Late Neogene monsoonal climate in the southeastern margin of the Tibetan Plateau revealed by leaf physiognomy evidence

Four fossil leaf assemblages from the Late Miocene to the early Late Pliocene of the Tengchong-Lianghe region, western Yunnan, China, are subjected to the Climate-Leaf Analysis Multivariate Program (CLAMP) and Leaf Margin Analysis (LMA) and compared with other late Neogene fossil flora from the southeastern margin of the Tibetan Plateau (SEMTP) and the eastern Himalayan foreland basins to reconstruct paleoclimate and capture ancient monsoon signature. The CLAMP-derived mean annual temperature (MAT) for the Late Neogene in Tengchong-Lianghe range from 17.9 ± 2.3 °C to 21.0 ± 2.3 °C, with the Early Pliocene being the warmest period, while the growing season precipitation (GSP) range from 1905 ± 481 mm to 2006 ± 481 mm with minimal change over time. The CLAMP and LMA results indicate a warmer and wetter climate in the late Neogene of the SEMTP and suggest that the paleoclimate in western Yunnan from the Late Miocene to early Late Pliocene was primarily influenced by global climate evolution rather than topographic changes. CLAMP results indicate that the modern pattern of the Asian Monsoon was established at least by the Late Miocene, though precipitation seasonality in the late Neogene of the SEMTP was weaker than today, likely attributed to the intensification of the East Asian Winter Monsoon driven by global cooling.