Détermination des paléo-taux d'érosion par l'utilisation des isotopes cosmogéniques. Cas de la transition pliocène-pleistocène

Abstract : In-situ cosmogenic nuclides analysis in ancient sediment could potentially provide high-resolution records of denudation rates, integrated over whole drainage basins, and on several million-year time scales. We successfully extended this method to sediments from the Tianshan (China), and the Himalayas (Nepal) piedmonts. These two areas are at the core of ongoing debates on climate-erosion-tectonics relationships since ~10 Ma. Four sections in the Tianshan, covering ~9 Myr and a broad spatial extent around this range, do not display a brutal increase in denudation at 3-5 Ma. On the other hand, they show at the regional scale a progressive increase (x4 between 4-9 Ma) and a subsequent stabilization since ~4 Ma. These results suggest a limited influence of Quaternary glaciations on erosion in this region. One section in the Himalayan piedmont (Siwaliks hills), neither display any significant increase since ~6.5 Ma that would be link to a major climatic shift. It has nevertheless probably recorded reorganizations of the drainage system and tectonics evolutions in this region. With these studies, we were able to produce the first cosmogenic nuclides-based high resolution records of denudation rates over 10 Myr. This method being potentially applicable in many geological and climatic settings, it will indubitably allow further advances in our understanding of past and present surface processes
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Nicolas Puchol. Détermination des paléo-taux d'érosion par l'utilisation des isotopes cosmogéniques. Cas de la transition pliocène-pleistocène. Sciences de la Terre. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0281⟩. ⟨tel-01750626⟩

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