Abstract

A relatively complete section of Paleozoic and Mesozoic rocks was deposited in the northern Rocky Mountain region, ranging in thickness from more than 50,000 ft (15,000 m) in western Wyoming and southeastern Idaho to generally less than 15,000 ft (4,500 m) in eastern Wyoming. During Paleozoic and early Mesozoic time, Wyoming, southeastern Idaho and western Montana were a part of the broad craton-miogeosyncline border zone (Cordilleran or Rocky Mountain Shelf) that extended the length of the western North America continent. Paleogeographic reconstructions indicate that during this time the central and northern Rocky Mountain region was located within the tropical to subtropical belt of optimum carbonate deposition between 30° N and 30° S latitudes. Transgressive marine carbonate facies dominated deposition during much of this time, with frequent regressive interruptions at which time clastic marine and continental deposits spread westward to cover the shelf region and intertongue with western carbonate facies. Major Paleozoic clastic source areas were located on and near the Canadian Shield and Transcontinental Arch to the east. In Late Jurassic time, episodes of clastic facies deposition from western source areas began, increasing in intensity with development of the Sevier orogenic belt. After Late Juassic time, North America drifted northward, and the western North America shelf region moved into middle latitude climatic zones. This event, along with continually increasing tectonic activity, resulted in dominance by marine and continental clastic deposition in post-Jurassic time.