696
Climatic Geomorphology
Catarina states in Brazil. The authors pointed out that the margins of the valleys are
terraced due to an alternation of dry stages, in which pediments are formed, and humid
stages in which weathering and incision predominate (Figure 25.46). Dry phases
corresponded to glacial periods, whereas wet ones can be correlated with interglacial
stages.
2.3.4. Aeolian action
Aeolian accumulations and landforms generated by deflation in the humid tropics are
excellent indicators of the occurrence of ancient arid stages. Most works on this field have
been carried out in central-southern Africa and in northern and central South America.
In southwestern Africa the aridity is controlled by the cold current of Benguela, which
reached its highest energy during the glacial periods, producing more aridity. It is stated
also that this current produced the drift toward north in the Angola basin, as the cores from
deep Atlantic Ocean confirm. Therefore, the ideas of De Ploey (1965) are reaffirmed,
regarding the aeolian sands of the Kalahari in the western Congo (Figure 25.47). This
extension can be probably explained by the expansion of the Benguela current (Selby et al.,
1979).
The work by Tricart (1985) is a good state-of-the-art review of the information about
dry climates in the centre and north of South America. In the margin of the Llanos del
Orinoco (Orinoco Plains) extensive dune fields have been described (Tricart, 1974a). In
Landsat images it is observed that in those areas are formed by longitudinal dunes with a
NE-SW direction, parabolic dunes also occur. These aeolian accumulations come from
the alluvial cover deposited by piedmont Andean rivers. Their age can be related with the
last glacial period, in which a glacioeustatic lowering occurred. During the Holocene the
climate was warmer and more humid. Dunes have been fossilized by alluvium and become
flooded in rainy epochs. Dunes and landforms produced by deflation, which are partially
fossilized by sediments corresponding to the Flandrian transgression, can be also
recognized near the Orinoco Delta (Tricart and Alfonsi, 1981).
The depression of the Mato Grosso marsh of southwestern Brazil, where current
precipitation is about 1200 mm, have many big alluvial fans coming from Paleozoic
mountains. These landforms seem to indicate a period of dry climate, with scarce
vegetation and dune formation. In the fan Taquari, the greatest, it is possible to identify
deflation basins of up to 3 km diameter. At present, E1 Pantanal, as indicated by its name,
is flooded or colonized by marsh vegetation (Tricart, 1982).
Climatic Geomorphology
Catarina states in Brazil. The authors pointed out that the margins of the valleys are
terraced due to an alternation of dry stages, in which pediments are formed, and humid
stages in which weathering and incision predominate (Figure 25.46). Dry phases
corresponded to glacial periods, whereas wet ones can be correlated with interglacial
stages.
2.3.4. Aeolian action
Aeolian accumulations and landforms generated by deflation in the humid tropics are
excellent indicators of the occurrence of ancient arid stages. Most works on this field have
been carried out in central-southern Africa and in northern and central South America.
In southwestern Africa the aridity is controlled by the cold current of Benguela, which
reached its highest energy during the glacial periods, producing more aridity. It is stated
also that this current produced the drift toward north in the Angola basin, as the cores from
deep Atlantic Ocean confirm. Therefore, the ideas of De Ploey (1965) are reaffirmed,
regarding the aeolian sands of the Kalahari in the western Congo (Figure 25.47). This
extension can be probably explained by the expansion of the Benguela current (Selby et al.,
1979).
The work by Tricart (1985) is a good state-of-the-art review of the information about
dry climates in the centre and north of South America. In the margin of the Llanos del
Orinoco (Orinoco Plains) extensive dune fields have been described (Tricart, 1974a). In
Landsat images it is observed that in those areas are formed by longitudinal dunes with a
NE-SW direction, parabolic dunes also occur. These aeolian accumulations come from
the alluvial cover deposited by piedmont Andean rivers. Their age can be related with the
last glacial period, in which a glacioeustatic lowering occurred. During the Holocene the
climate was warmer and more humid. Dunes have been fossilized by alluvium and become
flooded in rainy epochs. Dunes and landforms produced by deflation, which are partially
fossilized by sediments corresponding to the Flandrian transgression, can be also
recognized near the Orinoco Delta (Tricart and Alfonsi, 1981).
The depression of the Mato Grosso marsh of southwestern Brazil, where current
precipitation is about 1200 mm, have many big alluvial fans coming from Paleozoic
mountains. These landforms seem to indicate a period of dry climate, with scarce
vegetation and dune formation. In the fan Taquari, the greatest, it is possible to identify
deflation basins of up to 3 km diameter. At present, E1 Pantanal, as indicated by its name,
is flooded or colonized by marsh vegetation (Tricart, 1982).