Record of the Toarcian oceanic anoxic event in the Grands Causses Basin (southern France) and its implications for vertebrate preservation

Paleontological excavations realized by our group in Toarcian shales (Lower Jurassic) of the Grands Causses Basin in Roqueredonde (H&#233;rault, France), yielded several specimens of marine vertebrates. The newly discovered specimens are partly or entirely preserved in anatomical connection and include a partial ichthyosaur skeleton with soft tissues, and a 4&#160;m-long thalattosuchian longirostrine marine crocodile. A multi-proxy approach has been developed (XRD-bulk and clay mineralogy, Rock-Eval pyrolysis, phosphorus and mercury contents) in order to replace these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The fossiliferous succession exposes a 3&#160;m-thick upper Pliensbachian interval of marl and nodular carbonate beds, overlain by a 3&#160;m-thick interval of lower Toarcian laminated shales and limestone beds. Our high-resolution ammonite biostratigraphy, combined with inorganic and organic carbon isotope chemostratigraphy, shows that the fossiliferous Toarcian strata were deposited at a time of global warming and major carbon cycle perturbation known as the Toarcian Oceanic Anoxic Event (T-OAE). The studied succession shows several similarities with the classical coeval fossiliferous levels of the Posidonia Shale in SW Germany, including high organic matter and hydrocarbon contents as well as extremely reduced sedimentation rates. These results indicate that the unusual richness in well-preserved vertebrates of the studied site can be explained by a combination of warming-induced, low salinity and stratified waters, prolonged seafloor anoxia and reduced dilution by low carbonate and terrigenous input due to rapid sea-level rise. Our results also reveal a significant peak in mercury at the base of the T-OAE interval, consistent with that recorded in several coeval sections (e.g. Portugal, Morocco, Argentina, Chile). This mercury anomaly, most likely resulting from intense volcanic activity Karoo-Ferrar large igneous province, suggests that widespread exceptional vertebrate preservation during the T-OAE was initiated by a suite of severe environmental perturbations ultimately triggered by intense volcanic emissions.

Download Full-text

Global controls on phosphatization of fossils during the toarcian oceanic anoxic event

Scientific Reports ◽

10.1038/s41598-021-03482-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Sinjini Sinha ◽

A. D. Muscente ◽

James D. Schiffbauer ◽

Matt Williams ◽

Günter Schweigert ◽

...

Keyword(s):

Lower Jurassic ◽

X Ray ◽

Oceanic Anoxic Event ◽

Exceptional Preservation ◽

Level Change ◽

Environmental Controls ◽

Anoxic Basins ◽

Anoxic Event ◽

Anoxic Events ◽

Posidonia Shale

AbstractKonservat-Lagerstätten—deposits with exceptionally preserved fossils—vary in abundance across geographic and stratigraphic space due to paleoenvironmental heterogeneity. While oceanic anoxic events (OAEs) may have promoted preservation of marine lagerstätten, the environmental controls on their taphonomy remain unclear. Here, we provide new data on the mineralization of fossils in three Lower Jurassic Lagerstätten—Strawberry Bank (UK), Ya Ha Tinda (Canada), and Posidonia Shale (Germany) —and test the hypothesis that they were preserved under similar conditions. Biostratigraphy indicates that all three Lagerstätten were deposited during the Toarcian OAE (TOAE), and scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) show that each deposit contains a variety of taxa preserved as phosphatized skeletons and tissues. Thus, despite their geographic and paleoenvironmental differences, all of these Lagerstätten were deposited in settings conducive to phosphatization, indicating that the TOAE fostered exceptional preservation in marine settings around the world. Phosphatization may have been fueled by phosphate delivery from climatically-driven sea level change and continental weathering, with anoxic basins acting as phosphorus traps.

Download Full-text

Effects of the early Toarcian Oceanic Anoxic Event on ichthyosaur body size and faunal composition in the Southwest German Basin

Paleobiology ◽

10.1017/pab.2015.34 ◽

2015 ◽

Vol 42 (1) ◽

pp. 117-126 ◽

Cited By ~ 9

Author(s):

Erin E. Maxwell ◽

Peggy Vincent

Keyword(s):

