Abstract

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.

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