Extensional tectonic origin of gneissosity and related structures of the Feiran–Solaf metamorphic belt, Sinai, Egypt

The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S₁, and is almost everywhere parallel to lithological layering, S₀. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S₀. S₁ formed by coaxial pure shear flattening strain (Z normal to S₀, i.e. vertical; with X and Y both extensional and lying in S₁). This strain also produced chocolate tablet boudinage of some layers and S₁-concordant sills and veins. S₁ has a strong stretching lineation L₁ with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L₁-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F₁ folds with hinges parallel to the stretching lineation. F₁ fold asymmetry variations do not support previous models involving macroscopic F₁ folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia.     

Distribution of Boron in Some Egyptian Aquatic Environments

Concentrations of boron in seawater (from four regions along the Alexandria coastline, subjected to land disposal), brackish water (Lake Edku) and drains water (e.g. El-Umum Drain) were determined during the period from February to August 2000. Boron was determined spectrophotometrically by a modified curcumin method. For Lake Edku, boron concentration fluctuated between 0.023 and 0.105 mmol/l. There are several factors that affect the concentration of B in the Lake water: (a) effect of the drainage water via El-Khairy and Barsiek Drains, (b) utilization of boron by hydrophytes, and (c) water exchange through the sea-lake connection. It may be concluded that the level of boron in the Lake water cannot be considered a substantial hazard to the Lake organisms. Boron concentration varied from 0.392 to 0.522 mmol/l in seawater samples and from 0.141 to 0.458 mmol/l in the sites where the water from the drains (El-Umum Drain and El-Noubaria Canal) mixed with the seawater. The broader variation of boron (mmol/l)/salinity ratios for seawater samples (0.0106–0.0138) may be due to that the samples were collected from the upper seawater layers, where contributions from land run-off, atmospheric precipitation and differences in the biota affect the concentration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stability of waterfront retaining wall subjected to pseudo-static earthquake forces

Waterfront retaining walls supporting dry backfill are subjected to hydrostatic pressure on upstream face and earth pressure on the downstream face. Under seismic conditions, if such a wall retains a submerged backfill, additional hydrodynamic pressures are generated. This paper pertains to a study in which the effect of earthquakes along with the hydrodynamic pressure including inertial forces on such a retaining wall is observed. The hydrodynamic pressure is calculated using Westergaard's approach, while the earth pressure is calculated using Mononobe-Okabe's pseudo-static analysis. It is observed that when the horizontal seismic acceleration coefficient is increased from 0 to 0.2, there is a 57% decrease in the factor of safety of the retaining wall in sliding mode. For investigating the effect of different parameters, a parametric study is also done. It is observed that if φ is increased from 30° to 35°, there is an increase in the factor of safety in the sliding mode by 20.4%. Similar observations were made for other parameters as well. Comparison of results obtained from the present approach with [Ebeling, R.M., Morrison Jr, E.E., 1992. The seismic design of waterfront retaining structures. US Army Technical Report ITL-92-11. Washington DC] reveal that the factor of safety for static condition (k_h=0), calculated by both the approaches, is 1.60 while for an earthquake with k_h=0.2, they differ by 22.5% due to the consideration of wall inertia in the present study.     

Evaluation of twenty four new Gossypium hirsutum strains for growth, yield, fibre quality and ClCuV resistance under environment of Punjab, Pakistan

