Paper No. 123-4
Presentation Time: 9:00 AM-6:30 PM
PETROGRAPHY OF MODERN DEAD SEA SEASONAL HALITES WITH IMPLICATIONS TO ANCIENT HALITE SEQUENCES
Seasonal limnologic and environmental controls over the modern accumulation of halite layers in the deep hypersaline Dead Sea and their relations with the thermohaline stratification were determined by direct, in situ observations and measurements. These observations established the spatiotemporal dynamics of halite deposition pointing to a new paradigm for evolution of deep, hypersaline halite depositing basins in the geological record. Here we add systematic sedimentological and petrographic analyses of these deep basin halites as a modern analog to ancient halite deposits. Newly exposed, ~2-m-thick, post-1980 halite sequences accumulated under monitored hydroclimatic conditions during ~30 m of lake level decline. We analyzed the petrography of the sequence on a sub-crystal scale by thin sections, emphasizing recognition of season-dependent textures and indicators of depth, which is known also independently from lake level measurements. The petrographic features of the halite are then associated with high-resolution environmental processes/events/parameters assuming that they control their formation. The chronology of the sequence is based on four recognized surfaces of known age using the monitored environmental history of the lake. The bottom of the sequence is composed of summer-winter couplets with clear hypolimnetic deposition. The summer layers diminish up-section, reflecting epilimnetic deposition as a result of the lake level fall, and elevating of the sequence to the epilimnion. Earlier studies have shown that in the epilimnion the halite is dissolved during the summer. Ripple marks indicate halite deposition at depths shallower than wave base. The halite petrography demonstrates up-section shallowing of water depth. Thin detrital laminae reflect paleofloods adding to the environmental analysis. The combined petrography and monitored conditions during level decline are recorded by halite deposits, assisting in revealing level trends, water column characteristics and paleo-hydrological aspects in halite sequences.