3-D Structural
Model of Structures along the Western Margin of the Bighorn Basin, Wyoming
Banerjee, Subhotosh1,
Shankar Mitra1 (1) University of Oklahoma, Norman, OK
The western margin of the Bighorn basin, Wyoming, is marked by a series
of basement-cored anticlines formed along steep, easterly-dipping reverse
faults. These-second order anticlines, such as the Rattlesnake Mountain and
Hamilton Dome anticlines, are characterized by short steeply-dipping forelimbs
and long, gently-dipping back limbs. The cover rocks involved in the
deformation consist of alternating clastic and
carbonate sediments of Cambrian to late Cretaceous age above Precambrian granitic basement. Three-dimensional geologic models have
been constructed in the Rattlesnake Mountain anticline (RMA) and Horse Center anticline (HCA) areas,
for the Jurassic Gypsum Springs and Pennsylvanian Tensleep
Formations and the Basement. The models are constrained using a series of eight
cross sections, well tops from more than 200 wells, dipmeter
data from 22 wells, surface geologic maps, detailed field mapping, and remote
sensing data using color infrared digital orthophotos.
The Rattlesnake Mountain Anticline (RMA) and adjacent Horse Center Anticline
(HCA) show complex branching and lateral terminations of anticlinal
axial traces. Based on the 3-D modeling, these second-order structures are
interpreted as back-limb structures on a first order anticline. Relatively
smaller scale secondary detachment folds, which detach in the lower Cretaceous shales are present on the
east-dipping back limb of the RMA. These include several producing structures
such as the Cody, Shoshone and Shoshone North fields, which produce from the
Cretaceous Frontier, Permian Phosphoria, and
Pennsylvanian Tensleep formations. Understanding the
3-D geometry of these structures is critical in unraveling the structural
evolution of the Bighorn Basin and in interpreting
trap geometries in the Rocky Mountain Foreland basins.