Natural tracers in Senonian–Eocene formations for detecting interconnection between aquifers

Relatively high concentrations of dissolved bio-Barium and bio-silica in groundwater in Paleocene–Eocene carbonate aquifers caused by the Paleocene–Eocene thermal maximum are proposed as tracers for delineating zones of leakage into adjacent aquifers. In fresh, oxidized and not thermal groundwater (within a narrow range of temperatures) these tracers can be considered as conservative. In addition, certain trace elements (U, Mo, Se and Tl) of phosphates widespread in Senonian carbonate strata are suggested to serve as tracers of water originating from these sediments. The locally increased concentrations of these trace elements in groundwater of a carbonate aquifer underlying the Senonian strata were also proposed as tracers of water leakage from above. The proposed tracers of water in Eocene and Senonian strata have been used for delineating zones of local leakage into the underlying Turonian aquifer in the Yarkon-Taninim basin (YTB) of Israel. Results of geochemical survey of 208 wells in the Turonian aquifer of the YTB were used for Pearson’s correlation and Principal Component Analysis (PCA) for detection of interconnection zones. PCA revealed 4 factors explaining up to 86% of variance in groundwater chemistry in the Turonian carbonate aquifer. Two factors, first – with high loadings of Ba and SiO2, and second – with high loadings of U, Mo, Se and Tl, were interpreted to be related to local groundwater leakage from Eocene strata into the Turonian aquifer, fast and slow, respectively. Mapping of these two factors enabled delineation of areas where local inflow of water from the Eocene aquitard exists.