Evidence for Natural Late Paleozoic Hydrofracturing Event in Western West Virginia
J. B. Ferm, R. Ehrlich
Permeable rocks enclosed between less permeable strata can leak fluids into the enclosing facies. If the permeable stratum is a surface aquifer and is present at significant depth, large hydrostatic pressures can develop. If this aquifer is also pinched out downdip, then hydrostatic overpressuring can occur and permeability is enhanced in adjacent strata because new fractures open and existing planes of weakness are dilated. Evidence for a late Paleozoic hydrofracturing event is found in a core on the crest of Burning Springs anticline, Wood County, West Virginia, with the thinning St. Peter Sandstone acting as an aquifer. The sequence examined from 10,400 to 10,900 ft includes the uppermost part of the Knox Dolomite unconformably overlain by the 30-ft thick St. Peter San stone passing upward to Chazy carbonates. Principal evidence for overpressurizing is dilated, dolomite-filled stylolitic seams up to 10 mm thick, a permeability-controlled transition in the lower Chazy from dolomite to limestone, and stable isotope values that vary from the surrounding isotopically equilibrated rocks. The hydraulic fracturing event occurred after the Ordovician, but before major Alleghenian folding induced a set of undilated, inclined stylolites. Thus, the hydraulic fracturing event may have preceded major Appalachian thrusting, which may have helped localize thrust ramping at the Burning Springs anticline.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.