Fold - Fracture Relationships: Application at Sheep Mountain Anticline, Bighorn Basin, Wyoming
Personnel: N. Bellahsen, P. Fiore and D. D. Pollard
Sponsor: NSF Tectonics Program EAR-0125935; NSF Collaboration in Mathematical Geosciences EAR-0417521; Stanford Rock Fracture Project; Institut Français du Pétrole
Description: This project examines the relationship between the folding and fracturing of a Laramide, asymmetric, fault-cored fold of the Bighorn Basin in Wyoming. Field and thin section observations of fracture orientation, mode of deformation (opening or shear), termination relationships, and evidence for reactivation have been synthesized into a fracture evolution history that constrains the kinematics of the fold evolution. Analyses to date suggest that there was no lateral fold propagation and no hinge migration, and that limb rotation or limb flexure operated at different structural locations during folding. Further work will focus on (1) mechanical models that investigate the relationship between the heterogeneous distribution of certain fracture sets and stress field perturbations due to slip along the underlying thrust fault; (2) geochemical analyses of fracture cements to determine how cements within various fracture sets vary and what this may imply about fluid migration and the relative age relationships and regionality of the fracture sets; and (3) reprocessing three two dimensional seismic profiles located near Sheep Mountain to better constrain the subsurface fault geometry.

Aerial photograph of Sheep Mt. The upper right inset is a photograph and corresponding line drawing of an outcrop on the backlimb (southwest flank) of the anticline showing the deformation at Sheep Mt. on the order of meters. The lower left inset is a photomicrograph of a fracture sample taken from the same location, showing the deformation at Sheep Mt. on the order of millimeters.
Selected Publications:

Bellahsen, N., Fiore, P., and Pollard, D. D., The role of fractures in the structural interpretation of Sheep Mountain anticline, Wyoming. Submitted to the Journal of Structural Geology.