AbstractThe Early Jurassic was marked by several episodes of rapid climate changes and environmental perturbation. These changes culminated during the Toarcian Oceanic Anoxic Event (T-OAE), an episode of global warming that led to the widespread deposition of organic-rich shales. The Toarcian shales of NW Europe have also yielded exceptionally preserved fossils of marine vertebrates and invertebrates, but the potential links between the occurrences of these exceptionally preserved fossils and the T-OAE remain poorly investigated. Palaeontological excavations realised in Toarcian strata near Lodève (Hérault, S France) have yielded several specimens of marine vertebrates and abundant invertebrate fauna. We have developed a multi-proxy approach (ammonite biostratigraphy, XRD-bulk mineralogy, Rock-Eval pyrolysis, stable isotopes, trace element, phosphorus and mercury contents) to place these findings in a well-defined temporal and palaeoenvironmental context, and hence constrain the factors that led to their remarkable preservation. The Jenkyns Event interval, unambiguously identified at the base of the Toarcian organic-rich shales by a 5 ‰ negative carbon isotope excursion (CIE), 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 show that the deposition of the vertebrate-yielding horizons post-dated the T-OAE by several hundreds of kyr, and took place during a prolonged period of widespread oxygen-deficiency and elevated 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 due to reduced dilution by carbonate and detrital input.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5509789
Functional biogeography of marine vertebrates in Atlantic Ocean reefs
