Comparison of the graphic and moment methods for analyzing grain-size distributions: A case study for the Chinese inner continental shelf seas

Sediment grain-size distributions provide key information on sediment sources, transport, and deposition. The Folk and Ward graphic method and the Friedman moment method are generally used for rapid analysis of the qualitative and quantitative properties of sediment samples; whether the two methods yield the same results for any given sediment sample is not yet known. Little research attention has been paid to comparison of the descriptive terms used in both methods, although some work has been done on comparison of the numerical values. In the current study, sediment samples from six areas of the Chinese inner continental seas were investigated. The mean and sorting values obtained using the two methods are well correlated (0.821 ≤ R2 ≤ 0.998), but the skewness and kurtosis vary among study areas (0.035 ≤ R2 ≤ 0.816), which is consistent with previous studies where R2 is the coefficient of determination. The two methods yield significant differences for skewness (84.78%–98.04% of samples) and kurtosis (40.59%–67.29% of samples). The main reasons for these differences are variations in the grain-size distribution curves of the sediment samples and differences in the weighting applied to specified cumulative percentile values by the two methods. These results demonstrate that the differences between the two methods should be taken into account when analyzing sedimentary environments and studying historical data.