The Williston basin is a major producer of oil and gas, lignite, and potash. Located on the western periphery of the Phanerozoic North American craton, the Williston basin has undergone only relatively mild tectonic distortion during Phanerozoic time. This distortion is largely related to movement of Precambrian basement blocks.
Sedimentary rocks of cratonic sequences Sauk through Tejas are present in the basin. Sauk, Tippecanoe, and Kaskaskia sequence rocks are largely carbonate, as are the major oil- and gas-producing formations. Absaroka and Zuni rocks have more clastic content, but carbonates are locally important. Clastics of the Zuni sequence contain abundant lignite. Tejas sequence rocks are not significant in the production of minerals or energy, although glacial sediments cover much of the region.
Depositional environments throughout Sauk, Tippecanoe, and Kaskaskia deposition were largely shallow marine. Clastic sediments were transported into the southern part of the basin during Absaroka sequence deposition, a product of erosion of Ancestral Rocky Mountain orogenic structures. Continental and shallow-marine clastic sediments were deposited during Zuni sedimentation until Cretaceous deeper marine environments were established. Laramide orogenesis to the west provided detritus that was deposited in fluvial, deltaic, and marginal-marine environments, regressing to the east.
Major structures in the basin, and the basin itself, may result from left-lateral shear along the Colorado-Wyoming and Fromberg zones during pre-Phanerozoic time. Most structures probably resulted from renewed movement or “tensing” of pre-Phanerozoic faults.