Stratigraphy and structure of the northern and western flanks of the Black Hills uplift, Wyoming, Montana, and South Dakota

Abstract

This report describes the stratigraphy and structure of an area of about 5,000 square miles in northeastern Wyoming and adjacent parts of Montana and South Dakota. The area includes the northern end and part of the western side of the Black Hills uplift and the adjoining part of the Powder River Basin.About 11,000 feet of sedimentary rocks ranging in age from Mississippian to early Tertiary are exposed in the area, not including surficial deposits of Tertiary(?) and Quaternary age. The oldest rocks crop out in the southeastern part of the area and consist of 500 to 600 feet of light-gray cherty limestone that makes up the Early Mississippian Pahasapa limestone. Unconformably overlying the Pahasapa limestone is the Minnelusa formation of Pennsylvanian and Permian age. It is 650 to 800 feet thick in drill holes and at outcrops in the southeastern part of the •area, and it consists of interbedded lightgray and pink sandstone, gray sandy limestone and dolomite, some red shale and siltstone, and local beds of gypsum and. anhydrite. The Permian Opeche formation overlies the Minnelusa formation unconformably and comprises 60 to 90 feet of red fine-grained sandstone, siltstone, and silty• shale. Next in order is the Permian Minnekahta limestone, which is composed of light-gray and light purplish-gray thin-bedded limestone about 40 feet thick. The Spearfish formation, 450 to 825 feet thick, BLACK HILLS UPLIFT, WYOMING, MONTANA, SOUTH DAKOTA Weston County. It is composed of dark-gray shale, at places sandy and silty, interbedded with bentonite and numerous limestone and siderite concretions. The formation is divided into several members, which from base to top are the Gammon ferruginous member, 0 to about 1,000 feet thick; the Mitten black shale mem~r, 145 to about 870 feet thick; and the upper part of the Pierre shale including the Monument Hill bentonitic member 150 to about 220 feet thick, and the somewhat younger Kara bentonitic member about 100 feet thick. In the northern part of the area, the Gammon ferruginous member contains a zone of sandstone and sandy shale about 100 feet thick known as the Groat sandstone bed.The Fox Hills sandstone overlies the Pierre shale and is 150 to 200 feet thick. .Yellowish-gray sandstone and gray shale make up the Fox Hills sandstone at most places except in Carter County, Mont., where as much as 100 feet of very light gray cliff-forming sandstone crops out at the top of the formation and is mapped separately as the Colgate member .. Nonmarine sedimentary rocks overlie the Fox Hills sandstone and make up an essentially conformable sequence of sandstone, shale, •and coal beds that includes the Lance formation of Late Cretaceous age, the Fort Union formation of Paleocene age, and the W•asatch formation of Eocene age. The Lance formation is 1,600 feet thick in northern Weston County, Wyo., but thins northward to about 500 feet in Carter County, Mont. The overlying Fort Union formation, 1,500 to about 2,100 feet thick, also thins northward. It is divided into the Tullock member at the base...

Synthesis of late Paleozoic and Mesozoic eolian deposits of the Western Interior of the United States

“…Correlation with basal Morrison sandstone beds on the northwest flank of the uplift is not certain but seems reasonable (Robinson et al, 1964). As contoured from the available surface information, the Unkpapa and related units are restricted to the structural high marked by the Black Hills uplift, a structural feature known to have been active in Jurassic and Cretaceous time (Robinson et al, 1964). Studies by McKee et al (1956) and Szigeti and Fox (1981) suggest that the sandstone continues southeast from the Black Hills, but whether or not it is eolian in that area has not, to our knowledge, been determined.…”

“…Glen Canyon SS. Navajo Sandstone Navajo Sandstone Navajo Sandstone Navajo Sandstone Navajo Sandstone Navajo Sandstone Navajo Sandstone Navajo Sandstone Nugget Sandstone Nugget Sandstone Nugget Sandstone Nugget Sandstone Aztec Sandstone Aztec Sandstone Love, 1957Love, 1957Love, 1957Love, 1957Love, 1957Love, 1957Pacht, 1976 Pipiringos, 1968 Pipiringos, 1968 Pipiringos, 1968 Pipiringos, 1968Knapp, 1976 Pipiringos, 1968 Pipiringos, 1968 Pipiringos, 1968Love, 1957Love 1957Love 1957Love 1957Love 1957Love 1957Love 1957Love 1957Love 1957 Low 1957Love, 1957Averitt, 1962Weaver, 1980George, 1985Harshbarger et al, 1957Harshbarger et al, 1957Harshbarger et al, 1957Harshbarger et al, 1957Harshbarger et al, 1957 PI Harshbarger et at., 1957Bilodeau and Keith, 1986Bilodeau and Keith, 1986Bilodeau and Keith, 1986Bilodeau and Keith, 1986 Miller and Carr, 1978 Marzolf, 1983Thomas et al, 1945 Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964Robinson et al, 1964…”

Mineral resource potential and geology of the Black Hills National Forest, South Dakota and Wyoming with a section on salable commodities

“…Iron-formation units in the Flag Rock are impossible to tell from the Homestake Formation except that they tend to be thinner and are associated with different overlying and underlying rocks. The Flag Rock is more than 3,000 ft thick and may be thicker, but effects Staatz (1983), Pillmore and Mapel (1963), Robinson, Mapel, and Bergendahl (1964), Fashbaugh (1979), Jenner (1984, O'Toole (1981), White (1980), andWilkinson (1982 Harney Peak Granite (Early Proterozoic) Coarse-grained to pegmatitic muscovite granite and pegmatite containing accessory garnet, biotite, and tourmaline. Age {recalculated using decay constants recommended by Steiger and Jaeger (1977) from Rb-Sr whole-rock isochron is 1697+33 Ma (Riley, 1970 Norton (1976), Norton (unpub.…”

“…This section will therefore be a review of many works, especially those by Hayden (1872), Newton and Jenney (1880), Darton (1902Darton ( , 1904aDarton ( , 1905Darton ( , 1919, Darton and Smith (1904), Darton and O'Harra (1905, 1907, 1909, Darton and Paige (1925), Imlay (1947), Cobban (1952), Gries (1952Gries ( , 1964Gries ( , 1975, McCoy (1952), Waage (1959), Reeside and Cobban (1960), Gill and Cobban (1961), Robinson, Mapel, and Bergendahl (1964), Schultz (1965), Gott, Wolcott, and Bowles (1974), Harksen (1975), Merewether (1975), Rahn (1981), and numerous other authors.…”

“…data, 1985). This area contains favorable channel-sandstone stratigraphy (Robinson, Mapel, and Bergendahl, 1964;Maxwell, 1974) and has airborne radiometric uranium anomalies and a high ratio of uranium to thorium (EG&G geoMetrics, 1979b). Reconnaissance stream-sediment sampling by Warren and others (1980) reveals minor uranium anomalies in this area.…”