Calcareous nannofossil paleoceanography across Oceanic Anoxic Event 3: From local to global perturbations

The Coniacian-Santonian is the time of deposition youngest Cretaceous episode of anoxia namely the oceanic anoxic event 3 (OAE3). The OAE3 was confined to the equatorial Atlantic Ocean and adjacent basins rather than being global in scale. We focused on nannofossil paleoceanography of the late Turonian to early Campanian time interval and applied quantitative analyses to assess the response of calcareous nannoplankton to paleoenvironmental changes across OAE3. The study was conducted on sites from the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) situated in the Atlantic Ocean and the Indian Ocean. A detailed, revised, and high-resolution nannofossil biostratigraphy of the selected sites enabled correlations at a supra-regional scale. Quantitative analyses allowed us to characterize paleotemperature and nutrient changes before, during, and after OAE3. We identified relatively large fluctuations in abundance (“acmes”) of the genera Micula and Marthasterites, across OAE3. The onset of OAE3 coincides with a major increase in abundance (and local dominance) of M. furcatus, suggesting the rapid establishment of new and peculiar paleoceanographic conditions at a widespread to global scale. The most altered paleoceanographic conditions occurred during the core of OAE3 as characterized by the synchronous maximum abundance (climax) of M.staurophora on a global scale. In addition to their value for paleoenvironmental reconstructions, the Micula and Marthasterites “acmes” are useful for the biostratigraphic characterization of the Turonian/Coniacian, Coniacian/Santonian, and Santonian/Campanian boundaries and might be introduced as additional events in future nannofossil zonations for the Late Cretaceous. This research was funded through MUR for ECORD-IODP Italia.