Abstract

The lower Pennsylvanian Pottsville Formation, in the Appalachian foreland basin, constitutes a late Paleozoic clastic wedge formed close to the Appalachian orogenic belt. In this study, we analyzed Pottsville sandstone from the western bituminous and eastern anthracite fields in Pennsylvania to evaluate the detrital history of the sediments. Petrographic modal analyses show that sandstone in the western bituminous field ranges from quartzarenite to sublitharenite, with mean composition of Qt₈₄F₁L₁₅; sampled sandstone from the eastern anthracite field is dominated by sublitharenite to litharenite with mean composition of Qt₇₀F₂L₂₉. Heavy-mineral assemblages from both fields are dominated by ultrastable minerals (zircon, rutile, and tourmaline), apatite, sphene, spinel, siderite, and abundant opaques. Almost all the studied sandstone samples are garnet-depleted except one from the eastern anthracite field. The chemical composition of chromium- and zinc-rich spinel in samples from both fields might suggest exhumation of an arc terrane and ophiolitic belt with ultramafic igneous rocks. Particularly, the ternary plot of Fe³⁺–Cr³⁺–Al³⁺ end members for the chrome spinels possibly suggest a derivation from an alpine-type peridotite complex. Laser ⁴⁰Ar/³⁹Ar analyses of detrital muscovite from eastern anthracite fields and western bituminous fields record separate ages, with the former characterized by prominent Middle to Late Ordovician Taconic and Middle Devonian Acadian ages with two discrete modes at 463 and 369 Ma, and the latter dominated by Late Ordovician Taconic, Middle Devonian Acadian, and Late Devonian Neoacadian ages with discrete modes at 445, 397, 360, and 351 Ma. The new data suggest that early Pennsylvanian sedimentation in the Appalachian foreland basin was controlled by southward, southwestward, and westward drainage systems that originated in the Appalachian orogenic belt to the east and northeast.