Erosional modification of Bahama Escarpment
The precipitous (28° to 40°) Bahama Escarpment is characterized by abundant low-energy, restricted peritidal and lagoonal rocks and scarce high-energy, bank-margin rocks of Early and middle Cretaceous age at depths of >2,000 m. This indicates significant erosional modification of the slope. All models of carbonate platforms have high-energy facies at platform edges, with low-energy and restricted facies confined to platform interiors. Erosion has removed marginal deposits that constituted the original slope of the Bahama Platform and exposed peritidal and lagoonal facies rocks. On the basis of widths of facies belts of middle Cretaceous carbonate platforms in eastern Mexico and of erosional benches apparent in seismic profiles across the Bahama and Blake Escarpments, an estimated 5 km of material has been eroded from the base of the escarpment. Greatest erosion occurred between the Cenomanian and Maastrichtian, with additional erosion in the Paleocene and Oligocene, as documented by Tertiary and Late Cretaceous pelagic and forereef deposits that unconformably drape and fill fissures in the older shallow-water rocks. It is unclear whether erosion of the escarpment is occurring at present. Erosion of the slope deeper than 2,500 m is effected, in part, by spalling of joint blocks from shattered exposures. Jointing probably results from expansion of previously buried rocks exposed at the sea floor by erosion. Erosion of the Bahama Escarpment may have occurred by other processes acting in concert, or individually at different times, as well. Dissolution by corrosive water below the calcite compensation depth (CCD) and removal of sediments at the base of the slope by abyssal currents probably contributed most to erosional modification of the Bahama Escarpment. Bioerosion and jointing may aid dissolution by increasing surface area exposed to corrosive waters. Tectonic activity related to movements along fracture-zone trends might have contributed locally to erosion of the Bahama Escarpment. Erosion of the Bahama Escarpment shallower than 2,500 m has been less extensive and apparently proceeds by slumping of large, allochthonous blocks, as indicated by the presence of an apparently intact Eocene forereef deposit in the interval from 3,590 to 3,430 m off Eleuthera Island.