图解法与矩法沉积物粒度参数的对比

GRAIN-SIZE PARAMETERS DERIVED FROM GRAPHIC AND MOMENT METHODS:A COMPARATIVE STUDY

采用Folk Ward图解法公式和McManus矩法公式 ,分别计算了山东半岛月湖地区 2 70个底质样品的粒度参数 (粒度分析用Cilas 940L型激光粒度仪与筛析法相结合 )并进行了比较。分析结果显示 ,两种方法所获的平均粒径和分选系数基本相同 ,偏态值相差较大 (但仍存在显著相关性 ) ,而峰态值不能相互转换。偏态值差异的原因在于 ,图解法的偏态指示了主要粒度组分的尾部特征 ,而矩法的偏态反映了样品总体的尾部特征。峰态值的差异是由于图解法所反映的往往只是样品的某一组分的粒度特征 ,计算方法比较粗略 ,而矩法反映了样品的总体特征 ,计算方法比较精确。在沉积环境分析、粒径趋势分析、历史数据解译时 ,应充分考虑这两种方法的差异。

Grain size parameters of 270 seabed sediment samples from the Rongcheng Bay region, Shandong Province, China, were calculated using graphic and moment methods. A comparison between the graphic moment derived parameters (including mean grain size, sorting coefficient, skewness and kurtosis) shows that the mean grain sizes and the sorting coefficients are almost identical. However, the skewness values vary considerably, although there is a significant linear relationship between the two data sets. No clear relationship between graphic and moment kurtosis values is found. The differences in the skewness values are caused by the fact that graphic measures reflect the characteristics of a main part of a sample, whilst moment measures provide an overall pattern of the sample. Hence, the differences in the two methods must be taken into account in sedimentary environment and sediment dynamic studies and historical data comparisons.