Deep Tectonic Influence on Shallow Structures of Allegheny Plateau
T. K. Reeves, Jr., Jim Morris
The low plateau area of western Pennsylvania and western West Virginia is underlain by numerous salt-cored anticlinal structures. The locations of these anticlines have been controlled by disturbances in the salt and discontinuities on detachment horizons. These discontinuities were produced by deep-seated faults with ongoing movements that persisted into or through the time of Salina deposition.
Tilting of the basin during post-Salina sedimentation caused the salts to mobilize. These highly ductile units began to sag into the deep basin at a very early stage and moved by sliding until they reached the zones where faulting had disrupted the glide surfaces.
Seismic examples show how the pileup of salts along these fault-disturbed zones has produced the cores of the modern anticlines. Characteristic movements within these salt pillows have led to such familiar Appalachian features as anticlines that are steeper on the southeastern flank, fracturing and faulting with apparent thrusting in the Onondaga-Oriskany-Helderberg section, and zones of fracture porosity and enhanced producibility in the Devonian shales and shallow reservoirs.
An understanding of deep structures and salt deformation features in a shallow prospect area can lead to the discovery of zones of fracture porosity and can improve production in tight formations or permit the avoidance of areas where fracturing is so intense that no effective cap rock remains. Deep structure and salt tectonics can be relevant to shallow development work.
AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.