Unit Name: Flett Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: late Tournaisian - late Visean, V3 (349.9 - 328.3 ma)
Age Justification: Pelmatozoans, sponge spicules, bryozoans and brachiopods are the predominant fossils, but foraminifers and corals are locally common in the upper two thirds of the Flett. Scattered macroscopic plant remains exist in some sandstone intervals, scolecodonts and palynomorphs.
Province/Territory: Northwest Territories
Originator: Harker, 1961.
Type Locality:
West side of Yohin Ridge immediately north of Jackfish Gap, 32 km (20 mi) west of Nahanni Butte, southwest District of Mackenzie (61 deg 06'N, 123 deg 55'W).
Distribution:
Moderately widely distributed in southwest District of Mackenzie in the southernmost Mackenzie Mountains and on the immediately adjacent Interior Platform. However, its distribution is controversial and not well established because the Mississippian formational nomenclature used in the region and the definition of the Flett require revision. The type section is about 474 m (1,555 ft) thick and known thicknesses range between 0 and 867 m (2,845 ft).
Lithology:
Principally skeletal lime packstone and siliceous spiculites. Significant proportions are skeletal lime grainstone, shale and marlstone; dolomite is common at the top of the unit, and sandstone and siltstone occur in the middle Flett north of 60 deg 50'N. The proportion of lime grainstone and packstone increases upward and eastward, but that of the shales, spiculites and marlstones decreases. Much of the Flett comprise cycles in which limestone turbidites either become thicker and closer spaced upward or the converse. The principal sedimentary structures are graded beds, megascale intraformational truncation surfaces, horizontal laminations, ripple cross-bedding and sole marks.
Relationship:
In the southern Mackenzie Mountains, the Flett conformably overlies the Clausen and Besa River formations and is conformably overlain by the Mattson. Eastward its relationship to underlying units are not well known, but it is mainly unconformably overlain by the Fantasque Fm and Fort St. John Group. Lateral equivalents of the Prophet, Debolt, Golata and "Shunda" formations are in the Flett.
Other Citations:
Bamber and Mamet 1978; Bamber et al., 1968; Bamber et al., in prep; Braman and Hills, 1977a; Douglas, 1976a; Douglas and D.K. Norris, 1959, 1977a, 1977b; Douglas et al., 1970; Harker 1961, 1963; Mamet and Skipp, 1970; Nassichuk and Bamber, 1978; Patton, 1958; Pelzer, 1966; Richards, 1978; Sutherland, 1958.
Source: CSPG Lexicon of Canadian Stratigraphy, Volume 2, Yukon Territory and District of Mackenzie; L.V. Hills, E.V. Sangster and L.B. Suneby (editor)
Contributor: L.V. Hills; B.C. Richards
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 29 Apr 2003