Environmental factors controlling the distribution patterns and abundance of sclerobionts on the shells of Tridacna maxima from the Egyptian Red Sea coast

The living Tridacna maxima shell provides an example of a good substrate for many colonizing marine organisms (sclerobionts). Many factors affect the colonization choices of these organisms, such as morphology and size of the host shell, water depth (related to light penetration), suspended particulate load, and turbidity, among others. In addition to these factors, contamination plays an important role in the colonization choice along the coast of the Red Sea in Egypt. In the present study, 25 specimens of T. maxima shells of different sizes were collected at different depths from eight sites along the Egyptian Red Sea coast. There are two types of contamination at these sites. The first type results from anthropogenic activities, such as tourism, fishing, landfilling, shipping, renewal of ship operations, shipyards, dredging, and petroleum production; this type is represented by the El-Esh area, Hurghada Harbor, Safaga Harbor, and Quseir Harbor. The second type results from the natural inputs from wadis and is represented by the El-Esh area, Quseir Harbour, and Wadi El-Gemal, while the Abu Galawa Lagoon, the Abu Ghusun, and the Hamata Reefs represent uncontaminated areas (control areas). The present study documents the colonization phenomena on T. maxima shells at all of the study sites. These phenomena differed from one another in the abundance and diversity of sclerobionts, and unexpectedly, the contaminated areas recorded the highest abundance and diversity of colonizing organisms.     

Paleo-Tsunami deposits on the Red Sea beach, Egypt

The characteristics of the recent tsunami deposits threw light on some sources of deposition on the beach of the Red Sea. The studied area is delineated by latitudes 25°6′ N and 25°9′ N and longitudes 34°50′ E and 34°53′ E; it covers an elongate area of about 12 km² along the Red Sea coast, North Marsa Alam City (4 km). The area is bounded by Wadi Asalay to the north and Wadi Sifayn from the south. For evaluation of the area, a lot of information allows us to interpret the conditions prevailing during deposition of the sediments especially at the coast. To achieve the target, five wells were drilled to study core samples, well logging measurements, and 69 vertical electrical sounding stations were carried out. The studied area and adjacent areas were geologically surveyed to note geological features related to Paleo-earthquakes. From geological and geophysical studies, the dominant rock types at the western portions of the studied area are sandstone, sandy clay, clay, clayey sandstone, and gravels; at the middle portion of the studied area, the rocks are hard, but the eastern side of the area, especially at the beach of the Red Sea, several cycles of depositions of coral reefs occurred with intercalations of clastic deposits such as clay, sand, sandstone, conglomerate, gravels, pebbles, and a lot of fossils and shell fragments. The rocks are characterized by heterogeneous properties and ill-sorted. The area includes large numbers of faults due to highly tectonism of the area. The results indicated that the area has lateral variation of sediments. The carbonate rocks at the beach contain clastic fragments, and carbonate blocks are included within clastic rocks. With increasing the distance from the beach to the west, the sediments are less heterogeneous. The beach of the Red Sea was subjected to Paleo-tsunami waves due to highly Paleo-seismic activity inside the Red Sea and left their signature in geological column especially at the beach. The observation of some geological features such as Paleo-liquefaction and landslides indicate that the area subjected to strong earthquakes related to rifting of the Red Sea.     

Assessment of seismic hazards for Hurghada,Red Sea,Egypt

The entrance of the southern Suez Gulf of the Red Sea is known to be an area of high seismic activity in Egypt. The high rate of seismic activity in this area is mainly related to the adjustment in motion at the triple junction between the African plate, the Arabian plate, and the Sinai microplate. The present study attempts to estimate the Probabilistic Seismic Hazard Analysis (PSHA) for Hurghada site. This was done in two steps; the first one is by estimating specific parameters for the site, such as the mean seismic activity, λ, the Gutenberg-Richter parameter, b, and the maximum regional magnitude, m _max. The second step is by selecting a ground motion parameter that is applicable to Hurghada site. The procedure permits the combination of both historical and recent instrumental data. The results of the hazard assessment, expressed as the worst case scenario, detect that Hurghada is exposed to the maximum credible earthquake event of magnitude m _max = 7.1 ± 0.31, at hypocentral distance of 31.6 ± 10 km. The possibility of the maximum Peak Ground Acceleration (PGA), which occurred in relation to this event at Hurghada site, is equal to 0.29 g. The mean return periods with the selected accelerations for Hurghada, a horizontal acceleration of 0.1 g, is expected to occur once every 74–106 years, with an average of one every 90 years. This result which obtained from the hazard assessment can be used as an input data for a seismic risk assessment.     

