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AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 4. (April)

First Page: 581

Last Page: 592

Title: Continental Sabkha in Arava Valley Between Dead Sea and Red Sea: Significance for Origin of Evaporites

Author(s): Abraham J. Amiel (2), Gerald M. Friedman (2)

Abstract:

The Yotvata Sabkha, a continental sabkha having an area 45 sq km, fills the entire Arava Valley, whose width is about 10 km. The climate is one of the most arid in the world. Short, ephemeral streams (wadis), prevented by alluvial fans from reaching the Gulf of Aqaba, provide water that seeps into the soil, thus keeping the water table close to the surface. The capillary fringe above this water table marks the floor of the sabkha. The sediments of the sabkha interfinger with alluvial fans that extend from the scarps which control the valley.

The sediments of the sabkha consist of sand, silt, and clay brought in by the wadis. Three distinct zones exist in the sabkha: (1) the central barren zone, (2) the transitional zone, and (3) the outer vegetated zone with halophytic vegetation. The central barren zone forms the core of the sabkha. Depths to groundwater range from 90 cm in the central barren zone to more than 3 m in the outer vegetated zone. Chlorinity values in the groundwater are highest in the central barren zone (up to >= 200^pmil) and decrease toward the transitional and outer vegetated zones (<10^pmil); a sharp drop occurs near the contact between the central barren zone and transitional zone. The sulfate concentration in the groundwater is greatest in the transitional zone and decreases both toward the cent al barren zone and the outer vegetated zone. The Mg/Ca ratio of the groundwater parallels the trend in the sulfate concentration. Gypsum is the principal authigenic mineral in the transitional and outer vegetated zones, whereas halite predominates in the central barren zone. Despite an intensive search, authigenic dolomite and anhydrite were not found.

The sediments of the sabkha with their interstitial authigenic minerals contrast sharply with the sediments of the Dead Sea and the Red Sea, including the Gulf of Aqaba, in which evaporite minerals do not floor the bottom of the seas. Although gypsum forms continuously across the surface of the Dead Sea, it is broken down to hydrogen sulfide below the wave-influenced zone by sulfate-reducing bacteria.

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