Body Size ◽

Environmental Changes ◽

Marine Invertebrates ◽

Abundant Species ◽

Extinction Rate ◽

Oceanic Anoxic Event ◽

Environmental Perturbations ◽

Anoxic Event ◽

Posidonia Shale ◽

German Basin

AbstractThe Early Jurassic Toarcian Oceanic Anoxic Event is considered one of the most dramatic environmental perturbations of the Mesozoic. An elevated extinction rate among marine invertebrates accompanied rapid environmental changes, but effects on large vertebrates are less understood. We examined changes in ichthyosaur body size in the Posidonia Shale of the Southwest German Basin spanning the extinction interval to assess how environmental changes and biotic crisis among prey species affected large reptiles. We report no species-level extinction among the ichthyosaurs coinciding with peak invertebrate extinction. Large ichthyosaurs were absent from the fauna during the extinction interval, but became more abundant in the immediate aftermath.Stenopterygius quadriscissus, the most abundant species during the extinction interval, increased in body size after the biotic event. Rapid invasion by large taxa occurred immediately following the extinction event at the end of the first ammonite zone of the early Toarcian. Greater mobility permitting exploitation of ephemeral resources and opportunistic feeding behavior may minimize the impacts of environmental change on large vertebrates.

Download Full-text

The chemostratigraphy and environmental significance of the Marlstone and Junction Bed (Beacon Limestone, Toarcian, Lower Jurassic, Dorset, UK)

Geological Magazine ◽

10.1017/s0016756821000972 ◽

2021 ◽

pp. 1-15

Author(s):

Hugh C. Jenkyns ◽

Sophie Macfarlane

Keyword(s):

Carbon Isotope ◽

Oxygen Isotopes ◽

Lower Jurassic ◽

Carbon And Oxygen Isotopes ◽

Oceanic Anoxic Event ◽

Nodular Limestone ◽

Anoxic Event ◽

Reference Curves ◽

High Degree ◽

Organic Rich Sediment

Abstract Two fallen blocks of the Marlstone and stratigraphically overlying Junction Bed sampled on the beach below Doghouse Cliff in Dorset, UK (Wessex Basin) have been examined for carbon and oxygen isotopes of bulk carbonate as well as for strontium, carbon and oxygen isotopes and Mg:Ca ratios in the contained belemnites. The sequence, which contains most of the Toarcian zones and subzones within a metre or less of grey to yellow to pink, red and brown fossil-rich nodular limestone, is extremely condensed and lithologically similar to pelagic red limestones of the Tethyan Jurassic that are locally mineralized with Fe-Mn oxyhydroxides (e.g., Rosso Ammonitico). Strontium-isotope ratios of the contained belemnites are compatible with existing reference curves and both blocks show a rise to more radiogenic values post-dating the Pliensbachian–Toarcian boundary. The high degree of correlation between the relatively negative carbon and oxygen isotopes of the bulk carbonate is compatible with significant diagenetic overprint, and contrasts with higher carbon-isotope values in coeval condensed coccolith-rich limestones elsewhere. Evidence for the characteristic signature of the Toarcian Oceanic Anoxic Event, as represented by organic-rich sediment, is absent, possibly owing to a stratigraphic gap. Both blocks exhibit abrupt carbon-isotope shifts to lower values, one of which could represent the limbs of an incompletely recorded negative excursion associated with the Toarcian Oceanic Anoxic Event. That the Toarcian Oceanic Anoxic Event was also a significant hyperthermal is illustrated in both blocks by a drop in oxygen-isotope values and rise in Mg:Ca ratios of belemnites close to the base of the Junction Bed in the lowest part of the serpentinum zone.

Download Full-text

Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events

American Journal of Science ◽

10.2475/08.2018.01 ◽

2018 ◽

Vol 318 (8) ◽

pp. 799-860 ◽

Cited By ~ 32

Author(s):

Lawrence M.E. Percival ◽

Hugh C. Jenkyns ◽

Tamsin A. Mather ◽

Alexander J. Dickson ◽

Sietske J. Batenburg ◽

...

Keyword(s):

Large Igneous Province ◽

Oceanic Anoxic Event ◽

Igneous Province ◽

Oceanic Anoxic Event 2 ◽

Anoxic Event ◽

Mercury Cycle

Download Full-text

Major palaeoenvironmental upheavals in both marine and terrestrial realms during the Toarcian oceanic anoxic event: a multi-proxy approach

10.5194/egusphere-egu2020-21187 ◽

2020 ◽

Author(s):

Francesca Galasso ◽

Susanne FeistBurkhardt ◽

Annette Schmid- Röhl ◽

Stefano Benasconi ◽

Elke Schneebeli-Hermann

Keyword(s):

