Unit Name: Red River Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Caradoc - Ashgill (460.9 - 443.7 ma)
Province/Territory: Manitoba; Montana; North Dakota; South Dakota; Wyoming

Originator: Foerste, A.F., 1929a, b.

Type Locality:
"Tyndall Stone" quarries in the Garson-Tyndall area (NW/3-13-6EPM), and the Red River Valley area of southern Manitoba. Suggested reference core hole is Manitoba Core Hole M-3-80, Anama Bay (10-27-34-5WPM), between 9.3 and 100 m (31 and 328 ft). Subsurface reference hole is B.A. Morriseau 8-20-9-6WPM (Porter and Fuller, 1959), between 324 and 479 m (1,063 and 1,572 ft).

Distribution:
The Red River Formation extends throughout the Manitoba outcrop belt, and can be correlated throughout the entire Williston Basin area. Identical strata occur in the Hudson Bay Basin (Portage Chute Formation of the Bad Cache Rapids Group; Sanford et al., 1968). In the type area, at the southern end of the outcrop belt the formation is about 150 m (492 ft) thick; it thins progressively to the north, to less than 50 m (164 ft) near its northern erosional edge, and to the south, in the central part of the Williston Basin it reaches a maximum thickness of 215 m (705 ft).

Lithology:
In the central area of the Manitoba outcrop belt the lower Red River consists of a basal fossiliferous, mottled dolomitic limestone (Dog Head Member), overlain by a cherty dolomite (Cat Head Member) which is overlain by a second sequence of fossiliferous, mottled, dolomitic limestones (Selkirk Member). To the south the Cat Head Member becomes increasingly calcareous until, at the southern end of the outcrop belt it is indistinguishable from the underlying and overlying strata. In contrast, to the north of the type area the Dog Head and Selkirk members pass abruptly to mottled dolomites indistinguishable from the Cat Head. The Fort Garry Member maintains a relatively uniform lithology throughout the outcrop belt, consisting of finely crystalline and micritic, variably argillaceous dolomites, with a medial zone of shaly dolomite breccias, probably resulting from evaporite solution.

Relationship:
Red River strata overlie shales and sandstones of the Winnipeg Formation sharply and with possible slight unconformity (Kendall, 1976). They overstep strata of the Winnipeg Formation to rest unconformably on the Cambrian Deadwood Formation in western Saskatchewan, and on Precambrian in northern Manitoba. The Red River is overlain sharply and with possible slight disconformity by shaly beds of the Stony Mountain Formation. Subsurface equivalents of the outcrop units are: the Dog Head, Cat Head and Selkirk correlate with the Yeoman Formation; the Fort Garry correlates with the Herald Formation; and the Herald is further subdivided into the Lake Alma, Coronach and Redvers members with their associated anhydrite units (Kendall, 1976).

History:
Red River strata were first studied by Dowling (1900) along the west shore and islands of Lake Winnipeg. He correlated these strata with the "Trenton" of Minnesota and subdivided the sequence into three units, in ascending order the lower Mottled Limestone, the Cat Head Limestone and upper Monied Limestone. Foerste renamed the "Trenton strata the Red River Formation, and also renamed Dowling's members the Dog Head, Cat Head and Selkirk members. Subsequently McCabe and Bannatyne (1970), identified a fourth unit overlying the Selkirk Member and named it the Fort Garry Member. Sinclair (1959) determined that the so-called upper Mottled or Selkirk strata at the northern end of Lake Winnipeg were actually correlative with the Stony Mountain Formation; he went on to suggest that, since these strata overlay supposed Cat Head beds, this placed the Cat Head at the top of the Red River succession. He therefore suggested that the term Selkirk should be eliminated. Subsequent mapping and core hole studies (McCabe, 1980) indicated Sinclair's correlations of the Cat Head to be incorrect. The supposed Cat Head strata at the north end of Lake Winnipeg are, in fact dolomites of the Fort Garry Member, and the type Cat Head Member lies between the Dog Head and Selkirk members are originally defined. In the subsurface Porter and Fuller (1959) and Andrichuck (1959) indicated that the dolomites of the upper Red River were correlative with the Selkirk Member, inasmuch as no dolomitic unit was known to occur in the outcrop succession. The Selkirk is now known to correlate with the upper part of the lower Red River Formation.

Other Citations:
Andrichuck, 1959; Foerste, 1929a, 1929b; Kendall, 1976; McCabe, 1980; McCabe and Bannatyne, 1970; Porter and Fuller, 1959; Sanford et al., 1968; Sinclair, 1959.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: H .R. McCabe
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 19 Feb 2015