Soil evolution on the Central Swiss Plateau: comparing Middle Pleistocene with Last Glacial sediments

摘要

We compared soils within stratified soil parent materials (so-called cover-beds) at sites on the Central Swiss Plateau that remained unglaciated during the Last Glaciation with soils in pedostratigraphically equivalent deposits at locations covered by the Rhone-/Aare-Glacier during the Last Glacial Maximum (LGM). Using pedological and geochemical methods, we found regular differences in the degree of weathering and soil development between Middle Pleistocene and Last Glacial deposits. This allows relative dating of sediments of previously unknown age. Most suitable techniques for distinguishing degrees of weathering are based on total element analysis and micromorphological investigations, supplemented by clay mineral analysis. Iron oxides, by contrast, were shown to be a less reliable criterion, owing to greater variability and ambiguous interpretation. Within Middle Pleistocene sediments unglaciated during the Last Glaciation, remnants of pre-Wurmian weathering profiles are preserved on various relief positions, including hilltop sites. This implies limited erosion during the Last Glaciation. Instead, previously unweathered aeolian sediments contributed significantly to the upper part of these soil profiles (so-called Upper and Intermediate Layers), resulting in apparent retardation of overall degrees of weathering. This aspect should be considered when studying chronosequences spanning glacial cycles.