Geoscience Reference
In-Depth Information
Scientists had noted before us that the kaolinite cover on some
slopes in Brazil had crept down the slope in large sheets overlapped
like roofing tiles (Furian
et al.
1998).
'Collision' zone of upper slope and lower
slope. As the underlying bed is hard
(platform), there is bound to be dual heaving
at this level (cf. model of formation of a
mountain range by plate tectonics)
Flowage, that is, thinning of the
soil cover on the upper slope
Phenomenon of reversal (seen
in horizons containing stable
carbon compounds); cf.
(overthrust folds)
Forces
nappes
Lower slope
pushed back,
hence undulations
(cf. folds, in
geology)
Flattened
appearance of
the collision
zone
Fig. 2.14
Study of the morphological signs in Amazonia showing the effect of slope in
the downhill mass movement of soil and deformation of soil horizons. Drawn based on the
diagram given by Dubroeucq and Volkoff (1998, p. 253). In black, white and dotted, the soil
horizons. Hatched, the rock.
At times the structure on the slope is linked to variation in the
parent material factor. For example, marls capped by hard limestone.
Theoretically this is not a catena because there is no genetic relationship
between the stony soils of the upper slope and the clay soils of the
bottom. Actually the pebbles slide down the slope so easily that the
two kinds of soils are not totally independent. Such arrangements on
the slopes can be grouped under the generic term
toposequences
. These
sequences, seen as the topographically ordered assemblage of soils
and sometimes of natural vegetation and crops, often characterize a
landscape type.
In the mountains, at the hillside scale, the climate often induces
differentiation of soils. These are
climatosequences (climosequences)
. They
are present all over the world, particularly on acid or volcanic rocks
(granites, gneisses, basalts, etc.). Actually these rocks constitute the
Structures indirectly related to the slope
