Soil erosion and anthropogenic impact on landscape evolution over the past 2500 years: A case study of the Villers-Ecalles dry valley (Seine-Maritime, Normandy, France)

Résumé En

The present study analyzes archaeological and pedo-geomorphological data gathered from a Protohistoric settlement in Normandy (Northwestern France), in order to characterize upper Holocene landscape evolution, as well as to assess the impact of erosional processes in relation to human occupation over the past 2500 years. The settlement studied herein is located on the Pays de Caux plateau, in Villers-Ecalles, where luvisols, which have developed on Upper Pleistocene loess deposits, have been truncated by both natural and anthropogenic processes. This study compares the luvisol profiles along a catena / toposequence in a dry valley where a colluvial deposit record is observed. The latter is associated with an intense truncation of luvisols dating from the end of the Protohistoric period, especially during the Late Iron Age (La Tène period, 3rd century BCE), and during a Roman rural occupation (until the Later Roman Empire). Grain-size analysis and geochemistry allow characterizing the nature of colluvium and determine the signature as well as the sediment sourcing. The micromorphological analysis reveals the natural and anthropogenic processes at the origin of the studied microfacies (e.g., soil crusting, waterlogging, cultivation practices). The chronostratigraphy of the sequence is based on AMS 14C dating and archaeological remains, such as a fragment of a rotating grinding wheel from the La Tène period, providing a well-dated terminus post quem (TPQ). The colluviation has increased in modern times, probably due to a combination of both land use, as the main forcing factor, and the Little Ice Age (the LIA occurred approximately between 1550 and 1850 CE) as a secondary factor. The data enable us to reconstruct the diachronic evolution of the settlement over the past 2500 years. They also show the rhythmicity of erosional processes over the course of this period, linked with human and climate forcings.