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Lower Pocono Coastal Embayments, in Western Maryland and Vicinity, Related to Latest Devonian Eustatic Sea Level Rise

Jack D. Beuthin

New data from an exposure of upper Hampshire-lower Pocono in western Maryland document a transgressive-regressive sequence of three distinct depo-facies in this outcrop. A deltaic-alluvial plain facies of unfossiliferous Hampshire red beds is conformably overlain by a brackish fossiliferous facies of gray and green Pocono beds, disconformably overlain by a fining-upward, point-bar facies of unfossiliferous gray Pocono beds. The fossiliferous facies coarsens up from sideritic, Planolites-burrowed shales and siltstones bearing Lingula and Camarotoechia to fine-grained, Skolithus-bearing sandstones. This subtidal to intertidal depo-facies accumulated in a protected, shallow, brackish bay affected only by tides and storms.

An eastward-thinning, lower Pocono transgressive tongue occurs throughout the western Maryland area. This transgression, which halted the westward progradation of the Hampshire delta complex, resulted from a base-level rise. Resultant submergence of the delta complex created several estuaries and bays. Coastal sand barriers in West Virginia protected these embayments. Base-level drop caused westward regression, incision of major streams near their mouths, and some subaerial erosion of the emerged coastal area.

Regional stratigraphy supports correlation of the lower Pocono transgression in Maryland with the latest Devonian transgression in Ohio (Cleveland shale) and Pennsylvania (Oswayo shale). The late Fammenian eustatic cycle (IIf) from the Devonian eustatic sea level curve may explain the lower Pocono transgression-regression. Locally, the Devonian-Mississippian boundary may be the disconformity beneath the Pocono point-bar facies.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.