Organic-walled microfossils from the ca. 2.7 Ga Tumbiana Formation of Western Australia

Textural biosignatures such as microbialites, in conjunction with geochemical proxies for biological processes, indicate that a microbially dominated biosphere was well established in the Archean Eon. Despite these findings, the interpretation of most Archean body fossils remains contentious. Many reported Archean microfossils are disputed due to the potential for abiogenic processes to mimic fossil morphologies. In this study, we report carbonaceous specimens extracted from lacustrine calcareous shale of the ca. 2.7 Ga Tumbiana Formation in Western Australia, a formation renowned for its well-preserved biosignatures including exceptionally preserved stromatolites and distinctive geochemical signals. The specimens are spheroidal and considerably large (>50 µm), with some bearing a protrusion-like structure. Combining their morphological and compositional features revealed by Raman spectral analyses, these organic-walled specimens are interpreted as remains of microorganisms, adding a new record to the short list of Archean bona fide microfossils. In particular, these microfossils represent some of the earliest body fossils from lacustrine deposits, providing new insights into the composition of Archean lacustrine microbial communities.