| The abundance and deficiency of geochemical elements and various geochemical indicators have a good indication for regional climate change,while the surface characteristics of quartz particles can more intuitively show the dynamic effect of sediment experience and the transformation of sedimentary environment on the surface of particles.In this paper,eight major elements of Si O2,Al2O3,K2 O,Fe2O3,Na2 O,Ca O,Mg O,Ti O2 and eight microelements of Cr2O3,Mn O,Ni O,Cu O,Rb2 O,Sr O,Zr O2 and Ba O are selected to analyze their content change,CIA,weathering leaching coefficient,alkali removal coefficient,residual product coefficient,S/AF,K/N,C/M and R/S ratio,so as to infer the climatic evolution rules of the study area.In addition,due to the different degrees of transition between the surface characteristics of quartz particles with the changes of environment,there are many classifications of the surface characteristics.In this paper,quartz particles with a particle size of 1mm?0.125 mm are selected for observation and analysis under scanning electron microscope,a total of 33 characteristics with universal significance and landmark are selected.According to the characteristics of mechanical action and chemical action,the surface morphology of quartz particles is classified and counted,and the percentage of environmental particles is used for quantitative analysis.The dynamic environment and material source of sediment are inferred by the trace and combination characteristics of particle surface action.Based on the analysis of the geochemical characteristics and the surface morphology of quartz particles of the sandy sediments in Jincheng Road section,Changxing Island,the following results can be obtained :(1)According to the geochemical characteristics of elements,the main chemical elements of sandy sediments are Si O2 and Al2O3,the average content of which is 86.34%,which is the main element of their material composition.The fluctuation of the content of major elements and trace elements shows obvious stage characteristics,and the change of the content of elements accords with the general law of the soil forming process.CIA,weathering leaching coefficient,alkali removal coefficient,eluvial coefficient,S/AF,K/N,C/M and R/S ratio all show good correlation.Based on this,it is concluded that the weathering leaching,iron and aluminum enrichment degree and soil forming strength also show staged changes in the bottom-up accumulation process of sandy sediments.The weathering degree shows five stages of change : weathering enhancement—weathering weakening—weathering enhancement—weathering weakening—weathering enhancement.Through A-CN-K diagram analysis,it is concluded that the sandy sedimentary profile belongs to the low weathering in cold and dry climate,which is in the primary weathering stage but has not yet reached the middle weathering stage.(2)From the surface morphology of quartz particles,the roundness of quartz particles in sandy sediment is mainly sub angular shape,supplemented by sub circular shape,which belongs to mild roundness,and the overall roundness is poor,and the protrusion degree of particle surface is mainly medium protrusion,indicating that the sediment transport distance is relatively close.The characteristics of mechanical action are mainly manifested in the formation of high-energy wind and underwater environment,such as dished pits,crescentic percussion marks,pit and mechanical V-shaped pits,straight grooves and curved grooves.The superposition relationship between the two environmental characteristics is obvious,in which the water forming characteristics are clear and have not been strongly transformed by the late wind forming process,showing the characteristics of wind forming characteristics superimposed on the water forming characteristics.According to the characteristics of chemical action on the surface of quartz particles,the high-energy environment causes serious damage to the surface of quartz particles,which provides a development environment for chemical dissolution.However,similar to chemical precipitation,dissolution is not strong.Dissolution grooves and dissolution pits,as well as silica pellicle and silica squama,are only distributed in the local part of the particles,without the characteristics of chemical action and the whole particles.(3)During the Pleistocene,the ice age alternated with the interglacial period.When the ice age came,the temperature decreased,the sea level decreased,the shelf was bare,and the winter wind strengthened.According to the geochemical characteristics of the sandy sediments in the study area,although the climate environment fluctuates with relative increase of temperature and humidity or decrease of temperature and humidity,it is still in the primary chemical weathering stage under the dry and cold environment,and the overall weathering degree is not high.In the cold and dry climate,strong winter wind has become the catalyst for the remolding of sediment geomorphology,and the bare shelf area has provided sufficient material source for the formation of sandy sedimentary profile.According to the surface structure characteristics of quartz particles,the roundness of particles is poor,the sediment has not been carried and eroded in a long distance,and the source of indicator material is mainly from near source,supplemented by far source.The superposition of the characteristics of hydrogenesis and aeolian environment on the surface of quartz grains also indicates that the sediments may come from the shelf area that has experienced underwater environment,and they are transported by wind and deposited nearby when the shelf is exposed.(4)According to the geochemical characteristics of the sediments in the study area,the sandy sedimentary profile belongs to the low weathering under the cold and dry climate,which is in the primary weathering stage but has not yet reached the medium weathering stage.The climate environment shows the evolution law of turning to warm humidity,cooling and dehumidification,temperature and humidity environment,cold and dry,temperature and humidity increasing,with obvious cycle characteristics.However,these climate fluctuations are only relative,and the whole climate is still in a dry,cold and strong winter wind environment.According to the surface structure of quartz particles,the superposition of wind action on the hydrogenesis indicates that the sediments may have undergone the change from marine environment to land environment.At the same time,the undeveloped chemistry also indicates the cold and dry climate. |
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