowledge of the genomic regulation of feather development. Our work stems from ten years of collaboration with Chinese colleagues, during which we set ourselves the taks of understanding fossil feathers. Our first discovery was to answer the question, ‘Will we ever know the colour of dinosaurs?’. In 2010, we were able to announce the first objective evidence for colour in a dinosaur. Using ultrastructural studies of fossil feathers, we identified melanosomes for the first time in dinosaur feathers, and these demonstrated that Sinosauropteryx had ginger and white rings down its tail. Studies of other dinosaurs identified patterns of black, white, grey, brown, and ginger. This is part of a new wave in palaeobiology where we apply objective approaches to provide testable hypotheses, once thought impossible in the historical sciences.

How to cite: Benton, M.: The early origin of feathers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1318, https://doi.org/10.5194/egusphere-egu2020-1318, 2020.

EGU2020-21629 | Displays | SSP4.3

The sabkhas of Qatar: modern analogues for studying early life on Earth and on Mars

Tomaso Bontognali, Franziska Blattmann, Zulfa Al Disi, Hamad Al Saad Al Kuwari, Zach DiLoreto, Maria Dittrich, Jean-Luc Josset, Nikolaus Kuhn, Judith McKenzie, Fadhil Sadooni, and Kenneth Williford

The study of early life on Earth and the search for life on Mars often includes investigations of modern analogues: natural environments that share similarities to what we hypothesize may have existed on the early Earth and early Mars. The study of modern analogues provides key information on how biosignatures are formed and preserved, which is essential for interpreting the geological record. Research conducted in recent years in various modern sabkhas located along the coast of Qatar have demonstrated that these extreme evaporitic environments represent an inspirational gold mine for the field of geobiology and astrobiology.

The intertidal zones of the Qatari sabkhas are typically colonized by microbial mats. Their presence leads to the formation of Microbially Influenced Sedimentary Structures (MISS). Examples of studied MISS include polygonal, domical, blistered, tufted and crinkled microbial mats. We discuss biological vs. physiochemical factors responsible for their formation, as well as their fossilization potential. These MISS often occur in a precise sequence along a transect from the lower to the upper intertidal zone. We propose that a MISS sequence represents a stronger morphological biosignature than a single MISS. The community composition of some of the studied mats revealed an uppermost layer dominated by anoxygenic phototrophs. We propose that such mats represent a particularly good analogue for studying life in the Early Archean, a time when the cyanobacteria that usually dominate the uppermost photo-oxic layer of most modern mats probably did not exist.

Besides influencing sediment morphology, the extracellular polymeric substances (EPS) constituting the mats serve as nucleation sites for the precipitation of authigenic minerals. Among these possible precipitates, our research focused on microbially influenced Mg-rich carbonates and Mg-rich silicates. Linking these minerals to a microbial process is of particular interest in view of the forthcoming rover missions to Mars (i.e., ExoMars and Mars 2020). Indeed, orbital spectral analyses revealed the presence of Mg-rich clays and Mg-rich carbonates in the surroundings of the proposed landing sites. It will be exciting to test the hypothesis that, on Mars, some of these minerals may have formed at low temperatures from liquid water and may, therefore, represent a target phase for the investigation of biosignatures.

How to cite: Bontognali, T., Blattmann, F., Al Disi, Z., Al Saad Al Kuwari, H., DiLoreto, Z., Dittrich, M., Josset, J.-L., Kuhn, N., McKenzie, J., Sadooni, F., and Williford, K.: The sabkhas of Qatar: modern analogues for studying early life on Earth and on Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21629, https://doi.org/10.5194/egusphere-egu2020-21629, 2020.

We present the initial data on the distribution of benthic foraminifera (BF) on East Siberian Sea shelf. Previous researchers analyzed BF in the sediment cores from the continental slope and basin areas of the East Siberian Sea (Wollenburg et al., 2000; Mackensen et al, 2014; Barrientos et al, 2018) but not from central shelf. Last year we received boxcorer samples of bottom sediments from the shelf of the East Siberian Sea and the Laptev Sea during the 78th cruise of research vessel Akademik Mstislav Keldysh (September-October 2019). We examined the species composition of BF assemblages of Rose Bengal-stained surface samples from 2 stations in the East Siberian Sea and 7 stations in the Laptev Sea, and compared this data set with an existing data set along the East Siberian Sea and the Laptev Sea.

Recent studies (Shakhova et al, 2007, 2009, 2015; Nicolsky et al, 2009) state that the East Siberian Sea is one of the largest sources of methane emission into the atmosphere due to degradation of permafrost, ice complex retreat and decaying gas hydrates deposits. Perhaps this has an impact on the species composition of the BF assemblages and the morphological changes and defects of their shells, which we have identified. Samples from active methane seeps of the Laptev Sea have been studied to identify the relationship between methane emission and the reaction of benthic foraminifera. This data have been compared with “background” (i.e. non-venting, without any methane seeps activity) stations of the Laptev Sea and the East Siberian Sea.

The identified features require further detailed study.

How to cite: Tikhonova, A. and Merenkova, S.: The modern assemblages of benthic foraminifers of the East Siberian Sea initial and active methane seeps zones of the Laptev Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1337, https://doi.org/10.5194/egusphere-egu2020-1337, 2020.

EGU2020-2977 | Displays | SSP4.3

Environment, diversity, evolution and Cope's Rule: Drivers of size in planktonic foraminifera.

Heather Birch, Daniela N. Schmidt, Chloe Todd, Marci M. Robinson, and Andy Fraass

Within the marine fossil record, size is a fundamental trait providing information on both assemblages and individual species. Changes in size within an assemblage are largely driven by species composition typically related to environmental conditions. Changes in size of an individual species can be an indicator of health and whether optimal growth conditions (i.e. temperature, salinity and food availability) prevail. Over evolutionary timescales, individuals tend to increase in size (Cope’s rule) also altering the average size of the population.

