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Development of a Sedimentary Cover Above a Diapir: Mesozoic Dissolution, Burial and Continued Rise of the Gypsum Valley Salt Wall, Paradox Basin


The Gypsum Valley salt wall in the Paradox basin in southwestern Colorado is a northwest-trending diapir that exposes a history of progressive burial from the Triassic to the Cretaceous, a period of 100 Ma. The strata exposed in contact with the salt range from Pennsylvanian Honaker Trail Formation to Upper Cretaceous Mancos Shale. Shallow dips (2 to 7 degrees) in the youngest strata indicate that little deformation is associated with Laramide compressional folding and most of the structure is related to diapiric rise and subsidence into the adjacent minibasins. Triassic through Cretaceous strata illustrate the progressive burial and stabilization of parts of the diapir. Onlap and thinning onto the flanks of the diapir indicate that the diapir and adjacent minibasins were active during deposition of these units. However, local synclines above the diapir top expose strata that also thin and exhibit internal unconformities, showing syndepositional subsidence into the underlying diapir. Strata capping these synclines are shallowly dipping, indicating that little deformation occurred after the synclines formed. These synclines are interpreted to have formed through syndepositional dissolution of the underlying diapir. Each suprasalt synclinal basin seems to have buried only part of the diapir. The unburied portions of the salt wall continued to rise as sections were stabilized, resulting in a complex burial history. During the Late Triassic Chinle and Wingate deposition a shoulder formed on the NE side of the salt wall, from its NW end to approximately the center of the salt wall, narrowing the NW part of diapir. Exposed remnants of the shoulder extend in 800 m from the underlying diapir margin. Similar burial during Jurassic Kayenta and Entrada deposition extended and expanded this shoulder along the entire northeastern side of the salt wall. The most widespread event occurred with deposition of the Late Jurassic Morrison, which buried most of the northern 2/3 of the diapir, leaving a thin wall in the NW to continue rising during the Cretaceous. To the SE, a pattern of thickening into the diapir-flanking minibasins is evident in the lower Cretaceous Burro Canyon Formation. Although this may be due to compaction in the minibasins, the coincidence of higher dips with the areas where Cretaceous strata are in contact with the salt suggests continued diapirism in the SE end of the diapir.