Comparison And Analyses The Grain-size Measurement Of Glacial Sediments

As an important index to reflect the evolution of sedimentary environment and heal thepaleo-climate changes in the past, grain-size character of sediment has caused serious concernby many domestic and foreign scholars.However, the characteristic of grain size and thepretreatment of methods for glacier is very poor.This article analyzes the grain-size characterof eight typical profiles for the glacial deposit to the bordering of the Tibetan Plateau,comparing the effects of different pretreatment methods and specific reasons on the glacialdeposits, and discusses the characteristics of grain size and their relationship in differentregions and the same region. The results show: the grain-size of glacier sediment is mainlycomposed of sand and silt, clay content is relatively less. The standard deviation for58%samples is greater than2, and32%samples between1-2, that means the Sorting for thegrain-size of glacier is in poor or very poor.The samples are the positive skew distribution,and also have a great relationship with composition,structure, physical properties of the parentrock. The kurtosis including the wide front and narrow peak,that is mean the part of sedimenthas been transformed into a new environment,frequency curve are two or more.Comparing the grain size characteristics of glacier region,we found that the grain-sizecharacter of sediment has no obvious relation with the properties of the local glacier in thedifferent study area.The characteristics of grain size has a big difference in the same studyarea, that means the sediment of glacier is greatly influenced by local environment, whichmay be related to the parent rock,the intensity of glaciation and natural conditions (Includingthe precipitation, temperature, the slope of ridge, the form of vegetation).Different pretreatment method does not change the overall advantage of glacialsediments grain size.However, the content of the composition in each sample has changed indifferent degrees.The sample which have more organic matter and carbonate, its averageparticle sizes change from several to several dozen times after add the hydrogen peroxide andafter acid treatment.The sample which has less carbonate, its free particle back together againby the strong acid.The experimental results also show that the Supersonic treatment methodsare more sensitive for glacier sediment. In addition,adding0.05mol/L of the（NaPO3）6for glacial sediments are not obvious, because the average of the average particle sizes changes ina small, that means the grain-size for the glacier has important impacts on the concentrationof dispersant.Glacial sediment granularity experiment of measuring time and sample selectionparticularly prominent on the result of the experiment.The best measuring time should be2minutes for the glacial deposits.If the sediment contains more Coarse sand, the samplingquantity is0.5-2g, more Silt in the sediment quantity of samples is0.25-0.4g,The samplequantity of the sediment contenting more clay is0.08-0.1g. And it must be repeated severaltimes with aliquots of measurements to ensure accuracy of the experimental results of theexperiment.