La Tunisie presaharienne: etude geomorphologique

The internal structure of spring mounds of Nefzaoua oasis in Tunisia: Formation of an original geomorphic structure

“…Gypsum clearly accumulated on top of the spring mounds (Figure 13 step 10). These accumulations were more than 50 cm thick in profiles A and D. They were indurated as a gypsum crust (Figure S8D), as described by Pouget (1968), Watson (1985Watson ( , 1988 and Stivaletta & Barbieri (2009) and may have resulted from two different accumulation processes: i. Leaching from aeolian sediments, as suggested by Coque (1962) to explain the alignment of mounds considered as fossil sand dunes.…”

“…The recharge zone is mainly the Dahar chain, with a west‐facing slope, followed by the Tebaga chain, with a south‐facing slope. As in many other regions with desertic artesian springs, low playas (in southern California (Scholl, 1960; Neal & Motts, 1967), endoreic basins or flat depressions (Ponder, 1986) (in western Egypt (Powell & Fensham, 2015)), the spring mounds of the Nefzaoua basin are located in flat areas and associated with artesian systems (Coque, 1962; Pouget, 1968). Some aligned micro springmounds were described by Essefi et al (2014), in the Sidi El Habi sebkha in the north east Tunisia as direct consequence of groundwater upwelling triggered by tectonics and hydraulics.…”

“…However, the accumulation of aeolian gypsum by deflation occurs only leeward at the footslope North of the Tebagha range (Drake, 1997). In our case the gypsum dunes described by Coque (1962) are not randomly distributed such as sand dunes where the crests are exposed to the wind and moving with time, but are restricted to the top of the discontinuous sets of spring mounds in relation with tectonic faults. They never show a classical barkhane sand dune shape visible in the Grand Erg Oriental South West of the Chott el Jerid.…”

“…These species can maintain the density of their structures after sand accumulates, in part by constantly renewing adventitious roots, which provide them with water from reserves in the accumulated sand. These plants are associated with nebkas , dunes in the process of forming, and are able to create sand hillocks up to 2 m tall called rebdou (Coque, 1962). The hillocks contain alternating layers of sand and organic matter under the plants.…”

“…Tunisia, the smallest country of the Maghreb, is split in its centre into northern and southern parts by a vast synclinal oriented east-west that is filled by a set of flat evaporitic playas called sebkha: Chott Fjej and Chott El Jerid (Figure 1B). In the north, the Atlas massif was formed during the Alpine orogenesis, while the southern part is located in the Saharan platform (Coque, 1962). The Nefzaoua province in south-western Tunisia corresponds to the governorate of Kebili.…”