The Pliocene provides an excellent opportunity to look at environmental drivers and ecological responses to a warmer world, at high resolution and with extant species. A short glaciation phase, during marine isotope stage (MIS) M2, interrupted the Pliocene global warming between ~ 3.31 – 3.26 Ma. This event provides the ideal framework to quantify how biota, already adapted to warming conditions, respond to a short, but substantial cooling event. 

We analysed the size and species composition of samples collected as part of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project from a variety of locations around the globe. The samples cover the Atlantic, Indian and Pacific oceans at a range of latitudes (e.g. DSDP Site 521, 586, 607 and ODP Site 716, 754, 887). We measured the maximum diameter of planktonic foraminifera tests with a fully automated light microscope, enabling high resolution sampling at a multitude of sites, before, during and after the MIS M2 glaciation event. On average 2000 specimens were measured per sample, resulting in over a million analyses in total. Changes in planktonic foraminiferal assemblage composition were characterised by quantifying relative species abundances and augmented by determining the largest species.

Planktonic foraminiferal assemblage size shows a general increase during the Pliocene likely related to warming temperatures. What is unclear is if this change is driven by changes in diversity due to extinction and origination, responses to environmental change or a general increase in size of species found through the record. Here we discuss reactions of species and (or) ecological groups to environmental change and determine the individual drivers of size change across the world’s oceans.

How to cite: Birch, H., Schmidt, D. N., Todd, C., Robinson, M. M., and Fraass, A.: Environment, diversity, evolution and Cope's Rule: Drivers of size in planktonic foraminifera., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2977, https://doi.org/10.5194/egusphere-egu2020-2977, 2020.

Salt-marsh foraminifera are routinely used as sea-level indicators since their vertical distribution is closely linked with elevation relative to the tidal frame. In this study, 106 surface sediment samples were collected across separate intertidal transects established at five micro-tidal salt-marsh situated along the coasts of the Jiaozhou Bay, western margin of the Yellow Sea, dead and live foraminifera were identified respectively. The dead population contains the mixture of both subtidal species and salt-marsh species, and all the live assemblages consist of salt-marsh species which can provide exact information of salt-marsh foraminiferal distribution. The agglutinated species present in the five marshes including Trochammina inflata, Miliammina fusca and Jadammina macrecens are all cosmopolitan species, however, the calcareous species contain numbers of endemic species, overall, dominant calcareous species included Cribrononion porisuturalis, Pseudononionella variabilis, Elphidiella kiangsuensis and Pseudogyroidina sinensis. Vertical foraminifera zonations have been recognized in Daguhe and Hongshiya marsh samples with some species occupying strict latitude range, which primarily related to elevation, however, no obvious assemblages zonations can be recognized in Nvgukou, Shanjiaodi and Yanghe marsh. We hypothesize that salt-marsh foraminifera in Jiaozhou Bay possesses potential in paleoenvironmental studies as the key indicators for monitoring Holocene sea-level and environmental changes.

How to cite: Long, H. and Li, Z.: Distribution of Salt-marsh foraminifera in Jiaozhou Bay: Implications for sea-level reconstructions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10354, https://doi.org/10.5194/egusphere-egu2020-10354, 2020.

EGU2020-10598 | Displays | SSP4.3

Substrate temperature as a primary control on meiofaunal populations in the intertidal zone of the Arabian Gulf: a persistent kill zone linked to elevated temperature

Michael Kaminski, Abduljamiu Amao, Lamidi Babalola, Thomas Garrison, Fabrizio Frontalini, and Bassam Tawabini

In recent years the popular press has asked the question whether the sea surface temperatures in the Arabian Gulf are becoming too hot to sustain animal life. According to a climate modal published by Pal and Eltahir (2016), the hottest temperatures in the Arabian Gulf are likely to be seen in the area between Doha (Qatar) and Dhahran (Saudi Arabia). In order address this question, we are gathering baseline annual temperature data at several nearshore locations in Bahrain and Saudi Arabia. We measured seawater temperatures and substrate temperatures in the intertidal zone during the hottest time of the year at a lagoon in Askar, Bahrain. For the purpose of this study, we concentrated our attention on an exposed tidal flat that has a southward-facing slope. We additionally observed the distribution and behavior of marine benthic organisms in the intertidal zone. We repeated our observations every two weeks during the 2019 summer-autumn season.

The intertidal mudflat in Murray’s Pool south of Askar (Bahrain) experiences summer temperatures in excess of 52°C at low tide on a hot summer afternoon. A “kill zone” with regard to meiofauna is observed on the mudflat where sediment temperature rises above ca. 40°C. In summer, a community of living foraminifera, gastropods, ostracods and diverse worms is only present in the tidal channels that contain water at low tide. Living foraminifera in the tidal channel mainly consist of the genera Ammonia, Peneroplis, and smaller miliolids. In the summer-autumn season of 2019, “summer” conditions persisted until the end of October. Temperatures below 40° were finally observed on the mudflat the first week of November. At this time, living juvenile Peneroplis specimens were observed on the surface of the mudflat. The site is currently being monitored on a bi-weekly basis to determine the length of the growing season.

We conclude that the intertidal faunas in Murray’s Pool are thermally stressed, and the higher intertidal areas are already too hot to sustain benthic marine life during the summer-autumn season. This finding is in line with predictions of climate models, which foresee that portions of the Arabian Gulf will become too hot to sustain animal life in the next decades.

How to cite: Kaminski, M., Amao, A., Babalola, L., Garrison, T., Frontalini, F., and Tawabini, B.: Substrate temperature as a primary control on meiofaunal populations in the intertidal zone of the Arabian Gulf: a persistent kill zone linked to elevated temperature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10598, https://doi.org/10.5194/egusphere-egu2020-10598, 2020.

EGU2020-12381 | Displays | SSP4.3

Benthic foraminifera distribution and diversity in inner and outer lagoonal sediments of the UAE (United Arab Emirates)

Flavia Fiorini, Stephen W. Lokier, Yuzhu Ge, Chelsea L. Pederson, and Adrian Immenhauser

Live and dead benthic foraminifera assemblages were studied from 50 samples collected in a lagoon located between Yas Island and Ras al Gurhab Island (UAE) in a system dominated by carbonate sedimentation.

