SHRIMP ages of zircon in the uppermost tuff in Chattisgarh Basin in central India require ∼500-Ma adjustment in Indian proterozoic stratigraphy

The Chattisgarh Basin of east central India and many unmetamorphosed Proterozoic sedimentary basins of Peninsular India have been considered mostly Neoproterozoic (1000-545 Ma) in age. A newly recognized succession of rhyolitic ignimbrite, ash beds, and volcaniclastic sandstones near the top of the similar to 2.2-km-thick sedimentary fill of the Chattisgarh Basin is a chronostratigraphic marker. Euhedral igneous zircons from these units give U-Pb SHRIMP ages of 990-1020 Ma, indicating that the basin fill beneath this marker horizon is pre-Neoproterozoic. On the basis of newly reported zircon ages of Ma from the basal part of the Vindhyan Basin and accepting the consensus that all 1631 +/- 5 virtually undeformed and unmetamorphosed craton-interior Proterozoic sedimentary basins in peninsular India are approximately coeval, we conclude that these basins are approximately Mesoproterozoic (1600-1000 Ma) in age. The reassigned age for these rocks (1650 to 900 or possibly similar to 1000 Ma), up to 500 Ma in variance with the current notion (similar to 1100 to similar to 518 Ma; Naqvi 2005), calls for a thorough rethinking of contemporary models concerning tectonics, sedimentation, and other geological activity that affected the Indian shield in the Proterozoic Era.