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Investigating the Interaction of Sevier and Laramide Structural Development in the Rocky Mountains with 3D Seismic Mapping

John H. McBride1, R. William Keach, II1, Thomas H. Morris2, Will Monn1, and Tom Anderson3. (1) Department of Geology, Brigham Young University, S 371 ESC, Provo, UT 84602, phone: 801-422-5219, fax: 801-422-0267, [email protected]logy.byu.edu, (2) Department of Geology, Brigham Young University, S381 ESC, Provo, UT 84602, (3) Brigham Young University (Adjunct), Rocky Mountain Oilfield Testing Center, 907 N. Poplar, Suite 150, Casper, WY 82601

Three 3-D seismic reflection volumes have been procured by BYU in the western Green River Basin (GRB), the southwestern Powder River Basin (PRB), and the southern Uinta Basin (UB). State-of-the-art 3D visualization and attribute analyses furnish precise and detailed images of the interaction of Sevier (Mesozoic) and Laramide (Late Cretaceous-Cenozoic) deformation episodes and structural styles.

The position of the GRB volume between the Sevier frontal thrust and Wind River thrust, where they begin to approach each other, provides an opportunity to investigate close interactions between Sevier and Laramide deformation. Alternatively, the PRB and UB volumes both represent regions that are proximal to areas of mainly Laramide deformation. We have prepared structure maps of prominent seismic horizons as well as seismic attribute extractions in order to map and characterize varying deformation styles within each of and between the three seismic volumes.

The GRB volume shows the most complex structural variation, including both “thin-skinned” and “thick-skinned” deformation. Small-scale compressional structures in places show dual vergence, suggesting either a component of strike-slip or the interaction of two deformation episodes (Sevier and Laramide). A complex pattern of deeper high-angle faulting appears to penetrate the entire sequence and the top of basement and is accompanied by monoclinal and anticlinal flexure. The PRB and UB volumes show predominantly “thick-skinned” deformation with high-angle faults and/or strike-slip faults cutting through large-scale asymmetric compressional structures. The synoptic view provided from the three volumes allows a more generalized characterization of Laramide vs. Sevier subsurface deformation in the Rocky Mountain region.