COMPARISONS OF CLASTIC COMPOSITION AND 40AR/39AR DETRITAL MUSCOVITE AGES FOR THE POTTSVILLE FORMATION FROM THE BLACK WARRIOR BASIN AND CAHABA SYNFORM

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) presents the greatest accumulation of orogenic sediment in the southeastern Appalachian foreland. Previous studies of sandstones along the eastern margin of the GBWB (Cahaba synform, Central Alabama) documented detrital muscovite 40Ar/39Ar age distributions with modes of ca. 455, 375, and 330 Ma. Sandstones of the Cahaba synform have a relatively immature composition, and detrital mineral phases including conspicuous garnet, biotite and rutile, that are interpreted to indicate derivation from amphibolite facies rocks (Peavy, 2008). Samples from the depocenter of the GBWB (the Hendrix core) are dominated by detrital muscovite ages of 320 Ma, with varying prominence of a 370 Ma mode. The composition of sediment from the GBWB depocenter (sampled over a ca. 4000’ interval of section in North-Central AL) is relatively consistent and immature, similar to that of the Cahaba synform. Detrital hematite, apatite, zircon, biotite, tourmaline, and relatively rare garnet are evident in preliminary studies of heavy minerals from the depocenter. Conglomerates of the GBWB depocenter contain abundant clasts of chert, limestone (with bryzoans and echinoderms), shale, basalt (commonly submarine with quench textures), low-grade metamorphic clasts (phyllites), and quartzite. Initial studies of a ca. 2000’ section on the northern margin of the depocenter (the Brooks core, NW-AL) document more quartzose composition and conglomerates with clasts that seem dominated by quartzite. Considering the depocenter, the relatively consistent composition of sandstones, detrital muscovite age, and conglomerate clast types are interpreted to reflect derivation from a volcanic arc terrane containing relatively low-grade Alleghanian metamorphic rocks. We consider the Suwannee terrane to be a likely candidate for much of the sediment that reached the GBWB depocenter, whereas portions of the Carboniferous basin to the northeast derived a majority of sediment from the southeastern Blue Ridge and Piedmont terranes.