Reconstruction of the landslide history since late Pleistocene of theBaxie River Catchment in Linxia Basin

Landslide is an active process in the northwest part of the Loess Plateau since Late Pleistocene, especially since Holocene. Landslide events are the coupling results of endogenic and exogenic geological processes. The relics of landslides of different ages since late Pleistocene are well preserved in the Baxie catchment, Linxia Basin, providing ideal material for the research of past environmental changes. Through detailed fieldwork, the authors recognized the characteristics and patterns of landslide of different ages. There are four main formation styles of the loess-mudstone landslides in the research area, which are deep-seated pressure-fracture loess-mudstone slide, deep-seated slippage loess-mudstone slide, medium and shallow creep loess-mudstone slide, and loess collapse, respectively. Ancient landslides from late Pleistocene have distinct armchair terrain and steep scarps, the landslide deposits were often dense and weathered by gullies in the deposits surface. The old landslides since the early Holocene have also armchair terrain and steep scarps, but the deposits were relatively loose. The new landslide since late Holocene have more landslide signatures, such as cracks near the back and side boundaries. Many landslides experienced several sliding events, resulting in several terraces in the landslide deposits body. Organic material in the landslide buried surface, and deposits of short-term water body in the landslide depressions can be dated to define the timing of landslide events. Samples for 14C dating were from two types of materials: landslide buried animal and plant relics and organic-rich deposits formed in the short-term waterbody in landslide depression areas. OSL samples were from four types of materials: (1) chaotic sediments formed in the landslide processes; (2) sediments formed in the short-term waterbody in the landslide depression areas; (3) lowest part of landslide deposits; and (4) materials in the sliding surface. The dating results show there are five periods with relatively intense landslide activity since late Pleistocene: 100-63 kaBP, 45.2-41.5 kaBP, 33.3-28.2 kaBP, 22.5-15.2 kaBP and 10.4-0.2 kaBP, respectively. Among the five periods, 45.2-41.5 kaBP and 10.4-0.2 kaBP have higher landslide intensity.