Type Locality:

Windermere map-area, southeastern British Columbia.

Distribution:

The Windermere Supergroup occurs mainly in the Purcell Mountains, but also as inliers in the western Rocky Mountains. It thickens northward and westward from a combined depositional onlap/erosional limit in the western ranges of the Rocky Mountains south of Canal Flats, British Columbia. 200+ m (656+ ft) of Horsethief Creek strata are exposed in the Stanford Range from Invermere south to Canal Flats. In the Purcell Mountains, the thickness varies from 1,000 to 2,000 m (3,280 to 6,560 ft) in the type area to 1,000+ m (3280+ ft) in the Dogtooth Mountains, where the base of the section is not exposed (Young et al., 1973). Lis and Price (1976) noted 9,000 m (29,520 ft) in the southern Kootenay Arc and attributed the gross thickening to syndepositional tectonism associated with the ancestral St. Mary Fault.

Lithology:

The assemblage is characterized by coarse, immature clastic deposits with accessory mudrocks and carbonates, in marked contrast to the mature sediments of the underlying Purcell Supergroup. The basal Toby Formation consists of diamictic or polymictic conglomerates containing pebbles and boulders derived from the underlying Purcell Supergroup, and of interbeds of argillite and sandstone. The overlying Horsethief Creek Group also includes conglomerates which are compositionally immature (feldspathic wackes), but they are texturally more mature than the Toby: better sorted, better rounded and finer grained, and they have a markedly higher proportion of quartz, quartzite and feldspar clasts relative to argillite and dolomite clasts. Feldspathic wacke conglomerates within the Horsethief Creek Group grade into sandstones composed of angular, coarse sand sized quartz and feldspar, termed "grits" by many authors. Feldspathic grits and conglomerates characterize the uppermost and lowermost units of the Horsethief Creek Group in the northern Purcell Mountains and the Selkirk Mountains. The middle units comprise a lower pelitic and a middle carbonate division that are of variable thickness and extent; the carbonate exhibits shallow water features such as oolites and stromatolites.

Relationship:

The Windermere unconformably overlies strata of the Purcell Supergroup and is overlain by Cambrian rocks; the upper contact is gradational into the Hamill Group north of 51 deg N, but is unconformable south of 51 deg N, where the Cranbrook Formation oversteps the Horsethief Creek Group and Toby Formation southward. Northwest of Invermere dolomites of the Cambrian Jubilee Formation overstep the Cranbrook and Eager formations and unconformably overlie the Horsethief Creek Group on the early Paleozoic '"Windermere High" (Reesor, 1973). The Windermere Supergroup includes or is correlative with parts or all of the Miette Group of the northern main ranges; the Corral Creek and Hector formations of the upper Bow Valley; the Toby, Irene and Three Sisters formations of the southern Kootenay Arc, and the Kaza Group, Isaac, Cunningham and Yankee Belle formations of the Cariboo Mountains.

History:

Originally named Windermere Series (Walker, 1926), later extended by Walker (1929) to include the Hamill "Series", Badshot Formation and Lardeau "Series" in the Lardeau west half map-area, which are now known to be Paleozoic and are excluded from the unit. Reesor (1973) noted that the succession consists of a group and a formation spanning the interval ~800 Ma to Early Cambrian and used the term Windermere "System". Gabrielse (1972) noted this usage is incorrect since "system" in a time stratigraphic term; Young et al. (1973) therefore termed the succession Windermere Supergroup.

References:

Lis, M.G. and Price, R.A., 1976. Large-scale block faulting during deposition of the Windermere Supergroup (Hadrynian) in southeast British Columbia, in, Report of Activities, Part A, Blackadar, R.G., Griffin, P.J., and Dumych, Helen (Eds. and Compilers); Geological Survey of Canada, Paper 76-1A, pp. 135-136.

Reesor, J.E., 1973. Geology of the Lardeau map-area, east half, British Columbia. Geol. Surv. Can., Memoir 369.

Walker, J.F., 1926. Geology and mineral deposits of Windermere map-area, British Columbia; Geological Survey of Canada, Memoir 148.

Walker, J.F., 1929. Kootenay Lake district, British Columbia. Geological Survey of Canada Summary Report for 1928, part A, pages 119-135.

Young, F.G., Campbell, R.B., and Poulton, T.P., 1973. The Windermere Supergroup of the southeastern Canadian Cordillera. In: Belt Basin Symposium, v. 1; Bishop and Powell (Eds.), pp. 187-203.