A sequence of metamorphosed arkose, conglomerate and quartzite was first recognized by Dimroth (1964) along the Wheeler River (sheet 24B05). Dimroth (1968) tentatively introduced the name Milamar Formation to refer to this sequence and later formalized it (Dimroth, 1972, 1978). The unit takes its name from Milamar Lake (sheet 24B05) where it was defined. Dimroth (1972, 1978) subsequently provided a more detailed description of this metamorphosed unit of arkose, quartzitic arenite, conglomerate and interbedded dolomite, representing the upper part of the « Seward Subgroup » in the eastern Labrador Trough. Clark and Wares (2004) later reclassified it as the Seward Group, thus abandoning the name « Seward Subgroup ».

According to Dimroth (1972, 1978), the detrital material constituting the Milamar Formation is the result of the erosion of Archean rocks of the Wheeler Complex which formed a positive relief dome on the eastern margin of a shallow marine basin. Sedimentary rocks of the formation were deposited in a coastal environment, bordering an elevated terrain represented by the Wheeler Dome (Dimroth, 1972, 1978). According to Dimroth (1972, 1978), dolomites at the top of the Milamar Formation were deposited in a marine environment and reflect minor marine transgressions. Sedimentary rocks (Milamar Formation) and Archean bedrock (Wheeler Complex) on which they rest were subsequently transported onto volcano-sedimentary rocks of the Laporte Supersuite (Clark and Wares, 2004).

At the type locality, unit pPmm1 consists of arkose, polymictic conglomerate and quartzitic arenite deposited unconformably (erosion) on Archean gneiss of the Wheeler Complex (Dimroth, 1972, 1978; Kish and Tremblay-Clark, 1979). The unit locally contains interbedded dolomite. The arkose is composed of 50% subrounded cataclastic grains of quartz and feldspar in a fine-grained sericite-quartz-albite matrix. The conglomerate consists of gneiss pebbles 2-10 cm in diameter, rarely up to 30 cm, in a mylonitic albite-sericite-quartz matrix. The quartzitic arenite occurs as lenses or thick banks interbedded with arkose and conglomerate. The rock is white and mainly composed of quartz. It is locally feldspathic. Coarse-grained metamorphosed equivalents of unit pPmm1 are reported to the south of the type locality (Dimroth, 1972, 1978).

Milamar Formation 2 (pPmm2): Interbedded Quartz-Albite-Sericite Schist, Quartz-Sericite Schist and White Quartzite

Thickness and Distribution

The Milamar Formation belongs to the Romanet Lithotectonic Zone, previously defined as the Wheeler Zone by Clark and Wares (2004). It occupies an area generally oriented NW-SE along the Wheeler River between latitudes 56°N and 56°30’N (Dimroth, 1964, 1970, 1972, 1978). The rocks belonging to this formation were also mapped by Dimroth (1978) in areas south and east of the Wheeler Complex. Kish and Tremblay-Clark (1979) observed schists attributed to the Milamar Formation south of Duhamel Lake (sheet 24B06). Rocks of this formation are absent north of latitude 56°30’N (Dressler, 1979). The thickness of the Milamar Formation is poorly known: a thickness of ~300 m was suggested by Dimroth (1970, 1978, p. 67).

Dating

None.