Study On The Grain Size Characteristics Of Tamarix Cones Sedimentary Laminae In The Northern Area Of Lop Nur And The Changes Of Wind-sand Environment And Its Source

Grain size characteristics are one of the basic indicators of sediment research,which carry the initial information and change information during the deposition process,especially in the desert area under the wind-sand deposition environment,which can accurately and effectively reflect the source of sand in the sediments,Sedimentary dynamics and sedimentary environment.The northern area of Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang,adjacent to the Kumtag Desert in the east,the Kuluktage North Mountain in the north,and the Kuluk Desert widely distributed in the south.Its environmental evolution is the epitome of the environmental evolution of the entire Tarim Basin and surrounding mountains.This area is a typical extreme arid continental climate zone,with climatic characteristics such as scarce precipitation,large evaporation,large temperature difference,and strong wind.Tamarix cones is a biological landform formed under this special climatic and environmental conditions,and it is the product of long-term interaction between Tamarix chinensis and climatic environment.According to the sand material grain size characteristics of the sedimentary laminae of Tamarix cones,the sedimentary environment and the source of the sand materials can be revealed.According to field surveys combined with satellite images,it is found that Hongliujing and the lower reaches of the Kongque River are the main concentrated areas of Tamarix cones in the northern area of Lop Nur.This paper takes the Tamarix cones sedimentary layer in the northern area of Lop Nur as the main research object.Through field investigation and systematic sampling,using the method of aeolian sand geomorphology,the sedimentary layer of the Tamarix cones at two sampling points is firstly dated,and then two samples are taken.Tamarix cones point-deposited layer of grain size and characteristics of the different regions of sand sediment material comprehensive analysis,then analyze environmental changes in northern sand Lop Nur region,and to study its material source of sand,the results showed that:(1)Using the three dating methods of 210 Pb,137Cs and 14 C,the chronological sequence of the sedimentary laminae of Hongliushabao at two sampling points in the northern Lop Nur area was initially obtained as 1832?2019 and 1784?2019,respectively.(2)The two sampling points in the northern area of Lop Nur have the same size composition of the sedimentary layers of the Tamarix cones,and the sedimentary environment is the same.The average content of fine sand and coarse powder is the highest,while the average content of clay is very small and does not contain Very coarse grained.In the characteristics of the grain size parameters of the sedimentary layers of Tamarix cones at the two sampling points,the average grain size and the median grain size are between 2.76 and 3.70 ?,and the sortability is poor,the skewness value is negative,and the kurtosis is sharp.The size distribution curve and probability cumulative curve of the Tamarix cones sedimentary layer at the two sampling points are consistent.The curve shapes are highly similar and have a strong correlation.They have obvious indications for the changes in the wind and sand environment in the northern area of Lop Nur.(3)The grain size composition of surface sediments in different areas in the Lop Nur area is mainly fine sand and coarse powder,and the sum of the two content is as high as 83.51%,followed by coarse sand;According to the deposition types of sediments in different regions,the relationship between the content of coarse silt particles is as follows: formation sand> river sand> dune sand,and the relationship between the content of fine sand particles is as follows: dune sand> river sand>stratum sand,the relationship between the content of coarse sand particles is: river sand> dune sand> stratum sand.The average particle size is generally between 2.06 and 6.43 ?,which is a mixture of medium sand,fine sand and coarse silt sand.The overall sortability is poor,the skewness is negative,and the kurtosis is sharp.The average particle size ? of dune sand is smaller than that of formation sand and river sand,and the sorting ability is relatively good.(4)The sedimentary environment of the Tamarix cones sedimentary layer at the two sampling points is aeolian sediment,and the sand materials are mainly aeolian sand.A comprehensive analysis of the wind-sand environment changes of the red willow sandbags in the northern Lop Nur area through the kurtosis anomaly,sand dust material and sediment particle size characteristics,can be divided into four stages.The first stage: from 1832 to 1883,the windy weather became weaker,with less dusty weather and less precipitation,and the climate was a dry period.The second stage:from 1884 to 1945,there were more windy weather,gradual reduction of dusty weather,and relatively more precipitation,which was a humid period.The third stage:from 1946 to 1994,the windy weather was less normal,the dusty weather was more normal,the precipitation was relatively less,and the climate was dry.The fourth stage:From 1995 to 2019,the windy weather gradually increased,the floating dust weather appeared frequently,and the precipitation was more frequent,which was a humid climate.(5)The sedimentary environment of the Tamarix cones sedimentary layer in the northern Lop Nur area is relatively consistent,and the aeolian deposits are more obvious.The sand material of the Tamarix cones sedimentary layer in the Hongliujing area The main sources are the three-ridge sand dunes and the Yadan sandy layer in the northern part of the Kumtag Desert.It can be seen that the main source of sand material in the sedimentary layer of Tamarix cones in the lower reaches of the Kongque River is the surface sand of the Kuruk Desert.