雅鲁藏布江加查峡谷河段古洪水沉积特征

对雅鲁藏布江加查峡谷河段古洪水平流沉积物进行了野外调查与试验分析,结果表明:其野外沉积除具备一般的特征外,还常表现为细颗粒物充填巨砾的特殊堆积形态;其粒度特征表现为分选性较好,分选系数在1.2以下,以砂质、粉砂质颗粒为主,中值粒径在3~4之间等,且与谷坡沉积物、滩地泛滥沉积物的粒度特征之间存在明显差异;其重矿物组合特征与沉积类型及沉积物的搬运条件等相关;通过孢粉特征分析,确定了研究区域在大约距今3 000 a的气候条件与近现代气候条件具有较明显的一致性,为研究河段古洪水分析计算,以及藏木水电站的设计洪水确定提供了基础资料信息.

Characteristics of sediments of palaeofloods in Jiacha Gorge on Yarlung Zangbo River

The sediments of palaeofloods in Jiacha Gorge of Yarlung Zangbo River were studied based on the field investigations and experimental analyses. The results show that in addition to common characteristics, the field sediments exhibit some special features with the boulders' void filled by fine particles. The particles of advective sediments are characterized as follows: they are well sorted, the sorting coefficients are all bellow 1.2, the main particles are sandy and silty ones, and the median grain diameter is between 3 and 4. They are significantly different from the granularity characteristics of valley slope sediments and beach land sediments. The characteristics of heavy mineral composition relate with the sediment types and transportation conditions. Through the analysis of pollen characteristics, it is confirmed that the climatic conditions of the study region about 3000 years ago are in consistent with those in recent and modern times. It is useful for the extension and application of palaeoflood researches. It will provide basic data and information for the determination of the design flood of Zangmu Hydropower Station on Yarlung Zangbo River.