Geology Reference
In-Depth Information
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a
Tectonism: compression and warping
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b
Thalassostatic isostasy:
the see-saw effect
Hinge line
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c
Isostatic response: subsidence and lateral spread of
deposition,
Palaeoplain remnant
bulge and
uplift of adjacent land mass
Hinge line
Figure 15.12
Sequence of events following a marine incursion into an Australian cratonic basin, and consequent uplift of
adjacent land.
Source:
Adapted from Twidale (1994)
first suggested by James Hutton and implicit in Davis's
geographical cycle. An endless repetition of erosion cycles
would simply maintain a steady state with Silurian land-
scapes looking very much like Cretaceous landscapes
and modern landscapes. Evolutionary geomorphologists
contend that the Earth's landscapes have evolved as
a whole. In doing so, they have been through sev-
eral geomorphological 'revolutions', which have led to
distinct and essentially irreversible changes of process
regimes, so that the nature of erosion cycles has changed
with time. These revolutions probably occurred during
the Archaean aeon, when the atmosphere was reducing
rather than oxidizing, during the Devonian period, when
a cover of terrestrial vegetation appeared, and during
the Cretaceous period, when grassland appeared and
spread.
The breakup and coalescence of continents would
also alter landscape evolution. The geomorphology of
Pangaea was, in several respects, unlike present geomor-
phology (Ollier 1991, 212). Vast inland areas lay at
great distances from the oceans, many rivers were longer
by far than any present river, and terrestrial sedimen-
tation was more widespread. When Pangaea broke up,
rivers became shorter, new continental edges were reju-
venated and eroded, and continental margins warped
tectonically. Once split from the supercontinent, each
Pangaean fragment followed its own history. Each experi-
enced its own unique events. These included the creation
