Unit Name: Kuungmi Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Statherian - Ectasian (1800 - 1200 ma)
Age Justification: Geochronology and intrusive relationships. The Barrensland Group is constrained by a lower limit of 1720 ± 6 Ma (U-Pb radiometric age; Miller et al., 1989) for the Thelon Formation and an upper limit of 1276 Ma (LeCheminant and Heaman, 1989) for the Mackenzie diabase dykes which overlie the Barrensland Group (Peterson, 2006).
Province/Territory: Nunavut
Originator: Gall et al., 1992.
Distribution:
The Kuungmi Formation occurs within the Thelon basin and its outliers in the Nunavut-Northwest Territories. It is best exposed immediately northwest of an unnamed lake situated approximately 18 km southwest of Lookout Point on the Thelon River (Gall et al., 1992).
Locality Data:
Thickness(m): Typical 10.
Lithology:
Volcanic potassic tuff (Gall et al., 1992).
Relationship:
The Kuungmi Formation is the middle formation of the Barrensland Group. It overlies the Thelon Formation and is conformably underlain by the Lookout Point Formation. At the exposures revisited by Gall et al. (1992), they discovered contorted Thelon Formation sandstones, interpreted as soft sediment deformation structures, underlying thin (<1 m) amygdaloidal flows (Kuungmi Formation). Sandstones were also observed overlying the flows, limiting their total thickness to a few (<10) metres. Strong flow-top oxidation, abundant chalcedony in the vesicles, and a high content of hematite and oxidized "basalt" sand grains in the overlying sandstones indicate significant subaerial exposure. Similar mafic flows of uncertain stratigraphic position occur at the south end of Dubawnt Lake (Gall et al., 1992).
History:
During regional mapping of the central Thelon Plain, Donaldson (1969c) identified an aphanitic, green- to maroon-coloured "basalt" which overlies the Thelon Formation. Gall et al. (1992) revisited these exposures and proposed that the stratiform mappable volcanic unit be called the Kuungmi Formation. This name reflects the area of most extensive exposure in the centre of the Thelon Game Sanctuary. "Kuungmi Ujaqat Qanuittuuinga" is the Inuktituk term for "Thelon Game Sanctuary" (Inuit Cultural Institute, 1987) (Gall et al., 1992).
References:
Donaldson, J.A., 1969c. Descriptive notes (with particular reference to the Late Proterozoic Dubawnt Group) to accompany a geological map of central Thelon Plain, districts of Keewatin and Mackenzie (65M, N W1W2, 66 B, C, D, 75 P E1W2, 76A E1W2; Geological Survey of Canada, Paper 68-49, 4 p.
Gall, Q., Peterson, T.D. and Donaldson, J.A., 1992. Early Proterozoic stratigraphy of the Thelon and Baker lake basins, District of Keewatin: a proposed revision; in Current Research, Part C, Geological Survey of Canada Paper 92-1C, pages 129- 137.
Inuit Cultural Institute, 1987. ICI Inuktituk Glossary, Inuit Cultural Institute, Arviat, N.W.T.
LeCheminant, A.N. and Heaman, L.M., 1989. Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening; Earth and Planetary Science Letters, v. 96, p. 38-48.
Miller, A.R., Cumming, G.L., and Krstic, D., 1989. U-Pb, Pb-Pb, and K-Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada; Canadian Journal of Earth Sciences, v. 26, p. 867-880.
Peterson, T.D., 2006. Geology of the Dubawnt Lake area, Nunavut-Northwest Territories; Geological Survey of Canada, Bulletin 580; 56 p.
Source: Murray Frarey's Precambrian Lexicon
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 19 Nov 2010