Geological effects of the Gulf Stream System on the northern Bermuda Rise

Abstract

The Gulf Stream System contains a clockwise rotating set of bottom currents which influence the sea bed in the northern North American Basin. It is possible to interpret the present-day and historical record of current activity in this basin in terms of the deep flow of the Gulf Stream. This interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation. The present-day circulation of the Gulf Stream actively resuspends large quantities of sediment on and near the northern Bermuda Rise, and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow. During the late Cenozoic the Gulf Stream System was responsible for depositing and shaping the major acoustic/sedimentological units on the relatively smooth surface of the Horizon A complex. Fine-grained, mont-morillionite-rich sediments derived from the chemically weathered saprolites of the Hudson and St. Lawrence drainage basins, were injected into the deep ocean basins by turbidity currents during the late Paleogene and the Neogene. Fine-grained turbidites from the St. Lawrence spread southward down the southeastern Sohm Abyssal Plain across the eastward-flowing Gulf Stream and its westward flowing return flows. Portions of these fine-grained sediments were entrained by the main and return flows and deposited downstream as acoustically non-laminated accumulations on the Corner and Bermuda Rises, respectively. The Hudson River input was injected into the deep basin through the Hudson Canyon System. The interaction of these fine-grained turbidites with the northward flowing deep flow of the Gulf Stream System led to the formation of the Gulf Stream Outer Ridge, here defined for the first time. During the late Neogene or early Pleistocene the Gulf Stream Outer Ridge was partially eroded by the Gulf Stream System and portions subsequently covered by coarse-grained Pleistocene turbidites. The coarse-grained illite-rich turbidites that flowed across the southeastern Sohm Abyssal Plain also crossed the main and return flows of the Gulf Stream System. The finer portions of these sediments were entrained and deposited as Pleistocene acoustically laminated sediments on the plateaus of the Bermuda and Corner Rises.