Weathering intensity and pedostratigraphy of the Middle to Upper Pleistocene loess/palaeosol sequence of Wels-Aschet (Upper Austria)

摘要

On top of a fluvioglacial terrace near Wels-Aschet, a complex loess/palaeosol sequence has been investigated. To date, the terrace is classified as a classical Gilnz unit (Older Deckenschotter). Sedi-mentological and mineralogical analyses were carried out on the basis of palaeopedological field data. The results show that in terms of mineralogical composition, the palaeosols can clearly be differentiated and are characterised throughout by interglacial weathering intensity. Bulk mineralogical as well as clay mineralogical data allow a five-stage ranking of weathering intensity based on indicator minerals. From the bulk mineralogical perspective, slightly weathered loess still contains carbonate minerals and primary chlorite, whereas the intensely weathered soil horizons are characterised by the total or near absence of carbonate minerals and primary chlorite, micas, and feldspars. In clay mineralogical results, chlorite and the relation of 14 A- and 18 A-vermiculites, as well as mixed layer minerals, play an important role in determining the weathering stage. Primary chlorite can be present in slightly weathered loess loams, and vermiculite 14 A is dominant there (stage 1 and 2). From weathering stage 3 onwards, the amount of vermiculite 18 A increases considerably and dominates the following stage 4. Most intensive weathering causes the absence of illite (stage 5). Generally, the studied interglacial palaeosols belong to at least stage 3. With the applied methodology, four interglacial palaeosols have been demarcated, as well as a highly weathered palaeosol within the terrace gravels of the Giinz in Wels-Aschet. Pedostratigrapy points to a classification of the Older Deckenschotter in MIS 14 at minimum. However, since this glacial period was of low intensity and the weathering intensity of the basal palaeosol was significantly enhanced, a correlation of the Giinz terrace with MIS 16 also seems possible.