SWIFT, ANN, and WILLIAM DILLON, U.S. Geological Survey, Quissett Campus, Woods Hole, MA; and MYUNG LEE, Lakewood, CO

ABSTRACT: The Florida Cretaceous Carbonate Platform

The Florida carbonate platform evolved in three phases from shallow water platform buildup in the Lower Cretaceous to terminal drowning in the Upper Cretaceous that resulted in deep-water chalk and later (lagoonal?) evaporite deposition. The structure of five intervening Albian to Aptian formations and underlying basement are mapped from well-log analyses for an area from 26-29 degrees N, from the northern portion of the South Florida basin north onto the Peninsular Arch. Using multichannel seismic and well information, the carbonate buildups can be traced offshore to the east and west into the flanking Mesozoic rift basins.

The predominantly volcanic basement that underlies the platform varies from 1350-5500 m depth, with two large highs in the area: the Peninsular Arch underlain by pre-Cambrian to Cambrian age rocks and the Sarasota Arch underlain by Lower Cambrian igneous rocks. These highs which control the structure of the overlying carbonate units, were formed by Jurassic rifting associated with the opening of the Gulf of Mexico and the Atlantic.

The shallow-water carbonate platform buildup began during the post-rift cooling and subsidence phases. The mapped early and middle Aptian units, about 120 to 350 m thick, are mainly limestone and dolomite. An Aptian-Albian massive anhydrite unit with some limestone and dolomite thickens southward from 150 to 450 m. An Albian anhydritic limestone and porous dolomite unitalso thickens southward to a maximum of 150 m. The top of the Lower Cretaceous is the last carbonate unit that can be traced regionally. It is a very fine grained calcitic dolomite interbedded with thin limestone and anhydrites averaging 500 m thickness. The eroded West Florida and Blake Plateau escarpments mark the lateral extent of this Lower Cretaceous platform. A mid-Cretaceous drowning event (base of Atkinson marl) can be seen in all the wells and can be traced offshore as an unconformity. The Upper Cretaceous is a thick (about 850 m) chalk unit.

The carbonate platform deposition is also correlated in two cross-sections using synthetic seismograms and vertical seismic profiles at many well locations.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.