Revisiting the Hubbert-rubey Hypothesis for overthrust faulting: Inferences from progressive mineralization on bedding slip surfaces during flexural slip folding of Devonian Shale, the Appalachian Basin, Usa

Open Access
Author:
Aydin, Murat Gorkem
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 12, 2011
Committee Members:
  • Terry Engelder, Thesis Advisor
Keywords:
  • flexural slip folding
  • slickensides
  • cleavage
  • mirror-like surfaces
Abstract:
Both bedding-parallel slickensides and cleavage duplexes are abundant in core taken within black and gray Devonian shales of the Appalachian Basin. Slickensides are more abundant on the limbs of folds relative to hinge lines, an indication of flexural slip folding. The abundance and the orientation of slickensides in black shale relative to gray shale show that bedding-parallel slip during flexural-slip folding favored reduced effective normal stress. This reduction in effective stress is inferred to occur during the buildup of maturation-related pore pressure. Morphology of slickensides is dependent on the minerals decorating the slip surface. Chlorite rich films show mirror-like morphology polish but posses ridge-in-groove striations on microscopic scale. Quartz and calcite fibers are covered with ridge-in-groove type of striation on mesoscopic scale as well. Slip surfaces are characteristic of three internal detachment zones in the Appalachian foreland, all cutting black. The interpretation is that the Hubbert-Rubey model for low effective stress favors that development of these detachment zones rather than the inherent weakness of the shale. Since slip surfaces are natural fractures and the gas production from the low permeable rocks highly depended on finding pathways, this study can be useful for the industry.