10th Symposium on the Geology of the Bahamas
and Other Carbonate Regions
Bahamian Field Station, San Salvador, June 8-12, 2000

Description and Depositional History of an Open Carbonate Lagoon: Rice Bay, San Salvador, Bahamas

James L. Stuby and Cindy K. Carney, Department of Geological Sciences, Wright State University, 3640 Col. Glenn Hwy., Dayton, OH 45435
Mark R. Boardman, Geology Department, Miami University, Oxford, OH 45056

Rice Bay is an open, windward, sandy, carbonate lagoon, approximately 1 km x 1 km in area, located on the northeast corner of San Salvador Island in the Bahamas. It is separated from other lagoons and the open Atlantic Ocean by North Point, Cut Cay, and Man Head Cay (all eolianites). The subtidal surface of Rice Bay consists of a mosaic of subenvironments: barren carbonate sand and mud, seagrass meadows, subtidal beachrock, and patch reefs.

Forty-six intertidal and subtidal sediment samples were collected from the sea floor of Rice Bay along a 450 m long transect between beaches on Man Head Cay and the mainland (Transect A). Three sediment cores were taken from Rice Bay. Sediment thicknesses in the complete cores ranged from 3.58 m to 4.51 m. Two of the cores contain peat deposits, which have been radiocarbon dated to 6300 BP. Eight supratidal rock samples were collected from the southwestern side side of Man Head Cay. Surficial, core, and rock samples were point counted.

Results of point counting indicate that the subtidal surface of Rice Bay consists of 40% mollusks, 24% intraclasts, 14% algae, 7% peloids, 6% foraminifera, 6% other skeletal grains, 2% ooids, and 1% oolitic clasts. Pearson Correlation tests indicate that the density of seagrass exerts little control over composition of sediment within the meadows. Seven facies have been recognized in the sediment cores. Five are variants of poorly sorted lagoon deposits, one is a moderately sorted beach deposit, and the last is peat. Man Head Cay consists of skeletal grains, intraclasts, and peloids, with no ooids or oolitic clasts.

The depositional history of Rice Bay begain in the Late Pleistocene, with the formation of Man Head Cay (Oxygen Isotope Stage 5e highstand, ~119kA). A paleosol developed on San Salvador during the following lowstand. The Holocene history may be divided into three phases. Early Transgression (6-7kA): Platform edges were flooded and peat accumulated in restricted lagoon. Middle Transgression (6-5kA): Continuing sea level rise allowed open exchange of seawater and sediment production allowed formation of North Point dunes; ooids were generated. Late Transgression (5-0kA): Rice Bay continues to be filled with sand as North Point erodes.