CENOZOIC SEDIMENT ACCUMULATION ON DRIFTS IN THE NORTHERN NORTH-ATLANTIC

The northern North Atlantic sediment drifts have a much greater areal extent than has previously been indicated. The northern North Atlantic extends from the East Greenland to European continental shelves and f rom the Charlie-Gibbs Fracture Zone to the Greenland-Scotland Ridge. W ithin this region are seven major sediment drifts containing some of t he best clues for pre-quaternary bottom water circulation in the North Atlantic. Feni Drift is the oldest in the region, originating near th e Eocene-Oligocene boundary. It was followed by accumulation of Bjorn, Gardar, Hatton, and Snorri Drifts from the late Early to Middle Mioce ne. Eirik Drift may have started to accumulate in the Late Miocene, an d Gloria Drift in the Early Pliocene. Through analysis of the Cenozoic sediment mass/age distribution and the change in area of seafloor for the study area through time, it can be concluded that there is a defi cit of Oligocene to Miocene sediment in the region. This could be expl ained by sediment cycling; the erosion of older sediment to produce yo ung sediment. The mass of Pliocene to Quaternary sediment is much larg er than that of the older sediment and may have been derived primarily through the erosion of Eocene and Oligocene sediment by deepwater cur rents. The sediment drift portion of the total regional sediment mass, increased significantly three times during the Cenozoic. Each of thes e drift growth phases, lasted between 3 and 4 m.y. The first two growt h phases, from the Late Eocene to Early Oligocene and from the Early t o Middle Miocene, were accompanied by northward shifts of depocenters to the newly forming sediment drifts. The third and largest growth pha se occurred between 7 and 3 Ma, and may have been preceded by the init iation of accumulation on Eirik Drift, 8-7 Ma. This most recent growth phase was accompanied by high apparent accumulation rates over southe rn Gardar Drift as it expanded to the east. Erosion rates over Reykjan es Ridge may have been higher during the mid-Pliocene than in the Quat ernary. There are two main sites where dense water could have formed a nd flowed south through the Rockall Trough to start the accumulation o f Feni Drift. If the atmosphere were cool enough, dense water could ha ve formed in the Norwegian Sea or on the Faeroe Shelf. Dense water may also have formed on the Rockall Plateau due to salinity increase thro ugh evaporation in an arid climate. As an alternative to the hypothesi s of Arctic Ocean water overflowing the Iceland-Faeroe Ridge in the ea rly-middle Miocene, it is suggested that dense water formed along shal low segments of the Iceland-Faeroe Ridge and then flowed into the Sout h Iceland Basin to begin accumulation of Bjorn, Gardar and Snorri Drif ts. The initiation of sediment drift formation in the South Iceland Ba sin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a Middle Miocene uplift event along the Iceland-Faeroe Ridge. A second uplift event alo ng the Greenland-Scotland Ridge and a decreased production of Northern Component Water in the early Pliocene may be responsible for increase d sediment accumulation in Bjorn, Gardar and Eirik Drifts.