AN EXAMPLE OF QUATERNARY SABKHA, NORTH
WESTERN EGYPTIAN BORDER
ESSAM M. ELKHORIBY
Geology Dept., Fac. Sciences, ElMansoura Univ., Egypt
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The continental sabkha deposits at Melfa and Ein Zahra areas, at NW Egyptian frontier, were deposited in salt pan, and calcareous mud and calcareous sand flat (sabkhas) subenvironments. The sequence of some sabkha profiles revealed several sedimentary cycles. Each sedimentary cycle includes alternative layers of gypsum and calcareous sand and clay.
Gypsum and halite are the main evaporite minerals deposited within the sabkha profiles with small amount of polyhalite and theordite. Gypsum is the major cementing material while halite is a summer precipitate in the ephemeral salt pan and in the uppermost part of the profiles. The evaporites have grown within calcareous sandy and clayey host sediments as displacive and inclusive halite crystals, and as displacive random arrangement of lenticular and prismatic gypsum crystals. The clay minerals of the sabkha sediments include kaolinite, illite and a subordinate amount of stevensite.
The upward increase in the concentration of the Na and Cl ions and the similarity in the chemical composition of both the surface and ground water in the study area indicate that the evaporative pumping mechanism or the ground water plays a significant role in the upward movement of brines and formation of the evaporite minerals under arid conditions.
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