Red River Formation

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

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.

Subdivisions
The Red River Formation is composed of the following subdivisions from top to base:
 * 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 m in the center of the Williston Basin. At the along the Manitoba outcrop belt, it is 150 m thick and thins out northwards.

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.

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