Size and shape-sorting of coastal sands in the eastern part of the German Bight (North Sea)

Abstract

Size analyses of sand samples taken from the islands and sand flats in the eastern part of the German Bight indicate that each island shows a separate grain size population. This rules out important longshore sand transport from island to island. Comparison with sediment maps of the adjacent seafloor suggests that the islands were formed by wave action. On the other hand rollability analysis reveals that the percentages of angular grains in the samples increase towards the north. It is held that this increasing angularity reflects the shape sorting of the sediments of the seafloor. The spit of Skallingen shows a drecreasing angularity of the sand grains towards its end, probably caused by prevailing influence of shape selection by coastal erosion over longshore transport. In most cases the dune sands contain more angular grains than the beach sands.