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The North Sea Basin

Fig 5.2.1 Map of the North Sea
The North se is located between Scotland and Norway.The North sea has a very long and complicated history of subsidence. Deposition of sediment is particurly rapid during the Permian and Mesozoic time periods creating layers many kilometers thick.The figure above shows the major feateures of the north sea.The Humber group is dominated by marine mudstones and clays.These have been deposited after a large amount of subsidence.The Cromer Knoll group is dominated by calcareous mudstones and thin limestones.The chalk group dominates the Upper cretaceous and lowermost Paleocene ages.The late Palaeocene is dominated by sandy turbidites which represent large deposits from a submarine fan system.The Witch Ground Graben were formed in the late Jurassic due to a large rifting event causing alot of extension.Considerable amounts of thermal subsidence occured after this which continue to the present day.This rapid subsidence was interupted by an uplift due to the opening of the North Atlantic.

Fig 5.2.2 Stratigraphic column taken from the North Sea. This column illustrates the deposition history of the basin.
From the figure below we can see that there are two periods of rapid susidence followed by two periods of declining subsidence rates.On the figure curve 1 represents backstripped subsidence curve with a constant water depth.Curve 2 is a water loaded subsidence curve.Curve 3 is a theoretical water loaded subsidence curve.Curve 4 represents the water depth profile while curve 5 is the net subsidence curve.There is very rapid subsidence in the first twenty years of the basins history.This is due to the fact that rifting lasted from 150 Ma to 130Ma.During the late cretaceous there is a rapid increase in the amount of chalk deposition this leads to a rapid increase in subsidence.During the palaeocene there is another rapid increase in sediment input leading to further subsidence.

Fig 5.2.3. Subsidence curves for Location C in the North Sea.
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