Unit Name: Kotcho Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: middle Famennian (369.4 - 364.3 ma)
Age Justification: It contains a brachiopod fauna of mid-Famennian age similar to that of the Wabamun Group and the Palliser Fm.
Province/Territory: Alberta; British Columbia; Northwest Territories

Originator: Belyea and McLaren, 1962.

Type Locality:
Imperial Island River No. 1 well, 60 deg 09'29"N, 121 deg 08'16"W between 1,058.6 m (3,473 ft) and 1,269.5 m (4,165 ft).

Distribution:
The Kotcho Fm is mappable from approximately the 6th Meridian (120 deg W) to 122 deg W and from the southern part of the District of Mackenzie to the Peace River arch. In the type well it is 210.9 m (692 ft) thick but thins southwestwards to the Fort Nelson area where it is less than 30 m (100 ft) thick and to the Peace River arch where it dies out.

Lithology:
Shale, light greenish-grey to brownish-grey, non-calcareous to slightly calcareous; locally black bituminous shale occurs. Interbeds, near top and base, of buff and light grey, largely argillaceous limestones mostly in thin beds; lenses and nodules separated by greenish-grey and brown shale; some bioclastic limestones interbedded.

Relationship:
The Kotcho Fm grades eastwards along a line close to the British Columbia-Alberta border to limestone which cannot be discriminated from the upper part of the Wabamun Gp of the Alberta subsurface and the Palliser Fm of the Alberta Rocky Mountains. It is overlain by black shales and dark brown argillaceous limestones of Mississippian or late Devonian age which may be equivalent to the Exshaw Fm. It conformably overlies the Tetcho Fm. It is re-placed westward by the Besa River Fm.

Other Citations:
Bassett and Stout, 1967; Belyea, 1964; Belyea and McLaren, 1962; Gray and Kassube, 1963; Law, 1971.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 2, Yukon Territory and District of Mackenzie; L.V. Hills, E.V. Sangster and L.B. Suneby (editor)
Contributor: D.W. Morrow; P.A. Monahan; H.R. Balkwill
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 28 Jun 2004