Living and dead foraminifera tests are present at all of the sampled locations. The foraminifera assemblage is dominated by a high diversity of miliolidae together with epiphytic larger benthic foraminifera belonging to the genera Peneroplis, Spirolina and Sorites. Hyaline foraminifera, such as Ammonia and Elphidium, are commonly found at all the locations while agglutinated foraminifera are uncommon and have a scattered occurrence.

The abundance and diversity of benthic foraminifera were calculated for each sample. Four benthic foraminifera ecological indices were applied to the studied samples. For each of the samples we calculated: the total foraminiferal number (number of foraminifera in 1 g of sediment >125 μm); the percentages of agglutinated, porcellaneous and hyaline foraminifera tests; the ratio between living and dead benthic foraminifera; the ratio between larger benthic foraminifera with normal and abnormal test growth. The above-mentioned data have been applied to construct a foraminiferal assemblage database that facilitates the discrimination between inner and outer lagoonal environments.

How to cite: Fiorini, F., Lokier, S. W., Ge, Y., Pederson, C. L., and Immenhauser, A.: Benthic foraminifera distribution and diversity in inner and outer lagoonal sediments of the UAE (United Arab Emirates), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12381, https://doi.org/10.5194/egusphere-egu2020-12381, 2020.

EGU2020-17668 | Displays | SSP4.3

The relevance of epilithic foraminifera in ecological studies

Julia Wukovits, Jutta Wollenburg, Gernot Nehrke, Nicolaas Glock, Petra Heinz, and Alexandra-Sophie Roy

This study aims to emphasize the ecological importance of foraminifera contained within the > 1000 µm sediment fraction. Stones and gravel offer a habitat for diverse and rich epilithic foraminiferal communities. However, gravel-rich sediments > 1000 µm are usually not the subject of quantitative benthic foraminifera studies, because most foraminifera species used as proxies or bioindicators are sediment-dwelling and found within smaller sediment size fractions. Therefore, there is a current lack of knowledge about the biology and ecology of epilithic foraminifera, specifically about agglutinated species.

During a cruise at the Gullmarfjord/Sweden in September 2018, we retrieved a core at a station at 7 m water depth, which contained organic-rich material and a relatively large portion of gravel and shell fragments, which were densely populated by monothalamus, agglutinated foraminifera.

A faunal analysis of foraminifera in the > 1000 µm sediment fraction showed, that the most abundant species (> 85 %, 54 ind. 10 cm-3) in > 1000 µm consisted of Tholosina vesicularis, an unicellular agglutinated species that can reach up to 4 mm diameter. SEM-analysis revealed, that large quantities of partially decomposed diatom frustules were embedded within the protoplasm of T. vesicularis individuals, which were supposedly the remains of the foraminiferal diet. The sediment fraction of 125 - 1000 µm was dominated by Ammonia species (58 %, 190 ind. 10 cm-3), a genus known for its fast turnover of diatom-derived carbon and as key-players in benthic nutrient fluxes. Preliminary biovolume analysis of the two genera (T. vesicularis: n = 74, Ammonia spp.: n = 110) resulted in far higher values for T. vesicularis (853 ± 944 µm-3 10 cm-3, med. = 506 µm-3 10 cm-3), than for Ammonia spp. (117 ± 56 µm-3 10 cm-3, med. = 96 µm-3 10 cm-3), within the uppermost sediment layer of 0 - 1 cm. Therefore, T. vesicularis could be a main driver of benthic carbon turnover in gravel-dominated sediments. We hypothesize, that the epilithic fauna, when present is at least as relevant as sediment-dwelling species.

Additionally, biodiversity indices (species diversity, Shannon-Index, Evenness), show a slightly higher diversity and a more even distribution within the softer substrate, compared to the stones.

This is most likely due to the motility of the free-living forms of the smaller size fraction, which allows them a flexible response to spacial competition. However, niche separation between hard and soft-substrate allows the co-existence of the opportunistic species T. vesicularis and Ammonia spp..

In conclusion, this study shows, that if present, the > 1000 µm fraction can contain important information for the interpretation of ecological studies on the communities of live foraminifera and their role in marine ecosystems.

How to cite: Wukovits, J., Wollenburg, J., Nehrke, G., Glock, N., Heinz, P., and Roy, A.-S.: The relevance of epilithic foraminifera in ecological studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17668, https://doi.org/10.5194/egusphere-egu2020-17668, 2020.

EGU2020-18244 | Displays | SSP4.3

Distribution of benthic foraminifera upstream of the Elbe Estuary (Northern Europe): ecological interactions

Fabio Francescangeli, Yvonne Milker, Eric Armynot du Châtelet, and Gerhard Schmiedl

Estuaries are transitional ecotones influenced by both marine and terrestrial (fresh) waters. For the past 200 years, estuarine environments experienced intense and rapid environmental degradations due to anthropogenic action (e.g., urban sewage, industry, aquaculture, and agricultural runoff). The distribution of benthic foraminifera in estuarine areas is the result of complex interactions between a large number of biotic and abiotic parameters. The natural stress (such as variation in salinity, sediment size, organic load) may be associated to anthropogenic stresses, enhancing the high natural variability of these areas. The objectives of the present work are to describe the specific composition of benthic foraminifera and to investigate their ecological interactions upstream of the Elbe Estuary (Germany). In this important estuarine area, there is a lack of a comprehensive investigation in terms of benthic foraminifera. So far, the ecology of living benthic foraminifera has not been studied in greater detail and it is largely unknown which species occur in this transitional area. For this purpose, a surface sampling was carried out from 24 stations along the salinity gradient of the Elbe Estuary. Living and dead foraminiferal assemblages were analyzed and the relative correlation with environmental parameters (such as salinity, pH, temperature, sediment size, organic matter) was investigated. Living assemblages are characterized by very low densities and largely dominated by “Ammonia” group. Dead assemblages are more diverse and dominated by estuarine taxa (Ammonia aomoriensis, Haynesina germanica, and Cribroelphidium selseyense). Upstream of the estuarine area, the low salinity prevents the development of living benthic foraminifera while downstream, sediment grain size seems to be a major key-factor, influencing foraminiferal distributions. This work sheds new light on benthic foraminiferal ecology and biodiversity of this important estuarine area of Northern Europe.

