Abstract:
Quartzarenites in the Upper Mississippian and Lower Pennsylvanian of the central Appalachian basin have been attributed to fluvial or beach-barrier depositional environments. As part of the USGS basin analysis program, we reevaluated existing data and concluded that quartzarenites were deposited primarily in a high-energy marine environment dominated by tidal currents. These deposits are linear, trend toward the southwest, and are roughly parallel to the axis of the Appalachian geosyncline. Herringbone structures and bioturbation are abundant in the upper part of the deposits and near their margins. The lower and central parts of the deposits commonly display unidirectional festoon cross-beds having amplitudes up to 1 m. Basal contacts tend to be sharp and erosional in the high-energy central parts but are gradational near the margins. The spatial relation of these sandstone deposits to marine facies, their widespread distribution, and their lateral continuity are more compatible with a marine-dominated rather than fluvial origin. Their textural and mineralogical maturity also indicates winnowing typical of a high-energy marine system. Sedimentary structures typical of beach deposits or fluvial systems are rare.
These sandstones were apparently deposited in an epicontinental seaway, which, at times, may have been open at both ends. Because of the configuration of the basin, tidal and geostrophic energies were dominant over wave energy; tidal basin deposits predominated, and wave-energy beach-barrier deposits were rarely preserved. Ebb flow carried the winnowed fines into the southwestern part of the Appalachian basin or into the Ouachita geosyncline. Similar hydrodynamics and sediment transport occur today on the Sunda Shelf, the Bay of Fundy, and in the Bering Sea.