Response of tropical rainforest to warming during Middle Eocene Climate Optimum (MECO): Evidence from palynological record from the Bartonian deposits of Kutch Basin, Western India

Abstract

The Middle Eocene Climatic Optimum (MECO), at ∼40 Ma, is considered a transient global hyperthermal event that superimposed the long-term cooling phase of the middle to late Eocene. The event is largely construed from the marine province but less in the continental depositional systems. The present palynological and isotopic study from the age-constrained Harudi Formation succession of the Kutch Basin, Western India, aims to understand the impact of MECO warming on Eocene tropical rainforest and environments. The carbon isotopic characterization (δ¹³C values) of the studied succession exhibited a pronounced negative Carbon Isotope Excursion (CIE) of about 2.5 ‰, correlated to the peak warming phase of the MECO event. The middle Eocene climate was warm and wet, as indicated by the existence of a diverse array of tropical flora in the region. Notably, the peak warming MECO phase is characterized by the infringement of deciduous elements, indicating the seasonality in rainfall pattern. The subdued mangrove community is also a testimony to salinity fluctuations in the depositional system due to intermittent surges of fresh-water flux. During the recovery phase after the peak warming, the evergreen flora restored in tropical rainforests and mangroves flourished under relatively stable environmental conditions. However, the diversity patterns show an overall decline in diversity. On a wider perspective, the study demonstrates the sensitivity of the tropical rainforests and mangrove communities in response to fluctuating environmental conditions during the high atmospheric CO₂ levels and increased temperatures of MECO.