Évolution de l’environnement autour d’un site du second âge de Fer en position d’estran à Plougasnou/Saint-Jean-du-Doigt (Finistère, France) - Université de Rennes Accéder directement au contenu
Communication Dans Un Congrès Année : 2021

Évolution de l’environnement autour d’un site du second âge de Fer en position d’estran à Plougasnou/Saint-Jean-du-Doigt (Finistère, France)

Chantal Leroyer
Dominique Marguerie

Résumé

Palaeoenvironmental study of Plougasnou/Saint-Jean-du-Doigt (Finistère, France) coastal area has been carried out both on the marsh at the back of a gravel barrier and on the foreshore where an iron age settlement has been discovered, revealing a wooden fence and numerous organic archaeological remains preserved in a peat deposit. The archaeological intervention investigation suggests that the remains continue under and behind the cordon of pebbles that blocks the mouth of the Donan river. Then, in order to to shed light on the evolution of the site over time, both in terms of the context of human occupation and the changes in the surrounding environment, a multi-proxy approach has been developed, integrating archaeology, geomorphology, dendrochronology and palaeoecological study (pollen and non-pollen palynomorphs). On the foreshore, sampling was performed on the peaty and organic clayey levels of three archaeological surveys. A geomorphological survey was carried out on the marsh to reconstruct the depositional history of the infill by drilling and coring in a cross-section on both sides of the Donan River. The rhythmicity of deposits seeming different on both sides, two cores were selected for pollen analyse (pollen and NPP’s). The lower half of the two marsh’s sequences (4290 to 3500 cal BC) covers the period of the middle Neolithic period. It indicates a wooded landscape with Corylus associated with numerous deciduous trees (Quercus, Ulmus, Betula, Tilia, Fraxinus) and shrubs (Hedera, Lonicera, Sambucus, Rosaceae) in the dryland and with Alnus accompanied by Salix in the wetland. Herbs are scanty but some peaks of Apiaceae indicate hydrological changes. Crops and livestock farming are scarce. A large hiatus (2,5 Ky) is revealed in the march, not marked by a change in the nature of the deposits but by a profound break in the pollen assemblages, corroborated by radiocarbon dating and age-depth model. The organic filling of the valley floor thus took place in two stages: first between 4290 and 3500 cal BC during the Middle Neolithic and then between 1020 cal BC and 1000 cal AD (Final Bronze Age to the Middle Ages). This hiatus may be due to the dynamics of the river in response to variations in sea level: rising since 4300 cal BC (beginning of organic sedimentation), it experienced a negative oscillation around 1500 cal BC. When the sea level fell down, the Donan river flow was able to erode the deposits accumulated in its major bed. The upper half of the two marsh’s sequences provides information on the periods from the Late Bronze Age to the Middles Ages (1020 cal BC to 1000 cal AD). It indicates an open landscape with a marshy meadow in the place. Riparian woods and dry land forest had been exploited for crops and farming activities. The foreshore sequences associated with the Iron age settlement (dated of the 5th-4th centuriesy BC) fit into the first part of this ensemble. They indicate that the human groups, settled on the site, mainly developed pastoral activities there, setting up implanting their cereal crops at some distance away. The site is then disconnected from any marine input and the Iron Age settlement it was not located at a distance from on the foreshore: the gravel barrier was much further away off the current coastline .
Les recherches paléoenvironnementales, engagées à Plougasnou/Saint-Jean-du-Doigt (Finistère, France), couvrent deux secteurs : le marais en arrière d’un cordon de galets et l’estran qui a livré les vestiges d’une occupation du second âge du Fer (fin Ve - début IVe siècle av. J.-C.), fouillée depuis 2017. Dans le marais, un transect stratigraphique a été effectué afin de reconstituer la géométrie des dépôts et deux carottages ont été réalisés. Sur l’estran, trois coupes archéologiques ont également été échantillonnées. La moitié inférieure des deux séquences du marais (4290-3500 cal BC) indique un paysage très boisé (aulnaie et chênaie). La strate herbacée apparait réduite. Les activités agricoles sont rares. Un important hiatus est ensuite signalé par les cortèges polliniques et les datations. En effet, la moitié supérieure des deux profils (1020 cal BC-1000 cal AD) témoigne d’une profonde ouverture du milieu avec un retrait des boisements au profit de prairies humides pâturées. Les versants de la vallée sont dévolus aux activités agricoles. Les séquences d’estran s’inscrivent au début de cette seconde phase. Selon la palynologie, le site du second âge du Fer a été implanté dans un contexte de fond de vallée ouvert et marécageux, sans connexion marine.
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Dates et versions

hal-04253156 , version 1 (22-10-2023)

Identifiants

  • HAL Id : hal-04253156 , version 1

Citer

David Aoustin, Chantal Leroyer, Cédric Rossignol, Dominique Marguerie, Marie-Yvane Daire. Évolution de l’environnement autour d’un site du second âge de Fer en position d’estran à Plougasnou/Saint-Jean-du-Doigt (Finistère, France). Archaeology of coastal settlements and human/environment interactions in the Atlantic north of the Equator / Archéologie des peuplements littoraux et des interactions Homme/Milieu en Atlantique nord équateur. Colloque HOMER 2021, Catherine Dupont; Anna Baudry; Marie-Yvane Daire; CReAAH, Sep 2021, Oléron, France. ⟨hal-04253156⟩
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