About This Item
Share This Item
The most intense and widespread pre-Laramide structural deformation of Cretaceous sedimentary rocks in Wyoming is associated with the Wall Creek sandstone of the Frontier Formation. Most of the evidence of structural deformation is found immediately below the regional unconformity at the base of this sandstone.
Regionally, an isopach map from the top of the Frontier Formation to the top of the Mowry Formation shows strong and persistent thinning onto a north-trending arch in western Wyoming and thickening into a northwest trending basin in eastern Wyoming.
Part of the thinning onto the western arch is caused by progressively deeper erosion of a regional unconformity at the base of the Wall Creek sandstone, and regional onlap of the Wall Creek sandstone above the unconformity. There is also some westward thinning of the lower Frontier interval, however, which is not related to the Wall Creek unconformity.
Of the more specific paleostructures discussed, the north-trending anticlines in the vicinity of the Moxa arch in southwestern Wyoming are particularly well developed. An east-west anticline in the Bison basin area appears to have been faulted on the south flank, and a broad arch on the west side of the Powder River basin may have influenced paleocurrents and sandstone depositional trends of the productive "First Frontier Sandstone" of that area.
End_of_Article - Last_Page 1333------------