Development of the dune field in the area of Douz (SE Margin of the Chott Jerid)

The article describes evolution of a dune field located in a vicinity of Douz on south-eastern margin of the Chott Jerid. The aim of the research was to assess the migration rate of dunes and to find determining factors. Between 1997 and 2000 location of selected dunes was measured every month. Textural features of dune sediments were analysed in order to determine dynamics of aeolian processes and a source of the sediment. The dunes, mostly barchans in a youthful stage of development, 1,5-2m high and 40 m wide, migrated generally in two directions: E and NE in spring and SW and W in autumn. In winter and in summer the migration rate was much lower which is explained by seasonal changes in wind direction and speed. The dunes migrated with an average rate of 80m/yr eastwards with a maximum rate of 40m/month and 2-3m/day. The dune sediment mostly consists of fine and very well to well sorted sand which testifies for a long-lasting aeolian process. A share of quartz, very resistant to mechanical abrasion, is high and a share of gypsum is low which is a result of multiple and long-lasting process of redeposition. This is also supported by an analysis of heavy minerals among which minerals highly resistant to mechanical abrasion dominate (mostly garnet and epidotes). Results of sedimentological analysis combined with a broad phypico-geographical view of the area allow to conclude that, the migration rate of the researched dunes is determined by textural features of dune sediments. Such a high migration rate, much higher comparing with other dune fields in the world, is an effect of finer and better sorted sand which can be easily transported by weaker winds