Provenance of coastal dune sands along Red Sea,Egypt

Texture, mineralogy, and major and trace element geochemistry of 26 coastal dune sand samples were studied to determine the provenance and tectonic environment of two dune fields close to the beaches of Safaga (SF) and Quseir (QS) at the Egyptian Red Sea coast. Onshore winds generate fine, moderate, moderately-well to well-sorted, coarse-skewed to near-symmetrical dune sands with mesokurtic distributions. Winds pick up and transport grains from nearby beach sands and alluvial deposits into a wide Red Sea coastal plain at the border of the beach. The mineralogical (Qt–Ft–Lt) and geochemical composition of the sands, indicate that SF and QS coastal dune sands are mature and influenced by quartz-rich sands. The average CIA values in SF and QS coastal dune sands are low relative to the range of the PAAS, suggesting an arid climate and a low intensity of chemical weathering. The SF and QS coastal dune sand samples are plotted in the recycled orogen and partly in craton interior fields suggesting recycled older sedimentary and partly metamorphic-plutonic sources. The high content of quartz with shell debris and carbonates in coastal dune sands support the recycled sedimentary beach and alluvial sand sources. The dominance of heavy minerals like amphiboles (hornblende) and biotite in the coastal dune sands also supports the effect of metamorphic-plutonic source rocks. The new tectonic discriminant-function diagrams suggest that the coastal dune sands were deposited in a passive margin of a synrift basin. The results provide a good evidence for the extension in the Red Sea rift system during Oligocene-post Pliocene, which is consistent with the general geology of Egypt.     

Heavy metals contamination of the Quaternary coral reefs, Red Sea coast, Egypt

In order to assess pollutants and impact of environmental changes along the Egyptian Red Sea coast, seven recent and Pleistocene coral species have been analyzed for Zn, Pb, Mn, Fe, Cr, Co, Ni, and Cu. Results show that the concentration of trace elements in recent coral skeletons is higher than those of Pleistocene counterpart except for Mn and Ni. In comparison with recent worldwide reefs, the present values are less than those of Central America coast (iron), Gulf of Aqaba, Jordan (lead, copper), Gulf of Mannar, India (chromium, zinc, manganese), Costa Rica, Panama (chromium, nickel), North-west coast of Venezuela and Saudi Arabia (copper). The present values are higher than those of Gulf of Aqaba, Jordan (iron, zinc, manganese), Gulf of Mannar, India (lead, cobalt, nickel), North-west coast of Venezuela (lead, zinc, chromium, manganese), Australia (copper, nickel, zinc, manganese). The highest values were recorded in Stylophora pistillata (iron, lead and copper), Acropora cytherea (cobalt), Pocillopora verrucosa (zinc) and the lowest concentrations were recorded in Goniastrea pectinata (iron, chromium, copper and nickel), Favites pentagona (lead, zinc and manganese), and Porites lutea (cobalt). The differences in metals content among the studied species are attributed to differences in microstructure and microarchitecture.     

Geochemistry and origin of the Cretaceous sedimentary kaolin deposits,Red Sea,Egypt

This work reports, for the first time, the mineralogical and geochemical characteristics of the Cretaceous sedimentary kaolin deposits in the Red Sea area, Egypt and sheds the light on their source. Mineralogical and geochemical analyses of both bulk deposits and the sand and clay fractions of these deposits indicated that they are composed of kaolinite (average of 75 wt.%) and quartz (average of 22 wt.%). Traces of anatase (average of 1 wt.%) were identified in all kaolin samples, while traces of halite (average of 2 wt.%) and hematite (average of 1 wt.%) were reported in the majority of the analyzed samples. The clay fractions show relatively high contents of TiO₂ (average of 2.1%), Ni (average of 103 ppm), Nb (average of 98 ppm), Y (average of 67 ppm), and Zr (average of 630 ppm). Sum of the rare earth elements (ΣREE) in the clay fractions varies between 193 and 352 ppm. Chondrite-normalized REE patterns show enrichment of the light REE relative to the heavy REE ((La/Yb)_N = 9) and negative Eu anomaly (Eu*/Eu = 0.67).     

