Holocene salt-marsh sedimentary infilling and relative sea-level changes in West Brittany (France) using foraminifera-based transfer functions

In order to reconstruct former sea-levels and to better characterize the history of Holocene salt-marsh sedimentary infillings in West Brittany (western France), local foraminifera-based transfer functions were developed using weighted-average-partial-least-squares (WAPLS) regression, based on a modern data set of 26 and 51 surface samples obtained from salt-marshes in the bay of Tresseny and the bay of Brest, respectively. Fifty cores were retrieved from Tresseny, Porzguen, Troaon and Arun salt-marshes, which were litho- and biostratigraphically analysed in order to reconstruct palaeoenvironmental changes. A total of 26 AMS 14C age determinations were performed within the sediment successions. The Holocene evolution of salt-marsh environments can be subdivided into four stages: (i) a development of brackish to freshwater marshes (from c.?6400 to 4500?cal. a BP); (ii) salt-marsh formation behind gravel barriers in the bay of Brest (from 4500 to 2900 cal. a BP); (iii) salt-marsh erosion and rapid changes of infilling dynamics due to the destruction of coastal barriers by storm events (c.?2900?2700?cal. a BP); (iv) renewed salt-marsh deposition and small environmental changes (from 2700 cal. a BP to present). From the application of transfer functions to fossil assemblages, 14 new sea-level index points were obtained, indicating a mean relative sea-level rise of around 0.90±0.12?mm a?1 since 6300 cal. a BP.