Geoscience Reference
In-Depth Information
thereby opening new sediment transport passages. The former barrier eroded and the
sediment was incorporated in a new spit/barrier structure evolving further landwards
at higher elevations. Finally, where the sediment supply exceeded accommodation,
the bay was filled and the prograding beach matched the neighbouring coastal cell
lutionary types. It can be concluded that the barriers and spits transgressed only
to a minor extent and only when hinge points were drowned or abraded or when
space between anchor points was too large. The main processes in shaping of the
present coast have been stranding, progradation and elongation and are significantly
controlled by the inherited relief.
The rough volume calculation emphasizes the assumptions that the cliffs pro-
vided enough material to build up the barriers and that they receded between 1 and
2 km since the Littorina transgression reached the present coastal area. Therefore,
the anchor points of the spits experienced approximately the same dislocation. When
the sea-level rise decreased at 7,800 year cal BP and, hence, accommodation space
grew slower, the main phase of barrier building started. In the subsequent 1000 years
or so, the sediment supply from cliff erosion still continued due to ongoing coastal
re-equilibration but exceeded the steadily shrinking accommodation, thus causing
fast barrier building. However, this process was different in the three study areas.
While on Rügen the spits were rapidly closed to prograding barriers, this process
took much more time in the Darss-Zingst area and occurred in the Wismar Bight to
a very limited extent. The difference is caused by both factors: sediment starvation
in the Wismar area where cliffs providing sufficient sediment are rare and accom-
modation space, which decreased much faster on Rügen than at Wismar due to the
more rapid isostatic uplift.
The slowing down of sea-level rise between 6,000 and 1,200 year cal BP led
gradually to a decrease in sediment supply and - in sections - to cliff stabiliza-
tion, which must have been most pronounced on Rügen. Since c. 1,200 year cal BP,
coastal dynamics has increased again as is evident by the occurrence of transgressive
dunes. From the younger historical record, fast elongation of spits and impending
barrier breaching is known. The increased dynamics can be related to the onset of
the post-Littorina (Late Subatlantic) transgression, the timing of which is evident
from the accumulation of the cover peat.
12.6 Summary
To study the interplay between sea-level evolution, crustal movement, accommo-
dation and sediment supply, new and detailed investigations of the evolution of
the southern Baltic coast were conducted based on intensive drilling and geophys-
ical surveys both onshore and offshore. An important result of the project was
the identification of three local relative sea-level curves which clearly show that
a fading crustal upheaval occurred which is still in progress on Rügen and - to a
minor extent - on the Fischland area, while the movement ceased or changed to a
slight subsidence in the Wismar Bay. Because the new RSL curves are well proven
