Chemical composition of brines in the Pliocene Dead Sea basin: A fluid inclusion study of halite

The fluid inclusions in sedimentary and diagenetic halite from the Sedom diapir have been studied in 12 rock salt specimens composed of halite (97%), anhydrite (2%), and terrigenous material (1%). Bromine content of the rocks varies from 0.010 to 0.021%. Brine inclusions in sedimentary halite are characterized by low concentrations of sulfate ions. Major ions (in g/l) are: potassium-16.7 to 45.1: magnesium-61.5 to 77.6; sulfate ion-5.8 to 17.4; calcium-0.5 to 0.7. Sylvite daughter-crystals are typical for these inclusions. Fluid inclusion homogenization temperatures vary from 46 to 57 °C and the value of gas-saturation of solutions is very low (about 1 ml/l). The results provide evidence for the possible precipitation of sylvite in a shallow Pliocene basin whose waters were heated up to 60 °C. The inclusions in diagenetic halite are liquid, with a gas phase, and sometimes daughter-crystals of sylvite. The major ion composition (in g/l) of solutions is: potassium-12.5 to 22.7; magnesium-51.8 to 75.7; calcium-0.7 to 0.9; sulfate ion-4.1 to 26.8. CaCl₂ was not found. The fluid inclusion homogenization temperatures varied from 52 to 73 °C. The study shows that the original seawaters of Na-K-Mg-SO₄-Cl composition changed their chemical type to Na-K-Mg-Ca-Cl-SO₄ composition already at the stage of halite precipitation. Hydrothermal interaction between seawater and hot basalt in the late Pliocene-early Pleistocene basin is considered to be the process responsible for the metamorphosis of marine waters.