الفهرس 
ACKNOWLEDMENTSOnly 14 pages are availabe for public view
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Abstract
CONCLUSIONS
Recently Shalatein area has got more governmental interests and is regarded as one of the most promising regions for desert development due to its strategic location and as tourism, fishery, animal husbandry and mining activity.
It is characterized by arid to semiarid climatic condition, which is marked by low precipitation and high evaporation intensities. Shalatein is suffered for several decades from intensive aridity, over-grazing and desertifications.
The study area lies to the east of the basement rocks at the outlets of Wadi Hodein, Wadi Sefeira and Wadi Sha’b to the south of Shalatein town. It is geographically located between latitudes 22° 50` and 23° 05` N and longitudes 35° 20` and 35° 35` E.
The entire area represents a huge catchment area, which is drained by wadis and its tributaries into the Red Sea. The main collecting water is based on occasionally heavy showers of rainfall storms along the Sand Stone plateau and the Basement Mountains.
The geomorphologic features in the study area can be classified into the three morphological units that are the basement mountainous area which occupies the western part of the study area, the coastal plain which comprises many different subgeomorphic units such as sand sheets and piedmont plain to the west and Sabkhas to the east and the hydrographic drainage basins which most of them drain the catchment area along the Red Sea mountains into the Red Sea such as Wadi Rahaba, Wadi Hodein, Wadi Sefeira and Wadi Sha’b.
The surface of the study area is built mainly of Precambrian basement rocks, which are faulted up against Upper Cretaceous Nubia Sandstone. The Quaternary deposits occupy the surface of low-lying channels and the Piedmont and Coastal Plain. They are formed mainly of alluvial deposits. The exposed lithostratigraphic succession is described from older to younger as follows:
- Pre-Cambrian Basement Rocks which essentially consist of ultrabasics, metamorphic complex and granitic masses.
- Cretaceous Sedimentary Rocks (Nubia Sandstone) that rest nonconformably on the basement rocks and extends to form the surface between mountainous area and the basaltic dykes. They are composed of alternating sequences of fine to coarse grained sandstone intercalated with silty or clayey beds and comprises the following formations from base to top:
- Abu Aggag Formation (Turonian) which composed of conglomeratic to coarse –grained Kaolinite sandstone.
- Timsah Formation (Coniacian to Santonian) is composed mainly of nearshore marine to deltaic sequences of silt and fine-grained sandstone with thick shale intercalation.
- Umm Barmil Formation (Santonian to Early Campanian) composed of coarse to medium grained sandstone of large scale tabular and trough cross-bedding originated from a low sinuosity fluvial environment.
- Tertiary Volcanics are of very limited distribution and form several small masses and isolated hills in NW-SE direction near the feet of the mountainous area and the piedmont plain.
- The Quaternary sediments comprise gravel plain which covers most of the coastal plain, wadi deposits occupying the downstream portions of the wadis, sabkhas that extending along the Red Sea coast and occupy different pans according to the topography of the area and aeolian sediments which composed of wind blown sand and generally form the serir feature and also form the longitudinal or crescential dunes in the area.
The basement complex of the Eastern Desert represents a part of the African Pre-Cambrian Shield, which has been fractured and faulted during successive cycles of tectonics. It’s a part of an orogenic Precambrian belt. Pre-Cambrian basement rocks as well as the Cretaceous Nubia Sandstone are faulted. The main faulting system which is affecting the southeast of the Eastern Desert can be summarized in the following sets:
Red Sea faulting system (N25°-35°W), Gulf of Aqaba (Dead Sea) system (N20°E) and N50°-60°E trend. On the other hand, fractures, which have an important role in groundwater occurrence, were formed as an echo of the major faulting systems, and others are primary structures.
The total intensity of the earth’s magnetic field was measured along 10 profiles traversing the study area, four profiles have NW-SE direction intersected by 6 profiles with E-W direction to form more or less grid pattern form. The measured total magnetic values are corrected diurnally and plotted on profiles and contour maps. The resulting picture represents a total intensity magnetic map. This map is reduced to the pole by applying the reduction to the pole technique. Also the reduced to the pole total magnetic intensity map has been subjected to the band-pass filter technique in order to isolate the regional magnetic anomalies (low frequency) from the residual anomalies (high frequency).
From the qualitative observation (interpretation) of the measured profiles, it was clear that, are similar. These six profiles that extend in E-W direction. Its clear that the six profiles could be divided into two parts. The first part (extending from the west side of the study area to the east to a specific boundary) is represented by smooth uniform and relatively low magnetic values, which indicate, more or less, even basement surface. This smooth part of magnetic intensity is coordinates with the outcropping section of Nubia Sandstone (Abu Aggag Formation). The existence of the thick Nubia Sandstone section in this part of the study area explains the uniform smooth behavior of magnetic intensity function along this part of the traversed profiles, which is characterized by low amplitude, low frequency and gentle variations in the magnetic intensity values.
