The climatic control of sedimentary environment changes during the Weichselian – An example from the Middle Vistula Region (eastern Poland)

Abstract This study presents the sedimentary facies, stratigraphic framework and palaeoenvironmental conditions of the Weichselian sediments in the Middle Vistula Region. Based on sedimentological, palynological, palaeopedological and absolute age studies (luminescence and radiocarbon dating), a succession of three lithofacial complexes and the pattern of their evolution was distinguished. The lowermost, fluvial complex is composed of two parts separated by an extensive erosional surface. They were deposited in a braided river system during two distinct periods of Weichselian climate cooling: first at the end of the Marine Isotope Stage 5a and during the entire Marine Isotope Stage (MIS) 4, and then at the end of MIS 2 (Late Glacial). The middle, fluvio-aeolian complex was deposited during the Late Glacial as an effect of alternating fluvial and aeolian processes on abandoned, higher river terraces under periglacial conditions (discontinuous permafrost). It represents a record of climatic amelioration, culminating in the succession of tundra vegetation and sparse pine-birch forests, causing the formation of a soil in the top part of the middle complex. The uppermost, aeolian complex was deposited during the Older and Younger Dryas as a result of permafrost degradation. The deposition was interrupted by the expansion of boreal forest during the Allerod and the development of soils. Climate has been recognized as a major factor determining changes in sedimentary environments. The cooling of the climate during the Weichselian was conducive to the aggradation of sediments and permafrost. In contrast, climate warming resulted in increased erosion in the valley and creation of terraces.