Fischer, Mark P.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
Geology--Paradox Basin; Porous materials--Fracture--Colorado
The Gypsum Valley salt wall is one of a series of NW-trending, elongate salt structures which span the northeastern portion of the Paradox Basin of the western United States. At Gypsum Valley, the evaporites of the Paradox Formation form an approximately 50 km long and 2.5 km tall structure that is emplaced discordantly within Pennsylvanian through Jurassic strata and buried beneath several hundred meters of late Jurassic and Cretaceous sediment. In this thesis, structural modeling, restorations, field work, and geochemical analysis are used to characterize the nature of salt-related deformation at Little Gypsum Valley and determine the evolutionary history of the salt wall and the surrounding fracture-controlled, paleohydrogeologic system. Sequential restorations of a new regional cross section indicate that active salt diapirism began during the Pennsylvanian, resulting in the formation of an asymmetric, single-flapped diapir. Active diapirism continued until the mid-Permian, when the salt structure broke free at the surface and passive diapir growth ensued. Passive diapirism persisted through the mid-Jurassic, although progressive onlap and burial of the rising salt wall began during the late Triassic. By the end of the Jurassic, the salt wall was completely buried and salt rise had temporarily stabilized. Renewed active diapir growth occurred during the Cretaceous, resulting in arching and fracturing of the overburden to form the Gypsum Valley anticline and associated diapir-related fracture networks. The most prominent of these fracture sets are oriented parallel and perpendicular to the long axis of the salt wall along its length, and become concentric and radial around the termination of the structure. These fracture networks facilitated downward migration of meteoric fluids, which caused dissolution of the underlying salt and led to the collapse of the Gypsum Valley anticline throughout the Tertiary. The fracture networks also appear to have played an important role in determining the geometry and style of structural collapse features exposed above the crest of the salt wall, which include subvertical normal faults and monoclinal downwarps.
Hunter, Cory W., "Structural history and fracture network evolution of the Gypsum Valley salt wall, Paradox Basin, Colorado" (2016). Graduate Research Theses & Dissertations. 5079.
ix, 148 pages
Northern Illinois University
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