Carbon Isotope ◽

Seawater Temperature ◽

Black Shales ◽

Land Plants ◽

Open Pit ◽

Large Igneous Province ◽

Isotopic Study ◽

Data Set ◽

Oceanic Anoxic Event ◽

Anoxic Event

The Toarcian oceanic anoxic event (TOAE) ~183 Ma is not only associated with oceanic anoxia and rapid seawater temperature increase but also with a marine mass extinction event. These biotic and environmental upheavals are linked to the emplacement of the Karoo-Ferrar large igneous province. Negative carbon excursions and widespread deposition of black shales are typical for Toarcian sedimentary successions.The occurrence and growth of dinoflagellates is influenced by environmental factors like oxygen content, salinity, temperature and nutrient availability. For land plants, changes in dominance structure of ecosystems reflected in spore pollen assemblages can be indicative of ecological disturbance. Thus species composition (and morphology) of dinoflagellates and land plants can be used to understand major environmental perturbations.An extensively studied TOAE section is the former Rohrbach Zement quarry at Dotternhausen (today Larfarge-Holcim) with comprehensive data of carbon isotope analyses, total organic and inorganic carbon content and rock eval analysis. The Dotternhausen quarry is not accessible anymore but a new open pit in Dormettingen ~2 km NW of Dotternhausen offers excellent outcrop conditions. Litho- and biostratigraphy of the new section is well documented and calibrated to the old Dotternhausen section on subzone levels. Comparison of the two sites showed that sedimentology, geochemistry and faunal data are laterally constant. Palynological analysis of 59 outcrop samples from the Dormettingen section yielded an excellent quantitative data set of the Early Toarcian Posidonienschiefer sediments. Here we provide a high-resolution, multi-proxy study of this section including chemostratigraphy, particulate organic matter and palynology in order to understand the environmental conditions during the TOAE.Carbon isotopic study reveals a negative excursion during the TOAE, varying between -33.49&#8240; and -26.5&#8240;, with a negative shift in the Falciferum Zone (Elengatum, Exeratum and Elegans Subzone) concurrent with the dinoflagellate "blackout". &#160;The vegetation shows significant changes from a mixed assemblage of pollen and spores in the lower part of the section, to exclusively spore-bearing during the negative carbon isotope excursion. The isotopic signal, the marine dinoflagellate &#8220;blackout&#8221; and the changes in terrestrial vegetation indicate/document major palaeoenvironmental upheavals in both the marine and terrestrial realms.

Download Full-text

Quantifying the volcanic emissions which triggered Oceanic Anoxic Event 1a and their effect on ocean acidification

Sedimentology ◽

10.1111/sed.12335 ◽

2016 ◽

Vol 64 (1) ◽

pp. 204-214 ◽

Cited By ~ 10

Author(s):

Kohen W. Bauer ◽

Richard E. Zeebe ◽

Ulrich G. Wortmann

Keyword(s):

Ocean Acidification ◽

Volcanic Emissions ◽

Oceanic Anoxic Event ◽

Anoxic Event

Download Full-text

Biostratigraphic constraints of the Early Toarcian Oceanic Anoxic Event: new data from calcareous nannofossil investigations of Boreal and Tethyan sections

10.7287/peerj.preprints.27999 ◽

2019 ◽

Author(s):

Stefano Visentin ◽

Elisabetta Erba ◽

Joerg Mutterlose

Keyword(s):

