Geologists from Labrador Mining and Exploration (1949, see Frarey and Duffell, 1964) called a cherty breccia unit located in the Schefferville area the « Fleming chert breccia ». These authors placed this unit stratigraphically above the Denault dolomite and below the Wishart quartzite (see Frarey and Duffell, 1964). The name Fleming Formation was formalized by Harrison (1952) in his description of the geology of a NE-SW oriented strip at Schefferville (« Burnt Creek strip« ). It should be noted that the name Fleming does not refer to a particular geographical entity, but its use is well established in the literature and justifies its retention. Baragar (1967) subsequently described this unit between Helluva Lake and Le Fer Lake, but did not distinguish it on his map. Dimroth (1978) mapped the Fleming Formation from the Helluva and Le Fer lakes area to Knob Lake, south of Schefferville. He also included the Fleming Formation in the Attikamagen Subgroup, later reclassified as the Attikamagen Group by Clark and Wares (2004).

The Fleming Formation has been extensively described by several authors (Dufresne, 1952; Howell, 1954; Baragar, 1967; Gross, 1968; Dimroth, 1971; Birkett, 1991). It has also been the subject of geological reconnaissance work in the Schefferville area (Clark et al., 2008).

The base of the Fleming Formation generally comprises a 0.6 m to 3 m thick greenish grey argillaceous siltstone layer (Baragar, 1967; Dimroth, 1971, 1972, 1978). The latter is massive, locally laminated, and commonly contains chert lenses and veinlets. Argillaceous siltstone is overlain by chert breccia arbitrarily divided into two or three randomly interdigitating zones. The lower part of the Fleming Formation generally contains fragments of irregularly contorted laminated chert, laminated brecciated chert, chert breccia and siltstone in an argillaceous siltstone matrix. In the Le Fer Lake area, this part consists locally of massive or residual light grey chert probably derived from the replacement of laminated or intraclastic dolomite (Dimroth, 1971). The upper part of the formation comprises fragments of chert breccia, sandstone and cemented chert breccia in a medium to coarse-grained sandstone matrix. Siltstone is generally absent. At the top, the rocks locally possess dolomitic cement (Dimroth, 1971, 1972, 1978). Based on observations by Clark et al. (2008), the Fleming Formation contains in its upper part lenses and layers of quartzitic sandstone similar to that of the Wishart Formation.

Table 1: Characteristics of Fleming Formation Lithologies (Dimroth, 1971, 1978)

Fragments consist of massive, homogeneous microcrystalline chert, banded chert or quartz. Blocks of sandstone or quartz arenite (<30 cm) locally containing chert pebbles are also observed (Clark et al., 2008). Some of these blocks display relics of stratification with beds 5-10 cm thick (Dimroth, 1971 and 1978). Chert fragments are grey to milky white and range in size from pebbles to blocks (1-60 cm). Most are angular, but some are rounded (Dimroth, 1971; Zajac, 1974; Clark et al., 2008). Tabular fragments are observed in places (Baragar, 1967; Dimroth, 1971). Many chert clasts are derived from chalcedony cavity filling. Fragments from veinlet filling are also common (Dimroth, 1971, 1972, 1978). The rocks of the Fleming Formation are slightly metamorphosed to the greenschist facies (Fraser et al., 1978).

Rocks of the Fleming Formation were deposited at the bottom of a slope bordering a basin near the western margin of the Labrador Trough (Dimroth, 1971, 1978; Wardle and Bailey, 1981). The origin of chert breccia has been studied by several authors (Harrison, 1952; Dufresne, 1952; Howell, 1954; Baragar, 1967; Gross, 1968; Dimroth, 1971). According to Dimroth (1978), the Fleming Formation is derived from a stratified sequence of sandstone, siltstone, dolomite and gypsum, which was silicified and brecciated. Brecciation is thought to be the result of collapse by dissolution of evaporites and sliding. Birkett (1991) interprets chert breccia as a siliceous sediment formed in shallow water and associated with evaporites. This sediment would have undergone desiccation and synsedimentary slip (Clark et al., 2008).

Thickness and Distribution

The Fleming Formation belongs to the allochthonous Schefferville Lithotectonic Zone, as defined by Clark and Wares (2004). It is only recognized near the western margin of the Labrador Trough, south of latitude 55°30′N. It extends from the Helluva and Le Fer lakes area (sheet 23O06) to Schefferville (sheet 23J15), a distance of ~80 km (Dimroth, 1971, 1972, 1978). On the Labrador side, Fleming rocks have been followed SE to Marble Lake (sheet 23J08) (Evans, 1978; Wardle, 1979, 1982), an additional ~45 km. Fleming-like rocks have also been observed above the Denault Formation dolomite in the Marion Lake area (Harrison, 1952; Donaldson, 1966).

Near the western margin of the Labrador Trough, the Fleming Formation is ~15 m thick. It thickens eastward and reaches ~100 m in the Schefferville area, then gradually thins eastward (Harrison, 1952; Harrison et al., 1972; Gross, 1968; Dimroth et al., 1970; Wardle, 1979). According to Dufresne (1952, in Baragar, 1967) and Zajac (1974), the thickness of the central part of the formation varies from 100 to >120 m in the Schefferville area. Evans (1978) estimated the thickness to be ~130 m in the Dyke Lake area (sheet 23J10), SE of Schefferville.

Dating

None.