The South Coast Region - Southern England - page 95

FIG 95. Generalised bedrock succession for the South Coast region.
Bedrock movement, uplift and erosion by rivers
The overall geographical arrangement of the bedrock layers is largely the result of
gentle folding, which took place after the Tertiary sedimentation described above. The
distinctive Late Cretaceous Chalk layer acts as a clear marker for this late episode of
large-scale movement (Fig. 96). From northwest to southeast the Chalk marker curves
round the broad Weald uplift (or anticline ), is buried by Tertiary clays in the Hampshire
Basin downfold (or syncline ), and arrives at the surface again at the Isle of Wight step-
fold (or monocline ), which extends across Areas 4 and 5. There are also other gentle
fold structures in the area, and it is clear that they are the surface expression of a series
of west-to-east trending faults deeper in the crust which formed after the end of Tertiary
sedimentation (Figs 92 and 96). An early phase of extension or stretching, particularly
in the Jurassic, appears to have generated a series of normal faults, which became in-
active and were buried by continuing sediment deposition. A later phase of mid-Ter-
tiary compression and convergence reactivated these faults but in the opposite direc-
tion, pushing the sediment layers above into gentle folds. This model of crustal de-
formation seems a more likely explanation of the South Coast mid-Tertiary folds than
one linking them to the severe plate boundary convergence that generated the Alps and
the Pyrenees many hundreds of kilometres to the south, over the same period of time.