粒度分析中偏度系数的影响因素及其意义

Influencing factors and significance of the skewness coefficient in grain size analysis

利用粒度分析中的偏度系数对区分不同搬运动力和不同沉积环境下的沉积物具有重要的鉴定意义,通过对偏度系数内涵的深入分析和粒度分析不同方法的比较,研究表明:偏度是非正态粒度分布下的偏斜程度,可敏感地反映粒度分布两端的微量变化,正偏是沉积物粒度分布的细偏,负偏则是粗偏,偏度正负大小与多种因素有关,它主要受沉积物属性控制,既与沉积环境类型密切相关,又与环境能量是否对应平衡有关;偏度还受计算方法和测试方法等人为因素影响。筛析法结合图解法计算较适用于粒度粗、跨度大的沉积物粒度分析,激光粒度法结合矩法计算更适用于粉砂—黏土粒级沉积物的粒度分析。

The coefficient of skewness is an important parameter for the analysis of sediment gain size,which is vital to identify sediment under different transported dynamic and depositional environment.Based on the study of connotation of skewness and comparison of different methods of gain size analysis,the skewness is found to be a slanting asymmetry in an abnormal distribution,which sensitively reflects the trace variation of the grain size distribution.The positively biased is the grain distribution skewed to the segment of fine grain,while the negative skewness slants to the coarse grain.The positive or negative and the big or small values of the skewness are related to many factors,they are controlled by sediment property of not only sedimentary environment but also the balance of grain size and ambient energy,as well as the influence of human factors,including calculation and testing method.Sieve analysis combining graphic method is appropriates for the coarse grain when grain size span is large;laser grain analysis uniting moments method is appropriates to the grain size analysis of silt-clay sediments.