Unit Name: Borsato Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Frasnian (385.3 - 374.5 ma)
Province/Territory: Alberta; British Columbia
Originator: Price, 1965.
Type Locality:
In the southern Flathead Range, on the Continental Divide near North Kootenay Pass, 2,400 m (7,870 ft) east of Mount Borsato; section 14 of Price (1965).
Distribution:
It occurs within the southern Canadian Rocky Mountains west of (above) the Lewis thrust fault and south of about 49°45'N. It is 20 to 60 m (66 to 197 ft) thick. The Borsato Formation is thicker and more massive weathering where it underlies the carbonate facies of the Fairholme Group, than where it underlies the shaly facies.
Locality Data:
Thickness(m): Minimum 20, Maximum 60.
Lithology:
Dark brownish grey and brownish black, medium to coarse crystalline, saccharoidal, fetid dolomite in beds from about 10 cm to 1 m (4 in to 3 ft) thick; weathers medium brownish grey, with faint lamination etched into relief, and is a resistant unit that forms prominent topographic features. Amphipora, relict stromatoporoids and tabulate corals are important lithic constituents locally.
Relationship:
The lower contact is a relatively abrupt gradation into the Hollebeke Formation; the upper contact is gradational into argillaceous limestones of the Mount Hawk Formation or light grey dolomite of the laterally equivalent Peechee Member of the Southesk Formation. The Borsato Formation is gradational laterally into the dark shales of the Perdrix Formation in the shaly facies of the Fairholme Group, and into the dark "organic" dolomite that forms a transitional facies between the Mount Hawk and Southesk formations in the carbonate facies of the Fairholme Group (Price, 1962, 1964b and 1965).
References:
Price, R.A., 1962. Fernie map-area, east half, Alberta and British Columbia, 82G E½ (Report and Map 35-1961); Geological Survey of Canada, Paper 61-24, 65 p. + Preliminary Map 35-1961, Geology, Fernie (East Half), British Columbia-Alberta, Scale: One Inch to Two Miles = 1:126 720, NTS 82 G/NE and 82 G/SE.
Price, R.A., 1964b. The Devonian Fairholme-Sassenach succession and evolution of reef-front geometry in the Flathead-Crowsnest Pass area, Alberta and British Columbia, in, Flathead Valley, Special Guide Book Issue, Fourteenth Annual Field Conference, Goodman, A.J. (Jack) (Ed.); The Alberta Society of Petroleum Geologists, Bulletin of Canadian Petroleum Geology, vol. 12 (August), pp. 427-451.
Price, R.A., 1965. Flathead map-area, British Columbia and Alberta; Geological Survey of Canada, Memoir 336.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: R.A. Price
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 20 Jul 2009