Abstract

Archean stromatolites occur in a discontinuous dolomite unit at the contact between a major felsic volcanic buildup and a thick sequence of greywacke–mudstone turbidites in the vicinity of Snofleld Lake (67°18′N, 110°45′W). The stromatolitic unit is intimately associated with black carbonaceous mudstones that may also be of biogenic origin. The most common stromatolitic form is a generally flat variety with wavy to corrugated laminations, and contains small local convexities with relief of about 1 cm. A few small stromatolitic heads to low mounds that are formed from similar, even to corrugated, laminae also occur. Minor intraformational breccia layers are present, which in some cases contain larger clasts that have formed oncolites. Although Archean stromatolites are very rare, similar, more deformed and metamorphosed carbonate units occur at similar stratigraphie positions between felsic volcanic sequences and the turbidites elsewhere in the Slave Province. Thus, in an otherwise unstable, inhospitable Archean world, the development of stromatolites around emergent felsic volcanic islands was favored. This was due to a temporary environment with the right light conditions for photosynthesis and perhaps an abundant nutrient supply provided by local volcanic fumarolic activity, as indicated by the occurrence of several base-metal mineral deposits in the Slave Province at this same horizon.

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