The Northern Termination of the Crawford Thrust, Western Wyoming
Contributions to Geology
Displacement on the Crawford thrust in western Wyoming decreases rapidly as measured from south to north in the area where the surface trace of the thrust terminates. Structures in the thrust sheet developed to accommodate this loss of displacement. Folds in the Jurassic Twin Creek Limestone formed above a prominent decollement horizon in the Lower Twin Creek Limestone. The Sublette anticline, a large, overturned asymmetric anticline with Jurassic through Permian units on the remaining east limb shortens the rocks in the Crawford sheet north of the folds in the Twin Creek Limestone. Further shortening of the hanging wall was accomplished by the Sublette anticline thrust, a forelimb thrust which may splay off the Crawford thrust at depth. Evidence for the Cokeville normal fault shows that the normal fault breached the Sublette anticline in the post-Eocene, and the spatial relationship between the normal fault and the Sublette anticline is used to infer the presence of a ramp in the Crawford thrust at depth.
The Crawford thrust cores a cylindrical, overturned anticline which plunges to the north. This anticline is flanked by a conical syncline which plunges and opens to the north. Displacement is transferred locally and upsection to the thrust-cored anticline. North of the termination of the surface trace of the Crawford thrust, displacement continues to decrease, the thrust drops to a lower structural level, and folds formed in the Cretaceous and Jurassic section above the Twin Creek decollement. These folds are below the Meade thrust and above the Crawford thrust, and show that the Crawford thrust is at a lower structural level than the Meade thrust in the area.
Evans, J. P., and Spang, J. H., 1984, The northern termination of the Crawford thrust, western Wyoming, Contributions to Geology, v. 23, p. 15-32.