Documentation of the sub-Cambrian unconformity, Rocky Mountains Main Ranges, Alberta

Abstract

Much of the existing literature on the base of the Cambrian System in the southern Rocky Mountains tends to de-emphasize the importance of the stratigraphic hiatus represented. Although a sub-Cambrian regional unconformity has been reported by several authors, conclusive evidence of the unconformity has not been published.This paper documents profound truncation of Miette Group strata of Windermere age at the base of the Gog Group of Early Cambrian age, and draws attention to several localities at which Precambrian structures are truncated at the base of the Cambrian. The sub-Cambrian unconformity is comparable in style and magnitude to the sub-Devonian unconformity of the same region.

The initiation of the early Paleozoic Cordilleran miogeocline: evidence from the uppermost Proterozoic – Lower Cambrian Hamill Group of southeastern British Columbia

“…Additional support for an unconfonnity has been cited by other workers and includes local evidence for deposition of the Hamill Group on an eroded surface (Evans 1933), regional changes in the stratigraphic thickness of the underlying Windermere Supergroup (Lis and Price 1976;H@y et al 1981), and deposition of the Hamill Group on different stratigraphic units of the Windermere Supergroup (Poulton and Simony 1980 Supergroup suggest that it is correlative with a profound unconformity that has been documented between the Miette Group (Windermere Supergroup) and the Gog Group in the southern Canadian Rocky Mountains (Aitken 1969). The Hamill-Windermere contact is therefore considered part of a regionally significant unconformity that is associated with widespread uplift, large-scale tilting, and truncation of Miette strata prior to the deposition of uppermost ProterozoicLower Cambrian clastic deposits (Aitken 1969). Local geologic relations beneath this unconformity in the southern Canadian Rocky Mountains also indicate truncation of a northeast-trending mafic dike (the Crowfoot Dike) and fault-related structures that offset strata within the Miette Group (Aitken 1969;Bond, in preparation).…”

“…The Hamill-Windermere contact is therefore considered part of a regionally significant unconformity that is associated with widespread uplift, large-scale tilting, and truncation of Miette strata prior to the deposition of uppermost ProterozoicLower Cambrian clastic deposits (Aitken 1969). Local geologic relations beneath this unconformity in the southern Canadian Rocky Mountains also indicate truncation of a northeast-trending mafic dike (the Crowfoot Dike) and fault-related structures that offset strata within the Miette Group (Aitken 1969;Bond, in preparation).…”

“…The Miette Group typically consists of relatively deep water deposits that are dominated by dark-colored shales and beds and lenses of graded sandstones and conglomerates that are commonly arranged in sequences that thin and fine upward (Slind and Perkins 1966;Aitken 1969;Javor and Mountjoy 1976;Young et al 1973;Arnott and Hein 1986). These upper Miette strata are abruptly overlain by coarse-grained, feldspathic sandstones and conglomerates of the basal Gog Group, strata that were interpreted by Bond et al (1985) For personal use only.…”

Stratigraphy, sedimentology, and regional correlation of the Horsethief Creek Group (Hadrynian, Late Precambrian) in the northern Purcell and Selkirk Mountains, British Columbia

“…The quartz and feldspar pebble conglomerate units indicate activation of a granitic source area, which may be related to these fluctuations. Some of the conglomerates closely resemble those in upper parts of the Miette Group of the Bow River valley of the Rocky Mountains (see Aitken 1969), and suggest a similar source and origin, as well as correlation. The detailed stratigraphic relations of both the pelletoidal grainstones in the northern Dogtooth Mountains and the sediments of the Selkirk Mountains to the carbonate bank and slope assemblages have not been determined.…”

“…19). Thus there may be profound regional unconformity in the Dogtooths, as was also indicated by Aitken (1969) at the base of the Cambrian in the Rocky Mountains to the east.…”