Permafroststrukturer i Fjordane, Vest-Norge

Structures interpreted as cryoturbation phenomena have been found in sandy and silty deposits in Breimdalen (Nordfjord) and at Hatlebrekke (Sunnfjord) in the Fjordane area of Southern Norway (Fig. 1). Plates 1-3 illustrate various types of structures found in a glaciolacustrine terrace in Breimdalen, and Plate 4 shows similar structures in deposits near Hatlebrekke. Both localities are situated higher than the Late Glacial marine limit, and the structures occur 1.5-5 m below the surface. The structures seem to correspond to structures which occur in Sweden, south of the Middle-Swedish moraine, and which are described by JOHNSSON (1956), who considers them to be periglacial phenomena developed under permafrost conditions. lee pressure and slides can cause folding in glaciofluvial deposits, but, in such cases, fold axes should be recognizable in the sediments. In the structures herein described, no fold axes were found. In frost structures, the folds and pockets are intimately related and form a type of cellular pattern like the structures found in Breimdalen and at Hatlebrekke. It seems probable on the basis of structural features, the material, and the location in relation to the surface that the structures described are analogous to certain types of frost structures, described among others by JoHNSSON (1956) and WoLDSTEDT (1954), and commonly believed to be developed under permafrost conditions. The question is whether such structures are formed under permafrost conditions only. Jf so, it can be assumed that the structures in Breimdalen and at Hatlebrekke date from the Younger Dryas Period and that the deposits of the Ra Period are to be found east of these two localities. Jf not, it must be that the development of structures such as those described above does not demand permafrost conditions.