First published: 26 August 2019
Last modified: 29 March 2021
DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
| Author(s): | Wares and Goutier, 1990a |
| Age: | Paleoproterozoic |
| Stratotype: | None |
| Type area: | Strip between Dupoisson Lake to the south (NTS sheet 24C) and Roberts Lake to the north (sheet 25D) |
| Geological province: | Churchill Province |
| Geological subdivision: | New Quebec Orogen (Labrador Trough) |
| Lithology: | Flysch, iron formation and basalt |
| Category: | Lithostratigraphic |
| Rank: | Group |
| Status: | Formal |
| Use: | Active |
Background
Wares and Goutier (1989) initially proposed the informal name « Gerido Group » to group the Abner, Baby and Hellancourt formations (Bérard, 1965; Sauvé and Bergeron, 1965), which are located in the northern part of the Labrador Trough. These units were previously assigned to a third volcano-sedimentary cycle that was thought to overlie the platform of the second cycle of the orogen (Bérard, 1965; Sauvé and Bergeron, 1965; Dimroth, 1970; Dimroth et al., 1970). The discovery of a major thrust fault (Garigue Fault) underlying the Abner Formation (Clark, 1979; Goulet, 1986) led to a reinterpretation of the stratigraphy of the northern part of the orogen, thus refuting the third sedimentation cycle (Fournier, 1985; Clark, 1988; Clark and Thorpe, 1990). At that time, Hoffman and Grotzinger (1989) suggested that the Abner Formation was equivalent to the Denault Formation of the first volcano-sedimentary cycle, observed in the southern part of the orogen. Subsequently, Wares and Goutier (1990a) proposed the name Koksoak Group, named after the Koksoak River, to refer to the Abner-Baby-Hellancourt sequence, and used the name « Gerido » instead to refer to a regional structural domain. Following a reinterpretation of the stratigraphic column in the northern part of the Trough, the name « Koksoak Group » was adopted to group the Baby and Hellancourt formations, and the name « Abner Formation » was abandoned, as the unit is equivalent to the Denault Formation (Attikamagen Group) of the first sedimentary cycle (Clark and Wares, 2004).
Description
The Koksoak Group is an allochthonous volcano-sedimentary unit belonging to the second cycle of the Labrador Trough. It comprises turbiditic and iron-bearing units of the Baby Formation at the base, directly overlain by basalts of the Hellancourt Formation at the top. The Koksoak Group is thought to have been deposited in a basin east of the Ferriman Group platform sequence (Clark and Wares, 2004). Facies variations in sedimentary units of the lower Koksoak Group are indicative of a depositional environment in a progressively deepening basin from west to east (Clark, 1988; Goutier and Wares, 1991; Wares et al., 1988; Wares and Goutier, 1990a). The upper part of the Koksoak Group is marked by tholeiitic volcanism associated with a rifting episode (Rohon et al., 1993; Skulski et al., 1993). Skulski et al. (1993) also suggested that tholeiitic volcanism developed in pull-apart basins. Rocks of the Koksoak Group form a highly deformed and imbricated belt, associated with a basal detachment plane, and cut by numerous thrust faults (Wares and Goutier, 1990a, 1990b; Goulet, 1995). The degree of metamorphism of Koksoak Group rocks varies from greenschist facies in the west to amphibolite facies in the east and at the northern end of the Trough (Dimroth and Dressler, 1978; Fraser et al., 1978).
Thickness and distribution
The Koksoak Group extends over 400 km in a NNW orientation in the northern part of the Labrador Trough, between Dupoisson Lake in the south (sheet 24C) and Roberts Lake in the north (sheet 25D). It is adjacent to the western boundary of the Rachel-Laporte Lithotectonic Domain, which represents the eastern part of the New Quebec Orogen. According to estimates by Sauvé and Bergeron (1965), the Koksoak Group is ~50 km wide and 2100 to 2600 m thick near latitude 58 °N. The unit thins towards the south and north of latitude 59° N. The Koksoak Group is preserved in the Mélèzes, Gerido and Payne lithotectonic zones as defined by Clark and Wares (2004).
Dating
None.
Stratigraphic Relationship(s)
The Koksoak Group was deposited between 1.88 Ga and 1.87 Ga, the age of the second depositional cycle of the Labrador Trough (Clark and Wares, 2004). Considering that the Koksoak Group is the distal equivalent of the Ferriman Group, these two groups would be of the same age (Clark, 1988; Clark and Wares, 2004).
