A study on benthic molluscs and stable isotopes from Kutch, western India reveals early Eocene hyperthermals and pronounced transgression during ETM2 and H2 events

Abstract

The early Eocene greenhouse Earth experienced several transient global warming events, indicated by sharp negative excursions in the stable isotope ratios of carbon and oxygen. A huge amount of CO2, enriched with 12C, was released in the ocean–atmosphere system leading to warming. The Paleocene–Eocene boundary is demarcated by the most significant and well-known hyperthermal event, Paleocene–Eocene thermal maximum (PETM). The PETM is documented to be accompanied by a transgression. The later hyperthermals are relatively less studied. Information on the hyperthermals from the palaeo-tropical basins are relatively few. Here, we present a high-resolution litho-, bio- and isotope–stratigraphic analysis of the early Eocene succession from the Kutch Basin, western India. Stable isotopes of carbon and oxygen were analysed from sediments (δ13Corg) and mollusc shells (δ13Ccarb and δ18Ocarb). The succession, prevailingly with lignite, along with carbonaceous black shale and plenty of fossil plant remains, is primarily a product of terrestrial environment. A pronounced marine transgression, characterised by marine mollusc bearing glauconitic shale in the middle of the succession, indicates a coastal transitional setting between the ocean and land. The δ13C curve of organic carbon reveals five negative excursions, which are identified as the PETM, Eocene thermal maximum 2 (ETM2)/H1, H2, I1 and I2 in ascending order. The hyperthermal pair of ETM2–H2 corresponds with the marine interval. δ13Ccarb and δ18Ocarb from the middle part of the succession reveal concomitant negative excursions. The association between these hyperthermals and transgression appears to be regionally and globally valid, which strongly suggests a causal link between them.