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Communication Dans Un Congrès Année : 2013

Capturing the timing and rates of valley incision through cave dating in the Eastern Pyrenees : geodynamic implications

Résumé

Tectonic uplift in active mountain belts narrowly controls the rate and tempo of valley incision, with additional modulation effected by climatic change. There is no consensus over whether the Pyrenees still is an active orogen, even though surface uplift rates based on modern land levelling techniques register values of up to 1 mm/yr. Clarifying matters for the longer term should rely on opportunities to measure and date the vertical displacement of landforms of known initial geometry. Fluvial terrace systems in the Pyrenees have so far not yielded any dated sequences that reach further back in time than the latest Middle Pleistocene. Subterranean karstic networks, however, provide a fruitful alternative, with potential for obtaining coupled 26Al and 10Be burial ages for fluvial sediment which became trapped in limestone cavities while being conveyed through the catchment during valley incision. Suitable subhorizontal, gravel-filled phreatic cave galleries cross-cut by limestone canyon sidewalls occur in the Têt valley. These can effectively be treated as a bedrock straths correlatable with subaerial terrace treads situated further up- and downstream. Such markers also provide information about karstic base levels, which in this setting connect directly to the regional marine base level. The Têt valley exhibits a succession of cave levels spanning 300 m of vertical relief, two of which have been dated. Quartz-rich sediment samples were collected from of each system but also replicated among sand-sized and gravel-sized clasts, dated separately. Initial results reveal a continuous process of canyon incision throughout the entire Pliocene and Quaternary, with relatively steady mean incision rates. Nuclide inheritance in the samples provides added information about catchment-wide mean denudation rates. These rates are found to triple after 2 Ma, clearly reflecting a climatic signal linked to the onset of the Pleistocene glacial-deglacial cycles
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Dates et versions

halsde-00867013 , version 1 (27-09-2013)

Identifiants

  • HAL Id : halsde-00867013 , version 1

Citer

Marc Calvet, Y. Gunnel, Gabriel Hez, Regis Braucher, V. Guillou, et al.. Capturing the timing and rates of valley incision through cave dating in the Eastern Pyrenees : geodynamic implications. 8th International Conference (IAG) on Geomorphology, Aug 2013, Paris, France. ⟨halsde-00867013⟩
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