Type Locality:

Walcott gave the anomalous section on Mount Stephen as the type locality. Rasetti (1951) discussed the many difficulties with the Mount Stephen locality and moved the type section to Mount Bosworth, 8 km (5 mi) northwest of Lake Louise, Alberta, at 51 deg 28'N, 116 deg 19'W. There the section is contiguous with the type Cathedral Formation and representative of the regional character of the Stephen.

Distribution:

The Stephen Formation is 109.1 m (358 ft) thick at the type section. It thins westward onto the axis of the Kicking Horse Rim (Aitken, 1971), in part by the incorporation of basal peritidal carbonates into the Cathedral Formation, before thickening rapidly to 275 to 335 m (902 to 1,100 ft) in a largely deep water facies. It thins eastward to as little as 21.6 m (71 ft) at the mountain front at Ghost River, and continues thinning eastward in the subsurface. The maximum thickness of the "thin" Stephen is 370 m (1,214 ft) in the Chaba River section near Fortress Lake. The Stephen Formation dips westward out of view west of the Kicking Horse Rim. No specific western equivalent has been recognized. Eastward the Stephen passes into part of the subsurface Earlie Formation as the bounding Cathedral and Eldon carbonates change to inner-detrital facies (Pugh, 1971). A similar change takes place northward - as the Cathedral Formation becomes unrecognizable along a line slightly north of Athabasca Glacier and Sunwapta Peak the Stephen becomes part of the Snake Indian Formation, as the Stephen Member. Southward the Stephen plunges from view south of Mount Assiniboine.

Locality Data:

Thickness(m): Maximum 370, Typical 109.1.

Lithology:

Regionally the "thin" Stephen consists of interbedded shale and limestone. The shales are grey and greenish grey in the main ranges, and partly bright green and purple-red at mountain front and subsurface localities. Thin laminae of quartz siltstone are minor, and increase eastward. Limestones are predominantly thin-bedded, burrowed lime mudstone, but include ooid, oncoid and skeletal grainstones, stromatolites and flatstone and roundstone conglomerates. The "thick", or basinal Stephen deposits west of the Cathedral Escarpment are dominated in the lower part by thin bedded and laminated, partly turbiditic shale. Interbedded with shale is a small content of ooid-skeletal-intraclast packstone and mudstone redeposited from the shallow platform. The boundary limestone member occurs as a westward thinning wedge up to 100 m (328 ft) thick where it abuts the escarpment (McIlreath, 1977a, b). An upward shallowing trend is evident; the upper part of the basinal "thick" Stephen resembles the regional "thin" Stephen and is continuous with it.

Relationship:

The Stephen Formation may be regarded as a westward directed tongue of inner-detrital facies that invades the long-term locus of the middle carbonate facies belt (Cathedral and Eldon formations). The basal contact is conformable and gradational and, except near the Rim (see above), approximately time parallel. The upper contact (with the Eldon) is gradational and diachronous, becoming younger eastward.

History:

Walcott's publications (1908b, 1908c, 1928) on the Stephen, particularly the type section, were confused. In his earliest descriptions, and on p. 247 of his posthumously published synthesis (1928) he limited the Stephen to the shaly interval between Cathedral and Eldon massive carbonates, but on p. 315-319 he added an additional 58 m (190 ft) of "bluish-grey limestone with bands of dark, siliceous shale in its lower portion" to the top of the Stephen on Mount Stephen. This was a revision of his concept of the Stephen, dictated by his having included within the Stephen at Mount Bosworth and other localities the conspicuous, dark grey weathering limestones at the base of the pale Eldon dolomites that overlie the highest Stephen shales. Deiss (1939a, 1940) and Rasetti (1951) continued to include the dark limestones within the Stephen, although Rasetti suggested that they might be transferred to the Eldon. Rasetti's suggestion has been followed in subsequent work (Aitken, 1966; Aitken, Fritz and Norford, 1972; McIlreath, 1977a,b) to make the Stephen-Eldon contact a depositional, rather than a diagenetic one. Fritz (1971) and McIlreath (1977) distinguished the anomalously thick and lithologically distinct Stephen Formation of the western parts of Mounts Stephen and Field as the "thick" Stephen, as contrasted with the regional "thin" Stephen as represented by the Mount Bosworth section.

References:

Aitken, J.D., 1966. Middle Cambrian to Middle Ordovician cyclic sedimentation, southern Rocky Mountains of Alberta; Canadian Society of Petroleum Geologists, Bulletin of Canadian Petroleum Geology, vol. 14, no. 4 (December), pp. 405-441.

Aitken, J.D., Fritz, W.H., and Norford, B.S., 1972. Cambrian and Ordovician stratigraphy of the southern Rocky Mountains, 24th International Geological Congress, Guidebook, Excursion A-19, 56 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., 1971. Geological setting of the Burgess shale, in, Proceedings of the North American Paleontological Convention, Chicago, Ill., September 1969, E. L. Yochelson (ed.); Allen Press, Lawrence, Kansas, vol. 2, part 1, pp. 1155-1170.

McIlreath, I.A., 1977b. Accumulation of a Middle Cambrian deep water limestone debris apron adjacent to a vertical submarine carbonate escarpment, southern Rocky Mountains, Canada. In- Deep-water carbonate environments; Cook, H.E. and Enos, P. (Eds.). SEPM Spec. Pub. 25, p 113-124.

McIlreath, Ian A., 1977a. Stratigraphic and sedimentary relationships at the western edge of the middle Cambrian carbonate facies belt, Field, British Columbia; University of Calgary, Calgary, AB, Unpublished Ph.D. thesis, 269 p.

Pugh, D.C., 1971. Subsurface Cambrian stratigraphy in southern and central Alberta. Geological Survey of Canada, Paper 70-10.

Rasetti, F., 1951. Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains. Smithsonian Inst., Misc. Coll., v. 116, no. 5.

Walcott, C.D., 1908a. Nomenclature of some Cambrian Cordilleran formations; Smithsonian Miscellaneous Collections, vol. 35, no. 1.

Walcott, C.D., 1908b. Cambrian geology and paleontology: Cambrian sections of the Condilleran area. Smithsonian Miscellaneous Collections, vol. 53, no. 5, pp. 204-208.

Walcott, C.D., 1908c. Cambrian sections of the Cordilleran area. Smithsonian Miscellaneous Collections, vol. 53, no. 5, pp. 167-230.

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.