Origin and geochemical reaction paths of sabkha brines: Sabkha Jayb Uwayyid, eastern Saudi Arabia |
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| Authors: | Nasser A Alsaaran |
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| Institution: | (1) Department of Geography, College of Arts, King Saud University, P.O. Box 2456, Riyadh, 11451, Saudi Arabia |
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| Abstract: | Sabkhas are ubiquitous geomorphic features in eastern Saudi Arabia. Seven brine samples were taken from Sabkha Jayb Uwayyid
in eastern Saudi Arabia. Brine chemistry, saturation state with respect to carbonate and evaporate minerals, and evaporation-driven
geochemical reaction paths were investigated to delineate the origin of brines and the evolution of both brine chemistry and
sabkha mineralogy. The average total dissolved solids in the sabkha brines is 243 g/l. The order of cation dominance is Na+ >> Mg2+ >> Ca2+>K+, while anion dominance is Cl− >> SO4
2− >> HCO3
−. Based on the chemical divide principle and observed ion ratios, it was concluded that sabkha brines have evolved from deep
groundwater rather than from direct rainfall, runoff from the surroundings, or inflow of shallow groundwater. Aqueous speciation
simulations show that: (1) all seven brines are supersaturated with respect to calcite, dolomite, and magnesite and undersaturated
with respect to halite; (2) three brines are undersaturated with respect to both gypsum and anhydrite, while three brines
are supersaturated with respect to both minerals; (3) anhydrite is a more stable solid phase than gypsum in four brines. Evaporation
factors required to bring the brines to the halite phase boundary ranged from 1.016 to 4.53. All reaction paths to the halite
phase boundary follow the neutral path as CO2 is degassed and dolomite precipitates from the brines. On average, a sabkha brine containing 1 kg of H2O precipitates 7.6 g of minerals along the reaction path to the halite phase boundary, of which 52% is anhydrite, 35.3% is
gypsum, and 12.7% is dolomite. Bicarbonate is the limiting factor of dolomite precipitation, and sulfate is the limiting factor
of gypsum and anhydrite precipitation from sabkha brines. |
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| Keywords: | Brines Sabkha Geochemistry Reaction paths Evaporites Saudi Arabia |
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