Type Locality:

Type section is in the P.A. Pyrcz No. 1, in 12-25-50-26W4M, Alberta, between 1467.6 and 1543.8 m (4815 and 5065 ft).

Distribution:

The Winterburn Group is 76.2 m (250 ft) thick at the type section. To the south and southeast the group thins to less than 60 m (197 ft), and locally may be less than 30 m (98 ft) thick where it overlies Leduc Formation carbonate complexes. To the east and northeast it has been removed by truncation at the pre-Cretaceous unconformity. West of the Rimbey-Meadowbrook Leduc reef trend the group thickens to 120 to 150 m (394 to 492 ft) as it passes into the adjacent Winterburn shale basin. North and west it thins onto the Peace River Arch through onlap and is absent on the higher parts. North and west of the Peace River Arch the Winterburn Group averages 70 to 100 m (230 to 328 ft) in thickness, thinning to zero as it passes into the Upper Devonian shale basin in northeastern British Columbia.

Lithology:

At the type section the group consists of three formations, in ascending order the Nisku, Calmar and Graminia. The Nisku is divisible in central Alberta into a lower, carbonate dominated silty dolomite succession deposited in biostromal and restricted bank interior settings. The upper Nisku is a bedded, evaporitic sequence that overlies the lower unit. Locally, especially near the Stettler area the evaporitic upper phase comprises the majority of the Nisku Formation. To the west, towards the West Pembina area the carbonate portion of the Nisku dominates, eventually passing into argillaceous limestones and 'pinnacle' reefs along the east and southeast edge of the basin. The Nisku is overlain by mottled red and green siltstones of the Calmar Formation, which are succeeded by anhydrite, silty dolomites and siltstones of the Graminia Formation. To the south and east these two units become indistinguishable, but west of the Rimbey-Meadowbrook trend the Calmar becomes increasingly argillaceous and the Graminia thickens where a carbonate member (Blue Ridge) is developed within the formation.

Relationship:

Throughout most of Alberta the Winterburn Group rests conformably upon calcareous and dolomitic shales of the Ireton Formation (Woodbend Group). In northeastern Alberta it lies conformably on the Ireton Formation as well as, locally on the Grosmont and Hondo formations. In the area of the Peace River Arch it thins through onlap and interfingers with siliciclastic sediments mantling the Precambrian basement. The Winterburn is overlain conformably by carbonates of the Wabamun Group. In southern Alberta these are evaporitic, but pass further north into more carbonaterich sediments. To the east the Winterburn Group is absent due to erosional truncation at the pre- Cretaceous unconformity. In Saskatchewan it has correlatives in the upper Birdbear and lower part of the Three Forks Group. In Rocky Mountain outcrops it equates to the Grotto, Arcs and Ronde member of the Southesk Formation, as well as the Alexo Formation. Further north, in northern Alberta and northeastern British Columbia correlatives of the Winterburn Group include the Redknife and Kakisa formations of the Grumbler Group.

History:

The term Winterburn was established to replace the terms Darling Silt, Red Bed and D-2 zones, the terms used in central Alberta after the discovery of the Leduc field in 1947. Originally established as a formation of the Minnewanka Group (Geological Staff, Imperial Oil, 1950) it was recommended for elevation to group status by Andrichuk and Wonfor (1954).

Other Citations:

Geological Staff, Imperial Oil Ltd., 1950; Andrichuk and Wonfor, 1954; Watts 1987.

References:

Andrichuk, John Michael and Wonfor, John Stephen, 1954. Late Devonian geologic history in Stettler area, Alberta, Canada, American Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 38, no. 12 (December), pp. 2500-2536.

Geological Staff, Imperial Oil Limited, Western Division, 1950. Devonian Nomenclature in Edmonton Area, Alberta, Canada. Bulletin of the American Association of Petroleum Geologists, Vol. 34, No. 9, pp. 1807-1825.

Watts, N.R., 1987. Carbonate sedimentology and depositional history of the Nisku Formation in south-central Alberta, in, Devonian lithofacies and reservoir styles in Alberta; Krause, F.F. and Burrowes, O.G. (Eds.). 2nd Internat. Symp. of the Devonian System. 13th CSPG Core Conf., D. 87-152.