Stepwise hydroclimate changes in Northeast China linked to proto-Paratethys Sea retreats and global cooling during the Eocene.

Previous paleoenvironmental studies have revealed three latitudinally distributed climate zones across East Asia during the Eocene, including a vast humid climate zone in northeast China. However, the formative cause, long-term evolution, and related driving mechanisms of this humid climate remain largely unknown. Here, we reconstruct a long-term, continuous evolutionary history of Eocene hydroclimate and vegetation from the Fushun Basin (northeast China) by analyzing synthesized palynological and lithofacies records. These results reveal three distinct paleoenvironmental intervals with characteristic lithological and palynological features superimposed on a long-term stepwise cooling and drying trend during the Eocene. The interval from the late Paleocene to early Eocene is characterized by coal seams and the dominance of swamps and broadleaved forests, indicative of a warm and humid climate. The middle Eocene (∼46–41.2 Ma) is characterized by oil-shale deposits and a substantial increase in broadleaved forests, associated with a relatively warm and humid climate. The late Eocene (41.2–37.8 Ma) is distinguished by the onset of mudstone–shale cycles and a substantial increase in xerophytic shrubs and coniferous trees, associated with a cooler, drier climate and increased climatic variability. Notably, these phases temporally correlate with three progressively smaller incursions superimposed on a pattern of long-term proto-Paratethys Sea retreat. This finding demonstrates that the stepwise westward retreat of the proto-Paratethys Sea played at least an equally important role as long-term global cooling in regulating hydroclimate changes in mid-latitude Asia. • Eocene palynological and lithofacies records of Fushun Basin were synthesized. • Eocene climate and vegetation changes were divided into three distinct stages. • Northeast China's moisture driven by westerlies modulated by proto-Paratethys Sea. [ABSTRACT FROM AUTHOR]