Abstract
This study documents the deposits of an ephemeral, shallow lake that is recharged mainly from floods and torrential rainfalls from the Red Sea Mountains, in addition to seawater seepage at its western margin. The lake is desiccated in the summer months into several smaller, ephemeral pans and sabkhas due to excessive evaporation of its waters and decreased inflow of seawater seepage accompanied by the lowered hydraulic gradient between the Red Sea and the lake floor. The formation and distribution of microbial mats, gypsum and halite are discussed with respect to water supply and salinity. Microbial mats dominate the floor of the wintertime lake, and in the summertime, coastal pans where salinity is less than 126%. Gypsum crystals encrust microbial mats at salinities in excess of 182%. The central and eastern pans are floored with halite crusts at a salinity > 250% that develop into tepee polygons through desiccation. The slightly higher topographic sabkha areas around these pans contain subsurface, displacive, lenticular and tabular gypsum crystals, and clear, mosaic halite cement. Most of the water supplied to the supralittoral lake is during the wintertime, from episodic floods from the hinterland with a general increase in salinity towards the sea. However, the pattern of distribution and abundance of microbial mats-gypsum-halite facies are in a reverse order to the direction of water supply and increases in salinity. This ambiguity can be explained by the intermittent supply of seawater seepage from the Red Sea through an artificial barrier that is controlled by tidal range and fluctuations of sea level.