Displays

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.

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.

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.

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.

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.