الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 228 |  |  |
| | | from | 228 | | |
Abstract
This thesis is concerned with the groundwater chemistry and the composition of some Quaternary sabkha sediments in the Bahariya Oasis, in addition to its radioactivity. The sabkha inside the Bahariya Oasis occupy morphotectonic basins; originally formed as a result of folding and faulting, and later they were developed by the effect of weathering processes. The sabkha basins inside the Bahariya Oasis generally occur in number of low topographic basins, which are mainly fed by groundwater seepage in addition to irrigation waters from its surrounding cultivated land. Five localities represent the main important sabkhas in the depression. Several morphologic features were observed on the sabkhas surface; the most widespread are polygonal (tepee) crusts and salt ridges. Regarding the evaporate minerals that appeared in the sabkhas from Bahariya Oasis, halite and gypsum are the most dominant. Less common evaporate minerals include polyhalite, anhydrite, carnallite, sylvite, tachyhydrite, bassanite, epsomite and kieserite. The non-evaporate minerals are mainly represented by; quartz, kaolinite and illite in addition to accessory heavy minerals. The sabkha basins receive most of their clastic sediments from the surrounding bed rocks which are mainly composed of very fine sand, silt and clay. The Na2O and CaO contents dominate the evaporite minerals in all sabkha samples. The examined sabkha samples are discriminated into sodium rich group and calcium rich group. The trend of Na2O content shows a general upward increase where its maximum values occur at the surface; mainly due to the abundance of halite. The high content of CaO especially in El Esela sabkha is attributed to the presence of dominant gypsum which frequently occurs at the base of the sabkha sequence, in addition to anhydrite; calcite and dolomite. The Ca-rich samples are relatively enriched in siliciclastic sediments compared with the Na-rich samples. This may be related to frequent dissolution of the surficial halite crust by rising groundwater particularly in the winter when evaporation is retarded. The positive correlations between Fe2O3 vs. Cr, Zn, Ni and Pb suggest that these heavy metals are mainly absorbed on Fe-minerals. Regarding the water chemistry (groundwater and brine water) in Bahariya Oasis; the groundwater salinity ranges between 160 gm/l and 499 gm/l. The deep groundwater wells in the southern part of the Bahariya Oasis are generally lower in salinity compared with the northern part, suggesting a possible salinity increase northward. While the brine water salinity ranges between 43 and 207 g/l. The examined groundwater is dominated by chloride-calcium and chloride-sodium water types. The brine water is dominated by sulphate-magnesium and sulphate-sodium water types. The hydrochemical parameters of the groundwater reflect a marked increase of potassium, calcium, magnesium, sulphate ions compared with the normal sea water. This is attributed to the leaching of sediments by deep percolated meteoric water. On the other hand all brine samples have relatively low rCa++/rCl- ratios. This may be explained by the precipitation of gypsum. The high rSO4--/rCl- ratios suggest removal of Cl- due to partial precipitation of halite. The chemical composition of the groundwater in Bahariya Oasis reflects the mixed original NaCl, MgCl2 marine solution and the continental Na2SO4, NaHCO3 water types. The groundwater in Bahariya Oasis is generally suitable for domestic and agriculture uses. Only the high iron and manganese contents in the groundwater of Bahariya Oasis represent an essential problem for the public health; the water has to be exposed to the atmosphere (oxidiation). Regarding the radioactivity of the sabkha sediments, groundwater and brine water samples; the chemically determined uranium is relatively higher than the radiometrically measured one due to the presence of young uranium. This reflects a state of disequilibrium. The mean value of uranium in the brine water samples is relatively higher than the uranium concentration in the groundwater (3.349 & 1.206 µg/l, respectively). The uranium content of groundwater from Bahariya Oasis is somewhat high for typical deep groundwater but still under the limit of permissible and suitable for drinking purposes.