Geoscience Reference
In-Depth Information
From the present landscape point of view, the coarser deposits of the Sherwood
Sandstone Group have locally resulted in hills and slopes. In contrast, the Mercia Mud-
stone Group tends to have been eroded to form lower ground, except where more res-
istant sandstone layers (the Arden Sandstone) have produced small scarps.
The New Red Sandstone sediments of the Worcester Basin (
B1
) have been gently
moved into a downfold, with the younger Mudstone Group bedrock preserved in its
centre below Worcester and Droitwich. The older Sandstone Group forms the flanks of
this downfold, closer to the older bedrock of Carboniferous age (
A1
). The scenery loc-
ally reflects this change in bedrock type: in the east a number of northwest-southeast
ridges reflect landscape erosion of distinct sandstone layers, sometimes further picked
out by the presence of northwest-southeast trending faults. In the centre, slopes cut into
the mudstone are small, largely reflecting episodes in valley erosion by relatively small
tributaries of the River Severn. In the Kidderminster area, valley slopes have been cut
by the River Severn and its major east-bank tributary, the Stour. These have cut into the
sandstones, and local variations in sandstone erosional behaviour and in-valley down-
cutting histories have resulted in distinct sandstone ridges.
In the Knowle Basin (
B2
), the upper (younger) Mercia Mudstone is the bedrock
nearest to the surface, so the only slope features tend to be small and due either to
Arden Sandstone layers or to features of the surface blanket.
The Avon Valley Basin (
B3
) extends from Warwick via Leamington Spa towards
Rugby. There is a layer (up to 50 m thick) of Sherwood Sandstone along its northwest-
ern edge, resting on the Carboniferous area of
A2
. Apart from that, the local bedrock
is the Mercia Mudstone Group and the scenery is dominated by a surface blanket of
ice-laid and river deposits that are discussed below.
Landscape C: Jurassic bedrock
Younger than the New Red Sandstone bedrock - and above it in the succession - are
distinctive layers of Jurassic age found extensively in the southeastern parts of this
Area and beyond. This reflects a widespread change of environment, from the depos-
ition of New Red Sandstone in lakes and rivers during the Triassic to deposition in
shallow seas during the Jurassic. In the seas, subtle changes in environment may pro-
duce widespread and distinctive changes in the resulting bedrock. Because of this, the
Jurassic succession contains many distinct marker layers, and can be divided up and
traced like a layer-cake much more readily than the New Red Sandstone. There are five
marker layers that have been resistant enough to produce distinct erosional topography
in Area 9 (see Fig. 151 for their place in the bedrock succession).
