Abstract: Ferry Lake, Rodessa, and Punta Gorda Anhydrite Bed Correlation, Lower Cretaceous, Offshore Eastern Gulf of Mexico

Andrew J. Petty

The Lower Cretaceous Ferry Lake and Punta Gorda Anhydrite have been used as marker beds throughout the Gulf of Mexico, and divided into nine 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 twelve basinwide 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. Paleontologic data indicate that depositional water depths of the interbedded carbonates range from sea level to 100 meters. 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 reels 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 areawide 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 reels that rimmed the shelf edge.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana