Toward a Chronology of Storm Sedimentation and Paleoenvironmental Change, Storr's Lake, San Salvador Island, Bahamas

Marine lake basins such as those found in the Bahamas have recently received attention as likely sedimentary repositories of Quaternary paleoclimate.  One such basin is the Fortune Hill sub-basin of Storr's Lake, San Salvador Island, which because of its relatively thick (2 meter) sedimentary record and its proximity to the windward shore of San Salvador is ideally suited to paleoclimatic studies.  An integrated sedimentary and geochronological investigation of the Fortune Hill sub-basin was conducted.  This investigation involved lake bottom sediment sampling and coring, thin-section petrography and ¹⁴C AMS radiocarbon dating.  Results indicate that three end-member lake bottom facies occur:  a carbonate sand facies, a laminated microbial mat facies, and a stromatolitic crust facies.  The carbonate sand facies occurs primarily along the eastern margin of the sub-basin and consists of sediment derived from the adjacent coastal dune and beach.  The laminated microbial mat facies covers much of the central, western, and northern portions of the sub-basin and extends 5-20 cm beneath the lake bottom in areas where lake bottom carbonate sand is not present.  The stromatolitic crust facies is closely associated with the carbonate sand facies particularly in an area surrounding an exposed Pleistocene bedrock.  Cores collected from the Fortune Hill sub-basin reveal interbedded layers of skeletal sand and laminated microbial sediment.  ¹⁴C AMS analyses of organic material collected 11, 27 and 32 cm beneath the lake bottom yield radiocarbon dates of 500, 1,730 and 1,890 years BP (+/- 40 BP).  Given that the carbonate sand facies is allochthonous and attributable to wash-over events, sedimentation in the lake is clearly episodic, with storm-related sand deposition interrupting background microbial sedimentation.  Detailed analyses of the storm sands coupled with high-resolution geochronology should allow for individual storm events to be defined.