SUBMERGED UPPER HOLOCENE BEACHROCK ON SAN-SALVADOR ISLAND, BAHAMAS - IMPLICATIONS FOR RECENT SEA-LEVEL HISTORY

Sedimentological, petrographic and radiometric data from a submerged beachrock on San Salvador Island, Bahamas, provide new information about the Late Holocene sea-level history in this area. At French Bay, on the southern shore of the island, samples of beachrock collected at a depth of 1 m below low tide level yielded an average C-14 age of 965 +/- 60 years before present. These samples further display a well developed fenestral porosity and present an early generation of low Mg calcite meniscus cement. These features characterize intertidal and supratidal settings; they are not consistent with the present beachrock position and the reported Late Holocene sea-level history in the Bahamas. A 1.5-2 m low stand of the sea about 1 000 years ago would best explain the observed particularities of the French Bay beachrock. This example from San Salvador shows that the smooth trend of Late Holocene sea-level rise proposed by previous workers might be overprinted by high frequency, low amplitude fluctuations. Recognition of these fluctuations is fundamental when calculating rates of sea-level rise and evaluating the coastal response to a marine transgression.