Molecular fossils in Cretaceous condensate from western India     

Sharmila Bhattacharya  Suryendu Dutta  Ratul Dutta 《Journal of Earth System Science》2014,123(5):923-934

The present study reports the biomarker distribution of condensate belonging to the early Cretaceous time frame using gas chromatography–mass spectrometry (GC–MS). The early Cretaceous palaeoenvironment was inscribed into these molecular fossils which reflected the source and conditions of deposition of the condensate. The saturate fraction of the condensate is characterized by normal alkanes ranging from n-C₉ to n-C₂₉ (CPI-1.13), cycloalkanes and C₁₄ and C₁₅ sesquiterpanes. The aromatic fraction comprises of naphthalene, phenanthrene, their methylated derivatives and cyclohexylbenzenes. Isohexylalkylnaphthalenes, a product of rearrangement process of terpenoids, is detected in the condensate. Several aromatic sesquiterpenoids and diterpenoids have been recorded. Dihydro-ar-curcumene, cadalene and ionene form the assemblage of sesquiterpenoids which are indicative of higher plant input. Aromatic diterpenoid fraction comprises of simonellite and retene. These compounds are also indicative of higher plants, particularly conifer source which had been a predominant flora during the Cretaceous time.  相似文献   

Oxygen isotope analysis of bone and tooth enamel phosphate from paleogene sediments: Experimental techniques and initial results     

M. K. Bera  Kasturi Bhattacharya  A. Sarkar  A. Samanta  Kishor Kumar  Ashok Sahni 《Journal of the Geological Society of India》2010,76(3):275-282

Oxygen isotope composition (δ¹⁸O) of fossil bone and tooth enamel phosphate (bioapatite) is an important tool for estimating the isotopic composition of past environmental water. Lack of analytical facility was a hindrance for studying such bioapatites in spite of large number of fossil materials reported from various geological ages in India. We have established in our laboratory, based on available methods, the chemical procedure for extraction of very small amount (<1000 μg) PO₄ ⁻³ from bioapatite and on-line mass spectrometric measurement of its δ¹⁸O composition by high temperature (∼1450°C) pyrolysis. The achieved precision is ∼± 0.3 ‰ similar to obtained elsewhere, with interlaboratory calibration showing excellent agreement of standard phosphates. Inferred δ¹⁸O values of environmental water, based on the analysis of teeth and bones of sharks, fish and terrestrial mammals from the Paleogene successions of the northwest sub-Himalayan and the Peninsular India show strong correspondence with animal habitats. The freshwater δ¹⁸O values are much depleted having range similar to modern monsoon precipitation. However, owing to our small dataset it is not possible at this stage to infer about the existence of monsoon over the Indian sub-continent during the Eocene-Oligocene time.  相似文献   

Prospects of hard X-ray polarimetry with Astrosat-CZTI     

T. Chattopadhyay  S. V. Vadawale  A. R. Rao  S. Sreekumar  D. Bhattacharya 《Experimental Astronomy》2014,37(3):555-577

Astrosat is the first Indian satellite mission dedicated for astronomical studies. It is planned for launch during 2014 and will have five instruments for multi-wavelength observations from optical to hard X-rays. Cadmium Zing Telluride Imager (CZTI) is one of the five instruments aiming for simultaneous X-ray spectroscopy and imaging in the energy range of 10 keV to 100 keV (along with all sky photometric capability unto 250 keV). It is based on pixilated CZT detector array with total geometric area of 1024 cm². It will have two-dimensional coded mask for medium resolution X-ray imaging. The CZT detector plane will be realized using CZT detector modules having integrated readout electronics. Each CZT detector module consists of 4 cm × 4 cm CZT with thickness of 5 mm which is further pixilated into 16 × 16 array of pixels. Thus each pixel has size of 2.5 mm × 2.5 mm and thickness of 5 mm. Such pixilated detector plane can in principle be used for hard X-ray polarization measurements based on the principle of Compton scattering by measuring azimuthal distribution of simultaneous events in two adjacent pixels. We have carried out detailed Geant4 simulations for estimating polarimetric capabilities of CZTI detector plane. The results indicate that events in the energy range of 100 keV to 250 keV, where the 5 mm thick CZT detector has significant detection efficiency, can be used for polarimetric studies. Our simulation results indicate the minimum detectable polarization (MDP) at the level of ～ 10% can be achieved for bright Crab like X-ray sources with exposure time of ～500 ks. We also carried out preliminary experiments to verify the results from our simulations. Here we present detailed method and results of our simulations as well as preliminary results from the experimental verification of polarimetric capabilities of CZT detector modules used in Astrosat CZTI.  相似文献   

Contrasting pressure–temperature–deformation history across a vestigial craton–mobile belt boundary: the western margin of the Eastern Ghats Belt at Deobhog, India     

