No abstract

The nature of postglacial sea-level change and sediment infilling of the Gironde Estuary, SW France, has previously been reconstructed using a sequence stratigraphic model. This paper examines specifically the development of the St Ciers-sur-Gironde marsh during the late Holocene. The study area forms the largest expanse of coastal wetlands on the east bank of the Gironde. A geoarchaeological approach is used incorporating borehole survey, sedimentological and diatom analysis, radiocarbon dating, archaeological, documentary and cartographic evidence, which aims to test and refine the previous model of estuarine development.The later Holocene sequence is characterized by alternating clay-silt and peat facies. Diatom evidence indicates that clay-silt units represent sedimentation under marinebrackish estuarine conditions in intertidal mudflat, and potentially saltmarsh, environments. The palaeoenvironmental conditions represented by the main upper peat unit, dated to 5600-2600 BP, are currently unknown due to the absence of diatom evidence from these levels. Within an overlying trend of rising relative sea-level over the past 6000 years, 3 negative sea-level tendencies appear to have occurred. There is insufficient resolution in the present data set to determine the exact nature of each or their duration.