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全新世期间西北地区河流普遍发育多级河流阶地,而关于其形成原因和过程仍不甚明了。我们对祁连山东段13个河流横断面的全新世阶地进行了详细的野外考察,并利用~(14)C测年方法对阶地的形成年代进行了限定。结果显示,全新世河流下切主要发生在7.5~3.0ka B.P.,通过对比河流下切年代与区域气候变化,发现河流下切集中的3个时段(5.9~7.2ka B.P.,4.2~5.2ka B.P.和2.4~3.3ka B.P.)对应于区域气候较湿润时期,相对较高的径流量与植被覆盖较好、沉积物供给较低的条件下,河流发生下切。全新世河流的多次下切指示一次完整的河流下切过程可能是通过多次下切与短暂的堆积过程交替而完成的,但由于局地状况的差异,这种过程可能被高差较小的阶地记录下来,也可能被河流侧蚀抹掉。不同河流对气候响应的敏感性有差异,较大河流对短期的气候变化响应不敏感,主要受长尺度气候变化的控制作用。
During the Holocene, the rivers in the northwestern region generally developed multi-stage terraces, but the causes and processes of formation are still unclear. We conducted a detailed field investigation of the Holocene terraces of the 13 rivers in the eastern section of the Qilian Mountains and defined the formation age of terraces by the ~ (14) C dating method. The results show that undercutting of the Holocene occurs mainly in 7.5-3.0ka BP. By comparing the age of the river and regional climate change, three periods of undercutting (5.9-7.2ka BP, 4.2-5.2ka BP and 2.4-3.3 ka BP) corresponds to a relatively humid regional climate, relatively high runoff and vegetation coverage is better, the lower the sediment supply conditions, the river undercut. Multiple undercutting of the Holocene stream indicates that a complete river undercutting process may be accomplished by multiple undercutting and transient stacking processes, but due to differences in local conditions, this process may be recorded by terrains with small differences in elevation Down, may also be eclipsed by the river side. The sensitivities of different rivers to climate response are different. Larger rivers are insensitive to short-term climate change and are mainly controlled by long-range climate change.