Date of Award
Master of Science (MS)
The depositional environments of a 40 meter thick interval in the upper part of the Sentinel Butte Formation in southeastern McKenzie County, North Dakota have been determined from the sedimentary structures, geometry, distribution of grain· sizes, and stratigraphic relations of cyclic lithostratigraphic units. The top of the study interval is the top of the upper yellow marker bed.
An elongate, tabular sand bed was studied in detail. It is 12 meters thick and 3 kilometers wide and it is interpreted to have been deposited by lateral accretion in a high-sinuosity stream. Paleo current indicators are parallel to the long axis of the sand bed. In this bed are bodies of interbedded silt and clay that are interpreted as channel plug deposits. Epsilon cross-strata are common. Cross-stratification grades from large-scale at the base to small scale at the top of the bed and grain size decreases upward.
An elongate, trough-shaped sand bed 15 meters thick and 400 meters wide and an elongated trough-shaped sand bed 10 meters thick and 200 meters wide are interpreted as deposits of low-sinuosity streams. Paleocurrent indicators trend parallel to the trends of the sand beds. These beds lack the silt and clay bodies and epsilon cross-strata of the elongate, tabular sand bed, but they have similar vertical distributions of cross-stratification and grain size.
Yellow- to red-brown sand, silt, and clay beds occur above and adjacent to the three sand beds. The sand, silt, and clay beds become thinner and finer away from the sand beds. These characteristics, plus little organic matter, abundant iron-stained concretions, and climbing ripple cross-stratification, indicate that these beds are natural-levee and crevasse-splay deposits.
Laterally extensive, gray and brown silt and clay beds grade laterally and vertically from the natural-levee deposits. These highly bioturbated beds contain abundant plant fragments and are generally overlain by lignite beds. The gray and brown silt and clay beds and the lignite beds are interpreted to be floodbasin deposits.
Johnson, Robert Post, "Depositional environments of the upper part of the Sentinel Butte Formation, southeastern McKenzie County, North Dakota" (1973). Theses and Dissertations. 150.