Geology Reference
In-Depth Information
In like manner, etchplanation may have played a basic
role in the Tertiary evolutionary geomorphology of the
southern England Chalklands, a topic that has always
generated much heat. There is a growing recognition that
the fundamental erosional surface is a summit surface
formed by etchplanation during the Palaeogene period,
and is not a peneplain formed during the Miocene and
Pliocene periods (Box 15.1).
Box 15.1
TERTIARY LANDSCAPE EVOLUTION IN SOUTH-EAST ENGLAND
The study of Tertiary landscape evolution in south-
ern Britain nicely shows how emphasis in historical
geomorphology has changed from land-surface mor-
phology being the key to interpretation to a more
careful examination of evidence for past geomorphic
processes. As Jones (1981, 4-5) put it, this 'radical
transformation has in large part resulted from a major
shift in methodology, the heavily morphologically-
biased approach of the first half of the twentieth
century having given way to studies that have con-
centrated on the detailed examination of superficial
deposits, including their faunal and floral content, and
thereby provided a sounder basis for the dating of
geomorphological events'.
The key to Wooldridge and Linton's (1939, 1955)
classic model of landscape evolution in Tertiary
south-east England was three basic surfaces, each
strongly developed on the Chalkland flanks of the
London Basin (Figure 15.4). First is an inclined,
recently exhumed, marine-trimmed surface that
fringes the present outcrop of Palaeogene sediments.
Wooldridge and Linton called this the Sub-Eocene
Surface (but now more accurately termed the Sub-
Palaeogene surface). Second is an undulating Summit
Surface lying above about 210 m, mantled with thick
residual deposits of 'Clay-with-Flints', and interpreted
by Wooldridge and Linton as the remnants of a region-
wide subaerial peneplain, as originally suggested by
Davis in 1895, rather than a high-level marine plain
lying not far above the present summits. Third is a
prominent, gently inclined erosional platform, lying
between about 150 and 200 m and cutting into the
Summit Surface and seemingly truncating the Sub-
Eocene Surface. As it bears sedimentary evidence of
Elevation
(m)
300
Mio-Pliocene peneplain
200
100
0
Chalk
Palaeogene beds
Thick residual soils ('Clay-with-flints')
Figure 15.4
A sketch section of a Chalk cuesta depicting the three basic surfaces of Wooldridge and Linton (1955).
Source:
Adapted from Jones (1981)
