Unit Name: Imperial Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Frasnian - early Tournaisian (382.7 - 354.5 ma)
Age Justification: Very few megafossils have been found in the Imperial Formation especially in the lower part of the formation. Fossils are usually restricted to or near thin limestone beds (with the exception of trace fossils). The formation is characterized by brachiopods, corals, crinoids, a few ammonoids, ostracodes, pelecypods and conodonts. A large number of megaplant fragments are present in the beds. The most abundant fossil forms are megaspores and miospores. Megaspores have been utilized by Chi and Hills (1974, 1976) to characterize the type section biostratigraphy.
Province/Territory: Northwest Territories; Yukon Territory

Originator: Link, 1921.

Type Locality:
Front of Mackenzie Mountains on the Imperial River (65°07'N; 127°51'W) about 56 km (35 mi) west of Norman Wells.

Distribution:
At the type section 600 m (1,970 ft) of strata are present, whereas elsewhere in the Richardson Mountains it is up to 1,850 m (6,000 ft) thick. It outcrops and subcrops over vast areas of the District of Mackenzie and the Yukon from the area around 64°N latitude of the upper Mackenzie River Basin northward to the Mackenzie Delta and the Arctic coastline. It occurs from the Norman Wells area westward to Mackenzie Mountains, Richardson Mountains, and Ogilvie Mountains. Strata assigned to the Imperial Formation has been reported from the Barn Range of the northern Yukon. West of the Richardson Mountains it loses its character in a thick shale sequence.

Locality Data:
Thickness(m): Maximum 1850.

Lithology:
In the type area the Imperial Formation consists of cyclic sequences of grey-green, silty, thin-bedded, scar forming quartz sandstones which alternate with zones of softer grey-green to black, sandy shales. Rare conglomerates and thin fossiliferous limestones are also present. The amount of shale increases towards the top of the formation. Based on well data, Tassonyi (1969) subdivides the formation into two informal units: a Lower Member consisting of predominantly marine shale and an Upper Member consisting of interbedded marine siltstones, sandstones, shales and a few intercalated limestones. He also states that the Jungle Ridge Limestone Lentil and the Canyon Creek Sandstone Lentil are positioned in the Lower Member. These 'lentils' had formally been described as members within the Fort Creek Formation and have a limited extent within the Norman Wells area. Warren and Stelck (1950) refer to a sandstone member, the Bosworth Sandstone Member, which falls under the original Bosworth Formation concept. Tassonyi did not encounter the upper shale zone in any of the studied wells. Sandstones from the type area have been shown to contain 55% quartz and 21% clay and the boron content indicates deposition in a marine environment (Cauffman and Bayliss, 1976). Westward from the type area, changes are noted in lithology and depositional sequence. Turbidite deposition as pointed out by Glennie (1963), becomes a important component and consists of cycles including a sharp base with flute casts or other flow features, a massive basal unit (sometimes pebble conglomerate) grading upwards into a laminated zone, then a rippled zone (sometimes contorted), and finally into a shale. The formation should probably be subdivided because the essential characters present in the type area are missing in the northern Mackenzie Mountains and the Richardson Mountains.

Relationship:
In the type area the Imperial's lower contact is sharp (possibly disconformable) with underlying shales of the Canol Formation. On the east slopes of the Richardson Mountains it is in sharp contact with the siliceous shales and cherts of the Prongs Creek Formation. The upper contact is an erosional unconformity and may be overlain by Cretaceous beds of the Sans Sault Formation or by older units of Permian or Mississippian age (Norris, 1968). It is generally lithologically similar in the same stratigraphic position and age as the Crystal Peak Formation of the central Yukon, the Kanayut Formation of the Brooks Range and the Nation River Formation of central Alaska.

History:
Originally the formation was named Camp Creek Series (Bosworth, 1921a) and Bosworth Formation (Kindle and Bosworth, 1921). Both these names were preoccupied so it was renamed Carcajou Formation by Kindle (1936). Link proposed the name Imperial Formation and Hume and Link (1945) formally defined this combination stating that because only a small portion of the total formation was exposed at the type section of the Carcajou Formation, it is preferable to establish a new type section and to rename the formation. Caldwell (1964) has outlined these nomenclatural changes and stated, concerning the change from Carcajou to Imperial, that such action contravenes present day recommended procedure and accepted practice. Further, Pedder (in House and Pedder, 1963) has pointed out that the name Imperial is preoccupied by a formation in California. Caldwell (1964) argues for the retention of the Imperial Formation nomenclature based on general acceptance and the entrenchment of the name in the literature. Bassett (1961) proposed the inclusion of 110 m (361 ft) of grey shale in the Imperial Formation that was formerly called the Upper Non-bituminous Shales of the Fort Creek Formation. Pugh (in press) has erected the Tuttle Formation which is the equivalent of the upper conglomeratic unit of the Trail River section of the Imperial Formation (Norris, 1968).

Other Citations:
ASPG, 1960; Hume, 1954; Laudon, 1950; Lawrence, 1973; Norris, 1967b; Tassonyi, 1969.

