Depositional palaeoenvironment and economic potential of Khadsaliya lignite deposits (Saurashtra Basin), western India: Based on petrographic, palynofacies and geochemical characteristics

The lignite and associated shale of the Khadsaliya Clays Formation (Eocene) of Saurashtra Basin, India have been studied. Organic petrographic, palynofacies and organic geochemical analyses have been carried out to deduce the depositional palaeoenvironment, including the assessment of the hydrocarbon potential of this sequence. Petrographically, the lignites constitute huminite macerals in dominance (av. 60%). The organic facies, as derived from maceral composition and biomarker data, suggests that the peat biomass was formed from woody forest vegetation consists of angiosperms and pteridophytes. Microbial activity was also prominent over the peat biomass. The peat biomass was deposited in tropical-subtropical humid climatic conditions under deltaic control and brackish water influence. Further, there are signatures of intermittent floods in the mire, and is evident from the shift from mesotrophic to rheotrophic conditions. The organic matter has been categorized into two palynofacies and is derived from degraded terrestrial biomass. The extrapolation of Tyson's APP diagram and Pr/n-C17 vs. Ph/n-C18 plot suggest that deposition took place in dysoxic to sub-oxic conditions.