Abstract: The dynamical conditions of transport and deposition of sedimentary materials are usually inferred from their grain size, which is a fundamental property of the materials and may tell us much about the origins and history of the materials. Moment technique and graphical technique are the two principal methods to calculate grain size parameters for sedimentary analysis. In using the moment technique, calculation of the grain size parameters can be handled automatically with the help of computers, while in using the graphical technique the probabilistic cumulative frequency curve of a sedimentary sample has to be artificially drawn in?advance to obtain percentiles of the sample’s grain size distribution that are used to calculate the grain size parameters. Thus artificial drawing is a hard and time consuming work and is not beneficial to data in large batch processing. However, the difference in the grain size characteristics of the sediment samples from different sedimentary environments could be clearly shown in the probabilistic cumulative frequency curves with sub-population linear segments and the curves are widely used in sedimentary analysis. Therefore, drawing of the probabilistic cumulative frequency curves is an essential technique in sedimentary analysis even it is a troublesome job. The general calculating software, Origin, has very powerful functions for calculation and graphic drawing. It not only can calculate the particle size parameters by opening the embedded Excel Data Sheets that contain the grain size data and operate the data in batches, but also can directly draw grain size frequency distribution curves and probabilistic cumulative grain size curves with the linear sub-population segments simultaneously. The operation process for calculating the grain size parameters and drawing the cumulative curves in Origin is very easy and the whole process is simply to execute the menu command by mouse clicks without any programming. It is very suitable for analyzers, especially for those who have no coding skills, to analyze the data of particle size in sedimentary studies and thus has great application value. In this paper, we present an example in which a step by step guide to calculating the grain size parameters and drawing probabilistic cumulative grain size curves with the linear sub-population segments using Origin was carried out. Ten loose sediment samples, which were taken from different depositional environments in China, were selected for the calculation and drawing. The samples included beach sand, coastal wind sand, inland wind sand, river sand, lagoon sediment, old red sand and loess. The values of the percentiles and the grain size parameters obtained by this way were compared with the values that were calculated by artificial drawing. The comparison showed that the results calculated using Origin were very close to those calculated by the artificial method. The difference in values (absolute value average) between the two methods calculated from a single sample or all of the samples ranged from 0.003 7 to 0.013 3 with variances from 0.004 2 to 0.018 6. The comparison indicates that we can completely replace the artificial graphic technique with the calculation using Origin in grain size analysis.

Key words: the probability cumulative grain size frequency curve, Origin, interpolation, grain-size parameters