The base of the Koksoak Group, the lower unit of the Baby Formation, is in gradual contact with the underlying Denault Formation (Bérard, 1965; Sauvé and Bergeron, 1965; Clark, 1988; Wares et al., 1988; Clark and Wares, 2004). The Hellancourt Formation forms the top of the Koksoak Group (Wares et al., 1988; Wares and Goutier, 1989). Near latitude 57 °N, the Koksoak and Doublet groups are interdigitated and locally overlain by a carbonatite intrusion accompanied by volcano-sedimentary rocks belonging to the Le Moyne Group (Birkett and Clark, 1991; Machado et al., 1997; Clark and Wares, 2004). At the northern end of the orogen, the Hellancourt Formation structurally overlies (thrust contact) the Ferriman Group (Clark and Wares, 2004). The Koksoak Group can be correlated with the Ferriman Group in the northern part of the orogen, and with the Le Moyne and Doublet groups in the south-central and southern parts of the Trough (Clark, 1988; Clark and Thorpe, 1990; Rohon et al., 1993; Clark and Wares, 2004). The Koksoak Group is generally bounded to the east by a dextral oblique thrust fault separating it from the Laporte Supersuite. The latter possibly represents an equivalent of the Koksoak Group (Simard et al., 2013). Numerous mafic-ultramafic sills belonging to the Gerido Intrusive Suite (formerly Montagnais Sills) intrude both the Baby and Hellancourt formations (Sauvé and Bergeron, 1965; Clark and Wares, 2004).
Paleontology
Does not apply.
References
Publications Available Through SIGÉOM Examine
BERARD, J., 1965. REGION DU LAC BERARD, NOUVEAU-QUEBEC. MRN; RG 111, 175 pages, 2 plans.
CLARK, T., 1979. REGION DU LAC NAPIER (NOUVEAU-QUEBEC) – RAPPORT PRELIMINAIRE. MRN; DPV 663, 28 pages, 1 plan.
CLARK, T., 1987. STRATIGRAPHIE, PETROGRAPHIE ET PETROCHIMIE DE LA FORMATION DE FER DE BABY DANS LA REGION DU LAC HERODIER (FOSSE DU LABRADOR). MRN; ET 87-13, 44 pages.
CLARK, T., WARES, R., 2004. SYNTHESE LITHOTECTONIQUE ET METALLOGENIQUE DE L’OROGENE DU NOUVEAU-QUEBEC (FOSSE DU LABRADOR). MRNFP; MM 2004-01, 182 pages, 1 plan.
DIMROTH, E., 1978. Région de la fosse du Labrador entre les latitudes 54° 30′ et 56° 30′. MRN; RG 193, 417 pages, 16 plans.
FOURNIER, D., 1985. MINERALISATION DE LA PARTIE ORIENTALE DU GEOSYNCLINAL DU LABRADOR (GROUPE DE LAPORTE). MRN; ET 83-23, 57 pages, 4 plans.
GOULET, N., 1986. ETUDE TECTONIQUE ET STRATIGRAPHIQUE DE LA PARTIE NORD DE LA FOSSE DU LABRADOR – REGION DE LA BAIE AUX FEUILLES ET DU LAC BERARD. MRN; MB 86-27, 22 pages, 6 plans.
GOULET, N., 1995. ETUDE STRUCTURALE, STRATIGRAPHIQUE ET GEOCHRONOLOGIQUE DE LA PARTIE NORD DE LA FOSSE DU LABRADOR. MRN; MB 95-36, 41 pages, 1 plan.
GOUTIER, J., WARES, R., 1991. GEOLOGIE DU SECTEUR DE L’INDICE AURIFERE DESSUREAULT, FOSSE DU LABRADOR – RAPPORT INTERIMAIRE -. MRN; MB 91-10, 20 pages, 2 plans.
SAUVE, P., BERGERON, R., 1965. REGION DES LACS GERIDO ET THEVENET, NOUVEAU-QUEBEC. MRN; RG 104, 141 pages, 3 plans.
SAUVE, P., BERGERON, R., 1965. GERIDO LAKE – THEVENET LAKE AREA, NEW QUEBEC. MRN; RG 104(A), 131 pages, 3 plans.
SIMARD, M., LAFRANCE, I., HAMMOUCHE, H., LEGOUIX, C., 2013. GEOLOGIE DE LA REGION DE KUUJJUAQ ET DE LA BAIE D’UNGAVA (SNRC 24J, 24K). MRN; RG 2013-04, 62 pages, 1 plan.
