ORDOVICIAN FAULT SYSTEMS IN THE APPALACHIAN BASIN OF NEW YORK STATE

Over 400 miles (640 km) of reprocessed 2-D seismic reflection data in the Appalachian Basin of NYS integrated with Landsat lineaments, topographic lineaments, geopotential field gradients, and fracture intensification domains demonstrate a complex pattern of fault systems that affected the Ordovician section. Three fault trends are common: northerly-striking faults that follow Grenvillian suturing trends; faults that trace an arc across NYS, from NE-strikes in western NYS to E-strikes in central NYS; and cross-strike domains (CSDs) that trend both WNW and NW. The northerly striking faults were normal faults in early Taconic times, consistent with tectonic models that indicate E-W Laurentian plate extension related to plate flexure over the peripheral bulge. Such faults include the Clarendon-Linden Fault System in western NYS and the Mohawk Valley faults in eastern NYS. In later Ordovician time compressional features developed along the same northerly trends, including anticlinal structures in western NYS and thrusts across NYS. Local unconformities over the anticlines and thrusts observed on the seismic lines document the tectonic growth history of these structures as Late Ordovician. Many of these faults were active in Iapetan-opening time as well.

The faults that arc across NYS were generally considered to be shallow structural level Alleghanian thrusts in western NYS, but seismic reflection profiles reveal that the trends are related to Iapetan opening/Rome Trough-related faults as well. These faults were reactivated in Ordovician time and, based on simple tectonic models, these faults experienced sinistral followed by dextral motion. Seismic reflection profiles show that they also had a down-dip component. Based on the same simple tectonic models, cross-strike discontinuities (CSDs) experienced dextral followed by sinistral motion during the Taconic collision.

Migration of hydrothermal fluids along fractures promoted dissolution, dolomitization and vuggy porosity characteristic of carbonate reservoirs in the Trenton/Black River (TBR) of central NYS. Thinned Trenton/Black River sections, a characteristic of the TBR play, are associated with several of the structures observed on seismic reflection data.