Late early to early middle Eocene climate and vegetation change at Tastakh Lake (northern Yakutia, eastern Siberia)

The late early – early middle Eocene climate and vegetation evolution in northern Yakutia (Eastern Siberia) is quantitatively studied in detail for the first time, based on a palaeobotanical record. Palaeobotanical data for this time interval were obtained from 16 palynofloras from continental sediments on the southern shore of Tastakh Lake (the left bank of Indigirka River). In this first integrative study, we applied the Coexistence Approach for quantification of palaeoclimate, the Plant Functional Type (PFT) approach and Integrated Plant Record (IPR) vegetation analysis to quantify palaeovegetation. Our investigation documents the persistence of warm temperate and, at times, nearly tropical climate conditions in the earlier part of the record and the subsequent onset of a cooling trend. Overall humid climate conditions prevailed throughout the late early – early middle Eocene. Our reconstruction indicates low temperature seasonality and relatively strong seasonality in precipitation. Vegetation data as reconstructed are in good agreement with the climate evolution. PFT diversity spectra indicate the prevalence of mixed evergreen-deciduous forests of warm temperate character. The IPR method suggests that the mixed mesophytic forest biome persisted throughout the studied sedimentary succession. The presence of mangroves in our late early Eocene records (at the base of the section) is largely in line with our climate reconstruction and possibly can be related to the Early Eocene Climatic Optimum (EECO) hyperthermal event.