Sedimentology, mineralogy and geochemistry of Al-Awshaziyah inland sabkha, Central Saudi Arabia.

摘要

In the Kingdom of Saudi Arabia, a rising demand of municipal, agricultural and industrial sectors require better utilization of surface and groundwater resources. Some of the wadi and low depressions in the central Saudi Arabia are covered with salt (Inland sabkha). It is also suspected that the aquifers below receive substantial amounts of recharge from the above ground salt flat. It is, therefore, important to investigate the mineralogy and geochemistry of these salt-flats to determine their impact on groundwater chemistry. Al-Awshaziyah inland sabkha is a saline dry/wet land with an area of 18 km2 in the central Saudi Arabia. The study area was divided into six transverses beginning at a permanent marker. The distance of different profiles ranged between 200-300 m. Soil, groundwater and well water samples were collected for physical and chemical composition. Additionally, different soil and salt facies were measured in each profile. Three sedimentary facies, viz., silty sand; black mud, and salt facies (from bottom to top) had been delineated. The mineralogy by X-ray diffraction analysis (XRD) for silty-sand facies composed of quartz (25-74%), halite (11-16%), dolomite (5-27%), calcite (4-21%), and gypsum (4-8%); black mud facies composed of quartz (14-16%), halite (25-33%), dolomite (18-25%), calcite (20-25%) and gypsum (8-11%); and salt facies is dominated only by halite (100%). The delineated facies led to highlight the depositional environment; mineralogy and geochemistry were studied. The elemental concentrations of CaO, MgO, K2O, Na2O, Al2O3, and SiO2 have been analysed in order to understand the element behaviour of each delineated sedimentary facie of sabkha basin. The geochemistry data reveals that SiO2 increases with the depth and CaO, MgO, Al2O3, and K2O behave in the reverse with the depth of sabkha sediments. The geochemical data has good correlation with the mineralogy of the same profile. Thus, the relationship has been established for the evolution of sabkha basin on the basis of sedimentary facies, mineralogy, and geochemistry..