Boron isotopes in Heletz-Kokhav oilfield brines, the Coastal Plain, Israel

Boron isotope composition and elemental boron have been determined by negative thermal ionization mass spectrometry techniques in oil field brines from the Mediterranean Coastal Plain of Israel. The brines are classified into two groups: 1) The Heletz brines, associated with oil, from the Lower Cretaceous Heletz Formation; 2) The Mavqi'im brines from the Upper Miocene Mavqi'im formation. Both brine groups are characterized by marine Na/Cl and Br/Cl ratios, a Ca-chloride composition, and a high B/Cl ratio relative to those of modern seawater. It is suggested that these brines originated from evaporated Mediterranean seawater during the Messinian desiccation event and were trapped in the permeable Upper Miocene clastics and carbonates and in the Lower Cretaceous sandstones and dolomites. The high B/Cl ratios and the low δ¹¹B signature suggest that the original Messinian seawater was modified by diagenetic desorption processes. The relatively lower B/Cl ratios and higher δ¹¹B values of the Heletz oil brines suggest further modification and water-rock interactions such as adsorption onto clay minerals. -from Authors