DEEP ROCKS AND STRUCTURES OF THE ALLEGHENY PLATEAU REVEALED BY GEOTHERMAL EXPLORATION IN ITHACA NY

Cornell University’s aspiration to exploit direct-use geothermal energy to heat its central New York State Ithaca campus required exploration of potential reservoir formations at depths sufficient for a minimum geothermal temperature of 70 °C. The Ithaca campus location within the Allegheny Plateau limits potential reservoirs to the deepest parts of the Appalachian sedimentary basin and the underlying Precambrian basement. To document reservoirs and improve estimates of the cost of geothermal development, exploration borehole ESH #1 was drilled and completed in summer 2022 to a depth of 2,978 m (9,768 ft). Archival exploration data analyzed prior to drilling and new borehole data reveal the geological history of a region with scarce analysis of pre-Devonian rocks. Discoveries include a lower greenschist Neoproterozoic basin, sedimentological and stratigraphic features of Cambrian and lower Ordovician strata of the Appalachian passive margin, and structures developed during multiple stages of Paleozoic orogenic perturbations.

ESH #1 penetrated 60 m of unconsolidated glacial-related sediments and 739 m of Devonian strata, each thicker than regional trends in outcrops. The 704 m of Silurian strata include evaporites and mudstones which are thinner than regional subsurface trends, due to local deformation. The lithologies and thickness (839 m) of the Ordovician Queenston through Black River Formations are consistent with regional trends established by numerous gas exploration wells in central New York State. Below the Knox Unconformity (2,344 m), the borehole data for lithologic and bedding features of the Ordovician Tribes Hill and Cambrian Little Falls, Galway and Potsdam formations fill a regional information void. These strata are subhorizontal, well bedded, and dominated by dolostone and quartz arenite. Small scale sedimentary features are consistent with deposition in shallow marine conditions, except nonmarine deposits in the basal Potsdam. Basement rocks, 2,859-2,978 m below surface, consist of finely crystalline metasedimentary and metavolcanic lithologies with low-grade mineral assemblages. Basement compositional layers incline steeply northwest and there is a single identified foliation.