The palaeoenvironmental context of Toarcian vertebrate-yielding shales of southern France (Hérault)
Posted on 13.07.2021 - 11:37
The Early Jurassic was marked by climatic and environmental perturbation, which culminated during the Toarcian Oceanic Anoxic Event (T-OAE), an episode of global warming leading to widespread deposition of organic-rich shales. Exceptional preserved fossils of marine vertebrates have been yielded in Toarcian shales in South France, but their links with the T-OAE remain poorly investigated. A multi-proxy approach is developed (biostratigraphy, mineralogy, Rock–Eval pyrolysis, stable isotopes, phosphorus and mercury contents) to replace these findings in a well-defined temporal and paleoenvironmental context, and hence constrain the factors leading to their remarkable preservation. The T-OAE interval, identified at the base of the Toarcian shales, records higher mercury fluxes suggesting a causal link with the Karoo-Ferrar volcanic activity. This interval is very condensed and unfossiliferous, and might have been deposited under abnormally low salinity conditions. Our data show that the vertebrate horizons deposition post-dated the T-OAE and took place during a prolonged period of widespread anoxia and elevated carbon burial. 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 extreme condensation due to reduced dilution by carbonate and detrital input.
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Bomou, Brahimsamba; Suan, Guillaume; Schlögl, Jan; Grosjean, Anne-Sabine; Suchéras-Marx, Baptiste; Adatte, Thierry; et al. (2021): The palaeoenvironmental context of Toarcian vertebrate-yielding shales of southern France (Hérault). Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.5509789.v1
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Jeremy. E Martin