A new stratigraphic framework for the northern barrier spit of Sylt is presented based on an extensive ground-penetrating radar survey and sediment core data, allowing a spatial interpretation of sediment geometries and facies distributions. An age framework is provided by radiocarbon dating of mollusk shells. In parts the recent spit is underlain by coarse grained sediments showing northeastward dipping large scale foresets. The spit itself consists of a swash-bar sequence in the western part facing the open sea, and up to 3 m thick washover fans towards the backbarrier bay. The sedimentary architecture is the result of several stages characterized by either spit growth or erosion, and reflects sea-level fluctuations as well as strong climatic impacts. The stratigraphic model also reveals that the present-day shoreline of the northern spit does not reflect the orientation of the genetically build spit axis which strikes northwest southeast. A former eolian deflation surface, preserved as buried erosional unconformity at a depth of 1 m, indicates that the land surface of the spit tends to be in equilibrium with a given sea level. This results either in erosion during falling stages of the sea level, or in vertical aggradation during periods of sea-level rise; whereas sediment availability is an important prerequisite for spit aggradation during base-level rise. GPR and sediment-core data allow us to propose a model with different stages of spit evolution, summarizing the development of northern Sylt since around 5000 BP. This model challenges the nowadays widely accepted hypothesis of constant coastal retreat of northern Sylt.
Helmholtz Research Programs > PACES I (2009-2013) > TOPIC 2: Coastal Change > WP 2.3: Coastal Systems under Global and Regional Pressures