EGU22-6008
https://doi.org/10.5194/egusphere-egu22-6008
EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Toarcian marine vertebrate preservation in the Grands Causses Basin (France)

Brahimsamba Bomou1, Guillaume Suan2, Jan Schlögl3, Anne-Sabine Grosjean4, Baptiste Suchéras-Marx5, Thierry Adatte1, Jorge Spangenberg6, Stéphane Fouché7, Axelle Zacaï8, Corentin Gibert8, Jean-Michel Brazier9, Vincent Perrier2, Peggy Vincent10, Kévin Janneau11, and Jeremy E. Martin2
Brahimsamba Bomou et al.
  • 1University of Lausanne, Institute of Earth Sciences, Lausanne, Switzerland (brahimsamba.bomou@unil.ch)
  • 2Université de Lyon, UCBL, ENSL, CNRS, UMR 5276 LGL-TPE, 69622 Villeurbanne, France
  • 3Department of Geology and Paleontology, Comenius University, Mlynska dolina G, 84215, Bratislava, Slovakia
  • 4Paleorhodania, 69006 Lyon, France
  • 5Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France
  • 6Institute of Earth Surface Dynamics, University of Lausanne, Geopolis, CH-1015 Lausanne, Switzerland
  • 7Musée de Lodève, 1 place Francis Morand, 34700, Lodève, France
  • 8PALEVOPRIM Laboratoire Paléontologie Evolution Paléoécosystèmes Paléoprimatologie UMR CNRS 7262, Université de Poitiers, 86073 Poitiers Cedex 9, France
  • 9Institute of Applied Geosciences, Graz University of Technology, Rechbauerstrasse 12, A-8010 Graz, Austria
  • 10Sorbonne Université (CNRS-MNHN-UPMC) – Muséum national d'Histoire naturelle, Département Origines et Evolution, UMR CNRS-MNHN-UPMC 7207, Centre de Recherche en Paléontologie-Paris (CR2P), 57, rue Cuvier - 75231 Paris Cedex 05, France
  • 11Université de Strasbourg (UNISTRA), Jardin des sciences, 12 Rue de l’Université, 67000 Strasbourg, France

Several episodes of strong climate change and environmental perturbation marked the Early Jurassic, and culminated during the Toarcian Oceanic Anoxic Event (T-OAE), characterised by widespread deposition of organic-rich shales. Exceptionally preserved fossils of marine vertebrates and invertebrates have been discovered in the Toarcian shales of NW Europe, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Paleontological excavations realized in Toarcian strata near Lodève (Grands Causses Basin, southern France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multiproxy approach (ammonite biostratigraphy, X-ray diffraction-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors that led to their extraordinary preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5‰ negative carbon isotope excursion, records higher mercury fluxes, which suggest a causal link with intense volcanic activity of the Karoo–Ferrar large igneous province. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low-salinity conditions. Our data exhibit that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of ka, and took place during a prolonged period of widespread oxygen-deficiency and high carbon burial. Our results indicate that the unusual richness in vertebrates of the studied site can be explained by a combination of regional factors such as warming-induced, prolonged seafloor anoxia, and more local factors, such as extreme condensation owing to reduced dilution by carbonate and detrital input.

How to cite: Bomou, B., Suan, G., Schlögl, J., Grosjean, A.-S., Suchéras-Marx, B., Adatte, T., Spangenberg, J., Fouché, S., Zacaï, A., Gibert, C., Brazier, J.-M., Perrier, V., Vincent, P., Janneau, K., and Martin, J. E.: Toarcian marine vertebrate preservation in the Grands Causses Basin (France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6008, https://doi.org/10.5194/egusphere-egu22-6008, 2022.