PROTEROZOIC FAULT REACTIVATION IN THE APPALACHIAN BASIN, EASTERN OHIO, USA

The Appalachian Basin in Ohio is outside of the Appalachian fold-and-thrust belt of the northern Appalachian Mountains. However, open folds and low-displacement faults are documented in the Paleozoic strata. When available, seismic reflection data indicates many of these faults and folds in the Paleozoic section were initiated by preexisting faults from the Proterozoic. Further analysis of seismic data shows Paleozoic structures appear to have formed during orogenic events of the Appalachian orogeny. As more modern seismic data becomes available, Ohio’s Proterozoic fault network will become better understood.

The Moss Run Prospect (MRP), Killbuck Dome (KD), and Saybrook field (SF) are examples of Proterozoic faults propagating into the Paleozoic section. The Proterozoic faults in the MRP in southern Ohio propagate into Devonian-aged strata forming a positive sub-flower structure. At KD, in central Ohio, west-verging Proterozoic faults propagate into Upper Ordovician strata forming sub-flower structures. Isochron mapping at KD indicates early Cambrian extension motion along the faults followed by compressional motion during the Taconic and Salinic orogens. In northeastern Ohio, the SF’s Proteozoic faults reactivated as left-lateral strike-slip motion during the Taconic orogen.

Speculative seismic surveys by the private firm Evans Geophysical Inc. (EGI) display more Proterozoic faults reactivated during the Appalachian orogeny in Ohio. In southeastern Ohio (Monroe County), seismic line EGI-3 shows a series of faults at the core of a group of open folds. These faults do not propagate higher than the Middle Ordovician Trenton horizon suggesting faulting during the Taconic orogen. The orientation of these faults is unknown at present. Approximately 20 miles north, seismic line EGI-5 crosses the southern end of the N45^oE-striking Cadiz Anticline (CA) in Harrison County. The CA was mapped at the surface using Pennsylvanian coals. The CA is underlain by a series of Proterozoic faults and open folds. The faults do not propagate higher than the Middle Ordovician Trenton horizon; however, the structure is mapped via Pennsylvania exposures and reflector patterns indicate a change in the post-Taconic orogen structure, suggesting displacement along these faults during the Taconic and Alleghenian orogens.