Species diversity variations in Neogene deep-sea benthic foraminifera at ODP Hole 730A,western Arabian Sea

Deep-sea benthic foraminifera are an important and widely used marine proxy to understand paleoceanographic and paleoclimatic changes on regional and global scales, owing to their sensitivity to oceanic and climatic turnovers. Some species of benthic foraminifera are sensitive to changes in water mass properties whereas others are sensitive to organic fluxes and deep-sea oxygenation. Benthic faunal diversity has been found closely linked to food web, bottom water oxygen levels, and substrate and water mass stability. The present study is aimed at analyzing species diversity trends in benthic foraminifera and their linkages with Indian monsoon variability during the Neogene. Species diversity of benthic foraminifera is examined in terms of number of species (S), information function (H), equitability (E) and Sanders’ rarefied values, which were combined with relative abundances of high and low productivity benthic foraminifera at Ocean Drilling Program Hole 730A, Oman margin, western Arabian Sea. The Oman margin offers the best opportunity to understand monsoon-driven changes in benthic diversity since summer monsoon winds have greater impact on the study area. The species diversity was higher during the early Miocene Climatic Optimum (～17.2–16.4 Ma) followed by a decrease during 16.4–13 Ma coinciding with a major increase in Antarctic ice volume and increased formation of Antarctic Bottom Water. All the diversity parameters show an increase during 13–11.6 Ma, a gradual decrease during 11.6–9 Ma and then an increase with a maximum at 7 Ma. Thereafter the values show little change until 1.2 Ma when all the parameters abruptly decrease. The benthic foraminiferal populations and diversity at Hole 730A were mainly driven by the Indian monsoon, and polar waters might have played a minor or no role since early Neogene period as the Arabian Sea is an enclosed basin.     

Rare Earth Element Enrichment in Late Archean Manganese Deposits from the Iron Ore Group,East India

The major, trace and rare earth element (REE) composition of Late Archean manganese, ferromanganese and iron ores from the Iron Ore Group (IOG) in Orissa, east India, was examined. Manganese deposits, occurring above the iron formations of the IOG, display massive, rhythmically laminated or botryoidal textures. The ores are composed primarily of iron and manganese, and are low in other major and trace elements such as SiO₂, Al₂O₃, P₂O₅ and Zr. The total REE concentration is as high as 975 ppm in manganese ores, whereas concentrations as high as 345 ppm and 211 ppm are found in ferromanganese and iron ores, respectively. Heavy REE (HREE) enrichments, negative Ce anomalies and positive Eu anomalies were observed in post‐Archean average shale (PAAS)‐normalized REE patterns of the IOG manganese and ferromanganese ores. The stratiform or stratabound shapes of ore bodies within the shale horizon, and REE geochemistry, suggest that the manganese and ferromanganese ores of the IOG were formed by iron and/or manganese precipitation from a submarine, hydrothermal solution under oxic conditions that occurred as a result of mixing with oxic seawater. While HREE concentrations in the Late Archean manganese and ferromanganese ores in the IOG are slightly less than those of the Phanerozoic ferromanganese ores in Japan, HREE resources in the IOG manganese deposits appear to be two orders of magnitude higher because of the large size of the deposits. Although a reliable, economic concentration technique for HREE from manganese and ferromanganese ores has not yet been developed, those ores could be an important future source of HREE.     

