Palynological and organic geochemical studies of the middle Eocene Siju Formation of Garo Hills, Meghalaya, India

Detailed palynological and organic geochemical analysis of middle Eocene marlstones from the Siju Formation, Garo Hills of Meghalaya, were undertaken. All marl samples contained abundant organic wall dinoflagellate cysts and a few number of spores-pollen grains, foraminiferal linings and calcareous foraminifera. The palynological assemblage consists of 21 genera and 35 species with fungal remains. The occurrence of palynofloral assemblage indicates the prevalence of tropical–subtropical with humid climatic conditions. The deposition environment of the Siju Formation has been interpreted as the neritic setting. Organic matter is thermally immature representing type III–type IV kerogen with low total organic carbon (<0.72%). The biomarkers suggest microbial degradation of both reworked and terrestrial organic matter. Occurrence of polycyclic aromatic hydrocarbons indicate charred biomass transported from the land. Research Highlights An integrated study of palynology and organic geochemistry was carried out in the middle Eocene of the Siju Formation of Garo Hills, Meghalaya. Dinoflagellate cysts and spores, and pollen grains suggested that the Siju Formation has tropical-subtropical and neritic settings. The biomarkers indicated microbial degradation of both reworked and terrestrial organic matter. Rock-Eval pyrolysis and total organic carbon (TOC) analysis suggested the thermal maturity and type of kerogen