DIFFERENCES IN THE RESPONSE OF CALCAREOUS NANNOPLANKTON COMMUNITIES TO THE PETM EVENT: A SUMMARY AND PALEOBIOGEOGRAPHIC IMPLICATIONS

An important calcareous nannofossil turnover is registered at the Paleocene Eocene Thermal Maximum (PETM) at a global scale. In order to document the response of the nannoplankton communities below, within and above it, several successions of a wide range of environments and latitudes have been studied in detail, revealing that the calcareous nannofossil reaction was different in discrete paleogeographic areas. At high latitudes, as Site 690, the principal calcareous nannofossil change coincides with the onset of the CIE and is mainly characterized by the rapid replacement of cold water taxa by warm water taxa. This change was the result of a sudden expansion of warm water low latitude assemblages to higher latitudes probably due to an abrupt increase of the surface water temperatures. Moreover, an increase in abundance of Thoracosphaera spp.(dinoflagellate) below and within the CIE indicate also a stressed surface water environment. In the Tethys area the response of the calcareous nannofossil associations to the PETM is more complex. Calcareous nannofossil fluctuations begin below the onset of the CIE, as at high latitudes, increasing in frequency and amplitude at the benthic foraminifera extinction (BFE). At this level Zy. bijugatus suffered a sharp decrease in the relative abundance becoming almost absent throughout the entire PETM. Nevertheless, the most important feature that characterizes this interval in the Tethys is the presence of the so-called D. araneus-Rhomboaster assemblage, a new short lived species association lasting the duration of the CIE. Analyses of changes in surface water conditions affecting the initial recovery of calcareous nannoplankton, at different time in the Tethys and at high latitudes, are underway.