Fluid evolution in the Kolar Gold Field: evidence from fluid inclusion studies

Gold mineralization in the Kolar schist belt of the Dharwar craton occurs dominantly in the form of a sulfide-poor Au-quartz lode (the Champion lode exposed in the Mysore and other mines) and sulfide-rich auriferous lodes (from the Nundydroog mine). Fluid inclusion microthermometric experiments were conducted on primary inclusions in quartz intimately associated with Au-mineralization. Homogenization studies on aqueous-biphase (L + V), aqueous polyphase (L + V+ halite) and aqueous-carbonic (L_CO2± V_CO2 + L_aq) inclusions from the Champion lode furnish a temperature range of 120 to 420 °C. Freezing of aqueous biphase inclusions and dissolution of halite in the aqueous polyphase inclusions provide salinity of 5 to 50 wt.% NaCl equivalent. Fluid inclusion thermobarometry from the total homogenization of aqueous-carbonic inclusions and from intersecting isochores of coeval pure-carbonic (L_CO2± V_CO2) and pure-aqueous inclusions constrain the P-T path of evolution of the fluid in the Champion lode. Gold precipitation was likely to have been brought about in response to a sharp fall in pressure with attendant unmixing of liquid-CO₂ from the parent H₂O-CO₂ fluid of possible metamorphic origin. This would imply transportation of gold by some pressure-sensitive complex such as the Au-carbonyl. Fluid characteristics are different in the sulfide-rich auriferous lodes, as indicated by the virtual absence of the CO₂-bearing and the halite-bearing inclusions. The fluid evolution path, as evident from the crude positive colinearity of temperature and salinity, is due to mixing of a low (≤200 °C) temperature-low saline (≤7 wt.% NaCl equivalent) fluid with a high temperature (≥400 °C)-high saline (≥50 wt.% NaCl equivalent) fluid. The lack of CO₂ and association of Au with sulfides indicate a different mode of gold transport, as chloride or bisulfide complexing, deposition of which was possibly brought about by fluid mixing. Received: 17 April 1997 / Accepted: 30 June 1998     

Optimum tracking of ship routes in 3g-WAM simulated rough weather using IRS-P4 (MSMR) analysed wind fields

Rough weather ship routing is studied using model hindcast wave climate. With the launch of IRS-P4 (OCEANSAT-I), it became possible to carry out routine wave forecasting over the Indian Ocean. The MSMR channel of the satellite gives scalar wind, which is analysed at National center for Medium Range Weather Forecasting (NCMRWF), India for converting to vector winds. The same is used as input to third generation wave model for the rough weather month of July 2000. Simulations are carried out using Cycle-4 of third generation spectral wave model WAM for regional grid system. This simulated wave climate formed the basis for computing effective ship velocity in the irregular seaway. This study gives a quantitative estimation of change in ship velocity in the open Indian Ocean for a Liberty type ship. The optimal route is charted using Dijkstra’s algorithm for minimal time path between Calcutta and Sumatra. The optimum track information has broad scope for obtaining a safer route, least time route by avoiding delay in schedule with minimum fuel consumption.     

Classification of coal seams with respect to their spontaneous heating susceptibility—a neural network approach

The paper presents the application of adaptive resonance theory of artificial neural networks (ANN) for classification of coal seams with respect to their proneness to spontaneous heating. In order to apply this technique, 31 coal samples have been collected from different Indian coalfields covering both fiery and non-fiery coal seams of varying ranks spreading over 8 different mining companies. The intrinsic properties of these samples have been determined by carrying out proximate, ultimate and petrographic analyses. The susceptibility indices of these samples have been studied by five different methods, viz. crossing point temperature, differential thermal analysis, critical air blast analysis, wet oxidation potential difference analysis and differential scanning calorimetric studies. Exhaustive correlation studies between susceptibility indices and the intrinsic properties have been carried out for identifying the appropriate spontaneous heating susceptibility indices and intrinsic properties to be used for classification of coal seams. The identified parameters are used as inputs and adaptive resonance theory of ANN has been applied to classify the coal seams into four different categories. This classification system will help the planners and practising mining engineers to take ameliorative measures in advance to prevent the occurrence of fire in mines.     

Fluid evolution in quartz vein-hosted tungsten mineralization in Chhendapathar, Bankura District, West Bengal: Evidence from fluid inclusion study

Tungsten mineralization in Chhendapathar area is hosted by quartz veins that traverse mostly the metasediments in and around Jikhu Nala. Fluid inclusion microthermometric experiments reveal the presence of four distinct types of inclusions. These are: aqueous biphase, monophase carbonic, aqueouscarbonic and halite-bearing polyphase inclusions. Salinity-temperature variation points towards the presence of two fluids of contrasting salinities and both independently followed simple cooling paths without any indication of fluid mixing. The P-T of mineralization was calculated from the intersection of coexisting and coeval aqueous biphase, carbonic and halite-bearing inclusions. The deduced values range from 1.63kb/361°C to 2.30kb/385°C. However, the initial temperature must have been much higher as indicated from the high dissolution temperature (> 450°C) of halite. Transportation of tungsten in the high saline fluid was facilitated by cation-tungstate ion pairing, i.e., with the help of Na₂WO₄ and/or NaHWO₄ complexes. A rapid fall in solubility in such fluid with falling temperature (in the range of 300–400°C), and by occasional fluid-rock interaction triggered precipitation of wolframite.     

