Seabed sediments and current-induced bedforms in the Fehmarn Belt - Arkona Basin

The sediment map “Map sheet Fehmarn Belt—Arkona Basin, Late Quaternary sediments” is based on marine-geological investigations including shallow-seismic profiling and coring data. In addition to lithology, information on sediment ages, deposition environments and recent sediment dynamics is given. Due to the resolution of the seismic and coring
data the sediment map represents an average sediment type of the uppermost 0.5m.

Glacial till deposits form the eldest Pleistocene unit exposed in the shallow marginal parts of the survey area. At waterdepths above 20m, in the Fehmarn Belt–Mecklenburg Bucht–Arkona Basin areas, the till deposits are covered by varved clay bottomsets and in the Darss Sill area by sandy deltaic sediments. These sediments were deposited in the western part
of the dammed, late-glacial Baltic Ice Lake. Oscillating Holocene lake levels and the Littorina Sea transgression resulted in deposition of Holocene freshwater and marine fine-grained sediments and sandy palaeo coastal sediments, respectively.

The marine transgression of the Darss Sill and subsequent current activity are responsible for strong erosion in the western Fehmarn Belt area, where late-glacial clay is exposed and only a few remains of Holocene sediments exist along the margin of the basin. Eastward, the erosive effect diminishes and in the central parts of Mecklenburg Bay no current induced erosion is inferred.

Besides the removal of sediments, current-induced bedforms such as sandwaves and comet marks prove periodic, eastward inflow of saline bottom waters at water-depths of more than 15m, while westward outflow of low-salinity Baltic water influences the seafloor in the northern part of Fehmarn Belt at water-depths of less than 15m.

The characteristic sediment distribution and current-induced bedforms indicated on the map clearly reflect the postglacial development, whereas trawl tracks reveal recent human activity in the area.