How to cite: Francescangeli, F., Milker, Y., Armynot du Châtelet, E., and Schmiedl, G.: Distribution of benthic foraminifera upstream of the Elbe Estuary (Northern Europe): ecological interactions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18244, https://doi.org/10.5194/egusphere-egu2020-18244, 2020.

The study explored an end-to-end application of a ResNet convolutional neural network (transfer learning) to classify benthic foraminifera images using the FastAI library. 201 SEM images of 13 benthic foraminifera including Ammonia convexa, Ammonia tepida, Asterorotalia gaimardi,  Asterorotalia indica, Bulimina biserialis, Bulimina marginatta, Elphidium advenum, Elphidium hispidium, Elphidium jenseni, Elphidium neosimplex , Perenoplis arianus , Perenoplis pertusus and Quinqueloculina sp. The images were separated into two groups in a 80 -20 split for training and validation dataset respectively. We successfully trained a state-of-the-art image classifier for a very small dataset, achieving 96.5% accuracy in just a handful of lines of code on a very small dataset i.e. accurately predicting the binomial nomenclature of species. The fastai AI/Machine learning library we used offers interesting prospects in taxonomy where it can be used for multilabel image classification. Fastai’s recent research breakthroughs are embedded in the library, resulting in significantly improved accuracy and speed over other deep learning libraries, whilst requiring dramatically less code. The library sits on top of PyTorch and provides a single consistent API to the most important deep learning applications and data types. It also offers an opportunity to a novice user, new to data science to apply state of the art deep learning to practical problems quickly and reliably. It has several advantages over other known libraries is its flexibility to import data of various kind and from various sources. It is fast, has a large and friendly community backing and its immune to several limitation of other libraries.

How to cite: Amao, A. O. and Kaminski, M.: Multi-labelled taxonomic prediction using a small benthic foraminifera dataset trained on a FastAi library, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21465, https://doi.org/10.5194/egusphere-egu2020-21465, 2020.

EGU2020-21576 | Displays | SSP4.3

Dominant dextral to sinistral coiling change in planktic foraminifera Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean

Valeria Luciani, Roberta D'Onofrio, Wade Bridget S., and Dickens Jerry R.

Coiling direction is a basic characteristic of trochospiral planktic foraminifera. However, although modifications in the coiling direction within ancient planktic foraminiferal populations may reflect important changes in evolution or environment, they remain scarcely discussed. Here we present data on fluctuations in the coiling direction within morphologically defined Morozovella species from successions that span the interval of peak Cenozoic warmth, the Early Eocene Climatic Optimum (EECO; ~53-49 Ma). We selected three widely separated Ocean Drilling Program (ODP) sites in the Atlantic Ocean: the subtropical Site 1051, the equatorial Site 1258 and the temperate south Atlantic Site 1263. The surface-dwelling genus Morozovella is of particular interest because it dominated tropical-subtropical early Paleogene assemblages and  suffered an abrupt and permanent decline in abundance and taxonomic diversity at the start of the EECO. At all ODP sites investigated, morozovellids display a dominant dextral coiling preference during the interval preceding the EECO. However, all species became at all sites prevailing sinistral within the EECO. Specifically, the switch from dominant dextral to sinistral coiling occurred at all sites ~ 300 Kyr after the K/X event (~52.8 Ma). The coiling switch occurred ~550 kyr to ~650 kyr after a distinct drop in abundance. We provide therefore evidence of a coiling variation during the warmest interval of the early Paleogene. Our records highlight that the recorded coiling variations might provide a biostratigraphic tool for correlation of early Eocene marine strata. In order to establish whether this coiling switch was related to changes in morozovellid ecological niche we estimated stable carbon isotopes on dextral and sinistral species from samples located below and above the recorded coiling change. Results suggest that sinistral species moved higher in the mixed-layer after the coiling switch. It is thus possible that only species sinistrally coiled were able to keep the optimal environmental conditions for their survivorship. We need however more effort to understand the meaning of these modifications, such to verify whether variations in sea surface temperature or other parameters directly corresponded to the coiling change. Coiling switches can relate to ecophenotypic adaption (when a single species changes morphology in response to variation in environmental parameters, such as temperature) or genetic variance (when two almost identical morphotypes have different genetic signatures so they represent ‘cryptic’ species from a morphological point of view). Previous interpretations of coiling flips in planktic foraminifera in the early Eocene, especially including morozovellids, have favoured a genetic explanation rather than an ecological response. Our present data cannot validate or disprove this idea, but should stimulate renewed thought on the matter.

How to cite: Luciani, V., D'Onofrio, R., Bridget S., W., and Jerry R., D.: Dominant dextral to sinistral coiling change in planktic foraminifera Morozovella during the Early Eocene Climatic Optimum in the Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21576, https://doi.org/10.5194/egusphere-egu2020-21576, 2020.

The Mariana forearc system represents the only known currently active serpentine mud volcanism in a convergent margin setting. Here, International Ocean Discovery Program (IODP) Expedition 366 recovered material from three serpentinite mud volcanoes at increasing distances from the Mariana trench subduction zone along a south-to-north transect: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). Cores contain serpentinite mud with lithic clasts from the subducting Pacific Plate, forearc crust and mantle. Furthermore, at almost all drilled sites, a thin cover of pelagic sediment containing planktic and benthic foraminifera, calcareous nannofossils, radiolaria and sponge spicules was recovered, constraining the most recent mud volcano activity. The base of the seamounts overlies pelagic sediment and volcanic ash/tephra layers which establish a maximum age for the mud activity. Additionally, separate serpentinite mud flows are intercalated by distinct sedimentary layers.