S. Gupta  A. Bhattacharya  M. Raith  & J.K. Nanda 《Journal of Metamorphic Geology》2000,18(6):683-697

At Deobhog, migmatitic gneisses and granulites of the Eastern Ghats Belt are juxtaposed against a cratonic ensemble of banded augen gneiss, amphibolite and calcsilicate gneiss, intruded by late hornblende granite and dolerite. In the migmatitic gneiss unit, early isoclinal folds (syn‐D_1M and D_2M) are reoriented along N–S‐trending and E‐dipping shear planes (S_3M), with (S_1M–S_3M) intersection lineations having steep to moderate plunges. The near‐peak P–T condition was syn‐D_3M (≥900 °C, 9.5 kbar), as inferred from syn‐D_3M Grt+Opx‐bearing leucosomes in mafic granulites, and from thermobarometry on Grt (corona)–Opx/Cpx–Pl–Qtz assemblages. The P–T values are consistent with the occurrence of Opx–Spr–Crd assemblages in spatially associated high‐Mg–Al pelites. A subsequent period of cooling followed by isothermal decompression (800–850 °C, c. 7 kbar) is documented by the formation of coronal garnet and its decomposition to Opx+Pl symplectites in mafic granulites. Hydrous fluid infiltration accompanying the retrograde changes is manifested in biotite replacing Opx in some lithologies. The cratonic banded gneiss–granite unit also documents two phases of isoclinal folding (D_1B & D_2B), with the L_2B lineation girdle different from the lineation spread in the migmatitic gneiss unit. Calcsilicate gneiss (Hbl–Pl–Cpx–Scap–Cal) and amphibolite (Hbl–Pl±Grt±Cpx) within banded gneisses record syn‐D_2B peak metamorphic conditions (c. 700 °C, 6.5 kbar), followed by cooling (to c. 500 °C) manifested in the stabilization of coronal clinozoisite–epidote. The D_3B shear deformation post‐dates granite and dolerite intrusions and is characterized by top‐to‐the‐west movement along N–S‐trending, E‐dipping shear planes. Deformation mechanisms of quartz and feldspar in granites and banded gneisses and amphibole–plagioclase thermometry within shear bands in dolerites document an inverted syn‐D_3B thermal gradient with temperature increasing from 350 to 550 °C in the west to ≥700 °C near the contact with the migmatitic gneiss unit. The thermal gradient is reflected in the stabilization of chlorite after hornblende in S_3B shears to the west, and post‐D_2B neosome segregation along D_3B folds and shears to the east. The contrasting lithologies, early structures and peak metamorphic conditions in the two units indicate unconnected pre‐D₃P–T –deformation histories. The shared D₃ deformation in the two units, the syn‐D₃ inverted thermal gradient preserved in the footwall cratonic rocks and the complementary cooling and hydration of the hanging wall granulites across the contact are attributed to westward thrusting of ‘hot’ Eastern Ghats granulites on ‘cool’ cratonic crust. It is suggested that the Eastern Ghats migmatitic gneiss unit is not a reworked part of the craton, but a para‐autochthonous/allochthonous unit emplaced on and amalgamated to the craton.  相似文献   

Uniform anisotropic cosmological model with string source     

Sudeepto Bhattacharya  T. M. Karade 《Astrophysics and Space Science》1993,202(1):69-75

By adopting the comoving coordinate system, the axially symmetric models with string dust cloud source are obtained. Some of these models are singular free even at an initial epoch, where the geometric as well as thep-strings become singular.  相似文献   

Experimental p-y curves for liquefied soils from centrifuge tests     

Dash  Suresh R.  Bhattacharya  Subhamoy 《地震工程与工程振动(英文版)》2021,20(4):863-876

The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided.  相似文献   

Albedo-rainfall Feedback Over Indian Monsoon Region Using Long Term Observations Between 1981 to 2000     

Bimal Kumar Bhattacharya  Keshav R. Gunjal  Sushma Panigrahy  Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(3):393-406