Surficial calcareous crust of caliche type along the Red Sea coast,Egypt

Karstified features and surficial calcareous crust (caliche) develop on the upper most surfaces of the Middle Miocene rocks in the area between Quseir and Mersa Alam along the Red Sea coast, Egypt. Detailed studies of the caliche profile revealed various textures and fabrics denoting a cyclicity in deposition as well as diagenetic differentiation crystallization and deformation. The occurrence of these caliche deposits suggest that the Middle Miocene rocks in the study area have been subjected to alternating periods of rainfall and intense evaporation.

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Zusammenfassung Karstphänomene und Kalkkrusten (Caliche) haben sich auf den Oberflächen der Gesteine des Mittelmiozäns im Gebiet zwischen Quseir und Mersa Alam entlang der Küste des Roten Meeres in Ägypten entwickelt. Eingehende Untersuchungen von Kalkkrusten Profilen lassen unterschiedliche Strukturen und Gefüge erkennen, die sowohl zyklische Bildung belegen als auch diagenetische Kristallisations-Differentiation und Deformation. Das Auftreten dieser Caliche-Bildungen legt nahe, daß die mittelmiozänen Gesteine im Untersuchungsgebiet abwechselnd regenreichen Perioden und solchen mit starker Evaporation ausgesetzt waren.

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Résumé Des structures karstiques et des croûtes calcaires superficielles (caliches), se sont formées à la surface des roches du Miocène moyen dans la région comprise entre Ouseir et Mersa Alam, le long de la côte de la mer Rouge, en Egypte. L'étude détaillée de profils de la caliche révèle des structures variées qui indiquent un dépôt cyclique ainsi qu'une cristallisation différentielle et une déformation diagénétique. La présence de tels dépôts de caliche suggère que les roches du Miocène moyen de cette région ont été soumises alternativement à des périodes de pluie et d'évaporation intense.

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Quseir Mersa Alam — . , , , , . , .

     

Ability of corals to accumulate heavy metals,Northern Red Sea,Egypt

The concentrations of six heavy metals (Fe, Mn, Ni, Cu, Pb and Zn) were studied in 11 hard and 4 soft common coral species collected from Hurghada, Wadi Al-Gemal and Gola’an along the Red Sea coast to assess the differential abilities of corals to concentrate and assimilate the heavy metals inside soft coral tissues and hard coral skeletons. These results reveal the order of Fe > Zn > Ni > Pb ≥ Mn > Cu. Fe recorded significant high concentrations in mushroom (funnel) forms of the soft corals at the different sites; 125.19, 101.71 and 90.44 ppm at Gola’an, Hurghada and Wadi Al-Gemal, respectively. The soft coral species recorded the highest average concentration of Mn, Ni, Cu and Zn than the hard corals, which were 13.22, 16.05, 13.08 and 148.17 ppm, respectively. Generally, soft corals show higher metal concentrations than the hard ones; moreover, Hurghada recorded a higher trend of metal concentrations in soft and hard corals than the other sites. The study concluded that many biological and local environmental factors influenced the metal occurrences and uptakes in both coral forms such as, the exposed surface area for metal uptake, turbidity, overlying mucus thickness and the ability of metals to substitute inside the crystal lattice of the hard corals.     

Holocene environment and subsistence patterns near the Tree Shelter, Red Sea Mountains, Egypt

The Tree Shelter site dates to the Early to Mid-Holocene (8000 to 4900 ¹⁴C yr BP). Present conditions around the site are hyperarid, but charcoal remains indicate less severe aridity at the time of its occupation. The environment around the site then supported a rich wadi vegetation, which allowed hunting during the Epipaleolithic and herding during the Neolithic occupation. Although more favorable than today, the environmental conditions also displayed a desert character and seem to have limited the range of domestic herbivores introduced in the area.     

