Tuscaloosa Group, Alabama Gulf Coastal Plain
Mobile Alabama is located along a major embayment within the coastal plain of the Gulf of Mexico. Mobile is underlain by more than 10,000 ft of Tertiary and Mesozoic strata that generally dip and thicken seaward. A number of structural features and faults in the area (particularly the Mobile Graben) offset and alter the stratigraphy of many aquifers in the Mobile area.
Information Search and Selection
The subsurface of this area has been well studied, driven by the search for domestic and industrial water supplies, petroleum, and subsurface disposal of industrial liquid wastes. However, because shallow aquifers in the area contain copious water supplies, there is little need for hydrogeologic studies of deeper brine aquifers. Essentially all of the interest in petroleum exploration and development in the Mobile area is in the Jurassic Norphlet and Smackover Formations, whose depths exceed
10,000 ft in the Mobile area. There have been only a few brine-aquifer waste-disposal studies (Averson, 1970; Tucker and Kidd, 1973). Although these provide excellent site-specific information, they do not provide information regarding spatial distribution of deep brine-aquifer characteristics.
A number of potential porous, permeable and continuous sand units are beneath the Mobile area that could potentially be used for CO2 sequestration. Some of these include sands within the Eocene/Paleocene Wilcox and the Paleocene Midway Groups. However, we selected the Upper Cretaceous Tuscaloosa Group because the lower Tuscaloosa Group contains highly porous and permeable sands that are regionally extensive, and the unit is overlain by the thick, impermeable, regionally extensive Selma Chalk, which serves as an aquiclude. The Upper Cretaceous Eutaw Formation, which immediately overlies the Tuscaloosa Group, is another potential brine formation for CO2 sequestration, although it is much thinner than the Tuscaloosa sands. We suggest that the Wilcox, Midway, and Eutaw intervals be studied in more detail if CO2 sequestration becomes a serious possibility in the region.
The Tuscaloosa Group has been studied in the region for both hydrocarbon liquid and waste-disposal potential (Averson, 1970; Tucker and Kidd, 1973; Mancini and others, 1987). Miller (1990) provided a general summary of the hydrogeologic properties of this unit and referred to this subsurface interval as the Black Warrior River aquifer. The Tuscaloosa Group is commonly subdivided into a sandy upper, a clayey middle, and a sandy lower unit (Raymond and Copeland, 1987). The depth of the Tuscaloosa is commonly mapped by using the distinctive and widespread middle clay unit. The sands of the lower Tuscaloosa tend to be more porous, permeable, and continuous than those of the upper Tuscaloosa (Averson, 1970). The depth of the lower Tuscaloosa Group generally ranges from 1,500 to 22 m in the Mobile region.
Comments on Geologic Parameters
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Bolin, D. E., Mann, S. D., Burroughs, D., Moore, H. E., Jr., and Powers, T. J., 1989, Petroleum atlas of southwestern Alabama: Alabama Geological Survey, Atlas 23, 218 p.
Copeland, C. W., 1968, Geology of the Alabama coastal plain: Alabama Geological Survey, Circular 47, 97 p., 3 plates.
Epsman, M. L., Moffett, T. B., Hinkle, F., Wilson, G. V., and Moore, J. D., 1983, Depths to ground waters with approximately 10,000 milligrams per liter of total dissolved solids in parts of Alabama: Alabama Geological Survey, Map 199C, 1 sheet.
Grubb, H. F., 1998, Summary of hydrology of the Regional Aquifer Systems, Gulf Coastal Plain, south-central United States: U.S. Geological Survey, Professional Paper 1416-A.
Hinkle, F., Moffett, T. B., Epsman, M. L., Wilson, G. V., and Moore, J. V., 1983, Configuration of the top of the Eutaw Formation in Alabama: Alabama Geological Survey, Map 199A, 1 sheet.
Hosman, R. L., 1996, Regional stratigraphy and subsurface geology of Cenozoic deposits, Gulf Coastal Plain, south-central United States: U.S. Geological Survey, Professional Paper 1416-G, 35 p.
Mancini, E. A., Mink, R. M., Payton, J. W., and Bearden, B. L., 1987, Environments of deposition and petroleum geology of the Tuscaloosa Group (Upper Cretaceous), South Carlton and Pollard Fields, southwestern Alabama: American Association of Petroleum Geologists Bulletin, v. 71, p. 1128–1142.
Miller, J. A., 1990, Ground water atlas of the United States—segment 6, Alabama, Florida, Georgia, and South Carolina: U.S. Geological Survey, Hydrologic Investigations Atlas No. HA-730-G, 28 p.
Moffett, T. B., Hinkle, F., Epsman, M. L., and Wilson, G. V., 1984a, Configuration of the top of the Selma Group in Alabama: Alabama Geological Survey, Map 199CB, 1 sheet.
___________ 1984b, Configuration of the top of the Tuscaloosa Group in Alabama: Alabama Geological Survey, Map 199C, 1 sheet.
Moore, D. B., 1970, Subsurface geology of southwest Alabama: Alabama Geological Survey, Map 99, 1 sheet.
___________ 1971, Subsurface geology of southwest Alabama: Alabama Geological Survey, Bulletin 99, 80 p., 11 plates.
National Imagery and Mapping Agency, 2000, Digital terrain elevation data (DTED Level 0)
Pashin, J. C., Raymond, D. E., Rindsberg, A. K., Alabi, G. G., Carroll, R. E., Groshong, R. H., and Jin, G., 1998, Area balance and strain in an extensional fault system: strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama: U.S. Department of Energy Report DOE/PC/91008-20 (DE98000499), National Petroleum Technology Office, 221 p.
Raymond, D. E., and Copeland, C. W., 1987, Selected columnar sections for the Coastal Plain, Appalachian Plateaus, Interior Lowland Plateaus, and Valley and Ridge Provinces in Alabama: Alabama Geological Survey, Atlas 20, 43 p.
Raymond, D. E., Copeland, C. W., and Rindsberg, 1993, Post-Miocene sediments of the shallow subsurface of coastal Alabama: Alabama Geological Survey, Circular 168, 93 p.
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Prepared by Andrew Warne.