La dynamique des versants dans le bassin de la Dore durant la deuxième moitié de l'Holocène {Massif central, France) ; premières données géoarchéologiques et datations radiocarbone / The dynamics of slopes in the catchment of the Dore during the Late Holocene (Massif central, France) : preliminary geoarchaeological data and radiocarbone dating.

Abstract

During two years geoarchaeological studies have been conducted in the catchment of the Dore, a small fluvial basin -1716 km2- situated in the granitic Mountains of the French Massif Central. Our researchs aims to describe and explain the holocene environmental changes in this part of western Europe. In this paper we examine the slope dynamics, the colluvial deposits, and alluvial fans which lie on the flat of the alluvial plain of the Dore. We dug pits and drilled sediment cores so that to analyze stratigraphy and to take samples for sedimentological analysis. The discovery of charcoal layers and wood into colluvial deposits and alluvial fans allowed to obtain radiocarbon dating. However the results are very difficult to explain. Numerous dates concerned reworked material. They reveals ages of 7970 +/- 60 BP to 220 +/- 50 BP. These dates provide maximum ages for deposits and they allow to date especially some stages of each deposit. One date obtained come from in situ charcoal and ashes layer. Therefore we know the age of the beginning of the deposit : the second Iron age. Then archaeological and palaeoecological records together with "C dating of charcoal or wood samples are applied in this paper to the stratigraphy of alluvial fans and colluvial deposits to determine and understand changes m the slopes dynamics. About the second Iron age we discuss the assumption that geomorphic changes were associated with the agricultural activity. Anthropic assumption is also proposed so that to explain the development of the alluvial fans during the third millenium BC.