PASHIN, JACK C., and ANDREW K. RINDSBERG, Geological Survey of Alabama, Tuscaloosa, AL

ABSTRACT: Paleotopographic Control of Basal Chesterian Sedimentation in the Black Warrior Basin of Alabama

At the start of the Chesterian (Upper Mississippian), the Ouachita orogeny began along the southwestern edge of the Alabama promontory. The orogeny ended the upwelling circulation system of the Fort Payne-Tuscumbia carbonate ramp that persisted from the Osagian to the Meramecian. These events established the Black Warrior foreland basin, where carbonate and siliciclastic sedimentation were controlled by flexural tectonism and sea level variation. These factors governed deposition of the petroleum source rocks and reservoir rocks that account for most of the conventional hydrocarbon resources in the basin.

The Lewis interval is a thin (<100 ft), widespread veneer of carbonate and siliciclastic rocks that forms the base of the Chesterian Series in Alabama and contains significant gas, oil, and asphalt resources. Although thin, the Lewis interval is extremely heterogeneous and represents a spectrum of marginal- and open-marine environments, suggesting that depositional topography affected facies distribution. To test the effect of paleotopography on sedimentation, data from wells, outcrops, and cores were analyzed to model the relationship between the Fort Payne Tuscumbia ramp and the Lewis interval.

Sandstone bodies in the Lewis interval typically are elongate parallel to strike of the Fort Payne-Tuscumbia ramp. Along the lower ramp, siliciclastic and carbonate sedimentation took place exclusively in open-marine environments, and sand was deposited in sand waves and patches by storms. Topographic irregularity was especially pronounced on the upper ramp and gave rise to complex facies patterns. Exposure, reworking, and beach formation took place on topographic highs, whereas storm-driven marine sedimentation prevailed in topographic lows. Although inception of the Ouachita orogeny in the Alabama promontory had a marked effect on marine circulation, facies distribution in the basal part of the Chesterian Series was dominated by the ramp topography developed prior to orogenesis.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.