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11.
Fine grained sericite deposits occur at the interface between Archean Mewar Gneiss Complex and the Proterozoic Aravalli Supergroup
independent of shearing. They show a gradational contact with the basement granites and gneisses and a sharp contact with
the overlying quartz pebble conglomeratic quartzites. Rip-up clasts of these sericite schists are found in the overlying conglomerates.
The sericite schists are rich in sericite towards the top and contain chlorite towards the base. The sericite in these schists
was formed by metasomatic alteration of kyanite and not from the feldspars of the basement granitoids and gneisses. Uni-directional
variations of SiO2 and Al2O3, high Al2O3 content (>30%), positive correlation between Al2O3 and TiO2, Ti/Al and Ti/Zr ratios, high pre-metasomatic chemical indices of alteration (> 90), and enrichment of heavy rare earth elements
relative to the parent granites and gneisses—all these chemical characteristics combined with field evidence suggest that
the sericite schists are formed from a paleosol protolith, which developed on Archean basement between 2.5 and ~2.1 Ga in
the Precambrian of Rajasthan. The superimposed metasomatic alteration restricts the use of Fe2+/Ti and Fe3+/Ti ratios of these paleosols for interpretation of PO2 conditions in the atmosphere. 相似文献
12.
K. Sreenivas R. S. Dwivedi A. N. Singh S. Raviprakash 《Journal of the Indian Society of Remote Sensing》2010,38(1):119-132
Waterlogging due to rising ground watertable, being a sub-surface phenomenon, is not amenable to detection by optical remote
sensing. Microwave and thermal sensor data have, however, shown some promise in the detection of sub-surface waterlogging.
The present study was taken up to evaluate the potential of near-IR, short-wave IR (SWIR) and thermal-IR data from Moderate
Resolution Imaging Spectrometer (MODIS) aboard Terra-1 acquired during day-and-night time postmonsoon data for detection of
sub-surface waterlogging. The approach involves retrieval of day-and-night land surface temperature (LST), generation of normalized
difference of channel-2 and 6 (ND26); 2 and 7 (ND27); ground truth collection involving concurrent ground water table observations to satellite date of pass, thresholding of
normalized differences (NDs) and correlating the NDs with depth of ground water table. Amongst various spectral indices, day
and night-time LST difference (DLST) and night-time LST have been found to correlate well with the incidence of waterlogging
(water table depth < 2m), followed by normalized difference of band-2 (841–876 nm) and band-7 (2105–2155 nm). The sensitivity
of threshold limits for these indices was maximum for DLST followed by ND26 and ND27. Poor accuracy of detecting sub-surface waterlogging with thermal bands during day time is attributed to the non-corresponding
of the time of Terra MODIS data acquisitions with thermal maxima of the terrain. Though the ND27 gave better accuracy to detect subsurface waterlogging, it is very sensitive to threshold limits. 相似文献
13.
K. Sreenivas G. Sujatha K. Sudhir D. Vamsi Kiran M. A. Fyzee T. Ravisankar V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2014,42(3):577-587
Regional estimates of soil carbon pool have been made using various approaches that combine soil maps with sample databases. The point soil organic carbon (SOC) densities are spatialized employing approaches like regression, spatial interpolation, polygon based summation, etc. The present work investigates a data mining based spatial imputation for spatial assessment of soil organic carbon density. The study area covers Andhra Pradesh and Karnataka states of India. Field sampling was done using stratified random sampling method with land cover/use, soil type, agro-ecological regions for defining strata. The spatial data at 1 km resolution on climate, NDVI, land cover, soil type, topography was used as input for modeling the top 30 cm Soil Organic Carbon (SOC) density. To model the SOC density, a Random Forest (RF) based model with optimal parameters and input variables has been adopted. Experiment results indicate that 500 number of trees with 5 variables at each split could explain the maximum variability of soil organic carbon density of the study area. Out of various input variables used to model SOC density, land use / cover was found to be the most significant factor that influences SOC density with a distinct importance score of 34.7 followed by NDVI with a score of 12.9. The predicted mean SOC densities range between 2.22 and 13.2 Kg m?2 and the estimated pool size of SOC in top 30 cm depth is 923 Tg for Andhra Pradesh and 1,029 Tg for Karnataka. The predicted SOC densities using this model were in good agreement with the measured observations (R?=?0.86). 相似文献
14.
