Zur Geologie von Ayûn Mûsa am westlichen Sinai, Ägypten

Zusammenfassung Der geologische Aufbau des Untergrunds von Ayûn Mûsa am westlichen Sinai wird beschrieben. Mesozoische Gesteinsserien unter dem an der Oberfläche allein verbreiteten U. Miozän (Burdigal), wurden bei mehreren Bohrungen auf Kohle durchörtert.Der Nubische Sandstein, der örtlich verschiedenes stratigraphisches Alter aufweisen kann, wird hier in seiner gleichförmigen Ausbildung durch eingeschaltete marine Serien des mittleren und oberen Juras untergliedert. Etwa an der Wadi Araba—G. Somâr-Achse findet diese marine Ausbildung die südliche Begrenzung und die Abfolge geht in die kontinentale oder ästuarine Fazies des Nubischen Sandsteins über.Der vortertiäre Schichtenverband wurde im Gefolge der laramischen Gebirgsbildungen strukturelles Teilstück im Syrischen Bogen und damit aus dem marinen Sedimentationsbereich herausgehoben. Das NE-SW streichende flachwellige Faltungsgebiet unterlag an der Wende Mesozoikum-Känozoikum tiefgründiger Abtragung, bis im Eozän die Lutet-Transgression auch den Raum von Ayûn Mûsa erfaßt. Danach wurde der Sinai erneut aus dem meerischen Sedimentationsraum herausgehoben und wieder Abtragungsgebiet.Die miozäne Transgression (Globigerinen-Mergel des Burdigal) griff mit mächtigen Konglomeraten undAmphistegina-Sanden über das eingeebnete und absinkende Gebiet am westlichen Sinai. Der Einbruch des Roten-Meer-Grabens und die Heraushebung des Plateaus von El Tih im zentralen Sinai engte den marinen Bereich auf die heutigen Tiefenfurchen (Golf von Suez und Aqaba) ein. Im Gefolge dieser Grabentektonik wurde das Ayûn-Mûsa-Gebiet horstförmig zerschnitten.

---

The subsurface geology of Ayûn Mûsa (West Sinai) ist briefly described from several boreholes. Lower Miocene (Burdigalian) covers the entire region, underlain by a Mesozoic sequence.The Nubian Sandstone, which is of different age at various localities in Egypt, interfingers with marine Middle and Upper Jurassic beds, extending as far south as the Wadi Araba — G. Somâr Axis.The Pre-Tertiary beds of Ayûn Mûsa were gently folded with a NE-SW strike during the Laramic orogeny and became structurally part of the Syrian Arc.After the folding the region was deeply eroded until Eocene when the Lutetian transgression invaded Ayûn Mûsa area. This was followed by a general upheaval and further erosion of the Sinai structural complex.This period of erosion is followed by a Miocene transgression in the subsiding area of western Sinai. The basal part of the Lower Miocene consists of thick conglomerats andAmphistegina sands which pass upwards into BurdigalianGlobigerina-Marls. Later differential block movements caused the formation of the Red-Sea-Graben and the uplift of the Plateau of El Tih (Central Sinai) resulting in a local horst in the Ayûn Mûsa district. This restricted the marine sedimentation to the region of the Golf of Suez and Aqaba.

---

Résumé L'auteur décrit la constitution géologique du soubassement de Ayûn Mûsa dans la partie occidentale du Sinaï. Des séries de roches mésozoïques parmi lesquelles seul le Miocène inférieur (Burdigalien) affleure, ont été traversées par plusieurs sondages pour recherches de charbon.Le grès nubien, qui, suivant les endroits, peut être d'âge stratigraphique différent, est divisé ici dans un faciès uniforme, par des séries marines intercalées appartenant au Jurassique moyen et supérieur. Cette formation marine se termine vers le Sud a peu près suivant l'axe Wadi Araba — G. Somâr et la série passe au faciès continental ou estuairien du grès nubien.Le complexe de couches pré-tertiaires fut soulevé au cours de la formation des chaînes laramiques suivant l'arc syrien et soustrait ainsi au domaine de sédimentation marine. La région largement plissée dirigée NE-SW a subi, à la limite du Mésozoïque-Cénozoïque, une érosion profonde jusqu'au moment où, à l'Eocène, la transgression du Lutétien atteignit la région de Ayûn Mûsa. Ensuite le Sinaï a été soulevé à nouveau et soumis à l'érosion. La transgression miocène (Marne à globigerines du Burdigalien) a empiété avec ses conglomérats puissants et les sables àAmphistegina sur le domaine pénéplané et en voie d'affaissement à l'Ouest du Sinaï. L'affaissement du Graben de la Mer Rouge et le soulèvement du plateau de El Tih dans le Sinaï central a rétréci le domaine marin au sillon profond tel qu'il existe aujourd'hui (Golfes de Suez et d'Akaba). A la suite de cette tectonique en graben, le domaine de Ayûn Mûsa a été découpé suivant une structure en horst.

