SEISMIC EVIDENCE FOR IAPTEN FAULT CONTROL OF THE ARCUATE MAP PATTERN OF THE PENNSYLVANIA SALIENT

Reprocessed proprietary seismic data from the Appalachian Plateau of NYS and northern PA indicate that the arcuate structural pattern characteristic of the Alleghanian Pennsylvania Salient was strongly influenced by an arcuate system of Iapetan opening/Rome Trough faults.

In the Appalachian Plateau of NYS, shallow structural-level features were assumed to reflect Alleghanian salt-cored folds and associated thrusts related to the arcuate map pattern of the fold and thrust belt in Pennsylvania. Data sets included primarily shallow well logs and dips of surface rocks measured by leveling lines, some salt mine data and extremely limited seismic reflection data. Surface traces of the structures generally crossed major aeromagnetic gradients, supporting the hypothesis of minimal basement involvement. However, Scanlin and Engelder (2002) suggested that the shallow folds follow deep structures in SW PA.

In NYS proposed arcuate fault systems, based on EarthSat (1997) lineaments and gravity, are coincident with some aeromagnetic anomalies. Further, seismic data across NE-trending lineaments show that several lineaments, formerly believed to represent shallow folds, actually represent fault systems that affect the entire Paleozoic section. Some of these faults were initially Iapetan-opening growth faults. In northern PA, the Alleghanian Smethport-Sharon Anticline is coincident with an arcuate aeromagnetic anomaly, and reprocessed seismic shows a dramatic hinge in Iapetan opening time beneath the anticline. These and other examples suggest that the Iapetan opening faults in this “corner” zone have an original arcuate pattern. These early arcuate faults controlled (through weakened, fractured rock from fault reactivations) the locations of later Alleghanian faults (including ramps). Little (if any) tightening of the arc occurred through time (consistent with paleomagnetics); stress fields passed through the plateau, but did not rotate the rocks significantly.

In northern and central PA and western and central NYS, Devonian sandstones (such as the Elk and the Bradford sands) have depositional patterns that are orthogonal or parallel to the arcuate structure. Apparently interplay between the eustatic sea level and reactivation of the arcuate Iapetan-opening fault blocks guided sandstone deposition.