The Baby Formation was first described by Sauvé and Bergeron (1965) in the Gerido and Thévenet lakes area (sheets 24K03 and 24K04). The unit takes its name from Baby Lake, near which it is clearly visible. Within the Baby Formation, Sauvé and Bergeron (1965) distinguished three informal subunits which they named, from base to top: « Lower Phyllites », « Iron-bearing member » and « Upper Phyllites (or Micaschists on the map) ». The lower member of the Baby Formation (« Lower Phyllites ») consists of mudstones, phyllites and schists, with numerous quartzite beds near the top. The middle member (« Iron-bearing member ») consists of iron-bearing rocks and a smaller amount of phyllite. The upper member (« Upper Phyllites ») comprises mudstones, phyllites and a minor amount of quartzite. According to Sauvé and Bergeron (1965), phyllites of the lower and upper members are similar and can only be distinguished by their stratigraphic position in relation to the separating member of iron-bearing rocks.

The « Lower Phyllites », « Iron-bearing member » and « Upper Phyllites » subunits of Sauvé and Bergeron (1965) have also been referred to as the Lower, Middle (or Median) and Upper members of the Baby Formation (Clark, 1988; Wares et al., 1988; Wares and Goutier, 1989, 1990; Goutier and Wares, 1991); Lower, Middle and Upper Baby units or Lower, Middle and Upper Baby (Goulet, 1995; Clark and Wares, 2004), Lower, Middle and Upper Baby formations (Clark and Wares, 2004, Figure 33, page 55), Lower, Middle and Upper Baby formations (Clark, 2019). Given that the name « Baby » has been commonly used in the literature since its definition by Sauvé and Bergeron (1965), and that the stratigraphic position of the lower, middle and upper members of the Baby Formation is well established, the names « Lower Baby member« , « Middle Baby member » and « Upper Baby member » are adapted for the purposes of this stratigraphic record.

The Baby Formation includes sedimentary and volcanic rocks that are not attributed to either members of the formation. Current mapping is not sufficiently detailed to deduce their stratigraphic position. This may be determined in future fieldwork. Unsubdivided rocks of the Baby Formation have been described by Sauvé (1956a, 1956b, 1959), Freedman (1958), Gold (1962), Hashimoto (1964), Clark (1978) and Dressler (1979), among others.

Baby Formation 1 (pPbb1): Mudstone, Phyllite, Slate, Siltstone, Locally Micaceous or Carbonatized; Wacke and Chert Locally

Unit pPbb1 is located in the areas west of Hérodier and Le Moyne lakes. It consists mainly of mudstone, phyllite, slate and siltstone, locally micaceous or carbonatized. These rocks are generally grey to black in fresh surface and locally have a rusty altered patina due to the presence of pyrite. They are fissile or laminated and commonly graphitic. Wackes and chert are observed locally (Hashimoto, 1964; Clark, 1978; Dressler, 1979).

Unit pPbb2 consists mainly of dolomite south of latitude 57°30′N (Hashimoto, 1964; Sauvé and Bergeron, 1965; Dressler, 1979). Dolomite is generally interbedded with unit pPbb1 pelitic rocks. It is grey in fresh surface and has a light grey, locally buff or rusty alteration patina. Dolomite is very fine grained or aphanitic, massive or very well stratified. In places, it is cut in all directions by numerous quartz veinlets. In the Jogues Lake area (sheet 24F02), the rock has a ferrodolomite composition (Hashimoto, 1964). SE of Redcliff Lake (sheet 24C16), dolomite is adjacent to a unit of sulphidic iron-bearing rocks of the Middle Baby member (pPbb(m)). In the Gerido Lake area (sheets 24F13 and 24K04), it is accompanied by calcosilicate rocks containing actinolite-chlorite-rich beds (Sauvé and Bergeron, 1965). North of Feuilles Lake (sheets 24K13 and 24N04), unit pPbb2 includes more metamorphosed, coarse-grained varieties, notably diopside marbles and calcareous schists. These rocks are commonly interbedded with unit pPbb6 pelitic schists (Sauvé, 1959; Gold, 1962).

Baby Formation 3 (pPbb3): Wacke; Conglomerate Interstratifications (Turbidites)

Thickness and distribution

The Baby Formation belongs to the Gerido lithotectonic zone as defined by Clark and Wares (2004). The unit extends ~300 km from Hopes Advance Bay (sheet 24N05) to the area south of Le Moyne Lake (sheet 24C16). It occurs mainly in the area between Hopes Advance Bay and Feuilles Lake and in the area west of Hérodier and Le Moyne lakes. Small occurrences are located at Enish Lake (sheet 24K06) and south of Rale Lake (sheet 24F13). The total thickness of the Baby Formation, including the Lower, Middle and Upper Baby members, is estimated at >1100 m in the Gerido and Thévenet lakes area (Sauvé and Bergeron, 1965) and >1000 m in the Napier Lake area (Clark, 1979).

Dating

The Baby Formation is Paleoproterozoic in age. It belongs to the second cycle of Labrador Trough sedimentation dated 1.88 to 1.87 Ga (Clark and Wares, 2004). An age of 1874 ±3 Ma has been obtained for a glomerophyric gabbro sill cutting basalts at the top of the Hellancourt Formation, overlying the Baby Formation (Machado et al., 1997). The sequence formed by the Baby and Hellancourt formations is thought to be of the same age as the Ferriman Group (1880 ±2 Ma) (Clark, 1988; Chevé and Machado, 1988; Clark and Wares, 2004).