Archaean microbiota from the Donimalai formation, Dharwar supergroup, India

Abstract

Syngenetic microbial trichomes are recorded from a black chert band interlayered with the banded iron formation belonging to the > 2.6-Ga-old Sandur Schist Belt of the Dharwar sequence, Karnataka, India. The iron formation has interbeds of mafic pillow lava and tuffs. Although the fossil microbial community consists of highly biodegraded mats, some well-preserved structurally mineralized trichomes are also present. Electron microprobe analysis shows high percentage of SiO₂ and P₂O₅ in the filaments and the presence of carbon along the margins of some filaments. Rare earth element and isotopic data indicate a higher oxygen concentration than hitherto considered for Archaean seawater. In the present context there is presumptive evidence to suggest that this oxygen was produced by the photosynthetic activity of microbial biocoenoses.