Pleistocene calcareous nannofossil stratigraphy for ODP Leg 177 (Atlantic sector of the Southern Ocean)

Abstract

Seven Ocean Drilling Program (ODP) sites recovered during ODP Leg 177 in the Atlantic sector of the Southern Ocean were analyzed to study the Pleistocene calcareous nannofossil record. Calcareous nannofossil events previously described from intermediate and low latitudes were identified and calibrated with available geomagnetic and stable isotope stratigraphic data. In general, Pleistocene southern high latitude calcareous nannofossil events show synchronicity with those observed from warm and temperate latitudes. The first occurrence (FO) of Emiliania huxleyi and the last occurrence (LO) of Pseudoemiliania lacunosa are observed in marine isotope stages (MIS) 8 and 12, respectively. A reversal in abundance between Gephyrocapsa muellerae and E. huxleyi is observed at MIS 5. MIS 6 is characterized by an increase in G. muellerae and MIS 7 features a dramatic decrease in the proportion of Gephyrocapsa caribbeanica. This latter species began to increase its proportions from MIS 14 to 13. The LO of Reticulofenestra asanoi is observed within subchron C1r.1r and the FO of R. asanoi occurs at the top of C1r.2r. A re-entry of medium-sized Gephyrocapsa can be identified in some cores during subchron C1r.1n. The LO of large morphotypes of Gephyrocapsa is well correlated through the studied area, and occurs during the middle-low part of subchron C1r.2r, synchronous with other oceanic regions. The FO of Calcidiscus macintyrei and FO of medium-sized Gephyrocapsa occur in the studied area close to 1.6 Ma.