Micromorphological evidence of soil deterioration since the mid-Holocene at archaeological sites in Brittany, France

This paper presents data on the evolution of agricultural landscapes in Brittany from the end of the Atlantic chronozone to the Mediaeval period (450 BC-AD 1600), using soil micromorphology in a multidisciplinary palaeoenvironmental context. Buried soils and unburied sediments associated with archaeological structures in Brittany were examined. The study of well dated archaeological buried soils gives new information on the way the landscape of Brittany was affected by human impact, which has disturbed the Atlantic soil balance since the start of the Neolithic and has been a major factor in soil acidification in Brittany. Deforestation of primary woodland occurred however, over a long period. The analysis of down-slope sediment accumulation shows that colluviation of loam-rich soils was stimulated by deforestation and agriculture. Micromorphological study of archaeological ditches shows that some microscopical features are difficult to interpret in unburied conditions, especially in modern cultivated contexts, but that this can be done after comparison with experimentally reconstructed (or similar traditional) structures. Such results help our understanding of the history of bocage (land enclosure).