PERIGLACIAL STRUCTURES IN THE LAST INTERGLACIAL-GLACIAL LOESS SEQUENCES IN SW POLAND

The loess in SW Poland occurs in several isolated patches, which differ one from another in sediment thickness, stratigraphy and physical properties. The most representative loess sequences provide a good record of climate changes during the last interglacial-glacial cycle (Eemian – Weichselian). One of the most spectacular features of loess sequences in SW Poland is the occurrence of well preserved relicts of periglacial horizons. Within the Eemian - Early Weichselian pedocomplex two periglacial horizons exist: the older one consists of indistinct polygons of narrow frost cracks bent downslope in their upper part by slow solifluction processes; the younger represents polygons of frost wedges with primary (loess) infilling, associated with wind-abraded surface with ventifacts. The upper horizons of pedocomplex are deformed by cryostatic pressure and frost heave and finally straggled by solifluction (third periglacial horizon). Small (1-2 m) ice-wedge casts formed in loess stratum underlying the complex of tundra-gley soils constitute the fourth periglacial horizon. Interpleniglacial complex of tundra-gley soils is markedly reworked under the influence of cryohydrostatic pressure and solifluction in its upper part (fifth periglacial horizon). The uppermost (sixth) periglacial horizon consists of large (2-4 m) ice-wedge casts and associated thermokarst structures connected with degradation of permafrost. Periglacial horizons recorded in loess sequences of SW Poland were formed as a result of extreme climatic conditions and/or rapid environmental changes during cold events of the last glacial period. Some of these horizons can be used as a stratigraphical markers.