Stratigraphic position of the ∼1000 Ma Sukhda Tuff (Chhattisgarh Supergroup, India) and the 500 Ma question

U-Pb ages of magmatic zircons in tuff horizons in the Chhattisgarh and the Vindhyan Supergroups in India, backed up by paleomagnetic data, suggest that most Proterozoic basins in India are about 500 Ma older than the current consensus. The issue is hotly debated including questions about the stratigraphic positions of the tuff horizons. Thus, the geologic significance of the ∼1000 Ma age of the rhyolitic tuff near Sukhda and Sapos villages in the Chhattisgarh Supergroup in central India hinges on its proper stratigraphic placement. If the tuff is near the top of the Chhattisgarh Supergroup, then the Chhattisgarh and its equivalent sediments were deposited in the Mesoproterozoic and not, as has been the general notion, in the Neoproterozoic. The tuff lies conformably on the platform-facies Saradih Limestone of the Raipur Group (upper Chhattisgarh) and not on an Archean-Proterozoic basement; it is overlain by fluvial volcaniclastic conglomeratic lithologies of the Sarnadih Sandstone. Had this sandstone belonged to the basal Lohardih Formation deposited in fan-deltas of an opening basin, as is currently believed, it would have been overlain by prodelta deposits including mature quartz arenites and floored by crystalline rocks. Formation-mapping, facies analysis, and petrologic considerations place the Sarnadih Sandstone, and thus the ∼1000 Ma Sukhda Tuff, near the top of the sedimentary sequence of the Chhattisgarh basin. Consequently, rocks below the Sukhda Tuff must be pre-Neoproterozoic in age. Hence, rocks and tectonics of these Proterozoic basins are irrelevant to arguments about the Cryogenian or break-up of Rodinia, but are related more to the assembly of Rodinia and the break-up of Nuna. Metazoan and animal life forms, reported from the Chhattisgarh and equivalent basins, must also have originated and evolved in pre-Neoproterozoic time.