On the other hand, the second part (extends to the east of the first part) is characterized by abrupt change in the magnetic intensity behavior. This part of the study area exhibits irregular magnetic intensity function, sharp anomalies with repeated high and low magnetic intensity, high amplitude and high frequency. This part of the study area coordinates with the outcropping of tertiary dykes, which appear like numerous intrusions of different sizes and irregular shapes.
The four traversed profiles running in the NW-SE direction exhibit the same last mentioned two magnetic behavior discussed in the last mentioned six profiles.
According to visual inspection of the magnetic and geological maps, it was possible to group the different anomalies into four distinct anomalous zones of various magnetic characteristics.
The first zone extends along the western edge of the study area. It is characterized by moderately high magnetic field and extension varies along the different magnetic component maps. This zone lies adjacent to the Red Sea mountainous at the west. The second zone is located in the eastern south part of the study area. This zone coordinates with a remarkable granitic hill near the eastern south corner of the study area. The characteristic features of this zone that it is bounded by low magnetic anomalies from all sides. This zone posses steep gradient, suggesting that this anomaly may be due to uplifted basement block. The third zone covers the eastern part of the study area and extends in a NW-SE direction parallel to the direction of the Red Sea. High magnetic intensity and complex irregular pattern characterize it. The irregularity, sharpness and high frequency behavior of these magnetic anomalies are very logic, as the Tertiary volcanics has a very shallow depth, mainly outcrop at and disappear on the surface of the ground with different shapes and volumes. The forth zone extends in the western side of the study area till the center of the study area between zones I and II and the eastern north of the study area. This zone is associated with the Nubia Sandstone outcropping (Abu Aggag Formation) and is characterized by a large aerial extend and a low magnetic intensity.
In Quantitative Interpretation of Magnetic Data, five profiles were selected to be modeled to delineate the depth of the basement surface and the basement tectonic framework of the studied area. The first two profiles are taken in almost NW-SE direction, in order to be in almost right angle to the faults, which cut across all the area and the different wadis drained along. The other profiles running in almost E-W direction, nearly normal to the NW-SE structural trend (Red Sea trend) which is the prominent direction of faulting system that affecting the basement rocks within the studied area. By using all available geologic and topographic information and the results of qualitative interpretation as well as the log of the only drilled well in the study area; the basement cross-sections were assumed. The field was calculated iteratively for this geological model, till a reasonable fit is reached between the observed and computed magnetic profiles. The interpretation of the last mentioned five magnetic modeling with the other qualitative and quantitative interpretation has been used to delineate the dominant structural elements affecting the study area.
The tectonic trends interpreted from the last discussed interpretation express the trends NW-SE, E-W, ENE-WSW, NNE-SSW and WNW-ESE. The tectonic trends delineated in the studied area may represent the most important trends recorded in Egypt, especially in the Southern Desert.
A reasonable coverage for the study area was reached by a total of 26 Vertical Electrical Soundings (VES). The sounding stations were distributed, more or less, in the form of a grid.
The Schlumberger 4-electrode configuration was applied in the present investigation. The maximum current electrode separation (AB) ranges from 300 to 4000m. This electrode separation proved to be sufficient to reach the required depth that fulfils the aim of the study in view of evaluating the geologic and hydrogeologic conditions. The resistivity sounding data has been interpreted qualitatively and quantitatively.
The qualitative interpretation of the sounding curves reavealed that, the apparent resistivity values on the first logarithmic cycle of the field curves (i.e., at AB/2 = 1- 10m) show a common trend that is characterized by continuously decreasing apparent resistivity values (Q-type). In going downwards on the resistivity sounding curves (i.e., the second, third and forth cycles where AB/2 > 10m) it can be observed that almost all the field curves terminate with K-H type. This indicates that the field measurements have, most probably, reached the basement rocks or the hard scilicefied bedrock.
The detailed findings from the quantitative interpretation of the geoelectrical resistivity sounding data led to the detection of four main geoelectrical layers (A, B, C and D). Some of these layers have not been detected at some sounding stations. From the piezometer No. (1) to the west of the Tertiary volvanics and a drilled well to the east of the study area, it is clear that the geoelectrical layer (A) overlies directly the basement rocks to the east of the Tertiary volcanics, while it overlies the Nubian sandstone in the area lies to the west of the Tertiary volcanics. The distribution of the resistivities and thicknesses of the four geoelectrical layers (A, B, C and D) is given as follows:
• According to on the resistivity values and the data to the obtained from drilled wells, this geoelectrical layer (A) can be subdivided into four geoelectrical sub-layers (A1, A2, A3 and A4) as follows:
• The geoelectrical sub-layer (A1) consists of a group of thin layers that have been grouped together in one layer. The resistivity of such layer is plausibly expressed in terms of the average transverse resistivity (ρt). It shows it’s a vey wide range of resistivities (12-983 ohm-m.). The diversity of the resistivity values, characterizing this geoelectrical layer, is typically indicative of dry alluvium deposits. The thickness of this layer ranges from 2.2 m. to 73.7 m.
