Shelf, paralic, and fluvial environments and eustatic sea-level fluctuations in the origin of the Tuscarora Formation (Lower Silurian) of central Pennsylvania

Tuscarora deposition began at the beginning of the Silurian Period at the time of both glacioeustatic sea-level rise and renewed tectonic elevation of the Taconic source terrain. Braided alluvial systems transported coarse sediment northwestward to a wave-dominated coast, yet sea-level rise was so rapid that the shoreline retrograded from western to eastern Pennsylvania. At the time of transgression, shorelines varied from high-energy beaches to estuaries. Seaward of the shoreline, sand was fashioned into shelf sand-wave complexes. Much of the Tuscarora accumulated in this shallow-marine shelf environment. Later eustatic sea-level fall resulted in progradation of lower energy coastal sand/mud flats northwestward over the former shelf, shortly before a subsequent sea-level rise terminated Tuscarora development. The basal Tuscarora consists of two lithofacies of coastal origin: the horizontally laminated lithofacies (high-energy beach) and the pink transitional lithofacies (estuary). The main body comprises the eastern cross-laminated lithofacies (braided fluvial) and the western cross-laminated lithofacies (shelf sand-wave complexes). Capping the Tuscarora is the red, Skolithos-burrowed lithofacies (coastal sand/mud flats).--Modified journal abstract.