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Information about macroevolutionary history, past biodiversity, ecology, biogeochemical cycles, climate and environmental change is enclosed in the sedimentary rock record. This information can be extracted with traditional palaeontological, sedimentological and geochemical techniques. Nonetheless, preservation, diagenesis, erosion, sea-level changes, sampling strategies, and analytical approaches can distort this information and introduce biases in the reconstructions of past Earth processes. This problem has gained wider recognition with respect to palaeontological patterns, particularly in the field of stratigraphic palaeobiology addressing the impact of the sequence-stratigraphic architecture on fossil data. However, similar aspects can as well alter geochemical proxy records. For example, diagenetic trajectories specific to certain lithologies can dictate stratigraphic patterns in stable and radiogenic isotope as well as (trace) elemental composition. Hence, approaches that correct for these artifacts in palaeontological, sedimentological and geochemical time series might share many commonalities. We invite contributions that use frequentist statistics, Bayesian statistics, mechanistic models, and machine learning to tackle these problems across different timescales and disciplines, ranging from the Precambrian up to the Holocene, and which contribute to a holistic understanding of the Earth system.

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The geological information, obtained through traditional palaeontological, sedimentological and geochemical techniques, is often taken at face value. There is little doubt, that there is valuable information about evolutionary history, past biodiversity, ecology, biogeochemical cycles, climate and environmental change is enclosed in the sedimentary rock record. However, preservation, diagenesis, erosion, sea-level changes, sampling strategies, and analytical approaches can distort this information and introduce biases in the reconstructions of past Earth processes. This problem has gained wider recognition with respect to palaeontological patterns, particularly in the field of stratigraphic palaeobiology addressing the impact of the sequence-stratigraphic architecture on fossil data, as well geochemical proxy records. For example, diagenetic trajectories specific to certain lithologies can dictate stratigraphic patterns in stable and radiogenic isotope as well as (trace) elemental composition. Hence, quantitative approaches that correct for these artifacts in palaeontological, sedimentological and geochemical time series might share many commonalities. We herein highlight novel developments, which can greatly contribute to a more holistic understanding of the earth system. Examples range from the Paleozoic up to the Holocene.

This is a short description of how we will handle our session chat. We have allocated at least 4 minutes of time to discuss individual contributions after a brief introduction (5 minutes). We will finish our session with an open discussion (min. 25 min) allowing for more questions for individual talks (if necessary) as well as more general remarks on topics related with our session.

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Convener: Kenneth De Baets | Co-conveners: Emilia JarochowskaECSECS, Martin SchobbenECSECS, Melanie TietjeECSECS
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| Mon, 04 May, 08:30–10:15 (CEST)

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Chat time: Monday, 4 May 2020, 08:30–10:15

Chairperson: Kenneth De Baets, Emilia Jarochowska, Martin Schobben, Melanie Tietje
D1040 |
EGU2020-832
| solicited
| Highlight
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.

D1041 |
EGU2020-126
| Highlight
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.

D1042 |
EGU2020-1049
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).

D1043 |
EGU2020-3456
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.

D1044 |
EGU2020-5799
| Highlight
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:

  1. A drop of overall regional biodiversity of the Mediterranean due to environmental stress during the Messinian.
  2. A taxonomic and functional change between the Tortonian, Messinian, and the Zanclean, that is before and after the MSC, as well as during the precursor events to that actual crisis taking place after the Tortonian/Messinian boundary.
  3. The onset of the present-day west-to-east decreasing gradient in species richness, which has been related to the sea temperature and productivity gradients and the distance from the Gibraltar connection to the Atlantic.
D1045 |
EGU2020-7099
| Highlight
Adam Tomašových, Susan M. Kidwell, and Ran Dai

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.

D1046 |
EGU2020-9795
Silvia Danise, Steven Holland, and Gregory Price

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.

D1047 |
EGU2020-22640
| solicited
Michał Jakubowicz and Krzysztof Hryniewicz

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.

D1048 |
EGU2020-20678
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.

D1049 |
EGU2020-650
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.

D1050 |
EGU2020-950
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.

D1051 |
EGU2020-1057
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.

D1052 |
EGU2020-21707
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.

D1053 |
EGU2020-9349
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). 

 

D1054 |
EGU2020-7245
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.

D1055 |
EGU2020-7873
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.

D1056 |
EGU2020-7994
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.

D1057 |
EGU2020-9271
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.

D1058 |
EGU2020-10213
| Highlight
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.

D1059 |
EGU2020-22300
Anna Lene Claussen, Axel Munnecke, and Andrej Ernst

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.

D1060 |
EGU2020-22617
| Highlight
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.