|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)|
Table des matières
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.
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.
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.