About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Montana Geological Society



1997 Bighorn Basin Symposium Guidebook
July, 1997

Pages 100 - 112

Evidence for right-oblique-slip on a northern segment of the Big Trails Previous HitfaultNext Hit system, southern Bighorn Mountains, Wyoming

Alan J. Ver Ploeg, Wyoming State Geological Survey, Box 3008 University Station, Laramie, Wyoming 82071
Phillip L. Greer, Wyoming State Geological Survey, Box 3008 University Station, Laramie, Wyoming 82071


The Big Trails Previous HitfaultNext Hit is traditionally defined as a northeast-trending, basement-controlled, high angle Previous HitfaultNext Hit extending nearly 53 miles along the crest of the southern Bighorn Mountains. However, the authors have observed several features along this Previous HitfaultNext Hit typical for strike-slip or oblique-slip Previous HitfaultNext Hit models. The Previous HitfaultNext Hit begins at the intersection of the Owl Creek and the Casper arch thrusts on the south and terminates on the east-west trending Tensleep Previous HitfaultNext Hit to the north.

In an area mapped by the authors, the main Previous HitfaultNext Hit trace is an eighth to a half mile wide, and characterized in map view by multiple braided Previous HitfaultNext Hit strands. Variable displacement and reversals of displacement occur on the main Previous HitfaultNext Hit trace and on subsidiary faults. Horizontal to near horizontal slickensides were measured along the Previous HitfaultNext Hit; plunge of the striations ranged from 10-55° in a predominantly northerly direction. "Horsetail" Previous HitfaultNext Hit splays mapped in the west Previous HitfaultNext Hit block indicate drag from right oblique-slip. Horst and graben features identified in the Previous HitfaultNext Hit trace correlate with confining and releasing bends and the trace of the main Previous HitfaultNext Hit is near vertical in profile. Vertical offset, i.e., stratigraphic separation, which is down to the west along the majority the Previous HitfaultNext Hit, shifts to down to the east near the north end. Separation ranges from almost zero on the north end, where vertical offset shifts to down to the east, to a maximum of more than 4500 feet near the middle of the Previous HitfaultNext Hit. Horizontal offset in the form of right-slip is estimated at 2-3 miles.

The Big Trails Previous HitfaultNext Hit is basement controlled and coincident with zones of weakness. These zones are defined by northeast trending quartz diorite, mafic, and amphibolite dikes of early Proterozoic and Archean age. We suggest that the Previous HitfaultNext Hit may continue north of the Tensleep Previous HitfaultNext Hit and connect with the Crazy Woman "tear" Previous HitfaultNext Hit. The Crazy Woman Previous HitfaultNext Hit forms the southern boundary of the Sisters Hill segment of the large east verging thrust feature along the eastern flank of the Bighorn Mountains, west of the town of Buffalo. The Big Trails Previous HitfaultTop is a result of a northeast-southwest oriented horizontal compressional event in the Rocky Mountain foreland during the Laramide orogeny.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Protected Document: $10
Internal PDF Document: $14
Open PDF Document: $24