Type Locality:

The type section, exposed in the core of the Muskwa River anticline along an unnamed stream and on a ridge to the east, lies 6.4 km (4 mi) north of the Muskwa River; 57 deg 56'30"N, 123 deg 43'W, NTS 94G/13; western Rocky Mountain Foothills, northeastern British Columbia (Kidd, 1963; Taylor and MacKenzie, 1970).

Distribution:

The Besa River Formation is widely distributed from 54 deg 45'N in east-central British Columbia into southwestern District of Mackenzie (Pelzer, 1966; Taylor and MacKenzie, 1970; Taylor and Stott, 1973; Bamber and Mamet, 1978; McMechan, 1987; Thompson, 1989, Richards et al., in press). It is preserved mainly in the eastern Rocky Mountain Thrust Belt and southern Mackenzie Fold Belt, but in the northeast it is present on the western Interior Platform. The Besa River, up to 1,655 m (5,428 ft) thick (Richards, 1989, Table 1) is generally thickest in the foothills and on the extreme western part of the Interior Platform. Westward of this narrow belt there is a marked decrease in thickness (Pelzer, 1966; Bamber et al., 1968; Richards, 1989, Table 1). At the type section, where about 823 m (2700 ft) of Besa River are exposed (Pelzer, 1966), the lower part of the formation is folded, faulted and mainly covered.

Lithology:

A dark-shale lithofacies constitutes most of the Besa River Formation, but a spiculite lithofacies occurs in the upper part from east-central British Columbia into southwestern District of Mackenzie. In addition there is a sandstone and shale facies in the upper Besa River of northeastern British Columbia and southeastern Yukon and in the lower Besa River of the Rockies from about 55 deg 00'N to 55 deg 50'N (Pelzer, 1966; Bamber et al., 1968; Bamber and Mamet, 1978; Richards et al., in press). In the Rocky Mountains of east-central British Columbia the lower Besa River contains a resistant unit of brown weathering nodular, argillaceous limestone (McMechan, 1987). The dark-shale lithofacies, which generally underlies and grades eastward into the other facies is mainly dark grey to black, slightly calcareous to siliceous shale containing sponge spicules and radiolarians. At the type section most of the shale is calcareous, buff weathering and assembles that of the Banff Formation with which it is partly coeval. Macrofossils are rare in this lithofacies, and sideritic bands and nodules are locally common. Spiculite, bedded chert and spicule-rich carbonates constitute the spiculite lithofacies. All of these deposits are commonly intercalated with the dark-shale facies and occur as tongues that thin basinward (southwestward). The shale and sandstone facies consists of silty to sandy shale and mudstone interbedded with subordinate siltstone and sandstone turbidites and slump deposits. This lithofacies also locally contains plant bearing conglomerate (Muller, 1967, p. 80; Richards, in press).

Relationship:

