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The AAPG/Datapages Combined Publications Database
Strata of the Devonian subaerial and prodelta complex are preserved in 110,000 sq mi (260,000 sq km) of the Appalachian basin. Petroleum is obtained only from the western half, principally from higher permeability marine sandstones, although some is from prodelta dark shales. Absence of production in the east presumably is due to the escape of hydrocarbon from folds which bring potential reservoir strata to outcrop level.
Outcrops along the Allegheny Front from Maryland to Virginia were studied to interpret physical stratigraphy and environments of deposition and to understand better the factors controlling petroleum occurrence.
The deltaic clastic sediment came from an eastern quartzose source located in latitude from New York to Virginia. Depositional patterns of petroliferous sands resulted from gradual infilling of a subsiding basin, interrupted by rather abrupt eastward transgressions, which produced nearly synchronous, winnowed sands traceable across many counties. The earliest prodelta (Needmore Shale of Onesquethaw Stage) was derived from an upland near Baltimore. Cazenovia Stage deltaic siltstones and sandstones accumulated in Pennsylvania and New York. In late Tioughnioga time the winnowing zone extended to West Virginia (Clearville Siltstone) while terrestrial redbeds were accumulating in the Catskill Mountains. Early in the Taghanic, hundreds of feet of eustatic sea level rise shifted the shorelin scores of miles eastward. Throughout the rest of the Late Devonian the shoreline prograded generally westward, with fairly sudden eastward shifts of tens of miles during times of eustatic sea level rise. Younger petroliferous sandstones of the Cassadaga and Bradford stages accumulated in the western part of the basin during winnowing that accompanied shoreline shifts. Maximum westward encroachment of the subaerial Catskill delta was during Bradford times, followed by Early Mississippian transgression which produced Pocono Group sandstones.
Eustatic sea level changes leave sedimentary imprints which should be traceable for long distances in shallow marine sediments. Specific correlations from Virginia to New York are developed by matching times of sea level fluctuation.
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