Lower Cretaceous Carbonate Megabank, South Florida, Depositional Setting and Petroleum Potential: ABSTRACT

Abstract

Reinterpretation of the South Florida basin reveals that it was a keep-up carbonate shelf during the Lower Cretaceous. Until the Cenomanian, it was connected to the Bahamas and the Cay Sal Bank north of Cuba. The Cenomanian sea level rise was at least partially responsible for the formation of the Florida Straits, isolating the platform. The combination of an abrupt worldwide rise in sea level and subsidence caused the South Florida platform to founder, ending shallow-water and evaporitic sedimentation over the majority of the shelf. The Cay Sal and Bahamian platforms remained as active shallow shelves separated by the Old Bahamas Channel. The Lower Cretaceous sediments are characterized by shallow shelf limestones, dolomites, and evaporites (mostly anhydrite). The evaporite-rich sections, originally thought to represent basinal facies, are reinterpreted as supratidal to shallow subtidal evaporites, based on examination of core and cuttings. Influx of normal marine waters over rudist fringing reefs controls both the carbonate/evaporite cycles and biota. A major salinity barrier within the platform can be defined. Production to date from the South Florida platform is from rudist patch reefs within the Sunniland formation onshore Florida. The petroleum potential of the Lower Cretaceous Sunniland formation increases offshore where more normalmore » marine waters would have been encountered and might have allowed larger, coalescing, or even stacked rudist patch reefs to develop. The most porous reservoir in the Lower Cretaceous is the Brown dolomite member of the Lehigh Acres formation. This unit also would have much greater potential offshore as the underlying section of carbonate/evaporite source rocks thickens.« less