Geology, geochemistry and genesis of BIF of Kushtagi schist belt, Archaean Dharwar Craton, India     

R. M. K. Khan  S. M. Naqvi 《Mineralium Deposita》1996,31(1-2):123-133

The Banded Iron-Formation (BIF) of the Kushtagi schist belt, Dharwar Craton is interbedded with metavolcanics. The oxide fades cherty (Al₂O₃ < 2%) and shaley (Al₂O₃ > 2%) BIFs show large-scale variations in their major and trace elements abundance. Cherty Banded Iron-Formation (CBIF) is depleted in Al₂O₃, TiO₂, Zr, Hf and other trace elements like Cr, Ni, Co, Rb, Sr, V, Y and REE in comparison to Shaley Banded Iron-Formation (SBIF). Depleted REE, positive Eu anomalies and the flat to HREE-enriched pattern of CBIF indicate that Fe and SiO₂ for these BIFs were added to ambient ocean water by hydrothermal solutions at the AMOR vent sites. It is inferred that the higher amount of hydrothermal fluid flux with a higher exit temperature provided enormous quantities of iron and silica. Fine-grained sedimentation in the basin gave rise to the observed variability in the composition of BIF. During transgression a wave base was raised up, consequently deposition of CBIF became possible, whereas, during the regressive stage, these chemical sediments were buried by and/or mixed with the terrigenous sediments resulting in deposition of SBIF and interbedded shales. Volcaniclastic activity within the basin appears to have contributed significantly to the composition of some SBIF and shales. The hydrothermal exhalative hypothesis combined with the Archaean miniplate model explains most of the chemical features of the BIFs of greenstone belts.  相似文献   

The Genesis of Selected Hydrochemical Facies in Baton Rouge, Louisiana, Ground Waters     

Rashid A. Khan  Ray E. Ferrell  Gale K. Billings 《Ground water》1972,10(4):14-20

  相似文献   

Analysis of the geomagnetic field of the White Sea: The Gorlo Strait     

Yu. V. Brusilovsky  A. G. Gorshkov  A. M. Gorodnitskii  A. N. Ivanenko  S. V. Lukyanov  A. M. Filin  Yu. V. Khan 《Oceanology》2007,47(3):406-414

The objective of our research is the interpretation of the results of the geomagnetic survey of the geologic structure in the Gorlo Strait of the White Sea. We used the maps of the anomalous magnetic field (AMF) available and processed them with original interpretation software. As a result of this processing, we compiled a structural-tectonic chart of this region. We distinguished the boundaries of the major first-order tectonic structures such as the underwater extension of the Leshukon graben and a number of minor structures related to the Proterozoic and Paleozoic stages of the magmatic activity in the region. Modeling was performed for the most important objects, which allowed us to refine the geological structure of these objects and their genesis.  相似文献   

Behavior and brain chemistry correlates in mummichogs (Fundulus heteroclitus) from polluted and unpolluted environments     

G.M. Smith  A.T. Khan  J.S. Weis  P. Weis   《Marine environmental research》1995,39(1-4)

The ability of Fundulus from a polluted environment to capture a prey organism, the grass shrimp (Palaemonetes pugio), was compared to that of Fundulus from an unpolluted reference site. Fish from the unpolluted site took significantly more prey (p < 0.1) during the first 5–10 min of each trial than fish from the polluted site.Analysis of the neurotransmitters dopamine (DA) and serotonin (5-HT) and their metabolites, DOPAC, homovanillic acid (HVA), and 5-hydroxy-indolacetic acid (5-HIAA) in cerebellums and medullas was performed by HPLC. Mummichogs from the polluted site had significantly lower concentrations of 5-HT and its metabolite 5-HIAA in their medullas, but not cerebellums, than fish from the reference site (p < 0.05). Concentrations of DA, DOPAC and HVA were not different between populations in either part of the brain. Neurotransmitter concentrations were shown to be independent of size and therefore, presumably, age.Analysis of Hg in livers and brains of these mummichogs by atomic absorption spectrophotometry showed significant differences between the two populations for both organs. Earlier work showed that the behavioral deficit could be elicited by Hg; thus, this was the putative neurotoxic agent. However, there are other candidates which may contribute to neurotoxicity in the study site.  相似文献   

Effects of stand characteristics on tree species richness in and around a conservation area of northeast Bangladesh     

Muha Abdullah Al Pavel  Sharif A. Mukul  Mohammad Belal Uddin  Kazuhiro Harada  Mohammed A. S. Arfin Khan 《山地科学学报》2016,13(6):1085-1095

We investigated the effect of tree cover, forest patch and disturbances on tree species richness in a highly diverse conservation area of northeast Bangladesh. A systematic sampling protocol was adopted and 80 sub-plots from twenty five 1 ha plots were used for the vegetation survey. Linear regression analysis was performed to understand the effect of patch area, disturbances and tree cover on tree species richness. Ordination using Redundancy analysis (RDA) and Non-metric Multi Dimensional Scaling (NMDS) were also performed to explore the tree species compositional similarities along the stand characteristics gradient and locations of the sample plots. Our study revealed that, forest patch size has greater influence on species richness. Areas with medium level of disturbances have shown greater species richness. In constrained ordination the selected explanatory variables regulated the richness of common species. Our findings can be useful for better forest management and restoration of landscapes of conservation needs using ecologically important species.  相似文献   