---

Ayûn Mûsa (); , .

     

Petrology and geochronology of eclogites from the Variscan Schwarzwald (F.R.G.)

The Moldanubian basement of the Schwarzwald contains basic to ultrabasic rocks of both crustal and mantle origin which display high-pressure mineral assemblages or relics of such. In order to constrain the P-T-t evolution of the crustal high-pressure rocks, petrological and geochronological studies have been carried out on three eclogite samples. Geothermobarometric estimations indicate minimum metamorphic pressures of 1.6 GPa and equilibration temperatures of 670 750°C. Reaction textures document various metamorphic stages during exhumation of the high-pressure rocks. The age of high-pressure metamorphism is constrained by Sm-Nd isochrons of 332±13 Ma, 334±11 Ma, and 337±6 Ma defined by garnet, whole rock and clinopyroxene. For one sample, large garnets show prominent growth zoning in terms of major elements, Sm, Nd, and inclusions, dividing the grains into two growth stages. Sm-Nd isotope analyses on these garnets indicate that the time span between the two growth stages is too small to be resolved, reflecting a rather rapid metamorphic evolution. This result is further constrained by a Rb-Sr isochron age of 325±6 Ma on retrograde biotite and whole rock on the same sample. For one of the studied eclogites, formation of the magmatic precursor rocks is possibly approximated by the Ordovician U-Pb upper intercept age of a discordia from zircons.     

Quasi-nonhydrostatic extensions in an anelastic model of a gravity current

Summary The effect of simple quasi-nonhydrostatic approximations in a numerical model of a gravity current are discussed. Two methods for including non-hydrostatic effects are explored. The reasons for the limited success of a first method is discussed briefly.With 9 Figures     

New Relationship for Estimation of Wave Overtopping on Vertical Walls

Soft computing tools in the form of combination of multiple nonlinear regression and M5'' model tree were used for estimation of overtopping rate at the vertical coastal structures. For reliable and precise estimation of overtopping rate, the experimental data available in the database CLASH were used. The dimensionless overtopping rate was estimated in terms of conventional dimensionless parameters including the relative crest freeboard R_c/H_s, seabed slope tanθ, deep water wave steepness S_om, surf similarity ξ_om and local relative water depth h_t/H_s. The accuracy of the new model was compared with other existing models and also evaluated with some field measurements. The results indicated that the model presented in this paper is more accurate than other existing models. With statistical parameters, it is shown that the accuracy of predictions in the new model is better than that of other models.     

Near-infrared reflectance spectra from bulk samples of the two Martian meteorites Zagami and Nakhla

Abstract— Zagami and Nakhla are achondrites and belong to the Shergotty-Nakhla-Chassigny (SNC) meteorite group. It is generally accepted that Mars is their parent body. Mineralogical and chemical analyses have revealed that the major mineral phases of these two meteorites are pyroxene, olivine, maskelynite, and plagioclase. In this work, near-infrared biconical reflectance measurements were performed on sawed surfaces of chips from Zagami and Nakhla. Spectra obtained with an analytical spot diameter on the order of the mineral grain size reflect the heterogeneous distribution of different mineral phases. The characteristic absorption bands of the pyroxenes are numerically evaluated in terms of the modified Gaussian model. Spectra with overlapping absorption features are resolved into the basic absorption bands. From these results, it can be estimated what kind of clinopyroxenes belong to the investigated mineral assemblages. As a result, the major clinopyroxene phase in Nakhla is Ca-rich augite, whereas in Zagami both Ca-rich and Ca-poor pyroxenes are present. By means of such a procedure, laboratory spectra of minerals become more informative and may help in discussing Martian remote sensing data in the near-infrared region.     

Recognition of Space Weather Impact on the Isophot Detectors

The effects of changes in the space environment on the ISOPHOT photoconductivedetectors over the whole ISO mission were studied using the complete setof responsivity check measurements taken after the curing of the detectors.We found that the responsivity of the Ge-based, low bias voltage far-infrared detectors (P3, C100, and C200) is sensitive to the conditions of the Space Weather.We present evidence that an increased responsivity level (20% – 50%) after curing of the detectors is linked to the onset of geomagnetic storms. TheSi-based, high bias voltage detectors P1, P2 and PHT–SS show only small changesin their responsivity. An exception is the PHT–SL array which shows a similar,but less pronounced behaviour as the FIR detectors. While these relationshave been demonstrated by our study, a detailed physical understanding is still outstanding. The Space Weather dependent scatter of the responsivity,being the photometric scaling factor (conversion from measured photo currentto inband power on the detector), justifies the observing mode design to include frequent monitoring of its actual level.     

