Clay minerals in the middle-upper Miocene sediments of the Taman trough: Composition and paleogeographic significance

Abstract

The pioneer compositional analysis carried out for clayey sediments from most regional Miocene stages of the Taman trough made it possible to define the main types of clays and trace their variability through the section. It is established that the composition of these clays is largely controlled by the sedimentary rather than postsedimentary lithogenetic factors. The maximal hydromica (hereafter, illite) concentrations (up to 73%) are recorded in sediments deposited during orogenesis activation and major regressions (terminal Tarkhanian, Sarmatian, and early Pontian). The dominant role and elevated concentration of the smectite component are characteristic of sediments corresponding to transgressive phases of the basin development. The shallow-water sediments, which show a notable facies heterogeneity, differ from their deepwater counterparts by a higher diversity in the clay composition. These regularities in the distribution of clay minerals may be used for the lithostratigraphic subdivision of the sequences with a lower content of the fossil mollusc assemblages.