Formation and evolution of efflorescent halite speleothems beneath tepee structures in the Red Sea coastal evaporation settings, Jeddah, Saudi Arabia

Abstract

This study documents the occurrence of efflorescent halite speleothems of stalactites, columns, flowstones, stalagmites and popcorns beneath tepee structures in the Red Sea coastal sabkhas, desiccated halite pond and dykes of saltworks, Jeddah, Saudi Arabia. The study aims to interpret the formation and evolution of efflorescent halite speleothems due to the high relative humidity of the area. Field work and petrographic study revealed that the speleothems form from nighttime dissolution of the tepee halite crusts due to deliquescence at high relative humidity (DRH > 75%) and condensation of capillary vapor moisture at low relative humidity (RH < 75%). Dripping and flowing of deliquescent and condensed saline waters from the underside of the tepee structures by gravity and/or capillary forces are subjected to rapid evaporation in the daytime to deposit efflorescent halite speleothems. The evolution of the different types of efflorescent halite speleothems is controlled by the amount of saline waters droplets and flowing from deliquescence and condensation, air flow below tepee structures, evaporation rate and dynamic nature of the tepee crusts. The tepee structures are resulted from thermal expansion and contraction, and crystallization pressure exerted from growth of clear, early diagenetic and efflorescent halite crystals between primary chevrons, cornets and cubes of the crusts. In brief, the tepee structures form a barrier for escaping of the nighttime capillary vapor moisture to the atmosphere that condensed on the underside of the tepee structures. The daily capillary vapor diffusion, condensation of capillary moisture, deliquescence and evaporation are the factors that lead to precipitation of efflorescent halite speleothems beneath tepee structures in these particular settings of high humidity. The influence of rainfall or dew water for providing saline waters for the formation of the studied speleothems are of minor importance with regard to capillary vapor condensation and deliquescence, and in comparison to other studies described stalactites below tepee structures.