Integrated biostratigraphy, based on planktonic foraminifera and calcareous nannofossils, is used to assess the minimum and maximum age of mud flow activity and of the distinct sedimentary layers and serpentinite mud flow layers. Biostratigraphic information will also provide time indications on lower plate dehydration and serpentinization of the forearc wedge. Preliminary results from Fantangisña seamount (Site U1497 and U1498) reveal the existence of biostratigraphic marker species for both planktonic foraminifera and calcareous nannofossils. Specifically, the presence of Globigerinella calida, Globorotalia flexuosa, Globorotalia truncatulinoides, Globorotalia tumida, Sphaeroidinella dehiscens (amongst planktic foraminifera) and Gephyrocapsa spp., Pseudoemiliania lacunosa, Reticulofenestra asanoi, Discoaster deflandrei, Discoaster variabilis (amongst calcareous nannofossils) allow a possible age assessment from Late Pleistocene to Late Miocene.

Planktonic assemblages are dominated by (sub)tropical Globigerinoides forms such as G. conglobatus, G. ruber, G. elongatus, G. sacculifer, G. trilobus. Other common (sub)tropical species detected are G. menardii, and O. universa, whereas G. siphonifera, N. dutertrei, S. dehiscens and P. obliquiloculata are less common.

Benthic foraminifera are less abundant but show high diversity. Forms of Lagena, Cibicidoides, Fissurina, Ehrenbergina, Gyroidina, Melonis, Pullenia, Osangularia, Favulina, Reophax, Rhabdammina, Saccorhiza, and Hormosinella are present. To the best of our knowledge, the occurrence of benthic forms in such environments is highly unusual and has not been recorded in detail so far.

Quantitative and statistical analyses on foraminifera assemblages will provide information on water column and bottom water conditions. Moreover, a detailed comparison between assemblages pre- and post-volcanism may reflect possible changes in the ecological conditions.

Collected data will not only allow to constrain in time the evolution of submarine volcanoes in the Mariana convergent system but also to investigate foraminifera ecology in such an extreme environment.

 

How to cite: Del Gaudio, A. V., Piller, W. E., Auer, G., Grunert, P., and Kurz, W.: Micropaleontological proxies as tool to date serpentinite mud volcanisms and seamount subduction and to reconstruct paleoenvironmental conditions in the Mariana convergent margin system (IODP Expedition 366), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7139, https://doi.org/10.5194/egusphere-egu2020-7139, 2020.

EGU2020-7365 | Displays | SSP4.3

Evolution of plant terpenoids on a ‘biotic ferry’

Suryendu Dutta

Palaeogegraphic model suggests that the Indian plate was separated from Gondwana during Late Jurassic and started moving towards the northern hemisphere during the Early Cretaceous and remained as an island continent during the entire Cretaceous until it collided with Asia in Early Eocene at ca. 50 Ma.  It is believed that many vertebrate groups may have originated in India or other Gondwanan land masses and were carried on the rafting Indian plate and finally dispersed ‘out of India’ following the collision between India and Asia. However, the evolution of plants on the rafting continent is poorly documented.

 

A brief outline on evolution of plant terpenoids from Permian to Eocene on the Indian continent will be discussed during the presentation. The Permian coals are characterized by tricyclic and teracyclic diterpenoids. The possible source of these compounds is extinct seed ferns.

The molecular composition of Jurassic and early Cretaceous coals and sediments suggests that the vegetation was contributed by conifers (e.g. Arucariaceace, Podocarpaceae) during the period. Aromatic triterpenoids derived from angiosperms are detected in the sediments of Late Maastrichtian age. Drastic reduction of coniferous vegetation and proliferation of angiosperms in early Palaeogene are observed in the present study. The terpenoid signatures of early Palaeogene lignites suggest that the western India was covered by widespread thick closed rain forests dominated by family Dipterocarpaceae thriving under the influence of tropical climate.

How to cite: Dutta, S.: Evolution of plant terpenoids on a ‘biotic ferry’, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7365, https://doi.org/10.5194/egusphere-egu2020-7365, 2020.

EGU2020-18997 | Displays | SSP4.3

Molecular signatures of kerogens and bitumens from the Lower Devonian Rhynie chert: Insights into the botanical affinity of the earliest land plants

Anuradha Tewari, Kevin Lepot, Suryendu Dutta, Borja Cascales-Miñana, and Armelle Riboulleau

The Lower Devonian Rhynie chert of Scotland is an iconic geological formation that preserves the earliest known terrestrial ecosystem. This assemblage contains key evidence of earliest lineages of land plants, e.g., protracheophytes and paratracheophytes (former Rhyniaceae), together with animals, fungi, algae, and bacteria (Edwards et al., 2017). The exquisite preservation of this early biota provides an ideal scenario to explore the basal evolution of the land biosphere.

The Rhynie chert has been vastly studied from multiple viewpoints, however, the biomolecular composition, i.e., “molecular signature”, of the Rhynie flora, including the early detection of fossil lignin, remains clearly unresolved. Lignin biosynthesis has been considered as one of the crucial influences behind the survival and proliferation of land plants in terrestrial ecosystems. Here, we characterize the molecular fossils to help decipher the botanical affinities of the Rhynie flora.

