Unit Name: Horn River Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Middle Devonian - Late Devonian (397.5 - 359.2 ma)
Age Justification: Brachiopods, conodonts, tentaculitids (Emanuella sp., Leiorhynchus cf. castanea (Meek), Styliolina sp., Tentaculites sp. (A.W. Norris in Brideaux et al. 1976), Polygnathus dengleri, P. asymmetricus ovalis (from Fuller and Pollock, 1972).
Province/Territory: British Columbia; Northwest Territories

Originator: Whittaker, 1922 (Horn River shales); redefined by Douglas and A.W. Norris, 1960; subsurface definition by Gray and Kassube, 1963.

Type Locality:
Outcrop on Horn River, District of Mackenzie (Whittaker, 1922). 61 deg 44'N, 117 deg 45'W, West Nat. et al., Fort Nelson a-95-J, 94-J-10, 1,984.2-2215.9 m (6,510 to 7,270 ft) (Gray and Kassube, 1963).

Distribution:
As defined by Gray and Kassube (1963) the formation lies within a belt only a few kilometres wide immediately northwest of the Shekelie Barrier-complex (Middle Devonian), from northeastern British Columbia to Great Slave Lake, N.W.T. Along its southeastern margin the formation thickness is approximately equal to the height of the barrier-complex - up to 320 m (1,050 ft) in the Fort Nelson area; the formation thins to only a few tens of metres northwestward from the barrier-complex.

Lithology:
Dark coloured argillaceous limestone, often bituminous; grey, green, brown and black shale, variably calcareous, often siliceous. In northeastern B.C. Gray and Kassube (1963) subdivided the Horn River Fm in the subsurface into 1) the Evie Member (lowest) black micritic, silty limestone; 2) Otter Park Member (middle), grey calcareous shale; and 3) Muskwa Member (upper) bituminous highly radioactive shale.

Relationship:
As defined by Gray and Kassube (1963) the formation is overlain by the Fort Simpson Fm and underlain by carbonate rocks equivalent to the Keg River platform (Lonely Bay, Nahanni, Pine Point formations). It is equivalent to all of the Shekelie Barrier-complex (Middle Devonian), including the Slave Point Fm, and also includes the Muskwa Fm or Member, and the Waterways Member of Hay River Fm. Other definitions describe the top of the Horn River Fm as unconformable, below the Fort Simpson Fm (Belyea and A.W. Norris, 1962) or below the Muskwa Fm (Griffin, 1965). The term "Horn River" has also been applied to dark siliceous shales below the Fort Simpson Fm and above the Nahanni or Hume formations in the N.W.T. as far north as the Norman Wells area (Douglas and D. K. Norris, 1963; Douglas, 1970). The Muskwa Member is approximately equivalent to the Canol Fm to the north (A.W.N.). The Horn River Fm encloses the pinnacle reefs of the Horn Plateau Fm.

Other Citations:
Belyea and A.W. Norris, 1962; Brideaux et al. 1976; Chatterton, 1978; Douglas, 1970; Douglas and A.W. Norris, 1960; Douglas and D.K. Norris, 1963; Fuller and Pollock, 1972; Gray and Kassube, 1963; Griffin, 1965; Law, 1971; Whittaker, 1922; G.K. Williams, 1977a, 1977b.

Source: GEOLOGICAL SURVEY OF CANADA, CALGARY
Contributor: G.K. Williams; D.W. Morrow
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 04 Nov 2004