The Upper Devonian to Lower Mississippian Bakken Formation, Williston Basin, consists of: 1) a black mudstone Lower member; 2) a gray mudstone and sandstone Middle member; and 3) a black mudstone Upper Member. Nine lithofacies are recognized; a black mudstone that characterizes the Lower and Upper members and eight remaining gray mudstone and sandstone lithofacies from the Middle member. The hemipelagic black mudstone of the Lower and Upper members accumulated in a distal deep water (> 200 m) marine environment under stagnant bottom conditions characterized by: 1) quiescent bottom waters periodically disturbed by slow moving bottom currents; 2) a slow rate of elastic sedimentation; and 3) a substrate devoid of benthic macrofauna due to anoxic bottom waters containing elevated, probably toxic, concentrations of dissolved hydrogen sulfide. Mudstones and sandstones of the Middle Bakken Member accumulated in a shallow marine environment in offshore (10-200 m deep) and lower, middle and upper shoreface (< 10 m) settings. Trace fossils in the Middle member reflect a Nereites and Cruziana ichnofacies grading to Skolithos ichnofacies which support a shallow marine paleoenvironment interpretation. Deposition of three distinctive Bakken members reflects significant changes in water depth within the Williston Basin as a result of relative changes in sea level.