Leaf wax stable isotopes from Northern Tibetan Plateau: Implications for uplift and climate since 15 Ma

Abstract

The growth of Tibetan Plateau is considered to have played a key role during the evolution of Asian climate. Our understanding of the relationship between the plateau growth and Asian climate changes is limited, however, due to the scarcity of well-dated sedimentary sequences that could provide parallel information of the evolution of elevation and climate. Here, we report a high-resolution time series record of the stable hydrogen isotopic composition of leaf-wax n-alkanes (δDn-alk) from a continuous Neogene stratigraphic sequence (15–1.8 Ma) from the Qaidam basin on the northern Tibetan Plateau. These data are used to reconstruct the isotopic composition of meteoric waters (δDm) and subsequently applied to interpret the history of paleotopography and climate in Qaidam.Our results indicate four stages in the evolution of hydrology in the Qaidam basin. In Stage I (15 Ma to 10.4 Ma), δDm gradually decreases from −24.9‰ to −75.5‰, synchronous with a period of active tectonism. The estimated topographic growth of 2.1±0.3 km is comparable to the height of Qaidam basin relative to the foreland Hexi Corridor. We note that C3 plants were dominant in this region since the Miocene; we take this as independent evidence that this area was mountainous before the C4 expansion in late Miocene and Pliocene. δDm variability in subsequent stages appears to be related to shifts in dry and moist conditions and independent of topographical changes — a conclusion supported by other independent climatic records on the Tibetan Plateau. High δDm values in Stage II (10.4 Ma to 6.9 Ma) are related to severe aridity, and Stage III (6.9 Ma to 4.1 Ma) is marked by low δDm values, suggestive of moist conditions related to the strengthening East Asia Summer Monsoon. High δDm values in Stage IV (4.1 Ma to 1.8 Ma) reflect a climate, drier than the present.