Geology Reference
In-Depth Information
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Allitization
Kaolinization
Smectization
Little chemical weathering - hyperarid
Podzolization
Ice cover
Tectonically
active areas
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Figure 6.4
The main weathering zones of the Earth.
Source:
Adapted from Thomas (1974, 5)
associated with the tropical rainforest of the Amazon
basin, Congo basin, and South-East Asia.
Within each of the first five zones, parochial varia-
tions arise owing to the effect of topography, parent
rock, and other local factors. Podzolization, for example,
occurs under humid tropical climates on sandy parent
materials.
2
The
kaolinization zone
accords with the seasonal
leaching regime of the seasonal tropics and is associ-
ated with savannah vegetation.
3
The
smectization zone
corresponds to the subtropi-
cal and extratropical areas, where leaching is relatively
weak, allowing smectite to form. It is found in many
arid and semi-arid areas and in many temperate
areas.
The effects of local factors
Within the broad weathering zones,
local factors
-
parent rock, topography, vegetation - play an impor-
tant part in weathering and may profoundly modify
climatically controlled weathering processes. Particularly
important are local factors that affect soil drainage.
In temperate climates, for example, soluble organic acids
and strong acidity speed up weathering rates but slow
down the neoformation of clays or even cause pre-existing
clays to degrade. On the other hand, high concentrations
4
The
little-chemical-weathering zone
is confined to
hyperarid areas in the hearts of large hot and cold
deserts.
5
The
podzolization zone
conforms to the boreal
climatic zone.
6
The
ice-cover zone
, where, owing to the presence of
ice sheets, weathering is more or less suspended.
