Unit Name: Steel Formation
Unit Type: Lithostratigraphic
Usage: Currently in use
Age Interval: late Llandovery - Early Devonian (436 - 397.5 ma)
Age Justification: Biostratigraphy and stratigraphic relations. In the type area the Steel Formation contains Late Silurian, Ludlow fossils. The overlying basal Portrait Lake Formation contains Early Devonian graptolites and the underlying Duo Lake Formation uppermost Llandovery and mid Wenlock graptolites. This in its type area the formation may range in age from late Early Silurian (late Wenlock) to earliest Devonian (Gordey and Anderson, 1993). In the northeastern Niddery Lake map area the Steel Formation yielded abundant graptolites ranging in age from Early Silurian (late Llandovery) to Late Silurian. At least five different graptolite zones are represented, ranging from late Llandovery through Wenlock, Ludlow and Pridoli (late Early Silurian to Late Silurian). Misfortune Formation shale immediately above the Steel Formation yielded Early Devonian, Pragian graptolites, and therefore, the top of the Steel Formation may be as young as earliest Devonian (Cecile, 2000).
Province/Territory: Northwest Territories; Yukon Territory
Originator: Gordey and Anderson, 1993.
The type locality is situated along a ridge crest about 5 km southwest of Summit Lake in the Nahanni map area at lat. 62°19.5'N and long. 129°27.0'W. Steel Creek, after which the formation is named, lies 13 km to the east (Gordey and Anderson, 1993). A reference traverse (Section 19) was measured in a creek bottome west-northwest of Algae Lake (105-O/15). The traverse starts at UTM co-ordinates 403800 E, 7074100 N, and ends at 401900 E, 7073400 N, Zone 9 (Cecile, 2000).
The Steel Formation, like the Elmer Creek Formation, is probably a widespread unit of the Selwyn Basin to the west and southwest. It is mapped in the Sheldon Lake and Tay River map areas, which adjoin the Niddery Lake map area to the south and southwest (Gordey and Irwin, 1987). Steel Formation orange weathering argillites are mapped in the Lansing River map area to the west of the Niddery Lake map area (Roots et al., 1995a, b). The Steel Formation is found in the western one third of the northeastern Niddery Lake map area (Cecile, 1997a, c) and across the rest of the western (Cecile, 1998a, b, c, 1999) and southwestern Niddery Lake map area (Cecile, 2000). It outcrops sporadically across the entire southwestern part of the Nahanni map area from south of Woodside River to northeast of Placer and Don creeks (Gordey and Anderson, 1993).
At its type section the Steel Formation is 143 thick and consists of thin to thick bedded, siliceous, dark grey mudstone that weathers yellowish brown, dull olive grey, or dark yellow brown; one ten-metre interval is a dark blue-grey siliceous argillite with dark, wispy laminae. Locally in the Nahanni area, a thin member of orange weathering, massive, grey-green dolostone is present. In the southeastern Niddery map area, the reference section of the Steel Formation is 30 m thick and consists of rusty-orange weathernig green argillite with a prominent, medium thick bed of bright orange weathering grey dolostone. Some shale and dark wispy laminae are also present. As noted previously, the thickness along the traverse is determined mostly across fold limbs and is therefore considered a minimum. Its true thickness may be 20 to 100 per cent greater. Thin bedding, wispy laminae and some feed traces parallel to bedding are the most notable sedimentary features (Cecile, 2000).
Gordey and Anderson (1993) included the Duo Lake Formation within the Road River Group. Upper and lower contacts with the black siliceous shale and chert of the Portrait Lake and Duo Lake formations, respectively, are sharply delineated within scree, and presumed conformable (Gordey and Anderson, 1993). In the northeastern Niddery Lake map area the Steel Formation is in distinct and conformable contact with the underlying upper member of the Elmer Creek Formation. Orange weathering argillite and mudstone resembling the Steel Formation are known over a large part of the central and northern Canadian Cordillera (Cecile and Norford, 1993). An orange weathering Silurian argillite and carbonate unit is found in the upper part of the the type Road River Formation, and throughout the rest of the Richardson Mountains (Sd unit of Cecile et al., 1982, 100-144 m thick). An orange weathering Silurian argillite unit is recognized in the British and Barn mountains (Sa Unit of Lane and Cecile, 1989; Cecile and Lane, 1991). In northeastern British Columbia a Siluro-Devonian orange weathering argillaceous dolostone and siltstone outcrops over a large part of the Kechika Trough (SD unit of Cecile and Norford, 1979). This SD unit is 275-500 m thick and Middle and/or Late Silurian in age, and may possibly range into the Early Devonian. To the northeast the Steel Formation is partly equivalent to upper Duo Lake Formation. Farther northeast in the Misty Creek Embayment it is partly correlative with the Cloudy Formation (basin limestone and shale) and to the platform carbonates (Upper Ordovician to Lower Silurian formations). In the Nahanni map area it is partly correlative with the upper Duo Lake and Sapper formations (see Gordey and Anderson, 1993). In southeast Niddery Lake map area the Steel Formation is also partly correlative with the Duo Lake and Sapper formations (see Norford et al., 1993; Abbott, 1983a (his Sd1 = Sapper Formation)) (Cecile, 2000).
