The Mississippian history of the northern Cordilleran region of the United States consists of two principal depositional cycles separated by a cycle of epeirogenic uplift and erosion. Each depositional cycle is divisible into phases that represent significant changes in depositional patterns. During Cycle I (early Kinderhookian-early Meramecian), predominantly carbonate and evaporite deposition took place on a broad cratonic shelf bordered on the east by land and on the west by a deep trough that received terrigenous sediments from an adjacent western landmass. Kinderhookian transgression was followed by regression during the Osagean and early Meramecian. Regional uplift during latest early Meramecian time (Cycle II) drained the shelf area and caused the sea to be confined to the western trough. During Cycle III (middle Meramecian-Chesterian), the sea again transgressed onto the craton, which was differentiated into the Big Snowy-Williston, Wyoming, and Uinta basins, where terrigenous and carbonate sediments were deposited. The Big Snowy-Williston basin was uplifted during latest Chesterian time and lost its identity, but the Wyoming basin continued to expand into the Pennsylvanian, when it engulfed most of the Cordilleran platform and breached the Transcontinental arch. Application of generalized carbonate, terrigenous, and evaporite depositional models results in specific models that explain the Mississippian depositional patterns.
