The Neoproterozoic cratonic successions of Peninsular India

The Peninsular India hosts extensive record of Mesoproterozoic and Neoprote rozoic successions in several mobile belts and cratonic basins. The success ions provide excellent opportunities for chronostratigraphic classification , in tune with the chronometric classification adopted by IUGS for inter-re gional correlation on a global scale. Major tectono-thermal events at 1000- 950 Ma in the mobile belts, correlatable with the Grenville orogeny may be considered as the datum for Meso-Neoproterozoic classification in India. Pr inciples of chronostratigraphic classification, however, can not be applied yet to the cratonic successions of India because of inadequate radiometric data, paucity of biostratigraphic studies, and lack of regionally correlat able stratigraphic or palaeoclimatic datum. The kimberlite magmatism which affected the Peninsular India on a continental scale at about 1100 Ma, hold s the key to the identification of Neoproterozoic successions of the craton ic basins. Thus, the stratigraphically confined diamond-bearing conglomerat es and/or the tuffs associated with kimberlites, may be considered as the d atum to define the base of the Neoproterozoic,fixed at about 1000 Ma. Accor dingly, the Rewa and Bhander Groups in the Vindhyan basin, the Kurnool Grou p in the Cuddapah basin, the Jagdalpur Formation in the Indravati basin and the Sullavai Group in the Pranhita-Godavari basin are taken to represent t he Neoproterozoic successions in the Peninsular India. The Chattisgarh Grou p in the central India, the lower part of the Marwar Supergroup in western Rajasthan, the Badami Group in the Kaladgi basin, and the Bhima Group are t he other "possible Neoproterozoics" in the Peninsula. The closing phase of the Mesoproterozoic in all these basins are characteri sed by stable shelf lithologic associations attesting to high crustal stabi lity. The Neoproterozoic basins, by contrast, mark a new phase of rifting a nd extension, and the basin fills exhibit signatures of initial instability which evolved with time into a more stable platformal condition. A major e pisode of sea level rise has been recorded in most of the basins. The rifto genic origin and evolution of the basins are comparable with the history of Neoproterozoic basins of Australia though there is no unequivocal record o f glaciation in the Indian formations.