Integration and magnitude homogenization of the Egyptian earthquake catalogue

The aim of the present work is to compile and update a catalogue of the instrumentally recorded earthquakes in Egypt, with uniform and homogeneous source parameters as required for the analysis of seismicity and seismic hazard assessment. This in turn requires a detailed analysis and comparison of the properties of different available sources, including the distribution of events with time, the magnitude completeness, and the scaling relations between different kinds of magnitude reported by different agencies. The observational data cover the time interval 1900–2004 and an area between 22°–33.5° N and 25°–36° E. The linear regressions between various magnitude types have been evaluated for different magnitude ranges. Using the best linear relationship determined for each available pair of magnitudes, as well as those identified between the magnitudes and the seismic moment, we convert the different magnitude types into moment magnitudes M _W, through a multi-step conversion process. Analysis of the catalogue completeness, based on the M _W thus estimated, allows us to identify two different time intervals with homogeneous properties. The first one (1900–1984) appears to be complete for M _W ≥ 4.5, while the second one (1985–2004) can be considered complete for magnitudes M _W ≥ 3.     

A photochemical model of the martian atmosphere

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.     

Evolution of late Triassic rift basin evaporites (Passaic Formation): Newark Basin, Eastern North America

The Passaic Formation of the late Triassic Newark Supergroup is 2700 m thick and was deposited in series of wide, deep to shallow lacustrine environments in the Newark rift basin (eastern North America). The Passaic Formation can be divided into lower, middle, and upper sections based on depositional structures, composition and the distribution and morphology of its evaporites. Evaporites formed as a result of syndiagenetic cementation and/or displacive processes. Evaporitive minerals now include gypsum and anhydrite, although other mineral species, such as glauberite, may have originally existed. Most of the evaporites of the Passaic Formation occur within massive red mudstone and siltstone lithologies in the form of diffuse cements, void-fillings, euhedral crystals, crystal clusters and nodules. These evaporites grew displacively within the fine siliciclastic matrix as a result of changes in the hydrochemical regimes of the rift basin. A well-developed upward increase in the amount of evaporite material is present in the Passaic Formation. This resulted from: (1) long-term, progressive increase in aridity, and (2) significant increase in evaporation surface area of the basin during its tectonic evolution. A nonmarine source for the evaporites is evident from the isotopic data. Sulphate δ³⁴S ranges from 11%. to 3.3%. CDT, while δ¹⁸O ranges from + 15.1%. to + 20.9%. SMOW, indicating derivation from early diagenetic oxidation of organic sulphur and pyrite within the organic-rich, lacustrine deposits. The ⁸⁷Sr/⁸⁶Sr ratios in sulphate are radiogenic (average 0.71211), showing the interaction of basin waters with detrital components and that the Newark Basin was isolated from the world ocean. Most of the original evaporites show evidence of diagenetic change to polycrystalline and polymineralic pseudomorphs now filled with recrystallized coarse-grained anhydrite (1–3 mm size) and low-temperature albite. Homogenization temperatures of fluid inclusions within the coarse-grained anhydrite indicate crystallization temperatures for anhydrite in the range of 150° to 280°C. Such elevated temperatures resulted from circulation of hot water in the basin. Later exhumation of these rocks caused partial to total replacement of anhydrite by gypsum in the upper part of the section. The resulting increase in volume due to hydration of anhydrite at shallow depths also emplaced non-evaporative satin-spar veins (fibrous gypsum) along bedding planes and in fractures. While the local geology of the Newark rift basin controlled the distribution of facies, the sedimentological development of the Passaic Formation evaporites resulted from the world-wide climatic aridity that prevailed during the late Triassic. because the Newark Basin sequence was only covered with about 3 km of sedimentary overburden that correspond to about 100°C and hence suggests that evaporites have experienced alteration by hot fluids. 5 As the Triassic marks the greatest evaporite formation world-wide and profound sense of parched continentality throughout the world existed before the final break-up of the Pangea, the Passaic Formation evaporites are an example of the influence of these palaeoclimatic conditions at the eastern margin of North America.     

