Unit Name: Watrous Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Triassic - Jurassic (251 - 145.5 ma)
Province/Territory: Saskatchewan

Originator: Milner and Thomas, 1954.

Type Locality:
South-central Saskatchewan. Type well is the Tidewater Davidson Crown No. 1, in Lsd. 13, Sec. 4, Twp. 27, Rge. 28W2M, between 755 and 837 m (2,476 and 2,744 ft)

Although defined as one formation, there is by usage a tendency to separate the lower argillaceous member from the anhydritic upper. Both units are distributed across southern Saskatchewan south of 52 deg N, from the Manitoba border westward to 109 deg W. The lower member infills irregularities on the sub Mesozoic erosional surface and thus varies abruptly in thickness by about 30 m (98 ft). Combined thickness (both units) range from 110 m (361 ft) along the border with North Dakota to zero at the erosional edge.

Locality Data:
WELL 101130402728W200; DAVIDSON CROWN NO 1. Thickness(m): Minimum 0, Maximum 110. Interval(m): From 755, To 837.

Comprises a lower and an upper member. The lower member is typified by red shales and mudstones, frequently variegated with green, and thinly and irregularly interbedded with patches and blebs of laminated anhydrite and anhydrite inclusions. Basal beds across southern Saskatchewan are commonly marked by sandstones, conglomerates and, locally by brecciated cherty anhydrite, white, light grey and massive, interbedded with buff, earthy microcrystalline dolomite and grey shale; both are interrupted by veinlets of anhydrite. The upper member, a bed of massive anhydrite several metres thick laps over the lower units along the edge of the Watrous area of distribution.

The Watrous Formation is synonymous with the Amaranth Formation of Manitoba (Stott, 1955). Because the lack of fossils uncertainty exists as to the age of the lower member. The outward and upward expansion of marine facies in the Jurassic suggests that the lower member of Watrous Formation represents the beginning of the Jurassic marine transgression. However, on the basis of regional correlation it appears to be a northward extension of the Triassic Spearfish Formation of North Dakota. The upper member is correlated with the lower part of the Jurassic Nesson Formation.

Other Citations:
Barchyn, 1982; Francis, 1956; Milner and Thomas, 1954; Stott, 1955.

Milner, R.L. and Thomas, G E., 1954. Jurassic System in Saskatchewan. In: Western Canada Sedimentary Basin Amer. Assoc. Petrol. Geol., p. 250-267
Stott, D.F., 1955. Jurassic stratigraphy of Manitoba; Manitoba Dept. Mines and Nat. Res., Pub. 54-2.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: J.E. Christopher
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 04 Feb 2009