Magnetostratigraphic constraints on the age of the Hipparion fauna in the Linxia Basin of China, and its implications for stepwise aridification

Abstract Late Cenozoic sediments in the Linxia Basin of China, on the northeastern Tibetan Plateau, bear abundant fossils of the Hipparion fauna. From late Miocene times, these sections record a history of aridification in the Asian Interior, the evolution of the east Asian monsoon, and multiple uplifts of the Tibetan Plateau. In this paper, a new detailed magnetostratigraphic study of a sedimentary sequence from the Duikang (DK) section containing the Hipparion fauna is presented, to better understand interconnected ecologic and environmental changes. The 90-m-thick section reveals nine normal and nine reversed zones that span from chron. C5n.2n to chron. C3Ar or from chron. C4n.2n to chron. C2Ar, yielding magnetostratigraphic ages of ∼8.1 Ma - 3.7 Ma for the studied section and 5.3 Ma for the Hipparion fauna-bearing bed. Combined with all the previous magnetostratigraphic ages of the fauna-bearing sediments in the Linxia Basin, Hipparion can be distinguished as mainly having lived during five periods: Phase I (11.5 Ma), Phase II (8.2 Ma), Phase III (6.3 Ma), Phase IV (∼5.3 Ma) and Phase V (2.5 Ma). Based on comparison of climate records in the Linxia Basin with aridification records from surrounding regions and global cooling during the late Cenozoic, we suggest that the evolution of Hipparion from the Linxia Basin was mainly driven by continuous global cooling and tectonic uplift of the northeastern Tibetan Plateau since the late Miocene.