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Abstract

Biochronological models for the Southern Ocean have developed since the mid 1960s and early 1970s and have accompanied the completion of numerous biostratigraphical studies during the last 30 years. The voluminous bibliographic literature available for discussion has been limited here to selected articles that focus primarily on the development of diatom and radiolarian stratigraphies and the calibration of these stratigraphies to a Geopolarity Timescale (GPTS). This focused discussion reflects the emphasis of these stratigraphies in this current study.Prior to the DSDP and the ODP expeditions to the Southern Ocean, calibration of microfossil datums to a magnetostratigraphy was limited to stratigraphical successions obtained from relatively short piston cores (generally less than 10 m). This practice established age constraints for microfossil datums within the uppermost sedimentary sequence, i.e. approximately the last 4 million years. Age determination for older sequences was based on estimates derived from secondary and indirect correlations to a magneto-stratigraphy. The introduction of DSDP and ODP cruises to the Southern Ocean, commencing with Leg 28 (Hays et al. 1975) and continuing through Leg 120 (Wise et al. 1992) has both expanded the geographical coverage and the stratigraphical extent of sequences in which direct calibration of biostratigraphical data is possible.The current Cenozoic biochronological framework results directly from the eight DSDP and ODP Southern Ocean expeditions (DSDP Legs 28, 35, 36, 71; ODP Legs 113, 114, 119, and 120). The biochronological framework has been refined with each expedition, as additional sedimentary sequences with integrated magnetostratigraphical and biostratigraphical records were recovered.