Facies changes across a deforming salt shoulder, Chinle Formation, Gypsum Valley, Colorado
E.E. Heness, J. McFarland, R. Langford, and K. Giles
A unique exposure of the Chinle Formation in Gypsum Valley in the southern Paradox Basin in Western Colorado documents its interaction with a deforming salt diapir as it partially buried a salt diapir to form a salt shoulder. The Chinle Formation forms a southeastward tapering wedge that thins from 160 to 50 m across the shoulder. Thinning of shales is accommodated by pinchout of braided stream channel sands, and truncation by and onlap onto four unconformities of 2 to 6°. Eight facies associations represent deposition in braided and meandering streams, marshes, ponds, and overbank settings as well as deposition from debris flows shed from the adjacent topographically high diapir. Trends in facies result from syndepositional deformation of the adjacent and subjacent salt. Shales thin, and laterally stacked braided stream channel sandstones pinch out toward the diapir. Paleosols are replaced by marsh and pond deposits reflecting isolation from the main fluvial system. The location of marsh and pond deposits in local basins reflects syndepositional subsidence on the inboard parts of the salt shoulder. Salt shoulders are a previously unrecognized, but common element in the diapirs of the Paradox Basin. The unique setting allows preservation of both fluvial facies and deforming salt, and as far as we know, this is the first study relating sedimentation and deformation in this setting.
- Heness, E.E.; McFarland, J.; Langford, R.; Giles, K., 2017, Facies changes across a deforming salt shoulder, Chinle Formation, Gypsum Valley, Colorado, in: The Geology of the Ouray-Silverton Area, Karlstrom, Karl E.; Gonzales, David A.; Zimmerer, Matthew J.; Heizler, Matthew; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 68th Field Conference, pp. 159-167.