Ediacaran fossils from the Sekwi Brook area, Mackenzie Mountains, northwestern Canada

Ediacaran body fossils and trace fossils occur sporadically throughout more than one kilometre of strata in the upper part of the Windermere Supergroup in the western Northwest Territories of Canada. The Sekwi Brook biota lived in a deep-water, basin slope setting below storm wave-base. Most of the body fossils probably represent benthic polypoid and frond-like organisms. The body fossil assemblage is broadly similar to that described from correlative shallow shelf deposits in the Wernecke Mountains, Flinders Ranges and Russian Platform. The trace fossil assemblage is dominated by simple and irregularly meandering burrows, but contains some patterned meanders typical of the Nereites ichnofacies. The occurrence of this relatively diverse, mainly deep-water assemblage of benthic body fossils and infaunal burrows indicates that the initial radiation of metazoans extended to the deep sea, and that some aspects of Phanerozoic-style marine ecosystems were initiated during the earliest stages of metazoan evolution.