Paleoenvironmental, paleovegetational, and paleoclimatic changes during Paleogene lignite formation in Rajasthan, India

This study provides detailed information about the geochemistry and coal petrography of Paleogene lignite deposits of Bikaner-Nagaur Basin and the Barmer Basin of Rajasthan, India, which have been used to reconstruct paleoclimatic, paleovegetational, and paleodepositional conditions. Petrographic characteristics show the dominance of huminite group macerals followed by inertinite and liptinite group macerals in Rajasthan lignites. The mean random huminite reflectance value (%Ro m ) ranges from 0.27 to 0.33%, which put these lignites as low-rank lignite ‘B’. 13C NMR spectra show sharp peaks in the aliphatic region, indicting immaturity of organic matter. These peaks confirm the presence of aliphatic CH 2 , aliphatic –CH 3 bonding, protonated aromatic carbons, and oxygenated aromatic carbon atoms (Ar-O). δ 13 C values in xylite-rich lithotype range from − 25.04 to − 25.61‰, indicating the contribution of gymnosperm plants ( Taxodiaceae during) in peat. Whereas, δ 13 C in matrix-rich lithotype range from − 26.82 to − 27.44‰, and show the presence of angiosperm taxa ( Typhaceae , Iridaceae , and Gramineae ) during peat formation in the study area. The samples dominated by huminite group macerals have a slightly low δ 13 C value than inertinite-rich samples. In contrast, the least δ 13 C value has been recorded in the liptinite rich samples. δ 13 C values also suggest C 3 plants to be the main peat-forming vegetation in the study area during the Paleogene. The mineralogical study indicates peat formation in semi-arid to slightly arid climatic conditions. The presence of framboidal pyrite, alginite, funginite macerals, and high sulfur content of the studied lignites indicate marine incursion in the basin.