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21.
T. P. S. Rawat Madhuparna Roy G. B. Joshi 《Journal of the Geological Society of India》2018,91(1):25-31
Sonrai basin, located along the southwestern margin of Bundelkhand Granite-Gneiss Complex (BGC) is known for its base metal and phosphorite mineralization. Uranium mineralization of appreciable grade and thickness was reported in Pisnari block in the northern part of this basin during sub-surface exploration activity in 1976-97. This was in the form of uranium-bitumin association within fractures in the carbonate-terrigenous sediments of Gorakalan shale, Rohini carbonate and Bandai sandstone of Sonrai Formation of Bijawar Group. Similar mineralization was also noted within the lower chloritic shale member of Solda Formation of the same Group. During subsequent drilling activity at a later phase (2005-09), uranium rich zones within Rohini carbonate and chloritic shale members were corroborated by the interception of mineralized bands in two boreholes drilled near Pisnari. Petrographic study of radioactive core samples reveal that uranium mineralization is closely associated with globular carbonaceous matter and sulphides along the fractures. Uranium is either adsorbed in carbonaceous matter or occurs as ultrafine inclusions of coffinite within carbonaceous matter. An additional phase of secondary uranium mineral (uranophane) is also noted in one of the boreholes. The uranium minerals, in association with sulphides, fill up moderately dipping fractures (approximately 15o towards North) which are oblique to the core axis of the inclined borehole and thus, the mineralization is characterized as hydrothermal fracture-controlled vein type mineralisation. C-HN- S analysis of carbonaceous matter occurring in close association with the uranium minerals reveal heterogeneity in composition with respect to carbon and sulfur. The present paper aims at discussing the geological, petrological and radiometric aspects of this mineralization, so as to enhance the understanding of the same. 相似文献
22.
Veena U. Joshi 《Journal of the Geological Society of India》2018,91(5):554-562
Soil erosion by water has been a major problem since man introduced agriculture in the landscape. Soil erosion is a common hazard which is steadily increasing as a result of human activities in many parts of the world. Hunter Valley of NSW is located in subtropical eastern Australia. The region is known for its diversity in landscape that includes wide floodplains, extensive estuarine wetlands, undulating country, escarpments and rugged sandstone gorges. The region is also well known for wine production. The Hunter Valley has a long history of soil erosion following the European settlement 150 years ago. Currently there have been renewed human activities in the south central part of the region for coal mining, leading to clearance of vegetation and disturbance of soil. The present study addresses the issue of soil erosion in a part of Hunter Region by employing the Revised Universal Soil Loss Equation (RUSLE, Renard et al., 1977) model. The results indicate that the average annual soil loss from the area is 0.7 kg/m2/year, which is well beyond the tolerance limit of the soil. Statistical relationships between soil loss and each parameter of the RUSLE equation were obtained and it was found that C factor has significant influence on the average soil loss in the area. An overall picture that emerges out of the study is that the region is continuing to suffer as a result of disturbance in natural environment from the historical times till present. 相似文献
23.
Kapil Bisht Yogesh Joshi Shashi Upadhyay Poonam Metha 《Journal of the Geological Society of India》2018,92(2):173-176
Glaciers being very sensitive to climate change have been identified as one of the best indicators of climate change and evidences have proved that most of the Himalayan glaciers have receded with an increased rate during the recent past under the influence of global warming. Lichenometric study was carried out on the moraines of Milam glacier (located in Pithoragarh district of Uttarakhand) with the help of lichen species Dimelaena oreina having an average annual growth rate of 1.31 mm. The study revealed that Milam glacier has receded 1450 m in last 69.37 years with an average recession rate of 20.90 m/year. Since lichenometric studies are cost effective and ecofriendly in comparison to carbon dating, satellite and remote sensing based studies and also reliable, hence, it should be promoted in Himalaya which is an abode of glaciers. 相似文献
24.
Deformation of the Champaner Group of rocks that form a part of Southern Aravalli Mountain Belt, western India, occurred during the Grenville orogeny (ca. 1400–935 Ma). Two phases of deformation are recorded: \(\hbox {D}_{1}\), persistent throughout the group and characterised by westerly plunging tight isoclinal folds and \(\hbox {D}_{2}\), a localized phase of deformation associated with shortening of the earlier folds from the eastern margin. Both the phases of deformation are in association with the syn-tectonically emplaced Godhra granite. The present work records rootless calc-silicate folds in granite belonging to the older formation, located at the eastern fringe of the Champaner Group. Field evidences suggest superimposition of Type 2 interference pattern trending NE–SW over rootless Type 0 of varying trends from NW–SE to N–S. The superposed pattern obtained from the field study differs in terms of structural trends with the neighbouring Precambrian stratigraphic units. These stratigraphic units include the Champaner Group to which the study area belongs, the Kadana Formation of the Lunavada Group and Pre-Chamapaner Gneissic Complex. Rootless character of folds found within the study area imply syn-post plutonic emplacement of Godhra granite. 相似文献
25.
