Abstract
Piston cores from an exposure of a prominent seismic reflector in the Blake-Bahama basin recovered an early late Miocene turbidite. Reflection profiles show that this layer of turbidites covers a broad area of the basin, lapping upon the ancient Blake outer ridge formed by reflector X, and underlying nearly 1,000 m of sediment ponded west of the ridge. The late Miocene appears to mark a change in sedimentation regime to one in which sediments were deposited west of the Blake outer ridge onlapping the lower flanks, with very little sediment being deposited on the flanks. Before the late Miocene, sedimentation was concentrated along the crest axis to build the ridge 1,000 m above the Blake-Bahama abyssal plain. This important change in sedimentation is attributed to a change in depth and strength of the deep flowing contour currents, possibly related to a decrease in flow velocity caused by a rapid retreat of Antarctic glaciation.
