Analysis Of The Relationship Between The Grain Size And Provenance Of Holocene Loess Soil In The Middle Reaches Of The Yellow River And The Upper Reaches Of The Huai River

The sediment is generally generated under the comprehensive effect of multi sources,multi dynamic transport and secondary transformation in the process of deposition,so the combined feature of grain size is often a result of the comprehensive effect of many factors.The main source of the typical loess in the Loess Plateau of China is dust particles of sand storm carried by the East Asian winter monsoon from the northwest desert,and the far source dust carried by the upper westerlies also accounts for a certain share.The deposited dust of sand storm year after year has gradually formed a thick Loess Plateau along with the long geological history.The characteristics of the coarse and fine combination of the loess particles are under the control of the source and the handling power,and the influence of the secondary weathering transformation after deposition on the grain size will be equivalent to the source and the dynamic factors.The difference of the weathering resistance for different minerals is unavoidable.The secondary weathering transformation will shape the combined features of particle size.The grain size characteristics of the loess are the result of the superposition of various factors.If the complex multiple factors can be separated,it is possible to effectively identify the power,the source and the degree of secondary transformation.The grain size composition of the Holocene loess in the typical area of Loess Plateau is characterized by the finer grain size and the thinner sedimentary layer from the northwest to the southeast,respectively.However,after a comprehensive judgment of the variation of the magnetic susceptibility and the grain size in the transverse and longitudinal direction and the thickness of the sedimentary layer,it is recognized that the upper reach of Huaihe River on the southeastern margin of the Loess Plateau does not have the characteristics of the source composition at the typical loess plateau region,which has the near source sediment carried by the regional northeaster or the north wind.In this paper,5 loess-paleosol profiles with regional representative in the middle reach of the Yellow River and the upper reach of Huaihe River(of which one is the paleo flood sediment profile)are selected.The grain end member of 5 loess-paleosol profiles is divided mainly by the end member analysis method for deposition granularity,so as to identify the sediment dynamics and sources represented by the end members of each dynamic force,as well as the strength of later secondary transformation.In order to identify the periodic variation characteristics of each end member,the state on various scales at present and the possible changes in the future,a further wavelet analysis is carried out on the content of each end member of the high resolution loess-paleosol profile at the depth scale or age scale.At the same time,the magnetic susceptibility,grain size frequency distribution curve,triangulation type division,fractal dimension of grain size,edaphology granularity division,sedimentology granularity division and grain size parameters are compared and analyzed.Through the above analysis,the main conclusions are as follows:1)Characteristics of magnetic susceptibility:The magnetic susceptibility is widely used as a substitute index for summer monsoon.The magnetic susceptibility of four high resolution loess-paleosol profiles is compared.Horizontally,it can well reflect the strength of palaeosinization.Longitudinally,the magnetic susceptibility from the Changchengyuan profile-Xujianian profile-Yaohe Village profile increases in proper order,which is in accordance with the features of decreasing from north to the south and increasing from the west to the east,but the magnetic susceptibility of Gedazhang profile is not consistent with the above characteristics.By using the magnetic susceptibility,the annual average temperature and annual rainfall in the corresponding period are obtained by the formula summarized by predecessors.It is considered that the calculation results of the other profiles are in accordance with the actual conditions except that the Gedazhang profile is relatively lower.Therefore,it is preliminarily believed that the Gedazhang profile is obviously different from other profiles in terms of source compositions,so the formula for calculating the relationship between magnetic susceptibility and the annual average temperature and the annual average rainfall is not applicable to the "loess in Zhengzhou" represented by the Gedazhang profile.2)Particle size characteristics under whole sampleFrom the angle of particle size under whole sample,4 high resolution loess paleosol profiles and 1 paleo flood sediment profile are studied in terms of particle size frequency distribution curve of sediment,Shepard triangulation,fractal dimension of particle size,edaphology granularity division,sedimentology granularity division and grain size parameters analysis.The results show that the Changchengyuan profile and Xujianian profile are very close to the particle size frequency distribution curve,with the characteristics of fine tail in the clay and fine silt;the particle size distribution curve of Gedazhang profile has great difference,and the particle size of Yaohe Village profile in the Central Shaanxi Plain is the finest;the sediments of Changchengyuan profile,Xujianian profile and Yaohe Village profile are all the transition types of clay silt to silt,while the upper stratum of Gedazhang profile is sandy silt,and the lower stratum is the transition type of sandy silt to silt;the fractal dimension of particle size can reflect the attribute of coarse or fine grain size combination of the sediment;in the division of grain size,fine particles reflect the strong and weak change information of the summer monsoon,and the coarse particles represent the strong and weak change process of the winter monsoon,no matter by edaphology granularity division or sedimentology granularity division;the variation of grain size parameters obtained by these two methods is very close.On the whole,the average particle size and kurtosis coefficient seem to represent the change process of the winter monsoon approximately,and the standard deviation and the asymmetry coefficient seem to be approximately representing the change process of the summer monsoon.In view of particle size under whole sample,the above division of grain size under whole sample is artificial,and the grain size composition of the sediments in different regions is different,so the subjectivity and error are unavoidable.The paleo flood sediment profile in Luzhuang Village is obviously coarser than the loess paleosol profile from the grain size frequency distribution curve,indicating that the source of the stagnant sediments in the paleo flood is distinctly different from the loess-paleosol.The upper sedimentary layer is the sedimentary layer with the transition type from coarse silt to sandy,which is obviously larger than the loess grain fraction.At the same time,it also indicates that there is also the influence of near source sandstorm sedimentation.SWD of Luzhuang Village profile is silty sand,and the loess-paleosol layer is sandy silt.In the paleo-flood profile,the dimension of the SWD horizon is obviously lower than that of the loess paleosol layer,and the Q type clustering of the grain size parameters can identify the stagnant sediment layer of the paleo flood.3)Granularity end member analysis and wavelet analysisThrough the end member division,the Changchengyuan profile and Xujianian profile,located around the Liupan Mountain,have four distinct end member groups,which are East Asian winter monsoon,East Asian summer monsoon,South Asian summer monsoon and upper westerlies.The Yaohe Village profile in Guanzhong Basin and the Gedazhang profile at Xinzheng of Henan show three more obvious end member groups,respectively representing the East Asian winter monsoon,weathering transformation of summer monsoon and the near source sedimentary components carried by the regional north wind or the northeastern wind in the near source region.The wavelet transform in the depth(or time)scale of the component content of each end member group are further analyzed to determine the periodicity,current state and possible future trend of the change.The division of the grain end element of Luzhuang Village profile can also distinguish the sedimentary components representing different powers.The components of the hydrodynamic transport are obviously thicker than the wind power components,and the source and the loess-paleosol soil are distinctly different.Based on the above analysis,it is recognized that the loess soil located in the surrounding area of Liupan Mountain has the source characteristics of typical loess.It seems that the eluviation of the South Asian monsoon is obvious and the remote source dust carried by the upper westerlies account for a certain share.In the eastern part of Guanzhong Area,the upper reach of Yinghe River in Xinzheng of Henan,and the upper reach of the Huaihe River,the eluviation characteristics of the South Asian monsoon and the remote source dust carried by the upper westerlies are not shown,but the near source sediments under the regional northeaster and the north wind occupy a considerable share.