Mesozoic-cenozoic history of calcareous nannofossils in the region of the southern ocean

The Mesozoic-Cenozoic evolution of high southern latitude calcareous nannofossil assemblages developed in parallel with that of the Southern Hemisphere ocean basins and the attendant progressive changes in global climate. The equitable Middle to Late Jurassic climates are reflected in a cosmopolitan zonation although distinctive high latitude taxa developed in both polar regions. Monospecific or low diversity provincial assemblages characterized the incipient Early Cretaceous South Atlantic Basins until the introduction of Tethyan elements during the Aptian. Bipolar or austral provincial taxa are useful in erecting a biostratigraphic subdivision for the remainder of the Cretaceous sequence on the Falkland Plateau. In contrast to the middle Cretaceous, the global sample coverage of DSDP holes for the Campanian-Maestrichtian is sufficiently broad to demonstrate a distinct latitudinal distribution of species and assemblages. Provincial austral or bipolar taxa are relatively minor components of the Paleocene-Eocene assemblages, but quantitative methods document the existence of definable high latitude assemblages which shifted latitudinally in response to climatic changes. Indirect evidence suggests that calcareous nannofossils were deposited in the interior basins of Antarctica during this interval. Species diversities declined progressively through the Oligocene-Miocene epochs in response to the deterioration of Neogene climates and glacial episodes on the Antarctic continent, finally resulting in low diversity assemblages generally dominated by high latitude taxa. Sharp migrations of these assemblages occurred in response to glacial-climatic events. Plio/Pleistocene sediments deposited beneath the expanding Antarctic water mass are essentially barren of calcareous nannofossils, but coccoliths are widely distributed in the Subantarctic region as a result of the amelioration of Holocene climate and the Quaternary descent of the carbonate compensation depth. Two new taxa are described: Stephanolithion bigotii brevispinus n. ssp. from the Upper Jurassic and Gephyrobiscutum diabolum n.g., n. sp. from the lower Campanian.