Work Description:

The main emphasis of this study has been to to infer the preliminary thermal history analysis and provenance of Pranhita-Godavari (P-G) Basin sediments from a borehole using apatite fission track (AFT), organic maturity and zircon U-Pb data

Located at the boundary of Dharwar and Bastar cratons, Pranhita-Godavari (P-G) basin extends ~400 km trending NNW–SSE in the central Indian peninsula and offshore. This intra-cratonic Proterozoic rift basin hosts a Permo-Triassic Gondwana sequence attaining a total thickness up to 3000 m. AFT analysis was carried out on 15 samples from cores and cuttings collected over a depth range of 500-2950 m belonging to an exploratory borehole located in the southern part of the basin. AFT ages decrease systematically with depth from 242±23 to 11.5±0.5 Ma. U/Pb zircon ages (determined by LA-ICP-MS) on detrital grains from two Triassic samples in this borehole were carried out. The probability density distribution of the U/Pb ages from both samples are generally clustered into four groupings (i) 500 Ma and 650 Ma, (ii) 800 Ma to 1100 Ma, (iii) 1300 Ma to 1500 Ma and (iv) 2400 to 2600 Ma. Except the uppermost sample at the depth of ~540 m, all deeper samples yield AFT ages younger than the time of deposition. As the present day geothermal gradient in the well is ~29°C/km, this indicates that samples might have experienced some post-depositional heating. This is also confirmed independently by thermal maturity data (% Ro, Rock-Eval® pyrolysis). A preliminary interpretation suggests that this age pattern has resulted from the removal of at least ~1 km of overlying section. Evidence from palaeocurrent studies [Kent, 1991, Geology, 19, 19-23] indicating a sediment source from the southeast of the basin together with the U-Pb detrital zircon data (which correlate well with the earlier studies e.g. Veevers and Saeed, 2009, confirm Antarctica as the major source of sedimentation in the P-G basin.