Geoscience Reference
In-Depth Information
Along with the present-day pattern of rivers and coasts, the other major factor de-
termining the local scenery is the underlying bedrock. I have divided Area 15 into four
Landscapes (labelled
A
to
D
in Fig. 268), basing the division largely on the bedrock or
its surface blanket.
Landscape A: Triassic bedrock and the River Trent
This Landscape is defined by the presence of Triassic bedrock below the surface
blanket in two small patches in Area 15 (Fig 268). This bedrock consists of layers of
red mudstone that were deposited in an inland basin supplied with mud and occasional
sand by rivers over 200 million years ago (Fig. 225). Thin gypsum layers were depos-
ited periodically in lakes or arms of the sea when they dried out in the arid climate of
that time. The landscape here has been shaped by recent erosion into a gently undulat-
ing surface, except where the thin bedrock sandstones have resisted recent river erosion
to produce low escarpments.
FIG
268.
Bedrock distribution and structure of Area 15, showing Landscapes
A
to
D
and
two sub-areas (Vale of Belvoir, sub-area I, Fig. 269; and Oakham, sub-area II, Fig. 272).
The River Trent flows across this corner of Area 15 within a distinct floodplain,
which is 2-3 km wide, remarkably straight and constrained between steep valley walls
that are generally about 50 m high. The last events in the retreat of these valley walls
probably eroded the Triassic bedrock during times of low sea level since the Anglian
glaciation, and some of the floodplain has been constructed during the recent Flandri-
an sea-level rise. However, the Trent has a well-developed series of river terraces (see
Chapter 2, Fig. 11), and this suggests a long and varied early life from pre-Anglian
times.
The northerly part of Landscape
A
only contains small relict patches of Anglian
ice-laid material, probably because the rest of the cover has been removed by the Trent
as it shifted its course widely during its early history. The southern part of Landscape
A, near Leicester, has a more extensive cover of Anglian material, along with distinct-
ive incised valleys that have been carved in the 400,000 years since it was deposited.
