The geochronology and petrogenesis of Walash volcanic rocks,Mawat nappes: constraints on the evolution of the northwestern Zagros suture zone,Kurdistan Region,Iraq

Geological, geochemical, and geochronological investigations of the upper volcanics (UV) of Lower allochthon (LA) of Mawat nappes (MN) were used to elucidate the geologic relationships between the LA, the Qulqula Rise (i.e., accretionary complex terrane (ACT)) and peripheral Foreland Basin Assemblage (FBA), (Maastrichtian–Paleogene). The ⁴⁰Ar-³⁹Ar geochronological data suggest that the Middle to Late Paleogene magmatic history of Late Walash arc volcanic activity of UV can be divided into an early phase of andesitic volcanism around 43.1?±?0.3 Ma and subsequent extensional arc phase magmatism of a time lapse between 40.1?±?0.3and 32.3?±?0.4 Ma. The geochemical data establish the existence of gradients in trace element ratios (i.e., Ba/La, Th/Yb, U/La, Ba/Th, Rb/Y, Ba/Y, and Nb/Y) throughout the studied samples and reflect differences in the degree of mantle wedge depletion influenced by addition of a considerable proportion of sedimentary derived input of the subducting Arabian slab. The trace, rare earth elements and isotopes of the studied samples have emphasized differences in the geochemical characteristics of andesites in comparison with other members of Walash. The andesites have subduction-related signature with the isotope (low Nd and high Sr isotope ratios) characteristic of a melt component input from cratonically-derived sediments. The diabases intruding in the basalts and andesites have a transitional composition from andesitic to N-type mid-ocean ridge basalts geochemistry with a noticeable subduction-related signature, and are interpreted to form in an extensional arc evolving into back arc basin setting. As evidenced from infant arc magmatism (Albian–Cenomenian), MN recorded protracted kinematic at convergent plate margins with a most notable was the development of the ACT (i.e., Qulqula Rise) adhered to the Arabian platform carbonates (Albian–Cenomenian) leading to the inception of peripheral FBA occurred by the erosion and unroofing of advancing ACT. Notably, the volcano flysch of Walash and Nummulite carbonate of Naopurdan were still accumulating on the remaining oceanic lithosphere further to the northeast and in part coeval with Paleogene molasses sedimentation on flexural FBA further to the southwest of the ACT.     

Evaluation and numerical modeling of seawater intrusion in the Gaza aquifer (Palestine)

A numerical assessment of seawater intrusion in Gaza, Palestine, has been achieved applying a 3-D variable density groundwater flow model. A two-stage finite difference simulation algorithm was used in steady state and transient models. SEAWAT computer code was used for simulating the spatial and temporal evolution of hydraulic heads and solute concentrations of groundwater. A regular finite difference grid with a 400 m² cell in the horizontal plane, in addition to a 12-layer model were chosen. The model has been calibrated under steady state and transient conditions. Simulation results indicate that the proposed schemes successfully simulate the intrusion mechanism. Two pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and solute concentrations in the groundwater for a planning period of 17 years. The results show that seawater intrusion would worsen in the aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area, to moderate pumpage rates from water supply wells far from the seashore and to increase the aquifer replenishment by encouraging the implementation of suitable solutions like artificial recharge, may limit significantly seawater intrusion and reduce the current rate of decline of the water levels.     

Distribution of organochlorine compounds in water, porewater and sediments in Xiamen Harbour

I~IOXAmong a large number of man-made chemicals, organochlorines such as DDTs, HCHs (hexachlorobenzene) are of great concern due to their highly bioaccumulative nature and toxic biological effects. These chemicals are persistent in nature, can biomagnify in the food web and imalvarious toxic effects in marine mammals. They can cause abnormal thyroid function in Herringgull, feminising in western gull, and can impair Avian reproduction, among other deleterious effects (Carmichael, 1988).Th…     

Understanding how physical-biological coupling influences harmful algal blooms,low oxygen and fish kills in the Sea of Oman and the Western Arabian Sea

In the last decade, green Noctiluca scintillans with its symbiont and other dinoflagellates such as Cochlodinium polykrikoides, Prorocentrum micans and Scrippsiella trochoidea have become the dominant HABs, partially replacing the previously dominant diatoms and red Noctiluca scintillans, especially during the northeast monsoon. Fish kills in the Sea of Oman are linked to a slow seasonal decline in oxygen concentration from January to November, probably due to the decomposition of a series of algal blooms and the deep, low oxygen waters periodically impinging the Omani shelf. In the western Arabian Sea, cyclonic eddies upwell low oxygen, nutrient-rich water and the subsequent algal bloom decays and lowers the oxygen further and leads to fish kills. Warming of the surface waters by 1.2 °C over the last 5 decades has increased stratification and resulted in a shoaling of the oxycline. This has increased the probability and frequency of upwelling low oxygen water and subsequent fish kills.     

The geometric configuration of the newly discovered Abu Deleig sedimentary sub-basin,Central Sudan,using remote sensing,structural analysis,and geophysical survey

Abu Deleig area is a transitional area between the Butana basement terrain to the east; and the Khartoum and Shendi sedimentary basins to the west and northwest directions, respectively. The existence of sedimentary basins within this region of Sudan was previously unknown. Landsat images have been used for delineation of lineaments and drainage system, followed by a structural analysis and geophysical investigations including gravity and resistivity methods. The interpretation of the remotely sensed data revealed that the drainage pattern is structurally controlled. The structural analysis defined the trends of the shear and tensional fractures. The structural analysis revealed that Wadi Al Hawad is the southern continuation of the Keraf Shear Zone. The related minor fractures in a NE–SW direction exhibit normal faults governing the geometry of the Abu Deleig sub-basin. The geophysical investigations confirmed the findings of structural analysis and portrayed the subsurface geometry of the sub-basin. The newly discovered sub-basin has a prism-like shape with its apex occurring at Abu Deleig town and extends to 40 km in NW direction. The depth to the basement increases from 20 m at Abu Deleig in step form to more than 300 m, where it is linked with the Shendi Basin in the northwestern part. The results of this study, however, did not confirm any link of Abu Deleig sub-basin with Atbara Basin to the NE or Khartoum Basin to the west as have been previously suggested.     

