Quantitative Analysis Of Braided Channels In The Delta Plain Of Modern Sandy-gravely Fan In Xinjiang

The periphery of the Bosten Lake in the Yanqi Basin of Xinjiang is mainly composed of various modern sedimentary facies such as rivers,deltas,alluvial fans,fan deltas,beach bars,aeolian sand dunes and lakes.The research work on modern sedimentation can reveal the genetic relationship between sedimentary environment and sediment characteristics under the single source of near-source sedimentary system in small mountain basins in Xiniang,in order to compare and discriminate the corresponding sedimentary system environment in ancient times and restore the sedimentary environment phase and describe its microphase configuration elements,etc.This paper uses the theory and method of sedimentology and geostatistics,by means of the description of field sedimentary profiles,the planar distribution of braided channels and the observation and measurement of sediments,combined with remote sensing images and previous research results to study the active braided channel and to reveal the zoning characteristics on the plain of the Qingshuihe fan delta in the Yanqi Basin.The Qingshui River fan delta is located on the short axis of the Bosten Lake basin.The fan delta is mainly laterally oscillating and fan-shaped on the plane.The annual average runoff is 1.23×10~8m~3,the supply of material source is less,and the fan body has a limited extension in the direction of the source.The whole area is divided into three sections:the upper part of the fan,the middle part of the fan and the lower part of the fan.The upper part of the fan is divided into 1 section on the fan,2 on the fan and 3 on the fan.1st section on the fan occupies 8.4%of the total length of the Qingshui River fan delta plain,and the average slope is as high as 18.51‰.The gravel-single braided channel is developed,and the sediment is mainly composed of multi-level gravel,and the sandy content is extremely small.2nd section on the fan account for 30.6%of the total length of the fan delta plain,and the average slope is 18.38‰.The gravel-complex braided channel is developed.The sediments are dominated by multi-stage gravel,and the sand content is increased relative to the upper segment of the fan.3rd section on fan accounted for 17.1%of the total length,and the average slope decreased to 12.01‰.The gravel-single braided channel was developed,and the sand content increased significantly compared with the 2nd section on the fan.The middle segment of the fan accounts for 29.2%of the total length,and the average slope decreases further to 3.03‰,developing a sandy single-shaped channel.The lower part of the fan accounts for 14.7%of the total length,and the river gradually shrinks and disappears.Xinjiang Qingshui River Fan Delta Plain is rich in geological camps,mainly including gravity flow,traction flow,wind and lake flow.1st section on the fan is mainly composed of sheet flow and gravity flow;2nd section on the fan transitions from gravity flow to traction flow;3rd section on the fan is mainly traction flow;the middle part of the fan develops traction flow;the lower part of the fan is driven by wind and lake flow.The geomorphic elements in the braided channel of Qingshui River in Xinjiang include branch rivers,confluence channels andbars.The bar body is further divided into a bar head,middle of bar and a bar tail.according to the position,and a trench appears inside the bar body.The length(m)and width(m)of the dam have a relationship of L=4.817W+51.975,which reflects the proportional relationship between the length and width of the dam.The relationship between the length of the dam(m)and the width(m)of the longer channel is Y=0.1604X-3.9633,and the length of the dam is also proportional to the width of the channel.As the handling distance increases,the overall gravel diameter D(cm)decreases with the increase of the transport distance S(m),and the relationship is S=-32×ln(D)+120.14;the relative content of quartz is In a periodical increase,from 34.9%of the upper segment of the fan to 42.7%of the middle segment;the amphibole content decreased in stages,from 5%at the mountain pass to 0.8%in the middle segment.The median diameter of the a-axis of the second section of the Qingshui River fan in Xinjiang was reduced from 84.45cm to 16cm,the absolute reduction was 68.45cm,and the relative reduction was 81%.The gravel movement mode was mainly around the c-axis,followed by sliding along the ab surface.The absolute decrease of the median diameter of the b-axis of the 3rd on the fan is 7.87cm,which is a relative reduction of56%.The reduction is larger than the a-axis and the c-axis,indicating that the gravel movement is mainly around the a-axis.The median diameter of c-axis in the middle section of the fan is the largest relative reduction,correspondingly reduced from 4cm to3.25cm,the absolute reduction is 0.75,and the relative reduction is 18%,reflecting that the movement of gravel is mainly along the ab surface.The dynamic conditions are further weakened.The probability accumulation curve of gravel sediments on the river channel is mainly composed of three stages,which reflects that the gravel in this area has been flooded by three different water levels.The probability accumulation curve of sandy sediments in the Qingshui River channel in Xinjiang is mainly composed of three types:upper arch type,concave two-stage type and upper convex two-stage type,and the particle size range is between-1.8 and 5?.The particle size C-M diagram is dominated by the OP segment,the C value varies between 870 and 5656um,the M value ranges from 164 to 1274um,and the C value is substantially greater than 1000um,reflecting the characteristics of near-source deposition.