The term flood basalt is redefined emphasizing the importance of the subaerial environment. Using the well established physical criteria of aerial extent, internal structures, time of extrusion and associations, flood basalt activity is distinguished in the Archeans (Dharwars) of Mysore from the geosynclinal volcanics. Study of chemical composition of the Dharwar and other Archean volcanics in the light ofSugimura’s (1968) SWS index, and plotting of the chemical analyses on theMacdonald andKatsura’s (1964) alkali-silica diagram,Kuno’s (1968) alkali-alumina-silica diagram and Scheynamann’s silica-Niggli qz diagram shows both geosynclinal and subaerial volcanics are mainly tholeiitic. Therefore in deciphering the environment of volcanism, it is suggested that the physical criteria take precedence over chemical composition. 相似文献
15.
The mixed layer depths over the Arabian Sea were computed for the three successive years 2004-2006 using ARGO floats data. The large availability of ARGO floats for the above period resulted in better estimation of mixed layer depth (MLD) over the Arabian Sea. The results were compared with World Ocean Atlas 1994 MLD Climatology. Marked variability in MLD on a monthly time scale is observed and it was in accordance with the wind stress and/or net heat gain variability, which are the principal factors influencing mixed layer over Arabian Sea. With the availability of large number of ARGO profile data, an attempt is made to study the monthly variability of Mixed Layer. 相似文献
16.
Tarik Mitran T. Ravisankar M.A. Fyzee Janaki Rama Suresh G. Sujatha K. Sreenivas 《国际地球制图》2015,30(6):701-721
The relationship between soil salinity parameters and their influence on soil spectral characteristics were analyzed using both satellite data (Hyperion) and reflectance data of soil samples collected from parts of Ahmedabad district of Gujarat, India. The soil spectral reflectance curves were assessed using absorption feature parameters by DISPEC software to identify suitable spectral band for salinity characterization. The Hyperion data of the study area were processed and classified into different classes by spectral angle mapper algorithm using spectral library generated from soil spectra. The results showed that among all the observed soil parameters Electrical Conductivity, Exchangeable Sodium Percentage, Cation Exchange Capacity and Mg++ predictions can be made accurately based on partial least square regression models developed from selected wavelengths. Out of the total study area moderately saline-sodic, severely saline-sodic, severely saline and slightly saline soils occupy 23.5, 12.6, 10.9 and 0.04%, respectively. 相似文献
17.
