Unit Name: Twin Falls Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Frasnian (385.3 - 374.5 ma)
Age Justification: Corals and brachiopods (Atrypa ciliipes Crickmay, A. canadensis Webster, Hexagonaria bompasi (Smith), H. reticulata (Smith), Indospirifer sp., Mictophyllum modicum Smith, Pacellophyllum tructense McLaren, Pachyphyllum, Theodossia).
Province/Territory: Northwest Territories
Originator: Belyea and McLaren, 1962.
Type Locality:
On Hay River, District of Mackenzie, from the base of Alexandra Falls to 1.6 km (1 mi) upstream from Grumbler Rapids, ca. 60 deg 30'N, 116 deg W. Supplementary type section 25.4-160 m (90 to 525 ft) in Murphy Can. Alexandra Falls No. 2, 60 deg 15'31"N, 116 deg 41'42"W.
Distribution:
Between 120 and 200 m (365-610 ft) thick. Occurs within a northwest trending belt up to 120 km (75 mi) wide by about 180 km (112 mi) long, south of the Mackenzie River, District of Mackenzie.
Locality Data:
Thickness(m): Minimum 120, Maximum 200.
Lithology:
Thin-bedded, calcarenite, variably sandy, many shaly layers. The basal biostromal layer is the Alexandra Member.
Relationship:
Conformable contacts with the overlying Tathlina Fm and the underlying Hay River Fm. Shales out to the west into part of the Fort Simpson Fm (N.W.T.) or part of the Ireton Fm (Alberta). To the southeast it correlates with the upper part of the Grosmont Fm.
Other Citations:
Belyea and McLaren, 1962; Jamieson, 1971; G.K. Williams, 1977a, 1977b.
References:
Belyea, H.R. and McLaren, D.J., 1962. Upper Devonian formations, southern part of Northwest Territories, northeastern British Columbia and northwestern Alberta; Geological Survey of Canada, Paper 61-29, 74 p.
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: G.K. Williams; D.W. Morrow
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 26 Feb 2009