STRATIGRAPHIC AND DETRITAL SOURCE CONSTRAINTS FOR LOWER PALEOZOIC POTTSVILLE FORMATION OF ALABAMA AND MISSISSIPPI

The Black Warrior and Cahaba basins (BW-CB) of the southern Appalachians represent important late Paleozoic depocenters in eastern North America that have modern analogs in the the Bengal and Assam basins of the eastern Himalayas. Although much of the BW-CB clastic wedge remains deeply buried, outcrops and cores of synorogenic strata from the Pottsville Formation can be used to represent Early Pennsylvanian depositional history. Earlier work on sediment compositional from these basins suggests that the Pottsville detritus may have been derived partly from the Ouachita orogen in Mississippi. We, however, suggest a dominant Appalachian provenance based on petrofacies and detrital geochronology studies.

Laser incremental heating analysis of plagioclase crystals from a volcanic bed in the Black Warrior basin in Mississippi provides a plateau age of 308.58±0.92 Ma (2 σ precision), which provides the first depositional radiometric age constraint for the Pottsville Formation. ⁴⁰Ar/³⁹Ar analysis of muscovite crystals extracted from the lower Pottsville Formation of the Cahaba basin yield ages as young as Early Pennsylvanian, that are interpreted to reflect a very brief lag time for the deposition of some of the Alleghanian sediment. Prominent modes of ca. 460-450 Ma, 380-370 Ma, and 330-320 Ma are evident among the samples analyzed. These modes are interpreted to record derivation of sediment from catchments in the southern Appalachians containing Taconian, Acadian, and Alleghanian metamorphic and igneous rocks. Data from modal analysis suggest that Pottsville sandstones in the Black Warrior and Cahaba basins are less quartzose than that in the Ouachita belt. Most of Pottsville sandstone is compositionally and texturally immature. The dominance of rutile and almandine garnets suggests a medium– to high–grade metamorphic source supplied a large quantity of sediment to the Cahaba basin.

We interpret the Black Warrior and Cahaba orogenic repository to have received detritus via lower Pennsylvanian drainages of the southern Appalachians, analogous to the modern Ganges-Brahmaputra drainages of the Himalayas. Differences in Paleozoic age modes among the samples may reflect some combination of longshore drift, Alleghanian tectonic development, and progressive development of Appalachian catchments.