Unit Name: Stonewall Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Ashgill - Alexandrian (449 - 436 ma)
Province/Territory: Manitoba

Originator: Kindle, 1914.

Type Locality:
Stonewall Quarry, Stonewall, Manitoba (13-30-13-2EPM). Suggested reference outcrop core hole is Manitoba Core Hole M-1-86, Warren, 13-31-13-1WPM, between 40.7 and 53.7 m (134 and 176 ft). Reference subsurface hole is B.A. Morriseau 8-20-9-6WPM, between 266.7 and 286.5 m (875 and 940 ft).

The Stonewall Formation extends throughout the Manitoba outcrop belt and throughout the subsurface of the Williston Basin. Thickness ranges from 15 to 34 m (49 to 112 ft).

Locality Data:
Thickness(m): Minimum 15, Maximum 34.

Consists largely of pale yellowish grey, faintly mottled, finely crystalline, medium-bedded dolomite, generally sparsely fossiliferous. A basal unit about 3 m (10 ft) thick consists of grey to reddish and brownish argillaceous and/or sandy dolomite named the Williams Member (of the Stony Mountain Formation) by Smith (1963a, 1964). A thin sandy, argillaceous marker also occurs near the middle of the formation (T-marker of Porter and Fuller, 1959), and another similar marker occurs at the top of the formation. A brown, nodular anhydrite bed termed the Stonewall anhydrite (Porter and Fuller, 1959; Kendall, 1976) occurs toward the base of the formation and averages 2.5 to 3 m (8 to 10 ft) thick. Thin anhydrite beds are present in the central part of the Williston Basin.

Overlies the Stony Mountain Formation (Gunton Member) sharply and probably with slight disconformity. In more basinal areas it is overlain with possible slight disconformity by the Interlake Group (Fisher Branch Formation), but to the north, towards the edge of the basin upper Stonewall beds become increasingly conglomeratic and the contact with the overlying Fisher Branch probably is unconformable.

As proposed by Kindle (1914) the Stonewall Formation included all Silurian strata outcropping in Manitoba. However Baillie (1951) proposed the term Interlake Group for all Silurian strata and restricted the term Stonewall Formation to include only those strata between the Upper Ordovician Stony Mountain Formation and the overlying Virgiana beds (his unit B, subsequently named the Fisher Branch Formation by Stearn, 1956b). Baillie (1952) then further revised the Stonewall, placing a series of reddish, sandy, argillaceous marker beds occurring at the base of the formation into the underlying Stony Mountain Formation. General usage, however has retained these marker beds as the basal unit of the Stonewall Formation (Kendall, 1976). Stearn (1956b), on the basis of faunal studies showed that the Stonewall quarry beds (which comprise only the lower part of the Stonewall Formation) were Ordovician in age, and therefore removed the Stonewall formation from the Interlake Group. Brindle (1960b) suggested that the upper portion of the Stonewall above a medial argillaceous marker (T-marker of Porter and Fuller, 1959) was possibly Silurian in age.

Other Citations:
Baillie, 1957; Brindle, 1960; Kendall, 1976; Kindle, 1914; Porter and Fuller, 1959; Smith, 1963, 1964; Stearn, 1956.

Baillie, A.D., 1951. Silurian geology of the Interlake area; Manitoba Mines Branch Publication 50-1, 82 p.
Baillie, A.D., 1952. Ordovician geology of Lake Winnipeg and adjacent areas, Manitoba; Manitoba Department of Mines and Natural Resources, Mines Branch, Bulletin 51-6, 64 p. + 2 Maps.
Brindle, J.E., 1960b. The Faunas of the Lower Palaeozoic Carbonate Rocks in the Subsurface of Saskatchewan; Saskatchewan Department of Mineral Resources, Saskatchewan Industry and Resources (SIR) Report no. 52, 45 p., 1 table, 8 plates, 3 figures.
Kendall, A.C., 1976. The Ordovician carbonate succession (Bighorn Group) ot southern Saskatchewan. Saskatchewan Dept. Min. Res., Rept. 180.
Kindle, E.M., 1914. The Silurian and Devonian Section of Western Manitoba; Geological Survey of Canada, Summary Report 1912, pp. 247-261.
Porter, J.W. and Fuller, J G.C.M., 1959. Lower Paleozoic rocks of northern Williston Basin and adjacent areas. Amer. Assoc. Petrol. Geol. Bull., v. 43, p. 124-189.
Smith, Donald Leigh, 1963a. A lithologic study of the Stony Mountain Formation and Stonewall formations in southern Manitoba; University of Manitoba, Winnipeg, MB, M.Sc. thesis, 219 p.
Smith, Donald Leigh, 1964. A lithologic study of the Stony Mountain and Stonewall formations in southern Manitoba; Canadian Mining Journal, vol. 85, no. 6, p. 114.
Stearn, C.W., 1956b. Stratigraphy and palaeontology of the Interlake Group and Stonewall Formation of southern Manitoba; Geological Survey of Canada, Memoir 281.

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: 30 Mar 2009