• The geoelectrical layers (A2 and A4) are characterized by relatively low resistivity values (generally less than 8 ohm-m.). The resistivity values represent very-fined grained materials such as silt and clay beds. The thicknesses of both geoelectrical layers (A2 and A4) show continuos increase towards the northeast and the east respectively.
• The geoelectrical layers A3, which has been detected at some sounding stations, has been interpreted as clayey sand sheet. The resistivity of the geoelectrical layer (A3) ranges between 15 ohm-m. and 59 ohm-m. The thickness of this geoelectrical layer increases in the northeast and the east directions. This layer is interpreted as a water bearing layer.
• For the geoelectrical layer (B), it could be divided into three geoelectrical sub-layers (B1, B2 and B3), which are equivalent to (Abu Aggag Formation).
• The geoelectrical layer named (B1) is not detected outside the tertiary dykes and is not detected also at the VES’es adjacent to the basement outcrops at the western side of the study area. This layer exhibits different resistivities ranging between 16 and 99 ohm-m. This resistivity range is interpreted as water bearing sand and gravel with clayey interclations. This low resistivity may be attributed to the effect of an increase of the clay content and / or water salinity. The thickness of this layer varies from 5.9 m. to 21.3 m.
• The geoelectrical layer (B2) is characterized by relatively low resistivity values (generally less than 6 ohm-m.). This low resistivity range may represent very fine-grained materials mainly clay. Its thickness varies from 58.1 m. to 20.5 m. This layer has not been detected outside the Tertiary volcanics.
• The geoelectrical layer (B3) has been detected only at 7 soundings. This thin layer (5-9 m.) shows a very limited range of resistivities (99-120 ohm-m.). This resistivity range may represent siliceous sandstone.
• The geoelectrical layer (C) has been detected only at five soundings named adjacent to the outcropping Tertiary volcanics. This geoelectrical layer shows resistivity values more than 1000 ohm-m. The geoelectrical layer (C) is believed to be equivalent to the Tertiary volcanics.
• The geoelectrical layer (D) has been devided into two geoelectrical sub-layers (D1 and D2) as follows:
• The geoelectrical layer (D1) is interpreted as fractured basement. The resistivity of this geoelectrical layer ranges from 453 ohm-m to 922 ohm-m. The thickness of this geoelectrical layer does not exceed 12m.
• The lowermost detected geoelectrical layer (D2) has been recorded with a very high resistivity that exceeds 1060 ohm-m. According to the geological evidences and the results obtained from the ground magnetic survey, this layer represents the basement rocks. The depth to the basement rocks varies from 21.3m. to 135.3m.
The individual sounding interpretations have been used to generate six geoelectrical cross sections traversing the investigated area in different directions. Correlation of the geoelectrical parameters (resistivity and thickness) helps inferring the structural elements that affect the succession. The main findings reached from these six generated geoelectrical cross sections is given in the following:
• Four geoelectrical cross sections (A-A’, B-B’, C-C’ and D-D’) are running in the NW-SE direction, on the other hand, two geoelectrical cross-sections (E-D and F-F’) are running in W-E direction.
• Along the geoelectrical cross-sections A-A’ and B-B’, the geoelectrical succession from the top downwards is represented by wadi fills (layer A), Nubia Sandstone (unit B) and the basement rocks (unit C).
• Both geoelectrical cross-sections A-A’ and B-B’ are affected by two normal faults (F4 and F5) making a graben at VES No. 3 (sec. A-A’, Fig. 49) and at VES No. 11 (sec B-B’, Fig. 50). Beside faults F4 and F5, cross-section B-B’ is also affected by normal fault (F6).
• The geoelectrical cross-section C-C’ runs adjacent to the outcropping the Tertiary volcanics from the eastern side. The geoelectrical succession along this profile consists of wadi deposits (layer A), underlying by the volcanics (layer C) or the basement rocks (layer D), except at VES No. 14, where the Nubia Sandstone (layer B) is recorded.
• Cross-section D-D’ is running to the east of the Tertiary volcanics. The geoelectrical succession along this profile consists of wadi deposits (layer A) underlain by the basement rocks (layer D).
• The geoelectrical succession along the fifth cross-section E-D’ consists of the geoelectrical layers A, B, C and D units.
