Cenozoic deep-sea sedimentation in the southwest Pacific area was controlled by large changes in the patterns of bottom-water circulation and erosion. The circulation patterns were largely controlled by the development of the Circum-Antarctic Current south of Australia. Development of the Circum-Antarctic Current did not occur until the Middle to Late Oligocene when final separation occurred south of the South Tasman Rise, although initial sea-floor spreading between Australia and Antarctica commenced in the late Early Eocene. Before the Late Oligocene an erosive western boundary current flowed northwards through the Tasman and Coral Sea areas creating a regional unconformity centered near the Eocene-Oligocene boundary (Leg 21). When circum-Antarctic flow was established in the Late Oligocene, a regional Neogene unconformity formed south of Australia and New Zealand, and sedimentation recommenced in the northern Tasman-Coral Sea area. This was due to the western boundary flow which earlier passed through the region and was largely diverted to the area east of New Zealand and into the Tonga Trench. A world-wide Oligocene unconformity was created by a major change in bottom-water circulation, in turn caused by increased bottom-water production related to the onset of substantial Antarctic glaciation near the Eocene-Oligocene boundary. The separation of Australia from Antarctica led to a fundamental change in the world's oceanic circulation and its climate that marks the onset of the modern climatic regime.