Recent crustal deformation and seismicity studies at Abu-Dabbab area, Red Sea, Egypt

The Abu-Dabbab area is characterized by high seismicity and complex tectonic setting; for these facts, a local geodetic network consisting of 11 geodetic benchmarks has been established. The crustal deformation data in this area are collected using the GPS techniques. Five campaigns of GPS measurements have been collected, processed, and adjusted to get the more accurate positions of the GPS stations. The horizontal velocity vectors, the dilatational, the maximum shear strains, and the principal strain rates were estimated. The horizontal velocity varies in average between 3 and 6 mm per year across the network. The results of the deformation analysis indicate a significant contraction and extension across the southern central part of the study area which is characterized by high seismic activity represented by the clustering shape of the microearthquakes that trending ENE. The north and northeastern parts are characterized by small strain rates. This study is an attempt to provide valuable information about the present state of the crustal deformation and its relationship to seismic activity and tectonic setting at the Abu-Dabbab area. The present study is the first work demonstrating crustal deformation monitoring at the Abu-Dabbab area. The time interval is relatively short. Actually, these results are preliminary results. So, the continuity of GPS measurements is needed for providing more information about the recent crustal deformation in that area.     

Karst landform development and related sediments in the Miocene rocks of the Red Sea coastal zone,Egypt

Limestones and evaporites are the main rock types constituting the exposed Middle Miocene sediments of the Red Sea coastal zone between Quseir and Mersa Alam. These rocks represent typical conekarst and karst ridge landforms with minor surface and subsurface solution features.Mechanical, chemical and biogenic precipitates are the main recognized karst sediments. Oxides and sulphides of iron, lead and zinc and barite are also found in association with the karst features and karst products.The obtained observations elaborate the rule of the structure and lithologic characters of the country rocks and the paleoclimatic fluctuation on the formation of the karst features and the related precipitates.

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Zusammenfassung Kalksteine und Evaporite bilden die Sedimente des Mittelmiozäns im Gebiet zwischen Quseir und Mersa Alam. Diese Gesteine zeigen charakteristische Karstphänomene, d. h., regional Kegelkarst, kleinere Karstoberflächen und unterirdische Karstformen.Klastische, chemische und biogene Sedimente werden als Karstfüllungen beobachtet. Oxide und Sulfide von Eisen, Blei und Zink sowie Baryt sind mit dem Karst und den Karstsedimenten verknüpft.Sowohl der Einflu\ der tektonischen Strukturen als auch die Zusammensetzung des mittelmiozänen Ausgangsgesteins und die paleoklimatischen Veränderungen diktieren die Entwicklung des Karstes und die Bildung der Karstsedimente.

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Résumé Les sédiments du Miocène moyen exposés dans la région cÔtière de la Mer Rouge entre Quseir et Mersa Alam se composent essentiellement de roches calcaires et d'évaporites. Ces roches présentent des formes karstiques en cÔnes et en crètes, accompagnées de structures mineures de dissolution à la fois souterraine et de surface.Les principaux remplissages du karst sont des sédiments mécaniques, chimiques et biologiques. Des oxydes et des sulfures de fer, de plomb et de zinc, ainsi que de la barytine sont également reconnus en association avec les formes et les produits du karst.Les observations recueillies expliquent le rÔle de la structure et des caractères lithologiques des roches encaissantes, ainsi que des fluctuations paléoclimatiques sur la formation des karsts et les sédiments qui les accompagnent.

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Quseir Mersa Alam . , . . , . , . , , . , , .

