Migration History Of Dengkou Reach Of The Yellow River In Late Quaternary

Rivers, the cradle of human history and civilization, are the foundation of human beings and many other creatures.At the same time, as the most important force of the land surface, all sorts of landscape were strongly shaped by river, of which the formation and development can reflect the evolution of the regional landscape and environment.Hence the formation and evolution of the river have always been the focus of the research on fluvial geomorphology.The development process of the Yellow River, the second longest river in China is a hot spot in geomorphology.Many researches have been made on the upper and middle reaches where the Yellow River flows in valleys and significant progress and consensus have achieved. However, study of the formation and evolution of the Yellow River in Houtao Basin is relatively less for a lack of vector and attention.In this paper, 3 sedimentary cores are drilled which are 20 m deep in the Dengkou section of the Houtao plain. To study the evolution process of the river in the late Quaternary, sedimentary facies, environmental indicators and geochronological study, combined with exploration of the radar measurement are analysed together and preliminary results are as follows:1、Characteristics of modern sediments in different geomorphic units: Desert is dominated by fine sand, second in medium sand content, almost does not contain clay and silty sand, the average particle size ranging from 209.25μmto 260.21μm, well to mediumsorted, nearly symmetric, medium kurtosis. Riverbed is dominated by fine sand, second in medium sand content, the average particle size ranging from 73.51μm to 278.43μm, partial to very positively skewed and sorted poorly, kurtosis varying from flat to very sharp.Floodplain is dominated by silt, second in fine sand content. Lakes dominated by silt, second in clay content, the average particle size ranging from 40.35 to 66.29 μm, poorly sorted,nearly symmetric to very positively skewed, kurtosis varying from medium to sharp.In the lake was mainly silt, clay content times, average particle size between the 6.33~36.14μm, poor sorting and nearly symmetric to very positive skewness,kurtosis varying from medium to sharp.2、Drilled cores can be divided into five sedimentary facies: the channel phase, floodplain face, oxbow lake subface, alluvial fan face and desert face.Alluvial fan facies mainly distributedin cores DKZ09 and DKZ13 which are near the Ordos Plateau.Oxbow lake subfacies and riverbed subfacies are distributed alternately in the section,indicating that rivers and oxbows were coexisted in the past.Floodplain subfacies are distributed sporadically, indicating the Yellow River was wandering river in the past, leading the Sandy River floodplain binary structure was poorly saved.Desert facies are only distributed in the top 1.64 metres of core DKZ09,suggesting the history of the northward extension of the Ulan Buh Desert is late.3. Combined ground penetrating radar image analysis,sediment core structure, environmental indicators and geochronological, results showing that the formation and development of the river in this area can be roughly divided into three periods in the area. That is, before 20 ka, the Yellow River’s channel was mainly developed in the east of Dengkou, which was mainly braided river.During 20-5 ka,the Yellow River developed in the whole section, the river was anastomosed river, the whole channel migrated gradually westward;During 5-2 ka, the main channel of the Yellow River appeared in the vicinity of Dengkou, which was meandering river, but the Langshan Mountain also developed part of channel and small lakes.