Unit Name: Willow Lake Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Middle Devonian (397.5 - 385.3 ma)
Province/Territory: British Columbia; Northwest Territories; Yukon Territory

Originator: Law, 1971.

Type Locality:
Between 680.3 and 733.9 m (2,232 and 2,408 ft) in the Imperial Triad Willow Lake B 20 well (62 deg 17'05"N, 119 deg 04'25"W).

The formation is 23 m (76 ft) thick at the type section. Southwestern part of the District of Mackenzie, southeastern Yukon Territory and possibly into northeastern B.C.

Predominantly yellowish-grey microcrystalline to very finely crystalline dolomite, partly of lamellar appearance. Minor interbeds of micritic limestone occur near the top of the formation, whereas beds of anhydrite occur near the base. Thin green shale beds occur throughout the formation with a 7.6 m (25 ft) thick shale unit at the base named the Ebbutt Member. The member includes siltstone and sandstone on the north flank of the Tathlina arch.

The lower contact with anhydrites of the Bear Rock Fm may be disconformable whereas it is conformably overlain by limestone of the Lonely Bay Fm and is picked at the first occurrence of dolomite beneath limestone. It extends northwest to the base of the lower Hume, southeast into the Chinchaga, and west into the Headless formations.

Other Citations:
Law, 1971.

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.

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: J. Law; P.A. Monahan; L.V. Hills
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 21 Jan 2009