     

Effects of phosphate mining activity on groundwater quality at Wadi Queh, Red Sea, Egypt

The groundwater in Wadi Queh exists in two main hydrogeological units; fractured Precambrian basement and sedimentary rocks with high contribution for groundwater recharge. To study the impacts of phosphate mining activities on the groundwater quality in the area, three groundwater samples that represent all water wells in the area were collected and analysed for major ions and some heavy metals. In addition, three bulk samples representing the phosphatic sediments collected from upstream and downstream of the drainage basin were collected and analysed to understand the source of groundwater contamination. The total concentrations of dissolved solids suggest that the groundwater in the area grades from fresh to brackish water (961–1,580 mg/l), and is characterized by sodium–calcium–sulphate–chloride and sodium–magnesium–sulphate–chloride chemical types. The results showed high concentrations of the heavy metals in well nos. 1 and 2 in downstream parts compared to well no. 3 in upstream part reflecting their influence by the mining activities.     

Structural setup of Ras Banas area,Red Sea,Egypt, as inferred from aeromagnetic data

This study deals with the evaluation of the structural setup of the Ras Banas area on the northwestern part of the Red Sea by using magnetic data. Different analyzing techniques were applied to achieve this goal including regional-residual separation, trend analysis, depth estimation, Euler deconvolution, horizontal gradient, analytic signal, and magnetic modeling. The results of these techniques were used to construct a deep-seated structural feature map.Lineament analysis indicates that the area was mainly affected by the NW, WNW, and NE tectonic trends. The magnetic modeling was performed along four profiles supported by Euler deconvolution, horizontal gradient, and analytic signal profiles. The modeled profiles show that the basement rocks composed of uplifted and down-faulted blocks at different depths as well as step-like structure. The basement rocks seem to be acidic in nature intruded by basic/ultrabasic dikes. Generally, the magnetic susceptibility ranges from 0.0003 to 0.04 cgs indicating acidic to basic/ultrabasic rock composition. The basement relief map shows an irregular basement surface, which varies greatly in depth from 1 to 5.6 km below sea level. The deep-seated structure map shows that the basement was highly affected by two main fault trends in the NW and NNE directions. The NW trending structures were intersected by younger left lateral NNE transform faults. These cross-faults dissect the area into a number of alternated and elongated blocks.     

Distribution patterns of some heavy metals in the surface sediment fractions at northern Safaga Bay, Red Sea, Egypt

The distribution patterns, the index of geo-accumulations (MI_geo), and the enrichment ratios (ER _n ) of the contaminant metals: Fe, Mn, Zn, Cu, Pb, and Ni were studied in gravel, sand, mud, coarse, medium, and fine sediment fractions of the uppermost layer of the bottom sediments collected from 12 stations covering the northern part of Safaga Bay. The distribution levels of these metals were increasing with grain size decreasing toward the central axis of the bay that extends NE–SW and southward to Safaga Harbour indicating that these metals concentrated mainly in the fine, very fine, and particulate fractions of sediments and to many anthropogenic sources. The geo-accumulation factor of Zn was more significant (MI_geo?≈?0.62–4.23) relative to the other metals. The bay was classified as moderately to strongly polluted by Zn while it is unpolluted to moderately polluted with the other metals with accumulation sequence of: Zn>Ni>Cu>Mn≥Pb. Zn and Ni recorded the highest enrichment ratios (average ER_Zn?≈?3.07 to 8.89; average ER_Ni?≈?0.84 to 3.63) in the different sediment fractions relative the other metals. These enrichment ratios classified the bay as minimal enrichment, suggestive of no or minimal pollution, to significant enrichment, suggestive of a significant pollution signals with metals sequence of: Zn>Ni>Cu>Pb>Mn.     

Petrology and geochemistry of peridotites and associated vein rocks of Zabargad Island,Red Sea,Egypt

