Plant-controlled supratidal anhydrite from Al-Khiran, Kuwait
We report here that in the supratidal zone of the Al-Khiran sabkha, diagenetic anhydrite occurs exclusively in association with the living halophyte Halocnemum strobilaceum (Pallas) M .B. This anhydrite has a hair cream-like consistency and the bulk of it has formed as pseudomorphs after gypsum crystals. On the death of the plant at the end of its life cycle, the anhydrite is hydrated back to gypsum. This two-way transformation results in a series of characteristic textures, whose preservation could be due to the comparative ‘youth’ of the sabkha, which is in the very earliest stages of evaporite diagenesis.
Major evaporite deposition from groundwater remobilized salts
The coastal sabkhas of the western Gulf of Sirte, Libya developed in two stages behind a barrier-ridge complex following the penultimate and the last major sea-level rises. A strong north-to-south littoral drift led to the isolation of coastal lagoons by a seaward sand ridge following the stabilization of sea level and produced isolated basins in which evaporites have been and are depositing. A sulphur isotopic study of the groundwaters and sediments described here demonstrated that the brines mostly originated in continental groundwaters supplied from the deep aquifer by surface and sub-surface flows which carry sulphate and other ions remobilized from Cretaceous sediments.
ON THE SOLUBILITY OF ANHYDROUS CALCIUM SULPHATE AND OF GYPSUM IN CONCENTRATED SOLUTIONS OF SODIUM CHLORIDE AT 25 °C, 30 °C, 40 °C, AND 50 °C
The solubilities of anhydrous CaSO4 and CaSO4.2H2O in concentrated aqueous solutions of NaCl at a series of temperatures—25 °C, 30 °C, 40 °C, and 50 °C, have been determined. It was found that the transition temperature for the reactionwhich in pure water has a value of 42 °C, is shifted progressively to lower temperatures with increasing NaCl concentration. It was also found that the variation of the transition temperature with NaCl concentration could be adequately represented by the equationwhere ΔG, ΔH, and ΔS are the Gibbs free energy, enthalpy, and entropy of the reaction and P0 and P are the vapor pressures of pure water and the solution respectively at the absolute temperature T.