ABSTRACT
This study describes and interprets the primary deposition and diagenetic formation of the evaporite minerals gypsum, anhydrite and halite in the coastal and interdunal evaporation settings of sabkhas and saline pans in Egypt and Saudi Arabia. The high evaporation, low inflow of groundwater, rainfall, in addition to continental and marine floodings, and restriction of the evaporation settings allow the deposition of gypsum at salinities exceeding 120‰, anhydrite at 200‰–220‰ and halite >220‰. In the saline pans, gypsum and halite are precipitated freely from the brine column according to the brine salinity. Gypsum is deposited on the floor of saline pans as free, upward growing swallowtail, fibrous and rosette crystals, whereas halite crystallizes at the brine surface as rafts and cumulates, and on the floor of the pans as chevrons and cornets. In the sabkha areas, gypsum and anhydrite are formed by displacive, inclusive and replacive growth below the sediment surface of the sabkhas, whereas halite is precipitated as clear, mosaic cement and as efflorescent crystals between the sediment matrix grains. The saline pans are characterized by the deposition of ~30 cm thick gypsum and halite layers that may have thin laminae of microbial mats. The sabkhas are characterized by the occurrence of gypsum and anhydrite as nodules, enterolithic folds and random lenticular crystals, whereas halite occurs as cement and efflorescence. No recognized evaporite structures are specific to coastal or interdunal sabkhas and pans, except the occurrence of marine shells in the coastal evaporation settings and the dominance of clastic materials in the interdunal evaporation settings. Sinkholes are formed in the Red Sea and Arabian Gulf sabkhas due to the dissolution of underlying gypsum and/or halite layers by ascending, low-salinity groundwater and/or seawater seepage. The results of this chapter allow the recognition of the specific structures and textural characteristics of the sabkhas and saline pans that may help in the interpretation of similar features in the recent and ancient rock records.
