Organic geochemical characteristics of Nagaur lignites, Rajasthan, India, and their implication on thermal maturity and paleoenvironment.

Lignite samples from Nagaur district, Rajasthan, have been collected for petrographic and organic geochemical analyses following the pillar sampling method. The reflectance of Eu-Ulminite-B ranges from 0.20 to 0.49 with a mean of 0.33%Ro, putting them as “Low-Rank B” coal. Hydrogen index values imply type-III kerogen, while the values of Tmax (402 to 411°C) indicate that these coals are thermally immature. Gas chromatography data reveal the presence of n-alkanes from C14 to C33 with a predominance of odd n-alkanes over the even homologues. Pristane vs. phytane ratio indicates anoxic conditions during the deposition of the organic matter. Saturated fractions of studied lignites suggest a contribution from both conifers and angiosperms as source vegetation. [ABSTRACT FROM AUTHOR]