CONIACIAN-PALEOCENE CHRONOSTRATIGRAPHY OF THE JAMES ROSS BASIN: A SYNTHESIS (Invited Presentation)

Cretaceous-Paleogene marine units from the James Ross Basin constitute a highly fossiliferous reference section for the Southern Hemisphere. Its importance resides not only in the widely known K-Pg boundary at Marambio (Seymour) Island, but also in its almost continuous record of climate and biodiversity patterns preceding and following the terminal Cretaceous mass extinction. Chronology of these units has been traditionally based on bio- and chemostratigraphy, but endemism and early disappearance of several fossil groups in Antarctica requires an independent dating tool that also permits global correlations. We present a synthesis of the recent magnetostratigraphic studies from the James Ross Basin, summarizing a chronostratigraphic framework that precisely locates Santonian-Paleocene magnetic chrons, states the Santonian-Campanian and Campanian-Maastrichtian boundaries in Antarctica, and allows us to correlate sedimentary accumulation rates with Cretaceous uplift phases in the Andes. Paleotemperature and extinction patterns studies in the Maastrichtian-Danian units have identified at least two warming events and a likely two phased extinction, where the first phase affects primarily to benthik mollusks and the second one corresponds to the mass extinction. Stratigraphic studies in the Paleocene support the idea of sea level fluctuations in the northern Antarctic Peninsula related to i) global eustatic sea-level changes, ii) glacioeustasy, shown by the abundance of cold water dinoflagellates that could indicate the existence of ice in the continent by the Cretaceous already and, iii) a combined process between tectonic platform emergence, volcanism, and sea level fall.