WWRC 84-02
Tectonic Structures Responsible for Anisotropic Transmissivities in the Paleozoic Aquifers Southern Bighorn Basin, Wyoming
Abstract
Movement of groundwater in aquifers of Paleozoic age in the southern
Bighorn basin, Wyoming, is influenced by anisotropy which is the result of
deformation of the sedimentary rocks. The sedimentary rocks prior to the
Laramide orogeny were approximately 12,000 feet (3657 m) thick of which
approximately 2200 feet (670 m) are of Paleozoic age (Figure 1). The
sediments have been deformed into faulted folds ranging in size from
intermontane basins (Bighorn basin) to those with an amplitude ranging from
500 to 5000 feet (150 - 1500 m.) Essentially all folds result from movement
on reverse faults at the interface between the sedimentary cover and the
crystalline Precambrian basement. Faults steepen in dip as they propogate
upward through the sedimentary cover. Wedge shaped crustal segments of large
size result from reverse in dip of controlling faults, with resultant change
in asymmetry of folds.
The geologic structures in this tectonic province are considered to be
the result of a generally pervasive horizontal stress field during the
Laramide orogenic episode.
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