Abstract EN:

The Pliensbachian-Toarcian biotic crisis is often regarded as one of the most important extinction events of the Phanerozoic. Its origins are debated and include hypotheses such as the Karoo volcanism, the Early Toarcian OAE, and major eustatic variations. In this study, a transdisciplinary approach was used in order to explore the influence of climate changes on the evolution of biodiversity. Associated to the 87Sr/86Sr and clay mineral data, our 18O data measured on fossils confirm warming events with more humid conditions during the Pliensbachian and the Early Toarcian. Our 13C and Nd analyses suggest that these events could be linked to oceanic modifications, volcanic events, and methane releases. In parallel, the taxonomic, morphological, and biogeographic components of the ammonite diversity were reappraised over the whole interval. Our results underline major diversity and disparity variations, partly structured by a polyphased crisis. Five main extinction peaks, with distinct spatial, taxonomic, and selective dynamics, are identified and attributed to various environmental constraints. In addition, our analyses show a strong faunal provincialism during the Pliensbachian, its progressive dislocation during the Early Toarcian warming, and its reappearance during the Middle-Late Toarcian. By confronting the different data, it seems that the palaeoclimatic changes had an indirect impact on faunas, by influencing the latitudinal climatic gradients, glacioeustatism, oceanic circulation, and seawater oxygenation. Nevertheless, the mechanisms are very complex and the degree of interaction or the feedback between constraints may induce multiple biological consequences.