Biostratigraphy and floristic evolution of coal swamp floras of a part of Talcher Basin,India: a window on a Permian temperate ecosystem     

Shreerup Goswami  Kamaljyoti Das  Mrutyunjaya Sahoo  Soumyaranjan Bal  Sanghamitra Pradhan  Kamal Jeet Singh  Anju Saxena 《Arabian Journal of Geosciences》2018,11(17):524

The present megafloral assemblage recorded from the Barakar sediments of Dholpahar section along Singda rivulet near Gopal Prasad Village in Talcher Basin comprises of equisetaceous stems, Gangamopteris buriadica, Palaeovittaria kurzii and 19 species of the genus Glossopteris. Record of Gangamopteris, Palaeovittaria and many narrow mesh forms of Glosspteris viz., G. angustifolia, G. churiensis, G. communis, G. recurva, G. spatulata, G. stenoneura, G. tenuifolia, G. vulgaris and G. zeilleri from two older fossiliferous horizons demonstrates that these fossils were preserved during Lower Barakar sedimentation. The report of middle and broad mesh forms of Glossopteris viz., G. barakarensis, G. browniana, G. indica, G. intermittens, G. karharbariensis, G. nakkarea, G. oldhamii, G. taeniensis and G. retifera in the youngest fossiliferous horizons reveals that these fossils were preserved during the deposition of Upper Barakar sediments. The continuation of some of the Karharbari plant fossils in the early phase of Barakar Formation and their disappearance in the flora of Late Barakar suggests a shift in the climatic setup. Palaeoclimate and palaeovegetation of this area are also summarised in this study. Moreover, the fossil assemblages of different fossiliferous beds of Dholpahar section demonstrate the evolution of midrib and meshes in different reticulate leaves.  相似文献   

Benthic coverage and bottom topography of coral reef environment over Pirotan reef,Gulf of Kachchh region,India     

Mohit Arora  Nandini Ray Chaudhury  Ramesh Chander Patel 《国际地球制图》2019,34(10):1089-1097

Remote sensing measurements in coral reef environments commonly confront the problem of overlying atmosphere and modification of spectral signal due to water column over the bottom substrates. In order to correct these problems, hyperspectral observations offer an advantage over multispectral observations. Airborne hyperspectral remote sensing data from Airborne Visible Infrared Imaging Spectrometer- Next Generation (AVIRIS-NG) sensor was acquired during low tidal condition on 14 February 2016 at Pirotan reef, Gulf of Kachchh region, India. The objective of this study is to map benthic coverage and bottom topography over Pirotan reef. The methodology involved atmospheric correction, simultaneous retrieval of water parameters, bathymetry, water column correction and mapping. Atmospheric correction was performed by removing path radiance and aerosol contribution and dividing by atmospheric transmittance and incoming solar irradiance to obtain remote sensing reflectance. Model derived error minimization technique was used for simultaneous retrieval of water parameters and bathymetry. Derived water parameters were used to account for water column attenuation and retrieve concomitant true bottom signature.  相似文献   

Intergrated Airborne Gammaray Spectral and Satellite Data Analysis for U and REE Mineralisation — A Case Sudy from North Sagobandh Area, District Sonbhadra, Uttar Pradesh, India     

A P Dhurandhar  D N Saxena 《Journal of the Indian Society of Remote Sensing》1999,27(1):43-57

Airborne gamma ray spectrometric (AGRS) and magnetic (AM) surveys were undertaken between 1986-1987 by Atomic Minerals Division, to locate uranium mineralisation along Son-Narmada rift zone. The imaging and interpretation of gridded AGRS data revealed many areas of anomalous radio elemental concentrations. These areas have been defined by taking thresholds as U ≥ 6 ppm, Th ≥ 24 ppm, K ≥ 2.3% and Total counts ≥ 5000 cps. The AGRS data integration with the satellite data viz., Landsat Multi spectral Scanner (MSS), Thematic Mapper (TM), and IRS LISS II data on different scales indicated the lithostructural controls of uranium mineralisation and also the predominance of the potash metasomatism in the vicinity of the southern Son rift and soda metasomatism further away in the south. p ]Systematic follow up ground checking of the target area located in the North Sagobandh area resulted in delineating the areas of K metasomatism, anatexis and grissenisation as the areas showing ≥ 2.3%K values. The depleted K, Th, and high U/Th values show zones of albitisation and oligoelasisation. The trends of radiometric breaks depicted by total counts distribution patterns defined the tectonostratigraphic boundaries. Besides these 26 radioactive anomalies with grades ranging from eU3O/0./012–0.18%, U3Ox B/r <0.01–0.3% and ThO2 0.00.5–0.1% having strike length 50–500 meters and outcrop thickness .5–2.5 meters. Ten locations of inland riverine sand placers of heavy minerals containing REE bearing minerals i.e. xenotime, monazite, rutile, ilmenite, zircon and traces of columbite-tantalite have been identified by using thorium and mixed source (U+Th) anomaly map. These sand placers have channel lengths of 100 - >500 meters and width of 1–2.5 meters, containing l.5%–9.04% heavy minerals.  相似文献   

Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 February 1998     

Cowsik  Ramanath  Singh  Jagdev  Saxena  A.K.  Srinivasan  R.  Raveendran  A.V. 《Solar physics》1999,188(1):89-98

Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse.  相似文献   

Study of laser heated iron using third generation synchrotron X-ray radiation facility with imaging plate at high pressures     

