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Along-Strike Variations in Termination of the Darby (Hogsback) Thrust, Uinta County, Wyoming: Insights from New Seismic Data

Martindale, Kevin1, Byrd John2, Van S. Mount1, Tom Bergstresser1, Scott Young1
Anadarko Petroleum Corporation, Houston, TX
2 Anadarko Petroleum Corporation, The Woodlands, TX

Anadarko’s 300 mile long-offset, high fold, 2D seismic program across a 36 mile portion of the Darby (Hogsback) and Absaroka thrust sheets in Uinta County, Wyoming generated excellent imaging of significant along-strike structural style variations. These observations may not only impact future exploration of the Wyoming Overthrust Belt, but can also provide important insights for trap development in the frontal areas of thrust belts worldwide.

Duplexes of Paleozoic strata and frontal back thrust characterize the northern Darby, whereas the southern Darby is characterized by a single fault bend fold with segmented thrust slices of Cretaceous rocks at the toe of the thrust. The well-imaged duplexes are associated with a 25-30º dipping footwall ramp and an overlying roof thrust. Restorations suggest up to 25 miles of eastward displacement which contrasts with previous interpretations of up to 15 miles of displacement on a horse-tail splay of thrust faults at the front of the Darby. Development of a fault-ramp duplex-wedge structure is the most recent displacement on Darby and resulted in decapitation of the frontal back thrust and triangle. Southward along-strike a series of tear faults mark the transition to a 50-55º fault ramp angle and a single fault bend fold. The last-stage of displacement cannibalized footwall Upper Cretaceous strata in a series of thrust slices at the thrust tip.