Geoscience Reference
In-Depth Information
clay particles and resistant quartz are found together in them (read
Chap. 3, § 3.4.3).
Various authors have perceived as plausible the hydrolysis of clay
minerals in the Albeluvisols and Planosols of temperate environments
(Duchaufour and Lelong 1967; Fridland and Karayeva 1979; Bornand
1979; Chaussidon and Pédro 1979…). But direct proofs are tenuous.
Firstly, some evolution of the clay phase is seen in E and in the
tongues: expansion of 2/1 clay minerals and vermiculitization. Secondly,
aluminium is released and rightaway fixed, at least partly, by a process
of aluminization of clay minerals, leading to formation of secondary
chlorites. Lastly, the primary minerals (except quartz) still present show
traces of dissolution, which indicates an aggressive environment, at
least in the long term. Brinkman (1977) felt that the degradation of
clay minerals takes place through ferrolysis, that is, destruction of the
octahedral sheets by a complex mechanism involving oxidation of iron
in the dry season (Chap. 12).
Let us draw the texture triangle with the half-line
y
connecting the
clay apex to the point representing B (Fig. 8.4). If the movement of clay
had been what was said earlier, that is, a simple mechanical process
redistributing the clay from the E to the B without affecting the skeleton
grains that thus will play the passive role of a filter, the sand/silt ratios
would have been maintained. Thus the point representing E would be
on this half-line. Yet it is most often displaced to the left (Legros and
Pédro 1985)!
Granulometric arguments
All the points on this half-line have
the same sand:silt ratio
B
E
Deficit of silt in E
y
Silt
, %
Fig. 8.4
Abnormal position of E in relation to what it should have been if the soil considered
had evolved by a simple of translocation of clay from E to B. This is seen in well-differentiated
Albeluvisols.
