2003 Volume 73 Pages 20-37
In this paper, the author reviewed climatic and tectonic events recorded in the deep-sea cores located in the Southern Ocean sites based on sedimentological, geochemical and paleontological data. The author discussed the relationship among bioevents of calcareous and siliceous microfossils, climatic and tectonic events. The opening of the Tasmanian gateway and the subsequent development of the Antarctic Circumpolar Current occurred near the Eocene/Oligocene (E/O) boundary (ca. 33.5Ma), led to cooling in the Antarctic region and finally large expansion of Cenozoic permanent Antarctic ice sheets. The earliest Oligocene cooling caused the Oil isotope positive excursion, high productivity of biosiliceous sediments and deposition of ice-rafted detritus in the Southern Ocean. The Drake Passage had opened to surface/intermediate water either at 32Ma or at 29.7Ma. The opening of this gateway has not affected the cooling during the E/O transition. Faunal and floral changes of calcareous (foraminifers and nannofossils) and siliceous microfossils (radiolarians and diatoms) are gradual or stepwise from the Late Eocene through the Oligocene. The warm-water species gradually decreased and disappeared during the Late Eocene, while cool-water species rapidly increased just above the E/O boundary. However, the serious extinction events of each taxon were not recognized near the E/O boundary. Several origination events of siliceous microfossils near the E/O boundary may be related with appearance of upwelling divergent margin and the subsequent high productivity event in the Southern Ocean due to the formation of the Antarctic Circumpolar Current and/or global cooling around the circum-Antarctic region.
