The Red River Formation is a

stratigraphical Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...

unit of Late Ordovician

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

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.Foerste, A.F., 1929b. The cephalopods of the Red River Formation of southern Manitoba. Denison Univ. Sci. Lab J., v. 24, p. 129-235.

Lithology

Subdivisions

The Red River Formation is composed of the following subdivisions from top to base: * Fort Garry Member: crystalline and micritic

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

with an argillaceous dolomite

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

in the middle *

Selkirk Member 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 ...

: fossiliferous,

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

* Cat Head Member:

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

y dolomite, becoming calcareous to the south * Dog Head Member: fossiliferous dolomitic

Distribution

The Red River Formation reaches a maximum thickness of in the center of the Williston Basin. At the along the Manitoba outcrop belt, it is thick and thins out northwards.

Relationship to other units

The Red River Formation is slightly

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

overlain by the Stony Mountain Formation and sharply overlays the

Winnipeg Formation Winnipeg () is the capital and largest city of the province of Manitoba in Canada. It is centred on the confluence of the Red and Assiniboine rivers, near the longitudinal centre of North America. , Winnipeg had a city population of 749,6 ...

Manitoba Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...

, the Deadwood Formation in western

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

and the

Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the anc ...

in northern Manitoba. The lower Red River Formation is equivalent to the

Yeoman Formation Yeoman is a noun originally referring either to one who owns and cultivates land or to the middle ranks of servants in an English royal or noble household. The term was first documented in mid-14th-century England. The 14th century also witn ...

, while the Fort Garry Member correlates with the

Herald Formation The Herald Formation is a stratigraphical unit of Late Ordovician age in the Western Canadian Sedimentary Basin. It was defined in well ''Imperial Herald 1-31-1-20W2M'' by the Lower Paleozoic Names and Correlations Committee of the Saskatchewan ...

References

{{Western Canadian Sedimentary Basin, Saskatchewan=yes, Manitoba=yes Stratigraphy of Manitoba Ordovician southern paleotropical deposits