From southeast to northwest the lower contact of the Besa River becomes progressively older as the upper contact becomes younger. This reflects a lateral change from carbonate and sandstone dominated formations in the east to shale, mudstone and spiculite in the west (Taylor and Stott, 1973). In most of the region south of 60 deg N the Besa River abruptly overlies the Devonian (Eifelian to Givetian) Dunedin Formation, but in the eastern part of this southern area it locally overlies the upper Givetian Slave Point Formation. West of the basinward depositional limit of the Dunedin the Besa River overlies upper Eifelian deposits of the Road River Formation and, locally, Emsian carbonates of the Stone Formation. North of 60 deg N the Besa River generally overlies the Road River in the west and Givetian deposits of the Nahanni Formation in the east (Taylor and MacKenzie, 1970; Douglas and Norris, 1976; Morrow and Geldsetzer, 1988; Bamber et al., 1968). The Besa River passes eastward to southeastward into Middle Devonian (Givetian) to upper Lower Carboniferous (Visean and Serpukhovian) strata (Pelzer, 1966; Bamber et al., 1968; Taylor and MacKenzie, 1970; Morrow and Geldsetzer, 1988; Richards, 1989; Richards et al. in press). In southwestern District of Mackenzie and northernmost British Columbia the formation passes into the Devonian Fort Simpson, Imperial and Exshaw formations. In the region to the south the Besa River passes eastward into the Devonian Dunedin, Horn River and Exshaw formations. The Besa River passes eastward into the Lower Carboniferous Banff, Yohin, Clausen, Golata and Mattson formations and into the Rundle and Stoddart groups. In the east most of the Besa River is gradationally overlain by the middle Tournaisian to upper Visean Prophet Formation. The eastern Besa River of east-central British Columbia is locally gradationally overlain by middle Tournaisian carbonates of the Banff Formation and, locally, in District of Mackenzie the formation is gradationally overlain by the Yohin Formation. West of the basinal depositional limit of the Prophet sandstone of the Mattson Formation and Stoddart Group conformably overlie the Besa River. Permian strata locally unconformably overlie the western Besa River of British Columbia (Bamber et al., 1968; Pelzer, 1966; Richards, 1989; Richards et al., in press). The Besa River is lithologically and stratigraphically equivalent to the western Fort Simpson Formation as mapped by Douglas and Norris (1976), the Canol Formation (Bassett, 1961), and the Earn Group (Campbell, 1967). Its boundaries with the eastern Earn and the Fort Simpson are arbitrary and poorly known.

History:

The upper part of the type section sensu Kidd (1963) includes strata assignable to Sutherland's (1958) lower member A of the Prophet Formation. Bamber and Mamet (1978) recognized this problem and placed the top of the type Besa River at the base of the Prophet, but they did not formally restrict the stratotype. In southeastern Yukon and southwestern District of Mackenzie part of the succession that Harker (1961; 1963) assigned to the Etanda Formation in the region west of the La Biche syncline axis belongs to the Besa River. All deposits that Harker (1961, 1963) and Douglas et al. (1963) placed in the Etanda were included in the Besa River by Douglas (1976) and Bamber et al. (1984). However, Harker (1961, 1963) and Douglas et al. (1963) included Prophet and Golata equivalents in the Etanda at its type locality and in much of the La Biche syncline to the south. Richards (1989) abandoned the name Etanda Formation because that formation included the Besa River and other formations that had priority of publication.

Other Citations:

Bamber, Macqueen and Richards, 1984; Bamber and Mamet, 1978; Bamber, Taylor and Proctor, 1968; Bassett, 1961; Campbell, R.B., 1957; Douglas, 1976; Douglas, Harker and Norris, 1963; Douglas and Norris, 1976; Harker, 1961, 1963; Kidd, 1962, 1963; McMechan, 1987; Morrow and Geldsetzer, 1988; Muller, 1967; Pelzer, 1966; Richards, 1989; Richards et al., in press; Sutherland, 1958; Taylor and MacKenzie, 1970; Taylor and Stott, 1973; Thompson 1989.

References:

Bamber, E.W., Taylor, G.C., and Procter, R.M., 1968. Carboniferous and Permian stratigraphy of northeastern British Columbia; Geological Survey of Canada, Paper 68-15, 25 p.

Kidd, F.A., 1963. The Besa River Formation: Bulletin of Canadian Petroleum Geology, vol. 11, no. 4, pp. 369-372.

McMechan, M.E., 1987. "Stratigraphy and structure of the Mount Selwyn area, Rocky Mountains, northeastern British Columbia"; Geological Survey of Canada, Paper 85-28.

Pelzer, E.E., 1966. Mineralogy, geochemistry, and stratigraphy of the Besa River Shale, British Columbia; Canadian Society of Petroleum Geologists (CSPG), Bulletin of Canadian Petroleum Geology, vol. 14, no. 2 (June), pp. 273-321.

Taylor, G.C. and MacKenzie, W.S., 1970. Devonian stratigraphy of northeastern British Columbia; Geological Survey of Canada, Bulletin 186, 62 p.