Composition of Carboniferous Sandstones and Tectonic Framework of Southern Appalachian-Ouachita Orogen

Abstract

ABSTRACT Regional stratigraphic and sedimentologic studies in the Appalachian fold and thrust belt and Black Warrior foreland basin in Alabama indicate deposition of two converging clastic wedges during Carboniferous time. A northeastward-prograding clastic wedge (Floyd-Pride Mountain-Hartselle-Parkwood) reached Alabama by late Meramecian time; progradation continued with deposition of the Lower Pennsylvanian Pottsville Formation. A southwestward-prograding clastic wedge (Pennington-Pottsville) did not appear in Alabama until latest Mississippian time. The northeastward-prograding wedge indicates a source terrain southwest of the Black Warrior basin and implies orogenesis as a result of convergence along the southern margin of North America. Petrographic data from 79 sandstone and 6 conglomera e samples from the Parkwood and Pottsville Formations in Alabama provide information on the composition of the source rocks and. thus, on the crustal components and tectonic setting of the convergent margin. Foliated quartzmica rock fragments. unstable polycrystalline quartz, pelitic rock fragments, and polycyclic monocrystalline quartz suggest that the largest and/or most proximal source-rock province was a low-grade metamorphic and sedimentary fold-thrust belt. Detrital chert suggests derivation from a subduction complex or from bedded chert incorporated in a fold-thrust belt. Andesitic ± basaltic and dacitic volcanic rock fragments indicate the presence of an arc complex. A complex source terrain produced by juxtaposition of a fold-thrust belt, subduction complex, and arc sugge ts collision of the Alabama promontory of the southern margin of North America with an arc or with a microcontinent and associated continental-margin arc.