Structural interpretation of the Horse Center anticline, western margin of the Bighorn basin, Wyoming

Horse Center anticline is an asymmetrical structure on the western flank of the Bighorn basin. This type of basin-flank anticline has created structural traps for hydrocarbons throughout the foreland region. While no commercial hydrocarbons have been discovered at Horse Center, significant shows have been found in the Paleozoic section. Cretaceous and Jurassic sands and shales are exposed on the flanks of the structure, with the red beds of the Triassic Chugwater exposed in the core. Seismic data indicate that the Precambrian basement forcing block moves along a high-angle reverse fault. Resultant compressional folding of the overlying sedimentary section creates volumetric adjustments along detachment zones in less competent units. One such feature, a cross-crestal structure, can be observed at the surface, where bedding plane slip in Jurassic shales offsets the southern crest of the anticline. Although the fold axis trends northwest-southeast, typical of many Wyoming foreland structures, there is a distinct shift in vergence from southwest to northeast along the axis of Horse Center. Detailed analysis of well data and seismic data also confirms this change in asymmetry. This change may indicate the presence of a 'compartmental' fault, localized over a zone of weakness in the Precambrian basement. Surface mapping indicatesmore » that north of this change, there is an anticlinal/synclinal structural development on the western side of Horse Center. These paired structural suggest a possible 'plunging out' of anticlines, reflecting an en echelon arrangement of structures at depth, rather than a continuity along the axis of Horse Center, as has been previously mapped.« less