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Ten years of deep-ocean drilling have helped to assemble an enormous body of new data about the evolution of the physiography and sedimentary processes of the Cenozoic ocean basins. The formation of the Southern Ocean isolated Antarctica and allowed the evolution of the circum-Antarctic oceanic current regime during mid-Tertiary time. The opening of the Norwegian-Greenland sea during the early Tertiary and the final subsidence of the Iceland-Faroe Ridge during the late Miocene connected the main North Atlantic with the Arctic basin. This seaway was the final step in the formation of an ocean basin connecting the cold, polar water bodies of both hemispheres. The construction of the middle American land bridge and the interruption of the Tethys into separated shallow and de p basins led to a segmentation of the old global, equatorial seaway into different current regimes in the Indian, Atlantic, and Pacific Oceans. This physiographic-tectonic evolution of the ocean basins and the deterioration of the earth's climate during the Cenozoic led to important changes of the depositional regime in the deep oceans because of the initiation of a vigorous polar bottom-water formation and because of the generation of steep zonal hydrographic gradients in the surface-water masses. The effects of these changes on pelagic sedimentation cannot be separated easily, but they have resulted in many deep ocean basins and in lithofacies distributions along their continental margins that are asymmetric along zonal profiles. The DSDP data from the North Atlantic are a prominent ex mple of this Cenozoic evolution of the pelagic depositional environment.
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