Distribution pattern and controls of biosedimentary facies in backbarrier tidal flats of the central Wadden Sea (North Sea)

Facies analysis is a well-established tool in sedimentary geology, which allows the reconstruction of the depositional palaeoenvironment using sedimentological, ecological and geochemical proxies. Following an actualistic approach, we mapped the biosedimentary facies of a large backbarrier tidal flat system over a decade in the field covering four tidal basins with an area of 144 km(2). The spatial distribution of biosedimentary facies shows a complex pattern on a local scale, which superimposes the shore-normal energy gradient on a regional scale. The main controlling factors are hydrodynamic energy, the relative position to tidal channels, the duration of emergence, organism-sediment interaction and the presence of invasive species. Due to strongly fluctuating abundances of benthic organisms, the lateral extension of biosedimentary facies may differ significantly over the years. However, the grain size distribution reflects a more long-term equilibrium with the hydrodynamics of this coastal region. Additionally, we have documented a system shift of biogenic structures caused by the invasion of a non-native species, which functions as an ecosystem engineering species. Since we have focussed on tracemaking organisms, i.e., polychaetes and shell-bearing molluscs combined with abiotic parameters, the biosedimentary facies pattern of our study can be transferred into multidimensional facies analyses of sedimentary rocks deposited along ancient tidal coasts