{{Short description|Geologic formation in Canada}} {{Infobox rockunit | name = Red River Formation | image = | imagesize = | caption = | type = Geological formation | age = {{Fossil range|460|445|Caradoc to Ashgill}} | period = Ordovician | prilithology = limestone, dolomite | otherlithology = Breccia | namedfor = Red River of the North | namedby = A.F. Foerste | year_ts = 1929 | region = WCSB<br>Williston Basin | country = Canada<br>United States | coordinates = {{coord|51.9482|N|98.0563|W|display=inline,title|name= Red River Formation}} | unitof = | subunits = Fort Garry Member<br>Selkirk Member<br>Cat Head Member<br>Dog Head Member | underlies = Stony Mountain Formation | overlies = Winnipeg Formation | thickness = up to {{convert|215|m|ft|-1}}<ref name=lexicon/> | extent = | area = | map = | map_caption = }}
The '''Red River Formation''' is a lithostratigraphical 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.<ref>Foerste, A.F., 1929. The Ordovician and Silurian of the American arctic and sub-arctic regions. Denison Univ. Sci. Lab J., v. 24, p. 27-79.</ref><ref>Foerste, A.F., 1929b. The cephalopods of the Red River Formation of southern Manitoba. Denison Univ. Sci. Lab J., v. 24, p. 129-235.</ref>
==Lithology==
===Subdivisions===
The Red River Formation is composed of the following subdivisions from top to base: <ref name=lexicon> {{Cite web |url = http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl? |title = Formation |author = Lexicon of Canadian Geologic Units |accessdate = 2010-02-01 |url-status = dead |archiveurl = https://web.archive.org/web/20090416121153/http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl |archivedate = 2009-04-16 }} </ref> *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 {{convert|215|m|ft|-1}} 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 {{convert|150|m|ft|-1}} thick and thins out to less than 50m (164 ft) northwards.<ref name=lexicon/><ref>{{Cite web |title=Red River Formation |url=https://weblex.canada.ca/html/012000/GSCC00053012586.html |access-date=2025-01-28 |website=weblex.canada.ca}}</ref>
==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.<ref name=lexicon/>
The lower Red River Formation is equivalent to the Yeoman Formation, while the Fort Garry Member correlates with the Herald Formation.
==References== {{reflist}}
{{Western Canadian Sedimentary Basin|Saskatchewan=yes|Manitoba=yes}}
Category:Geologic formations of Manitoba Category:Ordovician southern paleotropical deposits Category:Geologic formations of Saskatchewan Category:Dolomite formations of Canada Category:Limestone formations of Canada Category:Lagerstätten