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Hubert Formation
Stratigraphic label: [ppro]hbt
Map symbol: pPhbt
 

First published: 23 October 2020
Last modified:

 

 

 

 

 

 

  DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail. 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
None
 
Author: Beaudette et al., 2020
Age: Paleoproterozoic
Stratotype: Reference outcrop 19-GL-2108 is located north of Katsuaq Lake
Type area: Bélanger Lake area, Nunavik (NTS sheet 35G06)
Geological province: Churchill Province
Geological subdivision: Ungava Orogen / Southern Domain
Lithology: Clastic sedimentary rocks (conglomerate and arenite)
Category: Lithostratigraphic
Rank: Formation
Status: Formal
Use: Active

 

 

Background

Beaudette et al. (2020) introduced the Hubert Formation to individualize sedimentary beds unconformably overlying (angular discordance) the Chukotat Group. These beds had already been mentioned by Roy (1989), Moorhead (1989) and Barrette (1990b), without, however, recognizing the angular unconformity observed more recently (Beaudette et al., 2020).

 

 

Description

The Hubert Formation consists of coarse silicoclastic beds of pebble conglomerate and sandstone having a brick-red patina and fresh surface. The presence of conglomerate beds and thin (4-40 cm) sandstone beds displaying parallel laminae, as well as the absence of fine deposits, imply a proximal energetic deposition environment probably of fluvial origin. Parallel laminations and several erosion surfaces allow the measurement of primary bedding with normal polarity towards the NW. The Hubert Formation is not magnetic.

 

Polymictic conglomerate contains joint fragments; the proportion of the sandy matrix is <20% and generally almost non-existent. Fragments are 5 mm to 25 mm in size. They consist mostly of angular reddish aphanitic volcanic rock fragments (20-90%), subangular to subrounded aphanitic or very fine-grained greenish grey rock fragments interpreted as being of volcanic origin (up to 15%) and, in smaller amounts, subrounded milky chert fragments (up to 5%), rounded massive gabbro fragments (up to 5%) and subrounded to rounded massive or foliated intermediate to felsic intrusive rock fragments (0-15%). Clastic sequences display normal sorting towards the NW. They consist of conglomerate covering a thickness of 50 cm to 2 m at the base and overlain by a sandstone bed 5 cm to 40 cm thick. The latter is generally truncated by the erosion surface of the next sequence.

 

In thin section, arenite is composed of an assemblage of subangular quartz and rarely twinned feldspar grains (50%), chlorite (30%) and interstitial carbonates (5%), as well as disseminated hematite (10%) and epidote (10%), as well as trace amounts of muscovite flakes. Epidote is heterogeneously distributed, either disseminated in the matrix or in clusters.

Conglomerate is characterized by a very low spaced schistosity defined by the local orientation of fragments and muscovite flakes observed in thin section. The difference between primary bedding (245°) and foliation (260°) is 15°.

The unconformity carries native copper mineralization (Dryade mineralized zone).

 

Thickness and Distribution

The Hubert Formation outcrops as elongated sedimentary basins of modest dimensions with a surface area of ≤1 km2. Outcrops are located at the structural and stratigraphic summit of the Chukotat Group, directly south of the boundary between the Northern and Southern domains, in the wall of the Bergeron Fault. The true thickness of the formation observed on outcrop 19-GL-2108 is ~90 m.

Dating

None.

 

Stratigraphic Relationship(s)

The Hubert Formation unconformably overlies (angular discordance) basalt of the Chukotat Group. The unconformity was directly observed on geofiche outcrops 19-GL-2108 and 19-GM-5188. It is marked by high hematitization of the underlying volcanic rocks. Its stratigraphic position and the fluvial origin of deposits imply the emergence of the Southern Domain before collision with the Northern Domain. Although volcanic fragments are undoubtedly the product of erosion of Chukotat Group basalt, the origin of intrusive rock fragments remains to be determined. The study of detrital populations will help define the sources and validate the hypothesis stated above if ages correspond to those of the Superior Province. If not, the Hubert Formation could represent a syn-tectonic basin resulting from collision of the Northern and Southern domains.

Paleontology

No fossils reported.

References

Publications Available Through SIGÉOM Examine

BARRETTE, P D. 1990. GEOLOGIE DE LA REGION DU LAC BOLDUC (FOSSE DE L’UNGAVA). MRN. ET 89-03, 48 pages and 3 plans.

BEAUDETTE, M., BILODEAU, C., MATHIEU, G. 2020. Geology of the Parent Lake Area, Ungava Orogen, Nunavik, Quebec, Canada. MERN. BG 2020-04, 1 plan.

MOORHEAD, J. 1989. GEOLOGIE DE LA REGION DU LAC CHUKOTAT (FOSSE DE L’UNGAVA). MRN. ET 87-10, 64 pages and 2 plans.

ROY, C. 1989. GEOLOGIE DE LA REGION DU LAC BELANGER – FOSSE DE L’UNGAVA – RAPPORT FINAL. MRN. MB 89-13, 119 pages and 1 plan.

 

 

Suggested Citation

Ministère de l’Énergie et des Ressources naturelles (MERN). Hubert Formation. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-de-churchill/formation-hubert_en [accessed on Day Month Year].

 

Contributors

First publication

Guillaume Mathieu, Eng., M.Sc. guillaume.mathieu@mern.gouv.qc.ca (redaction)

Mehdi A. Guemache, P. Geo., Ph.D. (coordination); James Moorhead, P. Geo., M.Sc. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); André Tremblay (HTML editing).

 
20 novembre 2020