Chemical and sulphur isotope compositions of pyrite in the Jaduguda U (–Cu–Fe) deposit,Singhbhum shear zone,eastern India: Implications for sulphide mineralization     

DIPAK C PAL  SURAJIT SARKAR  BISWAJIT MISHRA  A K SARANGI 《Journal of Earth System Science》2011,120(3):475-488

The Jaduguda U (–Cu–Fe) deposit in the Singhbhum shear zone has been the most productive uranium deposit in India. Pyrite occurs as disseminated grains or in sulphide stringers and veins in the ore zone. Veins, both concordant and discordant to the pervasive foliation, are mineralogically either simple comprising pyrite ± chalcopyrite or complex comprising pyrite + chalcopyrite + pentlandite + millerite. Nickel-sulphide minerals, though fairly common in concordant veins, are very rare in the discordant veins. Pyrite in Ni-sulphide association is commonly replaced by pentlandite at the grain boundary or along micro-cracks.  相似文献   

Meso-scale atmospheric events promote phytoplankton blooms in the coastal Bay of Bengal   总被引：1，自引：0，他引：1  

K MANEESHA  V V S S SARMA  N P C REDDY  Y SADHURAM  T V RAMANA MURTY  V V SARMA  M DILEEP KUMAR 《Journal of Earth System Science》2011,120(4):773-782

The Bay of Bengal is considered to be a low productive region compared to the Arabian Sea based on conventional seasonal observations. Such seasonal observations are not representative of a calendar year since the conventional approach might miss episodic high productive events associated with extreme atmospheric processes. We examined here the influence of extreme atmospheric events, such as heavy rainfall and cyclone Sidr, on phytoplankton biomass in the western Bay of Bengal using both in situ time-series observations and satellite derived Chlorophyll a (Chl a) and sea surface temperature (SST). Supply of nutrients through the runoff driven by episodic heavy rainfall (234 mm) on 4–5 October 2007 caused an increase in Chl a concentration by four times than the previous in the coastal Bay was observed within two weeks. Similar increase in Chl a, by 3 to 10 times, was observed on the right side of the cyclone Sidr track in the central Bay of Bengal after the cyclone Sidr. These two episodic events caused phytoplankton blooms in the western Bay of Bengal which enhanced ~40% of fishery production during October–December 2007 compared to that in the same period in 2006.  相似文献   

Measurement of marine productivity using <Superscript>15</Superscript>N and <Superscript>13</Superscript>C tracers: Some methodological aspects     

NAVEEN GANDHI  SANJEEV KUMAR  S PRAKASH  R RAMESH  M S SHESHSHAYEE 《Journal of Earth System Science》2011,120(1):99-111

Various experiments involving the measurement of new, regenerated and total productivity using ¹⁵N and ¹³C tracers were carried out in the Bay of Bengal (BOB) and in the Arabian Sea. Results from ¹⁵N tracer experiments indicate that nitrate uptake can be underestimated by experiments with incubation time <4 hours. Indirect evidence suggests pico- and nano-phytoplankton, on their dominance over microphytoplankton, can also influence the f-ratios. Difference in energy requirement for assimilation of different nitrogen compounds decides the preferred nitrogen source during the early hours of incubation. Variation in light intensity during incubation also plays a significant role in the assimilation of nitrogen. Results from time course experiments with both ¹⁵N and ¹³C tracers suggest that photoinhibition appears significant in BOB and the Arabian Sea during noon. A significant correlation has been found in the productivity values obtained using ¹⁵N and ¹³C tracers.  相似文献   

Characteristics of severe thunderstorms studied with the aid of VLF atmospherics over North–East India     

A GUHA  TRISANU BANIK  BARIN KUMAR DE  RAKESH ROY  ABHIJIT CHOUDHURY 《Journal of Earth System Science》2013,122(4):1013-1021

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HARMONIC INVERSION OF AN AEROMAGNETIC ANOMALY FROM A REMANENTLY MAGNETIZED PRECAMBRIAN SCHIST BELT (KARNATAKA,INDIA) *     

