John B. Hickman, Kentucky Geological Survey, University of Kentucky, Lexington, KY 40506-0107

The preexisting structure of the crystalline basement in eastern North America has influenced the subsequent structural history of later Paleozoic rocks. Past exploration for Trenton-Black River hydrocarbons has shown that basement faulting (often with a wrench component) and structural sags within the Ordovician Trenton and Black River carbonates can indicate the presence of hydrothermal dolomite reservoirs. In many cases, major basement faults have been reactivated by the later Appalachian orogenies, causing deformation of the younger overlying strata. Other basement faults in the area show little or no reactivation, and exhibit no shallow expression in the overlying Paleozoic rocks. Furthermore, since most basement faults did not propagate or otherwise deform any strata younger than the Late Ordovician, it can be inferred that these faults were reactivated only during the Taconic Orogeny.

The orientations of basement faults with respect to the changing regional orogenic stress field through time may be the primary control on what appears to be a selective reactivation history. Although faults oriented perpendicular to the primary tectonic force (σ₁) could be reactivated, the associated compression would tend to destroy porosity and permeability. Without this open path for hydrothermal fluids and hydrocarbons to migrate through, no reservoir would be created. If the preexisting basement fault (or even just a segment along one) was oriented so that the regional tectonic forces produced local transtension, however, this could reactivate the fault in such a way that the permeability of the fault zone would be enhanced, creating conduits for hydrothermal fluids.

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