TOPOGRAPHIC AND DRAINAGE CONTROL ON WEICHSELIAN ICE-WEDGE AND SAND-WEDGE FORMATION, VENNEBRUGGE, GERMAN-DUTCH BORDER

The climatic conditions under which ice- and sand wedges are formed ha ve been debated for many years. The temperature and humidity condition s controlling their formation have been studied in the present-day Arc tic. The results have been used to derive the palaeo-environmental and climatic conditions associated with the occurrence of ice-wedge casts and relict sand wedges in sedimentary sequences. In this paper a well -developed polygonal pattern of ice-wedge casts and relict sand wedges dating from the Weichselian Last Glacial Maximum is described. It has been found at the surface of a late Saalian sandur deposit close to t he border of western Germany and the eastern Netherlands. The ice-wedg e casts are present at the lower end of the sandur and probably formed in relatively humid conditions, while the relict sand wedges are excl usively present in the higher part of the sandur with drier conditions . Since both wedge types may have formed simultaneously, it is conclud ed that climatic differences are not the only factor controlling their formation. Local differences in soil humidity, land surface instabili ty and related aeolian sand transport have determined their infilling with either sand or ice. (C) 1998 John Wiley & Sons, Ltd.