Type Locality:

Tidewater Duperow Crown No. 1, in 4-9-35-16W3M, in Saskatchewan. Powley's original definition ascribed the interval between 1,008.9 and 1,374.6 m (3,310 and 4,510 ft) to the Duperow Formation. The 1953 redefinition adjusted the limits to between 875.1 and 1,094.8 m (2,871 and 3,592 ft) in this well.

Distribution:

The Duperow is present throughout the entire Williston Basin. The thickness within the Canadian portion of the basin ranges from less than 120 m (394 ft) in southwestern Manitoba to about 300 m (984 ft) in westernmost Saskatchewan. Southward the unit thins to zero in southwestern North Dakota. North and east of the area of Birdbear cover (about the latitude of Saskatoon) the unit thins as the result of post-Mississippian erosion.

Lithology:

Pale colored limestones and dolomites, with blue-grey anhydrite, argillaceous dolomites and local development of four halite units. Fossils are common and several widespread zones rich in sporomorphs are recognized (Kent, 1963, 1965a; Dunn, 1975). Cyclic sedimentation is evident, with local development of up to 27 cycles. Faunal descriptions are given in Warren and Stelck (1956), Wilson (1967), and Kent (1968a).

Relationship:

The unit conformably overlies argillaceous carbonates at the top of the Souris River Formation, although disconformity is present in local areas of basal Duperow brecciation. In Manitoba the base of the Duperow is commonly picked at the top of the lower of two shale breaks, thus making the contact with the Souris River Formation about 15 m (49 ft) lower than that adopted in the Saskatchewan subsurface (Norris et al., 1982). The upper contact is conformable or slightly disconformable with the overlying carbonates of the Birdbear Formation. Equivalent strata are: in eastern Alberta most of the Fairholme Group and the upper part of the Beaverhill Lake Formation; in central Alberta most of the Woodbend Group and the upper part of the Beaverhill Lake Formation; in Montana most of the Jefferson Group.

History:

As first proposed by Powley (1951), the limits of the Duperow Formation are not those now in generally accepted use. In 1953 the Williston Basin Nomenclature Committee used the term Duperow Formation, but assigned it to a different interval; the upper and lower limits of this new interval are approximately 137 and 168 m (449 and 551 ft) stratigraphically higher than those originally defined by Powley. Powley's '"Duperow" is therefore in large part equivalent to the Souris River Formation of currently accepted use. Despite the prior use and definition of the term Duperow in Powley's thesis, it is the Duperow Formation interval as defined by the Williston Basin Nomenclature Committee which is now firmly entrenched in the literature and usage of operators throughout the Williston Basin, even though the report of this committee was never published. In conformance with the commitiee's recommendation the North Dakota Geological Society (in 1954) defined the limits of the Duperow Formation at the Hunt Olsen No. 1 well in Bottineau Co., North Dakota. Sandberg and Hammond (1958) chose a standard reference section for Duperow rocks of the Williston Basin as the interval from 3169.9 to 3274.5 m (10400 to 10734 ft) in Mobil Oil Producing Co. No. 1 Birdbear well (C SE/4 NW/4-22-149N-91W) in Dunn County, North Dakota. Kent (1963, 1968a) selected a Saskatchewan Group reference section for western Saskatchewan and eastern Alberta: the Mobil Oil Woodley Sinclair Cantuar X-2-21 well (Lsd. 2-21-16-17W3M). A Duperow reference section for eastern Saskatchewan and western Manitoba was chosen by Dunn (1975) frorn the International Yarbo No. 17S well (Lsd. 1-24-20-33W1M) as the interval between 591.9 and 760.5 m (1,942 and 2,495 ft).

Other Citations:

Braun and Mathison, 1982; Dunn, 1975; Kent, 1963, 1968a; Kents, 1959; Norris et al., 1982; North Dakota Geological Society, 1954; Powley, 1951; Sandberg and Hammond, 1958; Stanton, 1953, 1960; Wilson, 1956, 1967.