Geoscience Reference
In-Depth Information
FIG
223.
The East Anglia Region.
Beneath the near-surface layers of the bedrock of East Anglia, there is older bed-
rock that can be examined only in boreholes, and by remote geophysical methods. This
has revealed evidence for an important geological episode some 300 million years ago,
during latest Carboniferous or earliest Permian times. Before this, the geography of the
Region was very different to that of the present, with sediments accumulating in some
areas while hills had formed elsewhere due to movements of the crust. Approximately
300 million years ago, the whole Region became a land area of general erosion, and
part of the area was uplifted to become what we now call the London Platform.
Since that time, younger sediments have been deposited and turned into bedrock.
Initially they only accumulated in the northwest of the Region but then, in Jurassic and
Early Cretaceous times, the area of deposition extended further southeast towards the
London Platform. Eventually, in Late Cretaceous times, the whole Region was sub-
merged and covered by accumulating Chalk. After this, during the Tertiary, the surface
was moved upwards and tilted, so that sediment accumulation became confined to the
southeast of the Region.
Although none of these sedimentary layers is uniform across the Region, the fact
that the 300-million-year-old landscape (labelled pre-Triassic in Fig. 224) is still so
close to the present surface shows that little vertical movement of the crust (less than
≈500 m) has taken place since that time. Its younger bedrock cover provides key in-
formation about the environments in which the sediments formed, and these are all
consistent with unusual stability and lack of crustal movement.
