Unit Name: Ashern Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: early Middle Triassic - early Middle Devonian (245 - 391.8 ma)
Province/Territory: Manitoba; Saskatchewan; North Dakota
Originator: Baillie, 1951.
Type Locality:
Outcrops near town of Ashern, Manitoba (vicinity of Twp. 25, Rge. 7WPM), but no type section defined because of poor exposure. Suggested reference subsurface section is Manitoba Mineral Resources Division core hole M-4-79, in Lsd. 2, Sec. 22, Twp. 27, Rge. 7WPM, between 3 and 10 m (10 and 33 ft) located at the Spearhill Quarry, 16 km (10 mi) north of Ashern.
Distribution:
Thickness variable and rather erratic, ranging from 3 to 4.6 m (10 to 15 ft) along the Manitoba outcrop belt. The subsurface thickness ranges up to as much as 55 m (180 ft) in North Dakota. Ashern strata extend throughout the Manitoba and Saskatchewan portions of the Elk Point Basin, except locally in the area of the Swift Current Platform, and at places on the basin flank where they are overstepped by Winnipegosis strata.
Lithology:
In outcrop poorly thin-bedded, brick red to greyish orange, unfossiliferous, slightly silty, argillaceous dolomite to dolomitic shale. In the subsurface the lower red bed facies commonly grades upward through variegated green and red shales to grey shales and argillaceous dolomite. Salt casts and minor amounts of anhydrite and iron sulphide are present. Basal beds show development of prominent carbonate breccia in places, and may contain significant amounts of quartz silt and sand.
Relationship:
The Ashern overlies Silurian and Ordovician carbonate rocks with pronounced, slightly angular unconformity; possibly local, incipient pre-Devonian karst development. It is overlain with possible slight unconformity by dolomites or limestones of the Winnipegosis Formation, or Elm Point Formation where it is developed. It correlates with the Contact Rapids Formation of central Alberta.
Other Citations:
Baillie, 1951, 1953; Grayston et al., 1964; Uyeno et al., 1980.
References:
Baillie, A.D., 1951. Silurian geology of the Interlake area; Manitoba Mines Branch Publication 50-1, 82 p.
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: 05 Mar 2009