Petrology of sandstones from the Bullion Creek and Sentinel Butte Formations (Paleocene), Little Missouri Badlands, North Dakota
Date of Award
Master of Arts (MA)
The mineralogy and petrology of sandstones of the Paleocene Bullion Creek and Sentinel Butte Formations were studied from exposures in the Little Missouri River Badlands in Billings, Golden Valley, and McKenzie Counties, North Dakota. Field work was conducted in the summer of 1977. Stratigraphic sections were measured and described from eight localities. Sandstones were sampled at 47 levels, and three samples were collected from each level. Fifty-one samples were collected from the Bullion Creek Formation and 90 from the Sentinel Butte Formation.
Thin-sections were prepared from plastic grain-mount blocks containing disaggregated sand grains, and 200 points per thin-section were counted, using the Glagolev-Chayes point-counting method. Counts were made of quartz, feldspar, lithic clasts, and accessory minerals. Lithic clasts were further subdivided, and, in decreasing abundance, are chert, plutonic, sedimentary, and volcanic. Variations in point-counting data within both sampling levels and formations are either minor or considerable.
The most abundant elastic constituent is quartz, accounting for 32-68 percent of grains from Bullion Creek sandstones and 20-62 percent of grains from Sentinel Butte sandstones. Feldspar accounts for 2-16 percent of grains in Bullion Creek sandstones and 8-43 percent of grains in Sentinel Butte sandstones. Lithic clasts account for 26-53 percent of grains from Bullion Creek sandstones and 18-54 percent of grains from Sentinel Butte sandstones. Accessory minerals, such as micas, are minor constituents in both formations.
Quartz/feldspar (Q/F) ratios are significantly higher in Bullion Creek sandstones than in Sentinel Butte sandstones: in the Bullion Creek, mean Q/F ratios are generally greater than 0.89, whereas in the Sentinel Butte, mean Q/F ratios are less than 0.74. However, the dark gray sand of the Bullion Creek Formation which occurs in the upper one-third of the formation, has mean Q/F ratios of 0.68-0.89. The lower and upper yellow beds, which both occur in the upper one-half of the Sentinel Butte Formation, have mean Q/F ratios greater than 0.81. Mature sandstones have higher Q/F ratios and an apparent inverse relationship exists between Q/F ratios and grain size.
Albite-twinned oligoclase, orthoclase, microcline, oscillatory-zoned plagioclase, and schistose plutonic clasts are abundant in the Sentinel Butte Formation, and the Black Hills of South Dakota are believed to be their supplier. Such constituents are generally lacking in Bullion Creek sandstones, and no specific source can be assigned to them.
The general maturity of Bullion Creek sandstones suggests syndepositional tectonic stability. The period of greatest tectonic instability is suggested for deposition of the basal Sentinel Butte sand. Lessening tectonic instability appears to have prevailed during the remainder of Sentinel Butte deposition.
Steiner, Mark A., "Petrology of sandstones from the Bullion Creek and Sentinel Butte Formations (Paleocene), Little Missouri Badlands, North Dakota" (1978). Theses and Dissertations. 286.