Type Locality:

Toby Creek, west of Invermere, southeastern British Columbia.

Distribution:

The Toby occurs in the Purcell Mountains between 50 deg N and 51 deg N and extends into the western Rocky Mountains to a southern erosional limit beneath the Lower Cambrian Cranbrook Formation in the northern Hughes Range (Leech, 1954). It extends along the western flank of the Purcell anticlinorium in the Kootenay arc, into northeastern Washington where it is called the Shedroof Conglomerate (Little, 1960; Aalto, 1971). Its thickness is highly variable, ranging up to 2,000 m (6,560 ft).

Locality Data:

Thickness(m): Maximum 2000.

Lithology:

Diamictic conglomerates (pebbly to boulder argillite or sandstone) are diagnostic: they range from brown to green-grey and are extremely poorly sorted. Phenoclasts are angular to slightly rounded, range from granules to boulders 2 m (7 ft) or more long, and are packed chaotically in a matrix ranging from mud to fine sand; at one locality in the Lardeau area the matrix is vesicular andesite (Reesor, 1973, Plate V). Clasts are mostly quartzites, dolomites and argillites derived from the underlying Purcell Supergroup, but boulders of granite gneiss occur at a few rare localities, and clasts derived from the Moyie Intrusions and syenitic intrusions occur locally elsewhere. Subsidiary rock types include argillite, sandstone and black limestone in beds 0.5 to 3 m (1.6 to 6 ft) thick. Beds are massive and defined by the presence or absence of clasts; they lack internal structures such as lamination, cross-lamination, etc. Aalto (1971) suggested a glaciogenic origin for these deposits.

Relationship:

The unit, part of the Windemere Supergroup, unconformably overlies the Mount Nelson Formation of the Purcell Supergroup over most of its outcrop area. Its basal contact cuts down section southward and eastward so that the Toby Formation oversteps the Mount Nelson and unconformably overlies the Roosville Formation in the northern Hughes Range. The contact with the overlying Horsethief Creek Group is apparently conformable and gradational. Lower Cambrian Cranbrook Formation quartzites overstep the Horsethief Creek Group southward, and unconformably overlie the Toby Formation in the northern Hughes Range.

References:

Aalto, K.R., 1971. Glacial marine sedimentation and stratigraphy of the Toby Conglomerate (Upper Proterozoic), southeastern British Columbia, northwestern Idaho and northeastern Washington; Canadian Journal of Earth Sciences, vol. 8, no. 7 (July), pp. 753-787.

Leech, G.B., 1954. Canal Flat, British Columbia; Geological Survey of Canada, Paper 54-7.

Little, H E.W., 1960. Nelson map-area, British Columbia, west half (82 F W1/2); Geological Survey of Canada, Memoir 308.

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.