Date of Award

2020-01-01

Degree Name

Master of Science

Department

Geological Sciences

Advisor(s)

Katherine A. Giles

Abstract

This study documents the style and distribution of deformation present in Triassic-age gypsic and carbonate caprock associated with the Gypsum Valley Salt Wall Salt Shoulder in the Paradox Basin, Colorado in order to determine the mechanism and timing of deformation. Mapping of gypsic and carbonate capstone facies shows that the caprock layering that was generated during formation has been deformed by large-and-small-scale folding and faulting, brecciation, and boudinage. Deformation within the caprock resulted in widely variable orientations along the length of the salt shoulder, that also varies locally in intensity of deformation and with proximity to the passively rising diapir on the inboard margin of the salt shoulder. Various hypothesized deformation mechanisms were analyzed including: regional tectonic extension, regional tectonic shortening, Triassic karst collapse, late-stage (Neogene) karst collapse, diagenetic crystal volume change, radial faulting during Triassic diapiric doming, diapir topography-driven gravity sliding, diapiric intrasalt shear, and late-Jurassic shoulder rollover folding and faulting.

The documented caprock deformation styles and trends, are interpreted to have formed in three different stages. The first stage was diapir topography-driven gravity sliding caused by the continued passive diapiric rise of the Gypsum Valley Salt Wall at the inboard margin of the Triassic salt shoulder. Diapir topography-driven gravity sliding accounts for most of the deformation documented including large and small-scale open and tight folding within both the gypsum and carbonate caprock as well as carbonate caprock clast and Chinle/carbonate caprock clast debris flow/slump deposits. The second stage, diapiric intrasalt shear occurred either simultaneously with the first stage or shortly after. Diapiric intrasalt shear may have formed small scale open and tight folding, and boudinage within the gypsum caprock layering. The third and final stage of caprock deformation occurred significantly later than the first two stages and after Gypsum Valley Salt Shoulder development. This stage of deformation is due to late-Jurassic shoulder rollover large-scale folding and normal faulting and is associated with salt withdrawal or salt dissolution from the salt shoulder area. The third stage is responsible for downfolding and minor fault-related off-set of the previously deformed caprock. Minor Triassic-age karst collapse brecciation and small-scale tight-folding related to diagenetic crystal volume change is locally present. Most of the mapped deformation within the caprock occurred directly after salt shoulder formation within the first two deformation stages, and prior to overlap by the Chinle Formation halokinetic wedge sequence (WHS-3). The inboard continued passive-diapiric rise-related processes responsible for salt shoulder formation directly correlates with the processes needed for diapir topography-driven gravity sliding, which is responsible for a majority of caprock deformation at the Gypsum Valley Salt Wall.

Language

en

Provenance

Received from ProQuest

File Size

144 pages

File Format

application/pdf

Rights Holder

Hanah Draper

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