泾河下游全新世古洪水滞流沉积物研究

通过对泾河流域广泛的野外考察,在泾河下游高陵县段发现了典型的全新世古洪水滞流沉积剖面,系统地进行采集样品和粒度成分、磁化率、烧失量、吸湿水含量等多指标分析。从沉积学角度将古洪水滞流沉积物与全新世风成黄土和土壤进行对比,证明了该剖面所夹古洪水滞流沉积物的性质为细砂质粉砂,属于河流洪水悬移质泥砂沉积物。根据地层结构及与流域内其它剖面的对比,结合OSL测年数据,确定泾河在全新世中期4200~4000 a B.P.发生了第1期古洪水事件,在全新世晚期3200~2800 a B.P.发生了第2期洪水事件。这些古洪水事件都发生在全球性气候突变转折时期,表明在这些时期气候极端恶化,变率增大,洪水和干旱事件皆有发生。该研究对于泾河防洪减灾、水资源开发利用,对于揭示水文系统对于全球变化的响应规律,具有重要的科学意义。

Sedimentary Studies of the Holocene Flood Slackwater Deposits in the Lower Reaches of the Jinghe River

Palaeo-hydrological investigations were carried out in the lower reaches of the Jinghe River.A Holocene loess-soil profile with interbedded flood slackwater deposits(SWD) was found at the YGZ site at the riverbank near the Yangguanzhai village.A set of sedimentary samples were taken from the profile and grain-size distribution,magnetic susceptibility,loss-on-ignition and content of calcium carbonate,etc.,were analyzed in the laboratory.The results show that the eolian loess consists of silt and the soils consist of clay silt,and the palaeoflood slackwater deposits consist of sandy silt.This palaeoflood SWD were deposited from the suspended sediment load in the floodwater.A pedo-stratigraphic correlation with the other studied sites and the OSL dates indicates that the three bedsets of the palaeoflood SWD have recorded two episodes of extreme flood events which occurred during 4200 ~ 4000 a B.P.and 3200 ~ 3000 a B.P.respectively.These events were well correlated to the global climatic events during the periods.These showed that the monsoonal climate was highly variable with both droughts and floods occurred in the middle Yellow River basin.These results are of great significance to mitigate flood disasters,and to exploit water resources,as well as to understand hydrological response to global climatic change.