Thin bedding and lack of shallow-water features suggest deposition of the Steel Formation in relatively deep water (Cecile, 2000).
Abbott, J.G., 1983. Geology of the MacMillian fold Belt, 105-O S.E. and parts of 105-P S.W.; Exploration and Geological Services Devision, Department of Indian and Northern Affairs, Open File Report (unnumbered) (3 maps and legend; scale 1:50 000).
Cecile, M.P. and Lane, L.S., 1991. Geology of the Barn Uplift; Geological Survey of Canada, Open File 2342.
Cecile, M.P. and Norford, B.S., 1979. Basin to platform transition, lower Paleozoic strata of Ware and Trutch map areas, northeastern British Columbia; in, Current Research, Part A, Geological Survey of Canada, Paper 79-1A, pp. 219-226.
Cecile, M.P. and Norford, B.S., 1993. Ordovician and Silurian; in Sedimentary cover of the Craton in Canada, (ed.) D.F. Stott and J.D. Aitken; Geological Survey of Canada, Geology of Canada no. 5, p. 125-149.
Cecile, M.P., 1997a. Geology of the Thor Hills map area (NTS 105-O/15); Geological Survey of Canada, Map 1899A, Scale: 1:50 000.
Cecile, M.P., 1997c. Geology of the Elmer Creek map area (NTS 105-O/10) and northern part of NTS 105-O/07; Geological Survey of Canada, Map 1901A. Scale: 1:50 000.
Cecile, M.P., 1998a. Geology of Einarson Creek (NTS 105-O/13); Geological Survey of Canada, Map 1944A, Scale: 1:50 000.
Cecile, M.P., 1998b. Geology of Marmot Creek (NTS 105-O/14); Geological Survey of Canada, Map 1923A, Scale: 1:50 000.
Cecile, M.P., 1998c. Geology of Arrowhead Lake (NTS 105-O/11); Geological Survey of Canada, Map 1943A, Scale: 1:50 000.
Cecile, M.P., 2000. Geology of the northeastern Niddery Lake map area, east-central Yukon and adjacent Northwest Territories; Geological Survey of Canada, Bulletin 553, 120 p.
Cecile, M.P., Fritz, W.H., Norford, B.S. and Tipnis, R.S., 1982. The lower Paleozoic Misty Creek Embayment, Selwyn Basin, Yukon and Northwest Territories; Geological Survey of Canada, Bulletin 335, 78 p.
Gordey, S.P. and Anderson, R.G., 1993. Evolution of the northern Cordilleran miogeocline, Nahanni map area (105I), Yukon Territory and District of Mackenzie; Geological Survey of Canada, Memoir 428, 214 p.
Gordey, S.P. and Irwin, S.E.B., 1987. Geology, Sheldon Lake and Tay River map areas, Yukon Territory; Geological Survey of Canada, Map 19-1987 (3 sheets), Scale 1:250 000.
Lane, L.S. and Cecile, M.P., 1989. Stratigraphy and structure of the Neruokpuk Formation, northern Yukon; in, Current Research, Part G; Geological Survey of Canada, Paper 89-1G, pp. 57-62.
Norford, B.S., Orchard, M.J., Norris, A.W., Uyeno, T.T., Cecile, M.P., Abbott, J.G., Jackson, D.E., Fritz, W.H., Hofmann, H.J., Nowlan, G.S., and Tipnis, R.S., 1993. Paleontological identifications and correlations, Niddery Lake map area, NTS 105-O, and immediately adjacent map areas; Geological Survey of Canada, Open File 2682, 88 p.
Roots, C.F., Abbott, J.G., Cecile, M.P., Gordey, S.P., and Orchard, M.J., 1995b. New stratigraphy and structures in eastern Lansing map area, central Yukon Territory; in, Current Reseach, Part A; Geological Survey of Canada, Paper 1995A, p. 141-148.
Roots, C.F., Abbott, J.G., Cecile, M.P., and Gordey, S.P., 1995a. Bedrock geology of Lansing Range map area (105N) east half, Hess Mountains, Yukon; Indian and Northern Affairs Canada, Exploration and Geological Services Division, Yukon Region, Open File 1995-7 (G).
Source: GEOLOGICAL SURVEY OF CANADA, CALGARY
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 03 Dec 2010