HR: 0800h
AN: PP11B-0559    [Abstracts]
TI: New Data On The Distribution Of Calcareous Nannofossils During And After The Paleocene/Eocene Transition
AU: * Raffi, I
EM: raffi@unich.it
AF: Dipartimento Scienze della Terra, Universita "G.d'Annunzio" di Chieti, Campus Universitario, via dei Vestini 31, Chieti Scalo, 66013 Italy
AB: Major changes occur among calcareous nannofossil assemblages at the transition from Paleocene to Eocene. In most known P/E boundary sections with complete sediment records, the changes are associated to the brief, intensive interval of global warming, the Paleocene-Eocene Thermal Maximum (PETM), and a concomitant huge perturbation of the global carbon budget, the Carbon Isotope Excursion (CIE). Changes in nannofossil assemblages include: (A) occurrence of {\it Rhomboaster} spp. - {\it D. araneus} correlative with the CIE; (B) decrease in diversification of {\it Fasciculithus} spp. at the CIE onset; (C) occurrence of {\it Zygrhablithus bijugatus} and {\it Fasciculithus} spp./ {\it Z. bijugatus} abundance cross-over within the upper part of the CIE-PETM interval; and (D) extiction of the Paleocene genus {\it Fasciculithus} just above the CIE, an event that is closely followed by the further evolution of {\it Rhomboaster - Tribrachiatus} plexus. The genus {\it Tribrachiatus} subsequently radiates over the next $\sim$1 million years, a time interval showing further steps in the evolutionary history of calcareous nannofossils (speciations among discoasters and sphenoliths) during the Eocene. Quantitative analyses of selected calcareous nannofossils in deep-sea sections recovered from the Atlantic (DSDP Site 550, ODP Site 929, and ODP Sites 1262 and 1263 of Leg 208) and paleo-equatorial Pacific (ODP Sites 1215, 1220, 1221 of Leg 199) provide new informations about calcareous nannofossils across the Paleocene/Eocene transition interval. The distinctive {\it Rhomboaster} spp. - {\it D. araneus} association (RD) was previously considered to have a marked provincialism, restricted to the Atlantic Ocean and partially extending to the Tethys seaway and westernmost Indian Ocean. Detailed study of Leg 199 sections (from equatorial Pacific) and preliminary analyses at the P/E boundary of ODP Site 929 (from Ceara Rise in western equatorial Atlantic) and ODP Sites 1262 and 1263 (from Walvis Ridge in southern Atlantic) indicate some difference in the RD distribution. The sudden appearance and short co-existence of {\it R. calcitrapa} gr. and {\it D. araneus}, and the lowermost occurrence of {\it R. cuspis} at the onset of CIE clearly can be extended to the equatorial regions of the Atlantic as well as the Pacific Ocean. The genus {\it Fasciculithus} undergoes a substantial decrease in diversification at the onset of CIE, and perish completely shortly afterwards. This significant turnover appears to represent a global event observed in all the known P/E boundary sections from different oceans and paleo-latitudes. The abundance cross-over between {\it Fasciculithus} spp. and {\it Z. bijugatus} has been observed to occur within the the CIE-PETM interval in several deep-sea sections. In the central paleo-equatorial Pacific Ocean, however, {\it Z. bijugatus} specimens were not present at all, whereas a marked increase in abundance of {\it R. cuspis} was observed in conjunction with the final decline of {\it Fasciculithus} spp. Data from the western paleo-equatorial Atlantic Ocean (Site 929) shows only few {\it Z. bijugatus}, implying that this particular early Eocene turnover is absent in these equatorial regions. {\it Thoracosphaera} spp. shows a short abundance peak immediately above the carbonate barren interval at the P/E boundary, during the CIE, at paleo-equatorial Pacific Site 1220, which probably reflects a stressed surface water environment.
DE: 9325 Atlantic Ocean
DE: 9355 Pacific Ocean
DE: 4855 Plankton
DE: 3030 Micropaleontology
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting