ABSTRACT: McFarland, et al.

Authors:
Joshua McFarland1, Katherine Giles1, Richard Langford1, and Mark Rowan2
1Department of Geological Sciences, University of Texas at El Paso, 500 W. University Ave., El Paso, Texas 79968–0555
2Rowan Consulting Inc., 850 8th St., Boulder, Colorado 80302–7409

Structural and Stratigraphic Development of a Salt­ Diapir Shoulder, Gypsum Valley Salt Wall, Paradox Basin, Colorado

Session:
Salt Tectonics—Gulf of Mexico and the World (GRBCC, Room 310ABC)
Monday, September 21, 2015, 10:45 am

Abstract:
A salt shoulder is a local geometric feature on the flank of some salt diapirs that refers to an abrupt upward narrowing of the diapir. Stratal anticline traps above salt shoulders are potential exploration targets in producing salt basins such as the Precaspian and Gulf of Mexico, yet no detailed predictive reservoir or formational models has been proposed for these structures. Structural, stratigraphic, and petrographic analysis of an exposed salt shoulder along the Gypsum Valley Salt Wall in the Paradox Basin, Colorado, are presented here in order to provide a basis for developing reservoir and formational models for this type of salt structure. Modern incision of the salt shoulder by the Dolores River has exposed the upper Triassic Chinle Formation unconformably onlapping carbonate caprock and Paradox.

Formation evaporites in a natural amphitheater, which allowed for the 3D study of the structure. The results of processing digital images in the photogrammetry software Agisoft Photoscan and subsequent editing in Vulcan Maptek software have been combined with geospatially referenced structural and stratigraphic field data to create a 3D model of the salt shoulder. The purpose of this model is to present a 3D interpretation of the facies distribution and transitions within the Chinle Formation on the flank of the salt wall. Documented syn-depositional relationships of the Chinle Formation with the passively rising salt wall include: thinning and coarsening of facies towards the diapir; intraformational angular unconformities and wedge halokinetic sequences; erosional incorporation of diapir-derived carbonate caprock into the Chinle Formation as debris flows and fluvial channel fills; and down-toward-the-diapir normal fault displacement of the supra-shoulder onlapping Chinle strata within the shoulder anticline.

Normal faults and inward stratal rotation are confined to the lateral boundaries of the salt shoulder and were generated by solution collapse/evacuation of diapiric salt beneath the onlapping Chinle and Wingate (?) strata.