Unit Name: Atan Group
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Early Cambrian (542 - 513 ma)
Province/Territory: British Columbia; Yukon Territory
Originator: Gabrielse, 1954.
No type section defined, but Gabrielse (1963, p. 26) stated that "Excellent exposures occur in the mountains north and south of French River and near Atan Lake, after which the group was named".
In the type area the lower Atan is approximately 500 m (1,640 ft) thick and the upper Atan approximately 1,000 m (3,280 ft) thick, although no complete section has yet been described. The Atan Group has been recognized over a considerable region outside the type area, including the Jennings River (104O) map-area to the west and in much of the northern Rocky Mountains and Cassiar Mountains north of Peace River east of the type area. Tentative recognition of the Atan Group has also been proposed in the Pelly Mountains of Yukon Territory.
The Atan Group comprises two distinct units: the upper Atan, consisting of carbonates, mainly thick-bedded limestones and carbonate debris flows with numerous anchaeocyathids; and a lower Atan, dominantly of clastic rocks, a basal white quartzite overlain by a thicker succession of brown to rust weathering, very fine-grained sandstone and siltstone.
In the type area apparently conformably overlies Good Hope (now Ingenika Group) clastics of late Proterozoic age, and is unconformably overlain by incompetent carbonate of the Kechika Group.
Gabrielse (1954) first described the Atan Group in the McDame (104P) map-area in north-central British Columbia, and in a second paper (1963) repeated the description, suggesting a type area. Fritz (1978, p. 7) designated a type section for the upper carbonate part of the Atan (geographical co-ordinates: top of section 59°16.25'N, 129°10.5'W, base of section 59°16.25'N, 129°13.25'W) and suggested that the type section for the lower clastic part be defined from the continuation downward of this section.
Mansy and Gabrielse, 1978.
Fritz, W.H., 1978. Fifteen stratigraphic sections from the Lower Cambrian of the Mackenzie Mountains, northwestern Canada; Geological Survey of Canada, Paper 77-33, 19 p.
Gabrielse, H., 1954. McDame, British Columbia (Map with Marginal Notes); Geological Survey of Canada, Paper 54-10, Scale: One Inch to Four Miles (1:253 440)).
Gabrielse, H., 1963. McDame map-area, Cassiar District, British Columbia; Geological Survey of Canada, Memoir 319, 138 p.
Mansy, J.L. and Gabrielse, H., 1978. Stratigraphy, terminology and correlation of Upper Proterozoic rocks in Ominica and Cassiar mountains, north-central British Columbia; Geological Survey of Canada, Paper 77-19.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: G.C. Taylor
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 17 Dec 2010