ABSTRACT

A detailed seismic profiler, bottom sampling, and bottom photographic study reveals considerable information about the surface and subsurface morphology of two small areas on the Blake Plateau. The northern area is a north-south trending depression (32°N, 78°30W) located near the continental slope, and the southern area is defined by a narrow northeast-southwest linear depression (30°50N, 78°30W). Both of these topographic features are erosional in origin, with subsurface strata cropping out on the sides of the depressions. The north-south depression is flanked by numerous biohermal coral banks that have developed above the flat underlying strata. Sediments in the vicinity of these banks are dominated by coral fragments, particularly Dendrophyllia. With increasing distance from the banks the sediment becomes primarily a globigerina sand and ooze, with varying amounts of pteropods. The distinctive sediment components in the southern depression area are manganese and phosphorite slabs and nodules; coral banks and coral sediment are practically absent. Indurated slabs of globigerina sands are locally common in both depression areas, and are believed to be restricted to the uppermost sedimentary strata and to have been lithified at present depths.