Kerogens were isolated by the standard HF/HCl extraction procedure, and bitumens were extracted from the kerogens using organic solvents. The bitumens were studied with GC-MS, and the kerogens were analysed using Py-GC-MS and Py-GC×GC–TOFMS in the presence of TMAH reagent. The bitumens are characterized mainly by some aliphatic compounds such as a series of n-alkanes, pristane, phytane, and a series of diterpanes in very low abundance, as well as a set of aromatic compounds such as naphthalene and methylnaphthalenes, phenanthrene and methylphenanthrenes and retene. The pyrolysates, obtained using Py-GC-MS are dominated by benzene and methyl benzenes, phenol and methylphenols, Polycyclic Aromatic Hydrocarbons (PAHs) like naphthalene and methylnaphthalenes, phenanthrene and methylphenanthrenes, anthracene and methylanthracene, fluoranthene, pyrene, etc. Series of fatty acid methyl esters (FAME) and of n-alkane/alkene doublets were also detected. The thermochemolysates acquired from Py-GC×GC–TOFMS include the same compounds; additional methoxybenzene derivatives, methoxy toluene, methoxy benzaldehydes, and benzoic acid methyl esters, generated by reaction with TMAH, were also identified. Phenols and methoxybenzenes in the pyrolysates and thermochemolysates originate from lignin, and this is the first time that lignin monomers are formally identified from Rhynie chert samples.

References:

Edwards, D., Kenrick, P., Dolan, L., 2017. History and contemporary significance of the Rhynie cherts—our earliest preserved terrestrial ecosystem. Philosophical Transactions B Royal Society 373: 20160489.

How to cite: Tewari, A., Lepot, K., Dutta, S., Cascales-Miñana, B., and Riboulleau, A.: Molecular signatures of kerogens and bitumens from the Lower Devonian Rhynie chert: Insights into the botanical affinity of the earliest land plants, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18997, https://doi.org/10.5194/egusphere-egu2020-18997, 2020.

EGU2020-20732 | Displays | SSP4.3

Land plants and terrestrial environmental changes during the onset of the end-Triassic event

Sofie Lindström, Hans Peter Nytoft, Gunver K. Pedersen, Grzegorz Niedzwiedzki, Karen Dybkjær, Leif Johansson, Henrik I. Petersen, Hamed Sanei, Christian Tegner, and Rikke Weibel

The end-Triassic mass extinction is considered to have been caused by voluminous and repeated emissions of CO2 and/or methane and other gases from magmatic activity in the Central Atlantic Magmatic Province. Despite improved geochronological dating and correlation between the magmatic activity and the extinctions, exactly how the biotic crisis commenced remains poorly understood. Here, we compile palynological and palaeobotanical data, bulk organic δ13C, biomarkers, mercury and other geochemical proxies, charcoal, and sedimentology, from a Rhaetian terrestrial succession in southern Sweden. Our results provide an insight into the climatic, environmental and ecosystem changes that took place at the onset of the mass extinction event.

How to cite: Lindström, S., Nytoft, H. P., Pedersen, G. K., Niedzwiedzki, G., Dybkjær, K., Johansson, L., Petersen, H. I., Sanei, H., Tegner, C., and Weibel, R.: Land plants and terrestrial environmental changes during the onset of the end-Triassic event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20732, https://doi.org/10.5194/egusphere-egu2020-20732, 2020.

Samples of detrital lignite have been collected for organic geochemical and carbon isotope analyses from the First Lusatian lignite seam at the Adamów, Jóźwin IIB and TomisÅ‚awice opencast mines, deposited after the last peak of the Mid-Miocene Climatic Optimum. The aim of the study is to improve the chemotaxonomic value of biomarkers by relating the results to existing paleobotanical data, and to gain information about the influencing factors on δ13C of lignite and lipids. Furthermore, biomarker and isotopic proxies are tested for their applicability in paleoclimate studies.

The relative abundances of mid-chain (C23, C25) n-alkanes and their 1–2‰ higher δ13C values compared to long-chain n-alkanes (C29, C31) argue for a minor contribution of macrophytes (graminoids, etc.) to peat formation, enhanced during periods of raised water level. The presence of ferruginol and dehydroferruginol testifies the contribution of taxodioid Cupressaceae. The abundances of pimarane-type diterpenoids and the presence of non-aromatic abietane-derivatives argue for the contribution of Pinaceae. Based on the presence of lupeol and lupane-type triterpenoids, an input of Betulaceae can be concluded. The contribution of further angiosperms cannot be specified based on the composition of pentacyclic triterpenoids. However, the results indicate mixed vegetation, and are in agreement with paleobotanical data highlighting abundant conifers of the Cupressaceae and Pinaceae families, as well as angiosperms of various families (e.g., Nyssa, Quercus, Fagus), including Betulaceae (e.g., Alnus, Betula, Corylus). Based on the relationship between the carbon preference index of n-alkanes and mean annual air temperatures, obtained from a global database of peatlands, an average temperature of 24.5 °C is obtained. This value is significantly higher as estimated from paleobotanical data (15.7–19.7 °C), probably due to the influence of changes in vegetation on carbon preference index.

The relative abundances of diterpenoids versus di- plus angiosperm-derived triterpenoids in detrital lignite samples revealed variable contributions of gymnosperms and angiosperms during the middle Miocene. Consistent with these results, a positive relationship exists between the di-/(di- + tri-) terpenoid biomarker ratios and δ13C of lignite samples, indicating the dominating role of varying gymnosperm/angiosperm contributions on the carbon isotopic composition of lignite. The C-isotope data of long-chain n-alkanes, diterpenoids, and angiosperm-derived triterpenoids co-vary within the profiles, arguing for an overall control of changes in δ13C of atmospheric CO2 on δ13C of plant lipids. Fluctuations in δ13C of individual compounds may also be related to changes in carbon cycling within the peat, humidity and air temperature.

How to cite: Bechtel, A., Widera, M., and Woszczyk, M.: Composition of lipids from the First Lusatian lignite seam of the Konin Basin (Poland): relations to vegetation, climate and carbon cycling during the mid-Miocene Climatic Optimum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15, https://doi.org/10.5194/egusphere-egu2020-15, 2020.

