Reconstitution des paléoenvironnements côtiers bretons à l'Holocène : interactions entre dynamiques sédimentaires, climatiques et anthropiques

The aim of this PhD is to discuss the chronology of Holocene paleoenvironmental dynamics that affected Brittany coasts. This multiproxy study involves sedimentological, palynological and micropaleontological analyses conducted on sedimentary archives retrieved along the north (Plouescat) and south (Bétahon and bay of Quiberon) Brittany coasts. Data allowed us discussing the sedimentary infilling model of the south-Armorican shelf during the marine transgression as well as natural and anthropogenic forcing at macro-regional and local scales. A major threshold at ~5.7 ka BP is associated to the establishment of the highstand system tract followed at 4.2 ka BP, by the amplification of winter fluvial discharges, under the control of the long-term orbital seasonal trend of the Late Holocene and the pluri-secular phases of enhanced subpolar gyre dynamics. These natural processes, coupled with increasing human activities at the Bronze Age, will be favorable to a better detection of anthropogenic pollen indicators in coastal archives. We distinguish three major regional pollen thresholds of anthropization (i.e., Bronze Age, 4.2 ka BP; first and second Iron Age, 2.7 ka BP; Middle Ages, 1.2 ka BP), as well as local disparities in anthropogenic signature between north and south Brittany coasts, due to local archeological settings, after taking into account hydro-climatic contexts that impacted all the studied site thought the time.