Linking Sedimentology and GPR Data: the Subsurface Holocene of Sylt Island (German Bight)

Fürstenau, Jörn¹, Sebastian Lindhorst¹, H. Christian Hass², Susanne Feindt¹, Christian Betzler¹ (1) University of Hamburg, Hamburg, Germany (2) Alfred Wegener Institute for Polar and Marine Research, List / Sylt, Germany

Sylt is a barrier island close to the German North Sea coast. In this study we link ground penetrating radar (GPR) and sedimentological data to reconstruct the Holocene development of the northern barrier spit. Present outcomes of the studies let us determine a distinct correlation of radar facies and lithofacies.

GPR data allow high-resolution investigation of the shallow subsurface. A GSSI SIR-3000 radar, either coupled with a 100 MHz or a 200 MHz antenna, was used. A penetration depth of 350-500 ns TWT is achieved which corresponds to approximate depths of 10-15 m. Refining GPR raw data in an appropriate processing flow which includes 1D- and 2D-filter, migration, deconvolution and gain, as well as topographic correction using ReflexW enhances quality and thus data interpretability. Different configurations of reflector amplitude, shape, orientation, continuity and termination type can be distinguished and separated as numerous radar facies types in the depositional succession of the spit system.

Lithofacies logs obtained from cores retrieved along the GPR lines and laser-diffraction grain size analysis serve as a key to deduce a genetic stratigraphic model from the GPR data. Linking energy regime distribution and evidence of transport mechanism to radar facies, distinct sedimentary environments can be reconstructed.

Correlation of lithological and GPR data reveal that high amplitude reflections are related to sudden change in grain size. Based on variations in grain size and sorting, porosity changes in the sediment can be derived. Correlation of distinct porosity intervals with radar facies therefore allows to propose a model of the subsurface porosity distribution.