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. Increasing concern over the evolution of coastal barrier systems due to future accelerated rates of sea-level rise calls for a better understanding of coastal barrier response to sea-level changes. The complex evolution and sequence stratigraphic framework of the investigated coastal barrier system is reconstructed using facies analysis, high-resolution optically stimulated luminescence and radiocarbon dating. During the formation of the coastal barrier system starting 8 to 7 ka rapid relative sea-level rise outpaced sediment accumulation. Not before rates of relative sea-level rise had decreased to ca 2 mm yr ^-1 did sediment accumulation outpace sea-level rise. From ca 5·5 ka, 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 coastal barrier system before the barrier shoreline stabilized between 5·0 ka and 4·5 ka. Back-barrier shoreline erosion due to sediment starvation in the back-barrier basin was pronounced from 4·5 to 2·5 ka but, in the last 2·5 kyr, barrier sedimentation has kept up with and outpaced sea-level. In the last 0·4 kyr the coastal barrier system has been prograding episodically. 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. The study demonstrates how core-based facies interpretations supported by a high-resolution chronology and a well-documented sea-level history allow identification of depositional environments, erosion surfaces and hiatuses within a very homogeneous stratigraphy, and allow a detailed temporal reconstruction of a coastal barrier system in relation to sea-level rise and sediment supply.