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The importance of the study of Archean sedimentary sequences in unraveling the early history of the earth and continental development is self-evident. To this end we made a detailed stratigraphic and sedimentologic analysis of an Archean basin typical of the many found in the Slave and Superior provinces of the Canadian shield. The sedimentary sequence chosen, probably between 5,000 and 10,000 ft thick, is exposed on the shores of East Bay of Minnitaki Lake in northwestern Ontario. The lower 4,400 ft was studied in detail.
The entire section consists of turbidites, the indigenous sediment being fine mudstone and siltstone commonly forming graded couplets 1 or 2 cm thick with distal aspect. Interbedded with this predominantly pelitic facies are proximal facies. These consist of coarse, graded graywacke and, in places, graded conglomerate, the latter with cobbles up to 40 cm in diameter. The conglomerate near the base of the section consists of quartz-porphyry debris with numerous large sedimentary intraclasts; that near the middle of the section is of "granitic" provenance and contains cobbles of "granitic" aspect.
The study demonstrates the dominant role of turbidity currents in the deposition of Archean sediments--even of coarse conglomerates--and establishes the non-volcanic origin of these sediments and a sialic plutonic source for most of the basin fill. The strata are not intra-volcanic but are, instead, a true epiclastic sequence deposited in a turbidite basin--perhaps similar to the younger turbidite basins of southern California.
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