Korak Formation
Stratigraphic label: [ppro]kk
Map symbol: pPkk

First published: 9 February 2016
Last modified:








Translation of original French




Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
Author: Lamothe, 2007
Age: Paleoproterozoic
Reference section: None
Type area: NTS sheets 35G04, 35H08, 25E04 and 25E05
Geological province: Churchill Province
Geological subdivision: Ungava Orogen / Ungava Trough / Southern Domain
Lithology: Detrital sedimentary rocks (arkosic sandstone, conglomerate)
Type: Lithostratigraphic
Rank: Formation
Status: Formal
Use: Active




This basal unit of the Povungnituk Group was originally described by Taylor (1982) and attributed by Moorhead (1989) to the Lamarche Subgroup (Lamothe et al., 1984), which was abandoned in this compilation. Despite its limited thickness and irregular distribution, the importance of this unit for the palinspastic reconstruction of the orogen was considered sufficient to elevate it to the rank of formation.




The Korak Formation is an allochthonous sedimentary unit located at the base of the Southern Domain. It forms the basal unit of the Povungnituk Group and consists of metre-thick lenticular beds of polymictic conglomerate and arkosic sandstone unconformably (angular discordance) lying on Archean bedrock (Taylor, 1982; Moorhead, 1989, 1996a, b; St-Onge and Lucas, 1993). North of Allemand Lake, sandstone overlies massive muscovite schist that Moorhead (1989) interpreted as paleoregolith. Bedrock underlying the Korak Formation has no visible Proterozoic deformation and, in some cases, retains an N-S foliation typical of the Archean craton (Moorhead, 1996a, b). Normal faults cutting both bedrock and its parautochthonous cover were observed locally (Moorhead, 1996b). The summital portion of the formation shows intense deformation associated with basal decollement of overlying allochthonous units (St-Onge et al., 1988; Lucas, 1989). Conglomerate pebbles are composed of granodiorite and hyaline quartz.



Thickness and Distribution

The Korak Formation is only exposed in a few locations at the base of the orogen, and is generally not visible on geological maps due to its limited thickness and discontinuous nature.



Stratigraphic Relationship(s)

Due to an angular discordance, the Korak Formation unconformably lies on Archean bedrock. With the exception of Burgoyne Bay erosion klippes (sheets 25E04 and 25E05), its summital portion is in thrust contact with overlying units of the Povungnituk Group. In the case of the Burgoyne Bay area, it appears that the Korak-Kuuvvaluk contact is transitional (St-Onge and Lucas, 1993). This contact is not visible at the current mapping 1:50 000 scale. The presence of the Korak Formation confirms that Archean rocks are indeed the basement upon which Povungnituk Group rocks were deposited, and that this platform extended at least to Burgoyne Bay. 


No fossils reported.


Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
LAMOTHE, D. Lexique stratigraphique de l’Orogène de l’Ungava. Ministère des Ressources naturelles, Québec; DV 2007-03, 62 pages. 2007
ST-ONGE, M.R. – LUCAS, S.B. Geology of the Eastern Cape Smith Belt: Parts of the Kangiqssujuaq, Cratère du Nouveau-Québec, and Lacs Nuvilik map areas, Quebec. Geological Survey of Canada; Memoir 438, 110 pages. 1993 Source
MOORHEAD, J. Géologie de la région du lac Chukotat, Fosse de l’Ungava. Ministère de l’Énergie et des Ressources, Québec; ET 87-10, 64 pages, 2 plans. 1989
TAYLOR, F.C. Reconnaissance geology of a part of the Canadian Shield, northern Quebec and Northwest Territories. Geological Survey of Canada; Memoir 399, 32 pages. 1982 Source



11 novembre 2019