The lower reaches of the Nemunas River at the end of the Last (Weichselian) Glacial and beginning of the Holocene

Abstract

The Russian–Lithuanian cross-border area around the Nemunas and Sesupė rivers confluence is a key area for solving palaeogeographic issues important for this region: when the Nemunas Delta started to form, why the essential changes of hydrographic network occurred, and so on. The results of conventional radiocarbon ( 14 C) dating and pollen analysis in the present dry valley between the Sesupė River and the Įrutis River as well as the results of former studies at the Riadino-5 archaeological site suggest that the essential changes in the Nemunas River hydrographic system occurred before 9.5 ka, most likely in Preboreal time, when the Nemunas River cut through the Vilkiskė Marginal Ridge and started to flow directly to the west from this ridge into one of the former basins of the Baltic Sea – to the Yoldia Sea, or to the Ancylus Lake. A new divide was formed between the Sesupė and Įsrutis rivers, and the basins of the Nemunas and Prieglius rivers (formerly a single hydrographic system) became two independent drainage basins of the Baltic Sea. The present Nemunas Delta formation started after the Litorina Sea transgression when the Nemunas River mouth moved from a Baltic Sea nearshore position to close to the western margin of the Vilkiskės Marginal Ridge. A set of palaeogeographic reconstructions of the Nemunas and Sesupė rivers confluence area for different periods of the very end of the Last (Weichselian) Glacial and the beginning of the Holocene have been constructed.