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位于官亭盆地的喇家史前灾难遗址被毁原因是近年来人们争论的焦点。笔者在野外调查和实验测试分析的基础上,对官亭盆地二级阶地上沉积的红色粘土层来源、成因机制进行了再探讨,揭示了山洪泥石流对官亭盆地喇家遗址的影响,以期为山间盆地区居民正确制定防灾减灾措施提供地质依据。主要取得了以下认识:1)官亭盆地剖面2.45m厚的红色粘土层其粒度特征以第二组分为优势组分,其中值粒径为9~11μm;磁化率值主要分布在20×10~(-8)~40×10~(-8)m~3/kg之间;2)该红色粘土层与积石峡峡谷区的湖相地层在发育年龄、颜色、粒度、磁化率、土体质地结构等方面具有明显区别,反映了二者不同的成因机制,红色粘土层与积石峡堰塞湖溃决无关;3)官亭盆地北侧由于地震等作用形成的山体古崩塌、古滑坡和第三系松散粘土物质被强降水近距离冲刷搬运堆积在山前坡地,遗址毁灭的洪水来自北侧岗沟等沟谷,而非黄河泛滥的洪水;4)官亭盆地红粘土的成因可能是:地震诱发滑坡、崩塌,同时造成山体疏松,在暴雨或持续降水作用下,滑坡崩塌堆积物和山体松散物质被洪水沿沟谷携带到沟口及地势较低的黄河二级阶地沉积,地震后发生的山洪泥石流灾害造成了喇家遗址的彻底毁灭。
The reason why the prehistoric site of the Lajia disaster in Guanting Basin was destroyed was the focus of controversy in recent years. On the basis of field investigation and experimental analysis, the author revisits the origin and origin mechanism of the red clay layer deposited on the second terraces in Guanting Basin, and reveals the influence of flash flood on the Lajia site in Guanting Basin. The mountain basin residents to correctly develop disaster prevention and mitigation measures to provide geological basis. The main achievements are as follows: 1) The grain size of the 2.45-m-thick red clay in the section of Guanting basin is dominated by the second component, and its median diameter is 9 ~ 11μm. The susceptibility values are mainly distributed in 20 × 10 ~ (-8) ~ 40 × 10 ~ (-8) m ~ 3 / kg; 2) The red clay layer and the lacustrine strata in Jishidong Gorge area have different development age, color, grain size, magnetic susceptibility, Body structure and so on. The red clay layer has nothing to do with the collapse of Jishixia barrier lake. 3) The ancient landslide caused by the earthquake and so on in the north of Guanting basin, And the Tertiary loose clay material was intensively washed away by heavy rainfall and piled up in front of the mountain. The floods destroyed by the ruins came from the ditch on the northern side of the valley instead of the flooding of the Yellow River. 4) The red clay in Guanting Basin may be caused by : Earthquakes induced landslides and collapses and loose hills at the same time. Under the influence of heavy rain or continuous precipitation, the landslide deposits and loose bodies were carried along the ditch by the floods to the Mizoguchi and the lower terraces of the Yellow River. After the earthquake, The flash flood disaster caused the Lajia ruins thoroughly destroy.