The concentrations and isotopic compositions of strontium of the noncarbonate fractions of sediment from a piston core taken in the median valley of the Red Sea have been determined. The results support the hypothesis that the silicate fraction of the sediment in this core is a two-component mixture. The observed 87Sr/86Sr ratios and Sr concentrations fit a hyperbolic curve that results from the mixing of volcanic-basaltic and terrigenous-sialic components. The Sr concentrations of these components were then derived by assuming reasonable values for the 87Sr/86Sr ratios. The concentration of the basaltic component in the sediment was calculated for each sample, using its observed Sr concentration. The variation of the abundance of volcanogenic material with depth in the core was used to define stratigraphic layers having either a normal, high, or low content of the volcanic component. The resulting Sr-isotope stratigraphy complements and refines the lithologic stratigraphy obtained by conventional means.

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