G2Sd: a new R package for the statistical analysis of unconsolidated sediments

Modern depositional environment are mainly investigated in terms of internal sedimentary structures and associated grain-size characteristics. The latter are an intrinsic feature of sediments and hence essential for quantitative descriptions. It is therefore useful to have a tool available which allows direct and rapid calculation of numerous statistical parameters for a large number of samples. The G2Sd package gives full descriptive statistics and a physical description of sediments based on grain-size distributions derived from sieve analyses using a decadic log-transformation of the millimeter scale. Statistics are calculated either by using arithmetic and geometric methods of moments, or the graphic procedure of R.L. Folk and W.C. Ward (1957) to calculate mean grain-size, standard-deviation, skewness, and kurtosis based on the binary log-transformation of the mm scale. Numerical results are thus provided both in metric and phi units. The mode can be determined graphically by the user. Several percentiles and two common indices are calculated: D10, D50, D90, D90/D10, D90-D10, D75/D25, D75-D25, Trask Index (So) and Krumbein Index (Qd). A physical description of texture, sorting, skewness and kurtosis parameters is provided, based on the sediment nomenclature described in R.L. Folk (1966). The weight percentage of particles falling into each predefined size fraction is also included in the results. This package runs within the CRAN R-project.