COMPETING DEPOSITIONAL SYSTEMS: 40AR/39AR DETRITAL MUSCOVITE AGE AND SANDSTONE COMPOSITIONAL ANALYSIS IN DETERMINING PALEODRAINAGE PATTERNS AND PROVENANCE OF THE POTTSVILLE FORMATION IN THE GREATER BLACK WARRIOR BASIN

⁴⁰Ar/³⁹Ar detrital muscovite ages, sandstone modal analysis, and the clast composition in conglomerates provide a powerful basis for delineating the provenance of ancient sandstones, inferring paleodrainage patterns and revealing the dominant tectonic activity of source regions. The Greater Black Warrior Basin (GBWB) contains the thickest accumulation of orogenic sediment in the southern Appalachian foreland, including the Pennsylvanian Pottsville Formation. No correlation has yet been made between the stratigraphy of the Pottsville in the Valley and Ridge and the foreland; in Alabama, this is represented as the Cahaba synclinorium and the Black Warrior basin. A sample from the upper Parkwood Formation, immediately beneath the Pottsville, yields muscovite with ca. 450, 375 and 320 Ma ages (similar to the age modes defined by samples of the overlying Pottsville). Basal quartzarenites from the Lower Pottsville in both the Cahaba and Black Warrior tend to be dominated by ca. 450 Ma muscovite, and an intervening sample of litharenite in the Lower Pottsville yields ca. 375 and 320 Ma ages. Sandstones from higher stratigraphic levels contain more labile grains and are litharenite, with muscovite that tends to be ca. 320 Ma with varying proportions of ca. 375 Ma ages. The muscovite ages obtained for mature sandstones at the base of the Pottsville are interpreted to represent far-travelled grains derived from source terrane(s) with Taconian lithologies that lacked substantial contribution from Alleghanian sources. In contrast, the immature sandstones sampled throughout the Pottsville are interpreted to represent grains from proximal sources with Acadian and Alleghanian lithologies, but that did not typically provide Taconic muscovite. This record of different sediment sources implies competing depositional systems during the early depositional history of the Pottsville Formation: aggradational shoreline deposition during lowstand was fed by a longitudinal foreland drainage system(s), and fluvial-deltaic deposition during highstand was fed by transverse drainages of proximal source areas. These findings are compatible with the interpretation that the Black Warrior basin received sediment from sources in the northeastern Appalachians as well as the southeast during the Alleghanian orogeny.