Abstract

The classic Sheep Mountain anticline on the southwestern flank of the Bighorn Mountains is an excellent example of a backlimb-tightening (BLT) structure, where a localized zone of shortening on the backlimb of a foreland arch can be explained by the bending of a basement slab over a listric master fault at depth. Previous work revealed that anticlines in the Sheep Mountain area have both east and west vergences, variable fold axis orientations and underlying faults that dip both northeast and southwest. Data from wells, seismic lines, and surface mapping have been used to resolve the 3D geometry of the Sheep Mountain area through the construction of balanced serial cross sections and 3D structural surfaces. Two-dimensional balancing constraints indicate that movement on southwest-dipping, out-of-the-basin basement faults occurred first and was followed by movement on northeast-dipping, into-the-basin faults. The restoration of 3D bedding surfaces show the complex interplay of the structures, with oblique structures transferring slip between faults and creating analogs for traps with 4-way structural closure.