| Belle Fourche Formation | |
|---|---|
| Stratigraphic range: Cretaceous | |
| Type | Formation |
| Location | |
| Region | Montana, North Dakota, South Dakota, Wyoming |
| Country | United States |
The Belle Fourche Formation or Belle Fourche Shale is a fossiliferous early Late-Cretaceous geologic formation classification in Wyoming. Named for outcrops in Belle Fourche River, Wyoming, this unit name is also used in Montana, North Dakota, and South Dakota.[1]
The unit records the gradual opening and expansion of the Greenhorn Cycle of the Western Interior Seaway, and as such is lithologically identical to the Graneros Shale Formation (that is, it is the same formation under a different name).[2]
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.