Calcareous Nannofossil ◽

Northern Germany ◽

Lower Saxony ◽

Oceanic Anoxic Event ◽

Anoxic Event ◽

First Occurrence ◽

Calcareous Nannofossil Biostratigraphy ◽

Posidonia Shale ◽

Boreal Realm ◽

Interval Expression

Calcareous nannofossil biostratigraphy was carried out in Upper Pliensbachian – Lower Toarcian sediments, which cover the Toarcian Oceanic Anoxic Event (T-OAE) interval. In particular, semiquantitative analyses were performed on a total of 156 samples in the composite Sogno Core (Lombardy Basin, Southern Alps) representing a pelagic Tethyan section. Quantitative investigations were applied to additional 168 samples across the Amaltheenton Fm. and Posidonienschiefer Fm., from two cores of the Boreal Realm (Lower Saxony Basin, northern Germany). Primary and secondary events of the Tethyan and Boreal zonations were recognized, allowing the identifications of the NJT5, NJT6 nannofossil Zones for the Sogno Core and the NJ5, NJ6, NJ7 Zones for the German sections, respectively. The sequence of nannofossil biohorizons is generally consistent with data available for various areas at lower and higher latitudes, confirming their reproducibility and reliability for intra and inter-regional correlations. Geochemistry evidences the presence of the negative C isotopic excursion across the “Fish Level” black shale interval expression of the T-OAE in the Sogno Core. The same anomaly is recorded in the German successions at the base of the Posidonia Shale witnessing the passage from well oxygenated to predominantly anoxic conditions. Our results show that the T-OAE C isotopic excursion recorded in the Sogno Core is excellently constrained by the first occurrence (FO) of Carinolithus superbus at the onset and the last occurrence (LO) of Mitrolithus jansae at the end. A significant decrease in abundance and size of Schizosphaerella punctulata (the “S. punctulata crisis”) and an abundance drop of M. jansae further characterise the T-OAE perturbation. Only S. punctulata shows a recovery at the end of the T-OAE, while M. jansae barely survived the palaeoenviromental stress and disappeared soon after its termination. The extreme rareness of S. punctulata and the absence of M. jansae in the Boreal Realm prevent the recognition of the “S. punctulata crisis” and the M. jansae decline. Our study reveals the LO of Biscutum finchii together with the FO of C. superbus as an additional event approximating the onset of the C isotopic excursion exclusively in the German successions. Further events, such as the LOs of Biscutum grandis, Crepidolithus granulatus and Parhabdolithus liasicus are detected within the C isotopic anomaly exclusively in the German sections. Nannofossil biostratigraphy permits the effective dating and correlating of Early Jurassic major palaeoceanographic events and particularly of the T-OAE which are of a great importance to derive a definitive model for the Posidonia Shale deposition.

Download Full-text

The early Toarcian extinction event and associated Pliensbachian-Toarcian palaeoenvironmental perturbations in Bulgaria

10.7287/peerj.preprints.27948 ◽

2019 ◽

Author(s):

Autumn Pugh ◽

Crispin TS Little ◽

Ivan P Savov ◽

Lubomir Metodiev ◽

Paul B Wignall ◽

...

Keyword(s):

Carbon Isotope ◽

Oxygen Deficiency ◽

Lower Jurassic ◽

Significant Loss ◽

Large Igneous Province ◽

Driving Mechanism ◽

Oceanic Anoxic Event ◽

Biotic Crisis ◽

Marine Realm ◽

Balkan Mountains

The Early Toarcian was characterised by the eruption of the Karoo-Ferrar large igneous province (LIP), rapid global warming, significant perturbations in the global carbon cycle, the development of widespread anoxia known as the Early Toarcian Oceanic Anoxic Event (T-OAE) and a biotic crisis in the marine realm known as the Early Toarcian Mass Extinction (ETME). Despite the purported global nature of these environmental and biotic changes, the majority of records come from Western European sections, and remain particularly focused on settings in which the T-OAE was clearly expressed. Fewer studies focus on sections where the manifestation of ocean deoxygenation appears to have been considerably weaker, or even absent. We herein focus on Lower Jurassic successions of the Moesian Basin in the Balkan Mountains of the Balkan Mountains (Bulgaria) that were deposited on an open-ocean facing carbonate shelf. The Bulgarian δ13C and δ18O profiles show similar trends through the Lower Jurassic to coeval European sections, suggesting that seawater in the Moesian Basin was recording global palaeoclimatic and palaeoceanographic conditions during this time. Analysis of the carbon isotope record reveals a broad positive carbon isotope excursion (CIE) of 3‰ in δ13Cbel through the Early Toarcian, interrupted by a negative CIE of 3.5‰ recorded in organic carbon (Tenuicostatum–Falciferum zones). Progressive warming of seawater and increased influx of freshwater into the Moesian Basin through the Early Toarcian is recorded in δ18Obel isotopes. Such changes are attributed to the eruption of the Karoo-Ferrar LIP, reflected in the Moesian Basin by an enrichment in Mercury (Hg) recorded as a shift in sedimentary Hg/TOC values synchronous with the negative CIE. A biotic crisis is recorded amongst bivalves and considered to be part of the ETME, which is here recorded in Bulgaria for the first time. Although a significant loss amongst bivalves during the ETME often coincides with the spread of anoxia, this link is not clearly seen in Bulgaria as geochemical and sedimentological records do not support the prevalence of anoxic conditions. As such, oxygen deficiency cannot be considered a key driving mechanism for the ETME in this part of the ocean and other factors such as rapid warming may have been more important in this central Tethyan region.

Download Full-text