ABSTRACT

For many years, the Lower Cretaceous Sunniland Formation oil producing horizons have been considered reefal in composition. Petrological evidence from cores and cuttings from producing and wildcat wells strongly indicate, based on faunal composition and character, that the fields are producing oil from mound-like shoals deposited in a tidal mudflat environment. It is proposed that this depositional environment is similar to that of present-day Florida Bay or the leeward side of Abaco Island, Bahamas. A petrological and petrophysical study was made of the wells drilled into the Sunniland Formation, in Florida Bay and the Keys areas to determine the Cretaceous environment in this area. It has always been assumed that this area, along the Florida Keys, was reefal in the Cretaceous, but the findings of this study indicate that this area is a very shallow back-reef lagoonal area, with oolite and shoal deposits, well behind a main Cretaceous reef. This Cretaceous main reef-crest is thought to occur intermittently along the southern part of the West Florida Escarpment, across the southern side of Cay Sal Bank, along the northern coast of Cuba and Hispaniola, and then along the eastern part of the Bahama Platform. It is considered that the southern part of Florida is a very shallow tidal, playa, and sabkha area located in the updip part of the Bahamas Basin, with the normal marine environment in the central basinal depression between Cuba and the Bahamas. This updip area is separated from the central basin by major faulting in the area of modern day Florida Straits.