6 DieKüste, 74 ICCE (2008), 1-17
1980; Zeiler et al., 2008). Its outline is still recognizable in the present bathymetry of the
German Bight whereas most of the smaller channel structures are buried below younger
deposits (Schwarz, 1996).
2.2.2 Holocene
After the LGM, melting of the inland ice caps led to a global sea level rise (Fig. 4). At the
end of the Pleistocene and in the early Holocene, the magnitude of the sea level rise was
approx. 2.1 m/100 years (Streif, 2002). The southern North Sea basin was flooded around
9,000 to 8,000 BP, which is documented by tidal flat deposits from that time (Eisma et al.,
1981). The depositional evolution along the German North Sea Coast began between 8,600
and 7,100 B.P, when the sea level rose from -45 to -15 m below the present German chart
datum NN (see Fig. 4). At that time, the coastline was presumably located 5-10 km seaward
of the present one (Sindowski 1973; Flemming and davis, 1994). During this period, tidal
currents and waves penetrated further into the hinterland and eroded the exposed higher
parts of the former submerged Pleistocene landscape. Large quantities of reworked sediment
were shifted landward, building up a wedge-shaped body of Holocene coastal deposits. This
sediment body, striking parallel to the coastline, has a width of 10 to 25 km. In the Weser- and
Elbe estuary, its length goes up to 80 to 100 km. While the accumulation wedge tapers off
towards the mainland, it can reach a thickness of more than 40 m (Ahrendt, 2006) at its
relatively steep seaward slope. Here it mainly consists of fine- to medium-grained sand.
With a decelerating sea level rise from 7,000-3,000 BP (Behre, 2003) coupled with an
increase of the tidal range from 1.3 m to 2.2 m (Franken, 1987), the coastal zone was formed
by salt marshes, tidal flat deposits and in parts by barrier islands with dunes of a height of up
to 30 m. With the phase of a slower sea level rise of only 0.11 m /century (Behre, 2003) over
the last 3,000 years BP, the Wadden Sea area was formed. This area is characterized by a
complex pattern of marine and terrestrial deposits, reworked postglacial siliclastic drainage
material of the underlying Pleistocene drainage deposits as well as several peat layers, which
were deposited between tidal, brackish and lagoonal sediment layers. In the “drowning”
landscapes, an also rising ground water table resulted in wide-ranging water logging and the
formation of peat bogs. Although subsequent frequently eroded by the transgressing sea,
these basal peat layers often mark the beginning of the Holocene depositional history of an
area (Streif, 2004).
Although regional differences exist, which are e.g. due to the palaeo-geomorphology,
the characteristic series of Holocene deposits consists of strata of fine-grained sand, silt, clay
and intercalated layers of peat (Fig. 5). Within this alternating sequence, marine and brackish
deposits overlying peat mark phases of transgression. On the other hand, regressive overlaps
with peat overlaying brackish and marine sediments indicate a seaward shoreline displace
ment (Streif, 2004) due to phases of a dropping or - more likely - stagnating or slowly rising
sea level.
The surface of the Holocene accumulation wedge is almost flat. Its elevation only varies
between -f m to +2 m in relation to the German reference datum NN. This also holds for
the North Frisian islets (Halligen), which are relicts of a former very much wider marshland
that was partly destroyed by storm surges in the 14 th and 17 th century. On the barrier islands
along the German North Sea coast, the land elevation is often higher. This is either related to
the presence of Holocene coastal dunes (East Frisian barrier islands) or to a combination of
Holocene deposits combined with elevated cores of Pleistocene (Amrum and Fohr Island)