Geological and geotechnical properties of the “Terres Noires” in southeastern France: Weathering, erosion, solid transport and instability

The geological formation known as the “Terres Noires” covers large areas of southeastern France, between the Rhône valley and the pre-Alpine hills. This formation consists mainly of dark marls of the basal Upper Jurassic. These marls are very susceptibility to weathering and are particularly prone to erosion, resulting in high solid transport. This paper attempts to quantify this transport in experimental catchment areas, and shows that a forest cover can play a major role in preventing this type of phenomenon. Weathering of this formation may also lead to gravity instabilities in fresh marl (although this is rare) and, much more frequently, in the surficial weathered material.