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711.
Prof. Dr. Hussein A. Hussein Dr. Ibrahim A. El Kassas 《International Journal of Earth Sciences》1980,69(2):567-580
The area of Wadi Um Gir, Central Eastern Desert of Egypt, is covered by Basement rocks of Late Precambrian age namely; the postgeosynclinal (Hammamat) sediments, intruded by a bostonite dyke of the younger postorogenic volcanics. The radioactive anomaly discovered at Wadi Urn Gir is a typical vein-type hydrothermal occurrence structurally controlled by a major fault which is among the youngest faults related to the formation of the Red Sea Rift Valley during Tertiary times. The net slip of this fault is determined by the orthographic projection method to be 260 m.Hydrothermal alteration is intense along the fault zone, and is represented by successive bands mainly of hematite, kaolinitic clays, carbonates, etc.The radioactivity is normally distributed in the fresh rocks with anomalous readings connected to the altered bostonite rock in the fault zone. The abnormal high radioactivity is found to be mainly due to secondary uranium mineralization, with a uranium content of 0.065%, and in a radioactive disequilibrium with slight deficiency of daughter elements which may be due to redistribution by the effect of ground water. The uranium mineralization is usually present as fracture-fillings or forming thin fissure veinlets mostly with hematitic alteration bands along the fault zone.Genetically; repeated movement along the major fault resulted in intense fracturing of the bostonite rocks and reopening of the tectonically related fissures. The fault provided an easy channel for the passage of the contemporaneous or immediately ascending uranium-bearing solutions. Subsequently, alteration of bostonite and radioactive mineralization took place in the secondary tension fractures. The physico-chemical conditions of the altered and sheared bostonite rocks afforded the favourable conditions for the deposition of uranium minerals carried by the hydrothermal fluids along the opened fractures.
Zusammenfassung Das Gebiet »Wadi Um Gir« in der zentralarabischen Wüste Ägyptens besteht aus Basisgesteinen von Präkambrischem Alter. Es handelt sich um die postgeosynklinale »Hammamat«-Serie, deren Sedimentabfolge von einem Bostonitgang des jüngeren postorogenen Vulkanismus durchbrochen wird.Eine Radioaktivitätsanomalie wurde in »Wadi Um Gir« festgestellt. Sie bildet ein typisch-gangartiges hydrothermales Vorkommen und ist von einem Hauptbruch der mit der Entstehung des Rotmeergrabens verbundenen jungen Brüche bestimmt. Eine Berechnung der Sprunghöhe dieser Verwerfung mit der orthographischen Projektionsmethode ergab einen Wert von 260 m.Intensive hydrothermale Umwandlung der Muttergesteine kommt entlang der Bruchzone vor. Sie besteht unter anderem aus Successiven Streifen von hämatitischem, kaolinitischem und karbonatischem Material.Die Radioaktivität, deren Verteilung in den frischen Gesteinen normal ist, zeigt Anomalien nur noch im Zusammenhang mit dem umgewandelten Bostonit der Bruchzone, wobei die abnormal hohen Radioaktivitäts-Werte mit der sekundären Uran-Mineralisation (Urangehalt 0,065%) in Einklang stehen. Es besteht jedoch durch geringe Verarmung an gewissen Tochterelementen eine Gleichgewichtsstörung. Dies könnte auf die Umverteilung durch Grundwassereinflüsse zurückgeführt werden.Genetische Überlagerungen führen zu der Annahme, daß die wiederholte Bewegung entlang der Hauptbruchzone eine intensive Fraktur der Bostonitgesteine veranlaßt hat. Dies führte zur mehrfachen Öffnung der in Zusammenhang stehenden Spalten und damit bildeten sich Bahnen für die aufsteigenden, syngenetischen, uranhaltigen Lösungen.Die Anlagerung uranhaltiger Mineralien in den sekundären Spannungsbrüchen wurde durch die physiko-chemischen Verhältnisse des umgewandelten und abgescherten Bestonits gewährleistet.
Wadi Um Gir - . , , . . , . 260 . . , . , , , . . . , . .. . - .相似文献
712.
The objective of this study was to investigate the removal mechanism of U(VI) from groundwater by magnetite as the main product of anoxic steel corrosion. For this purpose, a systematic sequence of batch experiments was conducted to focus the active role of magnetite in the reduction of U under different conditions. Results indicated that under anoxic conditions U(VI) was sorbed at the magnetite surface, whereas under reducing conditions at different H2(g) pressures, U was present in tetravalent form as amorphous UO2. 相似文献
713.
