Development of a mid-Holocene estuarine basin, Rhine-Meuse mouth area, offshore The Netherlands

A proper understanding of coastal development during periods of rapid sea-level rise is a prerequisite for the prediction of future coastal response to the expected acceleration in sea-level rise. However, the development of back-barrier basins, especially in river-mouth areas, during such periods is still not well understood. Here we show the response of back-barrier basins adjacent to the Rhine-Meuse river-mouth area, The Netherlands during the mid Holocene. A combination of high-resolution seismic data and cores was used to describe and explain late-Weichselian to early Holocene terrestrial and mid-Holocene back-barrier sequences. Along with dating and micropalaeontological analyses, these descriptions and explanations form the basis of a reconstruction of river-mouth and adjacent basin behaviour under conditions of rapid SLR. The nearby presence of the Rhine-Meuse estuary had a significant influence on the development of the adjacent back-barrier basin and especially its tidal channels. The back-barrier channels started to fill in between 8.3 and 7.4 ka BP due to decreasing rates of both sea-level rise and tidal-amplitude increase. During this time the Rhine relocated its mouth to the study area and the increased sediment delivery contributed to tidal-prism decrease and channel infill. Close to the Rhine-Meuse river mouth the back-barrier channels lay embedded in thick clayey, estuarine deposits and lateral migration of the tidal channels was limited. At greater distances, lateral migration rates increased as the thickness of cohesive back-barrier deposits decreases. The spatial pattern and stratigraphic setting of the northern channel fills suggests an episode of barrier overstepping between 7.5 and 6.6 ka BP. The mode and spatial limits of this overstepping are still not understood.