Date of Award
Master of Science (MS)
Approximately 163 meters (535 feet) of the Paleocene Sentinel Butte Formation crop out in southcentral Williams county, North Dakota. To determine their mode of deposition and stratigraphic position within the formation, twelve stratigraphic sections were measured. These strata were deposited in alternating fluvial and lacustrine environments as determined by sedimentary structures, lithology, lithologic sequences, and fossil occurrences. A fining upward trend in grain size of the tabular sandstones, and the identification of epsilon cross-stratification in the tabular sandstones support a fluvial origin for some of the strata. The strongest evidence for the interpretation of lacustrine deposition is the presence of limestone bodies within these strata. Examination of thin sections taken from some of the limestones revealed a primary mode of origin for the CaC03 • Additional evidence for lacustrine deposition is the presence of thin lignitic layers directly overlying strata lacking root traces.
The identification of the "upper sand" of the Sentinel Butte Formation within the uppermost exposures of this area, and the presence of the Sentinel Butte tuff marker unit in the region just south of the study area suggests that the upper 3/4 of the Sentinel Butte Formation is exposed in this area. Projection of the Bullion Creek-Sentinel Butte formational contact from a region to the east suggests that the maximun thickness of the Sentinel Butte Formation may be nearly 26 meters thicker than previously estimated.
Paleocurrent data from this area indicate a SSW flow direction. This information, combined with data from earlier studies, suggests that the source area for these sediments was not the Powder River Basin. Examination of the thicknesses of various lignite beds in the Nessen Anticline area does not reveal if the anticline served as a diversionary barier during the deposition of these strata. It is possible that the development of the anticline was more influential during late Sentinel Butte time.
Peck, Wesley D., "The stratigraphy and sedimentology of the Sentinel Butte Formation (Paleocene) in south-central Williams County, North Dakota" (1992). Theses and Dissertations. 221.