Origin of layering in cumulate gabbros in the Oman ophiolite: Insights from magnetic susceptibility measurements in the Wadi Sadm area     

Kiichiro  Kawamura  Takahiro  Hosono  Huda Mohamed  Allawati  Yujiro  Ogawa  Hidetsugu  Taniguchi 《Island Arc》2005,14(4):564-570

Abstract   Magnetic susceptibility and the anisotropy of magnetic susceptibility were measured on an 800-cm-thick succession of cumulate gabbro in the Sadm area of the Oman ophiolite. The section contained three distinct cumulate units. The susceptibility tends to decrease upward in each from a melanocratic layer (several tens of centimeters thick) to a leucocratic layer (a few meters thick). The susceptibility decreases in accordance with the decreasing number of magnetite grains, which are the alteration product mainly of olivine minerals. This suggests the cyclic downward accumulation of olivine in the cumulate gabbro. The apparent strain deduced from the patterns of magnetic and grain fabrics was the result mostly of simple shear, so that the layering of gabbro is understood to be formed primarily by a crystal cumulus process followed by simple shear deformation.  相似文献   

Interpretation of magnetic data using analytic signal derivatives     

Ahmed Salem 《Geophysical Prospecting》2005,53(1):75-82

This paper develops an automatic method for interpretation of magnetic data using derivatives of the analytic signal. A linear equation is derived to provide source location parameters of a 2D magnetic body without a priori information about the nature of the source. Then using the source location parameters, the nature of the source can be ascertained. The method has been tested using theoretical simulations with random noise for two 2D magnetic models placed at different depths with respect to the observation height. In both cases, the method gave a good estimate for the location and shape of the sources. Good results were obtained on two field data sets.  相似文献   

Interpretation of gamma-ray logs: The distribution of uranium in carbonate platform     

Mohamed Chaker Raddadi  Annie Arnaud Vanneau  Grard Poupeau  Elisabeth Carrio-Schaffhauser  Hubert Arnaud  Alice Rivera 《Comptes Rendus Geoscience》2005,337(16):96

High gamma-radioactivity in carbonates is usually ascribed to uranium of detrital minerals and organic matter, and to thorium and potassium of clays. The present study based on Urgonian marls and marly limestones (France) shows that some of the most radioactive values correspond instead to some ‘pure’ limestones. These peaks are generally associated with a sequence boundary or a maximum flooding surface. Low-level γ-spectrometry and ICP–MS analyses show that although high radioactivities are mostly associated with uranium, there is no obvious correlation between uranium enrichment and lithology. Also, correlation between high radioactivity and argillaceous beds might not be systematic. To cite this article: M.C. Raddadi et al., C. R. Geoscience 337 (2005).  相似文献   

Modelling load–displacement response of driven piles in cohesionless soils under tensile loading     

Ahmed Shlash Alawneh   《Computers and Geotechnics》2005,32(8):578-586

A new methodology for deriving the uplift load–displacement response of long driven piles in cohesionless soils is proposed. This method accounts for the effects of the friction fatigue processes during pile driving and the existence of locked-in residual stresses at the end of pile driving before commencing the pile load test. A hyperbolic formulation is utilized to simulate the nonlinear load transfer curves (the so-called t–z curves). The utility of this technique is demonstrated for a field pullout load test on a driven pile in sand. Predicted and measured load–displacement curves showed good agreement, indicating that this approach yields reasonable results as long as representative input parameters are employed.  相似文献   

Present environment and historic changes from the record of lake sediments, Dhaka City, Bangladesh   总被引：1，自引：0，他引：1  

Faruque Ahmed  M. Hawa Bibi  M. Hussain Monsur  Hiroaki Ishiga 《Environmental Geology》2005,48(1):25-36

Changes in the urban environment of Dhaka City have been evaluated from the geochemical compositions of bottom sediments from two lakes, Gulshan-1 and –2. Abundances of Pb, Zn, Fe₂O₃ and total sulfur in a Gulshan-1 core gradually increase toward the sediment–water interface. Three stages of condition change can be recognized in Gulshan-1, based on trace metal concentration patterns. The basal Stage I corresponds to background Dhaka sedimentation, whereas gradual increase in Stage II represents the beginning of pollution. Marked increases in Pb and Zn in Stage III reflect rapid urban development and increased emissions to the atmosphere. The condition of the Dhaka environment is compared to that of Japan based on Zn–Fe₂O₃ and Pb–Fe₂O₃ relations. Zn–Fe₂O₃ ratios in Stage I Dhaka sediments are similar to normal Japanese sediments, whereas Stage II data lie on the same trend as Japan urban sediments. Dhaka Stage III samples have greater Zn:Fe₂O₃ ratios than Japanese urban sediments, suggesting Zn pollution from poorly-controlled industrial sources. In contrast, the Dhaka Pb–Fe₂O₃ trend lies between normal and urban Japanese sediments. Although vehicle emissions in Dhaka are now significant, the data suggest that Pb pollution from this source remains in its early stages.  相似文献   

Geochemistry and Depositional Setting of Fort Munro Formation, Middle and Lower Indus Basins, Pakistan     

ShahidNaseem ShamimAhmedSheikh ErumBashir KhaulaShirin 《中国地质大学学报(英文版)》2005,16(2):160-169

INTRODUCTION Theinteractionofcomplextectonicphasesinthe IndusbasinduringtheCretaceoushasimpartedascal lopedoutlineinthesedimentarysequences.Thedevel opmentofdiversifiedsedimentaryformationsduringthe Cretaceousensuresexcellentsources(SembarandGoru formations)andreservoirs(MoghalKotandPabfor mations)forhydrocarbons.Numerousplaysandpros pectsofhydrocarbonareassociatedwiththeCretaceous system,consequentlytheIndusbasinisattractiveto petroleumexplorationcompaniesinPakistan(Sheikh andNa…  相似文献   

