Namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng Formation), British Columbia: Canada's oldest shelly fossils

摘要

The uppermost part of the Miette Group (Windermere Supergroup) in eastern British Columbia has yielded shelly macrofossils in cliff-forming biostromal carbonates (Byng Formation). The biostromes are made up of two principal elements: intergrowths of complex sinuous, plate-like stromatolites (cf. Platella), and intervening planar to curviplanar pockets filled with packstone and wackestone crowded with Namacalathus and Cloudina, presumed calcified metazoans of uncertain biological affinities. Preservation is best in limestone, and the shells are mostly obliterated where the carbonate is dolomitized. This assemblage was previously known only from the Nama sequence in Namibia. The new find in the antipodal Miette Group in the Canadian Rocky Mountains greatly extends its geographic range, and suggests a more widespread distribution in similar facies in inter-mediate areas. Both assemblages constitute the earliest occurrences of shelly fossils in their respective regions.