Abstract

Marine seismic refraction and reflection profiles correlated with deep wells on land reveal that the Blake Plateau is underlain by 7-11 km. of Jurassic and younger carbonates and evaporites, with some terriginous sediments. Rock dredges and cores show that the area is bordered by an apparently continuous reefal complex of Cretaceous and earlier age which extends from the Blake Escarpment through the Bahamas and Cuba to the West Florida Escarpment. JOIDES drilling on the Blake Plateau indicates that the Tertiary sedimentary section is abbreviated due to the erosional sweeping of the Gulf Stream. JOIDES Deep Sea Drilling Project results and more recent piston coring reveal a complex Cenozoic history of hemipelagic and turbidite deposition in the Blake-Bahama Basin and on the Blake Outer Ridge. Contour currents apparently built the Outer Ridge then shifted deposition west of the ridge into the basin in the Late Miocene.

The origin of the basement under the Blake Plateau and Bahamas is still unknown from direct evidence. Indirect geophysical evidence, including magnetic anomalies, gravity anomalies, and Rayleigh Wave dispersion data, suggest the possibility that the basement is about 10 km deep and of intermediate density and seismic velocity. Such a crust might be correlated with that of the present Red Sea, and the Blake Plateau-Bahamas crust could be interpreted to have formed in a similar way in the Jurassic, or possibly the Triassic, as North America and Africa rifted apart. Basement faulting associated with the rifting and plate rotation of North America controlled the formation and subsidence of the deep geosynclinal basin under the Blake Plateau.

Porous dolomite horizons and cavernous reefal limestones are known in the area. Regional dip caused by differential subsidence or compaction over reefs, faults affecting Cretaceous and older strata, and possible salt doming might offer entrapment situations for these existing reservoirs. Golden Lane analogies and Smackover continuations are possible and stratigraphic traps are very probable. The potential for large petroleum reserves is real but their exploration and exploitation will be difficult.