Unit Name: Pekisko Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Tournaisian (359.2 - 345.3 ma)
Province/Territory: Alberta
Originator: Douglas, R.J.W., 1953.
Type Locality:
Ridges north of Flat Creek, in the Mount Head map-area, Alberta.
Distribution:
Douglas gives a thickness of 134 m (440 ft) at the type section, but the Pekisko is considerably thinner in the plains area, averaging 46 to 91 m (150 to 300 ft) where unaffected by erosion. The Pekisko is erosionally truncated easterly below Cretaceous strata, a line drawn from Twp. 21 on Alberta's eastern border through Drumheller and thence to Lesser Slave Lake marking the approximate eastern edge. Northward of Lesser Slave Lake the unit disappears along an east-west trend by facies change to shaly Shunda Formation equivalents (Macauley, 1958).
Lithology:
Douglas divided the Pekisko into upper and lower intervals based on the predominance of coarsely crinoidal, massive limestone to the lower part, and very fine-crystalline to lithographic limestone, with a minor amount of coarsely crinoidal limestone in the upper part. To the east, in the subsurface this subdivision does not apply, as the Pekisko there consists predominantly of light colored, coarsely crinoidal and fragmental, to fine-grained, sparsely crinoidal, in part dense limestone (Penner, 1958). In the subsurface Pekisko lithology is virtually identical to that of the expanded Livingstone to the west.
Relationship:
Douglas (1953) showed the Pekisko to conformably overlie the argillaceous Banff Formation and to conformably underlie the Banner silt member and dark limestones of the Shunda Formation. The Pekisko constitutes the basal section of the lithologically similar Livingstone Formation in the southern Rocky Mountains and is completely replaced to the north, in the Peace River subsurface by Shunda shale facies. It is represented in southern Saskatchewan and Montana by the lower part of the Mission Canyon Formation.
Other Citations:
Douglas, 1953; Douglas and Harker, 1958; Macauley, 1958; Macauley et al., 1964; Moore, 1958; Penner, 1958.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: G. Macauley
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 04 May 2004