Swiss Journal of Geosciences volume , pages 1—21 Cite this article. Metrics details. Certain processes begin during the Younger Dryas. Pine forests dominate this cold period, which was unfavourable for pedogenesis; they remain throughout the first half of the Holocene. The meandering river system then becomes stable for more than four millennia. The first signs of human impact on the vegetal cover begin to appear around 3, cal BC Middle Neolithic.
An increase in hydric activity occurs between 3, and 2, cal BC. However, the earliest evidence of the cultivation of cereals dates only to about 2, cal BC Early Bronze Age. Extensive forest clearing and the emergence of cultivated plants occur after 1, cal BC. On the cleared slopes the soil erodes and at their foot colluvium deposits accumulate. The densification of the settlement from the Late Bronze Age 1,— cal BC until the beginning of the Iron Age — cal BC contributes to alluvial destabilization.
A palaeosol has been identified in all of the Holocene deposits in the valley. The deforestation intensifies between and cal BC while hydric activity decreases. The first centuries of our era record very limited pedo-sedimentary phenomena. However, human presence becomes less marked after cal AD.
The slopes are stabilized and the soil develops. From cal AD, an important increase in hydric activity takes place, a probable consequence of a wet fluctuation in the climate. Contemporary forest clearing causes deep gullies. After cal AD, drier conditions set in. This period of stability, marked by occasional rises in the water level, continues until 1,—1, cal AD Late Middle Ages.
Then superficial flows resume and entrenchment of the main waterways occurs, combined consequences of the Little Ice Age and the upsurge in human activity. Intense monitoring of the construction of the ATransjurane allowed us to reconsider the basic problem of the Quaternary in the Jura mountain range, in particular that of Holocene deposits. Essentially, the motorway project affected many diverse environments, cutting through archaeological sites as well as zones with little or no traces of human activities.
