The primary objective of Ocean Drilling Program (ODP) Leg 189 was to refine the hypothesis proposed by Kennett, Houtz, et al. (1975) that climatic cooling and an Antarctic cryosphere developed as the Antarctic continent was thermally isolated by the developing Antarctic Circumpolar Current (Exon, Kennett, Malone, et al., 2001). Documentation of the development of the Southern Ocean in the Tasman region through the Neogene was a key secondary objective. Comparison of these records to results from recent ODP Legs 177 (Atlantic Ocean) and 188 (Indian Ocean) will facilitate better characterization of the Southern Ocean.
Quaternary sediments were recovered at all five sites drilled during ODP Leg 189 in the Tasmanian Gateway region (Fig. F1). Site 1168 is located on the continental rise west of Tasmania, 80 km southeast of Deep Sea Drilling Project (DSDP) Site 282. Quaternary sediments consist primarily of light greenish to greenish gray nannofossil ooze with additions of foraminifers and clay and pyrite staining (Shipboard Scientific Party, 2001b). Site 1169, located on the South Tasman Rise (STR), was not included in this study. Heavy seas during coring resulted in highly disturbed cores that are unsuitable for further analysis (Shipboard Scientific Party, 2001c). Sites 1170 and 1171 are also located on the STR (Fig. F1), 270 km apart and south of the modern Subtropical Front (STF). Quaternary sediments at Sites 1170 and 1171 consist of white to greenish gray nannofossil ooze with additions of clay, diatoms, and foraminifers. Pyrite staining and laminations are common throughout (Shipboard Scientific Party, 2001d, 2001e). Quaternary sediments from Site 1172, located on the East Tasman Plateau (ETP) (Fig. F1), consist of light greenish gray to greenish gray nannofossil foraminifer ooze and foraminifer nannofossil ooze with additions of clay. Pyrite staining and lamination are common (Shipboard Scientific Party, 2001f).
The Tasman margin has previously been drilled; during DSDP Leg 29, 10 sites were drilled around Australia and New Zealand using the rotary core barrel system. Of the 10 sites drilled, three were located near Leg 189 drill sites. DSDP Site 282 was drilled at the foot of the continental slope west of Tasmania, and DSDP Sites 280 and 281 were drilled on the STR, south of the modern STF (Kennett, Houtz, et al., 1975). Edwards and Perch-Nielsen (1975) reported the calcareous nannofossil biostratigraphy and applied a Pleistocene zonation with only three zones. Nannofossils were common to rare, and the number of species reported was <10. A hiatus that eliminates the entire lower Pleistocene section was reported at DSDP Site 280, and at DSDP Site 282, a hiatus that extends from the upper Miocene to the lower Pleistocene was recorded. No hiatus was recorded at DSDP Site 281 (Edwards and Perch-Nielsen, 1975).
The objective of this study is to record the abundance of Quaternary calcareous nannofossils and improve on the biostratigraphic resolution as initially reported in the shipboard results (Shipboard Scientific Party, 2001b, 2001d, 2001e, 2001f). This study reports the qualitative abundance distribution of calcareous nannofossils of Holes 1168A, 1170A, 1171A, and 1172A. An age model was constructed using nannofossil datums and was compared to additional biomagnetostratigraphic and isotopic datums (Stickley et al., this volume). This data can be used to guide any future quantitative work in the Quaternary sediments recovered during Leg 189.