Stony Mountain Formation

The Stony Mountain Formation is a stratigraphic 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.

Lithology

Subdivisions

The Stony Mountain Formation is divided in the following sub-units:
;South

Penitentiary Member: argillaceous dolomite
Gunn Member: interbedded calcareous shale and fossiliferous limestone

;North

Gunton Member: crystalline dolomite
Lower Stony Mountain: argillaceous dolomite

Distribution

The Stony Mountain Formation occurs throughout the Williston Basin. It reaches a maximum thickness of 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.

Relationship to other units

The Stony Mountain Formation is slightly unconformably overlain by the Stonewall Formation and sharply overlays the Red River Formation or the Herald Formation.