Type Locality:

B.A. Pyrz No. 1 well, in 12-25-50-26W4M, in central Alberta, between 1,623.7 and 1,807.5 m (5,327 and 5,930 ft). Supplementary section: Imp. Leduc No. 530, in 8-17-50-26W4M, between 1,633 and 1,863 m (5,357 and 6,112 ft), continuously cored.

Distribution:

The name is applied to isolated reefal buildups and platform complexes that occur in the subsurface from the southern Alberta Woodbend shelf margin near Drumheller to the Peace River Arch area of northwestern Alberta. A number of authors have applied the name to similar Frasnian carbonate complexes in the mountains (see Southesk Formation) but the term remains primarily a subsurface one. Thicknesses vary from 180 to 300 m (590 to 984 ft) and locally more than 300 m where complete buildups are developed, to zero in inter-reef areas.

Lithology:

The Leduc Formation comprises a wide variety of facies attributable to deposition in a shallow water reef complex. Stromatoporoids exhibiting a wide variety of growth forms are the most predominant reef builders and characterize a wide variety of sediments from skeletal mudstones, boundstones and floatstones to more muddy skeletal packstones and wackestones. The formation is commonly dolomitized, although undolomitized occurrences are known (Golden Spike, Redwater, Willingdon and Pinedale reef complexes and the uppermost part of the Duhamel reef). For a more complete description of facies the reader is referred to the individual studies of Leduc reefs cited.

Relationship:

Conformably overlies the dolomite or limestone platform of the Cooking Lake Formation in south-central Alberta, with only a minor hiatus separating them in the Leduc-Windfall area of west-central Alberta it conformably overlies a thick Beaverhill Lake platform carbonate sequence whose upper developments may contain Cooking Lake equivalents. Around the Peace River Arch the fringing reef complex may rest directly on Precambrian or red beds of the Granite Wash. The Leduc Formation of the type area is enclosed by basinal sediments, first of the Duvernay, and later of the Ireton formations which eventually covered it. Prograding "shale" banks infixing the basin progressively restricted and finally terminated reef growth and, depending on basin position, Leduc reefs contain growth equivalents of all of the Duvernay and the greater parts of the Ireton and Grosmont formations. In other parts of the basin the Leduc is covered by the Woodbend shale and a similar process to that indicated above may characterize this relationship.

History:

Originally proposed as a member of the then Woodbend Formation to replace the informal term "D-3 zone" reef. It is unclear when this member was formally elevated to formation status but its informal elevation coincided with the elevation of the Woodbend to group status as recommended by Andrichuk and Wonfor (1954, p. 2050).

Other Citations:

Andrichuk, 1958, 1961; Andrichuk and Wonfor, 1954; Belyea, 1964; Downing and Cooke, 1955; Geological Staff, Imperial Oil Limited, 1950; Kirker, 1959; Klovan, 1964; Layer et al., 1949; Link, 1950; Lockwood and Erdman, 1951; McGillivray and Mountjoy, 1975; Stoakes, 1980; Waring and Layer, 1950.