A late Proterozoic microbiota occurs in a dark, shaly unit of the upper Miette Group near Mount Robson, southern British Columbia, Canada. The overlying part of the Miette and Gog Groups strata form an essentially conformable sequence containing the Precambrian-Cambrian boundary in the little-deformed southwest limb of the Mount Robson syncline. The Mount Robson microflora occurs about 2,600 m below the Early Cambrian Nevadella zone (base of the Mural Formation). Extensive pyritization and concomitant framboid formation in the organic fraction of the sediments has preserved a unique microflora. It is qualitatively different from the nannofossils of the stratigraphically lower Hector Formation, 280 km to the southeast, in which the microorganism Sphaerocongregus variabilis Moorman occurs. Differences in preservation between the Mount Robson and Hector microfossils are probably related to the local environment of deposition and early diagenesis. Light and scanning electron microscope study of the fossils suggests four possible origins for the Mount Robson microflora: blue-green algae, bacteria, eukaryotic algae, and (or) diagenetically formed pseudofossils.
CONTRIBUTION NO. 58, BIOGEOLOGY CLEAN LABORATORY, UNIVERSITY OF CALIFORNIA, SANTA BARBARA