Marine Science Faculty Publications

New Perspectives on the Geology and Origin of the Florida Middle Ground Carbonate Banks, West Florida Shelf, USA

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Gulf of Mexico, West Florida Shelf, carbonate ramp, carbonate banks, vermetid reefs, rapid sea-level rise

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Bathymetric and seismic surveys of the Florida Middle Ground area on the West Florida Shelf, aid in identifying the structure and origin of these unusual banks. Recent cores recovered from the area by other workers provide a useful context for interpreting geophysical data. Data indicate that high-relief banks may be largely biohermal, whereas low-relief banks are likely composed of clastic sediments with a vermetid gastropod carbonate caprock. The most seaward ridges reveal subtle internal aggradational stratal geometries indicating a possible origin as a subtidal shoal, or paleoshoreline, deposited during or immediately following the Younger Dryas. Bank locations appear to be related to the antecedent geology, specifically the occurrence of the highly weathered Miocene surface. High-resolution multibeam bathymetry and backscatter data reveal varied morphologies that suggest the influence of karst processes, linear trends suggestive of wave-reworked intertidal hardbottom, poorly lithified and benthic fauna-mantled beach ridges or sand waves, or perhaps surface-water flow patterns during lowstand exposure. Circular depressions on low banks are of the same scale and morphology as modern shallow karst features in the Everglades. An episodically active sand-wave field occurs in the northern study area, and provides sediment to the system. Scoured depressions surrounding carbonate banks also indicate intense, episodic current activity originating from shelf and wave currents. A partial modern analog for some of the morphology of this system may be the Ten Thousand Islands and portions of the Florida Everglades. Data indicate that the banks represent a brief period of reef growth (possibly mixed coral and vermetid) constrained by two rapid sea-level rise events, and impacted by changing water quality and trophic conditions.

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Citation / Publisher Attribution

Marine Geology, v. 355, p. 54-70