Rb-Sr and K-Ar isotopic systems of the Upper Devonian sediments in the Pripyat Trough,Belarus

The results of Rb-Sr and K-Ar isotope studies of the Famennian upper salt and suprasalt complexes sampled from the core material of exploratory boreholes drilled at the northwestern margin of the Pripyat Trough (Belarus) are presented. The suprasalt and saliferous portions of the sequence define an age of approximately 470 Ma. Despite multiple reworking of the material, we interpret this value as preservation of the provenance “memory.” Regardless of the Sr content in sample, the strontium isotope ratios obtained for low-Rb minerals (celestine, carbonate, and halite) varies throughout the section within 0.7083–0.7095, indicating the preservation of some primary features of the matter. The lowest isotope values obtained are slightly higher than those inferred for the upper Famennian. This fact confirms the concept that the studied complex was formed in a shallow-water setting. Data on sylvites show that the present-day isotopic characteristics of potassium salts were formed significantly later.