PLEISTOCENE REEF PRESERVATION MODELS FROM SAN SALVADOR, BAHAMAS

Recent investigations at six subaerially exposed outcrops (Crab Cay, North Storr’s Lake, Pigeon Creek, Salt Pond, Storr’s Lake Narrows, and the Gulf) of the Cockburn Town Member, Grotto Beach Formation, reveal diverse fossil reef assemblages possibly preserved by sudden burial and regressive subtidal packages as reef rubble and in situ facies on the eastern, Atlantic (windward), side of San Salvador Island, Bahamas. Previous studies of the Cockburn Town Member, deposited during oxygen isotope stage 5e (~131ka to ~119ka) when sea level was +6 m, report fifteen fossil reef outcrops with the most extensive, well-preserved exposures located on the western, Caribbean (leeward), side of the island; including the well-studied, in situ Cockburn Town and Sue Point reefs.

The outcrops at Salt Pond and Storr’s Lake Narrows are characterized as coral reef rubble or breccia facies containing disarticulated Acropora cervicornis, Diploria labryinthiformis, Diploria strigosa, Montastrea annularis, Porites porites, and Strombus sp. The outcrops at Crab Cay contain both in situ and disarticulated coral species of Acropora palmata, Agaricia sp., Manicina areolata, and Montastrea cavernosa, in addition to those species seen at Salt Pond and Storr's Lake Narrows. Both reef rubble and in situ outcrops contain well-preserved aragonite fossils with trace amounts of calcite and low magnesium calcite in a calcarenite matrix, which are overtopped by terra rossa paleosols up to 20 cm thick and in some cases by an additional caliche/calcrete crust. North Storr’s Lake and Pigeon Creek are characterized by regressive packages containing subtidal facies with abundant bivalves and gastropods. The Gulf is characterized by an A. cervicornis dominated reef that occurs below an eolianite, which dips approximately 30 degrees west. These six reefs present new types of preservation modes that can be used to model other Pleistocene reefs in the Bahamas, in addition to the model reported for the Cockburn Town and Sue Point reefs where eolianites overstepped the reefs.