Summary Zabargad (St. John's) Island in the Red Sea contains three ultramafic bodies, one of which bas produced the famous gem olivine (peridot). The ultramafic rock types consist of two major groups—the peridotites and the vein rocks within them. The peridotites are divided into three groups: primitive, depleted and metasomatized. The primitive peridotites are the most abundant and are represented by mainly pristine spinellherzolites which have chemical compositions representative of the subcontinental upper mantle. The depleted peridotites are mainly harzburgites and nome dunites and both are similar to worldwide occurrences. The most depleted peridotites also appear to have the greatest metasomatic additions of incompatible elements, as has been noted at other localities. Metasomatic additions were clearly accompanied by tectonic shearing. Metasomatism included infiltration of incompatible elements and the formation of porphyroblasts of clinopyroxene, amphibole, Al-spinel and plagioclase; il took place under a variety of p-T conditions and with fluids of differing compositions.The vein rocks are mainly monomineralic and comprise olivinites, orthopyroxenites, clinopyroxenites, websterites, hornblendites and plagioclasites. These rocks are believed to have formed from fluids similar to that which metasomatized the host rock, rather than by some kind of igneous process. The fluids were derived from peridotite reservoirs (fertile and depleted) and apparently were in equilibrium with these reservoirs. Highly abundant fluid inclusions document the hypersaline and CO₂-dominated character of these fluids. Monomineralic vein rocks are closely associated with metasomatic and tectonic processes, and there is a complete transition between metasomatic impregnation and formation of vein rocks. These processes may have also been active in other peridotite bodies of the world, as was earlier recognized and documented in the Seiad Ultramafic Complex, California. Metasomatism is evident along clinopyroxenite and hornblendite veins, whereas orthopyroxenites, olivinites and plagioclasites do not show any interaction with the wall rocks. Olivinites are probably the latest (lowest p-T) vein rock type, and the latest olivine which formed within their open cavities became the gem peridot.Zabargad ultramafic rocks preserve relic phases indicating an initial depth of origin greater than 85 km. Clinopyroxenites preserve the memories of the highest p-T conditions and they may be the first vein rock type formed in the peridotites. The p-T path of uplift coincides with the oceanic geotherm at great depth but deviates systematically from it with falling pressure in a series of tectonic stages accompanied by metasomatism and recrystallization. The p-T and petrologic history indicates rapid uplift, a feature which is supported by extensive contact metamorphism of the associated metasediments.

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Petrologie und Geochemie der Peridotite und der mit diesen vergesellschafteten Ganggesteine der Insel Zabargad, Rotes Meer, Ägypten

