Assessment of Thermal Maturity, Source Rock Potential and Paleodepositional Environment of the Paleogene Lignites in Barsingsar, Bikaner–Nagaur Basin, Western Rajasthan, India

Abstract

Investigations on the Paleogene lignites were carried out through geochemical, mineralogical and petrographic analyses to assess their paleodepositional environment, source rock potential and thermal maturity. The samples were collected from the Barsingsar lignite mines in the Bikaner–Nagaur Basin, Western Rajasthan, India. Huminite reflectance assigns these samples as lignite (low-rank coal). Barsingsar lignites are dominated by the huminite maceral group, while inertinites and liptinites occur in subordinated amount. The mineral matter is dominated by carbonates, pyrite and argillaceous (in descending order). Gelification index, tissue preservation index, groundwater index and vegetation index indicate the prevalence of a dry forest swamp having ombrotrophic to mesotrophic conditions in the paleomire. Rock–Eval pyrolysis indicates high hydrogen index relative to oxygen index and excellent hydrocarbon potential. The Barsingsar lignites are characterized by mixed type III and type II kerogens, which are thermally immature. Several minerals like quartz, coesite, siderite, aragonite and rutile minerals have been identified by XRD analysis, whereas selected trace elements primarily Sr, Zr, Cu, Pb, Zn, Cr, V, Ni, Rb and Co were also detected. Fourier-transform infrared spectroscopy pattern shows the dominance of clay minerals and the presence of aromatic, aliphatic and some oxygen functional groups in these lignites.