From a periglacial lake to an alkaline fen – Late Glacial/Early Holocene evolution of Lublin chalkland tracked in biogenic sediments of Bagno Staw (Western Polesie Lowland, E Poland).

• We reconstructed environment changes with the use of multi-proxy approach. • Permafrost degradation led to a radical transformation in the flow of groundwater. • The paludification of the basins was determined by local conditions. • The process of subsidence determined the characteristics of the sedimentation basins. The paper presents records of lithofacial succession in the sediments of the Bagno Staw alkaline fen (Western Polesie Lowland, Eastern Poland), documenting the phase of rapid morphogenetic transformations during LG/H in the Lublin chalkland. Environmental conditions responsible for the morphogenesis and evolution of the site (from a shallow periglacial lake to an alkaline fen) were reconstructed. A detailed geological survey in combination with the analysis of Cladocera assemblages revealed the presence of numerous palaeodepressions under the plain covered today by the alkaline fen, which were initially small shallow lakes with a well-developed phytolittoral zone. Geochemical data and the analysis of stable O and C isotopes indicated that these lakes were supplied by ascending waters. Karstic phenomena under periglacial conditions, including subsidence at the bottom of biogenic accumulation basins, played an important role in the transformation of this site. These changes were largely determined by the chronology and dynamics of permafrost degradation. [ABSTRACT FROM AUTHOR]