Vittoria Lauretano, Caitlyn R Witkowski , Alex Farnsworth, Shufeng Li, Shihu Li, Jan Peter Mayser, B. David A. Naafs, Robert A. Spicer, Tao Su, He Tang, Zhekun Zhou, Paul J Valdes, Richard D Pancost

During the late Eocene to the early Oligocene, marine records document a globally congruent record of declining carbon dioxide concentrations, Antarctic icesheet growth, and associated reorganisation of the global climate system. In contrast, the few existing terrestrial records demonstrate high heterogeneity of environmental change and are difficult to reconcile with those of the oceanic realm. Global drivers for climatic change are particularly difficult to disentangle from regional ones, especially those caused by the complex tectonic evolution of the Tibetan region and its influence on the Asian monsoon system and vegetation. Here, we reconstruct the climatic and environmental history from the late Eocene into the early Oligocene at Lühe Basin, Yunnan, China, a key sedimentary repository along the SE margin of the Tibetan Plateau and an important region for assessing Asian monsoon changes. We investigate a 340-m long section via a multi-proxy approach and climate model simulations. The organic geochemical proxies, via n-alkanes, terpenoids, and hopanes, suggest that thermally immature sediments were deposited in a terrestrial flood plain basin that was primarily occupied by gymnosperms and angiosperms. Branched glycerol diakyl glycerol tetraethers indicate relatively stable temperatures (ca. 10 °C) throughout the section, including across the Eocene-Oligocene boundary. This temperature, cooler than the modern-day average for this site (ca. 15 °C), suggests that this area has not undergone significant uplift since the Oligocene. To further contextualize our data, we tested a suite of climate model simulations with varying pCO2, paleogeography, and Tibetan topography across the Eocene-Oligocene boundary. This data-model comparison suggests that a response to regional factors might explain the absence of a pronounced cooling at Lühe across the Eocene-Oligocene boundary, supporting the emerging picture that the global expression of the EOT in terrestrial environments is more complex than indicated by the marine record.