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881.
882.
Carlos Alberto Spier Sonia Maria Barros de Oliveira Carlos Alberto Rosière José Domingos Ardisson 《Mineralium Deposita》2008,43(2):229-254
Several major iron deposits occur in the Quadrilátero Ferrífero (QF), southeastern region of Brazil, where metamorphosed and heterogeneously deformed banded iron formation (BIF) of the Cauê Formation, regionally called itabirite, was transformed into high- (Fe >64%) and low-grade (30%?2O3, with a higher amount of detrimental impurities, especially MnO, in the soft ore. Both hard and soft ores are depleted in trace elements. The high-grade ores at the Águas Claras Mine have at least a dual origin, involving hypogene and supergene processes. The occurrence of the hard, massive high-grade ore within “fresh” dolomitic itabirite is evidence of its hypogene origin. Despite the contention about the origin of the dolomitic itabirite (if this rock is a carbonate-rich facies of the Cauê Formation or a hematite–carbonate precursor of the soft high-grade ore), mineralogical and geochemical features of the soft high-grade ore indicate that it was formed by leaching of dolomite from the dolomitic itabirite by meteoric water. The comparison of the Águas Claras, Capão Xavier and Tamanduá orebodies shows that the original composition of the itabiritic protore plays a major role in the genesis of high- and low-grade soft ores in the QF. Under the same weathering and structural conditions, the dolomitic itabirite is the more favorable to form high-grade deposits than siliceous itabirite. Field relations at the Águas Claras and Capão Xavier deposits suggest that it is not possible to form huge soft high-grade supergene deposits from siliceous itabirite, unless another control, such as impermeable barriers, had played an important role. The occurrence in the Tamanduá Mine of a large, soft, high-grade orebody formed from siliceous itabirite and closely associated with hypogene hard ore suggests that large, soft, high-grade orebodies of the Quadrilátero Ferrífero, which occur within siliceous itabirite, have a hypogene contribution in their formation. 相似文献
883.
Franco Gianotti Maria Gabriella Forno Susan Ivy-Ochs Peter W. Kubik 《Quaternary International》2008,190(1):123
The Ivrea amphitheatre (IA) in NW Italy has been studied since 1850, on pedostratigraphic and morphological bases. Three stratigraphic groups of glacial sediments were distinguished. Newly recognized stratigraphic boundaries are based on interstadial/interglacial units, palaeosols and lacustrine organic layers interbedded with glacigenic deposits, and on pedostratigraphy. Mapping of morphological features and associated marginal and sub-glacial deposit facies was used to characterize and reconstruct glacial margin fluctuations. Based on the field evidence, the stratigraphical limits recognized at single sites can be interpolated over the whole amphitheatre. Ten stratigraphic units (referred to as alloformations: Afs) were distinguished and mapped. They are related to at least as many glacial episodes ranging in age from the end of the Early Pleistocene to the Late Pleistocene. The youngest three glacial units (Serra Af, Piverone Af and Ivrea Af) and one interstadial level (Alice Superiore Unit between Serra and Piverone Afs) are discussed in detail. Based on biostratigraphical and pedological, as well as sedimentological and morphological data, the Serra Af can be attributed to MIS 6 and Piverone Af to MIS 4. The 10Be surface exposure ages from two boulders (27.9±3.1, 32.4±4.0 kyr) on the Serra d’Ivrea moraine provide only a minimum age for moraine construction. The alignment of typical ice marginal landforms (moraines and kame terraces) for the more recent unit (Ivrea Af) has allowed recognition of 12 principal stadials during the LGM and Lateglacial; 6 stadials in the amphitheatre and 6 stadials in Dora Baltea Valley, and reconstruction of the nature of the last glacial retreat from the amphitheatre to the cirques. 10Be exposure ages from three boulders related to Ivrea Af are 13.1±1.0, 17.4±2.6 and 20.8±1.5 ka. The latter two ages indicate that the Dora Baltea Glacier deposited the Ivrea Af in the IA during MIS 2. The 10Be exposure ages of 14.6±1.2 and 14.0±0.9 ka from a polished bedrock surface some 15 km upstream from the amphitheatre provide a minimum age for ice decay. 相似文献
884.
Luisa Stellato Emma Petrella Filippo Terrasi Paolo Belloni Maria Belli Umberto Sansone Fulvio Celico 《Hydrogeology Journal》2008,16(4):701-712
222Rn was used to assess river–groundwater interactions within Castel di Sangro alluvial aquifer (Italy). The effectiveness of results obtained through this indicator was verified by also analyzing δ18O, major ions and temperature in both surface and groundwater, and carrying out piezometric head monitoring and discharge measurements. Hydrogeological investigations suggested that the river infiltrates into the aquifer in the south-eastern aquifer portion, while groundwater discharges into the river in the north-eastern portion. The latter phenomenon is supported by 222Rn data. Nevertheless, flow-through conditions cause the modelled discharge along this river reach, estimated by 222Rn data in a degassing-corrected two-component mixing model, to be greater than the measured discharge. Concerning river infiltration into the aquifer, δ18O, major ions and temperature data show that the river contribution is negligible in terms of aquifer recharge. Thus, the observed increase in 222Rn concentration in that portion of the aquifer is due to the enrichment process caused by infiltration of rainwater (222Rn free) which flows from the local divide area. Hence, in the study site, the use of only 222Rn to predict river–groundwater interactions causes some estimation inaccuracies and it must be coupled with other hydrochemical and hydrogeological parameters to gain a thorough understanding of such interactions. 相似文献
885.
