Dating on earth sub
Dating on earth sub
The channel incised during this period was later partly filled with sediment.The decline of agricultural land use from about 1915 onwards decreased sediment supply, while the increase of urbanisation from about 1950 amplified the flow energy of flooding by pluvial waters and overflows from storm basins, causing the presently ongoing incision in the area that began about AD 1975.
As a consequence, such dating approaches may overestimate the true time of sediment accumulation (e.g., Lang & Hönscheidt, 1999).
Our hypothesis is that the current incision in the rural area could be the result of a decline in sediment supply from hillslopes and the watershed, due to reduced agricultural activity (i.e. Conversely, the hillslope deposits in which incision occurs could have been deposited during times of higher agricultural activity.
This hypothesis could also explain why incision is so important in the peri-urban area, as it is enhanced by UI and CSO.
It is concluded that sediment deposition was mainly forced by sediment supply from ploughing areas.
Two short-lived phases of incision during the first half of the XIX century were probably caused by a decrease of sediment supply due to a decline in the frequency of heavy precipitation events.
In the last area streamflows are rare because of the high permeability of the subsurface.
Some discontinuous loess covers exist in the eastern part of the basin.
More generally, it seems crucial to place the current channel adjustments in a large temporal trajectory of the morpho-sedimentary dynamics of the valley bottoms.
This hypothesis is similar to the model developed for larger basins in the French pre-Alps and the Jura Mountains, where bed material is coarser (Bravard, 2002; Liébault & Piégay, 2002).
Deux approches conduisent à des âges OSL cohérents entre eux et bien corrélés à des dates radiocarbone.
Elles indiquent que tous les sédiments étudiés sont plus jeunes que 1500 ans ap. A partir de ces données une histoire complexe de phases de dépôt et d’incision est reconstituée sur les 500 dernières années.
Optically stimulated luminescence (OSL) dating is used to determine the (robust) chronology of the phases of sediment deposition and incision in a headwater sub-basin of the Yzeron Basin, France.