Date of Award
Doctor of Philosophy (PhD)
This study of the Fermo-Pennsylvanian Minnelusa Group in North Dakota was designed to clarify the stratigraphy, illustrate association of depositional environments, and to relate the geologic history and economic potential of these strata.
The Minnelusa Group is defined here to include strata above the unconformity on the Madison and Big Snowy Groups and below the Opeche Formation. The Minnelusa Group in North Dakota contains the Tyler, Alaska Bench, Amsden and Broom Creek Formations. The Amsden has been divided into three marker defined lithozones designated, in ascending order, Medora, Dickinson, and Bismarck.
Drill and core samples were examined and described interpretively and supplemented with sample studies from other sources. Geophysical log cross sections and structure, isopachous and lithofacies maps were prepared from data collected. The maps and cross sections were used to integrate Montana and South Dakota terminology, to study environmental distributions and associations, and to determine the hydrocarbon potential of various areas.
A reverse fault component is well demonstrated in the Red Wing fault zone in McKenzie County by the occurrence of repeated sections of the Kibbey Formation. Local thickening proximal to this fault throughout the entire section is interpreted to illustrate periodic activity of this feature during the Pennsylvanian and Permian periods. Dipmeter survey data was used to demonstrate that thickness differences indicating apparent changes in the direction of vertical differential movement of the fault blocks were actually a function of differences in dip of beds. Fault movement similar to that in the Red Wing fault is indicated in Bowman County.
Multiple modes of sandstone deposition in the Tyler Formation are indicated by physical and paleontological data. A modern delta is suggested as an analog for deposition of portions of the Tyler. During deposition of the Tyler, the North Dakota area was periodically isolated by positive elements from areas in central Montana. The Tyler Formation in North Dakota and Montana are stratigraphically equivalent.
The Alaska Bench Formation over much of the area is micritic ostracodal limestone with occasional brachiopod fragments and oolites. This suggests deposition in a shallow marine to brackish, generally low-wave-energy environment. The Alaska Bench in North Dakota and Montana are equivalent.
The Medora lithozone of the Amsden Formation is primarily dolomite, suggesting progressive restriction of the environment. Lithologic relationships suggest carbonate bank accumulations. This lithozone appears equivalent to all of the Roundtop Group in South Dakota and the entire Amsden in central Montana.
Most of the anhydrite in the Amsden is contained in the Dickinson lithozone. Marked changes of lithology suggest multiple changes of relative sea level and large scale migration of facies. The Dickinson lithozone is equivalent to much of the Hayden Group in the Hartville area.
A migrating littoral environment system is represented by the Bismarck lithozone and a decrease in restriction of the environment is implied. This unit is interpreted equivalent to the Meek Group and possibly part of the Hayden Group in South Dakota.
The Broom Creek Formation is interpreted to be Wolfcampian, equivalent to the Broom Creek in the Hartville area. Lithologic associations indicative of a high energy environment suggest deposition by a migrating beach and offshore bar system with associated carbonate environments.
The Tyler Formation exhibits several areas with good potential for additional petroleum reserves because of trapping conditions and proximity to source rocks. Porous and permeable intervals in the Dickinson and Bismarck lithozones and in the Broom Creek Formation have potential where trapping mechanism and source beds exist.
Ziebarth, Harold C., "The stratigraphy and economic potential of Permo-Pennsylvanian strata in southwestern North Dakota" (1972). Theses and Dissertations. 335.