Study On The High - Resolution Environment Evolution Of The Oxoyan Lake Sedimentation Recorded In The Middle Reaches Of The Yangtze River In Recent 100 Years

Zhong zhou oxbow lake，which is located in the area along the middle reaches of the YangtzeRiver，is considered as the study object. Cored Z2-2hole89cm gained sediment samples of thecentral of the lake，based on information from testing and calculating sediment grain size、magnetic characteristics，as well as sediment chronology, this study rebuilds the environmentalevolution during nearly the past100years of Zhong zhou oxbow lake. The main conclusions areas follows:1.Based on the sample dating results of210Pb from Core ZZ-2in central Zhong zhou oxbowlake, Segmented deposition dating, Combined with river and lake turn of event、Yangtze floodevent and sedimentary facies auxiliary dating,Established high-resolution chronology scale.Analysis shows that its average deposit rate is1.26cm/a, the section of the river deposition, itsaverage deposit rate is2.35cm/a, the upper section of lacustrine sediments，its average depositrate is0.8cm/a，so the whole core ZZ-2covers approximately72years since1941a. Changes inlake and river of oxbow lake occurred in Sedimentary depth42cm in1966a.2.Sediment from ZZ-2is mainly consisted of clay and fine silt, which takes over90%of thetotal content, and changes bigger, less content of other components, but changes also bigger.Magnetic characteristics changes is also very big, magnetic minerals are mainly absorbed bymedium silt (16?32|im) components, and them are mainly consisted of ferromagnetic minerals.Generally, the medium silt content is higher, the magnetic susceptibility is higher relatively, andthe magnetic mineral grain is coarser; on the contrary, the medium silt content is lower, relatively,the magnetic susceptibility is lower, while the magnetic mineral grain is finer.3.ZZ-2sediment relationship between grain size and magnetic parameters show significantsection phenomenon. Between I and II segments of sediment，grain size and magnetic parameterare significant different mutation obviously,in1966a. The reason mutation of Zhongzhou oxbowlake experienced a major environmental event in1966a, that changes in rivers and lakes.4.Zhongzhou oxbow lake irver and lake turn of event in response to ZZ-2hole deposition ofsediments is very significant. Through analyzed that select the size parameter clay content, themedium silt content, coarse silt content, silt content, the average particle size, sorting coefficient,kurtosis and magnetic parameter%, SIRM, Xfd%, x arm/X and x arm ISIRM as sensitive indicatorof river and lake turn of event. Zhongzhou oxbow lake sedimentary facies can be used as a sign ofdetermination in change in irver and lake.5.Considering the vertical variations of the sediment grain size and magnetic characteristics ofthe ZZ-2hole deposition of sediment.Further more,16tested indicators such as clay content、magnetic susceptibility and so on are selected to execute principal component analysis, then ifx12new integrated indicators to run cluster analysis, and finally this study creates the environmentalevolution sequence about the past100years,core ZZ-2was divided into3sedimentary chronological sections：194la?1966a),Rivers period before the oxbow lake, river runoff and water level changesviolent. The role of the Yangtze river reaches bloom is big flood period. In1945a，1949a，1954a isYangtze big flood event.1966a?1968a，Zhongzhou meander cut bay，Oxbow lake river and lake during thechanging environment changes.1968a?2012a, Oxbow lake stage, lakes of the obvious，gradually formed a stablelake environment. Yangtze flood event occurs in1980a,1983a，1998a. Since the1980s，Zhongzhou oxbow lake affected by human activities increasely, mainly theconstruction of a large basin of water projects，changes in land use patterns，increasein arable land, etc. Lead from the bottom up, sediment magnetic particles have atendency increase6.By responding to the study of the Yangtze River flood events over the pastcentury and ZZ-2hole sediments, reach conclusion before oxbow lake, sensitiveindicators of the formation of the Yangtze River flood response is the average particlesize, clay, sand subdivision, the silt, coarse silt，silt, sand, sorting coefficient,skewness and xx，SIRM, x ARM/x, arm/SIRM. After oxbow lake, sensitiveindicators of the ofrmation of the Yangtze River lfood response is the average particlesize, clay, ifne sand, the silt, silt, sorting coefficient and x/xx， ARM/SIRM. Insummary, Parameter indicators have formed the Yangtze flood response is sensitive tothe average particle size, clay, fine sand，the silt, silt, sorting coeiffcient and x ARM/x ARM/SIRM before and after oxbow lake.7.By frequency and intensity of floods and droughts analysis in Zhongzhouregional, we can get insight of the flood and drought disasters in Zhongzhou over thepast century. In the river stage of Zhongzhou oxbow lake，changes in sediment grainsize and magnetic parameters primarily in response to changes in the Yangtze Riversediment transport substances. Atfer oxbow lake, Zhongzhou oxbow lake is mainly inresponse to regional climate change and human activities. However, the formation ofa large flood plain of the Yangtze River Flood Response layer sandwich. With a stablehydrostatic lake environment, sediment grain reifnement obviously，However, thesevere impact of floods and droughts and human activities made the sediment grainsize has a trend of enlarge.8.By chronicles literature analysis, sorting out the important human activityevent of Zhongzhou, and analyzeing the responses in grain size and magneticparameters with ZZ-2hole sediment. Overall，Strengthen of human activity inZhongzhou oxbow lake, change substances into the lake apparently, sedimentresponse to human activities more significant.