L. S. Dubrovinsky  P. Lazor  S. K. Saxena  P. Häggkvist  H.-P. Weber  T. Le Bihan  D. Hausermann 《Physics and Chemistry of Minerals》1999,26(7):539-545

Iron pressurized to 60 gigapascal (GPa) was heated with laser up to temperatures of over 2200 K. The structural changes were determined in-situ using third generation synchrotron X-ray source; the changes were recorded on an imaging plate with a monochromatic beam. The results strongly support the existence of a phase transformation of the hexagonal close-packed (hcp) structure to the new polymorph (β-phase of iron) at high pressure and temperature. We interpret the X-ray data as belonging to the double hexagonal close-packed (dhcp) structure distorted by stress due to laser heating. Received: 2 February 1998 / Accepted: 23 August 1998  相似文献   

Geochemistry of Hindoli Group metasediments,SE Aravalli Craton,NW India: Implications for palaeoweathering and provenance     

Asha Saxena  M. K. Pandit 《Journal of the Geological Society of India》2012,79(3):267-278

The southeastern fringe of the Precambrian Aravalli fold belt has been designated as Jahazpur Belt, which includes two greenschist facies metasedimentary lithopackages, Hindoli (Late Archean/Paleoproterozoic) and Jahazpur (Paleoproterozoic) Groups. We present geochemical data on metapelite (phyllite) and metagreywackes from the Hindoli Group. Metapelites are enriched in alumina while metagreywackes show a wide range and higher abundance of silica. Covariance between TiO₂ — Al₂O₃, K₂O — Al₂O₃ pairs and moderate to high SiO₂/MgO ratios indicate a strong weathering control. Chemical Index of Alteration (CIA = 68 for metagraywackes; 75 for metapelites) reveals moderately weathered protoliths for them. Fractionated LREE pattern with almost flat HREE trend and moderate to high Eu anomalies (Eu/Eu* = 0.66 to 0.8) indicate feldspar bearing granite — granodiorite as probable compositions in the provenance. Very high PIA values (93) for metapelites reflect almost complete feldspar dissolution while the corresponding values for metagraywackes (68) are relatively lower. The diagnostic immobile trace elements (Sc, Zr, Th) can be interpreted as a variable felsic source (mainly granitic and subordinate granodioritic) for metagreywackes and a granodioritic (more mafic) one for metapelites. Considering the broad Precambrian geological set-up of NW India, the Banded Gneiss Complex (BGC), which predominantly comprises TTG gneisses and granites, amphibolite, etc. seems to be the most likely provenance for Hindoli sediments.  相似文献   

The solutions of certain generalized anomalous diffusion equations of fractional order     

B. B. Jaimini  Hemlata Saxena 《Astrophysics and Space Science》2010,330(2):289-293

In this paper we have proposed certain generalizations of anomalous diffusion equations for fractional order. These diffusion equations are solved by the method of Laplace transform with respect to the time variable and Fourier transform with respect to the space variable. The solutions of some known diffusion equations are also shown to be derived here.  相似文献   

Use of GPS in ocean‐bottom control     

Narendra Saxena 《Marine Geodesy》2013,36(1):101-103

  相似文献   

Study on water-soluble ionic composition of PM10 and related trace gases over Bay of Bengal during W_ICARB campaign     

S. K. Sharma  A. K. Singh  T. Saud  T. K. Mandal  M. Saxena  S. Singh  S. K. Ghosh  S. Raha 《Meteorology and Atmospheric Physics》2012,118(1-2):37-51

Aerosol (PM₁₀) samples were collected and its precursor gases, i.e., NH₃, NO, NO₂, and SO₂ measured over Bay of Bengal (BoB) during winter months of December 2008 to January 2009 to understand the relationship between particular matter (PM) and precursor gases. The observations were done under the winter phase of Integrated Campaign on Aerosols, gases and Radiation Budget (W_ICARB). The distribution of water-soluble inorganic ionic composition (WSIC) and its interaction with precursor gases over BoB are reported in present case. Average atmospheric concentration of NH₃, NO, NO_2, and SO₂ were recorded as 4.78?±?1.68, 1.89?±?1.26, 0.31?±?0.14, and 0.80?±?0.30?μg?m^?3, whereas WSIC component of PM₁₀, i.e., NH₄ ⁺, SO₄ ^2?, NO₃ ^?, and Cl^? were recorded as 1.96?±?1.66, 8.68?±?3.75, 1.92?±?1.75, and 2.48?±?0.78?μg?m^?3, respectively. In the present case, abundance of nss-SO₄ ^2? in the particulate matter is recorded as 18?%. It suggests the possibility of long-range transport as well as marine biogenic origin. Higher SO₄ ^2?/(SO₂?+?SO₄ ^2?) equivalent molar ratio during the campaign indicates the gas-to-particle conversion with great efficiency over the study region.  相似文献   

Sr isotopic signature of the Ganga Alluvial Plain and its implication to Sr flux of the Ganga River System     

Sandeep Singh  Munendra Singh  A. K. Choudhary  Anju Saxena  I. B. Singh  A. K. Jain 《International Journal of Earth Sciences》2010,99(8):1991-1997

The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the Ganga River, draining nearly 30,500 km² area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about 335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the alluvial plain rivers. This study establishes that elevated ⁸⁷Sr/⁸⁶Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain.  相似文献