Pierre Gangloff

Traces d'un pergélisol villafranchien dans les alluvions du sundgau

Abstract Evidence of villafranchian permafrost has been found at the southern end of the Rhine graben, 20km west of Basel. Two syngenetic ice-wedge casts were discovered in the “alluvions du Sundgau”. From a stratigraphical point of view, these coarse gravels were deposited after the Miocene and before the Gunz glaciation. The occurrence of syngenetic periglacial structures shows that they must be of Pleistocene (Villafranchian) age. A SEM study of sand from the infilling of one of the cryogenic structures showed numerous marks of glacial origin on the quartz grains. They are indicative of a pre-Gunz glaciation in the Alps. It is suggested that permafrost in villafranchian time developed only on the fringe of the alpine glaciation, but further studies will be needed for a better picture of villafranchian palaeogeography.