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31.
1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f… 相似文献
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M K PANDIT H DE WALL H DAXBERGER J JUST M BESTMANN K K SHARMA 《Journal of Earth System Science》2011,120(4):627-641
A small isolated mafic body occurs to the south of Sirohi near village Daba within the Neoproterozoic Erinpura Granite in
the southern sector of the Proterozoic Delhi Fold Belt in NW India. This mafic body occurs close to a 100 m wide NE–SW trending
shear zone (Daba Shear Zone) which overprints the felsic rock fabrics. Further south, a small mafic body near village Kui
was also sampled which forms the southern limit of the Phulad Ophiolite Suite which is a 300 km long major NE–SW trending
lineament, described as Western Margin Fault. Some of the lithological components of the Daba mafic body show locally preserved
magmatic fabric but completely transformed mineralogies under lower amphibolites facies metamorphic conditions where two-stage
deformation has been inferred. Magnetic fabric analysis underlines a general correspondence of structural elements in both
felsic and mafic lithologies. Binary correlations of Zr with other high field strength elements underline fractionation as
the main process in the evolution of Daba and Kui rocks. Geochemical characteristics indicate subalkaline tholeiitic basalt
affinity for these mafic rocks. The trace element characteristics, such as enriched LIL elements, high Th, absence of negative
Nb anomalies and depletion in compatible elements in Daba samples suggest an enriched mantle source and lower degree of melting.
The trace and rare earth element characteristics for Kui (Th anomaly, Nb–Ta trough and less spiked patterns, flat REE trends)
indicate derivation from a refractory mantle source affected by fluids derived from subduction. Distinct differences in trace
and REE characteristics between Daba and Kui can be interpreted in terms of different stages of ophiolite development. 相似文献
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ANINDITA DAS CHRISTABELLE E. G. FERNANDES SONALI S. NAIK B. NAGENDER NATH I. SURESH M. B. L. MASCARENHAS‐PEREIRA S. M. GUPTA N. H. KHADGE C. PRAKASH BABU D. V. BOROLE P. P. SUJITH ANIL B. VALSANGKAR BABU SHASHIKANT MOURYA SUSHANTA U. BICHE RAHUL SHARMA P. A. LOKA BHARATHI 《Sedimentology》2011,58(3):756-784
In order to investigate whether geochemical, physiographic and lithological differences in two end‐member sedimentary settings could evoke varied microbe–sediment interactions, two 25 cm long sediment cores from contrasting regions in the Central Indian Basin have been examined. Site TVBC 26 in the northern siliceous realm (10°S, 75·5°E) is organic‐C rich with 0·3 ± 0·09% total organic carbon. Site TVBC 08 in the southern pelagic red clay realm (16°S, 75·5°E), located on the flank of a seamount in a mid‐plate volcanic area with hydrothermal alterations of recent origin, is organic‐C poor (0·1 ± 0·07%). Significantly higher bacterial viability under anaerobic conditions, generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones, characterize core TVBC 26. In the carbon‐poor environment of core TVBC 08, a doubling of the 14C uptake, a 250 times increase in the number of autotrophic nitrifiers, a four‐fold lowering in the number of aerobic sulphur oxidizers and a higher order of denitrifiers exists when compared with core TVBC 26; this suggests the prevalence of a potentially autotrophic microbial community in core TVBC 08 in response to hydrothermal activity. Microbial activity at the northern TVBC 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tan‐green mottled zones. The southern TVBC 08 is autotrophic with increased heterotrophic activity in the deepest layers. Notably, the bacterial activity is generally dependent on the surface productivity in TVBC 26, the carbon‐rich core, and mostly independent in TVBC 08, the carbon‐poor, hydrothermally influenced core. The northern sediment is more organic sink‐controlled and the southern sediment is more hydrothermal source‐controlled. Hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep‐sea sediments. Thus, this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial responses in the Central Indian Basin sediments. 相似文献
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B M KUKRETI G K SHARMA PRAMOD KUMAR SANDEEP HAMILTON 《Journal of Earth System Science》2016,125(4):737-744
This paper discusses an experimental approach to examine uranium exploration avenue over the geologically extended parts of Mahadek basin in Meghalaya, amid some of the environmental constraints. Study comprises periodic measurements of prevailing ambient gamma levels across 320 georeference points, in relation to the major litho units of Mahadek basin, covering 673 line km of Khasi Hills. Acquired sample data points were then analysed in geostatistical software (SurferTM) to develop analytical model of sample variogram having bearing on the uranium exploration in the area. Study findings have given encouraging surface indicators with mostly elevated gamma levels over the parts of West Khasi Hills. Delineated gamma anomalous zones are lithologically well correlated including to that of existing uranium occurrences in the basin. Identified anomalous zones over the parts of West Khasi Hills by this study work, are mainly associated with the Mahadek sandstone (Upper and Lower Mahadek) and Precambrian basement granites. Lower Mahadek sandstone is host rock for uranium mineralisation in the basin. Initial findings suggest with the closer spatial resolution (～1 km) of sample data points, the approach adopted by the study work holds promising application in locating potential uranium exploration targets especially to the extended and inaccessible parts of the basin. 相似文献
37.
