Type Locality:

Along the Missouri River of south-central South Dakota and northeastern Nebraska, named after exposures near the Niobrara River, Knox County, Nebraska.

Distribution:

The chalk-limestone facies of the Niobrara forms an elongate zone (eastern platform of Hattin, 1975b) covering the central western interior of North America, extending from the San Juan basin of northeastern New Mexico to the Pasquia Hills of east-central Saskatchewan. In northeastern Nebraska the formation is 55 to 62 m (180 to 203 ft) thick. The Fort Hays Limestone constitutes 12 to 24 m (39 to 79 ft) of that total, with a distribution limited to eastern Colorado, Kansas and Nebraska. The Niobrara thickens westward with the increase in terrigenous clastic sediments; reaching approximately 150 m (492 ft) through extreme northeastern New Mexico, eastern Colorado, extreme eastern Wyoming and the western margins of South and North Dakota. In southern Manitoba the formation attains a thickness of 73 m (239 ft), but thins northwestward along the Manitoba escarpment to 15 m (49 ft) in the Pasquia Hills of Saskatchewan, marking the northernmost occurrence of the chalky facies of the Niobrara (McNeil and Caldwell, 1981).

Lithology:

Medium grey to olive-grey calcareous or chalky shale, limestone, chalk or marlstone. The Fort Hays Limestone Member consists of thick- to massive bedded, microcrystalline limestone. The Smoky Hill Chalk Member is an argillaceous limestone or impure chalk, thinner bedded than the underlying Fort Hays Limestone. Hattin (1981) described the chalk as laminated to nonlaminated, mostly a foraminiferal pelmicrite with packstone or wackestone texture. The type beds are about 80 percent calcium carbonate, mostly derived from foraminifers and coccoliths. A characteristic feature of the Niobrara is the abundant occurrence of chalky specks, which Hattin (1975a) determined as of fecal pellet origin composed of aggregates of coccoliths. The proportion of carbonate in the Niobrara decreases westwards from the type locality coincident with a proportionate increase in terrigenous clastic sediments derived from western source areas. The nomenclature reflects this change; the formation is referred to as the Niobrara Shale in central Wyoming; the name Smoky Hill Shale Member is applied in Colorado. In Manitoba the Niobrara consists of a lower, olive-black, carbonaceous, chalk-speckled calcareous shale, with minor beds of greyish-black shale, thin bentonite beds and, in its lowermost 1 or 2 m (3 to 7 ft) lenses of silty or fine quartzose sand. The upper Niobrara consists of 2 buff weathering chalky, olive-black shale with subordinate interbeds of black, noncalcareous shale and numerous bentonite beds. The upper chalky lithotype is developed prominently in Pembina Mountain, disappears northward towards Riding Mountain and reappears farther northwest in the Pasquia Hills. In Manitoba the calcite content reaches 55 percent (Bannatyne, 1970).

Relationship:

Lower and upper contacts of the Niobrara may be either conformable or unconformable. Unconformable boundaries are generally more characteristic of the eastern sections (Kansas, Nebraska, eastern South and North Dakota, and southern Manitoba), whereas western sections are generally in conformable contact. In Manitoba chalky shale of the Niobrara unconformably overlies black shale of the Morden Shale (formerly Morden Member, Vermilion River Formation). Black shale of the Pembina Member of the Pierre Shale lies unconformably on the Niobrara along most of the Manitoba escarpment. A westward thickening shale wedge, the Gammon Ferruginous Member of the Pierre Shale intervenes between the Pembina and the Niobrara in the subsurface of southern Manitoba. The Niobrara correlates westwards with shale and subordinate sandstone. It correlates with the Mancos Shale (part) in northwestern Colorado, the Cody Shale and uppermost Frontier Formation in central and northern Wyoming, the Hilliard Shale and contiguous sandy units in Utah, and the Kevin Shale Member of the Marias River Shale and the Telegraph Creek Formation in Montana. In Canada the Niobrara extends through southern Manitoba into eastern Saskatchewan, correlating westwards with the First (upper) White Speckled shale of the Colorado Group in western Saskatchewan and eastern Alberta and the Muskiki, Marshybank, Dowling, Thistle and Hanson members of the Wapiabi Formation in the central and southwestern Alberta Foothills.

History:

The "Niobrara division" was introduced by Meek and Hayden (1862) for chalky shales, limestones and chalk or marl occurring between the "Fort Benton group" (now the Graneros Shale, Greenhorn Limestone and Carlile Shale) and the "Fort Pierre group" (now the Pierre Shale) of the classical Nebraska section in the Missouri River Valley. The formation has been recognized since through much of the eastern and median facies belts of the western interior from New Mexico to Manitoba and has been subdivided extensively along that tract (Cobban and Reeside, 1952; McGookey et al., 1972; McNeil and Caldwell, 1981) in the type area of South Dakota and Nebraska the formation has been divided into the lower Fort Hays Limestone Member (Williston, 1893) and an upper Smoky Hill Chalk Member (Cragin, 1896). The name "Niobrara" was in up in Canada through the late nineteenth century (Tyrrell, 1892) and early twentieth century (Ells, 1923). It was, however, applied incorrectly during that period. Thus the "Niobrara" in Manitoba included beds of the upper "Fort Benton Group" (now the Favel Formation and the Morden Shale). In 1930 Kirk introduced a revised nomenclature based on units defined and named in the area of the Manitoba escarpment. The "Boyne beds" of Kirk (1930), later termed the Boyne Member of the Vermilion River Formation by Wickenden (1945), corresponded to the Niobrara Formation of the Missouri River Valley. The nomenclature of Kirk and Wickenden was used widely and unmodified until 1981, when McNeil and Caldwell recommended reintroduction of the name "Niobrara" into Manitoba. Their recommendation was based on lithologic similarity and lateral continuity of the chalky Niobrara lithofacies in the eastern facies belt of the western interior of Canada and the United States from the type area in South Dakota and Nebraska through to Manitoba. McNeil and Caldwell (1981) divided the Niobrara Formation of Manitoba into a lower calcareous shale member and an upper chalky member.

Other Citations:

Cragin, 1896; Cobban and Reeside, 1952; Ells, 1923; Hattin, 1975a, 1975b, 1981; Kirk, 1930; McGookey et al., 1972; McNeil and Caldwell, 1981; Meek and Hayden, 1862; Reeside, 1944; Scott and Cobban, 1964; Simpson, 1960; Tyrrell, 1892; Wickenden, 1945; Williams and Burk, 1964; Williston, 1893.