Interpreting colluvial deposits: Archaeopedological reconstruction of land use dynamics in southwestern Germany

Abstract

The aim of this study is to establish a concept to interpret colluvial deposits as archives and to use them to reconstruct past land use dynamics. The archaeopedological study is part of the project “B02: Favor-Disfavor? Development of Resources in Marginal Areas” within the framework of the collaborative research center SFB1070 RESOURCECULTURES. The analysis of 68 soil profiles at 13 archaeopedological sites and two bogs in southwestern Germany includes the agriculturally favorable Baar area and the unfavorable southeastern Black Forest and western Swabian Jura. Over the whole study area, dated charcoals indicate increased human activity from the Final Neolithic to the Latène period and also from the High Middle Ages to Early Modern times. OSL dating shows a different pattern of colluviation, and therefore intensified land use, with a focus on the Iron Age to Roman Empire and the High Middle Ages to Early Modern period. Following isolated colluvial deposits, dating to the Mesolithic, there is evidence of wide-ranging colluviation during the Neolithic, which coincides with the establishment of agriculture in the area. Focusing on differences between the landscapes shows a spatially heterogeneous colluviation and land use dynamic through time. The Baar area has a detailed and long stratigraphy of colluvial deposition beginning during the late Mesolithic, which can be linked to phases of intensive land use or land use change. In the Black Forest in contrast, few prehistoric colluvial deposits can be found. Still, charcoal ages indicate local and probably seasonal human activity. During the Middle Ages and the Early Modern period colluviation increased strongly which seems to result from land use change, specifically intensification and expansion. Even though a similar land use pattern was expected to be found in both unfavorable landscapes, the Swabian Jura shows increased colluvial deposition already during the Iron Age but only little colluviation during the Middle Ages. Sites close to the edge of the Swabian Jura have a similar land use pattern than the eastern Baar. The empiric study is associated with theoretical concepts like social-ecological systems and adaptive cycles, which provide a helpful approach to frame and interpret the agricultural development and colluvial deposition through time. The adaptive cycle of agrarian soil use begins in the Neolithic and transforms into a second adaptive cycle of agrarian soil use with the industrialization. This follows the reconstructed pattern of land use dynamics and colluvial deposition, which set in during the Neolithic and reach a new level during the Middle Ages. The reassessment of AMS-14C ages of anthropogenic charcoal fragments indicates that char-coals can be used to reconstruct human activities, but are not necessarily connected to the colluvial deposit, in which they were found. Thus, the sampling depth of charcoals found within colluvial de-posits is negligible. The dating of soil sediment by OSL, however, reliably dates the period of time when the colluvial deposit was accumulated. Therefore, OSL ages can be used to date colluvial deposition, which is linked to intensified land use or land use change. Nevertheless, temporary storage and a possible time lag between erosion and accumulation must be considered. The acquired data support the interpretation of certain colluvial deposits as former land sur-faces. Selected soil profiles show a detailed stratigraphy of colluvial deposits, which allowed the re-construction of phases of geomorphodynamic stability. During such phases no colluviation took place and pedogenic and biologic processes occurred. The changes in the upper part of a colluvial deposit, being the land surface, cannot be found. However, changes are rather found in the lower parts of colluvial deposits, possibly resulting from erosion and relocation of topsoil sediment with subsequent deposition on an eroded surface. Thus, material with increased soil organic matter content can be found in the lower parts of colluvial deposits, instead of in the upper parts. In summary, this thesis provides a thorough investigation of colluvial deposits as a proxy of land use dynamics in southwestern Germany. Theoretical ideas like the adaptive cycle concept and how to interpret and statistically use different dating methods help to understand past human-environment interactions.