Unit Name: Riding Mountain Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Campanian - Maastrichtian (83.6 - 66 ma)
Province/Territory: Manitoba; Saskatchewan

Originator: Kirk, S.R., 1930.

Type Locality:
Not specified, but inferred to be along Edward Creek, in Sec. 9, Twp. 23, Rge. 19WPM, on the north slope of Riding Mountain, Manitoba.

The Riding Mountain Formation is recognized in southeastern Saskatchewan and eastwards to its erosional edge in the Manitoba escarpment. The uppermost beds are truncated through much of the area by erosion, and only in Turtle Mountain is there a complete section of 280 m (918 ft) preserved.

Olive-grey clay and shale with clay-ironstone concretions common. The lower, Millwood Member is an olive-grey, silty clay in west-central Manitoba, but changes facies southeastward to clay and shale, then to interbedded calcareous and noncalcareous shale in Pembina Mountain in southern Manitoba and northernmost North Dakota, and finally to equivalent beds in South Dakota marked by prominent beds of chalk (McNeil and Caldwell, 1981). The facies change corresponds to a progression from the fine clastic, median facies belt to the eastern or mid-basin carbonate facies belt sensu Tourtelot (1962). Clay-ironstone concretions yielding bivalves and ammonites are common throughout the Millwood. The Odanah Member consists of a uniform siliceous, olive-grey clay or shale with minor beds of soft, olive-grey shale. Blackish-red weathering, manganese coated concretions are common through the member. Unknown to Kirk (1930) and Wickenden (1945) the siliceous shale is overlain by a softer olive-grey clay, silty in part, known mainly from the subsurface of Turtle Mountain (Bannatyne, 1970; Bamburak, 1978; McNeil and Caldwell, 1981). Bamburak (1978) separated these uppermost beds of the Odanah Member under the name Coulter Member; McNeil and Caldwell (1981) distinguished them as an unnamed member pending regional studies of their distribution.

The Riding Mountain lies with sharp, disconformable to probably paraconformable contact on the black shale of the Pembina Member, Vermilion River Formation (now Pembina Member, Pierre Shale). The contact with the overlying arenaceous Boissevain Formation is gradational, known only from the subsurface (Bamburak, 1978) The Riding Mountain correlates westward with the upper Lea Park, Judith River (Belly River) and Bearpaw formations of western Saskatchewan. In South Dakota its correlatives are the Gregory, DeGrey, Verendrye, Virgin Creek and Mobridge members of the Pierre Shale (Gill and Cobban, 1965).

Originally proposed for the soft, greenish grey shale between the black Pembina Shale and the siliceous Odanah shale. Wickenden (1945) expanded it, recognizing the Riding Mountain Formation as comprising both the soft shale and the siliceous shale (Millwood and Odanah), in contact with the Pembina Shale below and the Boissevain Formation above. McNeil and Caldwell (1981) recommended abandonment of the name Riding Mountain in favor of reintroduction of the name Pierre Shale, which includes the Gammon Ferruginous, Pembina, Millwood, Odanah, and an unnamed unit (Coulter Member of Bamburak, 1978) as members.

Other Citations:
Bamburak, 1978; Bannatyne, 1970; Gill and Cobban, 1965; Kirk, 1930; McNeil and Caldwell, 1981; Tourtelot, 1962; Wickenden, 1945.

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