Volume-, Weight-, and Number-Frequency Analysis of Sediments from Thin-Section Data

The Rosiwal method of planimetric analysis of thin sections gives the apparent proportion of grains in a series of arbitrarily selected size classes. The true volume-percentage distribution is calculated from the observed thin-section distribution by taking into account the statistical distribution of the thin-section diameters of spherical grains with given true diameters. The method of computation of the true distribution from a set of observed data is purely arithmetical. In the two sands studied, an excellent correlation between the reconstructed and sieving analyses is obtained. A new method of calculation of number-frequency analyses alternative to that of Greenman (1951b) is based on a consideration of the entire distribution function. It is not assumed, as was done by Greenman, that all the grains in any class are of one size. His method is more accurate for very well-sorted sediments.