The origin of the psychrosphere as recorded in changes of deep-sea ostracode assemblages



    1. Richard H. Benson, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560
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Cretaceous and Cenozoic benthic ostracodes and their species assemblage structure have been analyzed by several different association and distribution form techniques. 425 core samples were obtained by the Deep Sea Drilling Project from 77 sites of the first 14 Legs of its survey of the world ocean floor. These analyses of 80 species from 27 composite planktic-foraminiferal time zones representing the last 75 million years of deep-sea faunal development revealed that a major change took place at about 40X106 BP in Late Eocene or Early Oligocene, marking the time of origin of the present cold, bottom water-mass system (psychrosphere). Prior to this world-wide event another important, but previously unknown, ostracode fauna had been present in a wanner deep sea for at least 25 million years without significant change.