Characterization of Mangrol lignite (Gujarat), India: Petrography, palynology, and palynofacies

A multidisciplinary approach (petrographical, palynological and palynofacies) has been adopted to characterize and assess the depositional conditions of Eocene Mangrol lignite deposit from western India. The petrographic study reveals that the lignite is composed predominantly of huminite macerals produced from a woody forest. The reflectance values range from 0.27% to 0.32%, indicating a lignite rank. The variable values of tissue preservation index (TPI) and gelification index (GI) as well as the maceral composition indicate fluctuating ground water conditions and difference in the type of vegetation during peat accumulation. The palynofloral spectrum suggests the presence of angiosperms (including mangrove) and pteridophytes belonging to families of Bombacaceae, Annonaceae, Alangiaceae, Ctenolophonaceae, Liliaceae, Osmundaceae, Schizaeaceae, Matoniaceae, Cyatheaceae, among others as the peat biomass source materials for the origin of these lignites. The palynomorphs indicate that a tropical to sub-tropical climatic condition was present during deposition of the peat biomass and that the original mire likely occurred in a coastal setting. This interpretation is strongly supported by palynomorphs with affinity to brackish-water taxa. Palynofacies studies suggest peat deposition under dysoxic conditions in a marginal marine setting. High amount of amorphous matter (kerogen type I) in the shale bed above the lignite and very high content of liptinite in lignite, mainly comprised of resinite and liptodetrinite, suggest the potential of both shale and lignite for the generation of hydrocarbon.