One of the most important aspects of weathering is in the formation of soil, which, for a mature soil, depends
climate rather than rock type.
- Most rock types are made up a relatively few, chemically related minerals which will produce similar end products.
These are the feldspars, micas, amphiboles, pyroxenes and olivines. The one common mineral to make a difference is
calcite (in limestones).
-
Climate, however, is more variable. Chemical reactions work faster when the temperature is higher. The amount of
rainfall affects the concentration of the acids etc in the water. There is more chemical weathering in hot, humid
climates than in cold dry ones.
|
- Soils evolve into soil profiles with characteristic soil horizons. Soils are described and classified by the
nature of these horizons.
|
 |
For convenience, the standard exam classification is used:
Zonal soils
- occur in broad geographical areas or zones
- are mature, as a result of stable conditions over a long period of time
- may have distinct horizons
- are influenced more by climate and vegetation of the area rather than rock type
Examples of zonal soils include
- ferralitic and ferruginous soils
|
 |
Azonal soils( = 'without zones')
- are immature
- do not have distinct horizons
- do not depend on climate
- are closely related to the rock type
|
 |
Intrazonal soils ( = 'within zones')
- occur within other zonal soils
- are influenced by one factor
- calcimorphic - on limestone
- hydromorphic - waterlogged
- halomorphic - with soluble salts
|
 |
Occasionally, soils are preserved in the geological column.
Examples include
- red bole in basalt lavas
- seat-earth in the Coal Measures
|
 |
Geopix Study Guide "Soil Formation"
- gives a full image of each of these, and other, examples;
- describes the main types of soil profiles;
- describes in detail the processes involved in soil formation;
- gives examples of fossil soils (palaeosols)
(This Study Guide does not include aspects of farming, catenas, textures etc)
The Study Guide contains the following pages:
'Soil Formation' is part of the Geopix Weathering and Erosion Study Guide CD.
To order this CD go to the Geopix Online Store
