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   

The retention of ammonia and sulfur dioxide during riming of ice particles and dendritic snow flakes: laboratory experiments in the Mainz vertical wind tunnel     

Nadine v. Blohn  Karoline Diehl  Anke Nölscher  Alexander Jost  Subir K. Mitra  Stephan Borrmann 《Journal of Atmospheric Chemistry》2013,70(2):131-150

Laboratory experiments were carried out in the Mainz vertical wind tunnel to determine the retention of the trace gases ammonia and sulfur dioxide dissolved in supercooled cloud droplets during riming. The conditions during riming were similar to the ones in atmospheric mixed phase clouds: temperatures from ?18 °C to ?5 °C, liquid water contents between 1 and 1.5 g m^?3, liquid drop radii between 10 and 20 μm, liquid phase concentrations from 1 to 22 mg/l. As collectors, floating ice particles and snow flakes with diameters between 6 mm and 1.5 cm were used. After riming the retention coefficients, i.e. the fractions of the species which remained in the ice phase after freezing were determined. Retention coefficients lying between 0.1 and 1.0 were measured depending on the solubility and dissociation of the trace gas, liquid phase concentration, ambient air temperature, and shape of rimed collector. This can be explained from the chemists’ point of view by the effective Henry’s law constant of the species and physically with the rate of latent heat removal from the rimed collector during freezing. Parameterizations derived from the different experimental cases describe the retention coefficients as a function of temperature. In general, an average retention of ammonia of 92?±?21 % was determined independently of liquid phase concentration while mean values for sulfur dioxide were 53?±?10 % at low liquid phase concentrations and 29?±?7 % at high liquid phase concentrations.  相似文献   

Evolution of Ganges–Brahmaputra western delta plain: Clues from sedimentology and carbon isotopes     

A. Sarkar  S. Sengupta  J.M. McArthur  P. Ravenscroft  M.K. Bera  Ravi Bhushan  A. Samanta  S. Agrawal 《Quaternary Science Reviews》2009,28(25-26):2564-2581

Sedimentology, carbon isotope and sequence stratigraphic analysis of subsurface sediments from western part of Ganges–Brahmaputra (GB) delta plain shows that a Late Quaternary marine clay and fluvial channel-overbank sediments of MIS 5 and 3 highstands are traceable below the Holocene strata. During the Last Glacial Maximum (LGM) sea-level lowering of >100 m produced a regional unconformity (type 1), represented by palaeosols and incised valley. C4 vegetation expanded on exposed lowstand surface in an ambient dry glacial climate. At 9 ka transgression inundated the lowstand surface pushing the coastline and mangrove front 100 km inland. Simultaneous intensification of monsoon and very high sediment discharge (4–8 times than modern) caused a rapid aggradation of both floodplain and estuarine valley fill deposits between 8 and 7 ka. The Hoogli River remaining along its present drainage possibly acted as the main conduit for transgression and sediment discharge that was subsequently abandoned. C3 vegetation dominated the delta plain during this time. From 7 ka onward progradation of delta plain started and continued till recent. This period experienced a mixed C3–C4 vegetation with localized mangroves in the mid-Holocene to dominant return of C4 vegetation in the late Holocene period. The study indicates that while the initiation of western part of GB delta occurred at least 1 ka earlier than the global mean delta formation age, the progradation started at 7 ka, at least 2 ka earlier than thought before. The terrestrial vegetation change was modulated by changes in depositional environment, specific ecological niches and climate rather than pCO₂.  相似文献   

Rock-magnetic proxies of climate change from loess -paleosol sediments of the Czech Republic   总被引：6，自引：0，他引：6  

Eric A. Oches  Subir K. Banerjee 《Studia Geophysica et Geodaetica》1996,40(3):287-300

Summary Rock-magnetic characteristics of late Pleistocene loess-paleosol sequences in the Czech Republic show patterns of variation that reflect climate-related depositional and diagenetic processes which acted on the sedimentary profiles. Mass-normalized magnetic susceptibility is high in interglacial and interstadial paleosols, while uniformly low values are measured in unweathered loess horizons. Normalized ferrimagnetic susceptibility and anhysteretic remanent magnetization show an enhancement of ultrafine (superparamagnetic, SP) and fine (single-domain, SD, and pseudo-single-domain, PSD) grains in chernozem paleosols correlated with δ¹⁸O substages 5c and 5a as well as in the Holocene soil. The parabraunerde paleosol associated with peak interglacial conditions, correlated with δ¹⁸O substage 5e, shows evidence of diagenetic loss of fine grained magnetic minerals, although coarse (multidomain, MD) grains appear to be preserved. Low temperature remanence behavior plus high temperature susceptibility measurements of representative samples from each lithologic unit indicate that magnetite and maghemite are the dominant magnetic minerals within the sediments. Variations in concentration-independent rock-magnetic parameters are therefore primarily a function of grain size variations through the profile. It is anticipated that with additional magnetic and non-magnetic sedimentological and geochemical tests, a quantitative rock-magnetic — paleoclimate model can be developed for the central European loess region.  相似文献   

A preliminary magnetic study of soil samples from west-central Minnesota     

Özden Özdemir  Subir K. Banerjee 《Earth and Planetary Science Letters》1982,59(2):393-403

