SEDIMENT COMPOSITION AND 40AR/39AR AGES OF DETRITAL MUSCOVITE FROM POTTSVILLE CLASTIC WEDGES IN THE NORTHERN APPALACHIAN BASIN, PENNSYLVANIA: PROVENANCE AND DISPERSAL DURING THE LATE PALEOZOIC

Detrital modes of Paleozoic clastic strata in the Appalachian basin preserves unique information about orogenic processes, the specific sources of sediments, and the interrelationship of tectonic, climatic, and erosional events. The Lower Pennsylvanian Pottsville Formation in Pennsylvania is one of the Paleozoic clastic wedges that is the focus of this study that combines sandstone petrography and detrital muscovite ages to demonstrate spatial and temporal variations in sediment provenance. For this study, sandstone samples were collected from both surface exposures in the eastern anthracite field as well as from eight wells in the western bituminous field of Pennsylvania.

Petrographic modal analyses show that sandstones in the western bituminous field range from quartzarenite to sublitharenite with a mean composition of Qt₈₄F₁L₁₅ and that most of the sandstone units are texturally and compositionally mature. In contrast, the sandstones from the eastern anthracite field are relatively compositionally and texturally immature. There, sandstones are dominated by sublitharenite to litharenite with a mean composition of Qt₇₀F₂L₂₉. Most samples from both the anthracite and bituminous fields fall within the “recycled orogenic” provenance field on Qt-F-L ternary diagram.

Laser ⁴⁰Ar/³⁹Ar analyses on detrital muscovite indicate that the Appalachian orogen is the potential source terranes for Pottsville sediments in Pennsylvania. However, modes of muscovite ages in the Pottsville from both eastern anthracite field and western bituminous fields appear to record separate ages. The detrital muscovite cooling ages from eastern anthracite field are characterized by prominent Middle to Late Ordovician Taconic and Middle Devonian Acadian source terrane(s) with two discrete modes at 463 and 369 Ma. In contrast, Pottsville sandstones from the western bituminous field contain muscovite dominated by Late Ordovician Taconic, Middle Devonian Acadian and Late Devonian Neoacadian lithologies with discrete modes at 445, 397, 360 and 351 Ma. Overall, this study concludes that Early Pennsylvanian sedimentation in the Laurentia foreland was controlled by southward, southwestward, and westward drainage systems that all originated in the Appalachian orogenic belt to the east and northeast.