SOME DISCUSSIONS ABOUT THE SIEVING SIZE ANALYSIS

Abstract

Techniques of the size analysis are often used to distinguish the depositional environme:zts, especially to distinguish aeolian from marine environment. In Japan, many environmental studies by this method have been published since 1945, but the examinations of this method itself is still insufficient. The author examined the usefulness of the size frequency parameters obtained by both graphic and moment methods. Samples were collected from the foreshores, backshores, and the present dunes, and also from the ancient dunes and the ancient horizontally laminated sandbeds, of 34 areas of Japan. The results are briefly summarized as follows (1) When we want to require the precise frequency curve and its useful parameters, especially the skewness, it is desirable to sieve with quarter phi grade and weigh each fractions to 5mg, and moreover, it requires that the residual fractions on both the coarsest sieve and the pan fraction should be equal weight and less than 0, 5% weight, if possible, less than 0.01% weight. (2) The outline of each size frequency distribution is already determined after 10 minutes seining and it gives useful parameters enough to investigate each deposition) environment. (Sample weight: 100 gr.) (3) Mean, standard deviation and skewness by Inman's equations are no less useful than by Folk and Ward's equations. The complicated calculations by Folk and Ward's equations do not necessarily give better results than the simple calculations by Inman's equations. (4) Means of quarter phi grade obtained by both graphic methods (Mz, Mφ) are as useful as the mean of whole phi grade by the moment method. (5) Both graphic standard deviations (σI, σφ) of quarter phi grade have about the same usefulness as the moment whole phi value. (6) We cannot obtain the precise skewness value by both graphic equations. Therefore, we must calculate it by the moment method with half phi or quarter phi grade.