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Postglacial changes in fuvial morphologies of the upstream Loire catchment and the middle Cher river valley

Abstract : The present study aims to provide new insights of fluvial metamorphosis associated with postglacial environmental changes. Investigations were conducted on different points upstream to downstream of the Loire catchment (Loire itself, Dore river and Cher river). This work allows the role of catchment size to be discussed regarding sensitivity of fluvial environments to climate changes. Topography of the alluvial plain was analyzed using LiDAR DEM. Such datasets show topographic variations highlighting postglacial fluvial patterns and their relative chronology. Boreholes and electrical imaging survey help to estimate the geometry of former channels. Cores collected in palaeochannels provide organic materials suitable for radiocarbon dating and multiproxy analyses. In Dore valley, incision of Pleniglacial deposits and the building of the Holocene floodplain occur after 23136-23958 Cal. BP., the youngest date obtained from organic filling sampled in palaeochannels. The oldest dates obtained in the Holocene deposits take place around 8000 Cal. BP. On Burgundian Loire, Pleniglacial deposits are incised around 17 000 Cal. B.P. The fluvial pattern is then characterized by a braided system evolving to a meandering pattern probably active until 14 0000 Cal. B.P., when a new incision occurs and another braided system reworks previous deposits until 12 000 Cal. B.P. In the Cher river valley, some inherited landforms correspond to wide and straight palaeochannels interpreted as transitional multichannel system following a braided fluvial pattern. They might be associated with an incision of the Pleniglacial floodplain and their cutoff are dated from 15 000 to 13 500 Cal. BP. The beginning of the Lateglacial period is characterized by a significant incision occurring at different times. If this phenomenon is not unknown within postglacial alluvial deposits, such results can lead to a better knowledge of diversity and complexity of fluvial responses observed during the Lateglacial period on key positions of a fluvial network.
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Submitted on : Monday, December 14, 2020 - 5:04:29 PM
Last modification on : Monday, December 21, 2020 - 3:22:51 PM

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  • HAL Id : hal-03065144, version 1

Citation

Anaëlle Vayssière, Ronan Steinmann, Cubizolle Hervé, Cyril Castanet, Nathalie Carcaud, et al.. Postglacial changes in fuvial morphologies of the upstream Loire catchment and the middle Cher river valley. 9th International Conference on Geomorphology (9th ICG), Nov 2017, New-Dheli, India. pp.321-322, 2017, Book of Abstracts. ⟨hal-03065144⟩

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