临夏盆地巴谢河流域晚更新世以来滑坡发育历史重建

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

晚更新世以来,特别是全新世以来,黄土高原西北部发育了多期次的滑坡事件。临夏盆地巴谢河流域较好地保留了多期次滑坡的遗存,有研究历史滑坡发育规律的良好素材。文章通过详细的野外调查,初步厘清了滑坡空间分布及新老滑坡相互叠置关系,总结得到本地区滑坡的四种发展类型:压裂型深层黄土-泥岩滑坡、滑移型深层黄土-泥岩滑坡、蠕变型中浅层黄土-泥岩滑坡和塌滑型黄土滑坡。不同时期发育的滑坡在野外呈现明显不同的特征:发育于晚更新世的古滑坡有圈椅状的地形和高陡的后缘陡壁,滑坡堆积体已固结,堆积体表面冲沟发育;发育于全新世早期的老滑坡除了具有圈椅状地形和高陡后壁外,堆积体较为松散,堆积平台形态较为完整;发育于全新世晚期的新滑坡则保留了更多的滑坡特征,可见滑坡后缘和侧缘裂缝。巴谢河流域滑坡大多有多次滑动的迹象,不同期次的滑坡相互重叠,在同一范围发生多次滑动,形成多级滑坡堆积平台。滑坡埋压动植物、滑坡洼地短期水体沉积物等有着明显的滑坡指示意义。通过采集此类样品,利用14C和光释光等测年手段,获取了本地区一系列滑坡事件的年龄。对测年数据进行统计分析,得到巴谢河流域晚更新世以来的五个滑坡高发时段,分别为100~63 ka BP、45. 2~41. 5 ka BP、33. 3~28. 2 ka BP、22. 5~15. 2 ka BP和10. 4~0. 2 ka BP。以上滑坡高发时段的推断将为认识去环境变迁提供证据。

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 for14 C 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 ka BP,45.2-41.5 ka BP,33.3-28.2 ka BP,22.5-15.2 ka BP and 10.4-0.2 ka BP,respectively.Among the five periods,45.2-41.5 ka BP and 10.4-0.2 ka BP have higher landslide intensity.