References:
Alberta Society of Petroleum Geologists, 1960. Lexicon of geologic names in the Western Canada Sedimentary Basin and Arctic Archipelago, Workman, L.E. (Chairman); Alberta Society of Petroleum Geologists, Printed by John D. McAra Limited, Calgary, AB, 380 p.
Bassett, H.G., 1961. Devonian stratigraphy, central Mackenzie River region, Northwest Territories, Canada; pp. 481-498: in Raasch, G. (ed.), Geology of the Arctic, Alberta Society of Petroleum Geologists and University of Toronto Press, vol. 1, 732 p.
Bosworth, Thomas Owen, 1921a. The Mackenzie oil-field of northern Canada; Institute of Petroleum; London, Journal of the Institution of Petroleum Technologists, vol. 7, no. 28 (October), pp. 276-297.
Caldwell, W.G.E., 1964. The nomenclature of the Devonian formations in the lower Mackenzie River valley; Alberta Society of Petroleum Geologists, Edmonton Geological Society, and Saskatchewan Geological Society, Bulletin of Canadian Petroleum Geology, vol. 12, no. 3, pp. 611-622.
Cauffman, Lewis B., Jr., and Bayliss, Peter, 1976. Mineralogy and boron content of the Melville Island Group and Imperial Formation, N.W.T.; Canadian Society of Petroleum Geologists (CSPG), Bulletin of Canadian Petroleum Geology, vol. 24, no. 3 (September), pp. 471-480.
Chi, B.I. and Hills, L.V., 1974. Stratigraphic and paleoenvironmental significance of Upper Devonian megaspores, type section of the Imperial Formation, Northwest Territories Canada; pp. 241-257: in Aitken, J.D. and Glass, D.J. (eds.), Canadian Arctic Ge
Chi, B.l. and Hills, L.V., 1976. Biostratigraphy and taxonomy of Devonian megaspores, Arctic Canada; Bulletin of Canadian Petroleum Geology, vol. 24, no. 4, pp. 640-818.
Glennie, K.W., 1963. An interpretation of turbidita whose sole markings show multiple directional trends; Journal of Geology, vol. 71, no. 4, pp. 525-527.
House, M.R. and Pedder, A.E.H., 1963. Devonian Goniatites and stratigraphical correlations in Western Canada; Palaeontology, vol. 6, pt. 3, pp. 491-539.
Hume, G.S. and Link, T.A., 1945. Canol geological investigations in the Mackenzie River area, Northwest Territories and Yukon (Report and Three Maps); Geological Survey of Canada, Paper 45-16, 87 p. + Preliminary Map 45-16A, Lower Mackenzie River Area, Northwest Territories and Yukon, Sheet 1, Scale: 1 inch to 8 miles; Preliminary Map 45-16B, Lower Mackenzie River Area, Northwest Territories and Yukon, Sheet 2, Scale: 1 inch to 8 miles; and Preliminary Map 45-16C, Lower Mackenzie River Area, Northwest Territories and Yukon, Sheet 3, Scale: 1 inch to 8 miles.
Hume, G.S., 1954. The Lower Mackenzie River area, Northwest Territories and Yukon; Geological Survey of Canada, Memoir 273, 118 p.
Kindle, E.M. and Bosworth, T.O., 1921. Oil-bearing Rocks of Lower Mackenzie River Valley, Northwest Territories; Geological Survey of Canada, Summary Report 1920, Part B, pp. 37-63.
Kindle, E.M., 1936. Formation names in the Mackenzie River valley; Science (new series), vol. 83, no. 2140, pp. 14-15.
Laudon, L.R., 1950. Imperial River section, Mackenzie Mountains, Northwest Territories, Canada; American Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 34, no. 7 (July), pp. 1565-1577.
Lawrence, J.R., 1973. Old Crow Basin; pp. 307-314: in McCrossan , R.G. (ed.), The Future Petroleum Provinces of Canada: Their Geology and Potential, Canadian Society of Petroleum Geologists, memoir 1, 720 p.
Link, T.A., 1921. Unpublished geological report on the Fort Norman area: Imperial Oil Ltd., Calgary, Alberta, 81 p.
Norris, A.W., 1967b. Devonian of northern Yukon Territory and adjacent District of Mackenzie; pp. 753-780: in Oswald, D.H. (ed.), International Symposium on the Devonian System, Alberta Society of Petroleum Geologists, vol. 1, 1055 p.
Norris, A.W., 1968. Reconnaissance Devonian stratigraphy of northern Yukon Territory and northwestern District of Mackenzie; Geological Survey of Canada, Paper 67-53, 287 p.
Pugh, D.C., 1983. Pre-Mesozoic geology in the subsurface of Peel River map area, Yukon Territory and District of Mackenzie; Geological Survey of Canada, Memoir 401, 61 p.
Tassonyi, E.J., 1969. Subsurface geology, lower Mackenzie River and Anderson River area, District of Mackenzie; GSC Paper 68-25 (report and 11 figures), 207 p.
Warren, Percival Sidney and Stelck, Charles Richard, 1950. Succession of Devonian faunas in Western Canada; The Royal Society of Canada, Transactions of the Royal Society of Canada, Volume XLIV, Series III, June 1950, Section Four, Geological Sciences including Mineralogy, pp. 61-78.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 2, Yukon Territory and District of Mackenzie; L.V. Hills, E.V. Sangster and L.B. Suneby (editor)
Contributor: L.V. Hills; D.R. Braman
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 26 Oct 2018