Early Eocene biotic assemblage from the sedimentary deposits of the Tarkeshwar Lignite Mine, Gujarat and its palaeoenvironmental implications

Abstract

The Palaeogene biota and the palaeoenvironmental history from the low latitudes are remarkably well–preserved in theopen–cast lignite deposits from Western India. Lignite sequences of the Cambay Shale Formation (Gujarat) have been a majorsource to understand the concept of early evolution of fossils including flora, arthropods, vertebrates fauna, and several aquaticforms during the Early Eocene. The study deals with an extensive record of amber inclusions and extracted pollen, vertebratefragments, dinoflagellate cysts and Carbon isotopes from the lignite and associated sediments from the Tarkeshwar Lignite Mineto add insights into the palaeoenvironment and depositional conditions of the Cambay Basin during the Early Eocene period. Thecurrent study demonstrates that throughout the late Palaeocene and early Eocene epoch, the palaeoenvironment changed fromlow land, marshy (lower portion), to shallow marine environment, presumably due to hyperthermal event PETM (middle part).Age diagnostic taxa, viz. Auxiodinium longispinosum, Apectodinium parvum and early wetzelielloid (Vallodinium? sp.) excursionprovide late Palaeocene–early Eocene period (~56–53 Ma) for the dinocyst interval in the middle part of the section. A pronouncednegative Carbon Isotope Excursion (CIE) in the middle part is correlated to the second Eocene Thermal maximum (53.7 Ma),which is a globally recorded hyperthermal event. During the ETM–2 warming, the rise in pCO2 caused warm, humid conditionsas well as a rise in sea level, which may have contributed to the establishment of constrained shallow marine environments in theexamined middle unit sedimentary succession. Floral (spore–pollens, leaf, wood, seed, fruits) and faunal assemblages (Crocodiles,fish remains, amber insects) revealed the prevalence of a dense tropical luxurious rain forest (floral and faunal) near shore duringthe ETM–2 in the Tarkeshwar Lignite Mines, Cambay Basin.