Ice‐wedge pseudomorphs and frost‐cracking structures in Weichselian sediments, central‐west Poland

• Published in: Permafrost and Periglacial Processes
• Main Author: Marek Ewertowski
• Format: Article in Journal/Newspaper
• Language: unknown
• Subjects: Ice Sheet; Thermokarst
• Online Access: https://doi.org/10.1002/ppp.657

Wedge‐shaped structures are described from three sites in the central Wielkopolska region (central‐west Poland) in two main positions: (1) within fluvioglacial deposits below the Weichselian subglacial till and (2) within recessional deposits above this subglacial till. The wedges are interpreted as ice‐wedge pseudomorphs (Rensko site), relict frost cracks (Tomice site) and thermokarst‐affected ice‐wedge pseudomorphs (Annowo‐Kiszkowo area). The pseudomorphs suggest that thermal‐contraction cracking occurred in the region in front of the advancing Weichselian ice sheet, as well as following its recession. Frost structures, which are interpreted as having degraded slowly, were much more affected by thermokarst processes (Annowo‐Kiszkowo area) than those in the Rensko and Tomice sites which probably thawed rapidly, due to an insulating and warming effect of the overlying ice masses. The development of ice wedges was influenced by wet conditions in former depressions between ice‐cored ridges or by large amounts of meltwater in the proglacial environment. These periglacial features support previous hypotheses that climatic conditions in the Wielkopolska region after the last ice‐sheet recession changed gradually from glacial to periglacial. Copyright © 2009 John Wiley & Sons, Ltd.