Stromatolite-like Structures Within Microbially Laminated Sandstones of the Paleoarchean Moodies Group, Barberton Greenstone Belt, South Africa

Stromatolite-like structures, discovered within microbially laminated sandstones of the Paleoarchean Moodies Group in the Barberton Makhonjwa Mountains (3.22 Ga), challenge traditional notions of biogenic carbonate formation. These bulbous mounds, several centimeters in diameter, exhibit internal microlaminations composed of organic matter and sericite, suggesting a photosynthetic microbial origin. Their widespread occurrence along the sediment-water interface and restriction to the photic zone support this interpretation. However, similar structures also appear within fluid-escape conduits, hinting at potential abiotic or chemotrophic origins involving organic matter, methane, or hydrogen oxidation. The study proposes that these 'hybrid carbonates' may represent a mix of bioinduced and abiotic processes, complicating the unambiguous identification of biogenic components. This finding broadens criteria for life detection in siliciclastic, high-energy tidal settings, with implications for Mars exploration.

Heubeck, C., Reimann, S., & Homann, M. (2023). Stromatolite-like Structures Within Microbially Laminated Sandstones of the Paleoarchean Moodies Group, Barberton Greenstone Belt, South Africa. Astrobiology, 23(9), 926–935. https://doi.org/10.1089/ast.2023.0014