Abstract

Seismic data across the Blake Plateau and Bahama Platform have been tied to a COST well, DSDP drill holes and several deep exploration wells. A basin 7-13 km deep under the Blake Plateau is thought to have formed on transitional crust composed of Lower Jurassic sediments intruded by basaltic magmas. Lower to Middle Jurassic marine sediments, including carbonates and evaporites, were deposited in the basin by the early invasion of Atlantic waters.

Reorganization of the Atlantic Ocean spreading in Early to Middle Jurassic time was accomplished by a spreading centre jump, isolating the transitional crust basin under the Blake Plateau and western Bahamas, along with a possible fragment of the African crust under the edge of the plateau. New oceanic crust then formed east of the plateau in the new spreading centre along the Blake Spur magnetic anomaly. A possible continental fragment along the eastern edge of the Blake Plateau might explain a westward structural tilt of the prespreading centre-jump strata and the low isostatic gravity anomalies, which require a crust approaching continental thickness.

After the spreading centre-jump, in Middle Jurassic time, the Blake Plateau and Bahamas continued to subside smoothly. Deposition of shallow-water and reef-bank limestone and dolomite kept pace with subsidence through the Albian, after which the Blake Plateau and Bahama channels deepened, accompanied by the slow deposition of deep water calcareous oozes and chalks. Slow subsidence and deepening of the Blake Plateau-Bahama channels took place at rates similar to those of the regional Atlantic margin subsidence. Perhaps as early as Late Cretaceous time, strong Gulf Stream currents scoured the Florida Straits and Blake Plateau and have persisted to the present. In deeper-water, contour-following currents eroded and shifted Tertiary sediments on the Blake Outer Ridge and in the Blake-Bahama Basin.