Date of Award
Master of Science (MS)
The Lower Cretaceous Inyan Kara Formation, at the base of the Dakota Group, consists of sandstone, siltstone, shale, and coal. The stratigraphy of the Inyan Kara and facies relationships within the formation and with the underlying Swift and overlying Skull Creek Formations in the vicinity of the Nesson Anticline, northwestern North Dakota, were evaluated using 11 cross-sections, 163 borehole geophysical logs, and 1 well core.
The Inyan Kara can be differentiated on well logs into three members. The basal member, "A", consists of sandstone, siltstone, shale, and coal. It is about 200 feet (60 m) to 400 feet (122 m) thick in the study area. The member is characterized by abrupt facies changes of sandstone units. Log patterns in "A" suggest that the lower portion of the member was deposited in a dominantly deltaic environment whereas the upper portion of "A" was deposited in a dominantly fluvial environment. The member is approximately equivalent to the Lakota Formation in the Black Hills of South Dakota.
The middle member, "B", consists of sandstone, siltstone, and shale. It is about 20 feet (6 m) to 150 feet (46 m) thick in the study area. The member is characterized by gradual facies changes. Log patterns suggest that member "B" was deposited in a marginal-marine environment. The member is approximately equivalent to the Fall River Formation in Black Hills.
The upper member, "C", consists of interbedded siltstone and shale. It is about 15 feet (4.5m) to 40 feet (12 m) thick in the study area. The member is characterized by a lack of facies changes. The extent, continuity, and lithologies in "C" suggest that the member was deposited in a shallow marine environment. The member is approximately equivalent to the lower portion of the Skull Creek Formation the Black Hills.
Facies relationships suggest that the upper portion of the Swift Formation and the lower portion of member "A" represent a regressional sequence in the study area whereas the upper portion of member "A", members "B" and "C", and the Skull Creek Formation represent a transgressional sequence in the study area.
Thickness trends of members "A", "B", and "C" suggest that the Williston Basin and the Little Knife Anticline were active structures during the deposition of the Inyan Kara, that the direction of regression was from east to west, and that the direction of transgression was from west to east in the study area.
Evidence for an unconformity between the Swift and Inyan Kara Formations, as proposed by previous workers, in the study area is possibly ambiguous and inconclusive. Additional evidence suggests that both conformable and unconformable contacts exist between the Swift and the Inyan Kara.
Wartman, Brad L., "Stratigraphy of the Inyan Kara Formation (Lower Cretaceous) in the vicinity of the Nesson Anticline, northwestern North Dakota" (1983). Theses and Dissertations. 315.