Barrier islands, tidal flats, and coastal marshes resulting from a relative rise of sea level in East Frisia on the German North Sea coast

Abstract

The level of the North Sea has risen about 110 m during the last 15000 years, i.e. during the Weichselian Late Glacial and the Holocene periods. Only the last 46 m of this rise, covering the time interval since 8900 B.P., can be reconstructed on the basis of reliable radiocarbon dates from the southern North Sea and the German Bight.

Along the East Frisian coast, the formation of the present day barrier islands, tidal flats and coastal marshes started shortly after 8000 B.P. when the sea had risen above the —20 m level. Sequences of marine, tidal-flat, shoal and beach sediments, altogether 35 m thick, were formed in the zone of the barrier islands; these were covered by a thin layer of salt marsh deposits and in turn by dunes up to 20 m high. Thick sequences of intertidal and subtidal deposits occur in the seaward part of the tidal flats. In the landward part of the tidal flats and in the coastal marshes, layers of peat are intercalated in the tidal, brackish, and lagoonal deposits. These peat layers were formed since 6500 B.P. and document phases of retardation in the rise of the sea level, from 4800 to 4200 B.P. and from 3300 to 2300 B.P. Fossil soils on brackish sediments and decomposition horizons in the peat indicate that a temporary lowering of the water level took place at about 2700 B.P. and again at 2000 B.P.