Vertical Zonality Of Surface Sediments In The Shiyang River Basin And Its Application In Environmental Change

Latitude and vertical zonation is a basic principle of physical geography.The latitude zonation depends on the amount of solar radiation received at different latitudes and its seasonal distribution.The vertical zonation describes the natural layering of ecosystems that occurs at distinct altitudes due to varying environmental conditions.Temperature,humidity,soil composition,and solar radiation are important factors in determining vertical zones,which consequently support different vegetation and animal species.In the past global change research,quantitative paleoenvironmental reconstruction was largely based on latitudes.However,little research has been done on the use of vertical zonation.In the study,we presented sedimentary samples from different geomorphological units in the Shiyang River for analysis of lithology,grain-size and mineral indicators.The results are shown as follows.(1)we found four major common components,including fine particulates(<2?m),fine silt(2-20 ?m),sandy silt(20-200 ?m),coarse sand(>200 ?m),from basin-wide sedimentary samples.The fine particulates and fine silt components exist in all the sedimentary facies,which show long-term airborne aerosol changes and its transport by suspended load.There are some differences in ranges of sandy silt and coarse sand components,due to lake and river hydrodynamics,as well as the distance with the Gobi Desert.(2)Our records indicated that FS 2.5 content was relatively stable and less affected by monsoon intensities and circulations.Millennial-scale FS 10 content varied according to sedimentary facies,and it was negatively correlated with the winter monsoon intensity at eolian sediments.The FS 10 content increases dramatically at lacustrine layers in lake and alluvial sediments from the middle and lower drainage basin,which show its relationship with long-term moisture conditions that are closely related to monsoon precipitation.(3)Surface sedimentary samples were collected along the vertical zones of the study area from the upper reaches to the terminal area of the drainage system.The surface sediments in the upper reaches of the Shiyang River Basin are dominated by the Asian winter monsoon and the westerly winds,the surface sediments in the middle and lower reaches of the Shiyang River Basin are mainly affected by river or lakehydrodynamic.The environment of the Shiyang River Basin in modern times become arid,and the deserts of Tengger Desert and Badain Jaran Desert have great influence on it.Therefore,Surface sediments in the Shiyang River Basin are coarse.They are relatively small in the upper reaches,with high content of fine sand and silt,Quartz and Muscovite have higher contents,and their average value,maximum value and minimum value are higher than those of other three types of minerals.Compared to the Shiyang River Basin,the calcite content is low,and the average,maximum and minimum values are all low.Compared with the upper reaches,the surface sediments in the middle reaches are relatively coarser,the content of fine sand and silt is relatively low,and the sand content is relatively high.Quartz and Muscovite have higher contents,and their average value,maximum value and minimum value are higher than those of other three types of minerals.The Calcite content is higher than average of the Shiyang River Basin.Compared with the upstream and midstream regions,the surface sediments in the downstream regions are relatively coarsest,with the finest sand and silt content being the lowest,and the sand content being the highest.Quartz and Muscovite have higher contents,and their average value,maximum value and minimum value are higher than those of other three types of minerals.(4)The results showed that the driving forces of the Shiyang River Basin was consistent in the Holocene and the modern times.Aeolian deposition is dominant in the upper reaches,because they mainly were influenced by sand storms.Fluvial deposition is dominant in the middle reaches,and mainly influenced by suspended load and river hydrodynamic.Lacustrine deposition is dominant in the terminal lake area,because it mainly was influenced by suspended load transport and lake hydrodynamic.During the Holocene period,the Shiyang River was more humid than the modern climate and environment.