AN ASSESSMENT OF POTENTIAL OUACHITA AND APPALACHIAN SOURCES FOR SANDSTONES OF THE GREATER BLACK WARRIOR BASIN, BASED ON 40AR/39AR DATING OF MUSCOVITE

The Carboniferous Greater Black Warrior Basin (GBWB, including the Black Warrior, Coosa, and Cahaba basins) formed in a syntaxis between the Ouachita and Appalachian orogens. The relative contributions of clastic sediment to the GBWB from sources in the Ouachitas and the Appalachians is a subject of debate. Recent ⁴⁰Ar/³⁹Ar dating of detrital muscovite crystals, separated from quartz arenites and lithic arenites of the GBWB and analyzed in the Auburn Noble Isotope Mass Analysis Lab present a preponderance of Late Ordovician to Pennsylvanian ages. Prominent modes in the age distributions correspond to ages of micas known from igneous and metamorphic terranes of the Appalachians formed during Taconic, (Neo)Acadian, and Alleghanian events. These findings are in contrast to a lack of Neoproterozoic to Early Ordovician muscovite ages for GBWB samples. Thus, the data available for muscovite are taken to indicate that Appalachian sources provided a majority of clastic sediment to prominent sandstones from the Upper Mississippian to the Upper Pennsylvanian sections of the GBWB. Based on the premise that muscovite from peri-Gondwan, Pan-African/Brasiliano, and Alleghanian source terranes are to be expected in sediment derived from the Ouachita hinterland, we find no clear geochronologic evidence to corroborate inferences of an Ouachita source for the coarse sandstones of the GBWB. Basal quartz arenites of the Pennsylvanian Pottsville Formation are dominated by ~ 450 Ma, Taconic muscovite. Sandstones from upper sections of the Pottsville Formation contain abundant muscovite with ages of ca. 320-325 Ma, an approximate time for extensive, regional deposition of carbonates (e.g., Bangor limestone) along the southeastern Laurentian shelf. We suggest that barriers to Appalachian sediment transport, such as a Carboniferous forebulge, limited sediment transport from sources in the present-day southeastern Appalachians to the GBWB in the Early Pennsylvanian, when sources in the Taconian and Acadian hinterlands as preserved today in the northern Appalachians were favored. As Alleghanian orogeny progressed, such barriers did not limit supply of sediment from the southern Appalachians, with the result that muscovite from the upper sections of the Pottsville Formation are dominated by Alleghanian sources.