Évolution du littoral et du paysage, de la presqu’île de Rhuys à la rivière d’Étel (Massif armoricain – France), du Néolithique au Moyen Âge

Abstract

Les trois sondages, réalisés sur le pourtour du golfe du Morbihan et étudiés par la palynologie, permettent de retracer l’histoire du paysage de cette région depuis le Néolithique ancien jusqu’au Moyen Âge. Les oscillations du niveau de la mer flandrienne et les mouvements dunaires déterminent l’installation et l’évolution des marais maritimes (slikke et schorre), et des tourbières. En arrière de la frange littorale, le milieu est dominé par la chênaie caducifoliée, dans laquelle se développe Quercus ilex, dès l’Atlantique. Bien que l’habitat soit attesté dans toute cette région, l’activité humaine est peu sensible dans certains sites jusqu’à la fin de l’Âge du Bronze, même si la céréaliculture est présente, mais de façon sporadique. À partir de l’Âge du Fer, la déforestation est conséquente, mais ne semble pas pouvoir s’expliquer complètement, ni par l’élevage, ni par l’agriculture.Three samples from around the gulf of Morbihan (western France) studied using pollen analysis enabled us to trace the history of the landscape of this region from the early Neolithic to the Middle Ages. The oscillations of the sea level in the Flandrian along with dune movements gave rise to the development of salt marshes (slikke and schorre) and peat bogs. Back from the coastal fringe, the dominant feature of the landscape was deciduous oak in which Quercus ilex was found from the Atlantic chronozone onwards. Although signs of settlement throughout the region were established, human activity was not very noticeable in certain sites, until the end of the Bronze Age. However cereal cultivation was  present in sporadic form. Although at Locmariaquer studies confirm that new human groups settled in this region at the end of the Mesolithic period, at Suscinio it was only in the mid Neolithic I that human activity became marked, in a context of marine transgression certainly, but probably not very perceptible on the scale of generations. With a sea level still situated approximately at -8 metres in relation to the highest current levels, at the beginning of the Neolithic period the inhabitants had a large coastal plain at their disposal, more or less affected by tidal phenomena, covering or uncovering vast mudflats. The distance from the shore enables an understanding of the importance of the forest ecosystem in the vicinity of the sites of habitation. As the sea level rose, these deciduous oak stands, subject to sea spray, were pushed inland. This is undoubtedly one of the reasons for the significant deforestation noted on the pollen profiles during the Iron Age, to which should probably be added (more than the farming practices, limited by the weather conditions), the demand for wood required for extracting salt from seawater, from sand, from salt marshes, or from halophytic plants. Whereas in the Iron Age, new arrivals make themselves conspicuous around the edges of the gulf of Morbihan by the number of burial sites with ashes, there is an almost total absence of human habitation on the coastal fringe, which leads us to assume that the inhabitants settled further inland, only coming periodically to the coast to set up their salt extraction works (Lecornec, 2001). This theory is corroborated by the lack of significance of grain growing noted in the pollen profiles for sites right on the coast.