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Sedimentology and Paleogeography of Upper Devonian Sandstones in North-Central Pennsylvania and Western New York

Edgar M. Hopkins

Combination of subsurface data from north-central Pennsylvania and outcrop data from western New York yields a complex paleogeographic model for this part of the Appalachian miogeosynclinal basin during the Late Devonian. An irregular paleostrike is attributed to syndepositional tectonism; northwest-trending basement blocks were experiencing differential vertical motion that resulted in variations of attitude and elevation between individual blocks. This caused segmentation of sediment dispersal systems onto each block and changes along strike of sandstone depocenters and sedimentary environments.

A bend in basin strike occurred along the Pennsylvania-New York border. The Bradford oil field lies along a local promontory at the apex of this bend. Another promontory was located 80 km to the south. In between lay a large coastal embayment across which was built a series of large deltas along a north-northwest axis during deposition of the upper part of the "Bradford group."

In addition to the existence of several basement blocks, several northeast-trending basement highs or flexures repeatedly localized successive stillstands during the many transgressions and regressions of the Late Devonian sea.

The stratigraphy and directional sedimentary structures along the northern outcrop belt of the sandstones support an interpretation of an east-northeast to northeast basin strike in this region and a change in depositional environments from sand ridges along a weather-dominated shelf in the lower Bradford group to coastal barriers, tidal channels, and delta platform distributaries and interdistributary bays in the upper Bradford group and overlying Venango group sandstones.

With recognition of a complex tectono-structural framework within the sedimentary basin, regional tracing of individual shoreline trends is possible.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.