THE PENNSYLVANIA SALIENT: SEISMIC AND AEROMAGNETIC EVIDENCE FOR AN ARCUATE MAP PATTERN OF IAPETAN-OPENING FAULT SYSTEMS IN NEW YORK STATE

Since the time of the 2007 GSA session celebrating advances related to Bill Thomas’ 1977 paper, significant developments in procurement and analyses of seismic reflection data solidify the concept that an arcuate fault system (in map view) of Iapetan-opening/Rome Trough growth faults swings from NE trends in western NYS to EW trends in central NYS. This arcuate fault system influenced the location of shallower structural features characteristic of the arcuate Alleghanian Pennsylvania Salient. Reactivation of northerly trending, intra-Grenvillian suture fault systems north of, and truncated by, the arcuate fault system also occurred during Iapetan opening.

In the Appalachian Plateau of NYS, shallow structural-level features generally 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. However, these arcuate fault and fold systems are coincident with aeromagnetic anomalies, suggesting the structural systems have deep extensions that involve basement. Seismic data (2D and 3D) confirm that many of the fault systems have fault segments that extend down to Iapetan-opening growth faults. Recent well log and seismic studies show that the Salina evaporite-cored folds developed in the Devonian.

These examples suggest that the Iapetan-opening growth faults in the PA salient “corner” zone have an original arcuate map pattern. The arcuate faulting overprinted northerly-trending intra-Grenvillian suture faults that were also reactivated during Iapetan opening. The intersecting pattern of northerly and arcuate fault trends has an analog in the present eastern North Atlantic corner zone west of the UK where northerly-trending micro-continents such as Porcupine and Rockall banks lie north and east of the present deep Atlantic that sweeps around the banks and their intervening bathymetric deeps.

The Iapetan arcuate faults and intersecting faults controlled (through weakened, fractured rock from fault reactivations) the locations of later Alleghanian faults (including thrust ramps). Apparently little tightening of the arc occurred through time.