STRUCTURAL IMPACT OF THE TERTIARY BASALT SETTING ON THE GROUNDWATER AQUIFERS USING GEOPHYSICAL TECHNIQUES IN THE AREA WEST CAIRO-ALEX. DESERT HIGHWAY BETWEEN THE KM 42 AND 52

The interpretation results of 62 Vertical Electrical Soundings (VES) and the available well logging
data in the study area revealed that the geoelectrical succession is consisting of four units (A, B, C and D) corresponds
to Pleistocene deposits, Lower Miocene Moghra Formation, Oligocene deposits and Eocene limestone respectively.
Three water-bearing formations were identified in the study area. These water-bearing formations are namely, the
Lower Miocene Moghra aquifer (geoelectrical layers B2 and B3), the Oligocene aquifer (geoelectrical layers C4, C5
&C6) and the Eocene limestone (unit D). The Tertiary basaltic sheet (geoelectrical layer C1) acting as a marker bed
separating the overlying Moghra aquifer from the underlying Oligocene aquifer. The Tertiary basalt acts as a marker
bed separating the overlying Moghra aquifer from the underlying Oligocene aquifer. The Tertiary basalt is found at
shallow depths (4m.) in the southeastern part of the study area whereas; the depth increases gradually northwest wards
to more than 220 m. This is mainly attributed to the effect of a group of normal step faults with downthrown side west
and northwest wards. These faults cause the convergence of Moghra and Oligocene aquifers along the two sides of the
faults making a hydraulically connection of the two aquifers
The estimated shale volume percentage from natural gamma-ray logs with the sand of Lower Miocene Moghra and
Oligocene aquifers revealed that the Moghra aquifer has the lowest values but the Oligocene aquifer has the highest
values. According to these results, the northwestern part of study area has the priority of drilling new wells.
Key words: Structure, Tertiary Basalt, Groundwater, Aquifers, Vertical Electrical, Sounding (VES).