The sedimentology of the Dead Sea

Abstract

The Dead Sea, one of the most saline lakes in the world, has recently (1979) undergone a major change in its hydrologic regime resulting in the mixing of its once stable meromictis. Prior to, and during this change, a sedimentologic study was undertaken to document the types of sediments in the Dead Sea, covering the entire western half of the lake, to refine ideas on the formation of the evaporite sediments and to explain the distribution of sediments in the Dead Sea. Study of the mineralogy and particle-size distribution of sediments of the Dead Sea reveals that, of the primary minerals, gypsum concentrates in the coarse silt and sand-size fractions whereas aragonite falls in the clay and fine silt fractions. The predominant sediment is a clayey silt. The constituents of the bottom sediments fall into two groups: (1) particles of detrital or recycled rocks (limestone, quartz and clay minerals), and (2) crystals of minerals precipitated in surface waters (aragonite, gypsum, and halite). Aragonite concentrations are low in bottom sediments of the northern Dead Sea and increase southward. Gypsum occurs in bottom sediments from all water depths. This distribution shows that the rate of sulfate reduction does not keep pace with the rate of sulfate precipitation. Halite was found in the southern part of the northern basin. The areal distribution of primary minerals is a result of several processes. High concentrations reflect either periods of restricted circulation in certain areas, leading to massive precipitation, or high influx of saturated brines, leading to precipitation. By contrast, low concentrations reflect high input of detrital particles or periods of minor influx of highly saturated brine. The lack of large concentrations of evaporite minerals reflects: (1) the abundant supply of detrital particles being carried into the Dead Sea that lower the relative contribution of evaporite minerals; (2) dilution of surface waters by fresh water, and (3) the low values of HCO 3- and SO 4= in Dead Sea waters. © 1987 Springer.