Stratigraphic Column of
     Western North Dakota:
 
 

Notes for Stratigraphy of Western North Dakota.
   Individual letters designate geologic periods of time:  C (Cambrian), O (Ordovician), S (Silurian), D (Devonian), M (Mississippian), P in circle (Pennsylvanian), P (Permian), Tr (Triassic), J (Jurassic), K (Cretaceous), T (tertiary), and Q (Quaternary).
   The names Sauk, Tippecanoe, Kaskaskia, Absaroka, and Zuni, refer to major depositional events in North America.
   Relative thickness of rock units shown on this diagram is arbitrary and does not represent actual rock thicknesses.
   An unconformity is a buried surface between two bodies of rock representing a break or hiatus in the record of geological events.  It is often marked by erosional topographic features (buried hills and valleys), weathered rock, ancient soils (paleosols), or karst (caves weathered in exposed limestone).
    “Salts” refer to a variety of evaporite deposits, including anhydrite, gypsum, and halite (table salt).
   “Carbonates” refer to a variety of carbonate rocks, such as limestone and dolostone.
   “Clastics” refer to particles like sand or mud that have usually been transported to a region of deposition, such as by wind or rivers.
   References include publications dealing with specific rock units as well as the following:  L. C. Gerhard, S. B. Anderson, J. A. LaFever, and C. G. Carlson (1982) Geological development, origin, and energy mineral resources of the Williston Basin, North Dakota, AAPG Bulletin No 8, V 66, p 989-1020;  L. C. Gerhard and S. B. Anderson (1981) Oil exploration and development in the North Dakota Williston Basin: 1980 update ND Geol. Survey, Misc Series No 59, 19p.;  J. P. Bluemle, S. B. Anderson, C. G. Carlson (1981) Williston Basin Stratigraphic nomenclature chart ND Geol. Survey Misc. Series No 61.;  J. P. Bluemle (1991) The face of North Dakota, Revised Edition, ND Geol. Survey Educational Series, No 21, 177p.
   * Although the Morrison is illustrated in Gerhard et al. (1982) as being present in the subsurface of North Dakota, Bluemle (1991) indicates that it has not been shown to be present there.  We list it here because it is shown in several of the cited references and because it has been clearly identified across the border in Montana and South Dakota and represents an important stage of the regional geological history.
 

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