EGU2020-7615 | Displays | SSP4.3

Testing for the effects of depositional rates in multiproxy models of environmental and faunal change: the Silurian Lau δ13C excursion

Emilia Jarochowska, Madleen Grohganz, Niklas Hohmann, Axel Munnecke, and Theresa Nohl

The Silurian is characterized by several extinction events, among them the late Ludfordian Lau event, which mainly affected conodont and graptolite communities. This event was followed by the strongest global positive δ13C excursion of the Phanerozoic. This event has been first recognized in the classical succession in Gotland, Sweden, where a continuous increase in δ13C values of up to nearly 9 ‰ from the upper När Formation to the Eke Formation is observed. It has been attributed to large scale carbon cycle perturbations. This time period is also characterized by a regression and associated changes in sedimentation and deposition rates. This raises the question to what extent these factors contribute to the observed changes in faunal diversity and geochemical proxies.

A mechanism linking changes in seawater chemistry and the faunal turnover has been proposed based on a high abundance of malformed acritarchs observed during the onset phase of some Phanerozoic isotope excursions including the Lau isotope excursion. Malformations during the late Silurian Pridoli event coincide with a significant increase in trace metal content measured in fossils and host rock, which suggests the teratology to be caused by metal pollution. However, also in the case on an increase in the trace metal content the contribution of changing depositional rates has not been quantified.  

Models developed in the field of stratigraphic paleobiology have demonstrated that changing deposition rates have a substantial influence on the stratigraphic distribution of fossils. In the same sense, element concentrations can be altered by changing deposition rates, which may dilute or condense the primary element signal. For this study, concentrations of different trace elements were measured across a profile in an outcrop Bodudd (Gotland) which exposes the Lau isotope excursion from the upper När to the Eke Formation. Using a newly developed statistical method, the effects of changing deposition rates were quantified and the measured element signal corrected for these effects. This method uses a deposition model to transform the measured element signal, which is a function of the stratigraphic height in the outcrop, back into a temporal rate. The temporal rate reflects the primary element signal and is defined as a function of time instead of stratigraphic height. Thus, the effect of changing deposition rates is accounted for. Approximate deposition models were created based on Th concentrations measured across the profile, which act as a proxy for the rate of terrestrial input, and based on the chitinozoan yield, which reflects deposition rates. Pre- and post-transformation element patterns were compared for different deposition models and evaluated with respect to their ability to preserve element peaks.

How to cite: Jarochowska, E., Grohganz, M., Hohmann, N., Munnecke, A., and Nohl, T.: Testing for the effects of depositional rates in multiproxy models of environmental and faunal change: the Silurian Lau δ13C excursion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7615, https://doi.org/10.5194/egusphere-egu2020-7615, 2020.

EGU2020-11698 | Displays | SSP4.3

Time averaging and stratigraphic unmixing: reconstructing ecological decline in molluscan production (Holocene, Brijuni, NE Adriatic)

Adam Tomašových, Martin Zuschin, Ivo Gallmetzer, and Alexandra Haselmair

The northeastern Adriatic seafloor is formed by warm-temperate bioclastic carbonates with coralline algae, bryozoans and mollusks. These sediments represent a mixture of past and present-day production owing to low sedimentation rates and bioturbation. Although low sedimentation rates do not allow resolution of ecological history at centennial or even millennial scales on the basis of raw stratigraphic data, age unmixing based on radiocarbon-calibrated amino acid racemization shows that one of the major molluscan sediment producers – the infaunal suspension-feeder Timoclea ovata  – markedly peaked in production ~5,000 years during the maximum flooding and earliest highstand phase and significantly diminished in abundance during the late highstand phase at Brijuni, with a large proportion of dead shells now present in surface sediments representing shells that are several centuries old. This species still occurs in living assemblages but our analyses indicate that its former production was by several orders of magnitude higher. In contrast, stratigraphic trends in absolute and proportional abundance of this species in ~1.5 m-thick sediment cores show a gradual or a very mild upcore decline, indicating that raw stratigraphic data do not efficiently detect millennial-scale ecological dynamic. The temporal decline in production of Timoclea ovata is associated with an increase in water depth and an increase in sediment-accumulation rate, and led to a transition from molluscan oyster-scallop shell bed to late highstand bryomol sediments.

How to cite: Tomašových, A., Zuschin, M., Gallmetzer, I., and Haselmair, A.: Time averaging and stratigraphic unmixing: reconstructing ecological decline in molluscan production (Holocene, Brijuni, NE Adriatic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11698, https://doi.org/10.5194/egusphere-egu2020-11698, 2020.

EGU2020-7320 | Displays | SSP4.3

Linking macrobenthic fauna and seismic facies to improve stratigraphic reconstructions: the case of the Mid Adriatic Depression since the late glacial period (Central Adriatic Sea)

Michele Azzarone, Daniele Scarponi, Giulia Barbieri, Veronica Rossi, Claudio Pellegrini, Fabiano Gamberi, and Fabio Trincardi

Direct observations from the geologic record are commonly used in conjunction with indirect seismo-stratigraphic inferences to detail environmental settings and stratal architecture of sedimentary successions. However, examples of integration between seismic facies and macrobenthic insights are scarce and limited to the use of such a group as auxiliary to other proxies. This case study investigated mollusc and ostracod dynamics along an onshore-offshore profile that intersects the C2 clinothem (15.6 – 14.4 ky BP) of the Po River Lowstand Wedge (PRLW) and the overlying transgressive deposits formed in the central Adriatic Sea. Multivariate analyses were applied to benthic data to assess to what extent mollusc and ostracod assemblages can improve the resolution of seismic-derived depositional environments and stratigraphic architecture of cored succession. Along the profile of the C2 clinothem, seismic reflection facies correspond with three sedimentary environments. Specifically, i) High Amplitude Continuous reflections (HAC) are interpreted as delta plain/subaqueous shelf; ii) High Amplitude Continuous Wavy Dipping reflections (HACWDip) characterize prodelta deposits, and iii) Low Amplitude Continuous reflections (LAC) are associated with distal basin settings. The integration of quantitative palaeoecologic trends with the seismic-derived depositional environments allowed the subdivision of the HAC facies into a proximal (core LSD-26) and a distal (cores LSD-27 and -28) area. In particular, the proximal area with HAC seismic facies encompasses semi-barred lower delta plain with vegetated substrates that evolves to more open, nearshore settings. Conversely, the distal area with HAC seismic facies is distinguished by clusters reminiscent of ecological mixing due to strong bioturbation and gravity flows in offshore transition/inner shelf settings. The paucity of benthic fauna for the units with HACWDip (core LSD-05) and LAC (core LSD-04) seismic facies, hampered a complete reconstruction of the palaeoenvironmental dynamics. However, both benthic groups investigated support the seismic-derived interpretation of shelf and basinal settings respectively, both subjected to high sedimentation rates. Moreover, the integration of mollusc and ostracod multivariate-derived trends with grain-size data across the study profile reveals distinctive stratal stacking patterns useful in constraining the position of key stratigraphic surfaces such as the Maximum Regressive Surface that marks the initial phase of the abandonment of the PRLW.

