High-resolution reconstruction of a coastal barrier system: Impact of Holocene sea-level change

This study presents a detailed reconstruction of the sedimentary effects of Holocene sea-level rise on a modern coastal barrier system (CBS). Increasing concern over the evolution of CBSs due to future accelerated rates of sea-level rise calls for a better understanding of coastal barriers response to sea-level changes. The complex evolution and sequence stratigraphic framework of the investigated CBS is reconstructed using facies analysis, high-resolution OSL and radiocarbon datings. During the formation of the CBS starting 8−7 ka ago rapid relative sea-level rise outpaced sediment accumulation. Not before rates of relative sea-level rise had decreased to ~2 mm yr-1 did sediment accumulation outpace sea-level rise. From about 5.5 ka ago rates of regionally-averaged sediment accumulation increased to 4.3 mm yr-1 and the back-barrier basin was filled in. This increase in sediment accumulation resulted from retreat of the barrier island and probably also due to formation of a tidal inlet close to the study area. Continued transgression and shoreface retreat created a distinct hiatus and wave ravinement surface in the seaward part of the CBS before the barrier shoreline stabilised between 5.0 and 4.5 ka ago. Back-barrier shoreline erosion due to sediment starvation in the back-barrier basin, was pronounced from 4.5 to 2.5 ka ago but the last 2.5 kyr barrier sedimentation has kept up with and outpaced sea-level. The last 0.4 kyr the CBS has been episodically prograding. Sediment accumulation shows considerable variation with periods of rapid sediment deposition and periods of non-deposition or erosion resulting in a highly punctuated sediment record.