Unit Name: Gull Lake Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Early Cambrian - Late Cambrian (542 - 488.3 ma)
Age Justification: Stratigraphic relations and biostratigraphy. There are no fossil collections from within the northeastern Niddery Lake map area, however immediately west of the area, trace fossils were observed at several localities (Cecile, 1998a, b). These collections have been identified by H.J. Hofmann (in Norford et al., 1993) as consisting of the trace fossil Planolites. Also, immediately west of the northeastern Niddery Lake map area, a single Archeocyathid was recovered from the Old Cabin Formation, which intertongues with the Gull Lake Formation (see Norford et al., 1993). The Gull Lake Formation in the northeastern Niddery Lake map area is underlain by the Arrowhead Lake Member (Narchilla Formation) with trace fossils that range from Early Cambrian to earliest Middle Cambrian in age. It is overlain by Elmer Creek Formation, which is earliest Ordovician at the base. Because there are no known unconformities between the Gull Lake Formation and overlying and underlying units in the Niddery Lake map area, the Gull Lake Formation may represent a large part of the Cambrian Period (Cecile, 2000).
Province/Territory: British Columbia; Northwest Territories; Yukon Territory

Originator: Gordey and Anderson, 1993.

Type Locality:
The type section of the Gull Lake Formation is in the Nahanni map area at lat. 62°23.4'N and long. 129°19.2'W (section 8). It is located on the southwestern limb of Fork Anticline, about 4 km north-northeast of Summit Lake. Gull Lake, after which the formation is named, is located 28 km southwest of the type section (Gordey and Anderson, 1993).

Distribution:
Occurs within the Selwyn Basin. Southwest of the Sekwi-Backbone Blackwater Platform-edge the Gull Lake Formation outcrops over the entire northeastern Niddery Lake map area (Cecile, 1997a, b, c), as well as the remainder of the Niddery Lake map area (unit Ca of Cecile and Abbot, 1992) and beyond into adjacent map sheets to the north, west, south and southeast (Cecile, 2000). The Selwyn Basin extends for 1000's of kilometres from Alaska through the Yukon, western Northwest Territories and British Columbia, and into the United States (Nelson and Colpron, 2007) (Goodfellow, 2007). The Kechika Trough is a narrow sliver of coeval basinal strata and forms part of the Selwyn Basin. It continues south for ~500 km into British Columbia (Mair et al., 2006). The Gull Lake Formation occurs predominantly in the Yukon Territories (Gordey and Anderson, 1993; Cecile, 2000) and to a lesser extent in the western Northwest Territories (Barnes et al., 2007) and north-cental British Columbia (Gabrielse, 2003). In the northeastern Niddery Lake map area, and the rest of the Niddery Lake map area (Cecile and Abbott, 1992), the Gull Lake Formation is approximately 400 m thick, and similar in compostion to the Nahanni type section (Cecile, 2000). Most of the type section, which totals 1050 m in thickness, is underlain by scree, except for the upper part which is resistant weathering and well exposed (Gordey and Anderson, 1993).

Locality Data:
Thickness(m): Typical 400.

Lithology:
The Gull Lake Formation consists of buff-brown weathering, blue-grey slate and siltstone and minor limestone conglomerate exposed in the southwestern quadrant of the map area (Gordey and Anderson, 1993). At the Nahanni type section the Gull Lake Formation is divided into three members, from lower to upper: a discontinuous, basal, metre-thick unit of limestone conglomerate with archeocyathids; 662 m of orange-brown to rust-brown weathering slate and siltstone to fine grained sandstone; and 386 m of resistant, grey weathering, thick bedded bioturbated siltstone and mudstone. In the southeastern Niddery Lake map area, and the rest of the Niddery Lake map area (Cecile and Abbott, 1992), the Gull Lake Formation also includes a variety of minor, thin to thick stratigraphic units consisting of chert, shale, sandstone, grit and limestone. The Gull Lake Formation consists mostly of thin bedded argillite with some graded beds. Sandstone units are generally clean and vary in grain size and sorting. Limestone units are commonly thin bedded, some contain intraclast breccias and others have small-sclae, asymmetrical ripple crosslaminae (Cecile, 2000).