Mapping sediment thickness of Islamabad city using empirical relationships: Implications for seismic hazard assessment     

Sarfraz Khan  M Asif Khan 《Journal of Earth System Science》2016,125(3):623-644

Soft sediments make an important component of the subsurface lithology, especially in areas underlain by river/stream basins. Occupying a position directly above the bedrock up to the land surface, these soft sediments can range in thickness from few centimeters to hundreds of meters. They carry a special nuisance in seismic hazards, as they serve as a source of seismic amplification that may enhance the seismic shaking of many folds. Determination of the thickness of the soft sediments is therefore crucial in seismic hazard analysis. A number of studies in recent years have demonstrated that frequency and amplitude spectrum obtained from the noise measurements during the recording of natural seismicity can be used to obtain thickness of soft sediments covering the bedrock. Nakamura (1989) presented a technique to determine such spectrum using ratio of horizontal to vertical components of the Rayleigh waves. The present study is based on an extensive set of microtremor measurements carried out in the Islamabad city, Pakistan. Fundamental frequencies were obtained from weak motion sensors and Tromino Engy Plus instruments to show that the correlation is clearly valid for a wide range of sediment thickness. A simple formula was derived for the investigated area to determine directly the thickness of sediments from the main peaks in the H/V spectrum for seismometer and Tromino data separately. A comparison is made between sediment thicknesses derived from empirical relations developed in this study with those given in literature to demonstrate a positive correlation. The correlation of instrumental resonant frequencies with calculated resonant frequencies (theoretical) suggests that the relation derived from the noise measurements mostly depends on the velocity depth function of the shear wave. The fundamental frequency of the main peak of spectral ratio of H/V using the both instruments correlates well with the thickness of sediments at the site obtained from the borehole data. It is found out that there is a wide variation in soft-sediment thickness in the Islamabad area, but as a general rule, soft sediments are thicker adjacent to stream courses compared to the areas intervening the streams. The distribution of sediments in the studied area is illustrated by means of cross sections constructed from results of the microtremor analyses and available borehole data, which provides a visual distribution of the soft sediments underlying the Islamabad city.  相似文献   

Exploring underlying causes and assessing damages of 2010 flash flood in the upper zone of Panjkora River     

Shakeel Mahmood  Amin-ul-Haq Khan  Shaker Mahmood Mayo 《Natural Hazards》2016,80(2):1213-1230

  相似文献   

Geophysical characterization and earthquake hazard vulnerability of Dhaka Mega City,Bangladesh, vis-à-vis impact of scenario earthquakes     

Aftab Alam Khan 《Natural Hazards》2016,81(2):1147-1159

  相似文献   

Improving MODIS Spatial Resolution for Snow Mapping Using Wavelet Fusion and ARSIS Concept   总被引：1，自引：0，他引：1  

Sirguey  P. Mathieu  R. Arnaud  Y. Khan  M.M. Chanussot  J. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(1):78-82

We propose to fuse the high spatial content of two 250-m spectral bands of the moderate resolution imaging spectroradiometer (MODIS) into its five 500-m bands using wavelet-based multiresolution analysis. Our objective was to test the effectiveness of this technique to increase the accuracy of snow mapping in mountainous environments. To assess the performance of this approach, we took advantage of the simultaneity between the advanced spaceborne thermal emission and reflection radiometer (ASTER) and MODIS sensors. With a 15-m spatial resolution, the ASTER sensor provided reference snow maps, which were then compared to MODIS-derived snow maps. The benefit of the method was assessed through the investigation of various metrics, which showed an improvement from 3% to 20%. Therefore, the enhanced snow map is of great benefit for environmental and hydrological applications in steep terrain.  相似文献   

Photometry and discussion of the classical Algol systems U Sge and U Cep     

M. A. Khan  E. Budding 《Astrophysics and Space Science》1986,125(2):219-242

The (in many respects, similar) classical Algol-type eclipsing binary systems U Sge and U Cep are studied and compared against a background of photometric evidence, both broadhand and narrowband. Broadband photometry of the primary minimum of U Sge over a four year period fails clearly to confirm Olson's (1982b) finding of radial variations.On the other hand, the W-type pattern of variation indicated in Olson's (1976) H photometry of the primary eclipse of U Cep is also noticed for U Sge. These effects are analysed in terms of an emitting accretion disk, surrounding the primary components. Electron densities in these highly ionized structures are derived to be in the range 10¹⁰–10¹¹, for the H emitting region, with that of U Cep being 3 times greater than that of U Sge, though since the volume of the structure is 3 times bigger for U Sge, the overall masses are comparable.These findings can be placed in a Case B-type interacting binary context, which shows the studied accretion structures to be relatively tenuous; and, since the mean mass loss rate for U Cep is likely to be high than that of U Sge by more than an order of magnitude, suggests they are not so directly dependent on this mass-loss rate.  相似文献