A new shale-facies microbiota from the Middle Proterozoic Dismal Lakes Group, District of Mackenzie, Northwest Territories, Canada

Abstract

An assemblage of filamentous microfossils is preserved in black shales of the approximately 1.2 Ga old Dismal Lakes Group from a locality about 110 km west-southwest of Coppermine, Northwest Territories, Canada. These microfossils occur as empty, 1–13 μm wide, tubular structures which are compressed parallel to lamination. The wider filaments probably represent the empty sheaths of Lyngbya-like oscillatoriacean cyanophytes, whereas the narrower filaments could represent either oscillatoriacean filaments or bacterial filaments. Filaments 3.0–7.0 μm wide are comparable to Siphonophycus crassiusculum and rare filaments 10.5–13.0 μm wide are comparable to Siphonophycus beltensis, both from shales of the Middle Proterozoic Belt Supergroup, Montana. Sphaeromorphs are rare and lack distinctive surface features which would permit their assignment to particular taxa.This shale-facies microbiota appears to consist entirely of organisms that had relatively thick sheaths which were highly resistant to degradation and diagenetic alteration. This microfossil assemblage, as well as other Proterozoic shale-facies assemblages, probably are biased toward degradation-resistant taxa and may not be representative of the original microbial communities from which they were derived, nor of the Proterozoic biosphere. Nevertheless, such microfossils offer promise for intercontinental biostratigraphic correlation and provide data useful in understanding the evolution of Precambrian life.