Geoscience Reference
In-Depth Information
The tilting of the bedrock layers to the east is very gentle, but enough to take the
base of the Chalk (Late Cretaceous) from a few metres above sea level at Hunstanton
to a depth of 550 m below sea level under Great Yarmouth, 80 km to the east. This
amounts to an overall slope downwards to the east of less than 1 degree. The gentle
tilting took place during the Tertiary period, and can be regarded as part of the general
lowering of the Earth's surface that has caused great thicknesses of sediment to accu-
mulate in the area now covered by the southern North Sea. The tilting may also have
been linked to the volcanic activity and uplift of western Britain that occurred during
earliest Tertiary times, as the Atlantic Ocean continued to open with the movement of
its underlying plates.
FIG
292.
Bedrock pattern and structure of Area 16.
The hilly landscape created by the Late Cretaceous Chalk and Late Tertiary Crag
contrasts markedly with the flat landscape to the west, underlain by Jurassic mudstones
(Area 15).
The gentle bedrock tilt to the east that is the main feature of the structure of Nor-
folk is visible in the Hunstanton cliffs (Fig. 293), where the contact between the white
Chalk and the underlying brown Carstone slopes down to the left in the cliff line. These
cliffs are shown in more detail in Figure 297.
I have divided Area 16 into four Landscapes, labelled A to D in Figures 292 and
294, basing the division on the bedrock that underlies the surface blanket. In gener-
al the Landscapes recognised in this topic, though based on bedrock differences, are
similar to the character areas recognised by the Countryside Agency, which are based
largely on land-use patterns.
Landscape A: Late Jurassic mudstones of the Fens
There are only very small parts of Area 16 where the surface blanket is underlain by
the Late Jurassic mudstones of the Kimmeridge Clay. These occur along the western
edge of Area 16 and, in topographic terms, they form part of the main Fenland that is
discussed under Area 15.
