Evolution of Permian coals of Hasdeo Basin, India: Insights from Organic Petrology, Geochemistry, and Stable Isotope analysis.

Two coal mines namely Kurja and Jhiriya were selected for investigation using multiproxy approach which included organic petrology, geochemistry and stable carbon and nitrogen isotope to reveal coal characteristics, paleo-depositional conditions and precursors material responsible for the paleomire. The results from the analysis reveal that the degraded humic material for the coal deposits was supplied from the surrounding terrestrial vegetation typical as vitrinite dominates the maceral groups followed by inertinite and liptinites. The degraded organic detritus in the samples suggest regular inundation of the mire aiding in degradation of the organic matter. The mineral matter observed through coal microscopy are dominantly argillaceous which is supported by mineral phases supported by x-ray diffraction and x-ray fluorescence studies. It is more likely that the Hasdeo basin coals were possibly deposited in the lacustrine environment with intermittent influx of siliceous detrital matter through fluvial channels. The geological setting and tectonics probably aided syn-rift sedimentation during the Permian. The mires shifted from rheotropic to mesotrophic regime due to the fluctuations in the water table during the evolution of the mire. The various indices such as the CIA, ICV, PIA and CIW are suggestive of moderate to intense weathering condition prevailing in the basin, the sediments were chiefly sourced dominantly from felsic with lesser input from mafic sources. The samples are rich in volatile matter (25.34 - 42.44 wt% on daf basis) in Kurja and (30.2 - 40.12 wt% on daf basis) in Jhiriya revealing low in rank which is also corroborated by the maturity parameter, vitrinite reflectance (random) having mean 0.40% in Kurja and 0.43% in Jhiriya. High oxygen to carbon and low hydrogen to carbon ratio suggest oxidation of the organic detritus in the mire. The elemental ratio in conjunction with stable carbon and nitrogen isotope are indicative of sedimentary organic matter sourced from C3 terrestrial plants. The carbon isotopic excursion in the basin based on delta δ13C aligns well with the global data in the isotopic shift in the coal and carbonaceous material revealing the paleo atmospheric carbon during the Permian periods. The study establishes the coeval nature of evolution of the isolated Gondwana sequences in the Indian sub-continent and in the various parts of the world.