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 Petrographical studies and karst features of the Miocene microbial mats-dominated evaporite deposits in Rabigh area, Red Sea coast, Saudi Arabia دراسات رسوبية ومعدنية وملامح القشعات لمتبخرات المايوسين ذات الحصائر الميكروبية في منطقة رابغ ، ساحل البحر الأحمر ، المملكة العربية السعودية |
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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 syn-rift, Miocene evaporite rocks exist along the Red Sea coast of Saudi Arabia in several locations north of Jeddah area to Midyan Peninsula. In Rabigh area, the Miocene Dafin Formation includes the evaporites of the Jahfah Member that conformably overlies the siliciclastics of Al-Hakkak Member. The evaporite rocks are exploited by different Cement Companies such as Al-Alarabiya Cement Company and Al-Janobiya Cement Company.
Filed examination of the outcropped evaporite rocks and the faces of the active gypsum quarries indicate the existence of > 15 m thick section of massive and microbial, laminated, secondary gypsum rocks that mantled with 1-2 m thick anhydrite crust. The evaporite sequence is conformably overlain with the Pliocene siliciclastic rocks.
The evaporite layers are usually affected by karstification processes that developes sinkholes (dolines), solution pipes, caves and cavities. These karst features are filled with sand, muddy sand and pebbly sand, and partially cemented with lenticular gypsum crystals.
Microscopic examination of the studied evaporites allowed the determination of three facies types, these are gypsum, anhydrite and micritized, microbial laminae. Gypsum facies is discriminated into primary, depositional features and secondary, diagenetic features. Primary gypsum microfacies types include nodular, prismatic and fibrous gypsum scattered within micritized, microbial mats. The secondary gypsum microfacies type is; (a) porphyroblastic gypsum, (b) granoblastic gypsum, (c) alabastrine gypsum, and (d) satin spar gypsum veins. Anhydrite microfacies types are represented by secondary diagenetic prismatic, stair-step and felted anhydrite crystals.
The common presence of several microfacies types of gypsum and anhydrite in Rabigh area indicates that the evaporite minerals (gypsum and anhydrite) passed and affected by three diagenetic stages; 1) syndepositional (pre-burial) or early diagenetic stage, 2) burial diagenetic stage, and 3) uplift diagenetic stage.
Geochemical study of major, minor and trace elements indicate the dominant of SO3, CaO and Sr in all gypsum layers in concentration more than in the clay-rich gypsum veins. The clay layers are dominated with SiO2, Al2O3, Fe2O3, K2O, MgO, MnO, Na2O, P2O5 and TiO2, in addition to all minor and trace elements. Correlation coefficient between various elements indicate a very positive correlation of SiO2 with Al2O3, Fe2O3, K2O, MgO, MnO, Na2O, P2O5 and TiO2, and negative correlation with SO3, CaO and Sr. Also, positive correlation exists between SiO2 and most minor and trace elements. This indicates the dominance of SiO2 and the other elements in clay minerals that adsorbed trace and minor elements. A positive relation exists also between SO3, and CaO, LOI and Sr indicating the formation of gypsum and celestite minerals.
It is recommended to examine and map the karstic sediments in the gypsum quarries that decrease their purity and leaves large deposits unsuitable for cement industry. The presence of clay impurities in the gypsum layers make them suitable for agriculture purpose in addition to cement industry, but are not suitable for the manufacture of gypsum board. |
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Supervisor |
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Prof. Dr. Mahmoud Ahmed Aref |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1440 AH
2019 AD |
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Added Date |
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Tuesday, July 2, 2019 |
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Researchers
| حسان مأمون زواوي | Zowawi, Hassan Mamoun | Researcher | Master | |
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