--> Basement Backthrusts and Thin-Skinned Detachments Combine to Form Productive Traps on the West Flank of the Bighorn Basin, Wyoming, by P. H. Hennings and R. C. Hager; #90986 (1994).

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Abstract: Basement Backthrusts and Thin-Skinned Detachments Combine to Form Productive Traps on the West Flank of the Bighorn Basin, Wyoming

Peter H. Hennings, Richard C. Hager

Two basement thrusts form the productive "A" and "B" structures at Gooseberry Field on the west flank of the Bighorn Basin (T47N, R100W). Regional seismic data indicate that "A" and "B" are the result of backthrusts (A1 &B1) in the hanging-wall of the west-dipping Oregon Basin Thrust (OBT). The backthrusts nucleated at irregularities along the OBT and were accentuated by bending of the hanging-wall during thrusting. "B" is a fault-cored, asymmetric anticline/syncline pair with a maximum of 3,400 ft of structural relief. Geometric modeling, using a technique that balanced layer-parallel shear in the sedimentary cover with simple shear in basement, indicates that B1 dips to the east at 57°, is listric, and flattens at an elevation of -37,500 ft where it intersects the OBT. A1 d ps to the east at 55° and has 1,000 ft of structural relief. It is directly overlain by two west-dipping thrusts in the sedimentary cover (A2 & A3) which add an additional 800 ft of structural relief to "A". A2 has 700 ft of displacement and ramps up-section from the base of the Bighorn Dolomite through the Thermopolis Fm forming a fault-propagation fold. A3 has 2,000 ft of displacement and terminates in a thrust wedge within the Jurassic and Cretaceous section. Although early motion along A1 localized the thrust ramps of A2 and A3, its motion continued after the shallower thrusting ended. "A" is truncated in the south by a north-dipping thrust that aligns with Tensleep Lineament.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994