TY - JOUR
T1 - The evolution of a chloride sedimentary sequence-simulated evaporation of the Dead Sea
AU - Krumgalz, Boris S.
AU - Magdal, Ella
AU - Starinsky, Abraham
PY - 2002
Y1 - 2002
N2 - Calcium chloride brines, ([Ca2+] > [HCO3-] + [SO42-]), which were formed by alteration of evaporated seawater, are typical of subsurface waters. Very few lakes with such a composition exist today on Earth. Among those, the Dead Sea is the largest and most famous. The group of ancient potash MgSO4-poor evaporites, which is characterized by the mineralogical assemblage of halite-sylvite-carnallite-tachyhydrite-bischofite-calcium chloride tetrahydrate, was formed by the evaporation of calcium chloride brines rather than that of normal seawater. Based on Pitzer's approach for predicting mineral solubility in concentrated electrolyte solutions, a simulated fractional evaporation model for the Dead Sea at 25 °C was developed. The changes of the concentrations of the major ions (Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Cl-, Br-, and SO42-), as well as water activity during evaporation were calculated up to an enrichment factor of 50.2. The simulated precipitation minerals at this range were mainly chlorides, such as halite, carnallite, bischofite, tachyhydrite, and calcium chloride tetrahydrate. Minor amounts of anhydrite, barite, and celestite were included in the column of the precipitates. A columnar section built exclusively of the above minerals shows the following sequence and amounts: (1) 11.6 m of halite with disseminated sulfates (anhydrite, barite, and celestite); (2) 11.2 m of a mixture of carnallite (84%) and halite (16%): (3) 50.6 m of bischofite: (4) 5.4 m of tachyhydrite; (5) 8.6 m of a mixture of calcium chloride tetrahydrate (66%) and tachyhydrite (34%). Since evaporation can exist only when the water activity of brine is greater than the water activity of overlying air (relative humidity), the knowledge of the latter enables us to calculate the maximum paleohumidities of the evaporative environments. Based on water activity of brine data for primary late potash evaporites (tachyhydrite and bischofite) in the Dead Sea brine, it can be concluded that a series of climatic changes took place at the Aptian age in the supercontinent of Pangea. The atmosphere relative humidities in the deposition area (the present Brazil and Congo) are estimated to be extremely dry (down to ∼17.6%).
AB - Calcium chloride brines, ([Ca2+] > [HCO3-] + [SO42-]), which were formed by alteration of evaporated seawater, are typical of subsurface waters. Very few lakes with such a composition exist today on Earth. Among those, the Dead Sea is the largest and most famous. The group of ancient potash MgSO4-poor evaporites, which is characterized by the mineralogical assemblage of halite-sylvite-carnallite-tachyhydrite-bischofite-calcium chloride tetrahydrate, was formed by the evaporation of calcium chloride brines rather than that of normal seawater. Based on Pitzer's approach for predicting mineral solubility in concentrated electrolyte solutions, a simulated fractional evaporation model for the Dead Sea at 25 °C was developed. The changes of the concentrations of the major ions (Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Cl-, Br-, and SO42-), as well as water activity during evaporation were calculated up to an enrichment factor of 50.2. The simulated precipitation minerals at this range were mainly chlorides, such as halite, carnallite, bischofite, tachyhydrite, and calcium chloride tetrahydrate. Minor amounts of anhydrite, barite, and celestite were included in the column of the precipitates. A columnar section built exclusively of the above minerals shows the following sequence and amounts: (1) 11.6 m of halite with disseminated sulfates (anhydrite, barite, and celestite); (2) 11.2 m of a mixture of carnallite (84%) and halite (16%): (3) 50.6 m of bischofite: (4) 5.4 m of tachyhydrite; (5) 8.6 m of a mixture of calcium chloride tetrahydrate (66%) and tachyhydrite (34%). Since evaporation can exist only when the water activity of brine is greater than the water activity of overlying air (relative humidity), the knowledge of the latter enables us to calculate the maximum paleohumidities of the evaporative environments. Based on water activity of brine data for primary late potash evaporites (tachyhydrite and bischofite) in the Dead Sea brine, it can be concluded that a series of climatic changes took place at the Aptian age in the supercontinent of Pangea. The atmosphere relative humidities in the deposition area (the present Brazil and Congo) are estimated to be extremely dry (down to ∼17.6%).
UR - http://www.scopus.com/inward/record.url?scp=0038709465&partnerID=8YFLogxK
U2 - 10.1560/EL8J-PVU9-EH88-M083
DO - 10.1560/EL8J-PVU9-EH88-M083
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AN - SCOPUS:0038709465
SN - 0021-2164
VL - 51
SP - 253
EP - 267
JO - Israel Journal of Earth Sciences
JF - Israel Journal of Earth Sciences
IS - 3-4
ER -