Controls of uncertainty in acid rock drainage predictions from waste rock piles examined through Monte-Carlo multicomponent reactive transport

Stochastic Environmental Research and Risk Assessment - Heterogeneity in waste rock piles (WRPs) determines uncertainty in acid mine drainage (ARD) predictions from these deposits. Numerical...     

Plate motions and the viscosity structure of the mantle — Insights from numerical modelling

We use sulfur (S) isotope signatures within ancient sediments and a photochemical model of sulfur dioxide (SO₂) photolysis to interpret the evolution of the atmosphere over the first half of Earth's history. A decrease in mass-independent sulfur isotope fractionation has been reported in Archean rocks deposited between ~ 2.7 Ga and ~ 3.2 Ga, and is reinforced by new S isotope data that we report here. This pattern has been interpreted by some as evidence that atmospheric oxygen (O₂) was elevated during this time. In this paper, we argue against that conclusion, and show that it is inconsistent with other geochemical data. In its place, we propose a new model that can explain the sulfur isotope record that can also avoid conflicts with independent constraints on O₂ and account for concurrent glacial deposits. Specifically, we suggest that prior to the rise of O₂ excursions in the sulfur isotope record were modulated by the thickness of an organic haze. This haze would have blocked the lower atmosphere from the UV fluxes responsible for the anomalous sulfur photochemistry and would have caused an anti-greenhouse effect that triggered the glaciations. We used a photochemical model to verify that a haze could have affected the isotopic signal in this manner, and to examine how changes in atmospheric methane (CH₄) and carbon dioxide (CO₂) concentrations could have controlled haze thickness. Finally, we combined the resulting relationships with climate models and sulfur isotope and glacial records to deduce a new evolutionary sequence for Archean climate, surface chemistry, and biology.     

Model-based long-term reconstruction of weather-driven variations in chronic oil pollution along the German North Sea coast

Lagrangian passive tracer transport simulations covering the 46-year period 1958-2003 were utilized to compare the exposures of different parts of the German North Sea coast to ship-related chronic oil pollution. Assuming the spatial distribution of oil releases to be proportional to estimated ship traffic density, detailed drift reconstructions allowed for the reconstruction of wind-induced inter-annual variations in coastal pollution. For the winter months, a statistical relationship between simulated advective transports and prevailing sea surface pressure fields was established via Canonical Correlation Analysis. Wind effects were found to be more important for the northern (Schleswig-Holstein) than for the southern (Lower Saxony) part of the German North Sea coast. For Schleswig-Holstein, simulations showed consensus with beached bird survey data from this region. Proper identification of weather-driven inter-annual and spatial variations in monitoring data helps to avert misjudgments with regard to trends in the general level of chronic oil pollution.     

Continuous gas monitoring in the West Bohemian earthquake area,Czech Republic: First results

Two stations monitoring concentrations of carbon dioxide and radon in soil gas (Oldřišská and Novy Kostel) and one station monitoring flow of carbon dioxide at a mofette (Soos) have been operated in the area of the West Bohemian earthquake swarms. We present preliminary results obtained on the base of four-year observations. We found that data are not influenced considerably by barometric pressure. Although the CO₂ concentration varies greatly, the long-term trends at stations Oldřišská and Novy Kostel are similar, which indicates that the CO₂ flow is controlled by common geogenic processes. Also temporal trends of CO₂ and Rn concentrations in soil gas at individual stations are analogous. We found diurnal variations of both CO₂ concentration in soil gas and the CO₂ flow at mofettes due to the earth tides. A response to tides of semi-diurnal period is insignificant in CO₂ concentration and only weak in the CO₂ flow. We also examined possible pre-seismic, co-seismic and post-seismic effects of the intensive 2008 earthquake swarm on the CO₂ concentration at Oldřišská and Novy Kostel, and on the CO₂ flow at Soos. However, all potential indications were insignificant and there has not been proven any influence of the swarm on the CO₂ concentration as well as on the CO₂ flow. Nevertheless, a gradual decrease of amplitudes of diurnal variations before the swarm and the lowest amplitudes during the swarm is a noteworthy phenomenon, which might indicate the strain changes of the rock associated with earthquake swarm.