Strontium isotopes in discordant dolomite bodies of the Judea Group, Dead Sea basin

The dolomitization of the Upper Cretaceous limestones of the Judea Group by seawater of the Sedom lagoon is reflected by the chemical and ⁸⁷Sr/⁸⁶Sr isotope composition of discordant dolomite bodies, which are formed at the expense of the limestone. We have carried out a traverse through a discordant dolomite body in the Turonian limestone (Netzer Fm.), Nahal Boqeq. southern Judea Desert at the elevation of 80 m above MSL. The host limestone is characterized by ⁸⁷Sr/⁸⁶Sr ratios of 0.7074-0.7076 typical of the Cenomanian-Turonian ocean. The discordant dolomite exhibits significantly higher ⁸⁷Sr/⁸⁶Sr ratios, in the range of 0.7082 to 0.7086. Evaporitic minerals from the Sedom Fm. display ⁸⁷Sr/⁸⁶Sr ratios similar to those in the discordant dolomite. It is suggested that these minerals precipitated from Ca-chloride brines that were produced via dolomitization of the Cretaceous limestone by the Sedom lagoon water. The similarity between the ⁸⁷Sr/⁸⁶Sr ratios in the Sedom Fm. minerals and the discordant dolomite bodies supports earlier conclusions about the close relationship between the dolomite and the Sedom lagoon brines. The wide ⁸⁷Sr/⁸⁶Sr ratio range in the dolomite bodies studied, relative to its much narrower range in stratigraphic dolomite of the Sedom Fm., testifies that the Ca-chloride brines that were the late dolomitization agents did not return to the Rift Valley, but may have migrated further to the west.