| Stony Mountain Formation | |
| Type: | Geological formation |
| Period: | Ashgill |
| Prilithology: | dolomite, shale |
| Otherlithology: | Anhydrite, limestone |
| Namedfor: | Stony Mountain, Manitoba |
| Namedby: | D.B. Dowling, 1900 |
| Region: | WCSB Williston Basin |
| Country: |  Canada United States |
| Coordinates: | 49.9184°N -97.5265°W |
| Underlies: | Stonewall Formation |
| Overlies: | Red River Formation |
| Thickness: | up to 45m (148feet) |
The Stony Mountain Formation is a stratigraphical unit of Ashgill age in the Western Canadian Sedimentary Basin.
It takes the name from the community Stony Mountain, Manitoba, and was first described in the town quarry by D.B. Dowling in 1900.[1]
The Stony Mountain Formation is divided in the following sub-units:[2]
argillaceous dolomite
interbedded calcareous shale and fossiliferous limestone
crystalline dolomite
The Stony Mountain Formation occurs throughout the Williston Basin.[2] It reaches a maximum thickness of 45m (148feet) in the sub-surface at the Canada/United States border, and thins out towards the east, north and west. In Manitoba, where it is exposed at the surface in the erosion belt, it has a thickness of 30m (100feet).
The Stony Mountain Formation is slightly unconformably overlain by the Stonewall Formation and sharply overlays the Red River Formation or the Herald Formation.[2]