Abstract

The analysis of geophysical well log data from 20 deep wells in western and central Pennsylvania, southern New York, and northern West Virginia confirms the presence of anomalies in the distribution and thickness of the Lower Ordovician Beekmantown, Middle Ordovician Trenton, Lower Devonian Oriskany, and Middle Devonian Onondaga and Tully rock units. The nonuniformity of these rock units occurs in an area of western Pennsylvania referred to by W. R. Wagner in 1976 as the Olin basin. The margins of this feature are delineated by Upper Cambrian and Lower Ordovician growth faults. Wagner considered these faults to be extensions of Precambrian basement faults.

A structural depression in southwestern Pennsylvania and northwestern West Virginia hosted the depocenters of many of the Ordovician, Silurian, and Devonian sediments. This feature coincides geographically with the southern boundaries of the Late Cambrian Olin basin. Displacement along Precambrian basement faults coincident with this structure could have accounted for the distribution and thickness of the Beekmantown sediments in this region. The correlation of bentonite layers of the Trenton Group in western Pennsylvania indicates that faulting coincident with this depression appears to have affected the distribution and thickening of sediments across this basin.

Limited, renewed displacement of Wagner’s Upper Cambrian growth fault as a positive flexure, resulting in an uplift of basement highs in Devonian time, might have accounted for the minimum deposition of the Oriskany, Onondaga, and Tully units in western and north-central Pennsylvania.

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