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Article Dans Une Revue Comptes Rendus Géoscience Année : 2014

The subfossil tree deposits from the Garonne Valley and their implications on Holocene alluvial plain dynamics

Jean-Michel Carozza
Laurent Carozza
Philippe Valette
Muriel Llubes
Vanessa Py
Didier Galop
Mihaela Danu
  • Fonction : Auteur
  • PersonId : 950665
Laurie Ferdinand
  • Fonction : Auteur
  • PersonId : 950675
Mélodie David
  • Fonction : Auteur
  • PersonId : 971118
  • IdRef : 194738485
Laurent Sévègnes
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  • PersonId : 950676

Résumé

Subfossil tree trunks deposits are common in large rivers, but their status as a source for dating alluvial sequences and palaeoenvironmental studies is still discussed. Particularly their origin and the process(es) of deposition as well as a possible remobilization were pointed as a limit to their use to document river alluvial changes. In this work we report the discovery of the largest subfossil trunks deposits in the Garonne valley. These new data are compared to the previous ones. A set of 17 tree trunks and more than 300 smaller wood fragments were collected. The xylologic study shows the prevalence of Quercus and a single occurrence of Ulmus. These two hardwood species are commonly associated with riparian forest. The 14C dating carried out on seven trunks and a single branch of Quercus on the outermost identified growth rings, indicates age ranging from 8400-8000 cal. BP for the oldest fragment (bough) to 4300-4000 cal. BP for the most recent tree trunk. Radiocarbon ages of the trunks are aggregated into two main periods: 5300-5600 cal. BP (four trunks) and 4300-4000 cal. BP (three trunks). The radiocarbon (charcoal) dating of the top of the alluvial sequence overlaying the trunks gives an age between 1965-1820 and 1570-1810 cal. BP, i.e. between the 2nd and the 5th c. AD. In addition, the discovery of two unpublished subfossil tree trunks deposits in Finhan are reported (six trunks). At the light of these results, we discuss previously proposed models for the Garonne floodplain building.

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Géographie
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Dates et versions

halshs-01069926 , version 1 (30-09-2014)

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  • HAL Id : halshs-01069926 , version 1

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Jean-Michel Carozza, Laurent Carozza, Philippe Valette, Muriel Llubes, Vanessa Py, et al.. The subfossil tree deposits from the Garonne Valley and their implications on Holocene alluvial plain dynamics. Comptes Rendus Géoscience, 2014, pp.8. ⟨halshs-01069926⟩
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