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... and in the shape of yardangs up to 10 m high, they are found in the dune depressions of the ergs framing the Ténéré to the South and East (cf. figure 3), as well as in the endorheïc depressions West of isolated plateaus or the plateau remnants of the eroded scarplands of the South-Central Sahara (Busche 1998). ...
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Palaeoecological studies of terminal Pleistocene and Holocene deposits in the Central Sahara allow some new insights of the palaeoenvironmental development of the vast Ténéré sand plain, Erg of Fachi-Bilma and Erg of Ténéré region of Central Sahara, NE-Niger. The environmental changes are deduced from geomorphological, sedimentological and biological remains as well as from palaeolimnological and prehistoric evidence. Comparing the lacustrine sediments, three stages of water bodies with different conditions can be distinguished. Topographical factors, geomorphological evidence and biological remains (e.g. Lates niloticus) suggest that from 11.5 ka cal BP onwards a widespread lacustrine landscape existed with perennial deep-water lakes changing in size, water level and water balance. Following a change between 7.5 ka cal BP and 6.8 ka cal BP in the northern and central parts of Ténéré, and 6.5 ka cal BP in the southern part of the region studied, desiccation of the by now shallow permanent freshwater lakes began, coinciding with the establishment of seasonal ponds characterized by low water level and high pH. From 6.0 ka cal BP onwards in the north and 5 ka cal BP onwards in the south a more swampy environment developed fi nally. Concerning the Early Holocene, and towards the Mid-Holocene, the fi ndings suggest an increasingly steep precipitation gradient from SW to NE as well as a more pronounced seasonality, indicating a weakening contact between the summer monsoon front and the westerlies.
The Messak Settafet is a wide plateau located in the Libyan central Sahara (SW Fezzan); it is cut into the Nubian sandstone and interpreted as relic of a Tertiary peneplain, heavily affected by aeolian deflation. Notwithstanding degradation phenomena, discontinuous, thin soil bodies are locally preserved below the hamada. Several profiles, located in correspondence of different geomorphological units (the hamada, the endorheic depressions, and the southern escarpment), were described and sampled for micropedological analyses. Micromorphology outlined that the main characteristics of the residual B horizons from each geomorphological units are (i) high concentration of ferruginous nodules, (ii) multiple generations of clay illuviation, (iii) fragmentation and deformation of textural pedofeatures, and (iv) calcite mobilization and redeposition. According to horizon macro- and micromorphological characteristics, these pedologic bodies do not seem to be in equilibrium with the present-day climatic conditions and should be regarded as paleosols generated by processes regulated by large water availability and warm temperature, such as rubification, clay translocation, and calcite redistribution. The development of horizons acted mainly since the Early/Middle Pleistocene during subsequent pluvial periods and was interrupted by several erosional and aeolian input phases (arid periods). Pedological processes ended at the onset of the severe dry environmental conditions at the Mid-Late Holocene transition. The development of this kind of paleosols in the central Sahara is also discussed in comparison with pedogenetic processes occurring in temperate regions during interglacial and interstadial intervals.
