Geology Reference
In-Depth Information
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a
Sub-Cambrian peneplain
Fractures
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b
Deep kaolinitic weathering
along fractures in the Mesozoic
Saprolite
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c
Late Mesozoic partly stripped etchsurface
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d
Plains with residual hills;
the end result of Tertiary processes
Figure 15.8 The three basic relief-types within the Fennoscandian Shield. (a) Sub-Cambrian peneplain. This exhumed
and extremely flat palaeoplain, together with sub-Vendian and sub-Ordovician facets, is the starting point for all relief on
the Fennoscandian shield. (b) Deep kaolinitic weathering along fractures in the Mesozoic. This is not a basic relief type,
but led to (c) Late Mesozoic partly stripped etchplains, with a characteristic undulating hilly terrain and remnants of
kaolinitic saprolite and Mesozoic cover rocks. (d) Late Tertiary plains with residual hills, which are the product of Tertiary
surface denudation.
Source: Adapted from Lidmar-Bergström (1999)
In northern England, a variety of active, exhumed, and
buried limestone landforms are present (Douglas 1987).
They were originally created by sedimentation early in
the Carboniferous period (late Tournaisian and early
Viséan ages). Subsequent tectonic changes associated
with a tilt-block basement structure have effected a com-
plex sequence of landform changes (Figure 15.10). The
Waulsortian knolls are exhumed mounds of carbonate
sediment formed about 350 million years ago. Shales and
later chalk covered them, and then exhumation during
the Tertiary period produced reef knoll hills , which are
features of the present landscape. In the Clitheroe region,
they form a series of isolated hills, up to 60 m high and
100-800 m in diameter at the base, standing above the
floor of the Ribble valley. The limestone fringing reefs
formed in the Asbian and Brigantian ages today form
prominent reef knoll hills close to Cracoe, Malham, and
Settle.
Carboniferous sedimentation in the southernmost
section of the Gaspé Peninsula in eastern Quebec,
Canada, has fossilized a palaeosurface - the Saint Elzéar
surface - that erosion is now gradually exhuming (Jutras
and Schroeder 1999). Part of the surface is a nearly per-
fect planation surface, cut between 290 and 200 million
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