【摘要】 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9¹1μm;磁化率值主要分布在20×10^-840×10^-8m³/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。更多还原

【Abstract】 The destruction reasons of Lajia prehistoric disaster relics in Guanting basin is a hot and focus issue in recent years.In this paper,based on the results of field investigation analysis and laboratory tests,the deposition sources,formation mechanism of red clay layer,which lies in the second terrace of the Yellow River of Guanting basin has been explored.The authors revealed that the huge impact of the debris flow to the Lajia prehistoric disaster relics,this result will provide some geological basis of disasters prevention and mitigation in some mountainous area neighborhoods.The results of this research were:1)The depth of red clay layer profile is 2.45m in Guanting basin,the grain size distribution characteristics of red clay layer can divide into three components and the second is the dominant,which median grain size is 9¹1μm;magnetic susceptibility values of the red clay profile are mainly distributed between 20×10^-840×10^-8m³/kg;2)The obviously differences of developmental age,color,grain size distribution characteristics,magnetic susceptibility,soil structural parameters between the red clay layer profile of Guanting basin and lake sediments of Jishixia valley,which reflected that different formation mechanism between them,and the red clay sediments has unrelated with the dammed lake outburst of Jishixia valley;3) Due to earthquake or tectonic activity,some ancient landslides and mountainous collapses were formed,on the other hand,the Tertiary loose clay materials of north side of hillside of Guanting basin were all closely scour handling accumulation in the piedmont sloping sites by the heavy precipitation,the destroyed flooding of Lajia disaster relics came from some valleys of north hillsides,eg:Gang valley.Therefore,the flooding was not from the upper reaches of Yellow River;4) The forming mechanism of the red clay layer of Guanting basin may be:earthquake-induced landslides and collapses,at the same time,the mountainous loosely.Then,the deposits of landslides and collapses and the mountainous loose material were carried to exports of valley and the lower second terrace of the Yellow River along the valley by the heavy rain or sustained rainfall.Therefore,the debris flows induced by the flushing flood after earthquake was the actually reason of destruction of the Lajia disaster relics.更多还原