The application of geostatistics to analysis of grain size trend in the Eastern Beibu Gulf

A total of 71 surficial sediment samples are collected in the eastern Beibu Gulf, and then the moment parameters (i.e. mean size, sorting coefficient and skewness) are obtained by grain size analysis. By using kriging interpolating methods, the regular meshes of grain size parameters are calculated. A geostatistic analysis is applied to study the spatial autocorrelation for these parameters; while the range, a parameter in the semivariogram metering the bound of the spatial autocorrelation, is estimated. It shows that the range for sorting coefficient is physically meaningful, and also the obtained grain size trends are consistent with the annual ocean circulation pattern and sediment transport rates from previous studies. Thus, the range from the sorting coefficient variogram can be used as the characteristic distance in the grain size trend analysis model, which may remove the bias caused by traditional determination of characteristic distance (e.g. based on experience or testing methods). The sediment transport patterns are retrieved on the basis of grain size parameters interpolated with varied distances, which indicates that the small interpolation distance can produce better transport pattern with high resolution and give more detailed information. Hence, the results from geostatistic analysis can be guidable in determination of sampling stations density in the future field work.