Source and depositional conditions of early Palaeogene coal-bearing sediments, Meghalaya, Eastern India

The early Palaeogene coals of Meghalaya represent the primitive rainforest elements that evolved in eastern India and one of the principal source rocks of the Assam Basin. Yet, a comprehensive palynological study and information about the source, depositional environment, diagenetic and thermal alterations of biomolecules in terrestrial lipids are largely lacking. This study investigates the palynology, mineralogy, hydrocarbon potential, biomarker compositions, and stable carbon isotopes from early Palaeogene coal-bearing sediments from the Tura Formation, Meghalaya. Terrestrial elements that formed these coals were mainly derived from the Bombacaceae and Arecaceae families of angiosperms, Araucariaceae family of gymnosperms and pteridophytes of Osmundaceae and Schizaeaceae families, revealed by palynological and biomarker records. The thermal maturity of the coals ranges from the late diagenetic to the early catagenetic stage. The transformation of higher plant triterpenoids from parent lipid macromolecules is attributed to early diagenetic microbial changes in terrestrial environments and subsequent coalification. The palynofloras, carbon stable isotope and XRD results indicate that the Tura Formation was deposited in a marginal marine environment within tropical-subtropical latitudes, in humid and warm climatic conditions during the late Palaeocene-early Eocene.