Relationship:
The Gull Lake Formation sharply overlies maroon shales of the Narchilla Formation, and either unconformably underlies white weathering limestone of the Rabbitkettle Formation, conformably underlies the Elmer Creek Formation or sharply underlies the Old Cabin Formation (Gordey and Anderson, 1993; Cecile, 2000). In the northeastern Niddery Lake map area, and the rest of the Niddery Lake map area (Cecile and Abbott, 1992), the Gull Lake Formation in many places intertongues with beds of volcaniclastics or is interstratified with a mappable unit of volcanic rocks (Old Cabin Formation). In the type area of the Old Cabin Formation, the Gull Lake Formation argillite is overlain with a sharp contact by the Old Cabin Formation. In southeastern parts of the northeastern Niddery Lake map area it has a poorly exposed basal unit, the North Keele Member, which is approximately 10 to 40 m thick and consists of thin bedded limestone and limestone conglomerate. The North Keele member rests directly on the Arrowhead Lake Member (Narchilla Formation), and is only known north of Keele Peak. The contact between the Arrowhead Lake Member, Narchilla Formation, and the Gull Lake Formation is distinct and conformable and defined by a colour change. As noted above, in the north Keele Peak area the lower boundary is the base of the North Keele Member. The Elmer Creek Formation is in distinct conformable contact with the Gull Lake Formation. The contact is defined where very siliceous argillite or chert dominate the succession and can usually be placed to within a few metres. The contact between the upper and lower members is sharp and distinct and is marked as a change from drab grey siliceous argillite on top of massive chert, to black weathering siliceous shale or chert. The Gull Lake Formation is directly correlative with the same unit in the Nahanni map area. To the northeast the Gull Lake Formation is equivalent to the Sekwi Formation and is very likey and argillaceous equivalent of the Hess River and basal Rabbitkettle formations. Gordey and Anderson (1993) noted that the Gull Lake Formation in the Nahanni area is a direct equivalent of the Middle Cambrian Rockslide and Avalanche formations of the Mackenzie Mountains. In the Nahanni area, however, the Upper Cambrian to Lower Ordovician Rabbitkettle Formation continues basinward as a mappable unit and is shown resting unconformably on the Gull Lake Formation (Gordey and Anderson, 1993). The Gull Lake Formation is like widespread over the entire Selwyn Basin, but its extents reamins to be determined (Gordey and Anderson, 1993). Abbott (1992) has mapped Gull Lake Formation (?) strata in the northern Selwyn Basin about 200 km west of the northeastern Niddery Lake map area, and Roots et al. (1995a, b) mapped the Gull Lake Formation in the Lansing map area west of Niddery Lake. A similar unit is also found in the Barn and British Mountains (a unit of Cecile, 1988; Cecile and Lane, 1991; and Lane and Cecile, 1989). There, however, the unit is 200 to 500 m thick and consists of both green and maroon argillites with quartzite and limestone. The maroon lithologies contain the trace fossil Oldhamia (Hofman et al., 1994) and resemble the Arrowhead Lake Member of the Narchilla Formation (Cecile, 2000).

Remark:
The Gull Lake Formation in the Niddery Lake map area is considered to be a relatively deep-water unit on the basis of its graded bedding, dominance of fine grain size, and its facies position (Cecile, 2000).

References:
Abbott, J.G., 1992. Revised stratigraphy and new exploration targets in the Larsen Creek area (NTS 116A/10, 116A/11), southeastern Yukon; in, Yukon Exploration and Geology; Department of Indian and Northern Affairs, Exploration and Geological Services Division, Yukon Region, pp. 13-26.
Barnes, E.M., Groat, L.A., and Falck, H., 2007. A review of the Late Cretaceous Little Nahanni Pegmatite Group and associated rare-element mineralization in the Selwyn Basin area, Northwest Territories; in, Mineral and Energy Resource Assessment of the Greater Nahanni Ecosystem Under Consideration for the Expansion of the Nahanni National Park Reserve, Northwest Territories; Geological Survey of Canada, Open File 5344, p. 191-202.
Cecile, M.P. and Lane, L.S., 1991. Geology of the Barn Uplift; Geological Survey of Canada, Open File 2342.
Cecile, M.P., 1988. Corridor traverse through Barn Mountains, northernmost Yukon; in, Current Research, Part D; Geological Survey of Canada, Paper 88-1D, pp. 99-103.
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., 1997b. Geology of NTS 105-O/09 and northern part of Keele Peak map area (NTS 105-O/08); Geological Survey of Canada, Map 1902A. 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., 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., and Abbott, J.G., 1992. Geology of the Niddery Lake map area (NTS 105-O) at 1:250 000; Geological Survey of Canada, Open File 2465, 1 geological map (Scale 1:250 000) + 1 geological legend.
Gabrielse, H., 2003. Geology, Kechika River, British Columbia; Geological Survey of Canada, Open File 1633, 2 sheets.
Goodfellow, W.D., 2007. Base metal metallogeny of the Selwyn Basin, Canada; in, Goodfellow, W.D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, p. 553-579.
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.
Hofmann, H.J., Cecile, M.P., and Lane, L.S., 1994. New occurrences of Oldhamia and other trace fossils in the Cambrian of Yukon and Ellesmere Island, arctic Canada; Canadian Journal of Earth Sciences = Journal Canadien des Sciences de la Terre, vol. 31, no. 5 (May), pp. 767-782.
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.
Mair, J.L., Hart, C.J.R., and Stephens, J.R., 2006. Deformation history of the northwestern Selwyn Basin, Yukon, Canada: Implications for orogen evolution and mid-Cretaceous magmatism; Geological Society of America, Bulletin, v. 118, no. 3/4, p. 304-323.
Nelson, J. and Colpron, M., 2007. Tectonics and metallogeny of the British Columbia, Yukon and Alaskan Cordillera, 1.8 Ga to the present; in, Goodfellow, W.D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods; Geological Association of Canada, Mineral Deposits Division, Special Publication 5, p. 755-791.
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: LEXICON_BC
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 01 Dec 2010