Glacial Depositional Patterns:  Potential Clues to Basement Faulting in Northwestern Pennsylvania and Adjacent Areas

John A. Harper, Pennsylvania Geological Survey, 400 Waterfront Drive, Pittsburgh, PA 15222-4745

Patterns of glacial deposition and post-glacial stream development in NW Pennsylvania suggest that Pleistocene ice flow was influenced directly or indirectly by basement tectonics and Phanerozoic fracturing inherited from Late Precambrian-Early Paleozoic basement movement.  Orientations of sets of stratified drift deposits in buried glacial valleys, generally NW-SE, N-S, and E-W, appear related to fracturing associated with deep wrench faulting.  The NW-SE set coincides with the orientations of numerous established and suspected faults that have strike-slip components, with relative movement determined from offset of structure axes, discontinuities in depositional patterns, and other features farther to the southeast.  Orientation of the N-S and E-W sets probably is related to zones of tension fracturing associated with right- or left-lateral strike-slip movement along the wrench faults.  In addition, the extent of mapped maximum glacial advance in NW Pennsylvania coincides closely with the western edge of the Rome trough in NW Pennsylvania.  Reactivation or inheritance of trough fracturing occurred intermittently throughout the Phanerozoic.  Coincidence of maximum glacial advance with the edge of the Rome trough suggests the trough may have influenced glaciation in NW Pennsylvania by acting as a crustal pivot to slow ice flow, and by conducting crustal heat to the surface where increased ambient temperatures could have impaired ice advancement.   I suggest, therefore, that mapped glacial deposits in NW Pennsylvania, as well as in adjacent states, may be useful for predicting the existence of basement faults in advance of more costly remote sensing (e.g., seismic) techniques.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York