Abstract: Regional Stratigraphic and Facies Relationships in the Sherwood Subinterval of the Mission Canyon Formation, Southwest to North-Central North Dakota

David M. Petty

The Sherwood subinterval of the Mission Canyon Formation is defined by log marker beds which can be correlated between southwest and north-central North Dakota. Five Mission Canyon depositional facies are recognized in this area. Facies I consists primarily of evaporites deposited in a sabkha-salina setting. Lagoonal mudstones and wackestones comprise facies II and lie immediately basinward of the sabkha deposits. Facies IIIa was deposited in shoal-island environments along a broad belt between north-central and southwest North Dakota. Facies IV mudstones formed in a low-energy, restricted-marine environment and facies V wackestones and packstones formed in a low-energy, open-marine environment.

Sherwood deposition was aggradational in north-central North Dakota and progradational in southwest North Dakota. Facies arrangements define three progadation/aggradation styles in the Sherwood subinterval. Aggradation is defined by less than 0.5 km of progradation for each meter of facies I evaporite deposition (i.e., 0.5 km/m). Slow progradation occurred on portions of the Sherwood that display between 0.5 and 2 km/m of progradation, and a rapid progradation style developed on portions that display more than 2 km/m of progradation. Subfacies development in facies IIIa shoal-islands can be related to depositional styles. In aggradational areas, an ooid-pisoid subfacies developed seaward of an intraclast-ooid-pisoid subfacies and landward of a skeletal-intraclast subfacies. In areas o slow progradation, the ooid-pisoid subfacies is absent and in areas of rapid progradation, the skeletal-intraclast subfacies is the only subfacies developed.

AAPG Search and Discovery Article #90952©1996 AAPG Rocky Mountain Section Meeting, Billings, Montana