2 Die Küste, 74 ICCE (2008), 1-17 
and to the East by the western coasts of Scandinavia. It opens into the Atlantic Ocean to the 
North, via the English Channel to the Southwest, and it has a free connection to the Baltic 
Sea via the Skagerrak to the East. The sea-bottom of the relatively shallow southern North 
Sea off the Dutch and German coast shows no distinctive morphological variation. It is com 
posed of young Pleistocene and Holocene soft-rock deposits (Zeiler et ah, 2008). 
2.1 Palaeozoic to Palaeogene Development 
The basement of the North Sea basin consists of more than 543 million years old Pre- 
cambrian crystalline rocks and faulted metamorphic rocks of Palaeozoic age (for stratigraphy 
see Table 1). This basement rises towards North and continues in the Norwegian Mountains 
and the Scottish Highlands. In the North Sea basin, the top of this basement is located in 
depths of 8-10 km. It is overlaid by terrestrial, lagoonal and liminic deposits into which coal 
seams are partly incorporated. At the beginning of the Perm Period (Tab. 1), the continental 
basement was strongly influenced by volcanic activity splitting it into several parts. During 
the Upper Rotliegend, mainly arid conditions prevailed. Thick series of terrestric sandstones 
were deposited, which later functioned as reservoir rocks for the economically used North 
Sea gas. During Zechstein (Perm period), the sedimentary basin was periodically flooded 
from North-west. As a consequence of repeated transgressions and high evaporation rates, 
series of siliclastic rocks, carbonates and salt strata, the latter of up to 1,200 m in thickness, 
were deposited. (Richter-Bernburg, 1972). The maximum thickness of deposits can be 
found in the south-western-most part of the North Sea basin (Fig. 1). 
Tectonic activity and changing shallow marine and terrestrial conditions persisted 
throughout the Mesozoic period (251-65.5 million years BP). In general, the sinking ten 
dency of the North Sea basin as action at a distance of continental drift, continued, but 
‘Block-and-Graben’ tectonics led to some relative movements withpartiallly sinking but also 
uplifting tendencies. Already at the end of the Triassic period, the sediment load on top of 
the older salt strata started to deform the salt deposits by thermo-mobilisation, resulting in 
an early development of salt dome structures (Halocinesis). Later, as a consequence of on 
going salt tectonics and partly other factors leading to vertical dislocations, sills and deep 
anoxic basins were formed to later become the source areas for the development of hydro 
carbons. The mobility of the salt continues until today. In the subsurface of the North Sea, 
the Northern German und Dutch lowlands, and below the most south-western part of the 
Baltic Sea, salt diapers in elongated form (Fig. 2), up to 100 km in length, exist. They expand 
vertically from a depth of up to 8,000 m to the present surface (Ziegler, 1990). An obvious 
example for salt tectonics is the island of Helgoland. Here the characteristic red sandstones 
were uplifted by more than 4,000 m (Schmidt-Thome, 1987). Nowadays, not only the 
troughs along the salt structures are of economic interest as potential reservoirs for hydro 
carbons (e.g. Mittelplate oil field) but huge artificial caverns in the saltdomes can be used for 
the storage of energy sources such as oil, gas or compressed air and C0 2 as well. 
In the German part of the North Sea basin, the sedimentation history of the older 
Caenozoic period (Palaeogen, 65.5-23 million years BP) is characterised by shallow marine 
silica-clastic deposits. The subsidence, which already started during the Triassic period 
(Table 1), continued, giving the North Sea sedimentary basin its typical shape of a shallow 
bowl in which organic-rich sediments were subsided to depths, which allow the formation 
of oil and gas (Teichmuller et ah, 1979).