WARES, R., BERGER, J., ST-SEYMOUR, K., 1988. SYNTHESE METALLOGENIQUE DES INDICES DE SULFURES AU NORD DU 57e PARALLELE (ETAPE 1) – FOSSE DU LABRADOR -. I R E M; MB 88-05, 202 pages, 1 plan.
WARES, R., GOUTIER, J., 1989. METALLOGENIE DES INDICES DE SULFURES AU NORD DU 57e PARALLELE (ETAPE II) – FOSSE DU LABRADOR -. MRN; MB 89-38, 122 pages, 1 plan.
WARES, R., GOUTIER, J., 1990. SYNTHESE METALLOGENIQUE DES INDICES DE SULFURES AU NORD DU 57e PARALLELE – FOSSE DU LABRADOR – RAPPORT INTERIMAIRE – ETAPE III. IREM-MERI; MB 90-25, 104 pages, 2 plans.
Other Publications
BIRKETT, T.C., CLARK, T. 1991. Géologie et potentiel métallifère de la carbonatite protérozoïque du lac LeMoyne dans le nord du Québec. Geological Survey of Canada; Work in Progress Forum, Programme and Abstracts,, page 20.
CLARK, T., THORPE, R.I. 1990. Model lead ages from the Labrador Trough and their stratigraphy implications. In The Early Proterozoic Trans-Hudson Orogen of North America: Lithotectonic Correlations and Evolution (J.F. Lewry, J.F. and M.R. Stauffer, editors). Geological Association of Canada; Special Paper 37, pages 413-432.
DIMROTH, E. 1970. Evolution of the Labrador Geosyncline. Geological Society of America Bulletin; volume 81, pages 2717-2742. https://doi.org/10.1130/0016-7606(1970)81[2717:EOTLG]2.0.CO;2
DIMROTH, E., BARAGAR, W.R.A., BERGERON, R., JACKSON, GD. 1970. The filling of the Circum-Ungava geosyncline. In Symposium on Basins and Geosynclines of the Canadian Shield (A.J. Baer, editor). Geological Survey of Canada; Paper 70-40, pages 45-142. https://doi.org/10.4095/124922
DIMROTH, E., DRESSLER, B. 1978. Metamorphism of the Labrador Trough. In Metamorphism in the Canadian Shield. Geological Survey of Canada; Study 78-10, pages 215-236. https://doi.org/10.4095/104534
FRASER, J.A., HEYWOOD, W.W., MAZURSKI, M.A. 1978. Carte métamorphique du Bouclier Canadien. Geological Survey of Canada; Map 1475A. https://doi.org/10.4095/133909
HOFFMAN, P., GROTZINGER, J.P. 1989. Abner-Denault reef complex (2.1 Ga), Labrador Trough, N.E. Québec. In Reefs, Canada and Adjacent Area (H.H.J. Geldsetzer, N.P. James, and GE. Tebbutt, editors). Canadian Society of Petroleum Geologists; Memoir 13, pages 49-54.
MACHADO, N., CLARK, T., DAVID, J., GOULET, N. 1997. U-Pb ages for magmatism and deformation in the New Quebec Orogen. Canadian Journal of Earth Sciences; volume 34, pages 716-723. https://doi.org/10.1139/e17-058
ROHON, M.-L., VIALETTE, Y., CLARK, T., ROGER, G, OHNENSTETTER, D., VIDAL, P. 1993. Aphebian mafic-ultramafic magmatism in the Labrador Trough (New Quebec): its age and the nature of its mantle source. Canadian Journal of Earth Sciences; volume 30, pages 1582-1593. https://doi.org/10.1139/e93-136
SKULSKI, T., WARES, R.P., SMITH, A.D. 1993. Early Proterozoic (1.88-1.87) tholeiitic magmatism in the New Québec Orogen. Canadian Journal of Earth Sciences; volume 30, pages 1505-1520. https://doi.org/10.1139/e93-129
WARES, R., GOUTIER, J. 1990b. Deformational style in the foreland of the Northern New Québec Orogen. Geoscience Canada; volume 17, pages 244-249. https://journals.lib.unb.ca/index.php/GC/article/view
Suggested Citation
Ministère de l’Énergie et des Ressources naturelles (MERN). Koksoak Group. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-de-churchill/groupe-de-koksoak_en [accessed on Day Month Year].
Contributors
|
First publication |
Charles St-Hilaire, GIT, M.Sc. charles.st-hilaire@mern.gouv.qc.ca (redaction) Mehdi A. Guemache, P. Geo., Ph.D. (redaction and coordination); Thomas Clark, P. Geo., Ph.D. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Marie-Ève Lagacé and Nathalie Bouchard (HTML editing). |