Miriam Baglioni Emiliano Giovannetti Maria Vittoria Masserotti Chiara Renso Laura Spinsanti 《Transactions in GIS》2008,12(Z1):31-44
Querying geographical information systems has been recognized as a difficult task for non‐expert users. Furthermore, user queries are often characterized by semantic aspects not directly managed by traditional spatial databases or GIS. Examples of such semantic geospatial queries are the use of implicit spatial relations between objects, or the reference of domain concepts not explicitly represented in data. To handle such queries, we envisage a system that translates natural language queries into spatial SQL statements on a database, thus improving standard GIS with new semantic capabilities. Within this general objective, the contribution of this article is to introduce a methodology to handle semantic geospatial queries issued over a spatial database. This approach captures semantics from an ontology built upon the spatial database and enriched by domain concepts and properties specifically defined to represent the localization of objects. Some examples of the use of the methodology in the urban domain are presented. 相似文献
886.
Covadonga Brime Maria Cristina Perri Monica Pondrelli Claudia Spalletta Corrado Venturini 《International Journal of Earth Sciences》2008,97(6):1213-1229
Thermal evolution of the Palaeozoic–Triassic sequences of the Carnic Alps has been characterized by b cell dimension and Kübler Index (illite “crystallinity”) of K-white micas (KI), árkai Index (AI) of chlorites, clay mineral
assemblages and conodont Colour Alteration Index (CAI). Data indicate at least two metamorphic events, Variscan and Alpine.
In the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas. It was
characterized by low-intermediate pressure facies. The thermal peak was mainly due to an extensional regime during the Bashkirian.
A younger thermal overprint generated by Alpine orogeny was of lower grade, reaching high diagenetic–anchizonal conditions
characterized by high-pressure facies. Inverted metamorphic patterns are associated with middle to late Miocene thrusting.
Hydrothermal alteration in the northern part of the region can be linked with emplacement of Oligocene plutons and high heat
flow along the Periadratic lineament.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
887.
Aschonitis Vassilis Diamantopoulou Maria Papamichail Dimitris 《Theoretical and Applied Climatology》2018,132(3-4):1165-1186
Theoretical and Applied Climatology - The aim of the study is to propose new modeling approaches for daily estimations of crop coefficient K c for flooded rice (Oryza sativa L., ssp. indica) under... 相似文献
888.
Telma Castro Oscar Peralta Dara Salcedo José Santos María I. Saavedra María L. Espinoza Alejandro Salcido Ana-Teresa Celada-Murillo Susana Carreón-Sierra Harry Álvarez-Ospina Giovanni Carabali Valter Barrera Sasha Madronich 《Journal of Atmospheric Chemistry》2018,75(2):155-169
During the MILAGRO campaign, March 2006, eight-stage cut impactors were used to sample atmospheric particles at Tecámac (T1 supersite), towards the northeast edge of the Mexico City Metropolitan Area, collecting fresh local emissions and aged pollutants produced in Mexico City. Particle samples were analyzed to determine total mass concentrations of Ca2+, Mg2+, NH4 +, K+, Cl?, SO4 2?, and NO3 ?. Average concentrations were 22.1 ± 7.2 μg m?3 for PM10 and 18.3 ± 6.2 μg m?3 for PM1.8. A good correlation between PM10 and PM1.8, without influence from wind patterns, indicates that local emissions are more important than the city’s pollution transported to the site, despite the fact that Tecámac is just 40 km away from Mexico City. A lack of diurnal patterns in the PM2.5/PM1.8 ratio supports this conclusion. The inorganic composition of particles suggests that vehicles, soil resuspension, and industries are the main pollutant sources. Finally, the particles were found to be neutralized, in agreement with observations in the Mexico City Metropolitan Area. 相似文献
889.
Michael Traut Alice Larkin Kevin Anderson Christophe McGlade Maria Sharmina Tristan Smith 《Climate Policy》2018,18(8):1066-1075
The Paris Agreement, which entered into force in 2016, sets the ambitious climate change mitigation goal of limiting the global temperature increase to below 2°C and ideally 1.5°C. This puts a severe constraint on the remaining global GHG emissions budget. While international shipping is also a contributor to anthropogenic GHG emissions, and CO2 in particular, it is not included in the Paris Agreement. This article discusses how a share of a global CO2 budget over the twenty-first century could be apportioned to international shipping, and, using a range of future trade scenarios, explores the requisite cuts to the CO2 intensity of shipping. The results demonstrate that, under a wide range of assumptions, existing short-term levers of efficiency must be urgently exploited to achieve mitigation commensurate with that required from the rest of the economy, with virtually full decarbonization of international shipping required as early as before mid-century.
Key policy insights
Regulatory action is key to ensuring the international shipping sector’s long-term sustainability.
For the shipping industry to deliver mitigation in line with the Paris Agreement, virtually full decarbonization needs to be achieved.
In the near term, immediate and rapid exploitation of available mitigation measures is of critical importance.
Any delay in the transition will increase the risk of stranded assets, or diminish the chances of meeting the Paris Agreement's temperature commitments.
890.