Twenty four new strains were tested for their yield, quality and Leaf Curl Virus (ClCuV) resistance. NIAB-111/S, NIAB-98 and NIAB-999 were significantly high fruit bearing varieties at 90 days completing 59.54, 48.26 and 46.00% fruiting respectively. Seed cotton yield of VH-142 was highest with 5417 kgha^?1 and 52 per plant boll bearing, DNH-57 and NIAB-999 remained second and third with 5234 and 5095 kg ha^?1 seed cotton yield, respectively. BH-160 and CRIS-467 were found to be second and third highest boll bearing varieties with 50.97 and 40.20 per plant average bolls respectively. Plant height in CRIS-467, MNH-642 and SLH-224 was significantly higher in comparison to other varieties.NIAB-98, CIM-499 and CIM-506 were found short stature varieties in comparison with other but out of these NIAB-98 and CIM-506 were in high yielding position and CIM-499 was found medium yielder variety. GOT% of MNH-642 remained highest having value of 45.00%. While GOT%. of NIBGE-1, CRIS-168 and CRIS-467 was at lowest position with 35.73, 35.89 and 36.62% respectively. NIAB-111, CIM-499 and BH-160 were at first position in terms of fibre fineness with micronaire values 3.98, 4.00 and 4.07 ìg/inch having fibre length 28.53, 31.38 and 30.23 mm respectively. Out of 26 varieties, 16 varieties resulted maturity index in the range of 85.03% and 90.30% with highest maturity index in case of NIBGE-1 (i.e. 90.30%) followed by NIAB-999 and MNH-642 with 89.55 and 85.5% respectively.CRIS-168, CRIS-468 and CRIS-467 were found viral susceptible.     

Structure sismique du socle paléozoı̈que du bassin des Doukkala,Môle côtier,Maroc occidental. Indication en faveur de l'existence d'une phase éo-varisqueSeismic structure of the Doukkala basin,Palaeozoic basement,western Morocco: a hint for an Eovariscan fold-and-thrust belt

Seismic profiles and well data from the Doukkala basin unravel the structure of the Palaeozoic basement and suggest that this coastal zone of western Morocco was affected by a compressive phase during the Frasnian. This resulted in the formation of upright, plurikilometric folds associated with reverse faults (North Doukkala), and of asymmetrical folds associated with mostly west verging ramps (South Doukkala). Folding involved all pre-Upper Frasnian formations and caused partial or total hiatus of Upper Frasnian–Strunian strata. This event can be correlated with the orogenic phase reported from more internal domains of the Morocco Hercynian belt, where it is referred to as the ‘Bretonne’ or ‘Eovariscan’ phase. To cite this article: H. Echarfaoui et al., C. R. Geoscience 334 (2002) 13–20     

Simulation of individual particle movement in a gravel streambed

A two‐dimensional simulation model of travel distances of individual particles in a gravel‐bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed‐surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move. Copyright © 2002 John Wiley & Sons, Ltd.     

Geomorphology of the eastern coast of the Dead Sea, Jordan

This paper aims to investigate the geomorphological characteristics of theeastern coast of the Dead Sea as influenced by structural instability andclimatic changes. Aerial photos and map analyses served to distinguish mainmorphological features and slope classes, whereas geomorphological changesalong the cost, mainly those developed by the declining of the Dead Sealevels were located and examined in the field. The eastern coast of the DeadSea was considered an ultimate outcome of stream work practiced undercontrols of sea-level lowerings. Climatic, hydrological and structuralinstabilities characterizing the study coast put watersheds and wadisdraining into the sea under accelerated erosion that produced huge volumes ofsediments to be deposited in the upper levels of the subsiding former lakesof the Dead Sea. Retrogradation exposed subaqueous deltaic-fluviatileformations, contributing to coastal geomorphological development. Also,present climatic seasonal fluctuations, rejuvenating stream work, continue tosubject past depositional environments to denudation as the stream distanceof transport is increased, and newer subaqueous deltas are being formed.Weathering and mass-wasting processes added to such a development byenhancing the formation of karst, tofoni and pedestal features as well as thehigh erodibility rate of deltaic sediments which endagers constructionalprojects along the study coast.     