Zusammenfassung Auf der Insel Zabargad (St.John's Island) im Roten Meer befinden sich drei Peridotit-Körper von denen einer seit Jahrtausenden den berühmten Peridot (Edelolivin) geliefert hat. Die ultramafischen Gesteine von Zabargad gliedern sich in zwei Hauptgruppen: die Peridotite und die mit diesen vergesellschafteten Ganggesteine. Die Peridotite können in drei Gruppen gegliedert werden: die primitiven, die verarmten und die metasomatisch veränderten Peridotite. Am meisten verbreitet auf Zabargad sind die primitiven Peridotite. Diese sind meist Spinell-Lherzolithe mit einer chemischen Zusammensetzung, welche dem subkontinentalen Oberen Erdmantel entspricht. Die verarmten Peridotite werden hauptsächlich von Harzburgiten und einigen wenigen Duniten repräsentiert. Beide sind jenen aus anderen Vorkommen der Welt sehr ähnlich. Die am stärksten verarmten Peridotite scheinen auch die stärksten metasomatischen Veränderungen erfahren zu haben—ein Trend, der auch schon an anderen ultramafischen Komplexen erkannt wurde. Metasomatische Anreicherungen inkompatibler Spurenelemente sind häufig direkt mit tektonischer Verformung und Kataklase gekoppelt. Die Metasomatose ist als Infiltration inkompatibler Elemente erkennbar und führte auch zur Bildung von Porphyroblasten von Klinopyroxen, Amphibol, Al-Spinell und Plagioklas. Diese Bildungen fanden unter verschiedenen p-T-Bedingungen statt und erfolgten durch Fluide mit unterschiedlichen Zusammensetzungen.Die (meist ultramafischen) Ganggesteine sind häufig monomineralisch und umfassen Olivinite, Orthopyroxenite, Klinopyroxenite, Websterite, Hornblendite und Plagioklasite. Wir glauben, daß diese Gesteine von Fluiden gebildet wurden, welche ähnlich jenen waren, die die Metasomatosen der Peridotite verursachten. Diese Genese wird von uns der magmatischen vorgezogen. Die Fluide stammten aus peridotitischen Reservoiren (fertilen und verarmten) und waren mit diesen offenbar im Gleichgewicht. Die Ganggesteine sind sehr reich an fluid inclusions, welche allerdings keine Flüssigkeit enthalten, sondern nur Festkörper (Salze) und CO₂ (± N₂), also einen trockenen, hypersalinen Charakter haben. Auch die monomineralischen Ganggesteine sind eng mit tektonischen Prozessen verknüpft und somit auch mit metasomatischen Prozessen. Es existieren vollkommene Übergänge von metasomatischen Imprägnationen bis zu echten Ganggesteinen. Solche Prozesse waren offensichtlich auch weltweit in anderen ultramafschen Komplexen aktiv und wurden schon im Seiad Ultramafc Complex in Kalifornien erkannt und beschrieben. Metasomatismus begleitet überlicherweise die Klinopyroxenit- und Hornblendit-Gänge. Orthopyroxenite, Olivinite und auch Plagioklasite zeigen jedoch keine Wechselwirkung mit den Wirtgesteinen. Olivinite sind wahrscheinlich die zuletzt gebildeten Ganggesteine. Der zuletzt sich bildende Olivin wurde der schönste und zum gesuchten Peridot.Alle ultramafschen Gesteine von Zabargad enthalten Minerale aus verschiedenen Bildungsepochen. Einige Relikte erinnern an eine Herkunft aus einer Tiefe von mehr als 85 km. Klinopyroxenite konservierten die höchsten p-T-Bedingungen. Sie waren daher wahrscheinlich die ersten (noch erhaltenen) Ganggesteine, welche sich im peridotitischen Erdmantel unterhalb des heutigen Roten Meeres bildeten. Der p-T-Pfad der Zabargad Ultramafitite deckt sich in großer Tiefe mit der ozeanischen Geotherme. Mit abnehmender Tiefe entfernt sich dieser Pfad allerdings zunehmend von der Geotherme und läßt eine Reihe von tektonischen Aktivitäten verbunden mit Metasomatose und Rekristallisation erkennen. Die p-T-Geschichte der Zabargad Ultramaftite deuten auf einen raschen Aufstieg aus dem Erdmantel hin. Diese Daten werden durch die weitverbreitete und intensive Kontaktmetamorphose der mit den Peridotiten assoziierten Metasedimenten unterstützt.

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Dedicated to Prof. Josef Zemann on the occasion of his 70th birthday

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With 12 Figures     

Quaternary coral reefs of the Red Sea coast, Egypt: diagenetic sequence, isotopes and trace metals contamination

This study focuses on the diagenetic sequence under marine and meteoric conditions as well as isotopes and trace metals contamination in Quseir and Gebel Zeit areas along the Egyptian Red Sea coast through a series of modern and fossil corals, Porites lutea and Favites pentagona. The diagenetic sequence begins with deposition of thin fringes of syntaxial aragonite and micritic high-magnesian calcite in the modern corals to completely altered Porites and partially altered Favites to low-magnesium calcite in the oldest Pleistocene unit. Average δ¹⁸O and δ¹³C values of Pleistocene corals in the two studied areas were lower than those of modern corals. Values of modern corals and lower fossil unit indicated coralline limestone, while those of middle and upper fossil units indicated fresh water influences. Average values of trace metals in modern corals were higher than those of Pleistocene counterpart except for Mn. Modern coral samples recorded enrichment in the average values of Pb, Zn, and Mn at Quseir area and enrichment in Co, Cu, and Ni at Gebel Zeit area. This may be attributed mostly to different tourist activities, landfill due to increase urbanization and nearby of Quseir area from the old phosphate harbor at El Hamrawin area, as well as oil exploration and production activities in the Gulf of Suez area. Also, results indicated that most samples of Porites have high concentration of trace metals than in Favites, especially in Cu, Zn, Mn, and Pb. This may due to high amounts of intergranular porosity and high total surface area of Porites in contrast to Favites.     

