Description and interpretation of natural fracture patterns in sandstones of the Frontier Formation along the Hogsback, southwestern Wyoming

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Fractures exposed in outcrop can be classified into three general groups: J1 fractures strike generally north-south and were formed early, in a regime of east-west extension during basin subsidence. These fractures have the greatest potential for extrapolation into the subsurface of the basin. J2 fractures formed during the subsequent onset of thrusting that led to the Hogsback escarpment; J2 fractures were created by a north-south dilatancy in response to east-west tectonic compression and strike generally east-west. They may extend slightly east of the thrust belt. J3 fractures formed soon after J2 fractures as a mechanical response to local shear and torsion within the thrust plate. They will not exist beyond the limits of the thrust belt. Petrographic study of selected samples suggests that the mechanical properties that controlled fracture susceptibility changed through time, dictating the potential for the sandstones to fracture during given stress-producing tectonic events.


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