• The W-E cross-section F-F’ has the same geoelectrical succession of cross-section E-D’. From the structural point of view, the cross-section E-D’ is affected by three normal faults (F1, F2, and F3) where F1 and F2 make a graben and F2 and F3 make a horest. On the other hand, the cross-section F-F’ is affected by two faults (F2 and F3) making a horest.
In order to augment the feasibility of the geophysical results and to make them more illustrative and useful for a decision-maker, priority maps for groundwater exploration in the investigated area have been constructed. The construction of these maps depends on the mutual effect of the resistivity and thickness as well as the depth to water table. The priority maps are presented for both water bearing layers as well as the combined effect of the water bearing layers to show zones of different priorities for groundwater exploration throughout the whole study area. A simple BASIC program has been specially written for different classes (priorities).
As mentioned before, the Quaternary deposits composed of alternating sequence of sand and clay beds. The water-bearing layer throughout the Quaternary deposits is a clayey sand sheet, which is corresponding to the geoelectrical layer (A3). The depth to water ranges between 6 m. at the southwestern corner of the area to 27.8 m. at the northeastern side. This water-bearing layer does not also detected at the far western side of the study area adjacent to the Red Sea mountains.
The groundwater quality throughout the Quaternary aquifer layer has been qualitatively evaluated as the lower the resistivity, the higher the salinity of the groundwater and /or the higher the clay content and vise-versa. It is obvious that the southwestern part of the area represents, relatively, the best water quality within this layer. The groundwater quality decreases in the northeast direction towards the Red Sea. On the other hand, the maximum recorded thickness (21.3 m.) is at the northeastern area towards the Red Sea and decreases generally towards southwest.
As mentioned before, the water bearing layer is characterized by, more or less uniform thickness and the depth to water table is generally shallow. As the salinity plays a significant role in groundwater utilization, the resistivity parameter has been weighted by a factor of 80% and, thickness by a factor of 10% and the depth to water by a factor of 10%.
According to the priority map of the Quaternary aquifer, it can be concluded that the western part of the area is considered as the most promising area for drilling water wells. The quality of water decreases towards north and east.
On the other hand, the geoelectrical layer (B1) as a part of the Nubia Sandstone (Abu Aggag Formation) represents the water bearing formation in the area to the west of the Tertiary volcanics. The depth to water was found to be ranging from 22.5 m. beside the piezometer No. (1) to 73.7 m to the south of the study area. The water level varies from +21.1 m. to +90.9 m. The expected water table map shows that the groundwater flows regionally from west to the east (towards the Red Sea).
The groundwater quality throughout the extension of the layer has been qualitatively evaluated as the lower the resistivity, the higher the salinity of the groundwater and/or the higher clay content and vise-versa. According to this concept, the resistivity of the Nubia Sandstone was used to construct a map for water quality. From this map, it is obvious that the central part of the contoured area represents, relatively, the best water quality within this layer in the investigated area. On the other hand, the maximum recorded thickness of this concerned water bearing layer reaches 21.3 m. at the area lying in front of Wadi Sefeira. It is clear that, this area represents a graben that controlled by faults F4 and. The thickness of the layer decreases generally towards both north and south.
According to the above discussion of the characteristics of the Nubia Sandstone water bearing layers, a decision map has been generated for the water bearing layer. This map defines zones of different priorities for groundwater exploitation.
A combined priory map for decision-maker has been created from both the Nubia Sandstone aquifer and the Quaternary aquifer throughout the whole study area. Each aquifer parameters recorded in the database with its own category class. It is clear from this map that, the central and western part of the study area is considered as the most promising sites for drilling water wells. The quality of water decreases towards east and southeast.
According to the results of the present geophysical study, it could be concluded that:
1-There is not any evidence of the existence of the Nubia Sandstone to the east of the Tertiary volcanics and the Quaternary deposits seem to overly directly the basement rocks through this part of the study area.
2-Tertiary volcanics prevent the connection between the Nubia Sandstone aquifer (at the west) and the Quaternary aquifer (at the east), but also the existence of the clay throughout the gates along the Tertiary dykes. On the other hand, the existence of sand deposits at such gates permits the water flow from the west (Nubia Sandstone aquifer) to the east (Quaternary aquifer). This means that, both water bearing layers are connected at some localities and are not at others.
3- Groundwater throughout the study area is generally fair.
4- Generally, the western parts of the study area are found to be dominated by better water quality than the eastern parts.
5- The areas lying in front of Wadi Hodein, Wadi Sefeira and Wadi Kreiga represent the best locations for drilling wells.
6- The potentiality of the Quaternary aquifer is very limited due to its thin thickness and moderate quality.
7- The above mentioned results give an explanation for the reasons of the scarcity of drilled water wells in the study area.