Albedo determines radiation balance of land (soil-canopy complex) surface and influence boundary layer structure of the atmosphere. Accurate surface albedo determination is important for weather forecasting, climate projection and ecosystem modelling. Albedo-rainfall feedback relationship has not been studied so far using observations on spatial scale over Indian monsoon region due to lack of consistent, systematic and simultaneous long-term measurements of both. The present study used dekadal (ten-day) composite of satellite (e.g. NOAA) based Pathfinder AVHRR Land (PAL) datasets between 1981 and 2000 over India (68–100°E, 5–40°N) at 8 km spatial resolution. Land surface albedo was computed using linear transformation of red and near infrared (NIR) surface reflectances. The cloud effects were removed using a smoothening filter with harmonic analysis applied to time series data in each year. The monthly, annual and long term means were computed from dekadal reconstructed albedo. The mean per year and coefficient of variation (CV) of surface albedo over seventeen years, averaged over Indian land region, were found to show a significantly decreasing (0.15 to 0.14 and 60 to 40%, respectively) trend between 1981 and 2000. Among all the land use patterns, the inter-annual variation of albedo of Himalayan snow cover showed a significant and the steepest reducing trend (0.42 – 0.35) followed by open shurbland, grassland and cropland. No significant change was noticed over different forest types.. This could be due to increase in snow melting period and snow melt area. A strong inverse exponential relation (correlation coefficient r = 0.95, n = 100) was found between annual rainfall and annual albedo over seven rainfall zones. The decreasing trend in snow-albedo of accumulation period (September to March) follows the declining trend in measured south-west monsoon rainfall between 1988 (980 mm) to 1998 (880 mm) over India. This finding perhaps suggests the possible reversal of reported coupling of increased snowfall followed by lower monsoon rainfall.  相似文献   

Morphostratigraphy and palaeoclimate appraisal of the Leh valley,Ladakh Himalayas,India     

Dhananjay A. Sant  Sudesh K. Wadhawan  Rajinder K. Ganjoo  Nathani Basavaiah  Prabhin Sukumaran  Sourabh Bhattacharya 《Journal of the Geological Society of India》2011,77(6):499-510

In the present paper we study morphology, occurrence and mutual interrelationship of erosional (amphitheaters) and depositional landforms belonging to glacial (moraines), fluvio-glacial (glacial out wash), mass wasting (alluvial fans), aeolian (obstacle dune and sand sheets) and lacustrine (palaeo-lake sediments) processes within the Leh valley. These landforms are the geomorphic expression of past deglaciation grouped into five Formative Stages of Landform (FSL 1 to FSL 5) development in the Leh valley. The broad age bracket for the formative stages are based on the empirical relationship of the landforms, available chronology and their correlation with comparable climate phases. The retreat of glaciers in the Leh valley, along the southern slopes of Ladakh hill range and their retention over the northern slopes and Karakoram is further explained.  相似文献   

Inferring the hydro-geochemistry of fluoride contamination in Bankura district, West Bengal: A case study     

S. Chakrabarti  H. N. Bhattacharya 《Journal of the Geological Society of India》2013,82(4):379-391

In view of the recent reports of fluorosis in many parts of Bankura district, West Bengal, a detailed hydrogeochemical monitoring was carried out in the different blocks of Bankura to find out the level and extent of affectation. It is observed that the sub-surface environment of Bankura is appreciably contaminated with the deadly poison of fluoride. Out of the 3617 tube wells surveyed in 10 affected blocks, 612 sources are detected with fluoride above the desirable limit of 1 mg/l. In addition, down-the-hole rock drilling was performed at 15 different locations in 8 worst affected blocks of Bankura. Nearly 75% of the drill-hole rock chip samples and 62% of sub-surface water samples collected from different depths is found to have fluoride equal to or above 4000 mg/kg and 1 mg/l respectively. Detailed microscopic examination of drill chip samples has indicated diverse rock units in close succession, such as Chotanagpur Gneissic Complex, Singhbhum Group of rocks, anorthosite suite and unclassified metamorphics of Archaean-Proterozoic age. All these rocks have been intruded later by granitic fluids causing mineralization of fluoride to take place. Besides, fluoride is also found derived, to lesser extent, from Older Alluvium which bears different fluoride bearing minerals. Preliminary health surveys have revealed that dental and skeletal fluorosis are prevalent in the study area, which further corroborates with the analytical findings.  相似文献   

Monitoring of River Center Line and Width—A Study on River Brahmaputra     

Aveedibya Dey  Rajib Kumar Bhattacharya 《Journal of the Indian Society of Remote Sensing》2014,42(2):475-482

Monitoring of river width and centerline is one of the most important activities in river engineering. Changes in the width and center line can be attributed to several reasons and monitoring these changes can be conveniently achieved with the aid of remote sensing images. In this study, digital image processing techniques have been implemented using the image processing tool-box available in MATLAB for studying temporal variations of width and centerline of the river Brahmaputra in its 300 Km reach in the state of Assam, India. The current study uses relatively high resolution imageries acquired from the LANDSAT series of satellites. Apart from the LANDSAT imageries, the low resolution imageries acquired by MODIS program is also used in order to see the variation in the obtained results. The evaluation of the results shows that the digital image processing technique is very handy and can be applied to obtain the centerline and width of a river. The evaluation also shows that the low resolution image can also be used for obtaining centerline of a river. However, it may give erroneous result when width of the river is narrow or very large.  相似文献