Sedimentology And Climatic Background Of The Holocene Paleo-flood In The Shenmu-Extension Section Of The Middle Reaches Of The Yellow River

Natural disaster which characterized by the frequency,uncertainty and seriousness provide a devastating impact on production,life and property and plague people.For our country,flood is one of the most serious natural disaster which has destructive consequences.Coupled with the number of floods,the scope of the spread is relatively wide,so the flood control is particularly important.The Yellow River,as China’s second long river,is the most serious river that floods occurred.Therefore,it is necessary to carry on some flood research on the Yellow River Basin.However,the flood data acquired by measured flood and historical flood have short time scale and the flood sequence is half-baked.So the recurrence interval and frequency of the catastrophic flood can’t be calculated.Therefore,the extension of the flood scale has become an urgent need for flood research and water conservancy constructionThe Holocene flood research is born at the right moment.It is based on the palaeoflood slack water deposits(SWD)left at a certain point during the flood discharge period.With the help of knowledge about hydrology and sedimentology,the Holocene flood research need to recover the peak stage and peak flow of the palaeoflood,and acquire the age that the palaeoflood happed using the chronology and climatology.As the result,the chronostratigraphic framework can be built and response of river hydrological system to climate anomaly events also can be acquired.The theoretical results of the study can extend the flood’s time scale to the annual scale,and it can provide the basic data for hydraulic engineering construction,leading to the high reliability of engineering construction.My thesis takes LLT site and FTC site in the middle Yellow River for an example to research material source and sedimentology characteristics of the palaeoflood.At same time,recover the peak stage and peak discharge and calculate the flood’s age,including the climatic background.Through the detailed field investigation of the Yellow River Shanxi-Shaanxi Gorge,the palaeoflood SWD were found near Liu Lintan Village,named Liulin Beach(LLT).The palaeoflood SWD is compared with the typical loess-paleosol,and we can determine the palaeoflood SWD is a typical high-level flood suspended sediments.The III sand content in SWD1 was 79.71%,and the contents of SWD2 and SWD3 were higher than 50%.The SWD2 and SWD3 which consistent with the modern flood in physical and chemical properties,is flood deposition from the mainstream of the Yellow River.However,the SWDI And is not only different from the loess ancient soil,but also has some differences with SWD2 and SWD3.Combined with the location of the sediments,we compare with the Mu Us Desert about the grain size characteristics and other indicators,and find that the SWD1 in conformity with Mu Us Desert in physical and chemical properties.As the result,SWD1 is the Yellow River tributary of the Kuye River which is the Yellow River tributary floods that flooded from the Mu Us Desert area and deposited down in the LLT site.Based on the hydrological hydrology and other disciplines,combined with the actual situation,we use the relationship between thickness and sediment concentration to restore the peak stage and discharge in FTC site.Results are as follows:the four peak stage of the palaeoflood SWD between 526.93 m and 520.59 m,and the peak discharge is between 25 200 and 51 500 m3 · s-1.Want’s more,the test of the results is in allowable range.Extreme changes in climate are the main drivers of hydrological evolution.The results of OSL indicates that the three palaeoflood events in LLT site occurred in(11400±400)a BP,10500±300)a BP and(10100±500)a BP.This period is among the period that the Quaternary last glacial period transform to the Holocene conversion period,that characterized by the unstable climate.The three flood events are response the climate changing of this period.The results of OSL indicates that the four palaeoflood events in FTC site occurred in 3400～3000 a BP and 1900～1700 a BP.Combined with multidimensional and multidimensional analysis,the results show that during the period of the flood events occurred,the world is in the climate deterioration period.In our country,the manifestation is that the precipitation and the temperature change are obvious and the catastrophic event occurred now and then.This two periods corresponded to the end of Sang-the Western Zhou Dynasty and the Eastern Han Dynasty-the Western Jin Dynasty,which are the turmoil in Chinese history,with floods and drought disasters.