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Climatic Geomorphology
Three types can be differentiated on the basis of their structure and stratigraphic
position (Watson, 1979). The first type is horizontally stratified crust containing 50 to
80% gypsum. The second is subsurface crust, formed of either large, lenticular crystals
1 to 0.5 m in diameter, commonly known as desert rose, or mesocrystalline material with
0.05 to 1 mm diameter crystals. They can reach up to 5 m in thickness and have a gypsum
content of 50 to 70%. The third type is the surface crust, which basically consists of
alabaster gypsum with crystals of less than 0.05 mm, occurring in columnar form on a
scale of 1 to 2 m, or as loose, dusty deposits. They contain approximately 90% gypsum.
Gypsum crusts can be differentiated on the basis of their generation via capillary rise
and evaporation of sulphate-rich waters, or per descensum through gypsum-rich aeolian
dust (Watson, 1985; Heine and Walter, 1996). These authors state that Tunisian dust
originates primarily from the sebkhas, and that dust in the Namib Desert originates from
coastal clouds. The nonpedogenic gypsum scale model is based on the precipitation of
gypsum in subterranean waters and lacustrine environments.
Climatic Geomorphology
Three types can be differentiated on the basis of their structure and stratigraphic
position (Watson, 1979). The first type is horizontally stratified crust containing 50 to
80% gypsum. The second is subsurface crust, formed of either large, lenticular crystals
1 to 0.5 m in diameter, commonly known as desert rose, or mesocrystalline material with
0.05 to 1 mm diameter crystals. They can reach up to 5 m in thickness and have a gypsum
content of 50 to 70%. The third type is the surface crust, which basically consists of
alabaster gypsum with crystals of less than 0.05 mm, occurring in columnar form on a
scale of 1 to 2 m, or as loose, dusty deposits. They contain approximately 90% gypsum.
Gypsum crusts can be differentiated on the basis of their generation via capillary rise
and evaporation of sulphate-rich waters, or per descensum through gypsum-rich aeolian
dust (Watson, 1985; Heine and Walter, 1996). These authors state that Tunisian dust
originates primarily from the sebkhas, and that dust in the Namib Desert originates from
coastal clouds. The nonpedogenic gypsum scale model is based on the precipitation of
gypsum in subterranean waters and lacustrine environments.