Distribution:

The Belle Fourche Shale is recognized in Wyoming, Montana, and South and North Dakota. In eastern Saskatchewan and southern Manitoba it is recognized as the upper member of the Ashville Formation (McNeil and Caldwell, 1981), in central Montana it forms the lower member of the Colorado Shale. In the type area, flanking the western and northern Black Hills uplift the Belle Fourche Shale ranges form 113 to 229 m (371 to 751 ft) in thickness due to facies changes with the overlying calcareous shale of the Greenhorn Formation (Robinson et al., 1964). It is thinner eastwards, 61 m (200 ft) in South Dakota, 30 m (98 ft) in eastern North Dakota. In southern Manitoba the Belle Fourche Shale Member is approximately 45 m (148 ft) thick, but diminishes northwestward to 10 or 15 m (33 or 49 ft) in east-central Saskatchewan.

Lithology:

A uniform, greyish black, carbonaceous, noncalcareous shale with numerous bentonite beds and minor thin beds or lenses of silt, fine-grained sand, or calcarenite. Red weathering clay-ironstone concretions are rare to common in the Belle Fourche. In Manitoba the regional Fish-scale marker beds, which include lenses and laminae of silt and fish fragments occur at the base of the member. The upper Belle Fourche contains calcarenite beds termed the Ostrea beloiti beds, associated with a regional marker bentonite bed which, with the oyster-bearing calcarenite form a widespread marker in the eastern part of the Western Interior of Canada and the United States (McNeil and Caldwell, 1981).

Relationship:

The Belle Fourche Shale rests conformably on the siliceous Mowry Shale and passes by interdigitation into the overlying calcareous shale of the Greenhorn Formation. In southeastern Saskatchewan and southern Manitoba the Belle Fourche Shale Member rests conformably on dark shale of the Westgate Member and conformably underlies calcareous shale of the Favel Formation. Farther north a disconformity marks the contact between the Belle Fourche and the Favel. The Belle Fourche Shale correlates southward with the Graneros Shale of Colorado, Kansas and Nebraska. Westward it correlates with the lower part of the Frontier Formation in Wyoming. In western Saskatchewan and eastern Alberta it correlates with shale (upper part of Big River Formation of Simpson, 1975) in the lower Colorado Group situated between the base of the regional subsurface Fish-scale marker beds and Second (lower) White-speckled shale. In the central and southwestern Alberta Foothills the Belle Fourche correlates with the Sunkay Member (partly above and including the Fish Scale Sandstone) of the Blackstone Formation

History:

The "Belle Fourche Shale Member" was introduced as the upper member of the "Graneros Shale" in the Black Hills area of Wyoming by Collier (1920, 1922). It was defined as the shale unit between the Mowry Shale and the Greenhorn Limestone and has remained unmodified except for a change in rank from member to formation. The Belle Fourche Shale has been mapped extensively in Wyoming, Montana, and South and North Dakota (Hansen 1955; McGookey et al., 1972). In 1981 the name was introduced in Manitoba and eastern Saskatchewan by McNeil and Caldwell, who correlated the unit from its type locality northwards to the Manitoba escarpment, where it was designated as the Belle Fourche Shale Member of the Ashville Formation, replacing the informal name "upper Ashville" of Williams and Burk (1964).

Other Citations:

Collier, 1920, 1922; Hansen, 1955; Hattin, 1965; McGookey et al., 1972; McNeil and Caldwell, 1981; Price, 1963; Robinson et al., 1964; Simpson, 1975; Wall, 1967; Williams and Burk, 1964.

References:

Collier, A.J., 1920. "Oil field at Osage, Wyoming"; United States Geological Survey (USGS), Press Bull. 9065.

Collier, A.J., 1922. "The Osage oil field, Weston County, Wyoming", in, Contributions to economic geology (short papers and preliminary reports), 1922, Part II. - Mineral fuels, by Heald, K.C; United States Geological Survey (USGS), Bulletin 736-D, pp. 71-110.

McNeil, D.H. and Caldwell, W.G.E., 1981. Cretaceous rocks and their Foraminifera in the Manitoba escarpment. Geol. Assoc. Can., Spec. Paper 21