The late Eocene rise of SE Tibet formed an Asian 'Mediterranean' climate.

Southeastern (SE) Tibet forms the transition zone between the high interior Tibetan Plateau and the lowlands of southwest China. So understanding the elevation history of SE Tibet, a biodiversity hotspot, enlightens our understanding of the interactions between tectonics, monsoon dynamics and biodiversity. Here we reconstruct the uplift history of the Markam Basin, SE Tibet, during the middle−late Eocene based on U − Pb dating, plant fossil assemblages, and stable and clumped isotope analyses. Our results suggest that the floor of the Markam Basin was at an elevation of 2.6 ± 0.9 km between 42 Ma and 39 Ma, where the mean annual air temperature (MAAT) was 13.2 ± 2.4 °C. The basin then rose rapidly to 3.8 (+0.6/−0.8) km before 36 Ma. Integrated with existing paleoelevation data, we propose that the high plateau boundary (∼3.0 km) of SE Tibet formed during the late Eocene. Numerical climate modeling with realistic paleo-landscapes shows that with the rise of SE Tibet, a Mediterranean-like climate developed in the region characterized by bi-modal precipitation with two wet seasons in boreal spring and autumn. The high topographic relief of SE Tibet, coupled with this distinctive Mediterranean-like climate system, helped develop the high biodiversity of the Hengduan Mountains. • An absolute U Pb age framework of the Markam Basin gave a range of ∼42–36 Ma. • The Markam Basin stayed at ∼2.6 km during 42–39 Ma. • The Markam Basin uplifted to its modern elevation (3.8 km) before 36 Ma. • The high plateau boundary of SE Tibet formed during the late Eocene. • A late Eocene Mediterranean-like climate formed across SE Tibet and adjacent areas. [ABSTRACT FROM AUTHOR]