D. C. MISHRA 《Geophysical Prospecting》1978,26(3):572-580

The conventional methods of magnetic interpretation consider in general the induced magnetization only. However, in a computer oriented inverse method, the direction of magnetization can be taken as arbitrary. Following this procedure, this study aims to present a realistic interpretation of an aeromagnetic anomaly from Chitaldrug Schist belt (Mysore, India) assuming a three-dimensional configuration of the causative source possessing remanent magnetization. It further provides the direction of remanent magnetization of the source rock as obtained from the analysis of the magnetic anomaly. The total intensity map obtained delineates the surface and sub-surface structures in the region and provides informations regarding the characteristics of primordial crust.  相似文献   

A NUMERICAL METHOD TO COMPUTE THE RESISTIVITY TRANSFORM FROM WENNER SOUNDING DATA*     

RAKESH KUMAR  M. V. RAMANAIAH CHOWDARY 《Geophysical Prospecting》1982,30(6):898-909

A numerical technique to compute the resistivity transform directly from the observed Wenner sounding data has been developed. In principle, the procedure is based on a decomposition method and consists of two steps: the first step determines a function that approximates the apparent resistivity data and the second step transforms this function into the corresponding kernel by an analytical operation. The proposed method is tested on some theoretical master curves. A high degree of precision is achieved with very little computer time. The applicability is shown on two field examples.  相似文献   

Mass Spectrometric Isotope Dilution Determination of K,Rb, Cs,Ba and Sr In Five Geochemical Reference Samples*     

SURENDRA P. VERMA 《Geostandards and Geoanalytical Research》1981,5(2):129-131

A modified isotope dilution technique is described which has resulted in significant reduction of the time required for the determination of alkali (K, Rh and Cs) and alkaline earth (Ba and Sr) elements. The precision and accuracy of the results are shown to be quite satisfactory in measurements on the geochemical reference samples G-2, BCR-1, AN-G, BE-N and MA-N.  相似文献   

DEPTH ESTIMATION OF MAGNETIC SOURCES BY MEANS OF FOURIER AMPLITUDE SPECTRA*     

A. HAHN  E. G. KIND  D. C. MISHRA 《Geophysical Prospecting》1976,24(2):287-306

The Fourier transform of a square-shaped section of a magnetic survey, digitized in a square grid, forms a rectangular matrix of coefficients which can be condensed to a series of average amplitudes dependent only on their frequency and no longer on the direction of the respective partial waves. These average amplitudes together represent a spectrum which–when plotted in a semilogarithmic coordinate system (log amplitude versus frequency)–often shows straight segments which decrease with increasing frequency. By continuing the given field downwards these straight segments become horizontal at a certain depth, the so-called “white depth”. This white depth may be used as a first estimate for the depth of magnetic sources producing the respective part of the field. It is shown that the sources which correspond to such use of the white depth can be expected to be “randomly distributed with some positive autocorrelation”. As an example for such a depth estimation the interpretation of the aeromagnetic survey of NW-Germany by a relief in 8–16 km depth is given. The relief divides the subsurface in an upper nonmagnetic layer and a lower layer with magnetization M= 2 Am^?1.  相似文献   

REPLY TO COMMENT ON “TWO-DIMENSIONAL POWER SPECTRAL ANALYSIS OF AEROMAGNETIC FIELDS” BY A. SPECTOR AND F. S. GRANT*     

D. C. MISHRA  P. S. NAIDU 《Geophysical Prospecting》1976,24(2):400-400

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TWO-DIMENSIONAL POWER SPECTRAL ANALYSIS OF AEROMAGNETIC FIELDS *     

D. C. MISHRA  P. S. NAIDU 《Geophysical Prospecting》1974,22(2):345-353

A study of probability distribution function and spectrum of the Airborne Total Intensity Map for an area of 3000 Squ. miles covered by the Bundelkhand granite in India has revealed a close correlation between the Gaussian or non-Gaussian nature of distribution and the shape of unite value contour on the spectrum plot. Further studies of radial spectrum plots suggest that the surface magnetic sources are mainly responsible for the non-Gaussian character of the distribution function and as well as for irregular spectrum shape. The histogram of depth values for magnetic sources obtained from radial spectrum plots show three horizons, namely (i) surface (ii) 410 m(1400′) and (iii) 1000 m (3400′). Based on these informations blocks with ferromagnetic composition at the surface can be identified from those which are non magnetic at the surface.  相似文献