The Red River Formation is a

lithostratigraphical Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

unit of Late

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something 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 The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North Dakota, South Dakota, southern Saskatchewan, and south-western Manitoba that is known for its rich deposits of petroleum and potash. The basin is a ...

. It takes the name from the

Red River of the North The Red River (), also called the Red River of the North () to differentiate it from the Red River of the South, Red River in the south of the continent, is a river in the north-central United States and central Canada. Originating at the confl ...

, and was first described in outcrop in the

Tyndall Stone Tyndall Stone is a registered trademark name by Gillis Quarries Ltd. Tyndall Stone is a dolomitic limestone that is quarried from the Selkirk Member of the Ordovician Red River Formation in the vicinity of Garson and Tyndall, Manitoba, ...

quarries and along the Red River Valley by A.F. Foerste in 1929.

Lithology

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 Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

in the middle * Selkirk Member: 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 (see Dolomite (rock)). An alternative name sometimes ...

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

* 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

. It extends throughout the Manitoba outcrop belt, and can be correlated throughout the entire Williston Basin area. It is thick and thins out to less than 50m (164 ft) 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 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.Dowl ...

and sharply overlays the

Winnipeg Formation Winnipeg () is the capital and largest city of the Canadian province of Manitoba. It is centred on the confluence of the Red and Assiniboine rivers. , Winnipeg had a city population of 749,607 and a metropolitan population of 834,678, making ...

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 ...

, the

Deadwood Formation The Deadwood Formation is a geologic formation of the Williston Basin and Western Canada Sedimentary Basin. It is present in parts of North and South Dakota and Montana in the United States, and in parts of Alberta, Saskatchewan, and southwester ...

in western

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

and the

Canadian Shield The Canadian Shield ( ), also called the Laurentian Shield or 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), th ...

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

References

{{Western Canadian Sedimentary Basin, Saskatchewan=yes, Manitoba=yes Geologic formations of Manitoba Ordovician southern paleotropical deposits Geologic formations of Saskatchewan Dolomite formations of Canada Limestone formations of Canada