3.4.4
Sedimentology
3.4 Morphology and Sedimentology
33
Tidal sediments of the southern North Sea are by tradition divided into three sediment types on the basis of their mud content (Sindowski 1973; Gadow & Schafer
1973): a) muddy sediment (content of the fraction <63 flm of more than 50 %), b)
muddy sand (5-50 % of the fraction <63 flm) and c) sandy sediment (less than 5 %
of the fraction <63 flm). According to these criteria, there are only small isolated
spots of muddy areas in the backbarrier system of Spiekeroog. The by far largest
part consists of muddy sand and pure sandtlats, which dominante in the central part
of the backbarrier system (Flemming & Davis 1994).
The sediment distribution in the Spiekeroog backbarrier system follows an energy gradient from the island to the mainland which is reflected by a particle fining
trend in direction towards the mainland (Flemming & Nyandwi 1994). This landward fining trend is the result of a continuous sorting process that is driven by
repeated particle resuspension and sedimentation controlled by particle settling
velocities (particle size and density) and the local wave energy level (Flemming &
Ziegler 1996). This depositional sequence is interrupted by mud patches (mussel
beds - biodeposits of Mytilus edulis L.) in the central part of the catchment area
(Chap. 3.6.1 and see Fig. 3.5.1).
The East- and Westfrisian Wadden Sea is characterized by a pronounced sediment zonation parallel to the coast (Oost 1995). The finest, most landward sediment facies has lately shown a decrease in fine sands accompanied by a widespread lack of mud. This lack in fine grained sediments is a result of elevated
energy gradients in the backbarrier area, caused simultaneously by artificial sea
dikes and a rising sea level (Flemming & Nyandwi 1994). In the course of this sea
level rise the islands are shifted landward. This movement of the whole system is
the consequence of a sediment deficit in the backbarrier system resulting from the
rising sea level and leads to a further decrease of fine particles in the sediment.
There were only insignificant differences in the grain size distributions between
the Swinn- and Griininger Plate (Bartholoma, Flemming unpub!. data). The
Swinnplate has a slightly larger abundance of coarser fine sands (2.0-2.5 phi),
whereas the percentage of finer fine sands (2.5-3.0 phi) is somewhat smaller. Both
study areas were located outside the zone of physical mud sedimentation, i.e., nonbiogenic muds occur only in small and seasonally varying amounts. The
Swinnplate is characterized by the accumulation of biogenic muds (Bartholom~l,
Flemming unpub!. data). These are fine grained biodeposits (faeces and pseudofaeces produced by the mussel Mytilus edulis L. (Chap. 3.6.1)) with more than
50 % being contributed by the fraction <63 flm.
Large amounts of this mud are remobilized especially during storm events with
high wave energy. The consequences are small- to mid-scale modifications in
morphology and sediment composition. During calmer weather conditions, the
sediment distribution is reorganized according to the former distribution following
the large-scale zonation in accordance with the hydrodynamic equilibrium (Bartholoma, Flemming un pub!. data).
Particle sinking velocities are smaller in the winter months due to higher wave
energy and lower water temperatures (increased cinematic viscosity of the water)
(i.e., in winter, larger particles can stay longer in suspension; particle sizes are up
Sedimentology
3.4 Morphology and Sedimentology
33
Tidal sediments of the southern North Sea are by tradition divided into three sediment types on the basis of their mud content (Sindowski 1973; Gadow & Schafer
1973): a) muddy sediment (content of the fraction <63 flm of more than 50 %), b)
muddy sand (5-50 % of the fraction <63 flm) and c) sandy sediment (less than 5 %
of the fraction <63 flm). According to these criteria, there are only small isolated
spots of muddy areas in the backbarrier system of Spiekeroog. The by far largest
part consists of muddy sand and pure sandtlats, which dominante in the central part
of the backbarrier system (Flemming & Davis 1994).
The sediment distribution in the Spiekeroog backbarrier system follows an energy gradient from the island to the mainland which is reflected by a particle fining
trend in direction towards the mainland (Flemming & Nyandwi 1994). This landward fining trend is the result of a continuous sorting process that is driven by
repeated particle resuspension and sedimentation controlled by particle settling
velocities (particle size and density) and the local wave energy level (Flemming &
Ziegler 1996). This depositional sequence is interrupted by mud patches (mussel
beds - biodeposits of Mytilus edulis L.) in the central part of the catchment area
(Chap. 3.6.1 and see Fig. 3.5.1).
The East- and Westfrisian Wadden Sea is characterized by a pronounced sediment zonation parallel to the coast (Oost 1995). The finest, most landward sediment facies has lately shown a decrease in fine sands accompanied by a widespread lack of mud. This lack in fine grained sediments is a result of elevated
energy gradients in the backbarrier area, caused simultaneously by artificial sea
dikes and a rising sea level (Flemming & Nyandwi 1994). In the course of this sea
level rise the islands are shifted landward. This movement of the whole system is
the consequence of a sediment deficit in the backbarrier system resulting from the
rising sea level and leads to a further decrease of fine particles in the sediment.
There were only insignificant differences in the grain size distributions between
the Swinn- and Griininger Plate (Bartholoma, Flemming unpub!. data). The
Swinnplate has a slightly larger abundance of coarser fine sands (2.0-2.5 phi),
whereas the percentage of finer fine sands (2.5-3.0 phi) is somewhat smaller. Both
study areas were located outside the zone of physical mud sedimentation, i.e., nonbiogenic muds occur only in small and seasonally varying amounts. The
Swinnplate is characterized by the accumulation of biogenic muds (Bartholom~l,
Flemming unpub!. data). These are fine grained biodeposits (faeces and pseudofaeces produced by the mussel Mytilus edulis L. (Chap. 3.6.1)) with more than
50 % being contributed by the fraction <63 flm.
Large amounts of this mud are remobilized especially during storm events with
high wave energy. The consequences are small- to mid-scale modifications in
morphology and sediment composition. During calmer weather conditions, the
sediment distribution is reorganized according to the former distribution following
the large-scale zonation in accordance with the hydrodynamic equilibrium (Bartholoma, Flemming un pub!. data).
Particle sinking velocities are smaller in the winter months due to higher wave
energy and lower water temperatures (increased cinematic viscosity of the water)
(i.e., in winter, larger particles can stay longer in suspension; particle sizes are up