Type Locality:

Horn River (Meijer Drees, 1993).

Lithology:

Shale, bituminous, black; local interbeds of limestone, bituminous, shaly; marine, slope and basin (Okulitch, 2006).

Relationship:

The Horn River Group consists of the Middle Devonian Hare Indian Formation (black and grey shales), with its lateral facies equivalent, the Ramparts Formation (platform and reef limestones, siltstone, sandstone) and the Upper Devonian Canol Formation (black pyritic shale) (Pugh, 1983). It also includes a lower unit of black shale (the Evie Formation), a middle unit of interbedded limestone and shale (the Otter Park Formation), and an upper unit of black shale (the Muskwa Formation (or Member)). The Spence River Formation is equivalent to the upper part of the Horn River Formation of Belyea and Norris (1962) and Gray and Kassube (1963) and partly equivalent to the Muskwa Formation of Griffin (1965). The Muskwa Formation is equivalent to the Waterways Member (or Formation) of the Hay River Formation. The group is overlain by either the Imperial, Fort Simpson or Hay River formations. It is underlain by the Hume, Nahanni, Lonely Bay and Slave Point formations, and Pine Point Assemblage (Meijer Drees, 1993).

History:

The name Horn River Shale was used by Whittaker (1922) to describe dark coloured shale beds discontinuously exposed along Horn River for a distance of about 15 km (air distances) upstream from the confluence of Ferguson Creek and Horn River. Whittaker (1922, p. 52b) rightly referred the fossiliferous limestone beds, which locally overlie the Horn River Shale, to the Pine Point Formation. The beds underlying the shale are not exposed, and Whittaker left the lower boundary of the Horn River Shale undefined. He reported a thickness of more than 18 m (59 ft.). Norris (1965a, p. 42) estimated the thickness of the exposed beds to be only 10.6 m (35 ft.). Belyea and Norris (1962) introduced the map unit in the subsurface and defined the Horn River Formation as a unit consisting largely of dark shale variably interbedded with limestone, which overlies limestone of the Lonely Bay Formation or the lower part of the Pine Point Formation, and is either overlain by green shale of the Fort Simpson or Hay River formations, or, locally, near Horn Plateau, by reefoid limestone of the Horn Plateau Formation (Norris, 1965a). The description of the lower and upper contacts of the Horn River Formation was based on an interpretation of subsurface information. Belyea and Norris (1962) correlated the Horn River Formation with the Spence Fiver Formation of Hunt (1954) in the NWT Westerol 7A well and also used the term Horn River in the subsurface of northeastern British Columbia. Gray and Kassube (1963) accepted the Horn River Formation as used by Belyea and Norris (1962) and described the formation in the subsurface of northeastern British Columbia. They recognized three members, and selected type sections for the members in the West Nat. et al. Fort Nelson a-95-j well, in northeastern British Columbia. In the Fort Nelson area, the Horn River Formation includes a lower unit of black shale (the Evie Member), a middle unit of interbedded limestone and shale (the Otter Park Member), and an upper unit of balck shale (the Muskwa Member). The Elvie Member overlies the lower part of the Pine Point Assemblage and grades laterally into the middle part of the Pine Point Assemblage; the Otter Park Member appears to grade laterally into the upper part of the Pine Point, and into the Sulphur Point, Watt Mountain and Slave Point formations. The Muskwa Member overlies the Otter Park Member or the Slave Point Formation. Griffin (1965) showed that the Muskwa Member is widely distributed in northeastern British Columbia and northern Alberta and that its distribution is not related to the distribution of the other two members of the Horn River Formation. In this region, the Muskwa Member also overlies the Beaverhill Lake Group. Griffin (op. cit.) thus postulated the presence of an unconformity beneath the Muskwa Member and elevated it to formational status. Thus one may also give the Elvie Lake and Otter Park formation satus and regard the Horn River as a group (Pugh, 1983) (Meijer Drees, 1993).

Remark:

In summary, the name Horn River has been given a variety of seemingly different meanings: Whittaker (1922) - shales only at type locality; Douglas and Norris (1960a) - redefined to Whittaker's shales plus overlying limestone; Belyea and Norris (1962) - a) black shale; b) threefold, black shale-greenish grey shale-black shales; Gray and Kassube (1963) - threefold, Evie-Otter Park-Muskwa Members in British Columbia, spans Givetian-Famennian boundary; Douglas and Norris (1963) - dark grey to black shales, siltstones, sandstones, 62°-64°N; Griffin (1965) - reduced to twofold, Evie-OtterPark in British Columbia (unacceptable according to Code); Douglas (1970) - bituminous shales, dark limestones and greenish grey shales; - black pyritic shale = Evie + Otter Park + Muskwa = Hare Indian + Ramparts + Canol Formations, 65°N. (Pugh, 1983).

References:

Belyea, H.R. and Norris, A.W., 1962. Middle Devonian and older Palaeozoic formations of southern District of Mackenzie and adjacent areas; Geological Survey of Canada, Paper 62-15, 82 p.

Douglas, R.J.W. (Ed.), 1970. Geology and Economic Minerals of Canada: Geological Survey of Canada, Economic Geology Report, no. 1, 5th edition, 838 p.

Douglas, R.J.W. and Norris, A.W., 1960a. Horn River Map area, Northwest Territories; north halves of 85 and 95 (parts of); Geological Survey of Canada, Paper 59-11, 23 p.

Douglas, R.J.W. and Norris, D.K., 1963. Dahadinni River and Wrigley map-areas, District of Mackenzie, Northwest Territories; Geological Survey of Canada, Paper 62-33, 34 p.

Gray, F.F. and Kassube, J.R., 1963. Geology and stratigraphy of Clarke Lake Gas Field, British Columbia; America Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 47, no. 3 (March), pp. 467-483.

Griffin, D.L., 1965. The facies front of the Devonian Slave Point - Elk Point sequence in northeastern British Columbia and the Northwest Territories; Journal of Canadian Petroleum Techology, vol. 4, no. 1, pp. 13-22.

Hunt, C. Warren, 1954. Normal Devonian sequence in southern Mackenzie Basin, Western Canada; The American Association of Petroleum Geologists (AAPG), AAPG Bulletin, vol. 38, no. 11 (November), pp. 2290-2301.

Meijer Drees, N.C., 1993. The Devonian succession in the subsurface of the Great Slave and Great Bear plains, Northwest Territories; Geological Survey of Canada, Bulletin 393, 231 pages.

Norris, A.W., 1965a. Stratigraphy of Middle Devonian and older Paleozoic rocks of the Great Slave Lake region, Northwest Territories; Geological Survey of Canada, Memoir 322, 180 p.

Okulitch, A.V., 2006. Phanerozoic bedrock geology, Slave River, District of Mackenzie, Northwest Territories; Geological Survey of Canada, Open file 5281, Map Scale 1: 1 000 000.

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.

Whittaker, E.J., 1922. Mackenzie River District between Great Slave Lake and Simpson, Northwest Territories; Geological Survey of Canada, Summary Report 1921, Part B, pp. 45-55, with Map 1956, Mackenzie River District between Great Slave Lake and Simpson, Northwest Territories, Scale: 1 in. to 8 m. (see also Map 1585, Mackenzie River Basin, Scale 1 in. to 50 m.).