Late Palaeoproterozoic (∼1800–1600 Ma) stromatolites, Cuddapah Basin, southern India: cyanobacterial or other bacterial microfabrics?

Abstract

Late Palaeoproterozoic stromatolites from the Vempalle Formation of the Cuddapah Supergroup, south-eastern India, contain well-preserved microfabrics. These exhibit a range of complex clotted to bush-like micritic fabrics set in microsparite and sparite cements. No calcified microfossils confidently referable to calcified cyanobacteria have been recognized, although micritic masses crudely resembling the Phanerozoic calcified cyanobacterium Angusticellularia are present. It is suggested that these Vempalle stromatolitic microfabrics compare more closely with modern calcified non-cyanobacterial biofilms. This interpretation questions the widespread assumption that cyanobacteria were important components of stromatolite-building microbiotas during the Proterozoic and instead emphasizes the possibility that examples similar to those studied were dominated by non-cyanobacterial bacteria. It is generally thought likely that cyanobacteria were important components of stromatolite-building microbiotas during the Proterozoic, and that early lithification by carbonate precipitation was widespread and intense. If these assumptions are correct then the apparent absence of diverse calcified cyanobacteria suggests that these organisms, which are conspicuous in the Early Palaeozoic, underwent evolutionary radiation close to the Neoproterozoic–Cambrian boundary.