Martindale, Kevin¹, John Byrd¹, Van S. Mount¹, Tom Bergstresser¹, Scott Young¹ 
(1) Anadarko Petroleum Corporation, Houston, TX

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

Significant along-strike structural style variations are imaged by Anadarko Petroleum’s 300 mile long-offset, high fold, 2D seismic program across the Darby and Absaroka thrust sheets. Excellent quality seismic imaging of these features impacts not only the exploration of the Wyoming Overthrust Belt, but can also provide important insights for the exploration of frontal thrust belt worldwide. 
The area of investigation encompasses a 36 mile portion of the southern Darby–Hogsback thrust sheet in Uinta County, Wyoming. Duplexes of Devonian – Pennsylvanian strata capped by a roof thrust carrying Mississippian through Cretaceous age rocks typify the northern portion of the study area. Restoration of these duplexes across the 25-30º dipping footwall ramp suggests up to 25 miles of eastward displacement. Frontal structures are an early developed back thrust and triangle zone that dies out southward along-strike. The back thrust is decapitated by the last phase of movement on the main Darby thrust, which is manifested by failed forward propagation and development of a fault-ramp duplex-wedge structure. 
The ramp angle increases southward to 50-55º and hanging wall structure is characterized by a simple fault bend fold Segmented thrust slices of footwall Upper Cretaceous strata overlain by folded Paleocene and Eocene synorogenic deposits characterize frontal structures and last phase of movement along this portion of the Darby.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.