Unit Name: Peyto Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Cambrian (542 - 513 ma)
Age Justification: The Peyto Formation yields a late Early Cambrian Bonnia-Olenellus trilobite fauna (Rasetti, 1951).
Province/Territory: Alberta
Originator: Aitken, 1997.
Type Locality:
"The type section of the Peyto limestone is chosen in the cliffs formed by the west spur of Mount Thompson ... north of Bow Lake and south of Peyto Lake" (Rasetti, 1951). Hockley (1973) recognized a fault in the type section and accordingly recommended establishment of a reference section on the lower slopes of Mount Weed, in Banff National Park, Alberta. Aitken (1997) adopted Hockley's suggestion.
Distribution:
The formation is 35 m (115 ft) thick at the reference section on Mount Weed. Regionally it is confined to the main ranges and varies from a maximum of 125 m (410 ft) at Mount Kerkeslin, south of Jasper, eastward and southward to zero (Hockley, 1973). Thinning is by a combination of depositional thinning and sub-Middle Cambrian erosional bevelling.
Locality Data:
Thickness(m): Minimum 0, Maximum 125, Typical 35.
Lithology:
Limestone, locally dolomite, characteristically skeletal and colitic grainstones; sandy limestone; cryptalgal mounds; oncoidal beds; minor beds of greenish grey shale and calcareous sandstone. North of North Saskatchewan River passes to a partly red, lagoonal facies of pale, pelletal lime mudstone and cryptalgal laminite (Hockley, 1973).
Relationship:
The Peyto Formation rests with conformable, gradational and intertongued contact upon the uppermost quartzites and calcareous sandstones of the Gog Group, sandstones replacing carbonate rocks eastward. The upper contact is the base of the Mount Whyte Formation and a sub-Middle Cambrian unconformity (Rasetti, 1951; Aitken, 1997). The equivalent formation in the Mount Robson area is the Hota Formation (Fritz and Mountjoy, 1975).
History:
Walcott (1908, 1928) and Deiss (1939a, 1940) did not formalize the distinct limestone formation at the base of their Mount Whyte Formation and classified the Mount Whyte as Lower Cambrian. Rasetti (1951) recognized that the Mount Whyte, as earlier conceived comprised a Lower Cambrian limestone unit which he named the Peyto Member of the St. Piran Sandstone, unconformably overlain by an upper unit of Middle Cambrian shale and limestone, which he treated as the emended Mount Whyte.
References:
Aitken, J.D., 1997. Stratigraphy of the Middle Cambrian platformal succession, southern Rocky Mountains; Geological Survey of Canada, Bulletin 398, 322 p.
Deiss, C. F., 1939a. Cambrian formations of southwestern Alberta and southeastern British Columbia; The Geological Society of America (GSA), GSA Bulletin, vol. 50, no. 6 (June), pp. 951-1019.
Deiss, Charles Frederich, 1940. Lower and Middle Cambrian stratigraphy of southwestern Alberta and southeastern British Columbia; The Geological Society of America (GSA), GSA Bulletin, vol. 51, no. 5 (May), pp. 731-794.
Fritz, W.H. and Mountjoy, E.W., 1975. Lower and Middle Cambrian formations near Mount Robson, British Columbia and Alberta. Can. J. Earth Sci., v. 12, p. 119-131.
Hockley, G.D., 1973. Stratigraphy and paleoenvironmental patterns of the Peyto-Mount Whyte sediments (Lower-Middle Cambrian) of the southwestern Canadian Rocky Mountains. M.Sc. thesis, unpub., Univ. Calgary.
Rasetti, F., 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Inst., Misc. Coll., v. 116, no. 5.
Walcott, C.D., 1928. Pre-Devonian Paleozoic formations of the Cordilleran provinces of Canada; Cambrian geology and paleontology, Part S. Smithsonian Miscellaneous Collections, vol. 75, no. 5, p. 175-368.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: J.D. Aitken; P.H. Davenport
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 04 Jul 2008