Hypersaline brine diagenesis and evolution in the Dead Sea-Lake Lisan system (Israel)

Abstract

Water soluble salts were extracted from 57 aragonite and detrital laminae, sampled from the Pleistocene Lake Lisan sediments. The solutions and solids were analysed for Ca, Mg, Na, K, Sr, Cl, SO 4 and bicarbonate. Average Na Cl , Mg Ca , Sr Ca , Mg Cl , Ca Cl , Sr Cl , K Cl , K Na , and K Mg ratios, calculated for seven stratigraphie elevations in the Lisan column, indicate that the Dead Sea Rift sediment brine system has remained practically closed for 70000 years. The soluble salts reflect both the hydrologie evolution of the lake as well as diagenetic processes. Mg Ca ratios systematically decrease in younger sediments, and this decline is accompanied by a 1.5–4 fold Sr enrichment in aragonite solubles relative to salts extracted from detrital laminae. The major process responsible for these observations is dolomitization of Sr-rich aragonite by interstitial brine. Diagenesis was triggered by slow desiccation of the lake's sediments after the Lisan waters started to recede due to a change in climate. Very sharp chemical gradients, which developed in the sediments after deposition, have been preserved because further diagenesis was quenched by the advancing dry-out. H 2 O-loss by evaporation induced difrusional migration of Na and Cl from aragonite laminae into adjacent detrital layers. This lowered the Na Cl ratio in the aragonite and raised it in the detritus relative to the initial (Dead Sea) Na Cl ratio of 0.26. The early Lisan brine was similar in its chemical composition and total salinity to that of the present Dead Sea.