Determination of Sieve-Size Distribution from Thin-Section Data for Sedimentary Petrological Studies

The sieving methods presently in use for loosely consolidated rocks are inadequate for the determination of grain-size distribution in cemented and indurated sedimentary rocks. Thin-section study represents an alternative method of obtaining the particle size distribution for such rocks. The purpose of this study is to establish a correlation between sieve and thin-section grain-size analyses. Grain-size analyses were made on thirty-eight rock samples by both sieving and thin-section methods. The cumulative frequency curve determined from the apparent long diameter measured in thin-section lies toward the coarser size range with respect to the sieve-size distribution curve, but the discrepancy between the cumulative frequency curves for the two techniques is small. A plot of thin-section quartile parameters against sieving quartile parameters indicates a linear correlation between the two techniques. For all practical purposes, the same linear function expresses the relationship between quartile parameters as determined by the two methods, so that all three quartile measures (Ql, Md, Q3) can be combined into one plot. A graph based on 114 quartile measures for sieve and thin-section analyses forms the basis for the derivation of sieve-size dis tribution from thin-section data. A new graph paper has been developed which permits the construction of a cumulative frequency curve for sieving from thin-section data without mathematical conversions. Moreover, the graph paper allows the direct determination of sieving parameters. The usefulness of the new method is illustrated by comparing it with conversion techniques developed from mathematical analysis.