Titanomagnetites prepared at different oxidation conditions: Hysteresis properties

Atmospheres of different oxidation potentials were used to equilibriate samples at 1300°C starting with a stoichiometric composition xFe₂TiO₄·(1 ? x) Fe₃O₄ where x = 0.3 and 0.6. Samples were selected which appeared homogeneous in polished section and gave only spinel-type X-ray reflections. All specimens were found to have small amounts of included material of higher Curie point than the bulk material. Specimens were made by dispersing grains of known size in a non-magnetic matrix and the hysteresis properties were measured for these speciméns.     

Assessment of heavy metal contamination in the surficial sediments from the lower Meghna River estuary,Noakhali coast,Bangladesh

Sediment samples were collected from ten selected sites of the lower Meghna River estuary,and six heavy metals were analyzed with Atomic Absorption Spectrophotometry(AAS)to assess the contamination level and the metals’association with sediment grain size.The current results revealed that the mean concentrations of the studied metals were ranked in descending order of iron(Fe)(1.29×103 mg/kg)>zinc(Zn)(42.41 mg/kg)>lead(Pb)(12.48 mg/kg)>chromium(Cr)(10.59 mg/kg)>copper(Cu)(6.22 mg/kg)>cadmium(Cd)(0.28 mg/kg).The geo-accumulation,contamination,and pollution load indexes suggested that the lower Meghna river estuary was not contaminated by Fe,Zn,Pb,Cr,and Cu.The mean size of the sediment ranged from 28.92 to 126.2 mm,and the Pearson correlation coefficient showed a significant association between Fe and Pb(coefficient of determination,r2=0.836;p<0.05),and no significant correlation was found between individual metals and grain size,indicating no or low influence on the metals distribution.     

Depositional facies of the subsurface Neogene Surma Group in the Sylhet Trough of the Bengal Basin,Bangladesh: record of tidal sedimentation

The Bengal Basin, in the north-eastern part of the Indian subcontinent, contains a thick (± 22 km) early Cretaceous-Holocene sedimentary succession. The Neogene succession in the Sylhet Trough of the basin reaches a thickness of more than 6 km of which the Surma Group contains important sandstone reservoirs. Lithologically, the group consists of a succession of alternating shales, siltstones, sandy shales and sandstones, with minor conglomerates. This research work is a sedimentological analysis of the subsurface Neogene succession encountered in the petroleum exploration wells in the Sylhet Trough of the Bengal Basin. Detailed lithologic logs of the cores, based on considering texture and sedimentary structure, permit a subdivision into eight lithofacies, e.g., a shale-dominated facies, interbedded fine sandstones and mudstones, ripple-laminated sandstones, parallel-laminated sandstones, massive sandstones, cross-bedded sandstones, cross-bedded sandstones with pebble/granule lag and conglomerates. Characteristic sedimentary structures of the Surma Group, such as flaser-, wavy- and lenticular-bedding, bipolarity of ripple cross-stratification, evenly laminated sand/silt-streaked shales, reactivation surfaces within cross-bedded sandstone sets, mud-drapes on foreset laminae and herringbone cross-stratification as well as small-scale vertical sequences (several fining-upward cycles) are diagnostic for tidal influence. On the basis of the lithofacies associations and prograding character of the deposits revealed from the electrofacies associations, the Surma Group sediments have been interpreted as representing deposits of tide-dominated deltaic depositional setting.     

Geochemistry of subsurface Late Quaternary ironstones in Rajshahi and Bogra Districts,Bangladesh: implications for genetic and depositional conditions

The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe₂O₃* (* total Fe) (avg. 66.6 wt%), SiO₂ (avg. 15.3 wt%), Al₂O₃ (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe₂O₃* along with Al₂O₃ and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO₂ indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.

