24. LITHOSTRATIGRAPHY AND CLAY MINERALOGY OF THE WESTERN MARGIN OF THE ROCKALL PLATEAU AND THE HATTON SEDIMENT DRIFT1

Learning more about the history of oceanic sedimentation and its relationship to the development of abyssal circula-tion in the northeastern Atlantic was a major objective of Leg 81 drilling. Accordingly, sites were situated on an East-West traverse across the southwestern margin of Rockall Plateau and the Hatton Drift. All sites had a similar strati-graphic sequence of late Paleocene-early Eocene volcanogenic/shallow-water sediments lying below a major late Eo-cene-Miocene unconformity. Overlying this hiatus was a sediment-drift sequence of Mio-Pliocene pelagic ooze capped by a Plio-Pleistocene rhythmic sequence of ooze and marl deposited during glacial conditions. The clay-mineral compo-nents of these sediments reflect the developing exchange of water between the northeastern Atlantic and the Norwegian Sea as the Greenland-Scotland Ridge subsided during the Cenozoic. Evidence presented here suggests an early Eocene initiation of the Northeast Atlantic Passage. Major flow through this passage in the late Eocene/Oligocene stimulated changes in abyssal circulation throughout the North Atlantic, the regional mid-Tertiary unconformity being the most dramatic result