The geomagnetic storm of November 1998 is a unique event where IMF-Bz remained southward with values exceeding –15 nT for more than a day. The SYM/H index decreased from about 07 hr on 13 November 1998 reaching a minimum of about –120 nT around midnight of 13–14 November 1998. Features of the equatorial electrojet in the Indian region are studied during the geomagnetic storm event of 13–14 November 1998, based on the geomagnetic data from the chain of observatories in India. Sudden northward turning of IMF-Bz for a very short duration around 08 hr on 13 November 1998 resulted in a small and very short duration counter electrojet. A strong (–50 nT) and a long duration counter electrojet, right from 08 to 13 hr on 14 November 1998 was observed resulting in the absence of equatorial Es at Thumba. Absence of the equatorial ionization anomaly was also observed as seen from the ionograms over Thumba and ionspheric data from Ahmedabad. The delayed effect on 14 November 1998 is due to the disturbance dynamo effect. 相似文献
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The study aims to ascertain the hypothesis on the rich rotifer biodiversity of the floodplain lakes(beels) of the Brahmaputra river basin and to use these metazoans to assess trophic status or to characterize habitat variations of wetlands. The plankton samples collected from four beels of lower Assam revealed 160 Rotifera species belonging to 35 genera and 19 families. The richness is of biodiversity value as ~38.0% and ~57.0% of the rotifer species known till date from India and northeast India(NEI), respectively. One species each is new to the Oriental region and NEI, and three species are new to Assam; 23 species merit global biogeography interest and several exhibit distribution values in the Indian sub-region. The diverse Lecanidae Brachionidae Lepadellidae Trichocercidae and speciose littoral-periphytic L ecane Lepadella Trichocerca, and richness of Brachionus spp. following removal of aquatic macrophytes are noteworthy. Overall rotifer composition showed homogeneity amongst beels while lower monthly richness and community similarities affirmed heterogeneity within individual beels. We propose L/B quotient based on L ecane : Brachionus species ratios to characterize habitat variations of the sampled wetlands. Sláde?ek's B/T quotient based on B rachionus : T richocerca species ratios affirmed general 'meso-trophic' status of diff erent beels. Our results provided little insight on the influence of individual abiotic factors but the canonical correspondence analyses asserted higher cumulative influence of ten abiotic parameters on Rotifera richness in each beel. 相似文献
39.
The Fourier transform formula for a two-dimensional fault truncating a horizontal bed at an arbitrary angle of inclination is derived. The amplitude spectrum of the Fourier transform is found to give information about the depth to the top of the upper part of the faulted bed and the inclination of the fault-plane. Under suitable conditions the thickness and the displacement of the bed involved can be obtained. With actual field data, these transforms can be obtained at discrete points by a Fourier analysis of the gravity anomaly. A field example from the Logan fault area near Montreal, Que., Canada, is given. 相似文献
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P. VALLABH SHARMA 《Geophysical Prospecting》1967,15(2):167-173
A nomogram is presented which enables evaluation of the components of magnetic attraction of a homogeneous finite rectangular prism, and of gravitational attraction due to a uniform rectangular lamina. In practice any three-dimensional body could be approximated by a number of right rectangular prisms of varying dimensions governed by the shape of the body. The magnetic attraction of the whole body is then obtained by numerical summation of the effects of the constituent prisms. For evaluating the gravitational effect, the cross-section of the body corresponding to each elevation contour is approximated by a number of rectangular laminae (or by a stepping polygon) the attraction of which can be determined with the aid of the same nomogram. The total gravitational attraction of the body is obtained by a process of graphical integration along the vertical axis. 相似文献