Historical fluvial palaeodynamics and multi-proxy palaeoenvironmental analyses of a palaeochannel, Allier River, France

Abstract

A palaeoenvironmental study of a palaeochannel within the lower alluvial floodplain of the Allier River, France, has been carried out at a high temporal resolution. Research was based upon a multi-proxy approach using different sedimentological (magnetic susceptibility, sediment texture and loss on ignition) and palaeoecological (pollen, non-pollen palynomorphs (NPPs), diatoms – indicators). The palaeochannel was dated from six radiocarbon dates and spans from the second to the eleventh century AD. The cultural landscape history of this floodplain and the progressive hydrological disconnection of the palaeochannel between the Antiquity and the early Middle Ages could be reconstructed according to several characteristic environmental phases. Co-inertia analysis linking pollen, NPPs and diatom corroborated the significant co-structure of these proxies and allowed to distinguish functional palaeoecological groups in terms of landscape openness, on-site aquatic and hygrophilous vegetation, riparian woodland, soil moisture and grazing pressure. Results obtained underpin the importance of grazing as a major agent of landscape change in floodplains, especially since the ninth century AD, when the clearance of the riparian woodland is attested. Gallo-Roman and Late-Antiquity land-use systems, on the contrary, allowed for the preservation of riparian fluvial landscapes.