Orogenic Provenance of Mississippian Sandstones Associated with Southern Appalachian-Ouachita Orogen

Abstract

Mississippian clastic rocks in the Appalachian fold and thrust belt and Black Warrior foreland basin in northern Alabama are in the eastern part of a regionally extensive clastic wedge of Mississippian-Pennsylvanian age. The wedge thins onto the North American craton from the southern Appalachian-Ouachita orogenic belt and, like other clastic wedges along the orogen, may be interpreted to indicate uplift of a sediment source along the evolving orogenic belt. Mississippian clastic sediment in Alabama probably was derived from a provenance on the southwest within the Appalachian-Ouachita orogenic belt. However, an alternative interpretation proposes that the Mississippian clastic sediment was derived from a source on the north (unrelated to the Appalachian-Ouachita orogen) nd transported southward through the Illinois basin into the Black Warrior basin of northern Alabama. Petrographic data from outcrops of the two most sandstone-rich clastic units in the Mississippian of Alabama, the Hartselle Sandstone and Parkwood Formation, as well as compositional comparisons of the Hartselle-Parkwood sandstones with approximate time-equivalent sandstones in the Illinois basin, provide for discrimination between the alternative interpretations of provenance. Sandstones of the Parkwood Formation are lithic arenites (Q80F2R18) that contain metamorphic rock fragments and unstable polycrystalline quartz, indicating a low-rank metamorphic source. Lesser amounts of chert, pelitic rock fragments, and sandstone rock fragments suggest a secondary contribution from sedimentary source rocks. The Parkwood also has a minor component of volcanic rock fragments. The Hartselle Sandstone is mainly quartzarenite; compositional maturation was the result of marine depositional reworking. Despite the low concentration of labile grains, Hartselle samples contain high ratios of metamorphic to pelitic rock fragments and unstable to stable polycrystalline quartz. These data demonstrate a close affinity between the Hartselle and Pa kwood sandstones. The rock-fragment and quartz populations of the Hartselle and Parkwood sandstones indicate an orogenic provenance. The petrographic data and distribution of the clastic facies combine to indicate an orogenic source terrane southwest of the Black Warrior basin. Mississippian sandstones of the Illinois basin generally are sublitharenites (Q92F1R7), and the predominant lithic grains are chert and pelitic rock fragments, indicating a sedimentary source terrane. These data suggest that the Hartselle-Parkwood sandstones and Illinois basin sandstones were not derived from the same source but are consistent with the interpretation that Hartselle-Parkwood sediments were derived from an orogenic belt on the southwest while clastic sediment was supplied from the craton on the north to the Illinois basin. The orogenic provenance of Mississippian clastic sediments in Alabama demonstrates evolution of the Appalachian-Ouachita orogenic belt during the Mississippian.