Palaeoenvironmental and chronological constraints on the Early Pleistocene mammal fauna from loess deposits in the Linxia Basin, NE Tibetan Plateau

The Longdan mammal fauna from the central part of Linxia Basin, NE Tibetan Plateau, is the first Early Pleistocene fauna in China in which the fossils are derived loess deposits, and it provides an excellent opportunity to document mammalian and environmental evolution in Asia. However, the precise age and palaeoenvironmental setting of the fauna are controversial due to the poor exposure of the outcrop section. In the present study, a 105-m-long drill core was obtained from Longdan village and used for detailed magnetostratigraphic dating. The results demonstrate that the late Pliocene- Pleistocene loess deposits in the Longdan section deposited since ca. 3 Ma and that the Longdan fauna has an age range of 2.5-2.2 Ma. In addition, the results of lithological and rock magnetic analyses demonstrate that paleosols are weakly developed throughout the whole core and that in the lower and middle parts the core the magnetic susceptibility and its frequency dependence are relatively low and uniform. These observations, combined with the ecological characteristics of the Longdan fauna, indicate that during the Early Pleistocene the climate in the Longdan area, and even in the Linxia Basin, was sub-humid and that the aeolian dust was frequently subjected to post-depositional reworking by water.