Unit Name: Sombre Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Devonian - Middle Devonian (416 - 385.3 ma)
Age Justification: Poorly preserved stromatoporoids, colonial corals and amphiporids.
Province/Territory: Northwest Territories

Originator: Douglas and D.K. Norris, 1961.

Type Locality:
Type section extends eastward across the north end of Tundra Ridge (61°58'N, 124°54'W) in the Virginia Falls map area (95F), District of Mackenzie.

Distribution:
The Sombre is thickest near the type section where it is 1,101 m (3,613 ft) thick. It thins northward (eg. 488 m; 1,600 ft in the Delorme Range in the Root River map-area (95K)) and extends northwest throughout the Mackenzie Mountains. It thins rapidly eastward and is largely absent beneath the Mackenzie Plain.

Locality Data:
Thickness(m): Maximum 1101, Typical 1101.

Lithology:
At the type section and throughout most of its extent, the Sombre Formation may be subdivided into three informal members (map units 11, 12 and 13 of Douglas and Norris, 1960b): a thick banded lower member consisting of thick and medium beds of medium grey finely crystalline dolomite that grade upwards to thin-bedded and laminated light grey dolomicrite that in places is silty; a thin middle member of dark brownish-grey to black, fetid, medium- to thick-bedded, fine- to medium-crystalline stromatoporoid and coral-bearing dolomite; and an upper member of medium-grey, medium- to thick-bedded slightly fossiliferous dolomite with some light grey slightly silty interbeds.

Relationship:
Previously the Sombre was thought to be unconformably overlain by the Arnica Formation throughout the Mackenzie Mountains (Douglas and Norris, 1961), but more recent work (Gabrielse et al., 1973 and Morrow and Cook, pers. comm., 1979) suggests that instead, the upper part of the Sombre may be the lateral facies equivalent of the lower part of the Arnica Formation. The Sombre conformably overlies the Camsell and Delorme formations with an abrupt contact. Westward, the Sombre passes to shales of the Road River Formation. Northward, the Sombre correlates with the Gossage Formation, and southward it correlates with the lower part of the Stone Formation.

Other Citations:
Chatterton, 1978; Douglas and Norris, 1963; Gabrielse, 1967a; Gabrielse et al., 1965; Law, 1971; Perry and Lenz, 1978.

References:
Chatterton, B.D.E., 1978. Aspects of late Early and Middle Devonian conodont biostratigraphy of western and northwestern Canada; in, Western and Arctic Canadian biostratigraphy, Stelck, C.R. and Chatterton, B.D.E. (Eds.); Geological Association of Canada, P.S. Warren biostratigraphy symposium Western and Arctic Canadian biostratigraphy, Edmonton, AB, (May 19, 1976) (Conference), Special Paper 18, pp. 161-231.
Douglas, R.J.W. and Norris, D.K., 1960b. Virginia Falls and Sibbeston Lake map-areas, Northwest Territories (95F and 95G); Geological Survey of Canada, Paper 60-19, 26 p.
Douglas, R.J.W. and Norris, D.K., 1961. Camsell Bend and Root River map-areas, Northwest Territories; Geological Survey of Canada, Paper 61-13, 36 p.
Douglas, R.J.W. and Norris, D.K., 1963. Dahadinni River and Wrigley map-areas, District of Mackenzie, Northwest Territories; Geological Survey of Canada, Paper 62-33, 34 p.
Gabrielse, H., Blusson, S.L., and Roddick, J.A., 1973. Geology of the Flat River, Glacier Lake and Wrigley Lake map-areas, District of Mackenzie and Yukon Territory; Geological Survey of Canada, Memoir 366 (Parts I and II), 421 p.
Gabrielse, H., Roddick, J.A., and Blusson, S. L., 1965. Flat River, Glacier Lake and Wrigley Lake, District of Mackenzie and Yukon Territory, 95E, 95L and 95M (Report and Maps 35-1964, 36-1964, and 37-1964); Geological Survey of Canada, Paper 64-52, 30 p. + Preliminary Map 35-1964, Geology, Flat River, Yukon Territory - District of Mackenzie, Scale 1:253 440 or 1 inch to 4 miles, Preliminary Map 36-1964, Geology, Glacier Lake, District of Mackenzie, Scale 1:253 440 or 1 inch to 4 miles, and Preliminary Map 37-1964, Geology, Wrigley Lake, District of Mackenzie, Scale 1:253 440 or 1 inch to 4 miles.
Law, James, 1971. Regional Devonian geology and oil and gas possibilities, upper Mackenzie River area; Canadian Society of Petroleum Geologists (CSPG), Bulletin of Canadian Petroleum Geology, vol. 19, no. 2 (June), pp. 437-484.
Perry, D.G. and Lenz, A.C., 1978. Emsian paleogeography and shelly fauna biostratigraphy of Arctic Canada; in, Western and Arctic Canadian biostratigraphy, Stelck, C.R. and Chatterton, B.D.E. (Eds.); Geological Association of Canada, Special Paper 18, pp. 133-160.

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: L.V. Hills; D.W. Morrow
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 01 Dec 2010