Spatial pattern of variation in populations of Acacia nilotica in semi-arid environment     

S. Mahmood  A. Ahmed  A. Hussain  M. Athar 《International Journal of Environmental Science and Technology》2005,2(3):193-199

Variability among populations was analyzed in five provenances of Acacia nilotica from spatially variable habitats. Populations of A. nilotica developed in response to their habitat conditions. The level of variability was significantly high among the populations. Phenotypic variability was extremely high for leaf and stipular spine characteristics. The nature of morphological variability for vegetative traits appeared environmentally controlled. The differentiation of leaf and stipular spine expression seems to have an adaptive significance for the species in terms of water economy. Although, seed and pod characteristics are genetically controlled showing a lower proportion of variability but these traits supported r and k-selection that may allow the species to survive under a wide array of contrasting habitats. The study suggested that populations of A. nilotica are differentiated in relation to the heterogeneity of environment. These populations became adapted to their habitat through the variability of morphological expressions. The morphologically differentiated populations of the species had allowed them to maintain themselves in a wide array of environmental situations enabling A. nilotica to occupy ample ecological ranges.  相似文献   

Halocinèse précoce associée au rifting jurassique dans l'Atlas central de Tunisie (région de Majoura–El Hfay)     

Dorra Tanfous Amri  Mourad Bédir  Mohamed Soussi  Hajer Azaiez  Lahoussine Zitouni  M. Hédi Inoubli  Kamel Ben Boubaker 《Comptes Rendus Geoscience》2005,337(7):703-711

Seismic and sequence stratigraphy analyses, petroleum-well control and surface data studies of the Majoura–El Hfay region in the Central Atlas of Tunisia had led to identify and calibrate Jurassic seismic horizons. Seismic stratigraphic sections, seismic tectonics analyses, isochron and isopach mapping of Jurassic sequences show a differentiated structuring of platform and depocentre blocks limited by deep-seated NE–SW, north–south east–west and NW–SE faults intruded by Upper Triassic salt. The early salt migration seems to have started by the platform fracturing during the Lower Liassic rifting event. These movements are fossilized by thickness variations of Jurassic horizons, aggrading and retrograding onlap and toplap structures between subsiding rim-syncline gutters and high platform flanks intruded by salt pillows and domes. The salt migration is also attested by Middle and Upper Jurassic space depocentre migrations. Around the Majoura–El Hfay study blocks bounded by master faults, Triassic salt have pierced the Cretaceous and Tertiary sedimentary cover in a salt diapir extrusion and salt wall structures. To cite this article: D. Tanfous Amri et al., C. R. Geoscience 337 (2005).  相似文献   

Structure de socle,sismostratigraphie et héritage structural au cours du rifting au niveau de la marge d'Ifni/Tan-Tan (Maroc sud-occidental)     

Naïma AbouAli  Mohamad Hafid  El Hassane Chellaï  Mohamed Nahim  Mahmoud Zizi 《Comptes Rendus Geoscience》2005,337(14):1267-1276

Seismic reflection profiles from the Ifni/Tan-Tan Atlantic margin of southern Morocco, interpreted in the light of well data and field geology from the Western Anti-Atlas, allowed us to establish the seismostratigraphic framework of the syn-rift series and to reveal (i) a compressional structural style in the pre-Triassic basement similar to that established in the adjacent outcropping onshore basement but with an opposed western vergence, (ii) the importance of inherited anterior structures in the formation of Triassic-Liassic rift structures and (iii) an east–west propagation of these rift structures. To cite this article: N. AbouAli et al., C. R. Geoscience 337 (2005).  相似文献   

Integration of aquifer geology,groundwater flow and arsenic distribution in deltaic aquifers – A unifying concept          下载免费PDF全文

Mohammad A. Hoque  William G. Burgess  Kazi M. Ahmed 《水文研究》2017,31(11):2095-2109

Groundwater arsenic (As) presents a public health risk of great magnitude in densely populated Asian delta regions, most acutely in the Bengal Basin (West Bengal, India and Bangladesh). Research has focused on the sources, mobilisation, and heterogeneity of groundwater As, but a consistent explanation of As distribution from local to basin scale remains elusive. We show for the Bengal Aquifer System that the numerous, discontinuous silt‐clay layers together with surface topography impose a hierarchical pattern of groundwater flow, which constrains As penetration into the aquifer and controls its redistribution towards discharge zones, where it is re‐sequestered to solid phases. This is particularly so for the discrete periods of As release to groundwater in the shallow subsurface associated with sea level high‐stand conditions of Quaternary inter‐glacial periods. We propose a hypothesis concerning groundwater flow ( S ilt‐clay layers I mpose H ierarchical groundwater flow patterns constraining A rsenic progression [SIHA]), which links consensus views on the As source and history of sedimentation in the basin to the variety of spatial and depth distributions of groundwater As reported in the literature. SIHA reconciles apparent inconsistencies between independent, in some cases contrasting, field observations. We infer that lithological and topographic controls on groundwater flow, inherent to SIHA, apply more generally to deltaic aquifers elsewhere. The analysis suggests that groundwater As may persist in the aquifers of Asian deltas over thousands of years, but in certain regions, particularly at deeper levels, As will not exceed low background concentrations unless groundwater flow systems are short‐circuited by excessive pumping.  相似文献