TEMPERATURE SEASONALITY CONTROL OVER MODERN HALITE LAYERS IN THE DEAD SEA: IN SITU OBSERVATIONS AND IMLICATIONS TO PALEOHYDROLOGY AND PALEOCLIMATOLOGY

Layered halite sequences have accummulated in deep basins throughout the geological record. Analogs for such sequences, however, are studied in shallow environments. We present here active precipitation of halite layers from the hypersaline Dead Sea, the only existing modern, deep, halite-precipitating basin. In-situ measurements in the Dead Sea link seasonal thermohaline stratification, halite saturation, and forms of coevally forming halite layers. The monthly spatiotemporal halite precipitation in the lake is characterized by lake thermohaline stratification (temperature, salinity, and density), degree of halite saturation, and direct, under-water observations of textural evolution of depositing halite. We present the relationships between grain size, consolidation, and roughness of layered halite deposits and degree of saturation, reflecting the limnology and hydroclimatology. The lake floor is divided into a deep, hypolimnetic, and a shallow, epilimnetic lake floors. In the hypolimnetic lake floor, halite continuously precipitates throughout the year with distinct seasonal variations. In summer, consolidated coarse halite crystals form rough surfaces under slight supersaturation. In winter, unconsolidated, fine halite crystals form smooth lake floor under high supersaturation. This explains seasonal alternation of halite crystallization and crystal morphological changes in deep basins layered halite sequences. The shallow epilimnetic lake floor is strongly controlled by its seasonal temperature variations, imposing intensive summer dissolution of most of previous winter (and earlier leftovers) halite. This results in thin (or even zero thickness) sequences with annual unconformities. This emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers. Furthermore, precipitation of halite on the hypolimnetic floor, at the expense of the summer dissolution of the epilimnetic floor, results in large lateral focusing, drastic thickening of halite deposits in the deep basin, and thinning of the deposits in shallow marginal basins. These observations explain better the large thickness of layered halite sequences in many past deep basins; thick halite cannot be directly used in calculating negative hydrological balance.