New trail-like features associated with microbial mats from the early Neoproterozoic Sirbu Shale Member (Upper Vindhyan Group), Vindhyan Basin, central India

Numerous features, predominantly encountered upon the undersides of bedding planes and interpreted to be of biogenic origin, are described from the Sirbu Shale Member of the Upper Vindhyan Group, central India. Some of the features display surface trail-like or horizontal undermat burrow-like characteristics typically associated with microbial mats. Other features suggest the presence of macroscopic metazoans displaying bilateral symmetry or characteristics arguably of locomotion or of frondose origin, one strongly reminiscent of the fossil/trace fossil Bunyerichnus. Newly dated to ca 852 Ma (mid-Tonian Period), and thereby pre-dating the famed Ediacaran Biota by some 270 million years, these features are analogous to various biogenic structures from other stratigraphic horizons globally that, in places, extend back into the Paleoproterozoic Era. Additionally, geochemical proxies indicate oxygenated redox conditions prevailed within the Vindhyan Basin, which likely assisted these organisms to develop motility. However, whether these biogenic trail-like features reflect a subdued state and prolonged ‘slow burn’ of pre-Ediacaran evolution within an oxic enclave of an otherwise global anoxic ocean, or an early evolutionary flourish within an isolated, oxygenated intracratonic basin within the Rodinia Supercontinent remains to be determined.