Optically stimulated luminescence dating of young sediments a review

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.Il apparaît que l’aggradation est principalement liée à la forte fourniture sédimentaire issue des labours.

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.

The most important incision is observed in the peri-urban sub-basins where urban inflow (UI) and/or combined sewer overflow (CSO) increase peak flow and consequently the energy level during floods. However, incision also occurs in the upland rural area were CSO is absent and UI is much less common.

This raises the question of the origin of channel degradation in the rural area.

Two approaches result in OSL ages that are internally consistent and in excellent agreement with radiocarbon dating, indicating that all investigated sediments are younger than AD 1500.

From this data a complex deposition and incision history is constructed for the last 500 years.

L’incision de cette période fut par la suite partiellement comblée par des sédiments.

Le déclin des labours à partir des années 1915 diminua la fourniture sédimentaire alors que le développement de l’urbanisation après 1950 augmenta l’énergie des crues (rejets d’eaux pluviales et de déversoirs d’orages), causant l’incision actuelle qui débuta vers 1975.

A review of different dating methods has been provided by Lang (1999) showing that radiocarbon dating and dendrochronology are problematic for such sediments, as these methods will rely on the dating of reworked material (e.g., wood).

As a consequence, such dating approaches may overestimate the true time of sediment accumulation (e.g., Lang & Hönscheidt, 1999).

Des datations par OSL (Optically Stimulated Luminescence) sont utilisées pour reconstituer la chronologie de phases d’aggradation et d’incision dans un sous-bassin élémentaire du bassin de l’Yzeron (France).

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