Date of Award
Doctor of Philosophy (PhD)
The Colgate Member (Fox Hills Formation), Little Beaver Creek, Marmarth, Bacon Creek, Huff, and Pretty Butte Members (Hell Creek Formation), and lower Ludlow Formation in the Glendive area, Montana consist of sandstone, sandy siltstone, shale, and lignite. The Colgate is 24 m thick and consists of mostly sandstone, The Hell Creek Formation (Late Cretaceous) is 120 m thick, The basal member, the Little Beaver Creek, is up to 12 m thick and consists of about half sandstone and half shale. The Marmarth is 24 to 30 m thick and consists of mostly sandstone. The Bacon Creek is 36 m thick and the Huff is 42 to 48 m thick. Each is about half sandstone and half shale, but amounts vary locally from 10 to 90 percent, The Pretty Butte is generally less than 6 m thick and is mostly shale. Of the lower 50 m of the Ludlow Formation, sandstone forms 20 to 60 percent and the rest is mostly shale.
Sandstone units are very-fine- to medium-grained, light olive gray to yellowish gray, fluted, concretion-bearing, cross-stratified, and fossiliferous, Upward-fining intervals, each about 6 m thick, may stack vertically to tens of meters to form multilateral complexes tens of kilometers wide or elongated, locally tabular, distributary and braided belts 150 to 1700 m wide. Paleocurrents parallel the belt margins and trend mostly east and southeast. Sandy siltstonea flank the sandstone and are yellowish gray to dark yellowish orange, 1 to 4 m thick, poorly sorted, laminated, cross-laminated, and fossiliferous, Shale units are light olive gray, olive gray, pale brown, silty, bentonitic, lignitic, laminated, and fossiliferous. They are a few tenths of a meter to 6 m or more thick in areas between belts. Lignites are pale brown to black, a few tenths of a meter thick, and interbedded with shale. Dinosaur, crocodile, turtle, fish, freshwater invertebrate, and terrestrial plant fossils including leaves and rootlets are common in the Hell Creek.
Sandstones are interpreted to be point bar deposits of meandering distributary channels. Sandy siltstones are natural levee deposits. Shales are interdistributary floodbasin, lake, and abandoned channel deposits. Lignites are swamp and freshwater marsh deposits. The meander belts and floodbasins sggraded from a similar base level and produced three basic types of cyclic deposits. The streams were stable, moderately sinuous, mixed-load, about 115 m wide, 5.2 m deep, and 450 km long. There was a fining of load and a decrease in discharge, width, and depth with time. This correlates with a decrease in volcanic detritus.
Most sandstones are volcanic arenites and sedarenites consisting of rhyodacite-andesite fragments, quartz, chert, a little plagioclase, and fragments of shale, carbonate, and schist. The dominant source was probably the Elkhorn Mountains Volcanic field in western Montana.
The Hell Creek and adjacent strata are deposits of a highconstructive, sandy, shallow-water lobate delta that prograded into the Williston Basin and formed several fluvially-dominated lower delta plain fncies. F.nch facics is tens of meters thick and regionally widespread. They overlie prodelta shale (Pierre Formation) and delta margin sandstone and siltstone (lower Fox Hills). The Colgate and Marmarth are highly meandering channel sandstone facies. The Little Beaver Creek and Bacon Creek are slightly meandering channel sandstone and floodbasin shale facies. The Huff, Pretty Butte, and lower Ludlow are slightly too moderately meandering channel sandstone and floodbasin shale facies.
Butler, Raymond D., "Stratigraphy, sedimentology, and depositional environments of the Hell Creek Formation (Late Cretaceous) and adjacent strata, Glendive area, Montana" (1980). Theses and Dissertations. 44.