Unit Name: Willow Creek Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Late Cretaceous - Paleocene (99.6 - 55.8 ma)
Age Justification: Fossil fresh water mollusks have been found at various levels within the formation. Tozer (1956b) recognized two distinctive faunas, a lower of probable Cretaceous age, and an upper of Paleocene affinities. Dinosaur bones have been found in the lower part of the formation in Alberta (Tozer, 1956b, p. 25) and Montana (Russell, 1968).
Province/Territory: Alberta; Montana

Originator: Dawson, 1883.

Type Locality:
None designated by Dawson (1883), but in 1884 (p. 78C) he mentioned that these beds were first recognized at the mouth of Willow Creek and on the neighbouring part of the Oldman River in southwestern Alberta. Williams and Dyer (1930, p. 59) recorded the best exposures on the Oldman River east of Fort MacLeod, in the northern part of Twps. 9 and 10, Rge. 25W4M. Farther west, in the Alberta Foothills belt on the Oldman River in Secs. 5 and 6, Twp. 10, Rge. 1W5M Douglas (1950, p. 45) described an almost complete section of the lower part of the formation.

Distribution:
Thickness varies dependent on position relative to the axis of the Alberta Syncline. Carrigy (1971, p. 11) reported 1,006 m (3,300 ft) from a well drilled near the axis; Tozer (1956, p. 21) calculated 1,260 m (4,135 ft) for the outcrop on Castle River on the west side, and Russell (1932b, p. 140) computed 366 m (1200 ft) from exposures along the Oldman River on the east limb of the syncline. This nonmarine formation extends northward from Glacier County, northwestern Montana to about Twp. 15 in the Nanton area, Alberta, and westward from the Sweetgrass Arch to the foothills belt. Tozer (1956, p. 22) commented that beds of Willow Creek type are present on Little Bow River below the conglomerate correlated with the basal Paskapoo by Bell (1949, p. 12) and above this conglomerate on Mosquito Creek, 8 km (5 mi) southeast of Nanton. Carrigy's (1971b, p. 11) interpretation of the subsurface data is that the Willow Creek Formation occupies a distinct structural basin, separated by a sill or platform in the Calgary-Bow River area from the more northerly and larger structural basin occupied by the Paskapoo Formation. He further noted, however that the change in lithofacies from Willow Creek to Paskapoo aspect seems to take place south of the structural divide, being evident in outcrops near Nanton.

Lithology:
Alternating varicolored shales with calcareous concretions, and soft, light grey sandstones. Douglas (op. cit.) divided the formation into five zones, or members as they later became known, which are listed below in ascending order. Zone A: 163 m (536 ft), green, grey and purple shales with interbedded sandstones, most of which are grey, fine-grained, massively bedded and cross-bedded; limestone concretions. Zone B: 75 m (246 ft), green, red and mottled green and red shales and soft grey sandstones. Zone C: 4.5 to 9 m (15 to 30 ft), grey, coarse-grained, cross-bedded conglomeratic sandstone. Zone D: similar lithology to Zone B. Zone E: sandstones which are thicker, coarser and harder than those below and shales which change gradationally to darker and harder rocks with fewer calcareous concretions and red beds. Zones D and E comprise about 579 m (1,900 ft) of strata.

Relationship:
The lower boundary with the St. Mary River Formation is transitional and conformable in the foothills belt on the west limb of the Alberta Syncline, but Russell (1965) suggested this contain may be erosional on the east side of the syncline. On the Oldman River Tozer (1952, 1956), recognized the equivalent to the Battle Formation, including the Kneehills Tuff at the top of the St. Mary River Formation and underlying the Willow Creek Formation. The upper contact with the Porcupine Hills Formation appears to be transitional and conformable due to similarity in lithology above and below the assumed boundary. However, Douglas (1950, p. 44) indicated that the relationship between the Willow Creek and Porcupine Hills Formations in the Callum Creek and Langford Creek map-areas in the southern Alberta Foothills is that of an erosional unconformity, and this interpretation was said by Carrigy (1971b, p. 11) to be supposed by geophysical and drilling data cited by Bossort (1957). The lower part (Maastrichtian) of the Willow Creek Formation (members A, B, C and most of D) is correlative with the upper part of the Edmonton Group, i.e., the lower part of the Scollard Formation (sensu Gibson, 1977), in the central Alberta Plains, in part to the upper part of the Brazeau Formation of the foothills (and to part of informal Coalspur beds), the Frenchman Formation (sensu Furnival, 1946) of the Cypress Hills area in southeastern Alberta and southwestern Saskatchewan and the Lance and equivalent Hell Creek formations in the northwestern United States. The upper part (Paleocene) of the Willow Creek Formation (upper beds of member D and all of member E) is correlative with the upper part of the Scollard Formation and the lower part of the Paskapoo Formation (sensu Gibson, 1977) in the central Alberta Plains; the Ravenscrag Formation in the Cypress Hills area and the Fort Union Formation in the northwestern United States, based on distinctive molluscan fauna in common.

Other Citations:
Bell, 1949; Bossort, 1957; Carrigy, 1971b; Dawson, 1883, 1884; Douglas, 1950; Furnival, 1946; Gibson, 1977b; Russell, 1932b, 1965, 1968; Tozer, 1956b; Williams and Dyer, 1930.

References:
Bell, W.A., 1949. Uppermost Cretaceous and Paleocene floras of western Alberta; Geological Survey of Canada, Bulletin 13, 231 p.
Bossort, D.A., 1957. Relationship of the Porcupine Hills to Early Laramide movements. In: Alberta Society of Petroleum Geologists, 7th Ann. Field Conf. Guidebook, p. 46-51.
Carrigy, M.A., 1971b. Lithostratigraphy of the uppermost Cretaceous (Lance) and Paleocene strata of the Alberta Plains; Alberta Research Council, Edmonton, AB, Research Council of Alberta Bulletin 27, 161 p.
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.
Douglas, R.J.W., 1950. Callum Creek, Langford Creek and Gap map-areas, Alberta. Geological Survey of Canada, Memoir 255.
Dyer, W.S., 1930. Paleozoic geology of the Albany River and certain of its tributaries; Ontario Department of Mines, 38th Annual Report, Part 4, pp. 47-60.
Furnival, G.M., 1946. Cypress Lake map-area, Saskatchewan; Geological Survey of Canada, Memoir 242, 161 p. contains "A" Series Map 784A, Cypress Lake, West of Third Meridian, Saskatchewan, Scale: 1:253 440 or 1 Inch to 4 Miles and "A" Series Map 856A, Structure-Contours, Cypress Lake, West of Third Meridian, Saskatchewan, Structure-contour interval 50 feet, Scale: 1:253 440 or 1 Inch to 4 Miles.
Gibson, D.W., 1977b. Upper Cretaceous and Tertiary coal-bearing strata in the Drumheller-Ardley region, Red Deer River valley, Alberta, Geological Survey of Canada, Paper 76-35, 41 p.
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.
Russell, Loris S., 1968. A dinosaur bone from Willow Creek beds in Montana; Canadian Journal of Earth Sciences = Journal Canadien des Sciences de la Terre, vol. 5, no. 2 (April), pp. 327-329.
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, M.Y. and Dyer, W.S., 1930. Geology of southern Alberta and southwestern Saskatchewan; Geological Survey of Canada, Memoir 163.

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.H. Wall; P.A. Monahan; L.S. Russell
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 21 Jan 2009