Geoscience Reference
In-Depth Information
The reverse process is possible in dry environment when man
intervenes.
Calcaric
soil (i.e., calcareous soil)
(soil with CaCO
3
Carbonatation
(
Decarbonatation
(
CaCO removal
3
)
CaCO
enrichment
3
)
Ca saturated soil
(base saturation > 50%)
++
Dystric
soil on
acid
rock
Decalcification
(
Ca removal
++
)
Dystric topsoil
(base saturation < 50%) in the topsoil
Fig. 7.1
Possible transformations in soils in relation to carbonate status. Carbonatation will
be examined later on.
The soils are decarbonated starting from the surface, under the
influence of atmospheric agencies. Time intervenes; for example the soils
of the Vistula/Riss glaciation are more deeply decarbonated that those of
the Würm (Kern 1984). The dissolution affects more the finest particles
that have a high surface-area/mass ratio. In the Alps, for example,
it is usual to find a decarbonated matrix associated with calcareous
pebbles.
Calcareous soils and calcium-saturated soils have the following in
common:
Typical features of calcareous and base-saturated soils
A relatively high pH; it is close to neutral in base-saturated soils
and 7.5-8.5 in calcareous soils.
A good, fragmented and angular structure especially if the soil
is rich in clay; this structure is highly stable as determined by
appropriate tests.
High content of stable organic compounds; it has been shown
that the organic-matter content of the soils in the French Jura
is proportional to their exchangeable calcium content (Gaiffe
and Schmitt 1980); the stabilizing influence of calcium is thus
demonstrated.
Calcareous soils are easily identified by a test with 50 per cent
or 33 per cent hydrochloric acid. A drop of acid placed on the
sample provokes release of CO
2
that can be seen in the liquid
and is proportional to the lime content. The reaction is:
CaCO
3
+ 2
HCl
Æ
CaCl
2
+
CO
2
+
H
2
O
