Biomarkers Indicate Pliocene Uplift of the Maxian Mountains, Northeastern Tibetan Plateau

Knowledge of Late Miocene-Early Pliocene environmental change is critical for understanding the interactions among global cooling, regional tectonic activity and Asian climatic evolution. However, their relationships remain unclear, partly due to the scarcity of quantitative reconstructions of temperature and hydroclimatic conditions, which limits our understanding of the effect of topography on montane climatic evolution. Here, we quantitatively reconstructed the Late Miocene-Early Pliocene temperature, hydroclimate, and pH of the Xiaoshuizi peneplain, northeastern Tibetan Plateau (NETP), based on glycerol dialkyl glycerol tetraethers. Our results indicate that the Xiaoshuizi temperature was relatively high with large fluctuations during 6.2–4.6 Ma. The temperature then gradually decreased until 4.0 Ma, when this trend was interrupted by an intensive warming event. Additionally, the combined R_i/b and pH proxies revealed that the Xiaoshuizi region experienced a hydroclimatic transition from relatively wet to dry conditions after 4.0 Ma. Our integrated results show that the Xiaoshuizi climate became warm and dry during 4.0–3.6 Ma, in contrast to the global cooling trend and the occurrence of a humid climate on the eastern Chinese Loess Plateau and the North China Plain. We ascribe this anomalous change to a warm and dry climate during 4.0–3.6 Ma to a topographic Foehn effect triggered by surface uplift of the Maxian Mountains associated with extensive tectonic uplift of the NETP during the Middle Pliocene.