LINKS BETWEEN THRUST-RELATED DEFORMATION AT DEEP AND SHALLOW LEVELS, OVER 100 KM NORTH OF THE ALLEGHANY FRONT, TOMPKINS COUNTY, NEW YORK STATE

To assess resources and environmental risks for a geothermal energy project at Cornell University, we examined deep subsurface geology for the Appalachian Plateau in New York State. 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. The industry data, leased from Seismic Exchange, Inc., include 1980’s vintage and 2007-2008 seismic profiles, collected using multiple vibroseis sources. The 2018 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 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. As expected, we mapped abundant seismically imaged folds and thrusts in and above the Silurian Vernon Shale, which match well surface-mapped fold axes and, in some sectors of Tompkins County, clusters of sub-vertical faults terminate upward in “Trenton-Black River” grabens. Less expected is that many of the Silurian-interval-deformed zones correspond to small displacement thrust-style deformation zones beneath, in Lower Ordovician and Cambrian strata. Folds within the deepest-imaged strata suggest the existence of additional faults either within or below the basal Cambrian units. The deep thrust faults appear to have decollements at similar horizons as known in the Appalachian Valley and Ridge province. The deep folds and thrusts appear to be localized where there exists relief at the top of the basement. An interpretation of the origin of the relief is non-unique, such as sub-Potsdam Formation steep unconformities, steep faults in basement that were active in the Early Paleozoic but little reactivated during the Alleghany Orogeny, and basement faults that were strongly reactivated during the Alleghany deformation.