MIDDLE EOCENE - EARLY OLIGOCENE PALEOCLIMATE VARIABILITY AT ODP SITE 738 (KERGUELEN PLATEAU) INFERRED BY COMBINED CALCAREOUS NANNOFOSSIL, STABLE ISOTOPE, AND PALEOMAGNETIC DATA

Ocean Drilling Program (ODP) Site 738 (Kerguelen Plateau) is a significant site for the Southern Ocean biostratigraphy and for paleoclimatic studies. Hole 738B spans the entire Eocene, with particularly good core recovery (~97%) of an upper middle Eocene to lowermost Oligocene section. Given the importance of this site, we performed new calcareous nannofossil and paleomagnetic studies of cores from Hole 738B, spanning the interval between ~42 and 33 Ma. The main results of this study are: 1.a detailed biostratigraphy which highlights 14 bioevents from the late middle Eocene to the early Oligocene 2.a paleocological classification of the calcareous nannofossil assemblage which allowed us to identify abundance variations of selected taxa in response to changes in sea surface temperature (SST) and trophic conditions. 3.comparison of the nannofossil-based interpretations with detailed oxygen and carbon stable isotope stratigraphy 4.environmental magnetic record that identifies pulses in the flux of magnetic minerals to this site Our results, compared with the paleoecological data from ODP Sites 748, 744, 689 and 690 (Persico and Villa, 2004; Villa et al., 2008), allow us to define the paleoecological response of the nannofossil assemblage and to recognize SST variations in the Southern Ocean for this time interval. In particular, we could identify the MECO event at 40Ma, related with the regional exclusion of Paleogenic discoasters from the Southern Ocean, following, the progressive cooling trend is intensified during the cooling events at about 39 Ma, 37Ma and 35.5Ma. In the early Oligocene, changes in calcareous nannofossil assemblages are closely associated with Oi-1 event recorded in the oxygen isotope records. We also present a middle-upper Eocene magnetostratigraphic interpretation for Hole 738B, which is mainly constrained by the new quantitative analyses of calcareous nannofossil assemblages, and preliminary analyses of variations in composition, concentration and grain-size of magnetic minerals throughout the sequence. Environmental magnetic data (including analyses of the anhysteretic remanent magnetization- ARM and isothermal remanent magnetization- IRM) from ODP Hole 738B record significant down-core variations in the concentration of magnetic parameters with a marked decrease at 42 mbsf near the base of Chron C16n. The integrated records indicate a major pulse in terrigenous flux from East Antarctica at 36.2 million years ago and are interpreted to represent an increase in Antarctic weathering during an important deglacial phase. These results are synthesized and interpreted with consideration of the implications for Antarctic glacial history.