Carbonate Comparison of West Florida Continental Margin with Margins of Eastern United States

Larry J. Doyle

Temperate carbonate margins may have as many similarities to clastic margins as to other carbonate systems. An example is the west Florida continental margin north of Florida Bay, a vast area of more than 150,000 km². The facies of this area differ from those of other Holocene carbonates, such as the Bahama Banks, the Great Barrier Reef, and the Caribbean and Pacific bioherms. The west Florida margin is analogous to the predominantly clastic southeastern United States in both physiology and sedimentary processes.

The shelf facies is a veneer of carbonate sand, primarily molluscan shell fragments, with low sedimentation rates. It is similar to the southeastern United States sand veneer with the clastic component removed. Like the U.S. system, the west Florida shelf has a ridge and swale topography repleat with sedimentary structures, such as sand waves, with a series of drainage systems incised into its surface at lower stands of sea level. On the outer edge, it is commonly bounded by outcrops with considerable positive relief.

The upper slope of the west Florida margin is a calcilutite, a Holocene chalk deposit accumulating at rates of tens of centimeters/1,000 years, comparable to the clastic lutite depositional rates of the eastern U.S. continental slope, and two orders of magnitude higher than deep-sea oozes of similar composition. These relatively high rates are probably caused by fines pumped from and across the coarser shelf-sand sheets in both systems.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.