The opening of the Drake Passage in the latest Oligocene to early Miocene (25-20 Ma) resulted in the establishment of the deep circumpolar current, which led to thermal isolation of Antarctica and increased global cooling. Associated major turnover in planktic organisms. A major reorganization in deep-sea sedimentation and hiatus distribution patterns occurred near the early/middle Miocene boundary. Sediment distribution patterns changed dramatically with the sudden appearance of siliceous-ooze deposition in the marginal and east equatorial North Pacific by 16.0 to 15.5 Ma. The main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13.5 to 12.5 Ma, (hiatus NH 3), coincident with the establishment of a major East Antarctic ice cap.--Modified journal abstract.