Temperature seasonality control on modern halite layers in the Dead Sea: In situ observations

Abstract

Layered halite sequences are found in deep basins throughout the geological record. However, analogs for such sequences are commonly studied in shallow environments. Here, we studied active precipitation of halite layers from the only modern analog for deep, halite-precipitating basins, the hypersaline Dead Sea. In situ observations in the Dead Sea link seasonal thermohaline stratification, halite saturation, and the characteristics of the actively forming halite layers. The spatiotemporal evolution of halite precipitation in the Dead Sea was characterized by means of monthly observations of (1) lake thermohaline stratification (temperature, salinity, and density), (2) degree of halite saturation, and (3) textural evolution of the active halite deposits. We present the observed relationships between the textural characteristics of layered halite deposits (i.e., grain size, consolidation, and roughness) and the degree of saturation, which in turn reflects the limnology and hydroclimatology. The lake floor is divided into two principal environments: a deep, hypolimnetic lake floor and a shallow, epilimnetic lake floor. In the deeper hypolimnetic lake floor, halite continuously precipitates with seasonal variations: (1) During summer, consolidated coarse halite crystals form rough surfaces under slight supersaturation. (2) During winter, unconsolidated, fine halite crystals form smooth lake floor deposits under high supersaturation. These observations support interpretations of the seasonal alternation of halite crystallization mechanisms. The shallow epilimnetic lake floor is highly influenced by the seasonal temperature variations, and by intensive summer dissolution of part of the previous year’s halite deposit, which results in thin sequences with annual unconformities. This emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers. In addition, precipitation of halite on the hypolimnetic floor, at the expense of the dissolution of the epilimnetic floor, results in lateral focusing and thickening of halite deposits in the deeper part of the basin and thinning of the deposits in shallow marginal basins.