Impact of Lithofacies and Structures on the Hydrogeochemistry of the Lower Miocene Aquifer at Moghra Oasis, North Western Desert, Egypt

Abstract

The Moghra Oasis is one of the major Egyptian desert-reclamation projects. Understanding the hydrochemistry of the Moghra aquifer is an onus to properly plan and manage the agricultural activities in the North Western desert of Egypt. The basic geologic structure of the area under study was deduced from a detailed land magnetic survey. The resulted magnetic field map was analyzed using different filtering techniques and tomographic inversion. Field observation, stratigraphic setting, sedimentological studies, microfacies analyses and lithologic log of the studied wells were integrated to detect the lithofacies characteristics of the Moghra aquifer. Strong vertical and lateral variations of channel-fill and flat-laminated lithofacies beside several types of diagenetic processes caused the heterogeneity of the Moghra aquifer. The direction of groundwater flow in the heterogeneous Moghra aquifer is controlled by a fault system deduced from the magnetic study. Twenty groundwater samples from around Moghra Lake were collected and were analyzed hydrochemically for major ions and trace elements. The microfacies analysis (primary components and diagenetic processes), spatial variance in pH and ions concentrations, statistical and hydrogeochemical classifications, ionic ratios and relationships and saturation indices were helpful to understand the groundwater hydrogeochemical processes. The main hydrochemical type was Na–Cl. Ion-exchange due to seawater intrusion, sulfate ion reduction, iron-oxides reduction and mineral dissolution were the detected water–rock interaction processes. Dolomite precipitation was also proven. Iron oxides, quartz and carbonate minerals precipitation in the upper saline groundwater were expected. More mineral dissolution for evaporate minerals, silicate minerals and carbonate minerals in the lower saline groundwater is expected to occur.