MICROBIALLY INDUCED SEDIMENTARY STRUCTURES – A NEW WINDOW IN UNDERSTANDING EARLY LIFE: EXAMPLES FROM ARCHEAN SANDSTONES, SOUTH AFRICA

In siliciclastic marine environments, benthic microbiota do not form stromatolites, but ‘microbially induced sedimentary structures (MISS)’. Genesis and morphologies of the structures differ significantly from their precipitated counterparts, the stromatolites. MISS are found abundantly in modern depositional settings, and are widely distributed in the fossil record as well.

In this study, we describe MISS from sandstone successions of the Paleoarchean Moodies Group (~3.2 Ga), the Mesoarchean Pongola Supergroup (~3.0 Ga), and the Neoarchean Black Reef Formation (~2.5 Ga) in South Africa.

The morphologies of the structures permit conclusions on the physiological abilities of the benthic microorganisms to interact with the sedimentary dynamics. Thus the structures provide evidence for the former existence of photoautotroph, filamentous, and motile (?cyano-)bacteria constructing biofilms and mats in intertidal and shelf environments. Mineralogical, geochemical, and isotopic analyses support a biological origin for these structures.

This study demonstrates that MISS constitute a new window in understanding early life.