Identifying depositional and pedogenetic controls of Late Pleistocene loess-paleosol sequences (Saxony, Germany) by combined grain size and microscopic analyses

Late Pleistocene loess-paleosol sequences (LPS) often consist of complex layers of eolian or reworked loess-like sediments or both. Additionally, these layers may have been overprinted by pedogenetic processes. In the present paper we demonstrate how combining high-resolution grain size and microscopic analyses can be used to discriminate depositional and pedogenetic features of LPS from the Saxonian Loess Region. Grain size analysis was conducted by classical pipette and sieve procedures and eight grain size classes (coarse, medium, fine and very fine sand; coarse, medium and fine silt; clay) were distinguished.

Generally, it was observed that an increase of coarse material is linked to an increase of the minerogenic components which can be attributed to slope surface processes. Rounded Mn- and Fe-precipitates are mostly found in Early Weichselian humus layers and indicate strong interstadial soil development modified by subsequent redeposition. Further observations suggest that the class of medium sand is dominated by secondary precipitates. The varying amount of very fine sand shows that sequences are cyclically built up of pure loess comparable to the Nussloch section. When studying coarse grain size fractions by microscopic analysis, it is possible to differentiate between loessic layers formed by periglacial slope processes and layers overprinted by pedogenetic processes based on determining the nature and roundness of minerals. Furthermore, an increase of fine material and secondary Mn- and Fe-precipitates can be attributed to soil forming processes (clay formation, redoximorphic processes, illuviation).

The results reveal similar temporal and lithogenetic pattern of Weichselian eolian dynamics of the study area and other records from the European continent. Furthermore, lithogenetic interpretations based on grain size analysis conform to found age ranges obtained by Optical Stimulated Luminescence (OSL) dating. Reworked loess-like sediments show varying OSL-age estimates; eolian loess shows a systematic change of OSL ages. Therefore, we advocate a detailed grain size interpretation as a basis for further investigations on LPS