“Ghost structures” in alkaline fen microrelief as a consequence of Late Glacial periglacial activity in chalklands : a case study from the Chełm Hills (East Poland)

On the basis of high-resolution LiDAR data, collected at the surface of alkaline fens in the Chełm Hills area (Lublin chalkland, East Poland), structures deviating from the natural paludification processes related to the development of fens (“ghost structures”) were identified. At each of the sites analysed, field verification by means of drillhole cores indicates an indirect relationship between the modern topography of the peatlands and the morphology of their substratum, related to periglacial processes. Three categories of periglacial structure were recognized in the chalk bedrock: (1) solifluction sheets, lobes and terraces; (2) pingo-type structures (ramparted depressions, lithalsas); and (3) relict cryogenic mounds. A conceptual model of the development of slope and peatland relief in the Lublin chalkland during the Late Glacial and Holocene was prepared on the basis of the results obtained. The results indicate the role of the periglacially transformed chalk substratum in the development of alkaline fens in the chalklands, which rarely was considered in previous studies.