Geoscience Reference
In-Depth Information
Late Cretaceous Chalk level, has been eroded into the Chalk Downs, which have since
been gently folded and locally faulted by Earth movements.
We began this topic by wondering why it is that Southern England has such gentle
and generally rather low-lying landscapes. The answer seems to be that relatively little
Earth movement has taken place since the end of the Variscan plate convergence and
the onset of the New Red Sandstone pattern of movements. There has been gentle up-
lift in the west, probably linked in part to the divergence of the American and European
plates, and the growth of the Atlantic Ocean, but also probably linked to the growth
and sinking of the North Sea basin. But another important factor has been that much of
the sediment accumulating in the Southeast England Basin turned into soft mudstones
that have been relatively efficiently eroded by river action, with the exception of the
resistant levels of sandstone or limestone. These same mudstones have also been par-
ticularly prone to erosion by slope movement during the long cold episodes of the Ice
Age, when much of Southern England, though not glaciated, became frozen ground.
What has given the coastline of Southern England its 100-km-scale location and
shape?
We have seen how the coastline has retreated actively over the last 20,000 years as sea
level has risen due to the melting of the ice of the last cold episode of the Ice Age.
The shape of the present coastline depends primarily on the shape of the topography
invaded by this rising sea, although in many places significant erosion by the arrival of
storm waves has caused further retreat.
The pattern of river valleys (Fig. 318) has been responsible for the major features
of the invaded topography. These valleys include the English Channel and the Irish
Channel/Bristol Channel valleys that had earlier been eroded from the Atlantic Ocean
side, and the southern North Sea (Dogger Hills) valleys eroded from the North Sea
side. The shape of these valleys was already apparent in the pattern of downward Earth
movements that started in Permian and Triassic times when the movement patterns of
the convergent Variscan deformed belt, changed into the pattern of basins and uplands
of New Red Sandstone times (Fig. 317).
The existence of the Variscan deformed belt near the surface in the Southwest
Region, and its continuation under our South Coast Region, has provided a persistent
west-to-east element of erosionally resistant bedrock that has given the coastline its
greatest extent, north of which the British coastlines tend to converge to give Great
Britain its triangular form (Fig. 316).
