Calcareous nannofossils at the Paleocene/Eocene transition in the equatorial Pacific Ocean (ODP Leg 199) (abstract of paper presented at AGU Fall Meeting, San Francisco, 6-10 Dec 2002)

Calcareous nannofossil assemblages from the first Paleocene/Eocene sections ever to be sampled in the central tropical Pacific (ODP Sites 1215, 1220 and 1221) were preliminary studied with the purpose of obtaining informations on the evolutionary turnovers associated with the P/E boundary time and the peculiar global climatic conditions. We have documented the distribution ranges of some taxa, as {\it Ericsonia, Discoaster, Fasciculithus, Rhomboaster} and {\it Tribrachiatus}. Data were obtained through quantitative analyses on the assemblages. These detailed analyses were mainly focused on the evolution of {\it Rhomboaster- Tribrachiatus} lineage in the lower Eocene interval, and on the stratigraphic relationship of these taxa with the genus {\it Fasciculithus}. We have documented the consistent occurrence of {\it Thoracosphaera} cysts at the P/E boundary interval. Thoracosphaerids are considered representatives of opportunistic flora, and blooms of these forms are observed in sediments immediately above the extinction horizon of the Cretaceous/Paleogene boundary. Their abundance at the P/E transition could document a change of critical boundary conditions in surface waters. The analyses on calcareous nannofossils from the Early Paleogene sediments recovered during ODP Leg 199 provide also a new set of data for the nannofossil biostratigraphy and biochronology at the P/E transition interval