Attwa Mohamed El Mahmoudi Ahmed Elshennawey Ahmed Günther Thomas Altahrany Ayman Mohamed Lamees 《Natural Resources Research》2021,30(5):3407-3428
Natural Resources Research - Soil characterization in coastal areas is essential for strategic coastal engineering implementation and for understanding the paleo-environmental conditions. However,... 相似文献
714.
715.
Boleslaw Mielniczuk Moulay Said El Youssoufi Laurent Sabatier Tomasz Hueckel 《Acta Geophysica》2014,62(5):1087-1108
The study examines rupture of evaporating liquid bridges between two glass spheres. Evolution of the bridge profile has been recorded with the use of high-speed camera. Geometrical characteristics of the bridge were then used to calculate evolution of the variables during the process: Laplace pressure, capillary force, and surface tension force. For the purpose of reference, the bridge evolution is followed also during kinematic extension. During both processes the diameter of the neck decreases, with an acceleration of about 1–2 ms before the rupture. Two distinct rupture modes are observed, depending on the bridge aspect ratio. After the rupture, the mass of liquid splits, forming two separate oscillating drops attached to the spheres, and a suspended satellite droplet. Just before the rupture, an increasing repulsive Laplace pressure, and decreasing negative surface tension force develop. Capillary force follows the trend of the surface tension force, with an accelerating decline. Duration of the whole process and liquid mass stabilization is from 10 to 60 ms. 相似文献
716.
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718.
Ben Ameur W de Lapuente J El Megdiche Y Barhoumi B Trabelsi S Camps L Serret J Ramos-López D Gonzalez-Linares J Driss MR Borràs M 《Marine pollution bulletin》2012,64(2):241-251
The aim of the study was to evaluate the impact of environmental contaminants on oxidative stress, genotoxic and histopathologic biomarkers in liver of mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) collected from a polluted coastal lagoon (Bizerte Lagoon) in comparison to a reference site (the Mediterranean Sea). Antioxidant enzyme activities were lower in fish from the polluted site compared with fish from the reference site, suggesting deficiency of the antioxidant system to compensate for oxidative stress. DNA damage was higher in both fish species from the contaminated site indicating genotoxic effects. The liver histopathological analysis revealed alterations in fish from Bizerte Lagoon. Hepatocytes from both fish species featured extensive lipid-type vacuolation and membrane disruption. Results suggest that the selected biomarkers in both fish species are useful for the assessment of pollution impacts in coastal environments influenced by multiple pollution sources. 相似文献
719.
I. Anastasopoulos A. Callerio M. F. Bransby M. C. R. Davies A. El Nahas E. Faccioli G. Gazetas A. Masella R. Paolucci A. Pecker E. Rossignol 《Bulletin of Earthquake Engineering》2008,6(4):645-675
Field evidence from recent earthquakes has shown that structures can be designed to survive major surface dislocations. This
paper: (i) Describes three different finite element (FE) methods of analysis, that were developed to simulate dip slip fault
rupture propagation through soil and its interaction with foundation–structure systems; (ii) Validates the developed FE methodologies
against centrifuge model tests that were conducted at the University of Dundee, Scotland; and (iii) Utilises one of these
analysis methods to conduct a short parametric study on the interaction of idealised 2- and 5-story residential structures
lying on slab foundations subjected to normal fault rupture. The comparison between numerical and centrifuge model test results
shows that reliable predictions can be achieved with reasonably sophisticated constitutive soil models that take account of
soil softening after failure. A prerequisite is an adequately refined FE mesh, combined with interface elements with tension
cut-off between the soil and the structure. The results of the parametric study reveal that the increase of the surcharge
load q of the structure leads to larger fault rupture diversion and “smoothing” of the settlement profile, allowing reduction of
its stressing. Soil compliance is shown to be beneficial to the stressing of a structure. For a given soil depth H and imposed dislocation h, the rotation Δθ of the structure is shown to be a function of: (a) its location relative to the fault rupture; (b) the surcharge load q; and (c) soil compliance. 相似文献
720.
Herv Thbault Alessia M. Rodriguez y Baena Bruno Andral Delko Barisic Jos Benedicto Albaladejo Alexandru S. Bologa Redouane Boudjenoun Roberta Delfanti Victor N. Egorov Tahar El Khoukhi Heleni Florou Goran Kniewald Abdelkader Noureddine Vasile Patrascu Mai Khanh Pham Alfonso Scarpato Nikolay A. Stokozov Sayhan Topcuoglu Michel Warnau 《Marine pollution bulletin》2008,57(6-12):801
The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify 137Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured 137Cs levels were found to be very low (usually <1 Bq kg−1 wet wt) 137Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area. 相似文献