ABSTRACT

The Lower Cretaceous Ferry Lake and Punta Gorda anhydrite has been used as marker beds throughout the Gulf of Mexico, and divided into 9 individual anhydrite beds traceable from southern Mississippi to southern Florida. The underlying Rodessa Formation has an equally well developed anhydrite section in the offshore Eastern Gulf of Mexico and is divided into 12 basin-wide anhydrite bed groupings. The anhydrites of Ferry Lake and Rodessa Formations are traceable to the anhydrites of the Punta Gorda and Lehigh Acres Formations of South Florida.

Anhydrite beds appear to thicken in the central part of the trend interfingering with carbonates of the Lower Cretaceous shelf edge reef. Carbonates and anhydrites may be deposited simultaneously with carbonate patchreefs developing on crests of paleo highs with evaporites precipitating out of a hyper-saline solution on the flanks. Areas where poor anhydrite bed development occurs may indicate areas of patch reefs and, therefore, the best potential for hydrocarbon reservoirs.

Individual anhydrite beds have been correlated and color-coded on photocopies of compensated neutron density logs to determine their geographic distribution. Prepared cross sections show some beds to be area wide while others are more restricted. Isopach maps show .the configuration of the basin in which these beds were deposited with the basin's long isopach axis parallel to the reef trend. Anhydrite deposition occurred with evaporation of restricted highstand waters behind reefs that rimmed the shelf edge.