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Abstract The presc;nt thesis dt-s.ls with thEi study of th.:: laktt deposits (Pleistocene-Recent) in the New Valley area, from their geological, ~ineralogical and geochemical points of view, Eight locations were chosen for this study. These area Mahariqo, Genah, Bolaqll,· Baris, El-Max, (Khe.rga Oasis), Kh~rga-Dakhla road, El-Zayat and Mawhoob (Dakhla Oasis). The distribution of lake deposits bot4 vertically and horizontally, was studied in the field by measur~g 5eVeral sections. Their characteristic sedimentological and morphological features were studied and described. The lake deposits ~re generally situated in the low-lying areas and show a well-marked stratification, Different sedimentnry structures are observed within these deposits (e.g. graded bedding, c.rcss bedding, color banding, small scale faulting and unconfc~~ty), These deposits lack fossils ~xcept for some plant reooins which are collliUon in them. Lake deposita exhibit two main morphological forme: The first one, which is the most common is their extensive foriL, which is called ”flat plaina”· The second, is in the forxu of small l<Ollgitudill.a.l ridgQa o~urring in groups oriented in a NNVi-SSE direction. These forme are called ”hU.lL.Il.ocks”,GrR.in size R.nalysi_s o:f:’ lake deposits rev•’il>.ls that these deposits range in size be+;Vleen medium .sc nd. and me.J 1 ”’”” s • It They are well to moderately sorted, nearly sy~etrical skewed and range f’rom platykurtic to lepto:kurtic characters. The relation~hips between grain size parameters indicate that these deposits were deposited in an aeolianbeach environment (marginal). Discriminant functions of Sahu show that they were deposited in a shallow marginal environments of deposition (e.g. J.alres, J?onds, lagoons ••• etc.) with a significant role of t:uro:i.dit~- cnr~”•m+,<;, At soms stages of deposition, aeolian J?rocesses prevailed and the sediments were carried and deposited in these shall. ow environments giving rise to a small scale, deltaic-;-· like deposits. The aeolian processes prevailed in dry seasons. The ”CAll” pattern of Pa.ssega indicates that the finer materials were deposited from uniform suBoenslon and with a clear effect of turbidity currents • .Peti’ological studies indicate that these d~pos5.t9 consist mainly of different varieties of sands and si\~s (e.g. sand, mvi sand, si l:t~ sand, sandy sli-t ... etc.). Tho. sands :Lncreai!!IB and concentrate at the centre of o.epression, while 5 j It increase northward and westward. The carbonate content increases in the same ~nner as the S!lt content. The different varieties of heavy and light m:l_neral assembla-ge t;D.Count.red .in the lake deposi te. ar2 ’-’”” r,yforiLation :ad th~; iD.d.ividual W . .n~;rals haV~; the lia!Le characteristics. Based on their petrological. characters th” lake deposits are thought to have been tru.usported and deposited in a fresh-water tmviron.ment (as indicated :fron. plant ren.ains) and originated from the nearby formations. These deposits became more sandy near the Nubian sandstone fornation (at the centre) alld more si t”t~ and calcareous near the calcareous and the s i It”~ formations (northwa.rd 8ll.d westwa.rd) • Study of the morphological features of the clay minerals, using the electron microscope showed that kaolinite is found as moderately well-crystallized pseudobexagonal flake-shaged particles, six-sided, stick-like and aggregates with different shades. Montmorillonite is represented by irregular, n:.ore or less ”quidimensional thin flakes as well as by irregular flake-shaped aggregates. Illite is represente~ by swall poorly defined, platy particles, occasionalJ. y w’c +:h angular borders and colll.tr.only grouped .’.n irregular aggregates without any distinct outli.nes. Some Llontoorillonite-illite JLixod layer clay is re:;>resented in the electron micrograph by spherulitic clusters and thin platy particles of undefined habits. X-ray diffraction analysis of bulk samples and oriented samples (untreated, glycolated and heated samples) of lake quartz, calcite, dolomite and gypsum. Infrared analysis showed that the lake d~positF consist essentially of the main chemical groups! OH, Si-O~·b..i., Si-0, and c-o whic-h represent kaolinite, illite, quartz and carbonate minerals. Chemical analysis of the lake deposits shows that they consist essentially of Ri02 , A.l2o7 , calcareous and organic materials. The silica is present f’B qua-.:-tz and e .. « c. ~:1.-0 group within clttr structures (as d.eteeted. .from X-ra’Y e-c1 infrared l!.nalysee). A.lwnina occurs essentially in the form of clay minerals (kaolinite, illite, ruontmorillonite). The calcareous materials (CaO, MgO) occur in the form of caleite and dolomite. The organic matter is mainly due to plant remains present in the lake deposits. The san8.:7 lake deposits are generally poor in calcareous mate~ials ?nd the opposite is true in the case of the si IT~ d<erns;_+;s. S<”’ID<? salty materials ware detected in theBe d91}0s5r:o an rbf’0F!Bd from halite (NaCl) occurrence. The geochemical relatiouships (in the light of the results of Degens, 1965), indicate that the lake deposits are more enriched with the average shale, which con+-ai.ns more illite than kaolinite and montmorillonite. |