Geoscience Reference
In-Depth Information
1.2
METHODS FOR STUDY OF PEDOGENESIS
1.2.1 Field Observations
In science, everything or almost everything proceeds from observation.
It is therefore necessary to learn how soils in nature are appropriately
described. However, observation does not at all enable understanding
and interpretation. To demonstrate this, we shall take the following
theoretical case, similar to situations actually observed in the field in
tropical environment (Fig. 1.3).
Description of the soils
Ascent?
Transformation front
Descent?
Slightly sandy clay
Pure sand
Surface material
Fig. 1.3
Interpretation of the contact between a sandy layer and more clayey layer in a
soil cut.
A clayey layer upslope is associated with a sandy layer downslope.
At the boundary between them are seen interpenetrations, as shown
in the diagram. In the absence of other data, there are three possible
interpretations:
Things have been in this condition since the start of deposition
of the materials, but such immobility is unlikely considering the
strength of weathering phenomena in hot, humid climate.
Or, the clay moves downhill invading the sand, which would
progressively transform the pure sand to clayey sand or to
sandy clay. In this hypothesis we 'see' appear, in the sand, clayey
volumes or lenses, a kind of advance parties of the invasion.
Then the colonization is almost complete at the
clay front
. In the
rear, only a few isolated pockets of sand on the way to reduction
survive (in the meanings given to 'pocket' and 'reduction' in
battle!).
