| The weathering crust is the surface layer of the surface rock composed of the residual material of the original rock formed by weathering and denudation of surface rocks.The particle size distribution characteristics of weathering crust,the change characteristics of geochemical elements,the trend of geochemical indicators and the analysis of magnetic susceptibility are important judgments for indicating the source information and paleoclimate environmental change process.This paper selects the coastal red weathering crust of Chengshantou in Dalian as the research object.The sampling site is the coastal zone where the sea is closely connected.The development characteristics of weathering crust are studied by means of particle size analysis,geochemical elements,magnetic susceptibility and pH.Analytical research and comparison with the red weathering crust in other parts of the Liaodong Peninsula,the following conclusions were obtained:The Chengshantou section is dominated by three oxides of SiO2,Al2O3 and Fe2O3.The content of SiO2 is the highest,and the total content of the three oxides is 80.92%.The order of the other five major elements is Na2O>MgO>K2O>CaO>TiO2,the Na element content in the profile is higher than other profiles,and the average Na2O migration coefficient reaches 17.32.There are two reasons for this phenomenon:The first reason is that the weathering crust is in the coastal environment for a long time after formation.The long-term contact of the air with high salt-based ions?mainly Na ions?makes the salt-based ions mainly composed of Na ions enter the weathering crust,and the second is the influence of sea wave droplets on the weathering crust.The order of trace elements in order of increasing is MnO>P2O5>ZrO2>Rb2O>Cr2O3>ZnO>NiO>SrO>CuO.The mean value of the chemical alteration index CIA of Chengshantou section is 70.74,the mean value of salt-based leaching index is 0.56,and the mean values of S/R,S/A and S/F are 2.76,3.86 and 9.83,respectively.The mean migration coefficients of SiO2 and Al2O3 were-0.49 and 1.89,respectively.The content of silt grade in Chengshantou section is the highest,the content of silt is between 48.79%65.52%,the average value is 56.26%;the content of sand grade is middle,the content of sand is between 24.72%50.38%,average It is 37.34%;the content of clay particle size is the least,the clay content is between 3.19%and 15.49%,and the average value is 6.86%.The average particle diameter?value is 4.82?,the standard deviation is 2.54,the skewness average is 0.07,the skewness range is-0.130.30,most samples correspond to positive deviation,and the kurtosis average is 0.92,which belongs to medium kurtosis.The powder viscosity ratio is large,and the average value reaches 9.58.The Xlff variation range of Chengshantou section is 178×10-8m3/kg267×10-8m3/kg,the average value is 236×10-8m3/kg;the variation range of Xhff is 160×10-8m3/kg226×10-8m3/kg,the average value is 206.18×10-8m3/kg;the frequency magnetic susceptibility varies from10.1%to 14.4%,and the average value is 12.5%.The pH of the profile is between 6.23 and6.79,which is slightly weakly acidic.Through the study of the grain size characteristics,geochemical elements,pH value and magnetic susceptibility of the samples of Chengshantou weathering crust,it is found that the red weathering crust of Dalian Chengshantou has low clay content and high powder-to-viscosity ratio,and the particle size distribution is mainly concentrated in coarse grains.The end indicates that the developmental maturity of red weathering crust in this area is low,and the average value of chemical alteration index is 70.74,the mean value of salt-based leaching index is 0.56,and the average values of S/R,S/A and S/F are greater than2.The chemical indicators can also indicate that the weathering crust maturity of the study area is not high,which is consistent with the particle size analysis;whether it is from the change trend of the chemical alteration index or the change trend of the salt-based leaching index or the station From the perspective of the change trend of the migration coefficients of the main active elements of Si and Al,they jointly reflect a phenomenon,that is,the soil-forming effect of de-siliconization and aluminum-rich in the weathering crust of Chengshantou,except for several areas affected by tectonic movement and groundwater.In the section,it can be concluded that the weathering crust of Chengshantou is derived from the weathering of local bedrock;the geochemical indicators such as CIA,A/NK,A/CNK and salt-based leaching index change from the upper part of the section downward.The trend indicates that the weathering effect of the red weathering crust of Chengshantou has experienced three stages:enhanced weathering,weakened weathering and enhanced weathering.It indicates that the paleoclimate environment experienced three changes in the development of red weathering crust in Dalian.Gradually become warm and humid,and then it is more dry and cold,and finally warmed up;by comparing the eastern part of the Liaodong Peninsula,the Shantou section and the stone trough section,the western Qidingshan section and the coastal garden section,and the Huangnigou section in the middle,The east section has the highest maturity,the west side has the lowest maturity,and the middle part is the drama.It reflects the trend that the weathering degree of the weathering crust in the Liaodong Peninsula is gradually decreasing from east to west. |
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