Fossiele permafrostverschijnselen in Nederland

This paper deals with permafrost relics from the Weichselian (last ice-age) in the Netherlands. As an introduction a survey is given of the Weichselian stratigraphy (table 1). Next the occurrence of ice-wedge-casts is discussed (fig. 1). From their stratigraphic position it is deduced that a permafrost probably existed between approximatly 50.000-18.000 BP in the Netherlands. As yet it is not clear whether a permafrost was present during the Late Glacial. Pingo remnants are discussed in some detail in the next section (fig. 3 and 4). They are dated between 18.000 and 11.000 BP. The preceding pingos are estimated to have been formed between 25.000 and 18.000 BP as hydrostatic pingos; they are related to a continuous permafrost. As a result of the relation of the so far investigated pingo remnants with the geology of the subsoil three kinds of pingo remnants are discriminated (fig. 5). The Drentsche Aa type (fig. 6) is located on the floors of former, now abandonned, Pleniglacial valleys. The Mekelermeer type is a variation of the former type and is, besides of being related to valleys, situated above intrusion-like sand bodies in areas with thick till deposits. The Uddelermeer type is located in permeable sands, overlying an impermeable clay layer in the subsoil. Finally in this paper fossil cryoturbation phenomena and asymmetric valleys are discussed (see also fig. 7 and 8).