THRUST SPLAYS FROM A CAMBRIAN DECOLLEMENT OVER 100 KM NORTH OF THE ALLEGHANY FRONT, TOMPKINS COUNTY, NEW YORK STATE

The deep subsurface geology of the Appalachian Basin in New York State is poorly known outside of the hydrocarbon industry. We secured access to seismic reflection data from two sources and interpreted the geology in consultation with borehole data. The data include about 150 km of 2D hydrocarbon-industry seismic profiles and an academic project that surveyed 3 km² area on Cornell University property collected in 2018 by faculty and students. The interpretations provide background information useful to assess resource and environmental risks of a geothermal energy project at Cornell.

The industry data, leased from Seismic Exchange, Inc., include 1980’s vintage and 2007-2008 seismic profiles, collected using multiple vibroseis sources. The academic survey used a single rented vibrator truck, the NEES T-Rex (29,000 lbs), operated by the University of Texas at Austin, with 10-second sweeping from frequencies of 5–80 hz. Receivers were nearly 400 ZLand GenII nodes (™Fairfield Nodal) rented from the SAExploration Seismic Services (US), LLC.

The key mapping targets were the positions of faults, especially those below the Silurian salt-bearing units. The traditional interpretation of Appalachian Plateau structure consists of a decollement in the Silurian salt, which produced widespread thrust splays and folds, underlain by localized steep wrench faults which cut up to the base of the Upper Ordovician Utica Shale.

Five types of structural deformation are mapped. Seismically imaged folds and thrusts in and above the Silurian Vernon Shale are frequent and match well surface-mapped fold axes. In some sectors of Tompkins County, clusters of sub-vertical faults terminate upward in “Trenton-Black River” grabens. The data show evidence of small displacement, sub-horizontal thrust faults ramping across Cambrian through Lower Ordovician sedimentary rocks. Folding appears to affect some of the deepest-imaged sedimentary units, suggesting the existence of additional faults either at or below the depth of the Cambrian basal siliciclastic units. We infer that the thrust faults within the Cambrian through Lower Ordovician units may connect with decollements at similar horizons in the Appalachian Valley and Ridge province.