Abstract

Detailed examination of 20,000 km of seismic reflection profiles and data on cores and abyssal currents suggests that the Greater Antilles Outer Ridge has been constructed by differential deposition of sediment from the Western Boundary Undercurrent above the seismic reflector, Horizon A. Deposition of acoustically stratified sediments under the eastern sector of the outer ridge was apparently terminated in the late middle Eocene when the incipient formation of the present Puerto Rico Trench cut off downslope sediment movement from the northeastern Antilles. At about the same time, the newly formed Western Boundary Undercurrent, possibly interacting with Antarctic Bottom Water entering from the South Atlantic, began to preferentially deposit acoustically transparent sediment to form the eastern outer ridge. Stratified sediments were deposited in the region of the present western outer ridge until the middle Miocene, when increased Antarctic Bottom Water flow apparently diverted the sediment-laden Western Boundary Undercurrent and produced a flow pattern which initiated deposition of the acoustically transparent sediment now forming the western ridge sector. Since that event, the resultant morphology of the Greater Antilles Outer Ridge has diverted the Western Boundary Undercurrent into a contour-following flow, causing further depositional construction of the entire outer ridge.

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