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Paléo-environnement et contrainte fluviale à l'Holocène récent sur les sites de Langoiran et d'Isle-Saint-Georges : bilan de quatre années de recherches géoarchéologiques dans la basse vallée de la Garonne

Abstract : This study contributes to understanding the settlement dynamics of two archaeological sites currently located in the distal flood plain of the tidal Garonne River: the mediaeval Castéra of Langoiran and the protohistoric and antique community of Isle-Saint-Georges. The first one is a castrum constructed in the 11th century, heightened during the 13th century (motte) and abandoned the next century. The second one is a nucleated settlement built between the 8th century BC and the 1st century AD, and retracted between the 4th and the 2nd centuries BC. The Garonne River might have contributed to these settlement changes through the risk generated by flood and low-flow hazards, the environmental potentiality created by wetlands, and lateral, longitudinal and vertical geomorphological dynamics in the floodplain. The Garonne River had different hydrographical (location and number of channels) and hydrological (regime, discharge) characteristics during the sites occupancy. Our study aims to enlighten this paleoenvironmental background. Thanks to a hydrogeomorphological approach mixing historical, archaeological, geomorphological, geophysical, sedimento-logical, biological, and chronological data, we show that the societies settled down along (Isle-Saint-Georges) or close to the river (Castéra of Langoiran), probably attracted by the advantages of this situation (food supplies, trade). In Isle-Saint-Georges, the contraction of the settlement during the Middle Iron Age agrees with the end of the hydrological activity of the adjacent fluvial channel. At Langoiran, the settlement was closed to a wetland and submitted to the risk of flooding and of erosion of the proximal bank. These natural constraints can explain the local dynamics of the settlements but cannot be completely assessed in the absence of knowledge dealing with the regional, sociopolitical context.
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Séverine Lescure, Gilles Arnaud-Fassetta. Paléo-environnement et contrainte fluviale à l'Holocène récent sur les sites de Langoiran et d'Isle-Saint-Georges : bilan de quatre années de recherches géoarchéologiques dans la basse vallée de la Garonne. Aquitania, Pessac : Fédération Aquitania, 2015, 31, p.43-64. ⟨hal-01478700⟩

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