Multiproxy records in middle–late Miocene sediments from the Wushan Basin: Implications for climate change and tectonic deformation in the northeastern Tibetan Plateau

Abstract

AbstractTo help understand the relationship between global cooling and Tibetan uplift in the middle to late Miocene, multiple proxy data including carbonate stable isotope records, magnetic susceptibility, and sediment color references were obtained from a magnetostratigraphic section (14.5–6.0 Ma) of the Wushan Basin along the northeastern margin of the Tibetan Plateau. New proxies identify two phase changes that may have been controlled by global cooling and tectonic deformation at this time. During 14.5–13.2 Ma, positive shifts of ∼2.0‰ in δ18O and δ13C, an increase in lightness (L*), and a decrease in redness (a*) suggest gradually increasing aridity. Relatively high δ18O and δ13C values and low a*/L* and magnetic susceptibility values continue until ca. 10 Ma, when δ18O and δ13C significantly decrease and redness as well as magnetic susceptibility significantly increase. The negative shifts in δ18O and δ13C and increases in redness and magnetic susceptibility at 10 Ma are consistent with coeval basin environment and provenance changes. Combining these data with basin analysis, we suggest that global cooling was the dominant factor and Tibetan uplift was the subordinate factor for the middle Miocene aridification of the Wushan Basin. In contrast, the contribution of Tibetan uplift was dominant and global climate change was subordinate in the late Miocene basin paleogeographic reorganization.