Ubiquitous Growth of Paleoarchean Biofilms Recorded in White Chert Bands of the Buck Reef Chert

The 3.42 Ga Buck Reef Chert (Kromberg Formation, Barberton greenstone belt, South Africa) contains a geobiological record of microbial mats confined to the photic zone of anoxic Archean oceans. In order to better understand the early development of photosynthetic microbial systems, these records were surveyed at multiple scales using novel hydrofluoric etching methods, translucent slabs cut to mm-scale thickness, Raman spectroscopy, and thin section analysis. I demonstrate that mat growth in the photic zone was far more common and voluminous than previously thought. Biofilm growth and silica sedimentation dominated during mat growth, which was punctuated by the transport of large volumes of detrital carbonaceous grains. Further, cyclicity in the relative contributions of biomass and sedimentary silica in these microbialites can be demonstrated, showing that these cycles fall within a Poisson distribution that offers useful constraints in the growth processes that led to their formation.