Date of Award
Master of Science (MS)
The environment of deposition of the Bullion Creek and Sentinel Butte Formations (Paleocene) in western North Dakota has been variously ascribed to lacustrine, meandering fluvial, and deltaic settings. The purpose of this study was to interpret the depositional environments, depositional history, and provenance of the strata in T. 145 and 146 N., R. 102 W., McKenzie County, North Dakota.
A total of 24 stratigraphic sections were measured and described. In addition, paleocurrent data were gathered from primary sedimentary structures, positions of paleochannel outcrops were noted, and samples were collected. Laboratory work consisted of thin-section petrography, scanning electron microscopy, and X-ray diffraction analyses of sand stones, limestones, and claystones, respectively.
Two paleochannel systems are present in the Bullion Creek Formation in the study area. These systems are deeply incised and vertically stacked, with low width/depth ratios. Primary sedimentary structures within the channel fill include large-scale cross-stratification, climbing-ripple cross-lamination, and planar lamination. Also included at various levels within channel fills are claystone lag-gravel accumulations.
Two types of channels are present in the Sentinel Butte Formation. A basal channel system consists of fills which demonstrate waning flow upward, as indicated by a base-to-top sequence of trough cross-strata, climbing-ripple cross-lamination, and epsilon cross-strata. This channel system has a higher width/depth ratio than the Bullion Creek paleo channels. A second group of channels, located higher in the Sentinel Butte section, are much smaller in scale and less well defined than the basal system.
Most of the Bullion Creek strata resulted from lacustrine deposition with brief episodes of rapid base-level lowering and concomitant fluvial downcutting and channel formation. Three lacustrine cycles are present in the Bullion Creek; a fluvial system caps each sequence. The basal channel sequence of the Sentinel Butte caps the third lacustrine sequence in the Bullion Creek Formation and may represent the progradation of a minor lacustrine delta lobe. Above this basal channel system are strata probably resulting from deposition in minor lake basins. Paleocurrent data indicate a northwest source for the Bullion Creek and Sentinel Butte, sediments. Bullion Creek sands appear to have been extensively reworked, while the sands of the Sentinel Butte are derived from a dominantly volcanic source terrane.
Wallick, Brian P., "Sedimentology of the Bullion Creek and Sentinel Butte formations (Paleocene) in a part of southern McKenzie County, North Dakota" (1984). Theses and Dissertations. 311.