Abstract
In the coastal western part of Saudi Arabia at Thuwal area located close from the Red Sea, the shallow groundwater specific electrical conductivities measured at the drill holes range from 6 to 13 mS/cm. In order to study the origin of this salinity, a good knowledge is required of the aquifer geometry with depth. Ninety nine transient electromagnetic (TEM) soundings were carried out over an area of about 100 km (super 2) . From the TEM profiles, a conductive substratum with a resistivity of 1-13 Omega m was identified at most of the sites at depth ranging from 50 to 150 m. This substratum is related to Oligocene-Miocene sediments (Shumaysi Formation) which are mainly red clay-rich formation containing brines at coastal zones. Clayey sediments are more likely present in the southeastern part and along the faults that run NE-SW across the study area and parallel to the Quaternary volcanic which runs NW-SE. The study demonstrated the effectiveness of the TEM sounding method to map conductive zones. Copyright 2009 Saudi Society for Geosciences