Les travertins de Saint-Antonin : séquence géobotanique et climato-anthropique holocène (Bouches-du-Rhône, France)

Résumé En Fr

Travertine deposit of St-Antonin (Bovches-du-Rhône, France) : lithostratigraphy, palaeobotany and Holocene palaeoenvironments. Travertines are carbonate deposits formed generally during temperate climatic periods. The travertine of Saint-Antonin was formed during the Holocene in accordance with this model They usually present a succession of travertinous units and detrital sedimentary levels containing, respectively, leaf impressions and charcoal ; snail shells and archaeological material have also been preserved, essentially in detritial levels. Two kinds of plant remains (leaf imprints and charred wood) have been sampled and analysed, allowing the reconstruction of vegetation dynamics based on a well-defined sedimentary sequence. Our results were compared with those of previous malacalogical, archaeological studies and climatic changes. The Preboreal and Boreal sequence, characterized by travertine unites with detritial deposits, is dominated by a riverside vegetation (Populus alba, Salix sp., Phragmites communis) associated with some pubescent oak growing in the plateau. After this first period, detritial levels and hygrophilous species decrease. Correlatively travertinous facies and leaf impressions of mesophilous forest species increase (Quercus pubescent, Acer monspessulanum). They suggest the existence of homeostatic conditions, such as regular river flow, dense vegetation and few disturbances during deposition. The Middle Atlantic period shows optimal travertinisation and maintenance of forest environnement. But this period is characterized by the begening of the Quercus pubescens regression and the dominance of Acer monspessulanum. From the Atlantic to the first part of Subboreal, important detrital sedimentary levels disturb the deposition of carbonate. They contains reworked archaeological material dating to the Neolithic. Vegetation seems to have been profoundly affected by intensive human exploitation. This process has broken up the forested area into different plant communities and favoured the dominance of heliophilous and thermophilous species (Pinus halepensis, Rubus ulmifolius and Juniperus sp.).

Formés au cours de l'Holocène, entre le Préboréal et le Subboréal, les travertins de Saint-Antonin renferment des coquilles de gastéropodes, des vestiges néolithiques, des charbons de bois et des empreintes foliaires. De nouvelles datations et de récentes analyses, niveau par niveau, des divers macrorestes végétaux, couplées à l'étude détaillée des faciès sédimentaires, ont permis de préciser l'évolution des paléoenvironnements et de la dynamique morpho-sédimentaire au pied de la Sainte-Victoire au cours de cette période. Ces résultats sont confrontés aux rythmes des occupations humaines préhistoriques régionales et aux changements climatiques globaux.