Nayagarh氟化物污染区土壤的地球化学性质：因素分析评价

本文旨在研究奥里萨邦[印度邦名]Nayagarh区温泉地带土壤受氟化物污染的情况。文中分析两种土壤（大部分是在0-30cm深度采集的土壤以及0-90cm深度采集的剖面土壤）的总氟化物浓度（Ft）和0．01MCaCl2可萃取的氟化物浓度（Fca）主要的元素、pH、EC以及有机碳。通过对Singhpur村周围区域和温泉的观察，结果表明Ft和Fca浓度都高。大部分土壤参数的主要因素分析（PFA）表明，两种主要的化学过程是由于三个因素控制区域土壤的地球化学性质。第一个因素占总变化的37．11％，对Al、Si、Fe、F。和F。有很强的载荷能力，而且说明了土壤富集氟化物的原因；而第二和第三个因素分别占16．6％和12．2％，说明碳酸盐沉淀的控制过程和土壤的碱度。对因素做多元回归分析是为了取得土壤的氟化物污染指数。因素影响范围的大小（因素-1〉因素-2〉因素-3）影响污染指数。污染指数的空间分布可以用来划分污染区域的污染等级，即：高度污染区、中度污染区和未污染区。     

Numerical hindcast of extreme waves

The cyclone wave parameters are predicted using Young’s parametric hurricane wave prediction model. The input cyclone tracks for this work are obtained from Fleet Naval Meteorology and Oceanography Center, USA. Extreme value analysis is carried out to obtain the wave heights and periods for 1 in 5, 10, 50 and 100 years return periods, respectively. The deep-water hindcast wave corresponding to 100 years from probable directions are allowed to propagate to Visakhapatnam coastal waters using nearshore spectral wind-wave mode. The offshore wave height for one in 100-year return period is 11.9 m, and the corresponding nearshore wave height at 10-m water depth varies between 4.6 and 5.6 m depending on the directional spreading. Weibull distribution is chosen to fit the 24 cyclonic data sets over a total period of 30 years (September 1972 to November 2002). This paper demonstrates usefulness of Young’s wave model for deep-water extreme wave hindcasting. Further, the results of the present study would be highly useful for assessing the design wave height for Visakhapatnam coast.     

Contrasting fluid inclusion characteristics of staniferous and non-staniferous pegmatites of Southeast Bastar, Central India

Tin and rare metal-bearing granitic pegmatites in the Bastar–Malkangiri pegmatite belt of Central India are hosted by metabasic and metasedimentary country rocks. Fluid inclusion studies were conducted in spatially associated two-mica granite and the staniferous and non-staniferous pegmatites to characterize the physicochemical environment of mineralization, to distinguish different pegmatites in terms of their fluid characteristics and to envisage a possible genetic link between the pegmatites and spatially associated granite. Three different types of primary inclusions were identified. The type-I, aqueous bi-phase (L+V) inclusions are the most abundant and ubiquitous. Type-II polyphase (L+V+S) inclusions are rare. Type-III, monophase (L) and metastable aqueous inclusions, though less abundant than type-I inclusions, are ubiquitous. The fluid evolution trends indicate that mixing of two different fluids of contrasting salinities, one of high salinity (20–30 wt% NaCl equivalent) and another of low salinity (0–10 wt% NaCl equivalent), was responsible for precipitation of the bulk of the cassiterite. This mixing is the single most important characteristic that distinguishes the staniferous pegmatites from their non-staniferous counterparts. The non-staniferous pegmatites, on the other hand, are typified by the presence either of a high saline or a low saline fluid that evolved through simple cooling. The minimum pressure–temperature of entrapment, estimated from the intersections of the halide liquidus with the corresponding inclusion isochores of type-II inclusions, range between 2.1–2.2 kb and 300–325 °C. The similar P–T range of fluid entrapment of the staniferous and non-staniferous pegmatites indicates that they were possibly emplaced within a similar physical environment. Type-I inclusions from granite recorded only the high salinity fluid, the salinity of which compares well with that of the highly saline fluid component of type-I inclusions in the pegmatites. This is a possible indication of a genetic link between the pegmatites and spatially associated granite.