Method of Estimating the Integral Roundness Index for Detrital Zircons: A Case Study of Cimmeride Sedimentary Sequences in the Crimean Mountains

A technique to evaluate the degree of roundness of detrital zircons on a 5-point scale based on the preservation of crystal vertices, edges, and faces is presented. Based on measurements in individual grains, the integral roundness index R_s is calculated for a zircon grain set from various stratigraphic units. The obtained data make it possible to determine the proportion of different class grains in various sequences and to assess their similarity/difference degree, which can serve as an additional criterion for the differentiation of sedimentary sections. The proposed method is used to compare the roundness characteristics of detrital zircons from some Cimmeride sedimentary sequences in the Crimean Mountains. It is shown that relative to counterparts in the flysch sequences, sandstones of the Chenka sequence are characterized by a higher proportion of unrounded and weakly rounded zircons and a virtual absence of completely rounded grains. Value of R_s for the zircon grain set ranges from 3.41 and 3.95 for the Tauric Group to 2.55 for the Chenka sequence. Thus, R_s values in the sequences are marked by a significant difference, which is also confirmed by values of the mutual pair coefficient p calculated using the Kolmogorov–Smirnov test.