Red River Formation

The Red River Formation is a lithostratigraphical unit of Late Ordovician age in the Williston Basin.

Red River Formation
Stratigraphic range: Caradoc to Ashgill PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Sub-units	Fort Garry Member Selkirk Member Cat Head Member Dog Head Member
Underlies	Stony Mountain Formation
Overlies	Winnipeg Formation
Thickness	up to 215 metres (710 ft)[1]
Lithology
Primary	limestone, dolomite
Other	Breccia
Location
Coordinates	51.9482°N 98.0563°W / 51.9482; -98.0563 (Red River Formation)
Region	WCSB Williston Basin
Country	Canada  United States
Type section
Named for	Red River of the North
Named by	A.F. Foerste
Year defined	1929

It takes the name from the Red River of the North, and was first described in outcrop in the Tyndall Stone quarries and along the Red River Valley by A.F. Foerste in 1929.^[2][3]

Lithology

Subdivisions

The Red River Formation is composed of the following subdivisions from top to base: ^[1]

• Fort Garry Member: crystalline and micritic dolomite with an argillaceous dolomite breccia in the middle
• Selkirk Member: fossiliferous, dolomitic limestone
• Cat Head Member: cherty dolomite, becoming calcareous to the south
• Dog Head Member: fossiliferous dolomitic limestone

Distribution

The Red River Formation reaches a maximum thickness of 215 metres (710 ft) in the center of the Williston Basin. It extends throughout the Manitoba outcrop belt, and can be correlated throughout the entire Williston Basin area. It is 150 metres (490 ft) thick and thins out to less than 50m (164 ft) northwards.^[1][4]

Relationship to other units

The Red River Formation is slightly unconformably overlain by the Stony Mountain Formation and sharply overlays the Winnipeg Formation in Manitoba, the Deadwood Formation in western Saskatchewan and the Canadian Shield in northern Manitoba.^[1]

The lower Red River Formation is equivalent to the Yeoman Formation, while the Fort Garry Member correlates with the Herald Formation.