Surface Sublittoral Sediments of Florida Bay

I review previous work on the surface sediments of Horida Bay and present results of detailed analysis of sediments from the restricted Cross Banks area and the more open marine Buchanan Keys area. Sediments of the Cross Banks area are composed principally of mollusc and foraminifer grains with a pelleted, silt-sized matrix. Textures on the banks vary from windward mud-pebble-conglomerates, packstones and grainstones to bank-top leeward, and lake, wackestones and mudstones. The latter deposited in patchy to dense seagrass beds. Sediments of the Buchanan Banks area comprise grains of Halimeda, coral and lithoclasts in addition to mollusc and foraminifera grains. Windward facies are packstones, grainstones and some Porites framestones. Bank top and leeward margins accumulate peloidal mudstones and wackestones under seagrass cover. Lake floors are bare of have a thin packstone covering. In both areas facies consistently occur as bands paralleling the bank margins. Sedimentary structures, textures, seagrass rhizome depths and measurements of changes in bank morphology all indicate windward erosion and leeward deposition of mound sediment. This supports recent hypotheses of down-wind bank migration, and suggests that this occurs in normal but sporadic weather conditions.

When surface sediment composition and benthic communities are compared regionally within south Horida they show a trend of reducing diversity from the reef tract through to central Horida Bay. Sediment textures vary locally with windward and leeward environments but show few regional trends in their occurrence.