Stratigraphy and Depositional Environments of Part of Pennsylvanian Pottsville Formation in Black Warrior Basin, Alabama and Mississippi: ABSTRACT

Abstract

The upper part of the Pennsylvanian Pottsville Formation of the Black Warrior basin of Alabama and Mississippi is composed of cyclic sequences of conglomerates, sandstones, siltstones, mudstones, and coals, deposited in response to alternate phases of constructive and destructive deltaic sedimentation. The coal-bearing interval has been divided into seven coal groups (Black Creek, Mary Lee, Pratt, Cobb, Gwin, Utley, and Brookwood), each of which contains several coal beds. A detailed study of the three oldest coal groups, the Black Creek, Mary Lee, and Pratt, identified a variety of deltaic facies. These include distributary channel, interdistributary bay, crevasse splay, distributary mouth bar, lagoon/prodelta, and barrier island. The small, elongate deltas of the Black Creek, Mary Lee, and Pratt coal groups prograded northeastward from an orogenic source southwest of the Black Warrior foreland basin. A possible southeastern source terrain is suggested during deposition of Pratt strata. Distributary channels of the upper Black Creek and Mary Lee coal groups shifted extensively across the lower delta plain. Two general centers of deposition, one in Mississippi and one in Alabama, were maintained. Associated coals, trending northeast, accumulated in bays adjacent to the channels. In contrast, the northwest-trending coals of the lower Black Creek and Pratt coal groups were deposited in back-barrier settings during destructive phases of deltaic sedimentation. A single Pratt depocenter, located in Mississippi, is co ncident with the upper Black Creek and Mary Lee depocenter. Determination of depositional environments is based on the interpretation of geophysical log signatures and the distribution of sandstones and coals. Most of these data have been obtained from dual induction and density logs of wells drilled to underlying Mississippian reservoirs. The Pottsville sediments have not been a major petroleum objective; however, the numerous coal beds are a potential source of methane. End_of_Article - Last_Page 1447------------