Abstract
Abstract A 1200 Ma old microbiota is well preserved in black cherts of the Dismal Lakes Group about 130 km southwest of Coppermine, District of Mackenzie, Northwest Territories, Canada. These cherts appear to have formed by a combination of early diagenetic silicification of calcareous layers and permineralization of noncalcareous layers deposited in a very shallow subtidal or lower intertidal setting on a carbonate platform. The preserved assemblage is largely or entirely of cyanophytic affinity with coccoid forms dominating over filamentous forms. Many elements of this microbiota are morphologically similar to the 1900 Ma old Belcher Islands assemblage and 850 Ma old Bitter Springs assemblage. The following taxa are present: Chroococcaceae: Sphaerophycus parvum Schopf; Sphaerophycus medium n. sp.; Sphaerophycus? sp.; Myxococcoides grandis n. sp.; Myxococcoides? sp. Entophysalidaceae: Eoentophysalis dismallakesensis n. sp. Oscillatoriaceae: Oscillatoriopsis curta n. sp.; Oscillatoriopsis robusta n. sp.; Oscillatoriopsis sp.; Filiconstrictosus sp.; Eomicrocoleus crassus n. gen., n. sp. Incertae sedis: Archaeoellipsoides grandis n. gen., n. sp.; Biocatenoides? sp.
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