%0 Conference Proceedings %T Des problèmes de blanchiment chez lesall black où Impact et enregistrement dela dynamique de l’incision fluviatile (Rangitikei,Nouvelle Zélande) sur les géochronomètresOSL, IRSL %+ Géosciences Rennes (GR) %+ Netherland Center for Luminescence Dating %A Bonnet, Stéphane %A Reimann, Tony %A Lague, Dimitri %A Wallinga, Jakob %A Davy, Philippe %A Uwe, Rieser %< avec comité de lecture %B 24 ème Réunion des sciences de la Terre 2014 %C Pau, France %3 Réunion des sciences de la Terre 2014. Livre des résumés %P 16 %8 2014-10-27 %D 2014 %Z Sciences of the Universe [physics]/Earth SciencesConference papers %X Landscape response to climate induces periods of enhanced sedimentsupply to rivers promoting the formation of climatic-aggradation fluvialterraces whose age and height are used for estimating mean fluvial incisionrates. These rates must however be taken with caution. Numericalsimulations actually suggest that incision rates are not linear betweenthe formation of two successive terraces.The Rangitikei River (New Zealand) is downcutting in an uplifting basement.Entrenchment is punctuated by terraces, the more recent one(T1) being classically considered to formed from 30 to 15 ka. Sinceabandonment of T1, the river incised 75-meter deep gorges within thebedrock. We investigated this entrenchment using optical dating (IRSLon feldspars) of 17 alluvial deposits from strath terraces cut into the bedrock.We performed measurements using Multiple Aliquots or SingleAliquot Regenerative protocols on large aliquots of fine grains of feldspars(4-11 um) as well as measurements on single-grains on a coarserfraction (125-200 um) of the same samples but using Post-Infrared IRSL(p-IRIR) protocol.We show that :(1) abandonment of terrace T1 occurred 10 kyr ago, more recentlythan previous estimates(2) a period of very fast incision follows the formation of T1. Incisionrate then slows down ; this decrease coincides with the development ofextensive post-T1 terraces. Our data support numerical findings showingthat the ratio of vertical incision to lateral planation is driven largely byvariations in vertical incision rate(3) The distribution of single-grains ages depend on the river incisionrate, periods of fast incision being characterized by a larger proportionof unbleached grains in the samples. Accordingly, IRSL ages obtainedusing classical methods that consider measures on aliquots instead ofon singles grains, all show an overestimation of ages whose magnitudedepends on incision rate.We show that ion IRLL geochronology, the proportion of mixing betweenbleached and unbleached grains is intimately linked to variationsin the rate of bedrock erosion and related supply of unbleached grainsto the river. Our study consequently suggests that the shape and widthof IRSL age distributions obtained through single-grain measurementscould illuminate the past dynamics of rivers. %G English %L insu-01080342 %U https://insu.hal.science/insu-01080342 %~ INSU %~ UNIV-RENNES1 %~ UR2-HB %~ CNRS %~ GR %~ OSUR %~ UR1-HAL %~ UR1-SDLM %~ UR1-SDLMJONCH %~ GR-DIMENV %~ UNIV-RENNES2 %~ OSUR-OSU %~ TEST-UNIV-RENNES %~ TEST-UR-CSS %~ UNIV-RENNES %~ INRAE %~ UR1-ENV %~ GR-R