Approximately 2,100 km of 24-fold multichannel seismic reflection data reveal the subsurface geology of a large part of the continental margin in the Bahamas region. Discordance between the westward-dipping prebreakup sediments and the eastward-sloping basement along the edge of the Blake Plateau is interpreted as an effect of a splinter of continental margin derived from the African plate by a spreading-center jump in Middle Jurassic. Early rifting centered under the main part of the Blake Plateau became inactive, as a spreading-center jump shifted the active rift to east of the present Blake Escarpment along the Blake Spur magnetic anomaly.

In the northern Florida Straits the data reveal that the prebreakup unconformity, underlain by Triassic-Upper Jurassic(?) arkosic volcaniclastics, extends from southern Florida to the western Bahama Banks. These volcaniclastics are associated with the intermediate nature rift-crust formed just prior to and during breakup of the North American and African continental plates.

Back-reef platform deposits of limestones, dolomites, and evaporites of Late Jurassic to Albian age extend from the Blake-Bahama Escarpment under Florida. These covered what once was a huge megabank extending over a wider area than the present smaller isolated Bahama Banks. The formation of the modern Florida Straits and Bahama channels occurred in the Cenomanian transgression when the overall area deepened. Only on the present Bahama Banks and Florida platform did shallow-water carbonate deposition persist to maintain the

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shallow-bank environments.

Evidence of recurring scour by current erosion is found in the Florida Straits. Erosional events apparently occurred in middle Cenomanian, middle Paleocene, early-middle Eocene, and middle Oligocene, which are times of lower eustatic sea level. This evidence of Florida current scour indicates that the current was present as far back as the Cenomanian.

A carbonate bank margin and reef complex has been present along the Bahama Escarpment since Middle Jurassic. Apparently these organic buildups seeded on structural relief on oceanic basement created during the spreading-center jump along the Blake Spur anomaly. The bank margin apparently has retreated at least 15 km below the A^u unconformity.

Active faulting at least through the Late Cretaceous and perhaps into the Tertiary, occurred along the Great Abaco fracture zone. These relatively young tectonic events, along with the post-Albian faults in Providence Channel, indicate interactions between the Atlantic and Caribbean plates and extensions of faulting far to the northeast of Cuba and the greater Antilles.

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