Radiocarbon-dated sediment sequences from the Belgian coastal plain: testing the hypothesis of fluctuating or smooth late-Holocene relative sea-level rise

Abstract

The late-Holocene deposits of the coastal lowlands bordering the southern North Sea were formed by a renewed expansion of the tidal environment replacing freshwater peats. The sea-level history during the last 2500 years inferred from the post-peat deposits, containing little to no datable organic material, is characterized by two conflicting schools of thought. The first one supports a smooth sea-level curve. The second approach underpins fluctuating sea-level changes. The `fluctuating' approach also uses facies variations recorded in the post-peat deposits to provide a chronostratigraphical subdivision linked to transgressions and regressions. This paper examines the controlling factors responsible for the facies variations in the post-peat deposits in order to test the approach of the fluctuating sea level. The results of sedimentological investigation coupled with radiocarbon dates of intertidal shells from four shallow outcrops located in nearby sand-filled late-Holocene tidal channels in the Belgian coastal plain are reported. The integration with results from previous work has allowed the reconstruction of the mechanisms and processes of coastal evolution during the late Holocene. The changes in the coastal landscape reflected in the facies variations are caused by multiple factors. The major one is the dynamic nature of the tidal channels responding to changes in accommodation space and sediment budget, and finally, to storm incidence and human impact. The processes of the tidal channel networks, ie, their initiation and evolution, are similar, but the changes happened at different times in different places. The facies variations do not involve rises and falls of sea level, and therefore a fluctuating sea-level rise can not be considered as realistic.