Impacts of human activities on the sedimentological and geochemical characteristics of Mabahiss Bay, North Hurghada, Red Sea, Egypt

In Mabahiss Bay, north Hurghada City, Red Sea, Egypt, the bathymetric measurements show the irregular topography of the bottom. The bottom sediments are mainly composed of sand fractions (average 73.5%). Gravel and sand contents decrease with depth. On the other hand, silt and clay percents show indirect relation with depth. Abnormally, there are some spots found near the coast where the percent of both silt and clay increases. They also show carbonate sediments (average 90.15%) increasing toward the bay center. The narrow belt adjacent to the shore area has lower carbonate content reflecting the effect of clastic sediments input into the area. The sediments in the study area have more than one source as indicated from the results of the mechanical analysis. Wide range of grain size distributions, clay spots and low carbonate content near the shore indicate change in the nature of sedimentary environment (i.e., pollution) which may be caused by land filling accompanied with urbanization and building of touristic resorts and centers. The organic matter content in the sediments is much higher than that of the other areas in the Red sea (average 4.8%) with considerable accumulation in the inner most parts of the bay. This may be due to relative abundance of organic productivity, direct discharge of domestic waste in some spots along the coast of the study area, and/or local contamination of hydrocarbons (i.e., tar balls thrown out on shore by weak waves through the few inlets of the study area). The average concentrations of lead, nickel, copper, and cadmium are 44, 34, 51, and 3.1?ppm, respectively. The suggested origin of these metals is either organic (localized oil pollution), or using of antifouling and anticorrosive paints from fishing and tourist boats. Other metals, particularly manganese (average 77?ppm), cobalt (average 51?ppm), and zinc (average 16?ppm) as well as sodium (average 0.32%) and potassium (av. 0.10%) show a common trend of increasing concentration toward the outermost parts of the bay. Some parts along shoreline have increasing concentrations, even if these parameters having a common trend of increase towards the center of the bay. This may be either due to sewage and wastewaters discharges from many outlets of tourist centers and fishermen and cargo boats, and/or terrestrial sediments input. Direct comparison of the present levels of heavy metals in Mabahiss Bay with other published data along the Red Sea and Gulf of Suez shows that the study area has higher concentrations. Dredging, land filling, localized oil pollution, using of antifouling and anticorrosive paints from fishing and tourist boats (where the bay is used as harbor for many of fishermen and cargo boats), sewage, variable amounts of municipal wastewater from many outlets of tourist centers considered to be the sources of pollution within Mabahiss bay. There are many effects of pollution on Mabahiss Bay environment among which: (1) death of fishes, seaweeds, birds, marine mammals, etc., (2) damage of beaches and other recreational areas, (3) damage of marine ecosystem by eliminating or decreasing population of certain species, (4) hazard to human from ingesting contaminated food, and more.     

Trace-elements content of galenas and associated minerals in some Miocene lead-zinc deposits near Red Sea Coast,Egypt

The trace-elements content of some M. Miocene Egyptian galenas is given and the method is briefly described. The relative enrichment in Tl and Cd together with the irregular distribution and low Ag, Bi and Sb content indicate low temperature conditions of formation. The trace content of hemimorphites, cerussites, wulfenites and other minerals associated with galena shows that they are related to ascending exhalative solutions.

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Zusammenfassung Aus dem MiozÄn Ägyptens wurde Bleiglanz auf Spurenelemente hin untersucht. Die Arbeitsmethode wird kurz dargestellt. Die relative Anreicherung im Gehalt von Tl und Cd sowie die unregelmÄ\ige Verteilung und der niedrige Anteil an Ag, Bi und Sb zeigen niedrige Bildungstemperaturen an. Der Spurengehalt von Hemimorphiten, Cerussiten, Wulfeniten und anderen Mineralen gemeinsam mit Bleiglanz weist auf einen Zusammenhang mit aufsteigenden exhalativen Lösungen hin.

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Résumé Des galènes du Miocène d'Egypte ont fait l'objet d'une recherche sur la base des éléments en traces. La méthode de travail est décrite. L'enrichissement relatif en Tl et Cd, ainsi que la répartition irrégulière et la faible participation en Ag, Bi et Sb indiquent de basses températures de formation. La teneur en traces des hémimorphites, cérusites, wulfénites et autres minéraux associés à la galène indique une liaison avec des solutions exhalatives montantes.

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