Unit Name: St. Mary River Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: Late Cretaceous (99.6 - 65.5 ma)
Age Justification: Ostrea, Corbula and other forms indicative of a brackish water environment are common in the basal member as contributors to the limestone coquinas. Throughout the remainder of the formation well preserved and distinctive fresh water and terrestrial mollusk shells occur, the most important locality being on Pincher Creek west of the town of that name (see Tozer, 1956b). Dinosaur bones have been found at a number of localities and stratigraphic levels. A rich deposit occurs on Lee Creek, southwest of Cardston. At Scabby Butte, east of Nobleford dinosaur and other vertebrate remains occur near the base of the formation (Langston, 1975). One very distinctive dinosaur (Pachyrhinosaurus) described from here has also been found in the lower part of the Horseshoe Canyon Formation near Drumheller. Mammalian remains of Cretaceous affinities have been described from the Scabby Butte locality and from near the top of the formation on the Oldman River, north of Lundbreck (Sloan and Russell, 1974).
Province/Territory: Alberta; Montana
Originator: Dawson, 1883.
None designated by author (1883), but in 1884 (p. 54C) he mentioned the St. Mary River as affording the best and most typical display of these rocks. Williams and Dyer (1930, p. 52) assumed the type locality to be along the St. Mary River west of Magrath, Alberta, "where excellent exposures occur for more than 20 miles," (32 km). The outcrop along the river between Sec. 20, Twp. 4, Rge. 24W4M and Sec. 24, Twp. 6, Rge. 23W4M is the focal point for the lithostratigraphic study of the formation by Williams (1951).
354 m (1160 ft) thick in the type area on the St. Mary River (Williams, 1951, p. 892) and about 457 m (1500 ft) on Oldman River (Russell, 1932a, p. 34B). It thickens westward to the foothills, where Hage (1943, p. 11) estimated a thickness of about 762 m (2500 ft) on the Castle and Crowsnest rivers. The formation extends northward from Glacier County, northwestern Montana to Twp. 14 in Alberta and westward from the Sweetgrass Arch area to the foothills belt.
Hard, greenish-grey weathering, fine-grained, calcareous, commonly lenticular sandstones alternating with green and grey friable, silty shales. Thin carbonaceous shales and nodular, rusty weathering limestones are present in places. The basal zone or member, about 30 m (100 ft) thick consists of fissile grey shale, rusty weathering sandstone, coal beds and coquinoid limestone (Tozer, 1956, p. 8). The basal member is considered representative of lagoonal conditions by Williams (1951, p. 896) and of a lagoonal to marsh regime by Young and Reinson (1975) and Reinson (1979); the remainder of the formation is regarded as nonmarine.
Conformably overlies the Blood Reserve Formation or the Bearpaw where the former is absent in the foothills, and is conformably overlain by the Willow Creek Formation, except on the east limb of the Alberta Syncline, where Russell (1965) indicated the contact may he erosional. The St. Mary River Formation gives place to the Horseshoe Canyon (=Edmonton) Formation north of the Oldman River at about Twp. 10, but extends as a lens into the middle of the Horseshoe Canyon as far north as the Little Bow River in the vicinity of Carmangay, near the north boundary of Twp. 13 (Russell, 1932b, p 131; 1950, p. 38), where Irish (1968a) recognized hard sandstones and friable shales of St. Mary River lithology overlying typical Horseshoe Canyon sediments. On the east side of the Alberta Syncline, along the Oldman River in Sec. 25, Twp. 10, Rge. 25W4M Tozer (1952, p 4) identified a tuff bed at the top of the formation which he correlated with the Kneehills tuff "zone" of the Battle Formation of the central and southeastern Alberta Plains. Underlying this tuff are dark grey shale and white weathering sandstone which were thought to be the equivalents of the "mauve" shale of the Battle Formation and the Whitemud Formation, respectively. The St. Mary River Formation is also equivalent in part to the Eastend Formation of the Cypress Hills region.
Dawson, 1883, 1884; Hage, 1943; Irish, 1968a; Langston, 1975; Reinson, 1979; Russell, 1932a, 1932b, 1950, 1965; Sloan and Russell, 1974; Tozer, 1952, 1956; Williams, 1951; Williams and Dyer, 1930; Young and Reinson, 1975.
Dawson, G.M., 1883. Preliminary report on the geology of the Bow and Belly river region, Northwest Territory, with special reference to the coal deposits. Geological Survey of Canada, Report of Progress for 1880-81-82, Part B.
Dawson, G.M., 1884. Report on the region in the vicinity of Bow and Belly rivers, Northwest Territory. Geol. and Nat. Hist. Surv. and Museum Can., Rept. Progress 1882-8344, Part C, p. 1-169.
Hage, C.O., 1943b. Dyson Creek map-area, Alberta (Report and Map); Geological Survey of Canada, Paper 43-5, 20 p. and Preliminary Map 43-5A, Dyson Creek, West of Fifth Meridan, Alberta, Scale: 1 inch to ½ mile + sections.
Reinson, G.E., 1979. Facies models 14. Barrier island systems; Geoscience Canada, vol. 6, pp. 51-68.
Russell, L.S., 1932a. Fossil non-marine mollusca from Saskatchewan. Roy. Can. Inst. Trans., vol. 18, Part 2, pp. 337-341.
Russell, L.S., 1932b. Stratigraphy and Structure of the Eastern Portion of the Blood Indian Reserve, Alberta; Geological Survey of Canada, Summary Report 1931, Part B, pp. 26-38.
Russell, Loris S., 1965. The problem of the Willow Creek Formation; Canadian Journal of Earth Sciences = Journal Canadien des Sciences de la Terre, vol. 2, no. 1 (February), pp. 11-14.
Sloan, R.E. and Russell, L.S., 1974. Mammals from the St. Mary River Formation (Cretaceous) of southwestern Alberta. Roy. Ont. Museum, Life Sciences Contributions, no 95, p. 1-24.
Tozer, E.T., 1952. The St. Mary River-Willow Creek contact on Oldman River, Alberta; Geological Survey of Canada, Paper 52-3.
Tozer, E.T., 1956b. Uppermost Cretaceous and Paleocene non-marine molluscan faunas of western Alberta; Geological Survey of Canada, Memoir 280, 125 p. + 3 figures in back pocket.
Williams, Edwin Philip, 1951. Saint Mary River Formation in Spring Coulee-Magrath area, Alberta, Canada; American Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 35, no. 4 (April), pp. 885-898.
Williams, M.Y. and Dyer, W.S., 1930. Geology of southern Alberta and southwestern Saskatchewan; Geological Survey of Canada, Memoir 163.
Young, F.G. and Reinson, G.E., 1975. "Sedimentology of Blood Reserve and adjacent formations (Upper Cretaceous), St. Mary River, southern Alberta", in, Guidebook to selected sedimentary environments in southwestern Alberta, Canada, Shawa, M.S. (Ed.); Can. Soc. Petrol. Geol., Field Conf., p. 10-20.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: L.S. Russell; J.H. Wall
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 31 Mar 2009