Geoscience Reference
In-Depth Information
substrata that scarcely hinder changes dictated by the climate-vegetation
couple. On calcareous rocks on the contrary, the environment is buffered
by its wealth of basic cations and the differentiation of soils according
to altitude occurs, but is more feebly expressed. The climatosequences
are spectacular in the intertropical zone because of greater variation of
climate with altitude. The island milieu intensifies this phenomenon
(cf. Reunion).
2.4.2 Paléoaltérites and Regoliths
Many soils are not directly differentiated on the rocks seen in the
environment but are linked to derived formations. Often the latter
result from the action of cold climates that ensured the fragmentation
and transport of materials without modifying them much so far as
mineralogy is concerned. These formations are called
paléoaltérites
(BRGM, France) or
regoliths
(USA).
It is useful to study them below the soil proper. Thereby we can
better work out the manner of subsurface circulation of water, the
reserve of plant-available water, the kinds of deep root growth, the
hazards of pollution of groundwater, the possibilities of deepening of
soils, geotechnical hazards, etc. Observing from the soil surface just
the plough layer and analyzing it is indeed useful from the agronomic
viewpoint, but it does not substitute for the study of the soil profile and
the regolith under it, in a deep pit or on an exposed road cut. Which
physician will pretend to have done a complete check up of a patient
by examining just the patient's head?
We shall now discuss a few common regoliths in nature without
going into considerations that only fall within the purview of
geomorphology.
Scree proper results from the fragmentation of rocks, often in cold
conditions. It is distinguished by the elegance of its line. Its surface
is smooth and regular, concave towards the sky, like one limb of a
hyperbola.
Scree (talus)
Bedded limestone splinters are particular screes characterized by
limestone fragments of almost uniform size (a few cm) organized in
beds parallel to the slope and cemented by an equally calcareous finer
Bedded limestone splinters
