Document Details
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Document Type |
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Thesis |
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Document Title |
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SEDIMENTOLOGICAL AND GEOCHEMICAL EVALUATIONS OF COASTAL EVAPORITING BASINS, RED SEA, SAUDI ARABIA: EXAMPLES FROM JIZAN AND KHOMRAH AREAS (WITH POSSIBLE INFERENCE TO CLIMATIC CHANGES) التقييم الرسوبي والجيوكيميائي لأحواض المتبخرات الساحلية، البحر الأحمر، المملكة العربية السعودية: أمثلة من منطقتي جيزان والخمرة (مع إمكانية الإستدلال على التغيرات المناخية) |
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Subject |
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Faculty of Earth Sciences |
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Document Language |
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Arabic |
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Abstract |
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The present work deals with the sedimentology, petrography, sediment geochemistry and brine chemistry of Sarum saline ponds, Khomrah area, south Jeddah, and Jizan sabkha area on the Red Sea coast of Saudi Arabia. It aims to understand the components of the non-evaporite sediments, their sources, methods of transport and dominant sedimentary processes in the geomorphological units, facies and microfacies types and their vertical and lateral distribution. Salinity variation in the salt ponds and sabkha area and its role in the deposition of the evaporite minerals: gypsum, anhydrite, halite and flourishing of microbial mats are also dealt with. The calcium carbonate content, major and trace elements and their environmental significance, and the relationship between the studied variables and present climate conditions are also the aims of this study.
Geomorphologically, Sarum saline ponds (gypsum and halite ponds) are surrounded with sabkha, raised beach, Quaternary coral reef terrace and sand sheets. On the other hand, Jizan area shows several geomorphological features including beach, mangroves, tidal flats, sabkha, coastal dunes, alluvium deposits, loess and inland sand dunes.
The Sarum sediments are coarser than Jizan sediments, which reveal varying energy condition. There are many processes controlling transportation and deposition of these sediments. In Sarum area, the prevailing processes are waves and tidal currents that erode the bioclastic materials from the Quaternary reef terraces in addition to the aeolian transportation of fine sand-sized material from the land side. In Jizan area, the main factors controlling the movements, sorting and distribution of the sediments are occasional floods through wadies, wind action, waves and tidal currents.
Application of change detection technique in the satellite images of the last 44 years shows the intensive contraction occurred in Sarum lagoons due to the construction of the main Red Sea asphaltic road that led to convert them to hypersaline ponds. Using several digital image processing methods in Jizan satellite image helped in differentiation between the different geomorphologic features.
The main petrographic components of Sarum sediments are carbonates, evaporites and few siliciclastic grains. Four microfacies types have been distinguished in Sarum area, which are gypsum, halite, carbonate and siliciclastics. Each microfacies type includes several submicrofacies such asloose to slightly cemented carbonate materials, carbonate mud-rich sediments, peloidal carbonate, foraminiferal carbonate reefal boundstone, peloid and shell fragments-rich grainstone, selenitic gypsum, clastic gypsum, lenticular gypsum, poikilotopic gypsum, halite cumulates, rafts, chevrons and cornets. Microscopic dissolution features and diagenetic halite are recorded.
The petrographic components of Jizan area are composed mainly of siliciclastic grains as groundmass and a significant amount of evaporites. Rare bioclastic grains are observed. Two microfacies types (siliciclastic and evaporitic) have been identified in Jizan sediments. The evaporite microfacies is subdivided into several submicrofacies types including gypsum, anhydrite and halite minerals. The identified gypsum morphologies are individual lenticular, twinned lenticular, twinned complex lenticular, swallowtail twinned, rosette gypsum, gypsum nodules and clastic gypsum. The gypsum crystal size ranges from gypsrudite to gypslutite. The gypsum crystals showed different growth natures including displacive and inclusive growth.
Based on the petrographic logs of Sarum sediments, a distinctive depositional sequence showing vertical changes from carbonate mud of the coastal lagoon setting to gypsum and halite that are formed in the hypersaline ponds setting. Jizan sediments show a distinctive depositional cyclicity that indicates fining upward sequence reflecting the quite condition. It may be attributed to the effect of seasonal wadi flooding.
The dominant diagenetic processes in Sarum and Jizan areas are the diagenetic growth of gypsum within the sabkha sediments and dissolution and cementation of the halite crusts.
The chemical compositions of the brine samples of the Sarum saline ponds and Jizan sabkha are similar to that of the Red Seawater that may be modified by the reaction and ion exchange with clayminerals from the groundmass sediments. The brines may be chemically evolved from deposition of calcium carbonate at low salinity to calcium sulfate and sodium chloride rich brine in Sarum and Jizan areas.
The concentrations of major and trace elements in the sediments of Sarum area are under the natural limit and can be considered as non-polluted sediments. The possible source of elements is from the terrigenous material input from the adjacent rocks that were subjected to physical weathering in an arid climate. Whereas, the major elements in Jizan sediments are originated from the effect of physical weathering on the source rocks under arid climatic condition. Although some parts of the sediments have undergone slightly chemical weathering during the humid, rainy seasons. The relatively high concentrations of trace elements in the sediments of Jizan sabkha may be attributed to the terrigenous material input by occasional wadies flooding and wind transportation, in addition to the anthropogenic impact of the different human activity in Jizan city. These activities result in increasing the concentration of environmentally sensitive, trace elements in the sediments of Jizan sabkha.
Analysis of variation in climatic data of the last 44 years in the two study areas is consistent with the global warming. This climate change increases the degree of aridity that may be indicated by the presence of the evaporites in the coastal sediments with accounting the impact of human activities. |
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Supervisor |
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Prof. Mahmoud Ahmed Aref |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1440 AH
2019 AD |
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Co-Supervisor |
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Prof. Rushdi Jamal Taj |
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Added Date |
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Wednesday, August 21, 2019 |
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Researchers
| علي عبد الرحمن خوفاني | Khawfany, Ali Abdurrahman | Researcher | Doctorate | |
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