Snowmelt makes an essential component of the hydrological system of Kashmir Himalayas. The present study was carried out to examine the status of Snow Cover Area (SCA) using Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day Snow Cover Product between 2000 and 2016. The intra- and inter-annual variability in SCA and in meteorological parameters was observed and various statistical tests were used to study the interrelationship. Results of statistical analysis indicate decrease in maximum temperature (?0.05 °C/year) and minimum temperatures (?0.02 °C/year) while rise in precipitation (19.13 mm/year). It also showed an increase in annual mean SCA (43.5 sq km) during the study period. The analysis was also carried out on a seasonal basis. The results revealed that in Kashmir Himalayas, climate plays a dominating role in controlling the SCA. The results depict the short-term fluctuations in SCA and show the magnitude of change between two successive values being very large in SCA. 相似文献
26.
Jeewan Chandra Pandey Subhajeet Karmakar Arti Joshi Saurabh Sharma Shashi Bhushan Pandey Anil Kumar Pandey 《天文和天体物理学研究(英文版)》2019,(1)
Using long-term optical, ultraviolet(UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V-band light curve obtained from the All Sky Automated Survey(ASAS) shows short as well as long-term variability. The short-term variability could be due to rotational modulation of CV Cha. We derive the rotational period of 3.714 ± 0.001 d for CV Cha. UV light curves obtained from Swift also show the variations. X-ray light curves from XMM-Newton and Swift do not show any significant short as well as long-term variability. However, the light curve from Chandra appears to be variable, which could be due to the emergence of flaring activities. X-ray spectra from all observations are explained well by the single temperature plasma of 0.95 keV with X-ray luminosity of 1030.4erg s-1in the 0.5–7.5 keV energy band. It appears that variability in optical and UV bands could be due to the presence of both hot and cool spots on the surface, while X-ray emission is dominated by magnetic processes. 相似文献
27.
In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015. 相似文献
28.
K. Chakraborty P. K. Joshi K. K. Sarma 《Journal of the Indian Society of Remote Sensing》2009,37(1):99-106
Meghalaya is a landlocked state where the progress of industrialization is very slow. Majority of the population (rural) depends
on agriculture. Agriculture in the state is carried on in primitive ways with Jhumming prevailing in many parts. This practice is considered destructive as vast forest areas are cleared and burnt. Such areas
are used for cultivation and left out. After a gap of few years (2–3 years as of now and 15–20 years in past) the area is
revisited for cultivation without allowing to rejuvenate. The present work provides a status and trend of Land use land cover
dynamics in parts (at watershed level) of Meghalaya. The geospatial tools have been used to assess (a) the changes in land
use land cover since 1970s to 2005; (b) patch dynamics for understanding the degree of fragmentation; (c) changes along the
terrain topography. Umngot watershed of Meghalaya is taken as experimental area, which is a representative of mid-altitudinal
watershed particularly in the Jaintia hills district of Meghalaya. 相似文献
29.
Stotts S. A Koch R. A. Joshi S. M. Nguyen V. T. Ferreri V. W. Knobles D. P. 《Oceanic Engineering, IEEE Journal of》2010,35(1):79-102
30.
A. Mudroch S. R. Joshi D. Sutherland P. Mudroch K. M. Dickson 《Environmental Geology》1989,14(1):35-42
Gold mining activities generated wastes with high concentrations of arsenic and zinc in the vicinity of Yellowknife, Northwest Territories, Canada. Some of the waste material has been discharged into Yellowknife Bay of Great Slave Lake. Concentrations of arsenic and zinc were determined in sediment cores collected at the depositional areas of Yellowknife Bay. Sedimentation rates were estimated using two different radiometric approaches: the depth profiles of Cs-137 and Pb-210. Geochemical composition of the sediment cores indicated input of similar material into sampling areas over the past 50 years. Age profiles of the sediment constructed from the radionuclides measurements were used to determine historical trends of arsenic and zinc inputs into Yellowknife Bay. The historical record was in good agreement with implemented remedial actions and usage patterns of both elements. 相似文献