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Impact du dernier cycle glaciaire interglaciaire sur la dénudation dans les Alpes Maritimes Françaises

Abstract : Denudation is a key parameter controlling the formation and evolution of landforms across the Earth's surface. The interaction between surface processes (namely denudation) and climatic variations at the geological time scale is a highly debated issue, due to the lack of continuous sedimentary records unaffected by tectonic forcing. In order to constrain this interaction, this thesis focuses on the Var watershed (French Maritime Alps) and on its sedimentary archive which allow to track the variations of denudation rates from the present until 75 000 years ago. This period covers the end of the last glacial cycle (the Würm) as well as the transition to the current climatic period (the Holocene). The measurement of 10Be (cosmogenic isotope) in sediments allows the quantification of denudation rates integrated over the entire watershed. This method, applied to present-day sediments of the Var, constrained the current denudation rate of the Var catchment at 0.24 ± 0.04 mm yr-1. The same method was then applied to samples from two sedimentary cores constituting a continuous and high-resolution sedimentary archive of past Var sediments. The results show that the Last Glacial Maximum glaciers' advance (between 19 000 and 26 500 years) induced a significant increase on denudation (~ × 2), whereas during the previous glacial stages (between 26 500 and 75 000 years), the denudation was steady and similar to present-day value. This nonlinear response of denudation to climate change suggests the existence of a threshold controlled by the erosive dynamics of glaciers, which was close to ~ 2 mm yr-1 during the Last Glacial Maximum and ~ × 4 lower between 75 000 and 26 500 years.
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Submitted on : Friday, October 23, 2020 - 2:17:14 PM
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Apolline Mariotti. Impact du dernier cycle glaciaire interglaciaire sur la dénudation dans les Alpes Maritimes Françaises. Géomorphologie. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0033⟩. ⟨tel-02929428⟩



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