Detrital History of the Lower Pennsylvanian Pottsville Formation In the Cahaba Synclinorium of Alabama, U.S.A.

Abstract

Abstract: The Greater Black Warrior Basin (GBWB) is an important late Paleozoic depocenter of the southern Appalachian foreland basin containing a thick (> 2.5 km) synorogenic clastic wedge belonging to the Lower Pennsylvanian Pottsville Formation. Pottsville clastics are cyclothemic, consisting of interbedded sandstone, siltstone, claystone, shale, and numerous coal beds, with orthoquartzite sandstone and conglomerate at the base. Basal Pottsville is dominated by quartz-rich sediments; feldspars increase upsection. Presence of heavy minerals, including garnets and rutile, suggest exhumation of deeper sections of orogenic belts for Pottsville sandstones. Compositions of these sandstones (Qt 60 F 7 L 33 ) reflect a “recycled orogenic” provenance. 40 Ar/ 39 Ar analysis of detrital muscovite from the Pottsville Formation yields ages as young as Early Pennsylvanian, that appear to reflect a very brief lag time for the deposition of some of the Pottsville sediment. Prominent detrital-muscovite age modes of ca. 460–450 Ma, 380–370 Ma, and 330–320 Ma are evident among these samples, and are interpreted to represent sediment from catchments containing Taconian, Acadian, and Alleghanian lithologies. We interpret the GBWB orogenic repository to have received detritus via Lower Pennsylvanian drainages of the southern Appalachians, analogous to the modern Ganges–Brahmaputra drainages of the Himalayas. There are dramatic differences in single-crystal 40 Ar/ 39 Ar age modes for muscovite among these samples that likely reflect combinations of changes in transverse and longitudinal sediment supply, Alleghanian tectonics, and progressive development of Appalachian catchments.