Type Locality:

On the shore of Dawson Bay, at the north end of Lake Winnipegosis, Manitoba. Subsurface reference section (Lane, 1959): Winsal Beaverdale 3-32-26-7W2M, in Saskatchewan, between 867.2 and 930.2 m (2,845 and 3,052 ft). The reference core section in Manitoba is hole M-6-70 (9-16-30-17W1M) between zero and 45.4 m (149 ft), from which the uppermost 6 m (20 ft) is eroded (Norris et al., 1982).

Distribution:

Uniform thickness of about 40 to 50 m (131 to 164 ft) from the outcrop area to west-central Saskatchewan, from where the beds progressively thin to the west. An exception is in central Saskatchewan where halite accounts for an additional thickening of nearly 20 m (66 ft). The zero isopach runs from the southwestern corner of Saskatchewan to southern North Dakota before turning north to the outcrop area in western Manitoba. The subcrop to the north runs northwestward from Lake Winnipegosis to south of Buffalo Narrows in western Saskatchewan. In eastern Alberta the formation thins and is no longer recognizable.

Lithology:

Basal dolomitic mudstone, overlain by microcrystalline to cryptocrystalline, fossiliferous limestone with hardgrounds in the lower half of the carbonate sequence. Overlying this unit is an agillaceous carbonate which is succeeded by microcrystalline to sucrosic, bituminous limestones, locally reefoid. Capping the sequence is dolomite, anhydrite and, in central Saskatchewan halite.

Relationship:

The Dawson Bay Formation is part of the Manitoba Group. In the outcrop area argillaceous strata at the base of the Dawson Bay Formation rest disconformably upon carbonates of the Winnipegosis Formation. In the subsurface the contact with the underlying Prairie Evaporite is disconformable. The contact with the overlying First Red Beds of the Souris River Formation is transitional. In Manitoba the Dawson Bay Formation is divided into the Mafeking Member and members B, C, and D (Bannatyne, 1975; Norris et al., 1982). In Saskatchewan the formation was divided by Lane (1959) into six members (DB1-DB6), and later by Dunn (1982) into four members - Second Red Bed Member (= Mafeking Member and DB1); Burr Member (= member B and most of DB2 and DB3); Neely Member (= members C and D and part of DB3, plus DB4 and 5). The Hubbard Evaporite, named by Lane in 1959, was also described by that author as DB6. The name "Hubbard Evaporite" was retained by Dunn (1982) as his fourth and uppermost member. In Alberta strata equivalent to the Dawson Bay may be the Watt Mountain Formation and the Gilwood Member, or there may be no lateral equivalent. Faunal evidence suggests that the latter may be the case (Braun and Mathison, 1982; Norris et al., 1982).

Other Citations:

Crickmay, 1954; Edie, 1959.

References:

Baillie, A.D., 1953a. Devonian System of the Williston Basin area; Manitoba Mines and Natural Resources; Mines Branch, Publication 52-5, 105 p. + 5 Maps.

Bannatyne, B.B., 1975. High-calcium limestone deposits of Manitoba; Man. Dept. Mines Res. and Env. Management, Pub. 75-1.

Braun, W.K., and Mathison, J.E., 1982. Ostracodes as a correlation tool in Devonian studies of Saskatchewan and adjacent area. 4th Internat. Williston Basin Symp; Christopher, J.E. and Kaldi, J. (Eds.). Saskatchewan Geol, Soc., Spec. Pub. 6, p. 43-49.

Crickmay, C.H., 1954. Paleontological correlation of Elk Point and equivalents. In: Western Canada Sedimentary Basin, Ralph Leslie Rutherford Memorial volume; Clark, L.M. (Ed.), American Association of Petroleum Geologists, Tulsa, Oklahoma, p. 143-158.

Dunn, Colin E., 1982. Geology of the Middle Devonian Dawson Bay Formation in the Saskatoon Potash Mining District, Saskatchewan; Saskatchewan Energy and Mines, Saskatchewan Geological Survey, Sedimentary Geology Division, Saskatchewan Industry and Resources (SIR) Report No. 194, 117 p., 21 plates, 5 tables, 17 figures (10 in pocket).

Edie, R.W., 1959. Middle Devonian sedimentation and oil possibilities, central Saskatchewan, Canada; American Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 43, no.5 (May 1959), pp. 1026-1057.

Lane, D.M., 1959. Dawson Bay Formation in the Quill Lakes-Qu¿Appelle area, Saskatchewan. Saskatchewan Dept. Min. Res., Rept. 38.

Norris, A.W., Uyeno, T.T., and McCabe, H.R., 1982. Devonian rocks of the Lake Winnipegosis-Lake Manitoba outcrop belt, Manitoba Geol. Surv. Can., Memoir 392 (Manitoba Min. Res., Pub. 77-1).