Rock composition and origin of the Duwi Formation calcareous rocks, Upper Egypt

Upper Cretaceous phosphorite beds of the Duwi Formation, Upper Egypt, are intercalated with limestone, sandy limestone, marl, calcareous shales, and calcareous sandstone. Calcareous intercalations were subjected to field and detailed petrographic, mineralogical and geochemical investigations in order to constrain their rock composition and origin. Mineralogically, dolomite, calcite, quartz, francolite and feldspars are the non-clay minerals. Smectite, kaolinite and illite represent the clay minerals. Major and trace elements can be classified as the detrital and carbonate fractions based on their sources. The detrital fraction includes the elements that are derived from detrital sources, mainly clay minerals and quartz, such as Si, Al, Fe, Ti, K, Ba, V, Ni, Co, Cr, Zn, Cu, Zr, and Mo. The carbonate fraction includes the elements that are derived from carbonates, maily calcite and dolomite, such as Ca, Mg and Sr. Dolomite occurs as being dense, uniform, mosaic, very fine-to-fine, non-ferroan, and non-stoichiometrical, suggesting its early diagenetic formation in a near-shore oxidizing shallow marine environment. The close association and positive correlation between dolomite and smectite indicates the role of clay minerals in the formation of dolomite as a source of Mg^2＋ -rich solutions. Calcareous rocks were deposited in marine, oxidizing and weakly alkaline conditions, marking a semi-arid climatic period. The calcareous/argillaceous alternations are due to oscillations in clay/carbonate ratio.     

Metal binding to dissolved organic matter and adsorption to ferrihydrite in shallow peat groundwaters: Application to diamond exploration in the James Bay Lowlands,Canada

The speciation and solubility of kimberlite pathfinder metals (Ni, Nd, Ba and K) in shallow peat groundwaters is investigated over the Yankee, Zulu and Golf kimberlites in the Attawapiskat region, James Bay Lowlands, Canada. The purpose of this study is to examine the relationship between dissolved organic matter (DOM) complexation with kimberlite pathfinder metals and determine the spatial distribution of those metals in shallow peat groundwaters along sampling transects over subcropping kimberlites. Nickel, Nd, Ba and K complexation with DOM and the adsorption of these metals onto ferrihydrite were calculated using Visual MINTEQ 3.0 and the NICA-Donnan database. Calculations predict almost 100% of soluble Nd, Ni and Ba form complexes with DOM at sampling sites with little to no contribution from upwelling groundwater (i.e., dissolved organic C (DOC) concentrations = 40–132 mg/L, pH = 3.9–5.5, and log ionic strength ??3). In only the most ombrotrophic peat groundwater conditions does a majority fraction of K bind to DOM. By contrast, under conditions with large contributions from upwelling groundwaters (i.e., DOC concentrations ?40 mg/L, pH = 5.5–6.5, and log ionic strength = ?3 to ?2), as little as 10% of Nd and Ni, and 0% K and Ba are predicted to complex with DOM. The modeling calculations suggest the dominant control on metal–DOM complexation, particularly with respect to Ni and Nd, is competitive effects for DOM binding sites due to elevated ionic strength where there is evidence of strong groundwater upwelling. Visual MINTEQ modeling of metal adsorption on ferrihydrite surfaces predicts that under strong upwelling conditions, Ni and Nd are scavenged from solution due to increased ferrihydrite precipitation and decreased fractions of metals complexed with DOM. Analytical geochemical data are consistent with model predictions of metal adsorption on ferrihydrite. Total dissolved Ni and Nd concentrations at sites of strong upwelling are up to five times lower than waters with little to no upwelling and log ferrihydrite saturation indices (logSI_ferr) indicate precipitation (values up to 5) at sites of strong groundwater upwelling. Where the majority of Ni and Nd complex with DOM and ferrihydrite is highly under saturated (logSI_ferr = ?18 to ?5), the concentrations of total Ni and Nd are elevated compared to other sites along sampling transects. Metal complexation with DOM effectively inhibits metal scavenging from solution via adsorption and/or from forming secondary mineral precipitates. Also, because alkaline earth metals do not compete strongly with Ni and Nd for adsorption sites on ferrihydrite surfaces, but do compete strongly for insoluble organic sites, Ni and Nd are more likely to adsorb onto ferrihydrite.     

Geological and geophysical studies of the Agoudal impact structure (Central High Atlas,Morocco): New evidence for crater size and age

Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km²) and 1:15,000 (2.25 km²) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1‐2 and br2) could be produced by erosion–sedimentation–consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31°59′13.73?N, 5°30′55.14?W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4–4.2 km in diameter. Cosmogenic nuclide data (³⁶Cl) constrain the local erosion rates between 220 ± 22 m Ma^?1 and 430 ± 43 m Ma^?1. These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3–1.9 Ma. This age is older than the Agoudal iron meteorite age (105 ± 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.