664
Climatic Geomorphology
Figure 25.19. Small trench excavated in the boundary of the sebkha E1Melah. The base corresponds to
gray rhythmic sediments and the top consists of a fine sand level, Zarzis, southern Tunisia.
fluvial basins that supplied the paleolake. Any important variation that modifies the water
discharge can be incorrectly interpreted as a climate change.
The study of the stratigraphic record of a lacustrine depression provides relevant data to
know its history (Figure 15.19). Geomorphologic, sedimentologic, mineralogic,
geochemical, paleontologic and palynologic research provide keys for obtaining suitable
paleo-environmental information on the different events through which the lacustrine
system has undergone (Figure 25.20).
Lake expansions are due to a rise in precipitation or to a fall in temperature that
produces a decrease in evapotranspiration. These circumstances correspond to the old
concept of the pluvial period or lacustrine phase (Rognon, 1980). Nevertheless,
conclusions obtained do not have the same verisimilitude that conclusions do based on
the analysis of dune systems, because the relationship between precipitation and lake
levels get complicated because of the temperature and other nonclimatic factors (Goudie,
1992). Some lakes, as with those related to the Rift Valley in eastern Africa (Figure 25.21),
have a marked tectonism during the Quaternary, which can modify the geometry and
capacity of the lake. Similarly, volcanic activity, mainly effusive, produces very
pronounced modifications. Despite these circumstances, works carried out by numerous
authors on lakes in eastern Africa and the southern Sahara indicate that they are excellent
paleoclimatic indicators (Figure 25.22). In the deserts on shields and platforms (Mabbutt,
1977) large lakes develop in shallow structural depressions during relatively wet periods.
Lake Chad is the largest known endorheic basin (Figure 25.23), whose boundaries are on
the Guinea ridge, Congo watershed and in the massifs of central Sahara. This lake has been
studied by many researchers (Barbeu, 1961; Grove and Warren, 1968; Pias, 1970; Servant
Climatic Geomorphology
Figure 25.19. Small trench excavated in the boundary of the sebkha E1Melah. The base corresponds to
gray rhythmic sediments and the top consists of a fine sand level, Zarzis, southern Tunisia.
fluvial basins that supplied the paleolake. Any important variation that modifies the water
discharge can be incorrectly interpreted as a climate change.
The study of the stratigraphic record of a lacustrine depression provides relevant data to
know its history (Figure 15.19). Geomorphologic, sedimentologic, mineralogic,
geochemical, paleontologic and palynologic research provide keys for obtaining suitable
paleo-environmental information on the different events through which the lacustrine
system has undergone (Figure 25.20).
Lake expansions are due to a rise in precipitation or to a fall in temperature that
produces a decrease in evapotranspiration. These circumstances correspond to the old
concept of the pluvial period or lacustrine phase (Rognon, 1980). Nevertheless,
conclusions obtained do not have the same verisimilitude that conclusions do based on
the analysis of dune systems, because the relationship between precipitation and lake
levels get complicated because of the temperature and other nonclimatic factors (Goudie,
1992). Some lakes, as with those related to the Rift Valley in eastern Africa (Figure 25.21),
have a marked tectonism during the Quaternary, which can modify the geometry and
capacity of the lake. Similarly, volcanic activity, mainly effusive, produces very
pronounced modifications. Despite these circumstances, works carried out by numerous
authors on lakes in eastern Africa and the southern Sahara indicate that they are excellent
paleoclimatic indicators (Figure 25.22). In the deserts on shields and platforms (Mabbutt,
1977) large lakes develop in shallow structural depressions during relatively wet periods.
Lake Chad is the largest known endorheic basin (Figure 25.23), whose boundaries are on
the Guinea ridge, Congo watershed and in the massifs of central Sahara. This lake has been
studied by many researchers (Barbeu, 1961; Grove and Warren, 1968; Pias, 1970; Servant