A method for estimating of integral roundness index for a detrital zircons set: a case of the sequences from the Cimmerides of the Mountainous Crimea

Abstract

A technique that allows to evaluate the degree of roundness of detrital zircon grains on a five-point scale according to the degree of preservation of the vertices, edges and faces of the crystals is presented. Based on the results of the degree of roundness of individual grains, the integral index SOs is calculated for a sample from various stratigraphic units. The obtained data makes it possible to determine the proportion of grains of different classes in different strata, to assess the degree of similarity/difference of samples, which can be an additional criterion when dividing sedimentary sections. The proposed method is used to compare the roundness characteristics of detrital zircons from a number of sedimentary sequences of the Cimmerides of the Crimean Mountains. It is shown that the sandstones of the Chenka sequence, relative to the sandstones of the flysch sequences, are characterized by a higher proportion of unrounded and weakly rounded zircon grains and a virtual absence of completely rounded grains. The values of the integral roundness index SOs for zircons from sandstones of the Tauride Groupe have showed values of 3.41 and 3.95, and for the Chenka sequence – 2.55. Thus, a significant difference in SOs was recorded between the studied strata, which is also confirmed by the values of the mutual pair coefficients p, calculated using the Kolmogorov–Smirnov test.