Cornell University has explored the rocks beneath its Ithaca, New York, USA campus for potential geothermal energy resources sufficient to heat its buildings. The effort included drilling a 2,978 m borehole in 2022. Cornell is located in the Allegheny Plateau of southern and western New York, overlying the Paleozoic Appalachian Basin. Correlation among widely separated archival borehole data sets and archival 2D seismic reflection profiles revealed the overall structural setting, of gently south-dipping strata with small-scale thrust-related folding expected in the Silurian and Devonian rocks.
Although a narrow belt of Cambrian-Devonian outcrops in New York State provided the foundation for early stratigraphic studies in the United States, there has been scant analysis of the pre-Devonian geological history of the Plateau, with an area in New York similar area to Belgium. The new borehole, ESH #1, illuminates features of the Iapetan-facing flank of the Cambrian-early Ordovician “great American carbonate bank” which covered much of the Laurentian continent. The borehole data for lithologic and bedding features of the Ordovician Tribes Hill and Cambrian Little Falls, Galway and Potsdam formations show the passive-margin basin fill to be 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.
Completely novel in the Allegheny Plateau, the drilled basement rocks (2,859-2,978 m) consist of greenschist-grade siliciclastic metasedimentary and of mafic and felsic metavolcanic rocks. Given the rock compositions, a 5000 km2 magnetic low anomaly is now inferred to be the extent of the corresponding sedimentary rift basin. Overall, the Precambrian borehole rocks imply that >25 km erosion post-dated final Grenvillian orogenesis ~1 Gy, followed by >1 km of basin subsidence as expected regionally due to Rodinian continental breakup. Either overlapping with rifting or subsequently, deformation buried the basin fill to 5-10 km depth while temperature reached ~350 C, and then erosional removal of 5-10 km of crust, all prior to ~510 Ma.
The Cornell borehole achieved its primary objective, by providing the information needed to plan to extract geothermal heat from a deep reservoir. Moreover, the borehole also permitted advancement of geological knowledge of the Rodinian continental breakup and Iapetan passive margin basin – a second big success.