Abstract: Loess-paleosol sequences were recognized as one of the most completed terrestrial records of palemonsoon climate evolution. The chemical parameters and metallic elements were normally used to indicate the soil sources and environmental changes. This study investigated the characteristics of the long-term climate evolution in the upper reaches of the Hanjiang River Valley using the heavy metallic elements variations, which was not commonly adopted by previous researchers. Loess-paleosol soil samples were collected from the first step terrace of the upper reaches of the Hanjiang River Valley. The heavy metallic element contents of Ni、Mn、Cu、Zn、As、Ti、V、Pb in the soil were measured and analyzed as the main climate change indicators. Magnetic susceptibility, Rb/Sr ratio and clay content were selected as the supplement indicators. The results showed that Cu, Ni, As, Pb and Mn contents in the soil were affected by climate changes and the pedogenesis environment and were significantly and positively correlated with the index of Pedogenic (magnetic susceptibility, Rb/Sr ratio and clay fraction of particle-size). Strong pedogenesis made some soluble elements migrate to deeper soil layers, leading to relative enrichment of heavy metals in the paleosol. According to the vertical distribution of the heavy metallic elements, the upper reaches of the Hanjang Valley experienced 5 stages of the climatic changes since the lift of the first step terrace. The climate was warm and humid in the Mid-Holocence except a cold and dry event happened at 6-5 ka B.P.

Key words: loess-paleosol, heavy metal, climate evolution, the upper reaches of the Hanjiang River Valley