Subsurface data presently available are inadequate for a detailed sedimentational analysis of the stratigraphy of North Dakota, but some preliminary interpretations are possible. This paper is a progress report on a continuing study, the results of which will be presented in detail when the current drilling program has provided the necessary data.

Thickness maps and facies analysis are used to interpret and to illustrate the stratigraphy. The Williston basin in North Dakota was a gently subsiding intracratonic basin during most of post-Cambrian time. Differentiation of the pre-Cambrian basement suggests pre-Huronian folding in the area later occupied by the basin.

Middle Ordovician marine shales and quartzose sandstones cover most of the state. Western North Dakota was the center of Ordovician deposition, and the sands were apparently derived from erosion of the shield area to the southeast. Continued gentle downwarp was accompanied by deposition of Upper Ordovician and Silurian carbonates. The center of Silurian deposition was to the northwest in Canada, and some Silurian sandstones were derived from erosion in the southeast. Reef structures are possible in the Silurian, and the top of the system is marked by a disconformity.

Middle Devonian through Middle Mississippian rocks are largely carbonates and evaporites. A northwesterly plunging uplift, herein named the Burleigh uplift, is apparent in thickness maps of the Silurian and Devonian systems in the south-central part of the state. The uplift was the site of non-deposition and clastic deposition. The Upper Devonian series is restricted to the northwestern part of the state. The Upper Devonian evaporite and carbonate basin extended into Montana, and the Middle Devonian extends into Manitoba and Saskatchewan.

Lower and Middle Mississippian rocks cover the western three-quarters of the state and thicken toward the west and northwest. The present eastern edge is near the original shoreline, and the Charles evaporite facies is restricted to the western half of the state.

The Upper Mississippian Big Snowy group and Amsden formation are largely marine clastics deposited during a westward regression of the seas. Local concentrations of shoreline sands may provide stratigraphic traps.

No Pennsylvanian or Permian rocks have been recognized in the state, and the Amsden and Big Snowy sediments are overlapped by Triassic redbeds and evaporites. Evaporites and a thick section characterize the Triassic in the west, whereas the system is thin and sandy in the east.

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Overlapping marine Jurassic rocks cover most of the state, with clastics and sandstones in the west and relatively more limestone and evaporites in the east.

Marine Cretaceous rocks cover most of the state, and more than 4,000 feet were deposited in western North Dakota. Shallow Lower Cretaceous sandstones tentatively correlated with the Newcastle of the Black Hills offer interesting possibilities where they pinch out to the east and north in the central and southeastern part of the state.

Non-marine Tertiary sediments cover most of western North Dakota.

The stratigraphy of North Dakota is inadequately known. No great tectonism or facies variations are expected to be found, but further knowledge of the details of the offlap and onlap relations of the sediments and the gentle folding during the Paleozoic may lead to further oil exploration based on stratigraphic information.

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