Periodic variations of alpine glaciation and desertification of the NE Tibetan Plateau: Evidence from the loess-paleosol sequences in the Menyuan Basin

The NE Tibetan Plateau (NETP) is one of the most ecologically vulnerable areas, with large expansion and retreat of desert area since the Last Glacial Maximum. However, the long-term history of desertification in this area and its mechanisms are still unknown due to lack of long-term and well-dated records. Here we present the results of sand particle content (a proxy of local materials) and detrital-zircon ages from a high-resolved loess-paleosol section spanning the past 420 ka in the Menyuan (MY) Basin lying in the NETP. Our results show that the provenance of loess units (formed in glacial periods) was strongly influenced by local desertified materials that were mainly produced by alpine glaciers surrounding the basin, which was significantly different from the paleosol units (formed in interglacial periods). The strong signals of ∼100 kyr and ∼ 20 kyr cycles in the content of local materials suggest that the desertification of the MY Basin was controlled by both the late Quaternary ∼100-kyr ice age and the ∼20-kyr precession cycles, which is obviously different from the periodicities of the classic Luochuan loess section in the mainland of the Chinese Loess Plateau (CLP). The strong ∼20-kyr cycle in the MY Basin suggest that the alpine glaciation activities in the NETP were driven by local summer insolation. These results allow us to characterize the long-term natural variability of desertification in the NETP, as well as the mechanisms for the spatial and glacial-interglacial variations of loess provenance on the CLP.