Structure and Origin of Southeastern Bahamas

The structural framework of the southeastern Bahamas has been reconstructed from seismic profiler, magnetic, and gravity data. The Bahama Escarpment that marks the boundary between the southeastern Bahamas and the deep-sea floor may follow an ancient fracture zone. The geophysical data suggest that the crust beneath the southeastern Bahamas has a thickness (20 km) intermediate between those of the crusts of continents and ocean basins, and that this basement is partly volcanic in origin. The Bahamas may have formed by subsidence of a continental crust and carbonate accretion. If the southeastern Bahamas were formed in this manner, the crustal foundation must be very thin because the carbonate apron may be as thick as 10 km. Another explanation is that the Bahamas are unde underlain by oceanic crust, in which case the Bahamas could have been formed in two ways. The northwestern Bahamas may be located at the site of a trough formed before or at the time the Atlantic Ocean was open. After this trough was filled nearly to sea level with terrigenous sediment, carbonate deposition was initiated. The southeastern Bahamas, on the other hand, may be located along a fracture zone that was formed during the opening of the Atlantic. The sedimentary section may be entirely carbonate. As the continents separated, the sediment-filled trough and the fracture zone subsided with carbonate accretion keeping pace with subsidence. The interpretation of the southeastern Bahamas being built on oceanic crust eliminates the problem of its overlap onto Africa in continental drift reconstructions.