ABSTRACT

The Ferry Lake Anhydrite was deposited within a stratopycnal free-flow exchange basin, which functioned as a broad lagoon behind the Stuart City reef Alternating restriction and circulation with open marine waters led to the deposition of cyclical gypsum/carbonate beds. Freshwater clastic influx led to the deposition of siliciclastic shale beds also found within the formation. Increased circulation of normal salinity waters into the lagoon may have been facilitated by a rising sea level, or autoclastic destruction of the reef from storms, or the destruction of the reef framework from the hypersaline lagoonal water.

Hydrocarbon production has been established in Caddo-Pine Island field from a thin carbonate bed, Haygood Limestone, found near the base of the Ferry Lake Anhydrite. The Haygood Limestone is an intraclastic/bioclastic grainstone-packstone that was deposited as an intertidal shoal during a period of increased circulation of open marine water. Two additional carbonate beds that are separated from the Haygood Limestone by thin anhydrite beds also were cored during the development of the field. These two beds, the A Member and the B Member, were deposited as peritidal carbonate facies within subtidal to supratidal settings. Facies relationships in the B Member record deposition from storm activity.

Diagenetic alteration within the three carbonate beds studied differ somewhat, due in part to the different depositional environments of the beds and their isolation from one another by thin anhydrite beds. Diagenetic realms range from early meteoric phreatic to deep subsurface phreatic realms. Petrographic analysis indicates that highly reducing pore fluids evolved at relatively shallow burial depths. Precipitation of the numerous overlying gypsum beds could explain this occurrence. Aside from the A Member, which is a dolomudstone, dolomitization in the carbonate beds is surprisingly rare, considering their association with evaporitic environments. Hydrocarbon migration within the Haygood Limestone occurred after six different diagenetic events had altered the rock.

Hydrocarbon production has been established from thin carbonate beds within the Ferry Lake Anhydrite in scattered fields within the interior salt dome basins. In some cases, halokinetic movement may have been responsible for creating paleotopographic highs on the lagoonal floor where localized intertidal carbonate grainstones developed. Salt movement does not seem to be a factor in the formation of the tidal shoals within the study area during deposition of the Haygood Limestone.