Geochemistry of an island-arc plutonic suite: Wadi Dabr intrusive complex, Eastern Desert, Egypt

The Wadi Dabr intrusive complex, west of Mersa-Alam, Eastern Desert, Egypt ranges in composition from gabbro to diorite, quartz diorite and tonalite. The gabbroic rocks include pyroxene-horn blend e gabbro, hornblende gabbro, quartz-hornblende gabbro, metagabbro and amphibolite. Mineral chemistry data for the gabbroic rocks indicate that the composition of clinopyroxenes ranges from diopside to augite and the corresponding magma is equivalent to a volcanic-arc basalt. Plagioclase cores range from An₇₅ to An₃₄ for the gabbroic varieties, except for the metagabbro which has An _11–18. The brown amphiboles are primary phases and classified as calcic amphiboles, which range from tschermakitic hornblende to magnesiohornblende. Green hornblende and actinolite are secondary phases. Hornblende barometry and hornblende-plagioclase themometry for the gabbroic rocks estimate crystallisation conditions of 2–5 kb and 885–716°C.The intrusive rocks cover an extensive silica range (47.86–72.54 wt%) and do not exhibit simple straight-line variation on Harker diagrams for many elements (e.g. TiO₂, Al₂O₃, FeO^*, MgP, CaO, P₂O₅, Cr, Ni, V, Sr, Zr and Y). Most of these elements exhibit two geochemical trends suggesting two magma sources.The gabbroic rocks are relatively enriched in large ion lithophile elements (K, Rb, Sr and Ba) and depleted in high field strength elements (Nb, Zr, Ti and Y) which suggest subduction-related magma. Rare earth element (REE) data demonstrate that the gabbroic rocks have a slight enrichment of light REE [(La/Yb)_N=2.67−3.91] and depletion of heavy REE ((Tb/Yb)_N=1.42−1.47], which suggest the parent magma was of relatively primitive mantle source.The diorites and tonalites are clearly calc-alkaline and have negative anomalies of Nb, Zr, and Y which also suggest subduction-related magma. They are related to continental trondhjemites in terms of Rb---Sr, K---Na---Ca, and to volcanic-arc granites in terms of Rb---and Nb---Y.The Wadi Dabr intrusive complex is analogous to intrusions emplaced in immature ensimatic island-arcs and represents a mixture of mantle (gabbroic rocks) and crustal fusion products (diorites and tonalites) modified by fractional processes.     

Production of a molybdophore during metal-targeted dissolution of silicates by soil bacteria

Although many bioessential metals are scarce in natural water and rock systems, microbial secretion of high-affinity ligands for metal extraction from solid phases has only been documented for Fe. However, we have discovered that Mo is extracted from a silicate by a high-affinity ligand (a possible “molybdophore”) secreted by an N₂-fixing soil bacterium. The putative molybdophore, aminochelin, is secreted as a siderophore under Fe-depleted conditions, but is also secreted under Fe-sufficient, Mo-depleted conditions. Presumably, molybdophore production facilitates uptake of Mo for use in Mo enzymes. In contrast, an Fe-requiring soil bacterium without a special Mo requirement only enhances the release of Fe from the silicate. Fractionation of Mo stable isotopes during uptake to cells may provide a “fingerprint” for the importance of chelating ligands in such systems. Many such metal-specific ligands secreted by prokaryotes for extraction of bioessential metals, their effects on Earth materials, and their possible utility in the recovery of economic metals remain to be discovered.     

Hydrobiological variables as a regulatory factor on the abundance of heterotrophic flagellates in an urban pond

The seasonal abundance of flagellates has been monitored over a period of 1 year from December2013 to November 2014(divided into 4 conjugative seasons namely winter, spring, summer, and autumn) in an experimental pond located in Rajshahi City Corporation area, Bangladesh. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships among heterotrophic flagellates(HF),bacteria and zooplankton in Bangladesh and the result obtained by this study will be beneficial for similar water ecosystem all over the world. Standard methods were used to determine the prescribed hydrological parameters and zooplankton cell density. Maximum HF abundance(14 346.00 cells/mL) was found in the spring and the minimum(5 215.00 cells/mL) occurred in the summer. Inverse to HF, significantly(P0.05)higher zooplankton abundance was found during the winter(782.00±47.62 cells/mL) and the lowest value was found in the autumn(448.00±39.15 cells/mL). Whereas similar to the HF, total bacterial abundance was significantly higher during the spring((2.25±1.05)×10~5 cells/mL) and lower in the summer((0.79±0.06)×105 cells/mL). Multivariate analyses(ANOSIM and MDS) have shown significant seasonal differences for cell numbers where MDS ordination plot and cluster analysis based on similarity in the genera abundance of HF revealed overlapping condition between winter and spring. Canonical correspondence analysis(CCA) also showed a distinct separation among the genera based on the prevailing hydrological situation and indicated that temperature, pH, BOD_5, and NO_3~- were the most important environmental variables in determining the observed variation in HF community structure. Among the biological factors, zooplankton showed negative but total bacteria were positively correlated with HF abundance.