Eocene Hyperthermal Events Drove Episodes of Vegetation Turnover in the Fushun Basin, Northeast China: Evidence from a Palaeoclimate Analysis of Palynological Assemblages

The response of terrestrial ecosystems to Eocene hyperthermal events remains poorly understood. In this paper, we report palynological assemblages from an astronomically-calibrated Eocene succession in the Fushun Basin of northeast China, in which previous δ13C studies have identified the Eocene Thermal Maxima 2 and 3 (ETM2, ETM3), the Early Eocene Climatic Optimum (EECO), and the Middle Eocene Climatic Optimum (MECO). In the samples that are directly associated with hyperthermal events, palynoassemblages show significant increases in the abundance of conifer pollen, especially Abietineaepollenites and Taxodiaceaepollenites, and fern spores of Polypodiaceaesporites, while angiosperm taxa reduce in frequency. Quantitative palaeoclimate parameters derived through the application of the Coexistence Approach to palynological assemblages indicate marked changes in temperature and humidity during hyperthermal events. These changes were most significant during ETM2 when mean annual temperature increased by 3–5 °C and mean annual precipitation increased by approximately 600 mm above background levels, but similar perturbations are also associated with the other hyperthermal events. An increase in organic abundance in lacustrine oil shale facies during hyperthermal events may imply that elevated humidity drove enhanced runoff, nutrient supply, and eutrophication of the hydrologically-open lake basins at a time when terrestrial carbon export from humid forests was also enhanced. Findings demonstrate that short-term bursts of Eocene warming drove major turnovers in the mid-latitude vegetation of Asia, reworking landscapes, and transforming regional hydrology.