Unit Name: Horsethief Creek Group
Unit Type: Lithostratigraphic
Rank: Group
Status: Formal
Usage: Currently in use
Age Interval: Late Proterozoic (900 - 542 ma)
Province/Territory: British Columbia

Originator: Walker, J.F., 1926.

Type Locality:
Horsethief Creek, northwest of Invermere, British Columbia.

Distribution:
The assemblage occurs mainly in the Purcell Mountains, with partial sections exposed in the western ranges of the Rocky Mountains. Its thickness is extremely variable, increasing to the west and north from a combined depositional onlap/erosional limit southeast of Canal Flats, British Columbia, to 200+ m (656+ ft) in sections in the Stanford Range between Canal Flats and Invermere (Henderson, 1954). The base is not exposed in these Rocky Mountain exposures. Within the Purcell Mountains the thickness varies from approximately 1,000 m (3,280 ft) in the type area to 1,700 to 2,000 m (5,576 to 6,560 ft) in the northern Purcell Mountains (Reesor, 1973). More than 1,000 m (3,280 ft) are present in the Dogtooth Range, where the base is not exposed. Lis and Price (1976) estimated 8,500 m (27,880 ft) in the Kootenay Arc north of the St. Mary Fault and attributed the gross thickening to syndepositional tectonism associated with the ancestral St. Mary Fault.

Lithology:
The Horsethief Creek is a heterogenous assemblage of coarse-grained, angular, feldspathic wackes ("grits") and immature quartzo-feldspathic conglomerates, plus intercalated argillite and carbonate. Young et al. (1973) proposed a four-fold subdivision of the Horsethief Creek Group in the Dogtooth Range near Golden, British Columbia. The lowest unit comprises feldspathic grits and pebble conglomerates, with interbedded grey and black argillite and rare carbonate. In contrast to underlying polymictic conglomerates of the Toby Formation these conglomerates are texturally mature, consisting of moderately well- to well-sorted, subangular to well-rounded pebbles of white quartzite, white to blue (rutilated) quartz and locally abundant creamy white feldspar. Dolomite and argillite cobbles are common at a few localities. The grit division is succeeded in most areas by a pelitic division comprising thin beds of siltstone and brown to grey argillite, often graded, together with rare beds of dolomitic sandstone. The carbonate division overlies the lower pelitic division and is highly variable in thickness and character. It usually includes oolitic and stromatolitic dolomites that commonly display evidence of early subaerial exposure and erosion, and rarely are included as blocks in carbonate debris flows. The upper clastic division caps the unit; it contains conglomerates, grits and argillites similar to those in the lower grit division. North of 51 deg N they grade up section into quartzites transitional into the Cambrian Hamill Group. This subdivision appears to be valid throughout the area of exposure.

Relationship:
The Horsethief Creek Group conformably overlies the Toby Formation. It is overlain conformably by Lower Cambrian Hamill Group quartzites north of 51 deg N, and unconformably by correlative Lower Cambrian quartzites of the Cranbrook Formation to the south. The upper contact becomes progressively sharper southward as the Cranbrook Formation progressively oversteps the Horsethief Creek Group and Toby and Mount Nelson formations. Northwest of Invermere, British Columbia the Cranbrook Formation is overstepped and a thinned succession of dolomites of the Cambrian Jubilee Formation unconformably overlies Horsethief Creek strata across the "Windermere High" (Reesor, 1973). The Horsethief Creek Group is laterally equivalent to parts or all of the Miette Group of Jasper; the Corral Creek and Hector formations of Bow Valley; the Irene Volcanics, Monk Formation and Three Sisters Formation in the southern Kootenay Arc; and the Kaza Group, Issac, Cunningham and Yankee Belle formations of Cariboo Mountains (Young et al., 1973).

Remark:
belongs to Windermere Supergroup

Other Citations:
Evans, 1933; Henderson, 1954; Leech, 1954, 1959; Lis and Price, 1976; Poulton, 1973; Reesor, 1973; Rice, 1941; Walker, 1926; Young et al., 1973.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: W. K. Foo; R.A. Price
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 21 Jul 2006