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The aim of this ongoing study is the detection and interpretation of shallow subsurface on the German North Sea islands Sylt and Amrum using geophysical and sedimentological data. The main focus of the investigation lies on the reconstruction of the geological development of the southern barrier spit of Sylt, and the northern part of Amrum during the Holocene. The sedimentary structure and architecture of these island spit systems were investigated through an integrated approach using ground-penetrating radar (GPR) and sedimentological analyses of shallow sediment cores. Maximum penetration depths to 350 ns TWT which correspond to approximate depths of 15 m were reached. GPR surveys were orientated in 2D and 3D survey geometries with individual profile lengths between 30 m and 5 km. The topographic data of the GPR transects were collected by using a differential GPS. Different standard processing steps were chosen to increase the signal-to-noise ratio and to improve resolution. Until now, a total of 38 km GPR transects have been collected on the islands of Sylt and Amrum. To link GPR results with sedimentological data, 7 vibracores that reach a depth of 8 m below the surface were drilled at selected positions along the radar profiles. The combination of cores and high-resolution GPR data allows a detailed facies analysis and provides new insights into the complicated sedimentary architecture of the barrier island of Sylt and Amrum. Sedimentary architecture and internal structure of variety coastal elements has led to the definition and interpretation of different coastal environments as well as leads to new theories about the development of both barrier island spits.

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Abstract. Barriereinseln und Außensände, geformt durch eine Kombination aus Wind, Wellen, Strömung und Küstenlängstransport gelten als morphologisch hoch aktive Küstenbereiche und variieren häufig in Ursprung, Genese und Entwicklung. Sie besitzen durch ihre dissipative Wirkungsweise eine bedeutende Schutzfunktion für rückwärtige Inseln, Halligen und Festlandbereiche und bilden vor der Küste Nordfrieslands die westliche Außengrenze des Wattenmeeres. Ziel der nachfolgenden Studie ist es, anhand hochauflösender Georadarmessungen und sedimentologischer Daten aus Bohrungen die Landschaftsgeschichte an der Westküste Amrums sowie die Entstehung und interne sedimentäre Architektur des der Insel westlich angelagerten Kniepsandes zu untersuchen und die Prozesse, die zur Genese geführt haben, durch Datierungen zeitlich einzuordnen. Auf Grundlage der gewonnenen Daten wurden zwei stratigraphische Modelle entwickelt, welche die geologisch-geomorphologischen Prozesse und Sedimentationsbedingungen im Westküstenvorfeld erklären.

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