RECENT EVOLUTION OF A BAHAMIAN OOID SHOAL - EFFECTS OF HURRICANE-ANDREW

Hurricane Andrew, a category 4 hurricane having wind velocities of sim ilar to 240 km/hr, passed north of Joulters Gays, Bahamas, in a wester ly direction on August 23, 1992. We documented three sedimentary facie s in a 2.7 km(2) study area dominated by mobile ooid sands before the hurricane, using aerial photographs, surface observations, and shallow coring. The shoal crest at this locality had aggrading and northward- prograding (parallel to depositional strike) washover bars composed of cross-bedded, well-sorted ooid sands. Burrowed, poorly sorted ooid sa nds were present seaward of the washover bars, whereas poorly sorted o oids and mud occupied a stabilized area bankward of the actively migra ting shoal and local areas between washover bars on the crest of the s hoal. The shoal was cross-cut by tidal channels, and older washover ba rs were being dissected by tidal currents. Although Hurricane Andrew p rofoundly changed surface features within the study area, its effects will probably be only partly preserved. The hurricane eroded washover bars and transported sediment seaward, leaving a nearly flat shoal cre st overlain by a laterally continuous, decimeter-thick lens of well-so rted ooid sand that thins seaward and bankward. Post-hurricane tidal c urrents deposited a centimeter-thick discontinuous layer of carbonate mud over this lens of well-sorted ooid sand and transported ooids seaw ard off the shoal. The well-sorted ooid sand layer will most likely be reworked when an actively migrating shoal crest is reestablished, alt hough some of this storm deposit may be preserved on the shoal crest w here the ooid sand layer was deposited in areas of normally less agita ted conditions. Ooids may also be preserved in finer grained sediments seaward of the shoal, as suggested by previous studies. Mud deposits on the shoal crest may be preserved where buried beneath reestablished washover bars, although some of this mud will be removed by reworking during diurnal tides.