Sedimentological characteristics and geochemical evolution of Nabq sabkha, Gulf of Aqaba, Sinai, Egypt

Abstract

Nabq sabkha exists 16 km north of Sharm El Sheikh City occupying the low land topography in the alluvial fan zone along the coastal area, Gulf of Aqaba, Sinai, Egypt. The long axis of the sabkha trends NW–SE receiving water from two different sources: meteoric water drained from the surrounding mountainous area and seawater seepage. Field observations help to divide the area into raised beach, hill slopes, sabkha basin, and coastal area. The sabkha basin can be subdivided from its center outward into (1) basin center hypersaline lake flourished with microbial mat and precipitation of halite as rafts, cumulates, and chevrons, (2) saturated saline sand and/or mud flat zone with the extensive growth of gypsum and halite crystals growing displacively as well as different forms of petee structures, and (3) an elevated marginal dry zone with tepee structures. Mineralogical analysis reveals that quartz, halite, and gypsum are the dominant minerals with subordinate amount of aragonite, anhydrite, thenardite, and/or polyhalite. In addition, clay minerals in the mudflat zone are presented by illite and smectite, indicating derivation of soil from the surrounding basement rocks. Chemical analysis of the collected brine samples reveals alkali character in the saline lake (pH = 7.6) and high concentrations of Na+ (680 meq/l), Cl− (940 meq/l), Mg2+ (208 meq/l), Ca2+ (70 meq/l), SO42+ (30 meq/l), and HCO3− (6 meq/l). The high salinity values are due to the aridity of the area, which favors precipitation of halite. Using comparative sedimentological, chemical, and mineralogial methods between such modern and ancient evaporitic environments and by detailed field, petrographic and mineralogical studies of modern evaporite environments help to interpret paleo-depositional environments of ancient evaporites sequences still in debate.