Hydrologic Framework of A Sabkha Along Arabian Gulf

Abstract

During the last 4,000 to 5,000 years, sedimentary offlap and a relative fall in sea level have resulted in the development of broad, gently seaward sloping (about 1:3,000) planar areas, or sabkhas, along much of the south shore of the Arabian (Persian) Gulf. The depth of the water table below the sabkha surface increases with distance from the sea until it reaches 1.0 to 1.5 m, after which it remains constant. When the water table depth is in the range of 1.0 to 1.5 m, the sabkha surface has reached a state of deflational equilibrium. The water table beneath the sabkha always slopes seaward indicating that the direction of ground-water flow is toward the sea. The subsurface flow system beneath the sabkha is part of a regional seaward flowing groundwater regime. In the seaward part of the sabkha, a downward flow component is superimposed on the general seaward ground-water flow pattern as a result of the infiltration and percolation of water from shallow bodies of seawater that are propelled inland over the sabkha surface by strong onshore winds. Farther inland where marine flooding does not occur, the vertical flow component is directed upward in response to evaporative losses at the sabkha surface. The net rate of evaporation from the central parts of the sabkha is on the order of 6 cm ( ± factor of 2) of ground water per year. A regional ground-water flow system which causes the water table level to rise as the sabkha progrades appears to be a requirement for the development and the preservation of broad sabkhas. Fluctuations in sea level during sabkha development influence the rate of progradation and the thickness of sedimentary facies. The refluxing of sabkha brines beneath the lagoons in the Abu Dhabi area indicates a mechanism for preserving anhydrite during marine transgressions, thus permitting the development of stacked sabkha successions which are common in the rock record.