Évolution d’un marais littoral atlantique au cours de l’Holocène : le cas de Brouage (Charente‑Maritime, France)

A multi‑proxy study of a sedimentary sequence located upstream of the Brouage marsh (Charente‑Maritime, France) has enabled a partial reconstruction of the evolution of this sector of the marsh during the Holocene. It shows that the intersected channel evolved from a fluvial channel to a tidal channel around 8200 cal. BP. The tidal channel remains functional and generally stable throughout the Holocene, although the sediment record is marked by significant hiatuses at around 4 m depth, i.e. 7900‑5800 cal. BP according to 14C date and possibly at 1 m depth, i.e. 2050 cal. BP according to palynological data. Aggradation, first by marine then continental processes, is extremely rapid until around 5500 cal. BP and remobilizes coarse detrital sands derived from Cenomanian sands, distinguishing this sequence from the classic “bri” formations described on a regional scale. Marine influences gradually decreased with the deceleration of sea‑level rise from 5000 cal. BP, the progradation of the schorre and were reinforced with the confinement of the marsh associated with the formation of barrier beaches starting from 3700 BP. Palynological data show that the first signs of anthropization, initially discreet, during the Middle Neolithic around 5300 BP. The decrease in wooded areas between the beginning of the 1st millennium CE could be related with the exploitation of resources for the production of igneous salt. However, the chronology of the upper part of the sequence needs to be strengthened. The possibility of the channel being used for navigation into Antiquity is confirmed, but remains conjectural for the Middle Ages due to its silting‑up, while the last millennium remains poorly documented.