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New data from the loir river fluvial system upstream Vendôme (Loir‑et‑Cher, Centre Region, France): morphosedimentary context, ESR chronlogy, recent tectonics and prehistory

Abstract : In the Vendôme area, the Loir valley incises the southeastern margin of the Faux-Perche domain. The river crosses over a patchwork of cretaceous, eocene and oligocene formations structured by numerous tectonic events affected by neogene and recent reactivations. Related to this paleogeography, two equal length sectors were defined : an upstream sector called Haut-Vendômois sector, and a downstream sector called Bas-Vendômois Sector, in which alluvial basins linked by trenches are following. In the Haut-Vendômois sector, nine fossil fluvial formations were dated by the Electron Spin Resonance method. The beginning of river incision occur during late Early Pleistocene and dating results indicate later irregular phases of incision‑aggradation. More recently, seven fossil fluvial formations were dated in the Bas-Vendômois sector. The ESR ages are similar to the ages obtained for the usptream sector. As in the previous studies, important gaps (10 to 25 m) were observed for the relative altitude of some alluvial deposits in relation to the chronological data. These gaps also affected the stratigraphy in the local substrata. These gaps and the topography of the Loir valley should result from two pleistocene tectonic events with distributive faulting and local extensive accidents. The first event should have occur just before the aggradation of the highest fluvial formation which was deposited around 1,1 - 1 Ma. The grabens, where the river is presently flowing, could have been created during this distensional phase, as well as the beginning subsidence of the alluvial basins. The second event should occur around 400 - 350 ka. The incision of a narrow trench, 15 m deep in the chalky formations, should result from acceleration during the orogenic uplift in the south area of the Paris Basin. The uplift or the tilting of the blocks that partitioned the plateau and the slopes should be contemporary of the trench incision. Indeed, the heights of the uplifts, and also of the fault throws, correspond to the gaps observed for the relative altitudes of the alluvial sheets. In the trench channeled by chalky scarps, the three last alluvial deposits are embedded according to a following of a probable slowing down of the Paris Basin’s orogenesis.
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Submitted on : Tuesday, August 2, 2022 - 3:33:12 PM
Last modification on : Wednesday, August 31, 2022 - 3:16:52 AM

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Jackie Despriée, Hélène Tissoux, Pierre Voinchet, Gilles Courcimault. New data from the loir river fluvial system upstream Vendôme (Loir‑et‑Cher, Centre Region, France): morphosedimentary context, ESR chronlogy, recent tectonics and prehistory. Quaternaire, AFEQ-CNF INQUA, 2021, pp.123-152. ⟨10.4000/quaternaire.15817⟩. ⟨hal-03744161⟩

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