Petroleum Geology of Appalachian Plateau of Alabama

N. K. Shepard, J. L. Coleman, Jr., B. K. Shepard

The Appalachian Plateau of northern Alabama is a mildly deformed, gently dipping region of flat-lying Paleozoic strata, bordered by the Sequatchie anticline to the southeast, the Black Warrior basin to the southwest, and the Nashville dome to the north. It lies cratonward of the Appalachian fold and thrust belt and is the southwestward extension of the Plateau province of West Virginia and Pennsylvania, the oldest hydrocarbon province in the United States. Structural flexures associated with basement faulting or topography, or subtile lower-level thrusting dominate the structural style in the Alabama Plateau. The stratigraphic section is dominated by carbonate units from the Upper Cambrian to the Mississippian. Terrigenous units occur at the top and base of the section an as very thin intervals throughout the carbonate package. As with most cratonic sedimentary sequences, unconformities, hiatuses, and non-depositional surfaces are present throughout the stratigraphic column. Reservoirs are quartz sandstones and fractured, dolomitic carbonates. Only one bona fide terrigenous source rock is widespread across the plateau, the Upper Devonian Chattanooga Shale, and this shale is thermally immature. Lopatin modeling demonstrates that, with the exception of the Cambrian-Ordovician Knox Dolomite, all potential source rocks are too thermally immature to be effective source rocks. Field and well sampling confirm this conclusion.

The absence of significant field discoveries in the Alabama Plateau in the past 100 years may be attributable to the absence of effective source rocks, the failure of the regional unconformities to conduct the hydrocarbons generated in the peripheral basins to the southwest and southeast, or just plain bad luck. Those fields, not directly attributable to Black Warrior basin sources, are apparently unconformity-related and independent of structure. The true potential of these fields was evidently never realized, because of inadequate development drilling.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.