Geomorphological system and landscape coevolution in Mercurey (Burgundy, France): hypothesis of an early soil maintenance strategy

Vine introduction in Burgundy (east central France) two millennia ago is responsible for land use changes and increased soil erosion to which societies have tried to adapt. In this paper we seek to figure out the relationship between land uses, agricultural practices and geomorphic dynamics in the Mercurey terroir during the Late Holocene. The method employed is based on the analysis of sedimentary deposits observed in the valley bottom and along hillslopes. It is complemented by a pedoanthracological study derived from a trench excavated into a riverbank, in order to interpret the variability of the reconstituted sedimentary signal. Our results highlight two major stages of detritism over the last 2,800 years. At least from 800 cal. BC, frost heave screes (stored since the Late Pleistocene) are transported from the upper part of hillslopes to the valley bottom by high-energy geomorphic processes (e.g., solifluction flows). This sequence of coarse colluviums is associated with the development of an agro-pastoral landscape marked by an opening forest cover. A second phase begins after 1400 cal. AD. It is characterized by a fine sedimentation and a high concentration of vine charcoal. Indeed, wine-growing spread in the medieval landscape comes with the building of agricultural infrastructures. It leads to a decrease of sediment connections from the source areas to valley bottom. The coarser sediments are retained on the hillslopes, thus bringing out soil maintenance strategy.