GEOLOGIC MAPPING IN THE APPALACHIAN BASIN OF WESTERN NEW YORK STATE

Bedrock mapping conducted between 1996 and the present has resulted in twelve 7.5’ geologic quadrangle maps that cover parts of Allegany, Cattaraugus, Erie and Wyoming counties, western New York State. Although the area has experienced intense glaciation, we found over 2000 bedrock outcrops from which we collected sedimentologic, stratigraphic and structural data.

The study area consists of Upper Devonian clastic sediments in the West Falls, Canadaway, Conneaut and Conewango groups of Frasnian-Famennian age. Syndepositional fault activity strongly influenced the lithologies and geometries of formations within the Canadaway Group. Fault basins permitted the development of an anoxic environment during the deposition of the Hume Formation. One model for the deposition of the Lower Sandstone Member of the Rushford Formation includes uplift and rotation on many small fault-blocks during a period of lowstand. The localized changes in topography promoted the deposition of chenier ridges on the upthrown fault blocks. Unconformably overlying conglomerate lags mark the beginning of the transgressive sequence tract and end of the clastic deposition of the Lower Rushford Member. Lenticular sandstone bodies in the overlying units generally represent offshore sand-ridges whose locations reflect a coincidence with active faulting.

Detailed structural analyses in these quadrangles, including fracture analyses, enabled us to map the traces of major structural features at the surface, as well as locate subsurface faults. Major structural features in the area include: 1) north-south trending Clarendon-Linden Fault System, 2) northeast-trending Appalachian faults and related folds, including the Bass Island Trend and 3) northwest-trending cross-strike discontinuities.

These new stratigraphic and sedimentologic data have promoted a better understanding of the depositional systems for the correlative, historically important, Upper Devonian petroleum reservoirs. Structure analyses have enabled us to determine potential seismic hazards for zoning considerations.