Central to the mission of Leg 189 was (and is) to analyze the Eocene siliciclastic sediment sequence for better understanding of paleoceanographic and paleoclimatic conditions before Antarctic Circumpolar Current development and to determine the timing and the effects of the deepening of the Tasmanian Gateway and presumably related Antarctic Circumpolar Current development on the paleoceanography of the Pacific Tasmanian margin. Clearly, our results indicate great potential for the application of quantitative palynological analysis for these stratigraphic, climatic, and environmental reconstructions (except perhaps for the upper Oligocene-Pliocene interval) using materials from Site 1172. Further study, involving higher-resolution analysis is presented in follow-up contributions, notably on nature of the KTB, PETM, and E-O transition (e.g., Sluijs et al., this volume; Stickley et al., submitted [N2]; Röhl et al., submitted [N1], [N3]; Schellenberg et al., submitted [N4]). A compilation of Site 1172 stratigraphically important dinocyst events and comparisons with global dinocyst stratigraphic distribution is provided in Williams et al. (this volume).
Comparison between results from Site 1172 and other Leg 189 sites with previous circum-Antarctic dinocyst studies, including the recent CRP results, reveals that early Paleogene assemblages are throughout comparable, with the exception of the south coast of Australia—offshore eastern Tasmania (Site 1168) (Brinkhuis et al., this volume; Huber et al., submitted [N5]). It follows that surface water conditions (i.e., paleoceanographic and climatological conditions) must have been roughly similar throughout the circum-Antarctic region at this time. This aspect drastically changes across the E/O boundary. The—albeit in a single sample—recovered earliest Oligocene dinocyst assemblage of Site 1172 has a distinct warm-temperate cosmopolitan character, whereas coeval assemblages immediately to the south remain endemic Antarctic or bipolar in nature (Hannah et al., 2000; CRP results). Meanwhile, endemic Antarctic Paleogene dinocysts are virtually absent at Site 1168 (Brinkhuis et al., this volume). Considering that dinocysts should strongly reflect surface water conditions, a complex evolution of the Southern Ocean oceanographic circulation pattern across the E/O boundary thus emerges from our study. Comparison with results from other (micro) fossil groups and the resulting paleoceanographic implications, including possible relationships between the deepening of the Tasmanian Gateway, circulation changes, and initial Antarctic cryospheric development, is considered outside the scope of this study, but are presented and discussed elsewhere (Stickley et al., submitted [N2]; Huber et al., submitted [N5]).