Paleozoic Tectonic Effects on Trenton-Black River Hydrothermal
Reservoirs
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