SEDIMENTATION AND TECTONICS OF LOWER PENNSYLVANIAN POTTSVILLE FORMATION FROM WESTERN BITUMINOUS FIELD OF PENNSYLVANIA

The lower Pennsylvanian Pottsville Formation is found from Northern Appalachian basin in Pennsylvania to the Greater Black Warrior Basin (BWB) in Alabama & Mississippi. In the northern depocenter of Pennsylvania, the Pottsville sediments are found in both outcrop and subsurface sections in western Bituminous and eastern Anthracite fields. The thickness of the Pottsville Formation increases from northeast (69 to 263 feet in northeastern Tioga County) to southwest (1917-2092 feet in Greene County) in Pennsylvania. The formation disconformably overlies older Mississippian and possibly Devonian rocks. The Pottsville sequences in the western Bituminous field in Pennsylvania consist of alternating sandstone, shale, claystone, siltstone, coal beds and occasionally limestone. Sandstone composition reveal the provenance history of these fluvio-deltaic to shoreface deposits.

Compositionally the Pottsville sandstones are orogenic which range from being quartzolithic to quartzofeldspathic. Quartz grains are subangular to subrounded and are mostly composed of monocrystalline grains. Feldspars are dominated by potassium feldspar. Lithic fragments include roughly equal amounts of sedimentary and metamorphic types. Upper-grade metamorphic lithic fragments (phyllitic to schistose) are common. The volcanic lithic fragments are scarce. Like the Pottsville sandstones from BWB (about 8000 feet) in southern Appalachian depocenter, the Pottsville sandstones in the western Bituminous field in Pennsylvania also plot in the “recycled orogenic” provenance field of Dickinson (1985). However, the four-fold greater thickness of the Pottsville in BWB relative to the Bituminous field in Pennsylvania implies that the Alleghanian collision was less pronounced in the northern Appalachians which could not create a greater accommodation space for the Pottsville as it did in BWB. Dominance of quartz also suggest possible derivation partly from the cratonic areas to the northwest. The abundance of potassium feldspar and upper-grade metamorphic lithic fragments suggests a felsic plutonic and deeper-crustal metamorphic source. Ongoing work on detrital geochronology and microprobe work will provide better constraints on the depositional and detrital history of the Pottsville Formation.