A Study Of Paleoflood Sedimentary Record For The Caijiacun Profile In The Yihe River Basin

Through careful field investigation of Yihe River and its tributaries, Caijiacun profile ofYihe River overbank was selected as the typical profile of the paleoflood record,144high-resolution sedimentary samples were collected in high flood plain during the summervocation in August2013. Granulometric composition and geochemical elements and OSL wereused to analyze the flood events of Caijiacun. We can get the following conclusions:(1) The profile of Caijiacun can be divided to three periods of flood. The thickness ofCaijiacun Profiles which deposit by extreme flood is723cm. Medium sand and coarse sand arethe mainly compositions in profile Caijiacun. In this section, the content of medium sand reachedthe maximum value with a mean of34.11％. The second is the coarse sand with the averagecontent of32.95％, followed by fine sand with the average content of11.46％, followed by acoarse sand with the average content of10.62％, followed by silt, the average content of6.95％,followed by a very fine sand with the average content of3.89％, clay composition is almost zero.(2) According to the analysis results of sediment particle size, it is found that sedimentparticle size composition, distribution and size parameters have great significance in indicatingthe occurrence of flood. Caijiacun profile is mainly composed of sand and a small amount ofclayey sand. The CM Figure of particle size indicated that deposited mainly suspended in rollingway during the flood period. The frequency curves of particle size are mainly unimodal andbimodal with high peak and nearly symmetry, which demonstrates that the sedimentarydynamics are similar and the source of the sediments is also the same originating from themiddle and upper reaches of Yihe River. The particle size composition of the sediment inCaijiacun reflects the water dynamic change of the floods in different sedimentary periods. Thecoarse-grained sediments indicate the large-scale floods and the fine-grained sediments indicatethe relatively small-scale floods.(3) All dating results are between2.83±0.26ka and0.20±0.01ka. The sample(CJC-1) withdepth of22cm in Caijiacun profile indicated that the flood sediment formed in0.20±0.01ka.And the location of the sample doer not show obvious late bioturbation, so we believe that the floods in this area formed in the modern society. Caijiacun profile formed in about threethousand years ago, and the profile position is very closed to the Lizhaung profile. Lizhaungprofile formed in about1000years ago and was found three periods of flood sediment. Caijiacunprofile recorded at least three periods of flood in the past one thousand years. This shows that thefrequent outbreak of the great flood in Yihe and shuhe River basin in the past one thousand years.By comparing the dating results with Lizhaung and Beizhai profile, we know Yihe and shuheRiver basin paleoflood have regional.(4) The age results of the three periods of floods all located in the time scale of Little IceAge, and the flood occured frequently in Caijiacun during this period corresponding with thecharacteristics of climate in Little Ice Age. The historical documents show that the climate ofYihe and Shuhe River basin during this period is very unstable and the frequent occurrence offloods causing serious disasters to the local people. For this reason, the reliability of our OSLdating results gets proved from the other side. The fourth stage flood is in the transition stagewhich is the transition from the mid Holocene and big warm period to the late Holocene anddrought period. The climate during this stage is very harsh and extreme weather events occurfrequently.