Texas A&M University, United States

The opening of the Tasmanian Gateway between Australia and Antarctica at the Eocene/Oligocene bounday was a profoundly important event that affected global oceanographic circulation and climate. Ocean Drilling Program Leg 189, together with other geoscience information, has increased our understanding of the Late Cretaceous and younger tectonics and depositional history of the region. From the mid-Cretaceous until the lates Eocene, Australia and Antarctica faced each other across an ever-widening Australo-Australian Gulf, terminated to the east by a Tasmanian land bridge (Tasmania and South Tasman Rise (STR)). Siliciclastic sediments poured into the rifts from Antarctica, Australia and parts of the land bridge, forming deltas in a low-oxygen environment. Sedimentation kept up with subsidence, except on oceanic crust in the spreading Tasman Sea. The west Tasmanian margin ODP site had gradual increases in carbonate content through the Oligocene. In nearby areas of Antarctica, non-marine and shelfal siliciclastic sedimentation gave way to glacigene detrital or diatomaceous sedimentaiton at the Eocene-Oligocene transition. (mod. journ. abst.)