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:

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).”

Thickness and distribution

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).

Dating

None.