DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Stratotype:||Type section described by Clark and Globensky (1976b) on the left bank of the Ouareau River, immediately upstream of the Road 158 (formerly Road 41) bridge near Crabtree; sections described by Clark and Globensky (1976a) in NE Joliette Hill, 0.5 km SE of the Grande-Chaloupe Range parallel to the La Chaloupe River, and along a small road that descends towards the La Chaloupe River, 800 m west of the Road 158 bridge, ~4 km south of Sainte-Élizabeth|
|Type area:||Ouareau River area (NTS sheet 31H13)|
|Geological province:||St. Lawrence Platform|
|Geological subdivision:||St. Lawrence Lowlands Platform|
|Lithology:||Micritic and nodular limestone, argillaceous; shale|
Okulitch (1939) noticed on the Ouareau River a section of interstratified beds containing fauna typical of the Trenton and Black River groups. He called this section the “Ouareau transition zone.” Husain (1955) related the lithology to the Trenton Group. Clark (1959) considered this unit contemporaneous to the Hull Formation. Clark and Globensky (1976a, b) affirmed that the abrupt fauna distinction between the Ouareau Formation and the underlying Leray Formation (Black River Group) and the marked colour difference between the Ouareau and overlying Deschambault formations were sufficient to define a distinct formation: the Ouareau Formation.
The Ouareau Formation consists of dark grey micritic limestone, irregularly bedded (with strong external undulations) and thin-bedded (7-15 mm), nodular, argillaceous and interstratified with shale (Clark and Globensky, 1972, 1976a, b; Brun, 1974, 1975; Harland and Pickerill, 1982; Globensky, 1983, 1986, 1993; MNRF, 2009a, b, c; Thériault, 2014). Shale and most limestone beds are bioturbate (abundance of gastropod and ostracod bioclasts) although locally they appear laminated or cross-bedded. Brown (1974, 1975) noted the presence of disseminated mineralization of pyrite and more locally of sphalerite, but mainly of brown or white calcite eyes. Clark and Globensky (1976b) described a type section of the Ouareau Formation on the left bank of the Ouareau River, immediately upstream of the Road 158 bridge (formerly Road 41) near Crabtree:
In the NE part of Joliette Hill, 0.5 km SE of the Grande-Chaloupe Range parallel to the Chaloupe River, there was a clearing (now occupied by the Turnbull Quarry which exploits limestone of the overlying Black River Group) where there are discontinuous outcrops that can define a section at the base of which the Ouareau Formation is found (Clark and Globensky, 1976a):
Approximately 4 km south of Sainte-Élizabeth and 800 m west of the bridge across the La Chaloupe River, a section can be constructed from a few outcrops staggered along a small road down the river (Clark and Globensky, 1976a):
From five sections (Miron Ltd. Company Quarry, Montreal; St-Vincent de Paul Quarry, St-Vincent-de-Paul; Sintra Quarry, St-Jacques; Ciments Indépendants Inc. Quarry, Joliette; Turnbull Construction Inc. Quarry, St-Thomas), Brun (1974, 1975) defined boundary stratotypes between the Leray (Black River Group), Ouareau and Mile End formations: “Leray-Ouareau boundary: Sharp transition from a small bed of very dark grey siliceous ‘mudstone’ limestone with many white calcite eyes and disseminated mineralization of brown calcedony (Leray) to alternating small, wavy beds of massive ‘mudstone’ limestone and beds of black grey schistose argillite containing gastropods (Ouareau). Ouareau-Mile End boundary: Transition from alternating small, very wavy beds of massive ‘mudstone’ limestone with calcite eyes and beds of black grey schistose argillite containing gastropods (Ouareau) to a very large ‘wakestone’ limestone bed with numerous internal discontinuous undulations (Mile End).”
The Ouareau Formation reaches a thickness of 6 m north of Montreal, but generally ranges from 4 to 5 m (Clark and Globensky, 1976a, b; Globensky, 1993). It outcrops mainly in the Joliette area along a thin N-S to NE-SW strip (<500 m wide) for nearly 50 km, between Sainte-Anne-des-Plaines and Joliette (north of sheet 31H12, sheet 31H13 and SW corner of sheet 31I03). It extends for about 12 km NE of Joliette in the Saint-Thomas area (SW quarter of sheet 31I03).
Because of its stratigraphic position, Harland and Pickerill (1982) correlates the Ouareau Formation with the Fontaine, Pont-Rouge, Mile End and Sainte-Anne formations, as all these formations represent basal units of the Trenton Group, overlying the Leray Formation (Black River Group) and in contact with the overlying Deschambault Formation. The Ouareau Formation is generally in discordance with the underlying Leray Formation and the overlying Deschambault Formation. However, the Ouareau Formation is separated from the Deschambault Formation by the Mile End Formation on several sections established in careers of the Montreal and Joliette areas (Brun, 1974, 1975).
The restricted fauna of the Ouareau Formation is somewhat similar to that of the Black River Group, but extensive sampling has allowed this formation to be associated with the Trenton Group (Husain, 1955; Clark and Globensky, 1976a, b; Globenski, 1987, 1993). Thus, Foerstephyiium and Stromatocerium are associated with the Leray and Ouareau formations, while Sowerbyella sericea and Paucicruara rogata are associated with the Trenton Group.
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