     

Viewing Angle Effect on the Remote Sensing Monitoring of Wheat and Rice Crops

Abstract

Bidirectional reflectance characteristics of a wheat and a rice canopy were studied using radiometric measurements over the two canopies with an Exotech Radiometer Model 100AX. For both rice and wheat, the measurements exhibited significant variations in reflectance amplitude for varying viewing zenith angles and their values decreased from backward to forward scattering direction. Reflectance obtained its maximum value in the backscatter direction for the viewing angle that corresponds approximately to the solar zenith angle at the time of measurements. Canopy background condition (irrigated or non‐irrigated) was an important determining factor of canopy reflectance particularly in the near‐infrared region of the solar spectrum. Furthermore, bidirectional response characteristics of a vegetation canopy were influenced by the amount of vegetation cover.     

Site response analysis for deep and soft sedimentary deposits of Dhaka City,Bangladesh

Natural Hazards - The ground motion intensity of an earthquake is significantly changed when seismic waves propagate from the bedrock to the near-surface soft geological materials. The ground where...     

Spatio-temporal analysis of road traffic accident fatality in Bangladesh integrating newspaper accounts and gridded population data

Road traffic accidents pose serious threats to human lives and often cause premature deaths, disabilities, and socioeconomic impacts. The objective of this study is to analyze the fatal road traffic accidents in Bangladesh by performing a space–time characterization of fatality rates involving an innovative newspaper-based method in concert with gridded population data to construct a road traffic fatality database. Kernel density estimation, temporal data plots and space–time pattern mining tools that combine the Getis-Ord Gi* statistic with the Mann–Kendall test are used to describe spatio-temporal hotspots/coldspots and trends. Results show different patterns between the urban and rural areas of Bangladesh and higher rates of road traffic accidents occur in the metropolitan regions (Dhaka) and in a northern region centered on Sirajganj area. Most of the road traffic accidents took place in between 9:00 and 12:00 pm while the accident rates remain low between 12:00 and 3:00 am. Spacetime analysis results reveal a core region of persistently high rates along with four smaller regions with high and intensifying rates. The output of this study could be useful to reduce road traffic fatalities, injuries, increase awareness, and adopt necessary interventions for public safety through integrating both the local, regional, and central level decision makers of public transportation policy and issues in Bangladesh. The approach has potential to be translated to other developing countries.     

Numerical modelling of multiphase immiscible flow in double‐porosity featured groundwater systems

A numerical model describing the flow of multiphase, immiscible fluids in a deformable, double‐porosity featured soil has been developed. The model is focused on the modelling of the secondary porosity features in soil, which is more relevant to groundwater contamination problems. The non‐linear saturation and relative permeabilities were expressed as functions of the capillary pressures. The governing partial differential equations in terms of soil displacement and fluid pressures were solved numerically. Galerkin's weighted‐residual finite element method was employed to obtain the spatial discretization whereas temporal discretization was achieved using a fully implicit scheme. The model was verified against established, peer‐reviewed works, and the assumption that the immiscible fluids (non‐aqueous phase liquids) will flow preferentially through the secondary porosity features in soil was validated. Copyright © 2011 John Wiley & Sons, Ltd.     

A new ophiolite occurrence in NW Sudan – constraints on Late Proterozoic tectonism

Mafic–ultramafic sequences in the Jebel Rahib fold-and-thrust belt of NW Sudan comprise the metamorphosed equivalents of obducted oceanic lithosphere. Primary features like pillow-structures, quenchtextures, igneous layering and primary minerals like chromian spinels and pyroxenes are partly preserved. Geochemical investigations confirm the field evidence and reveal the occurrence of harzburgites, ophiolitic chromites, gabbros, gabbroic cumulates and basalts of primitive tholeiitic compositions resembling transitional MORBs. The age of low-grade overprint of the basaltic rocks can be limited to 860–740 Myr (K–Ar). The existence of an ophiolite, as well as its close interfingering with highly deformed basin sediments, provides unambiguous evidence for a cycle of extensional and compressional tectonics in NW Sudan during Pan-African times. Consequently, the concept of an older, stable Proterozoic, or even Archaean, ‘African Craton’onto which the juvenile Pan-African Nubian Shield assemblages were accreted, needs revision.