Variabilité des faciès organiques durant les événements anoxiques Toarcien et Cénomano-Turonien: influence des facteurs environnementaux locaux et globaux

Soutenance de thèse de Carolina Fonseca, dirigée par Carine Lézin et Joao Graciano Mendonça Filho

Résumé

Oceanic anoxic events (OAEs) mark periods of profound climatic, paleoenvironmental and paleoceanographical changes at a global scale, representing major disturbances in the global carbon cycle. In this study, the complete characterization of the organic record of the early Toarcian (T-OAE) and Cenomanian—Turonian (OAE2) events was achieved using advanced organic petrographic and geochemical techniques. The role of global versus regional control mechanisms was assessed, with the T-OAE and OAE2 organic facies variability being, in great part, explained by the diversity of the local paleoenvironmental contexts. Paleogeography, paleogeomorphology and oceanic circulation patterns variability are considered as the main factors responsible for the organic signature of these events. In addition, this study constitutes the first record of Closterium in sediments from the Cretaceous, and the first identification of choanoflagellates, the closest living relatives of Metazoa, in the fossil record.