Ca-chloride brines at common outlets of the Bet Shean-Harod multiple-aquifer system, Israel

Abstract

The Bet Shean and Harod Valleys are regional recipients and mixing zones for groundwaters draining into them from a multiple-aquifer system, which includes carbonate and basalt aquifers and deep-seated reservoirs of brine. The outlets of the three aquifers are located at the mountain border separating the valleys from the Gilboa and Ramot Issakhar Mts. The aquifers drain through two types of outlets — unique and common. The latter type is mainly conditioned by the occurrence of fault blocks acting as connecting media between the aquifers. Upon reaching the interconnecting zones, fresh groundwater flowing from carbonate and basalt aquifers intermix, losing their hydrochemical identities. Ca-chloride brines originating from deep-seated and confined reservoirs, leak along the deep-seated faults characterizing the common outlet zones and contaminate the relatively fresh mixing products originating from the three regional aquifers. Two types of dilute Ca-chloride brines were identified in the study area. The Devora type is a hot and hypersaline source brine which was identified at great depth and under very high hydrostatic pressures. This brine could be the residual product of seawater that evaporated during the Cambrian-Cretaceous continental interval and subsequent prolonged interaction with surrounding carbonate rocks. The Neve Ur-type brine seems to be genetically related to the Neogene inland Sdom Sea that preceeded the contemporary Dead Sea.