| Graneros Shale | |
|---|---|
| Stratigraphic range: | |
 Graneros Shale at outlet of El Vado Reservoir, New Mexico, USA | |
| Type | Formation |
| Unit of | Colorado Group (Great Plains) Benton Group (Colorado, South Dakota) Mancos Group (Colorado, New Mexico) |
| Sub-units | See text |
| Underlies | Greenhorn Formation |
| Overlies | Dakota Formation |
| Thickness | 114–1,000 feet (35–305 m) |
| Lithology | |
| Primary | Shale |
| Other | Sandstone, limestone |
| Location | |
| Coordinates | 38°16′35″N 104°42′44″W / 38.2763°N 104.7121°W |
| Region | Colorado, Iowa, Kansas, Minnesota, Montana, New Mexico, Nebraska, North Dakota, South Dakota, Wyoming |
| Country |  United States |
| Type section | |
| Named for | Graneros Creek, Walsenburg quadrangle, Pueblo Colorado |
| Named by | G.K. Gilbert (from R.C. Hills) |
| Year defined | 1896 |
  Graneros Shale (the United States)  Graneros Shale (Colorado) | |
The Graneros Shale is a geologic formation in the United States identified in the Great Plains as well as New Mexico that dates to the Cenomanian Age of the Cretaceous Period.[1] It is defined as the finely sandy argillaceous or clayey near-shore/marginal-marine shale that lies above the older, non-marine Dakota sand and mud, but below the younger, chalky open-marine shale of the Greenhorn. This definition was made in Colorado by G. K. Gilbert and has been adopted in other states that use Gilbert's division of the Benton's shales into Carlile, Greenhorn, and Graneros. These states include Kansas, Texas, Oklahoma, Nebraska, and New Mexico as well as corners of Minnesota and Iowa.[2][3] North Dakota, South Dakota, Wyoming, and Montana have somewhat different usages — in particular, north and west of the Black Hills, the same rock and fossil layer is named Belle Fourche Shale.[4][5]
- ^ Cobban, W.A.; Scott, G.R. (1972). "Stratigraphy and ammonite fauna of the Graneros Shale and Greenhorn Limestone near Pueblo, Colorado". U.S. Geological Survey Professional Paper. Professional Paper. 645. doi:10.3133/pp645. Retrieved 3 September 2020.
- ^ "Geologic Unit: Graneros". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2021-03-12.
- ^ Siliciclastic and calcareous sedimentary rocks of early Late Cretaceous age in the Western Interior of the United States have been assigned to, in ascending order, the Graneros Shale, Greenhorn Formation, Carlile Shale, Niobrara Formation, and their lateral equivalents (including members of the Frontier Formation and overlying formations). Merewether, E. Allen; Cobban, William A.; Obradovich, John D. (2007). "Regional disconformities in Turonian and Coniacian (Upper Cretaceous) strata in Colorado, Wyoming, and adjoining states - Biochronological evidence". Rocky Mountain Geology. 42 (2): 95–122. Bibcode:2007RMGeo..42...95M. doi:10.2113/gsrocky.42.2.95.
- ^ Donald E. Hattin (1975). Stratigraphy and Depositional Environment of Greenhorn Limestone (Upper Cretaceous) of Kansas, Kansas Geological Survey, Bulletin 176. University of Kansas Publications, State Geological Survey of Kansas. p. Stratigraphy.
The Graneros Shale was named by Gilbert (1896, p. 564) for 200 to 210 feet of argillaceous or clayey shale lying between the top of the Dakota and the base of the overlying Greenhorn Limestone." "[In northwestern Nebraska and around the Black Hills] the thicknesses are for the combined Mowry and Belle Fourche shales but, as noted above, only the Belle Fourche is lithologically equivalent to the Graneros.
- ^ Donald E. Hattin (1965). "Stratigraphy of the Graneros Shale (Upper Cretaceous) in Central Kansas". Kansas Geological Survey Bulletin (178). Kansas Geological Survey: Stratigraphy / Graneros Shale / Name and Definition. Retrieved September 6, 2021.
The lithologic equivalent of the Graneros in the Black Hills and surrounding areas is the Belle Fourche Shale. Considerable similarity exists between these two formations, and, if the name Graneros is to be perpetuated in the Black Hills region, it would be best used to replace the name Belle Fourche over which the former has priority.