This thesis investigates the sedimentary evolution of a Holocene barrier coast with special focus on how barrier system stratigraphy is affected by changes in sea-level and sediment supply.
Coastal barrier systems comprise about 13% of the world’s coastlines and they are mportant components of the stratigraphic record of the Earth. Sea-level rise and sediment supply are the two most important factors controlling barrier system evolution.
Detailed depositional reconstructions of a number of barrier systems from the Danish Wadden Sea area have been carried out in order to evaluate the sedimentary effects of Holocene sealevel rise. Core-based facies analysis, ground-penetrating radar surveys and optically stimulated luminescence and radiocarbon datings facilitate the investigation of the complex evolution of the barrier coast (at a high spatiotemporal resolution).
The data show that the formation and evolution of the barrier system was controlled by changes in the rate of sea-level rise, sediment supply as well as the inherited Pleistocene topography and the regional-scale coastal morphology. The initial Holocene transgression as diachronous and took place between 7.5 to 7.0 ka ago. As the rate of transgression progressively decreased, topographically low area flooded more rapidly than opographically high areas. A retrogradational infill stratigraphy was therefore more likely to develop in the rapidly transgressed areas as compared to the elevated areas. It appears that the nuclei of he investigated barrier systems are perched onto topographic highs. The first major infilling took place between 6.5 and 4.0 ka ago forming an approximately 10 m thick littoral wedge. The infilling commenced when the rate of Holocene sea-level rise had decreased to less than 2 mm a -1.
An alongshore sediment supply imbalance exists in the Danish Wadden Sea as a onsequence of the pronounced convex-concave-convex form of the barrier chain. elatively more sdiment has been deposited where the shoreline is embayed as ompared to the protruding areas. These large-scale variations in sediment supply along the studied shoreline resulted in a distinct stratal stacking pattern of each of the investigated coastal barrier systems.
We conclude that the overall infilling of the barrier systems over the Holocene was mainly controlled by sea-level rise and sediment supply. However, major storms and tidal channel migration have greatly affected the local sedimentation over the short-term periods. It is evident from our study that the depositional history of closely situated barrier systems subjected to near-similar sea-level forcing, may produce a significantly different epositional architecture and sedimentary record. It can thus be concluded that the response of barrier systems to future sea-level rise will be highly depend on local to regional scale sediment.