Petro-chemical characterisation and depositional paleoenvironment of lignite deposits of Nagaur, Western Rajasthan, India

Abstract

The objective of this study was to know about the depositional environment and petrographic characteristics of lignite deposits of the Nagaur district, Rajasthan, India, and to decipher source rock potential. Lignite samples have been collected from all the working and exposed lignite seams from Matasukh lignite mines of Nagaur following the pillar sampling method. The petrographic study has been done following the International Committee for Coal and Organic Petrology and ISO norms. The study has shown that Nagaur lignites are mostly dominated by the huminite group of macerals followed by liptinite group. The huminite group is mainly represented by attrinite, textinite and ulminite, whereas liptinite is represented mainly by primary liptinites such as resinite, sporinite, suberinite and cutinite. An inertinite group of macerals occurs in the least concentration as compared to the huminite and liptinite group macerals and mainly represented by the semifusinite, funginite and inertodetrinite. In these lignites, carbonate mineral matters are dominating over the pyrite and argillaceous mineral matter. The maceral constituents present in the studied samples indicate a high proportion of type III kerogen and are capable of generating gases only. Based on the reflectance of Eu-ulminite B maceral, Nagaur lignites may be classified as ‘Low-rank B’ (lignite B). The study reveals that lignites originated in the bog forest under ombrotrophic to mesotrophic hydrological conditions. Gelification Index and the Tissue Preservation Index suggest an accumulation of peat in the marshy environment.