Geoscience Reference
In-Depth Information
Fig. 5.7
Regions of the world where Ferralsols (South America, Africa) and Acrisols (south-
eastern Asia) are mainly found.
Role of the parent material
On acid rocks (granites, gneisses), pedogenesis is directed toward
the quartz-kaolinite association (termed
paragenesis
).
On basic rocks (basalts), the medium richer in bases favours the
neoformation of 2/1 clays; also, iron is abundant and leads to
formation of thick cuirasses.
On calcareous rocks, because large quantities of Fe, Al and
Si are not available, the existence of Ferralsols is theoretically
impossible. Studies however show that bauxites (Al oxides) are
often associated with limestone, especially in European forma-
tions. But transport is involved.
In perhumid climate, the topslopes are subtractive environments;
footslopes are sites where water accumulates (Fig. 5.8). In climates with
a long, dry season, the higher points continue to lose silica; lower points
concentrate silica and possibly salts too (Chapter 6, § 6.6).
Role of topography
It was stated in the introduction that a dense primary forest, that is,
one never opened up by man and evergreen, that is, never defoliated, is
evidently the ideal site for limiting erosion and for favouring preservation
of very deep soils. Erhart (1956) in his work
La Genèse des Sols en tant
Role of vegetation and man
