The First Results of U–Th–Pb Isotopic Dating of Detrital Zircons from the Chenka Sandstones – a Contribution to the Stratigraphy of the Cimmerides of the Mountainous Crimea

Abstract

The first results of U–Th–Pb isotope dating of detrital zircons (dZr) from the Chenka sandstones of the Cimmerides of the Mountainous Crimea are presented. Carboniferous–Triassic dZr dominate among dZr from Chenka sandstones. Analysis of previously obtained sets of dZr ages from the different-age and lithology formations of Cimmerides of the Mountainous Crimea has revealed the certain regularities in the change in time of the provenance signal and, accordingly, of the sources, the erosion products of which compose the studied formations. A comparison of the obtained of U–Pb ages of dZr from Chenka sandstones with similar data for sandstones from the Upper Triassic–Jurassic formations has shown that the provenance signals of the Chenka sandstones and Upper Triassic–Lower Jurassic flysсh strata are different, but the provenance signals of the Chenka sandstones and Middle–Upper Jurassic coarse clastic strata are similar. Detrital zircons from the Chenka sandstones are characterized by the parameters of the distribution of Th/U values intermediate between those from sandstones of flysch strata and from sandstones of coarse-grained strata. In general, the obtained isotope-geochronological and geochemical data and some features of the internal structure of dZr from the Chenka sandstones can be used as a strong argument in favor of interpretation of Chenka sandstones as an independent stratigraphic unit with an age not older than the Middle Jurassic. The similarity of the characteristics of dZr from sandstones of the Chenka sandstones with those of Middle–Upper Jurassic coarse clastic sequences casts doubt on the correlations of the Chenka sandstones with a number of lithologically similar units of the southwestern regions of the Mountainous Crimea, specified as Early Jurassic in age based on faunal finds.