Neogene and Quaternary paleoenvironmental history of Deep Sea Drilling Project Leg 71 sediments, Southwest Atlantic Ocean.

Abstract

The Neogene and Quaternary sedimentary record of Leg 71 and previously drilled sequences from the Southern Ocean reveal evidence of a major late Miocene change of oceanic and glacial conditions in the southern high latitudes during paleomagnetic Chron 9. The characteristics of late Miocene sedimentation and in particular the study of erosional patterns and ice-rafted debris suggest the following conclusions. 1) In the late Miocene, the Polar Front first migrated to the northern latitudes of the Southern Ocean and surface water temperatures became similar to those of today. 2) Extensive ice shelves or ice tongues were not present along the Antarctic margin until late Chron 9(-9.0Ma). 3) Before Chron 9, West Antarctica was occupied by an archipelago and the West Antarctic Sea. 4) The newly formed West Antarctic ice sheet was probably unstable and frequently became an ungrounded ice shelf, thus accounting for the scarcity of late Miocene ice-rafted debris. In addition, radiolarian faunas of Hole 514 record at least eight migrations of the Polar Front to the north of the site during the past 4.07Ma. -from Authors