Various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west-central Minnesota. There is a marked change in magnetic properties as a function of depth in the core. X-ray analysis and Curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil. The intensity of anhysteretic remanent magnetization (ARM) decreases sharply as the depth increases. In contrast, the stability of ARM was found to be higher for the subsoil. The surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization (VRM). The VRM acquisition coefficient (S_a) of the subsoil (S_{a= 3.18 × 10^?6emu g^?1, 3.18 × 10^?6A m² kg^?1}) was about ten times weaker than that of the top soil sample (S_a = 3.868 × 10^{?7emu g?1, 3.868 × 10?7A m2 kg?1}). The magnetic domain state indicator, the ratio of coercivity of remanence to coercive force, H_cr/H_c, was 1.5 and 3.85 for the top soil and subsoil, respectively. It appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size. We conclude that the magnetic grains in surface soil samples were more single-domain (SD) like whereas the magnetite grains in the subsoil samples were more likely in pseudo-single-domain (PSD) or small multidomain (MD) range. The observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs.  相似文献   

The magnetism of a glacial aeolianite sequence from Lanzarote (Canary Islands): coupling between luvic calcisol formation and Saharan dust trapping processes during wet deposition events off northwestern Sahara     

David Williamson  Mike Jackson  Subir K. Banerjee  Nicole Petit-Maire 《Geophysical Journal International》2004,157(3):1090-1104

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The magnetic layer of the ocean crust—How thick is it?     

Subir K. Banerjee 《Tectonophysics》1984,105(1-4)

Special features of linear marine magnetic anomalies and the magnetic measurements made on samples of the ocean crust require that the thickness of the marine magnetic source layer be thicker than the 0.5 km thick pillow lava layer (seismic layer 2A) alone. It is proposed here that the magnetic properties of the samples studied to date indicate a two-layered source to be the most likely: an upper 0.5 km thick pillow lava layer with a natural remanent magnetization of 5 A/m and a lower 3.5 km thick dike and upper gabbro layer with a magnetization of 0.5 A/m.  相似文献   

Nutrient modeling of an urban lake using best subset method     

J. K. Biswas  B. Bera  R. Chanda  S. K. Sarkar  J. Majumdar  S. Majumder  S. Hazra 《International Journal of Environmental Science and Technology》2018,15(9):1867-1878

Lakes are functionally integral and biologically complex freshwater ecosystems which provide a vast array of ecosystem goods and services to society. Nowadays aquatic ecosystems are being used, misused and abused by diverse anthropogenic activities at an unprecedented rate. The management of lake water quality is usually directed to resolution of conflicts between maintenance of desirable water quality and human-induced degradation of aquatic environment. Nutrients play a decisive role in determining lake’s environmental state through regulation of its primary production. The present study on Saheb Bundh Lake located in Purulia District, West Bengal, India, was undertaken to assess the status of nutrients (nitrogen and phosphorus) subject to certain anthropogenic activities, and to construct models using best subset method which could be adopted as a nutrient management tool. The water samples were monitored for different physicochemical parameters adopting standard methods. It was found that the set of variables including turbidity, temperature, pH, redox potential and total hardness has been championed as the best subset of water quality explaining the dynamics of total phosphorus concentration of freshwater Saheb Bundh Lake. The suite of factors comprising dissolved oxygen, pH, temperature, turbidity and total hardness has been proved as the best subset for estimating total nitrogen concentration. The models developed have been validated for total phosphorus and total nitrogen concentration. For total phosphorus, the model values were found to be very close to the measured values but the values varied widely for total nitrogen, championing the former as a very potent down-to-earth model.  相似文献   

Utilization of Landsat data to quantify land-use and land-cover changes related to oil and gas activities in West-Central Alberta from 2005 to 2013     

Subir Chowdhury  Dennis K. Chao  Todd C. Shipman  Michael A. Wulder 《地理信息系统科学与遥感》2017,54(5):700-720

Land use and land cover (LULC) change detection associated with oil and gas activities plays an important role in effective sustainable management practices, compliance monitoring, and reclamation assessment. In this study, a mapping methodology is presented for quantifying pre- and post-disturbance LULC types with annual Landsat Best-Available-Pixel multispectral data from 2005 to 2013. Annual LULC and land disturbance maps were produced for one of the major conventional oil and gas production areas in West-Central Alberta with an accuracy of 78% and 87%, respectively. The highest rate of vegetation loss (178 km²/year) was observed in coniferous forest compared to broadleaf forest, mixed forest, and native vegetation. Integration of ancillary oil and gas geospatial data with annual land disturbances indicated that less than 20% of the total land disturbances were attributable to oil and gas activities. In 2013, approximately 44% of oil and gas disturbances from 2005 to 2013 showed evidence of vegetation recovery. In the future, geospatial data related to wildfire, logging activities, insect defoliation, and other natural and anthropogenic factors can be integrated to quantify other causes of land disturbances.  相似文献   

Ovi-caprid dung as an indicator of paleovegetation and paleoclimate in northwestern China     

Ruby Ghosh  Subir Bera  Hong-en Jiang  Cheng-Sen Li 《Quaternary Research》2008,70(2):149-157

Diverse palynomorphs and phytoliths recovered from coprolites of ovi-caprids (sheep, goat) collected from Yang-Hai Tomb at Xinjiang Province, China, have been used to elucidate the dietary pattern of ancient livestock and to reconstruct the paleovegetation and paleoclimate of this part of northwest China ca. 2500 ¹⁴C yr BP. Palynological and phytolith data suggest that a rich dry temperate vegetation prevailed in the area during the said period. Climatic conditions and grassland vegetation type of the area are explored using phytolith indices.  相似文献