Problematic bedding-plane markings from the Middle Proterozoic Manganese Subgroup, Bangemall Basin, Western Australia

Abstract

Enigmatic bedding-plane markings, impressions resembling isolated strings of beads, occur in sandy and argillaceous strata of the Stag Arrow Formation in the Middle Proterozoic Manganese Subgroup, Bangemall Group, of the Bangemall Basin, east of Newman, Western Australia. Markings are abundant at two localities and traces are found at a third. Structures similar in both morphology and dimension have previously been reported from the Appekunny Formation in the Middle Proterozoic Belt Supergroup of U.S.A. The Manganese Subgroup structures provide further details of morphology, enabling comparison with a variety of biogenic and non-biogenic structures. A source for the markings still cannot be determined with certainty, but a biogenic origin is favoured, and affinities with the green or brown algae suggested. Such an origin is consistent with records of megascopic algae from rocks of similar age.