Sedimentary Studies Of The Holocene Paleoflood Deposits And Loess In The Zhouyuan Region

The Holocene was the quickly development and prosperity period of the mankind's civilization, and also the great change period of the mankind's civilization, and also the great change period of the global environment. ZhouYuan area is locate in the southeast of the loess tabland, is one of the prehistoric culture centers in China, and there are a great of ancient ruins of human activities widely distributed in it. Existing research results reveal that floods and droughts were so frequent in this area in Holocene that brought significant impact on the process of Chinese civilization. Deep studies on the Holocene loess-paleosoil sequences and the slackwater flood deposits profiles around the ancient sites, identifying and obtaining the paleoflood information recorded in them, ensuring the amount, frequency, time and scale of the extreme Holocene paleofloods, has important practical significance in testing water and flood control projects,flood-designing of traffic engineering and improving the reliability of engineering. It is also very helpful in revealing the characters and rules of the environment change during Holocene in this drainage basin and in the middle reach of the Yellow River.Based on detailed field investigation, we choose Jiangyang village and Huxizhuang village two sections as typical of loess accumulation and paleoflood sediment in Fufeng and Wugong of Zhouyuan area. First we have some experiments in the lab about two sections' environment identification such as size and Susceptibility, second analyses experiments results and combined sedimentary features in the wild, then we identify paleoflood sediment of Qishui River a tributary of Weihe River, and finally we still compare ancient flood sediment of Qishui River with loess accumulation formed by windy, which can further reveal the rule of environment evolution and human activity the Holocene period of the Holocene period of the Holocene period of Zhouyuan area, and provide some basis for the interaction between the two. This article's main conclusions are as follow:1,On the QSH-HXZ-E profile, we can see paleoflood slackwater deposits coloure is similar to the loess deposits. But the slackwater deposits conformation are different from the loess deposits. The slackwater deposits have thin level layer or sinuate layer. Sometimes also may see have the putty soil texture silt unique chap structure. Single-layer thickness below 20cm, becomes the loess deposits to have the obvious difference. Certain paleoflood slackwater deposit formation represents an paleoflood period. Below this section plane 260cm includes four paleoflood slackwater deposite. Four issue of paleofloods occur age between 4100～4600a B.P.2,Through to the magnetic susceptibility determination, we can see the paleoflood advection deposit magnetic susceptibility average value for 145.80×10^-8m³kg^-1, be bigger than the loess deposit most greatly the magnetic susceptibility value 74.60×10^-8m³kg^-1. From the magnetic susceptibility frequency dependence (Freq. Dep/%), we can see the paleoflood slackwater deposit also bigger than the loess deposit. And the value of clay slackwater deposit SWD₂,SWD₄ are bigger than the silty sand slackwater deposit SWD₁,SWD₃.3,The grain characteristic is the most important target to distinguish the paleoflood slackwater deposit. Because the deposition way of the paleoflood slackwater deposit and the loess deposit are different, therefore the two have the big difference in the grain characteristic. The paleoflood slackwater deposit is under the close still water environment the deposit formation. Therefore its size composition fine-grain material are many, namely the clay and the thin fine-grained sand account for the proportion to be big, but the loess deposit to have the obvious difference in the size composition with the paleoflood slackwater deposit, the loess deposit and the paleosoil the coarse particles material are many in the size composition, namely the thick fine-grained sand and the sand level pellet accounts for the proportion to be big. We can see from the granularity parameter, slackwater deposit average grain diameter (Mz) must be smaller than obviously the paleosoil and the Malan loess, and skewness (SK), kurtosis (Kg) also must be smaller than the paleosoil and the Malan loess. The slackwater deposit is obviously thin, the separation is good. May see according to the free frequency distribution curve, the paleoflood slackwater deposit curve is located the loess and paleosoil left, the particle size scope is small. In the granularity C-M chart may see, the paleoflood slackwater deposit is located the slackwater deposition and in the turbidite two regions, some part falls in the slackwateraerosol deposition region. This indicated the paleoflood slackwater deposit deposition way is approximate in the slackwater deposition, but also has a part of paleoflood slackwater deposit in the process of deposition the fluent power influence, belongs to the muddy stream impetus deposition. The loess deposition way and the paleoflood slackwater deposition has obviously different, the Malan loess is located in the turbidite region in the C-M chart. Mainly distributes in PQ and in the QR two scopes, the granularity must be bigger than the paleoflood slackwater deposit.