Subsurface evidence for faults in the Appalachian basin, western New York State

Over 1,000 well logs in the Appalachian basin of northwestern Chautauqua County, western New York State, were used to construct trend surface residual anomaly (TSRA) maps on the tops of the Devonian Dunkirk Shale, Hanover Shale, and Onondaga Formation, the Silurian Medina Formation, and the Ordovician Queenston Shale. These maps provide the first well log evidence for several N-, NW-, and NE-striking geologic structures. The newly-recognized N-striking Dunkirk fault and the linked, previously-proposed Charlotte Center fault affect all units studied. Northwest-striking cross-strike discontinuities (CSDs) are evident across the map area in all units, but are especially prominent in the Onondaga and deeper units. The TSRA maps of the Devonian units confirm the NE-striking Chautauqua anticline (Bass Islands structural trend) and also suggest a NE-striking anticline northwest of the Chautauqua anticline, the Lakeshore anticline. The TSRA maps of the Medina and Trenton units indicate local NE-striking deep faults beneath both anticlines. This study illustrates that TSRA mapping can be a valuable tool for recognizing small-structural relief features in nearly flat-lying strata.