The Stratigraphy of Selected Mission Canyon Wireline Log Markers, U.S. Portion of the Williston Basin, North Dakota

Abstract

The Mission Canyon Formation along the northeast flank of the US Williston basin has been informally subdivided into intervals (members) based on wireline log markers. Wireline log responses of the markers are produced by both lithologic changes and radioactive elements present within these thin stratigraphic intervals. The wireline markers were originally described as transgressive events. Detailed stratigraphic analyses of the Sherwood and State A markers indicate they were deposited during progradation and sea level stillstand. A typical facies tract from east to west within the Sherwood marker contains anhydrites and anhydritic dolomites deposited in sabkha environments; patterned dolomudstones along shoreline trends (the Sherwood argillaceous marker); and limestones in shoaling environments along the Mission Canyon shelf (Sherwood gamma marker). During stillstand, brines produced in sabkha environments (east of the Sherwood shoreline) were enriched in magnesium and potassium. These brines migrated basinward first, dolomitizing mudstones. These brines were magnesium depleted by the time they reached shoals along the shelf. Potassium, however, remained in the system and is present within the marker along the shelf, as shown by a slight increase in API units on Spectrologs.