陇西盆地晚更新世风成堆积物粒度参数的对比

A COMPARATIVE STUDY ON GRAIN SIZE PARAMETERS OF AEOLIAN DEPOSITS IN THE LONGXI BASIN DURING LATE PLEISTOCENE

计算了末次冰期旋回陇西盆地的黄土古土壤和风成砂的粒度参数,并对图解法与矩值法粒度参数进行了对比。结果表明,对黄土古土壤来说两种方法所获得的平均粒径基本相同,分选系数、偏度和偏态的相关性逐渐降低,对风成砂和砂黄土来说,除了平均粒径呈较好的线性相关外,其他参数则差别很大。造成这种差异的主要原因是由于它们粒度组分的分布不同所致。图解法主要反映了样品总体中主要粒度组分的粒度特征,而矩值法则反映了样品的总体特征。在沉积环境的分析和比较中,应充分考虑这两种方法的差异,并建立不同的标准。激光粒度仪和吸管法对平行样品测试的图解计算结果表明,粒度参数的变化趋势比较接近。

Grain size parameters represent the fundamental property of sediment particles, affecting their entrainment,transport and depostion. The grain size of loess-palaeosol is regarded as a good proxy record of climate and environment changes in Quaternary in North China. Grain size parameters of more than 200 aeolian sediment samples from the Longxi Basin, were calculated using graphic and moment methods by GRADISTAT. A comparison between grain size parameters （including mean,sorting,skewness and kurto- sis） of graphic and moment method shows that the mean grain size and sorting are almost identical, and there is a significant linear relationship between the two datasets for skewness and kurtosis in loess-paleosol sequence during the last glacial cycles. However, it is different for the sand deposits near desert. Graphic method reflects the characteristics of a main part of a sample. Besides,there are large differences in grain size distribution between loess and sand deposits. So the differences in the two methods must be taken into account in sedimentary environment studies. We also study the correlation between the grain size parameters measured by the laser sizer and sieving method using graphic methods;it shows that the grain size parameters have a similar tendency.