From Peat Mire to Petroleum Source: Kerogen Characteristics, Transformation Kinetics, and Depositional Controls on the Jalipa Lignite Deposits, Western India

ABSTRACT The lignite and associated carbonaceous shales of the Jalipa mine sequence, Barmer Basin, were investigated using integrated petrographic and geochemical approaches to reconstruct the paleodepositional environment, evaluate kerogen transformation kinetics, and assess their hydrocarbon generation potential. The lignite samples are characterized by the dominance of huminite group (51.3–82.6 vol.%), with subordinate liptinite group (4.4–29.5 vol.%) and minor inertinite group (from 0.4 to 8.5 vol.%). The mineral matter content varies from 3.3 to 36.2 vol.%. The total organic carbon (TOC) content in lignite ranges from 41.54 to 60.76 wt.%, whereas the TOC content of carbonaceous shale varies from 24.51 to 39.58 wt.% suggesting organic richness. The hydrogen index (HI) varies from 136 mg HC/g TOC to 549 mg HC/g TOC, and the T max value varies from 386°C to 422°C. The lignites are generally characterized by intense aliphatic (–CH 2 and –CH 3 ), aromatic (C = O and C = C), and broad hydroxyl (–OH) peaks, whereas carbonaceous shales showed both organic and inorganic constituents. Together, the Rock‐Eval pyrolysis and Fourier transform infrared spectroscopic (FTIR) parameters suggest mixed Type III–II kerogen in the studied samples. The kinetic behavior, including activation energy ( E a ) distribution, kerogen transformation ratio (KTR), and hydrocarbon generation rate (HGR) profiles, is strictly governed by variations in reactive maceral (RM) and organic matter (OM) heterogeneity. The individual dominance of huminite maceral and the presence of mineral matter indicate a woody plant material source, wet moor environment with intermittent moderate flooding in the depositional milieu. Topogenous‐to‐coastal depositional condition existed in this region as inferred from the sulfur and TOC contents; however, the overall low sulfur values indicate marginal or minimal marine influence. Nevertheless, the sharp increase in the paleoredox factor (PRF) and relative hydrocarbon potential (RHP) is an indication of the occasionally elevated water level conditions in the basin. Overall, the studied lignites and carbonaceous shales exhibit favorable characteristics for hydrocarbon generation (oil and gas) and potential for sustainable utilization.