Clastic Coastal Environments in Ordovician Molasse, Central Appalachians

Abstract

Marginal-marine rocks of inferred tide-related origin occur in the lower Bald Eagle Formation (Upper Ordovician) of the Central Appalachian miogeosynclinal sequence. The marginalmarine sequence averages 65 meters thick, and separates underlying delta-slope shales and turbidities (Reedsville Formation) from overlying fluvial sandstones and conglomerates of the upper Bald Eagle (Thompson, 1968). The entire lithofacies sequence comprises the lower parts of the Taconic clastic wedge, which prograded northwestward during Late Ordovician time as indicated by both marine and continental facies changes and paleocurrents. The resultant northwest-sloping paleoslope provided the framework for the origin and geometry of the marginal-marine rocks, which developed along the margins of an advancing delta front.