The geological history of Pliocene-Pleistocene evaporites in Mount Sedom (Israel) and how strontium and sulfur isotopes relate to their origin

Evaporites, comprising of gypsum, anhydrite and halite are described from t he Pliocene Sedom Formation, the Caprocks units and the Pleistocene 'Amora Formation in Mount Sedom, Southern Jordan Valley, Israel. Strontium and sul fur isotopic compositions of the evaporite minerals, and their Sr/Ca and Br /Cl ratios were used to interpret their environments of deposition and proc esses of formation and diagenesis. Some of the evaporites of the Sedom Form ation were deposited from evaporated seawater. Others were deposited from a mixture of seawater and brines. The brines were composed of seawater which penetrated the carbonate rocks of the Rift margins, participated in dolomi tization processes and, when hydrologic conditions allowed, seeped out into the Sedom basin and were mixed with evaporated seawater. These processes y ielded non-homogeneous fluid masses of mixtures, as indicated by their wide range of Sr-87/Sr-86 ratios (0.70824 - 0.70905) as compared to the narrow Sr/Ca ratios of the derived evaporites. Their marine origin is indicated by their delta S-34 values which are around 20 parts per thousand. The evapor ites of the 'Amora Formation were precipitated from Ca-chloride brines only , which were originally evaporated seawater trapped in the Rift walls in th e "Sedom Formation times", returning to the Sedom basin after its disconnec tion from the sea. The high Sr content and Sr/Ca ratios indicate that the a nhydrites existing today in the Sedom and 'Amora formations were originally deposited from the evaporated seawater as gypsum which was later recrystal lized at depth, at high pressures and temperatures. The caprocks are residu al rocks of marine origin, formed by the dissolution of the exposed rock-sa lt units in the Sedom Formation. They represent mainly the gypsum (or anhyd rite) beds intercalated in the rock-salt units of the Sedom Formation in Mo unt Sedom rather than Ca-sulfates disseminated in the halites.