Periglacial slope deposits and their pedogenic implications in Germany

Abstract

Disconformities within soil-parent materials are frequently reported from locations throughout the world, but they are rarely within the goals of systematic research. This article provides an overview of the current state of knowledge on such materials and their pedogenic relevance in Germany. It intends to encourage further discussion on stratified soils in other parts of the world. The slope deposits in Germany are divided into (1) the upper layer that is ubiquitously distributed and displays a relatively constant thickness; (2) the intermediate layer that is restricted to flat relief, to hollows, and to lee-ward facing slopes; and (3) the basal layer that is rather widespread again. Both the upper and intermediate layer contain intermixed loess, while the basal layer is free of loess. These layers were mainly formed by periglacial solifluction. Such deposits are referred to as cover-beds. The upper layer formed during the Younger Dryas within a relatively short episode. In contrast, the lower layers may be diachronous; nevertheless, they display recurring vertical sequences. This is probably due to the fact that loess-free layers usually could not deposit as long as there was loess in the environs. Thus, the last phase of surface wash, during which older loess was removed, determines the age of the lower layers. The composition of the layers differs, reflecting the varying portions of loess and of rock allocated from upslope. In twofold sequences, the cover-beds influence the formation of the soils as they provide weathered material, and as their boundaries, where properties such as texture and bulk density abruptly change, determine the soil-horizon boundaries. Some pedogenic processes are favored (oxidation, depletion of clay), or hindered (podzolization) due to the loess content of the upper layer. Even exceeding this, the dominant loess content of an intercalated intermediate layer in threefold sequences may completely decouple pedogenesis from bedrock influence. In all, soil formation is largely influenced by the constellation of cover-beds at any given site.