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通过对黄河源区玛曲段河谷开展野外考察,在太吾若(TWR)发现典型的古洪水滞流沉积剖面。根据野外沉积学宏观特征判别,并结合粒度分布、磁化率、地球化学元素和石英颗粒微形态特征等室内实验分析测定结果,准确鉴别出TWR剖面所夹一组多层洪水滞流沉积物(SWD),属典型的河流洪水在高水位滞流环境下沉积的悬移质泥沙。结果表明,TWR剖面古洪水SWD和现代洪水SWD沉积学分类为沙质粉沙,现代土壤为黏土质粉沙,现代风成沙为中沙。古洪水SWD粒度自然分布频率曲线为正偏,呈单峰,主峰高且峰值集中,分选性良好。古洪水SWD和现代洪水SWD磁化率较低,介于现代土壤和现代风成沙之间,化学元素明显区别于现代土壤和现代风成沙,表明它们尚未受到风化成壤作用影响,为古洪水悬移质快速沉积形成的滞流沉积物。石英颗粒微形态特征的分析表明,古洪水SWD和现代洪水SWD石英颗粒表面分布明显的三角痕、V形坑、撞击坑和凹面等水成沉积物的典型特征,属于河流沙类型。采用单片再生剂量法(SAR)光释光技术测年,证明在13.6~13.0 ka BP,黄河源地区经历了一期多次的大洪水事件,发生时段对应末次冰消期向全新世转折的时期,与欧洲和格陵兰冰芯记录末次冰消期中的Bolling/Aellrod暖期相对应,此时青藏高原地区冰川大规模消融,这期古洪水事件正是流域内冰融水大量下泄汇入黄河而形成的大洪水。
Through the field investigation on the Maqu section valley in the source region of the Yellow River, a typical flood flood sediment profile was found in TWR. Based on the field sedimentology macroscopic characterization and indoor laboratory analysis and determination of particle size distribution, magnetic susceptibility, geochemical elements and quartz particle micromorphology, a set of multi-layered flood stagnate sediments (SWD ), Is a typical river flood in suspended sediment suspended sediment under high water level environment. The results show that SWR sediments of ancient flood SWD and modern flood TWR are classified into sandy silt, modern sandy soil is clayey silt, modern sandy silt is middle sand. The natural distribution frequency curve of SWD granularity of flood was positive, showing a single peak, the main peak is high and the peak concentration, good sorting. SWD and modern flood SWD paleomagnetic susceptibility is low, between modern soil and modern wind sand, chemical elements significantly different from modern soil and modern wind sand, indicating that they have not yet been affected by weathering and pedophilia, the ancient flood Suspended deposit formed by rapid deposition of suspended matter. The analysis of the microscopic features of the quartz grains shows that the typical features of triangular sediments, V-shaped pits, craters and concavities, which belong to the type of river sand, are the surface distribution of the ancient flood SWD and the modern flood SWD quartz grains. Based on the single photon emission optical dating (SAR) technique, it was proved that the flood season experienced a period of multiple floods from 13.6 to 13.0 ka BP, corresponding to the transition from the last ice-age to the Holocene Period, corresponding to the Bolling / Aellrod warming period in the last ice-cooling period recorded by the ice cores in Europe and Greenland. At this time, the glaciers in the Qinghai-Tibet Plateau were ablated in a large scale. The ancient flood event was caused by a large amount of ice melt into the Yellow River The formation of the flood.