Facies Changes Associated with Formation of an Extensive Salt Shoulder by the Coastal and Eolian Carmel and Entrada Formations, Gypsum Valley, Colorado
A salt shoulder forms a zone at the margin of a salt diapir where that margin steps relatively abruptly inward. These shoulders form when the salt rise rate near the diapir margin substantially decreases or stops relative to the salt rise rate at the inboard central part of the diaper. Based on current models of interactions between these salt shoulders and overlying sediment, it was anticipated that the thickness changes of the Entrada and Carmel formations would be only gradual and that any notable thinning would take place proximal to the neck portion of the diapir that would still have been moving upward during the time of deposition. Facies distributions of the Entrada and Carmel were expected to be consistent with the typical drying upward sequence observed in other parts of the region across which the erg extends. In this study, one stratigraphic section was measured at Slick Rock Canyon, away from the influence of the diapir, that exemplifies these characteristic facies and was compared to those on the shoulder. Sections measured across the shoulder at Little Gypsum Valley revealed occurrences of relatively drastic thickness variations (up to 50 percent) observed across short distances (less than 1km) on the salt shoulder. Careful documentation of the facies distributions also showed that the salt-sediment interaction between the shoulder and the Entrada/Carmel formations resulted in aqueous facies being present at a stratigraphically higher position than what was previously predicted and the unique presence of a paleosol in one of the sections. In addition, petrographic analysis exposed the presence of carbonate material within some petrofacies associations that is interpreted as originating from the diapir.^
Ronson, Ryan Burtron, "Facies Changes Associated with Formation of an Extensive Salt Shoulder by the Coastal and Eolian Carmel and Entrada Formations, Gypsum Valley, Colorado" (2018). ETD Collection for University of Texas, El Paso. AAI10931517.