Towards the reconstruction of flood histories: luminescence dating of paleoflood deposits

Résumé

The accurate dating of paleoflood deposits plays a key role in the understanding of river flooding events, which are one of the main natural hazards related to climate, causing severe damage on mankind¿s life. The challenge of accurate dating these events has motivated developments in the measuring and analysing processes applied to OSL dating that are making this technique highly reliable to assess chronologies for Quaternary processes. This Thesis has focused on the application of the technique in cases in which it can be hampered. This is the case of fluvial young sediments which are likely to suffer from incomplete bleaching and for which any extrinsic factor could lead to a dramatic misestimate of the burial age. Samples from four rivers of the Iberian Peninsula have been used for this study to provide wide variety sediments. A sequence of eight modern (40¿1000 a) flash flood deposits, potentially incomplete bleached, from Guadalentin River with available age control from historical records and radiocarbon dating, has been used to compare the behaviour of robust statistics, CAM, MAM and IEU models on distribution from single grain and multi¿grain aliquots measurements. Modifications were made to use the CAM and MAM models on dose distributions containing zero and near zero values. The assessment of the over¿dispersion has been based on dose recovery test carried out on gamma irradiated samples. The effect of the over¿dispersion value assessed on the behaviour of MAM and IEU age models was studied. The suitability of small aliquots in combination with IEU approach for the accurate estimation of the ages was also tested finding good agreement with the known values. Achieved conclusions have been applied to date the samples from the remaining three rivers: Rambla de la Viuda (Mediterranean), Huebra and Duero Rivers (Atlantic). The most suitable methods for each specific case avoiding the effect of feldspar contamination, incomplete bleaching of grains and mixture of grains population found in developed soils and reworked deposits for agricultural purposes, has been proposed.