Science et changements planétaires / Sécheresse


Origin and distribution of salt in the Senegal river valley (Senegal-Mauritania) Volume 12, issue 4, Décembre 2001


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Faculté des sciences et techniques de Nouakchott, BP 5026, Mauritanie.
  • Page(s) : 251-7
  • Published in: 2002

In the middle valley of the Senegal river, saline areas exhibit a large variability in the chemical profile of salinity, over a small distance. Morphological and geochemical condiderations allow us to attribute these saline areas to former clay dunes. They developped under similar environmental conditions to those observed today in the delta, where clay dunes formation is still under way. These clay dunes are the result of aeolian deflation on saline pans, more or less acid, depending on the development of a former mangrove vegetation. Two contrasted pans (neutral and acid) are studied in order to characterise the main geochemical features and the salt precipitation sequence. In the acid environment, the salt precipitation sequence is the following: gypsum > thenardite > halite. By contrast, in the neutral pan, the salt precipitation sequence is calcite > gypsum > halite. This difference in the salt precipitation sequence is not sufficient to explain the morphological and geochemical features of saline areas located upstream in the middle valley. Two origins for salt accumulation are proposed: one is aeolian deflation, and the other, the dissolution of shells banks under acid conditions.