Takashi Murakami Bulusu Sreenivas Subrata Das Sharma 《Geochimica et cosmochimica acta》2011,75(14):3982-4004
The increase in atmospheric oxygen during the Precambrian is a key to understand the co-evolution of life and environment and has remained as a debatable topic. Among various proxies for the estimation of atmospheric oxygen levels, paleosols, ancient weathering profiles, can provide a quantitative pattern of atmospheric oxygen increase during the Precambrian period of Earth history. We have re-evaluated the chemical compositions of paleosols, and presented a new method of applying Fe2+ oxidation kinetics to the Fe2+ and Fe3+ concentrations in paleosols to decipher the quantitative partial pressure of atmospheric oxygen (PO2) between 2.5 and 2.0 Ga. We first estimated the compaction factor (CF, the fraction of original thickness) using the immobile elements such as Ti, Al and Zr on equal volume basis, which was then used to calculate retention fractions (MR), a mass ratio of paleosol to parent rock, of redox-sensitive elements. The CF and FeR values were evaluated for factors such as homogeneity of immobile elements, erosion, and formation time of weathering. FeR increased gradually within the time window of ∼2.5-2.1 Ga and remained close to 1.0 since ∼2.1 Ga onwards. MnR also increased gradually similar to FeR but at a slower rate and near complete retention was observed ∼1.85 Ga, suggesting an almost continuous increase in the oxidation of Fe2+ and Mn2+ in paleosols ranging in age between ∼2.5 and 1.9 Ga.We have modeled PO2 variations during the Paleoproterozoic by applying Fe2+ oxidation kinetics to the Fe2+ and Fe3+ concentrations in paleosols, which enabled us to derive an Fe2+ oxidation term referred to as ψ. Possible changes in temperature and PCO2 during this time window and their effects on resulting models of PO2 evolution have been also considered. We assumed four cases for the calculations of PO2 variations between 2.5 and 2.0 Ga: no change in either temperature or PCO2, long-term change in only PCO2, long-term changes in both temperature and PCO2, and short-term fluctuations of both temperature and PCO2 during the possible, multiple global-scale glaciations. The calculations indicate that PO2 increased gradually, linearly on the logarithmic scale, from <∼10−6 to >∼10−3 atm between 2.5 and 2.0 Ga. Our calculations show that the PO2 levels would have fluctuated significantly, if intense, global glaciation(s) followed by period(s) of high temperature occurred during the Paleoproterozoic. This gradual rise model proposes a distinct, quantitative pattern for the first atmospheric oxygen rise with important implications for the evolution of life. 相似文献
18.
R. S. Dwivedi K. Sreenivas K. V. Ramana P. R. Reddy G. Ravi Sankar 《Journal of the Indian Society of Remote Sensing》2006,34(4):351-367
Realizing the potential of spaceborne multispectral measurements in providing spatial information on natural resources, and
of Geographic Information System (GIS) in integrating such information with the socio-economic data and other collateral information
to arrive at derivative information, we report here the results of a study which was taken up in a watershed in Charkhari
block of Mahoba district, northern India, to generate the information on natural resources from Indian Remote Sensing Satellite
(IRS-1B) Linear Imaging Self-scanning Sensor (LISS-II) images through a systematic visual interpretation, and its subsequent
integration with the collateral information in a GIS environment to develop optimal land use plan/action plan for sustainable
development of its land resources. Since permanent vegetation cover in the watershed has been dwindling due to population
pressure, the need for establishing more vegetation cover has been stressed. 相似文献
19.
Bulusu Sreenivas Sukanta Dey Y.J.Bhaskar Rao T.Vijaya Kumar E.V.S.S.K.Babu Ian S.Williams 《地学前缘(英文版)》2019,10(4):1359-1370
The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials. 相似文献
20.
R. S. Dwivedi K. V. Ramana K. Sreenivas 《Journal of the Indian Society of Remote Sensing》2007,35(2):173-184
Waterlogging and subsequent salinization and/or alkalization is the major land degradation problem in the irrigation commands of the semi-arid regions. Information on the nature, extent and spatial distribution of waterlogged areas is a pre-requisite for restoration of fertility, which has hitherto been generated conventionally. Realising the potential of spaceborne multispectral measurements in providing reliable information on spatial patterns of waterlogged areas in a timely and cost-effective manner, a study was taken up to delineate and monitor the spatial distribution pattern of waterlogged areas in Mahanadi command Stage-I covering parts of Orissa state, eastern India using Landsat-TM, Indian Remote Sensing satellite (IRS-1A) Linear Imaging Self-Scanning Sensor (LISS-II) and IRS-ID LISS-III data. A systematic on-the-screen visual interpretation approach after geo-referencing and radiometric normalization of digital multispectral data in a Silicon Graphics work station using ERDAS/ IMAGINE software was followed to realize the objectives. Results point to a significant increase in the spatial extent of waterlogged areas. Seasonally waterlogged areas increased from 29330 ha to 33421 ha and permanent waterlogged areas from 10870 ha to 12973 ha during the period 1988–89 to 1999–2000. Methodology and results are discussed in detail. 相似文献