How to cite: Azzarone, M., Scarponi, D., Barbieri, G., Rossi, V., Pellegrini, C., Gamberi, F., and Trincardi, F.: Linking macrobenthic fauna and seismic facies to improve stratigraphic reconstructions: the case of the Mid Adriatic Depression since the late glacial period (Central Adriatic Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7320, https://doi.org/10.5194/egusphere-egu2020-7320, 2020.

EGU2020-7572 | Displays | SSP4.3

Major environmental and ecological shifts in late Holocene marine sediments of the NW Adriatic Sea

Michaela Berensmeier, Adam Tomašových, and Zuschin Martin

Sediments of the NW Adriatic Sea preserve important information about environmental changes during the Holocene and due to recent anthropogenic impact. This study is based on new data of a 3-m-long gravity core taken from 31 m water depth. Large environmental and ecological shifts are indicated by changes in geochemistry (XRF core scanning data, geochemical bulk analyses) and molluscan composition, particularly in the uppermost decimeters.

Sedimentologically, the record can be divided into 4 facies types: (1) laminated silty sediments with some sands, terrestrial plant remains, and scarce mollusc shells (at 175-300 cm sediment depth), (2) bioturbated silty, fine-sandy sediments with terrestrial plant remains, scarce mollusc shells, and calcirhizomes (70-175 cm), (3) strongly bioturbated, clayey silt with increasing abundance in mollusc shells (20-70 cm), and (4) clayey silt with a peak in molluscan shell abundances and diversity, with abundant bivalves (Corbula gibba) and gastropods (Turritellinella tricarinata, 0-20 cm).

Corbula gibba valves were used for C14-calibrated amino acid racemization (AAR) analyses of valves. The resulting shell ages show a bisection in the record: (1) an uppermost, surface-mixed layer with very young shells (median age = 50 years) and (2) an age-homogeneous composition down to 30 cm sediment depth (median age = 3000 years). This downcore shift in age distributions probably indicates that the 20th century shells of Corbula gibba are not mixed beyond 10 cm. This pattern implies decreasing bioturbation and increasing sedimentation in the study area in the 20th century.

How to cite: Berensmeier, M., Tomašových, A., and Martin, Z.: Major environmental and ecological shifts in late Holocene marine sediments of the NW Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7572, https://doi.org/10.5194/egusphere-egu2020-7572, 2020.

EGU2020-17636 | Displays | SSP4.3

Response of benthic species to post-glacial sea-level rise on the northern Adriatic shelf revealed by stratigraphic unmixing of fossil assemblages

Rafał Nawrot, Daniele Scarponi, Adam Tomašových, and Michał Kowalewski

Late Quaternary fossil record offers a window into ecosystem dynamics during episodes of abrupt climate warming and sea-level rise following the Last Glacial Maximum, but in marine settings ecological inferences might be hindered by high time-averaging affecting transgressive deposits. However, the signature of temporal shifts in local skeletal production rates may be preserved in the age-frequency distributions (AFDs) of death assemblages. We use carbonate-target radiocarbon ages of 191 shells to examined variation in AFDs among four bivalves species collected from a 2.3-meter-long core recording the post-glacial transgression on the northern Adriatic shelf over the last the last ~14,500 yr.

The scale of time-averaging within species (interquartile age range) varied from 200 to 7,400 yrs, while the between-species age offsets (differences between the median ages of species) ranged from ~2 to 6,400 yrs within 5-cm-thick core intervals. Although the median ages of Varicorbula, Timoclea and Parvicardium increased with increasing burial depth, shells of Lentidium appeared age-homogeneous throughout the core. Age unmixing revealed a single massive peaks in the abundance of this opportunistic, shoreface species around 14 cal ka BP, coincident with the initial marine flooding of this shelf area during the melt-water pulse 1A. Moreover, a prominent gap in the AFDs between 11 and 12.5 cal ka BP corresponds to a minor sea-level fall associated with the Younger Dryas cold spell. Importantly, the reconstructed onsets and durations of shell production pulses across the four species are consistent with independently-derived relative sea-level history at the site. The species gradually replaced each other through time as the dominant component of the assemblage in accordance with their bathymetric preferences estimated from surveys of the modern Adriatic benthic fauna.

The diachronous production histories of four bivalve species coupled with subsequent exhumation of old shells and burial of younger shells through bioturbation and sediment reworking resulted in the ecologically mixed fossil assemblages. These assemblages are thus characterized by multi-modal age distribution and millennial-scale age offsets between species co-occurring in the same stratigraphic increments. Although this stratigraphic homogenization and disorder greatly limits the resolution of the raw stratigraphic record, our results demonstrate the power of AFDs to capture shifts in abundance of benthic species during recent episodes of rapid sea-level rise. Fossil assemblages from transgressive deposits preserved on continental shelves represent a rich and underutilized source of data on long-term biotic responses to global climate change and associated shifts in sea level.

How to cite: Nawrot, R., Scarponi, D., Tomašových, A., and Kowalewski, M.: Response of benthic species to post-glacial sea-level rise on the northern Adriatic shelf revealed by stratigraphic unmixing of fossil assemblages, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17636, https://doi.org/10.5194/egusphere-egu2020-17636, 2020.

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