The Purana Basins of Southern Cratonic Province of India - A Case for Mesoproterozoic Fossil Rifts

Since its cratonization in the Palaeoproterozoic, southern peninsular India witnessed the development of a number of large intracratonic sedimentary basins, traditionally referred to as Purana basins, spanning in age from late Palaeoproterozoic through Neoproterozoic. The localization of these intracratonic basins, namely Pranhita-Godavari (PG), Chattisgarh and Cuddapah basins, is apparently controlled by pre-existing sutures and/or weak zones. The PG basin and the Cuddapah basin host unconformity-bound, thick, sediment-dominated successions attesting to several cycles of fluvial-shallow marine to shelf-slope-basin sedimentation. Deposition was punctuated by block uplifts resulting in local hiatuses and/or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites. Basin-margin deep faults apparently played a role in the facies distribution in these basins. Based on these features we propose that these basins initiated as continental rifts which, however, never opened up into a full-fledged ocean basin, but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the Chattisgarh succession. Spatial distribution of facies and sediment thickness in the Cuddapah and PG basins suggest that an open seaway existed to the east of the south Indian cratonic province during the Mesoproterozoic, while similar criteria point to the existence of an open seaway north of the Chattisgarh basin. Development history, including nature of inversion, suggest that the southern cratonic province of India existed as a single large continental mass since the Mesoproterozoic, in spite of episodes of supercontinent build-up and fragmentation involving India and East Gondwana during the Proterozoic.