Holocene coastal environmental changes and human occupation of the lower Herault River, southern France

摘要

Sea-level rise, human impacts and climate change have deeply affected coastal environments during the Holocene. These forcing factors are studied using the Lower Flerault valley, which constitutes a very representative Mediterranean case study because of (i) its very early, intense and continuous land use since Neolithic times, and (ii) its sensitivity to sea-level rise and Mediterranean climate changes over a relatively small watershed. 34 cores and 61 AMS radiocarbon dates, associated with biological and geochemical analyses, have allowed us to precisely reconstruct the Holocene evolution of the lower valley. Until 6500 cal yr BP, a wave-dominated morphology and retrogradational dynamics were reconstructed. During this phase, ephemeral channels and successive river mouths formed and were rapidly submerged by sea-level rise. The progradational phase began after 6500 cal yr BP, and the alluvial plain gradually built seawards with the formation of a beachridge system outside the valley. Growth of the fertile alluvial plain was coeval with the development of Neolithic agriculture. This alluvial progradation gradually filled the estuary with advances of the mouths, several shallow lagoons and sandbar. The high density of information collected allows us to recognize, for the first time, a pronounced fluvial-dominated deltaic morphology, especially 3000 years ago, during the Bronze Age. Lagoonal and coastal shores were continually inhabited. Human land use continually adapted to geomorphological and environmental changes. Around 300 years ago, the delta shifted to a wave-dominated system. (C) 2019 Published by Elsevier Ltd.