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

Sedimentological, petrographic and radiometric data from a submerged b eachrock on San Salvador Island, Bahamas, provide new information abou t 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 devel oped fenestral porosity and present an early generation of low Mg calc ite meniscus cement. These features characterize intertidal and suprat idal settings; they are not consistent with the present beachrock posi tion 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 explai n the observed particularities of the French Bay beachrock. This examp le from San Salvador shows that the smooth trend of Late Holocene sea- level rise proposed by previous workers might be overprinted by high f requency, low amplitude fluctuations. Recognition of these fluctuation s is fundamental when calculating rates of sea-level rise and evaluati ng the coastal response to a marine transgression.