A modified rock physics model for analysis of seismic signatures of low gas-saturated rocks

In seismic applications, the bulk modulus of porous media saturated with liquid and gas phases is often estimated using Gassmann's fluid substitution formula, in which the effective bulk modulus of the two-phase fluid is the Reuss average of the gas and liquid bulk moduli. This averaging procedure, referred to as Wood's approximation, holds if the liquid and gas phases are homogeneously distributed within the pore space down to sizes well below the seismic wavelength and if the phase transfer processes between liquid and gas domains induced by the pressure variations of the seismic wave are negligible over the timescale of the wave period. Using existing theoretical results and low-frequency acoustic measurements in bubbly liquids, we argue that the latter assumption of “frozen” phases, valid for large enough frequencies, is likely to fail in the seismic frequency range where lower effective bulk modulus and velocity, together with dispersion and attenuation effects, are expected. We provide a simple method, which extends to reservoir fluids a classical result by Landau and Lifshitz valid for pure fluids, to compute the effective bulk modulus of thermodynamically equilibrated liquid and gas phases. For low gas saturation, this modulus is significantly lower than its Wood's counterpart, especially at the crossing of bubble point conditions. A seismic reflector associated to a phase transition between a monophasic and a two-phase fluid thus will appear. We discuss the consequences of these results for various seismic applications including fizz water discrimination and hydrocarbon reservoir depletion and CO₂ geological storage monitoring.     

Ash Shutbah: A possible impact structure in Saudi Arabia

We have investigated the Ash Shutbah circular structure in central Saudi Arabia (21°37′N 45°39′E) using satellite imagery, field mapping, thin‐section petrography, and X‐ray diffraction of collected samples. The approximately 2.1 km sized structure located in flat‐lying Jurassic Tuwaiq Mountain Limestone has been nearly peneplained by erosional processes. Satellite and structural data show a central area consisting of Dhruma Formation sandstones with steep bedding and tight folds plunging radially outward. Open folding occurs in displaced, younger Tuwaiq Mountain Limestone Formation blocks surrounding the central area, but is absent outside the circular structure. An approximately 60 cm thick, unique folded and disrupted orthoquartzitic sandstone marker bed occurring in the central area of the structure is found 140 m deeper in undisturbed escarpment outcrops located a few hundred meters west of the structure. With exception of a possible concave shatter cone found in the orthoquartzite of the central area, other diagnostic shock features are lacking. Some quartz‐rich sandstones from the central area show pervasive fracturing of quartz grains with common concussion fractures. This deformation was followed by an event of quartz dissolution and calcite precipitation consistent with local sea‐ or groundwater heating. The combination of central stratigraphic uplift of 140 m, concussion features in discolored sandstone, outward‐dipping concentric folds in the central area, deformation restricted to the rocks of the ring structure, a complex circular structure of 2.1 km diameter that appears broadly consistent with what one would expect from an impact structure in sedimentary targets, and a possible shatter cone all point to an impact origin of the Ash Shutbah structure. In fact, the Ash Shutbah structure appears to be a textbook example of an eroded, complex impact crater located in flat‐lying sedimentary rocks, where the undisturbed stratigraphic section can be studied in escarpment outcrops in the vicinity of the structure.     

Equilibria of a charged artificial satellite subject to gravitational and Lorentz torques

The attitude dynamics of a rigid artificial satellite subject to a gravity gradient and Lorentz torques in a circular orbit are considered. Lorentz torque is developed on the basis of the electrodynamic effects of the Lorentz force acting on the charged satellite's surface. We assume that the satellite is moving in a Low Earth Orbit in the geomagnetic field, which is considered to be a dipole. Our model of torque due to the Lorentz force is developed for an artificial satellite with a general shape, and the nonlinear differential equations of Euler are used to describe its attitude orientation. All equilibrium positions are determined and conditions for their existence are obtained.The numerical results show that the charge q and radius ρ0of the center of charge for the satellite provide a certain type of semi-passive control for the attitude of the satellite. The technique for this kind of control would be to increase or decrease the electrostatic screening on the satellite. The results obtained confirm that the change in charge can affect the magnitude of the Lorentz torque, which can also affect control of the satellite. Moreover, the relationship between magnitude of the Lorentz torque and inclination of the orbit is investigated.     

巴基斯坦海域油气勘探方向探讨

为了寻找巴基斯坦海域油气勘探方向,对收集的大量文献资料进行了整理和分析,并对最新采集的柱状样进行了测试分析,发现巴基斯坦海域烃源岩普遍存在,而储集岩主要为始新统的生物礁和中新统的河道砂岩。巴基斯坦海域北部的马克兰增生楔物源可能主要为细碎屑岩,中新统的河道砂岩分布局限,油气勘探前景差;而在巴基斯坦海域东部的印度扇,中新统河道砂岩分布广,储集性能好。因此,巴基斯坦海域的油气勘探应以东部印度扇为勘探靶区,其主要的勘探层位应以陆架区中新统的河道砂岩和深水区始新统的礁灰岩为主。     

Interpretation of Magnetic Data Through Particle Swarm Optimization: Mineral Exploration Cases Studies

Natural Resources Research - This paper emphasizes the use of the particle swarm optimization to infer second moving average residual magnetic anomalies. This approach was used to remove the impact...