Record of Early to Middle Eocene paleoenvironmental changes from lignite mines, western India

Abstract. Various Eocene hyperthermal events have been recorded from lignite sections of western India in the past decade. To infer the paleoenvironment, during a warm paleotropical climate of India, we have assessed multiple microfossil groups like pollen/spores, dinoflagellates and foraminifera from Early Eocene lignite mine sections from the Cambay (Surkha) and Barmer (Giral) basins and Middle Eocene sections from the Kutch Basin (Matanomadh and Panandhro mines) of western India. The Surkha and Giral sections exhibit a dominance of rainforest elements ( Arengapollenites achinatus, Longapertites retipilatus ), thermophilic mangrove palm Nypa and (sub)tropical dinoflagellate cyst Apectodinium, Cordosphaeridium and Kenleyia . This palynomorph assemblage is indicative of a marginal marine setting within a hot and humid climate. During the Middle Eocene, the diversity of dinocyst assemblage increased and a decrease in percentage of mangrove elements was observed in the Matanomadh and Panandhro mine sections of the Kutch Basin as compared to the Early Eocene sections of western India. Bloom of triserial planktic ( Jenkinsina columbiana ) and rectilinear benthic ( Brizalina sp., Trifarina advena rajasthanensis ) foraminifera indicates eutrophic conditions of deposition during the Late Lutetian–Early Bartonian in the lignite sections of the Kutch Basin which later changed to oligotrophic, open marine conditions towards the Bartonian (planktic E12 zone). This change to oligotrophic conditions coincides with a drastic increase in diversity of planktic foraminifera in the top portion of lignite mines of the Kutch Basin which may be correlated with the Kirthar–Wilson Bluff transgression event in the Bartonian observed across basins in India, Pakistan and Australia potentially linked to sea level rise around the Middle Eocene Climatic Optimum.