Evolution of Early and Middle Pleistocene river valley systems in Polish-Ukraine-Belarus cross-border areas based on geological and malacological proxies

The geological setting of the Bug-Pripyat interfluve and the close proximity of the source of the Pripyat River to the well-developed Middle Bug River valley suggest that these rivers may have been connected in the past. Analysis of geological cross-sections around the Polish-Ukraine-Belarus cross-border areas together with study of associated Pleistocene palaeoflora shows that buried alluvial deposits of the proto-Bug and proto-Pripyat clearly represent the Preglacial (MIS 103-23), Podlasian/Turskian-Donian/Brest Interglacial (Cromerian I-II; MIS 21-17) and the Mazovian/Likhvinian/Alexandrian Interglacial (Holsteinian; MIS 11c). Their elevated position in mid-eastern Poland suggests the possibility of accumulation by proto-Bug waters flowing eastwards, which determined the formation and development of the lower-lying proto-Pripyat valley system in northwestern Ukraine at those times. The occurrence of the Ponto-Caspian species Lithoglyphus naticoides (C. Pfeiffer, 1828), Borysthenia naticina (Menke, 1845) and Corbicula fluminalis (O.F. Müller, 1774) in the mollusc assemblages of the Mazovian/Likhvinian/Alexandrian Interglacial implies that the main watershed between the Baltic Sea and the Black Sea drainage basins might have been situated in the northern part of the area studied. Presumably its main part was drained by the waters of the proto-Bug catchment connected with the proto-Pripyat and flowing farther to the east towards the Dnieper River entering the Black Sea.