Geoscience Reference
In-Depth Information
there is no recycling. The displacement is relative. These are the horizons
that penetrate (see the fronts marked at the right of the diagram).
Production of organic acids and of H
+
A
Progressive
descent of the
weathering
fronts
CO
2
Q
(residual)
E
H
+
Degradation
Front of
degradation
of complexes
3
Organic
residues
(roots)
Maturation
Fe , Al
B
h
2
Front of
formation of
humic-acid
complexes
Insolubilization
Complexation
Silicates
H
+
B
Fe
Limited
displacement
1
Front of silicate
weathering
C
Partial export of soluble Al
and Fe complexes
Dissol. and evacuation of Si and bases
Fig. 11.10
Differentiation of Podzols following the weathering front model.
The main point is that complexation occurs in the B, not in the E.
According to Schmidt
et al
. (2000), '
In Podzols, the organic matter is leached
from the forest floor and E horizon into the B horizon where it is intimately
combined with the mineral phase'
.
Our view (Legros 1982) certainly does not explain everything, but
answers primarily the 11 objections raised above to the classic theory.
The reader could reflect on them. To summarize, (1) it does not call
upon large mineral-organic migrations for forming the B horizons;
(2) because of weathering
in situ
it is normal that large quantities of
non-complexed iron and aluminium be present in the B; (3) the Bh/
Bs pair cannot be separated, it represents the two phases of the same
weathering-degradation mechanism; (4) no correlation is found between
the contents of C and Al because only the former travels between A and
B; (5) a strong correlation between Si and Al contents is normal when
they come mostly from weathering
in situ
of the same parent material; (6)
the boundaries of all the horizons attacked from behind tend to become
Advantages of the model
