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81.
82.
In this study, single crystals of pure enstatite (Mg2Si2O6) were synthesised under water-saturated conditions at 4 and 8 GPa and 1,150°C with variable silica activity, leading to phase assemblages enstatite + forsterite, enstatite or enstatite + coesite. Run products were investigated using an FTIR spectrometer equipped with a focal plane array detector enabling IR imaging with a lateral pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show two different groups of absorption bands: group 1 (wavenumbers at 3,592 and 3,687 cm?1) shows strongest absorptions for E||n β, whereas group 2 (wavenumbers at 3,067 and 3,362 cm?1) shows strongest absorptions for E||n γ. The groups are related to different defect types, group 1 to tetrahedral defects (T-site vacancies) and group 2 to octahedral defects (M-site vacancies). The intensity ratio of the bands within one group (i.e. A 3067/A 3362 and A 3592/A 3687) and the intensity ratio of E||n γ and E||n α in group 2 bands remain constant within error. In contrast, the intensity ratio of group 2 to group 1 absorption bands [e.g. (A 3362)/(A 3687)] is sensitive to the SiO2 activity and pressure. On the basis of the results of this and previous studies, a barometer for pure orthoenstatite coexisting with forsterite can be formulated:\( P\,[{\text{GPa}}] = 1.056 + \sqrt {{\frac{{1.025 - A_{{\left( {3362} \right)/\left[ {(3362) + (3687)} \right]}} }}{0.009}}} , \) where A (3362) and A (3687) are the integral absorbances of the component E||n γ of the absorption bands at 3,362 cm?1 and the component E||n β of the absorption band at 3,687 cm?1, respectively. 相似文献
83.
84.
Emma J. Pearson Steve Juggins Jan Weckström David B. Ryves Roland Schmidt 《Geochimica et cosmochimica acta》2011,75(20):6225-6238
Quantitative climate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Recent advances in molecular geochemistry have led to calibrations using glycerol dialkyl glycerol tetraethers (GDGTs), a group of temperature-sensitive membrane lipids found in Archaea and bacteria. GDGTs have been used to construct temperature indices for oceans (TEX86 index) and soils (MBT/CBT index). The aim of this study is to examine GDGT-temperature relationships and assess the potential of constructing a GDGT-based palaeo-thermometer for lakes. We examine GDGT-temperature relationships using core top sediments from 90 lakes across a north-south transect from the Scandinavian Arctic to Antarctica including sites from Finland, Sweden, Siberia, the UK, Austria, Turkey, Ethiopia, Uganda, Chile, South Georgia and the Antarctic Peninsula. We examine a suite of 15 GDGTs, including compounds used in the TEX86 and MBT/CBT indices and reflecting the broad range of GDGT inputs to small lake systems.GDGTs are present in varying proportions in all lakes examined. The TEX86 index is not applicable to our sites because of the large relative proportions of soil derived and methanogenic components. Similarly, the MBT/CBT index is also not applicable and predicts temperatures considerably lower than those measured. We examine relationships between individual GDGT compounds and temperature, pH, conductivity and water depth. Temperature accounts for a large and statistically independent fraction of variation in branched GDGT composition. We propose a GDGT-temperature regression model with high accuracy and precision (R2 = 0.88; RMSE = 2.0 °C; RMSEP = 2.1 °C) for use in lakes based on a subset of branched GDGT compounds and highlight the potential of this new method for reconstructing past temperatures using lake sediments. 相似文献
85.
Assessing potential repositories for geologic sequestration of carbon dioxide using numerical models can be complicated, costly,
and time-consuming, especially when faced with the challenge of selecting a repository from a multitude of potential repositories.
This paper presents a set of simple analytical equations (model), based on the work of previous researchers, that could be
used to evaluate the suitability of candidate repositories for subsurface sequestration of carbon dioxide. We considered the
injection of carbon dioxide at a constant rate into a confined saline aquifer via a fully perforated vertical injection well.
The validity of the analytical model was assessed via comparison with the TOUGH2 numerical model. The metrics used in comparing
the two models include (1) spatial variations in formation pressure and (2) vertically integrated brine saturation profile.
The analytical model and TOUGH2 show excellent agreement in their results when similar input conditions and assumptions are
applied in both. The analytical model neglects capillary pressure and the pressure dependence of fluid properties. However,
simulations in TOUGH2 indicate that little error is introduced by these simplifications. Sensitivity studies indicate that
the agreement between the analytical model and TOUGH2 depends strongly on (1) the residual brine saturation, (2) the difference
in density between carbon dioxide and resident brine (buoyancy), and (3) the relationship between relative permeability and
brine saturation. The results achieved suggest that the analytical model is valid when the relationship between relative permeability
and brine saturation is linear or quasi-linear and when the irreducible saturation of brine is zero or very small. 相似文献
86.
Inferring reservoir data from dynamic production data has long been done through matching the production history. However, proper integration of available production history has always been a challenge. Different production history data such as well pressure and water cut often occur at different scales making their joint inversion difficult. Furthermore, production data obtained from the same well or even the same reservoir are often correlated making a significant portion of the dataset redundant. Thirdly, the massiveness of the data recorded from wells in a large reservoir over a long period of time makes the nonlinear inversion of such data computational demanding. In this paper, we propose the integration of multiwell production data using wavelet transform. The method involves the use of a two-dimensional wavelet transformation of the data space in order to integrate multiple production data and reduce the correlation between multiwell data. Multiple datasets from different wells, representing different production responses (pressure, water cut, etc.), were treated as a single matrix of data rather than separate vectors that assume no correlation amongst datasets. This enabled us to transform the multiwell production data into a two-dimensional wavelet domain and subsequently select the most important wavelets for history match. By minimizing the square of the Frobenius norm of the residual matrix we were able to match the calculated response to the observed response. We derived the relationship that allows us to replace a conventional minimization of the sum of squares of the l 2 norms of multi-objective functions with the minimization of the square of the Frobenius norm of the integrated data. The usefulness of the approach is demonstrated using two examples. The approach proved very effective at reducing correlation between multiwell data. In addition, the method helped to reduce the cost of computing sensitivity coefficients. However, the method gave poor prediction of water cut when the datasets were not scaled before inverse modeling. 相似文献
87.
Reinaldo L. Bozelli Adriano Caliman Rafael D. Guariento Luciana S. Carneiro Jayme M. Santangelo Marcos P. Figueiredo-Barros Joo J.F. Leal Adriana M. Rocha Letícia B. Quesado Paloma M. Lopes Vinicius F. Farjalla Claudio C. Marinho Fabio Roland Francisco A. Esteves 《Limnologica》2009,39(4):306-313
Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll-a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers. 相似文献
88.
James K. Sheppard Alex B. Carter Len J. McKenzie C. Roland Pitcher Robert G. Coles 《Continental Shelf Research》2008
The distribution and nutritional profiles of sub-tidal seagrasses from the Torres Strait were surveyed and mapped across an area of 31,000 km2. Benthic sediment composition, water depth, seagrass species type and nutrients were sampled at 168 points selected in a stratified representative pattern. Eleven species of seagrass were present at 56 (33.3%) of the sample points. Halophila spinulosa, Halophila ovalis, Cymodocea serrulata and Syringodium isoetifolium were the most common species and these were nutrient profiled. Sub-tidal seagrass distribution (and associated seagrass nutrient concentrations) was generally confined to northern-central and south-western regions of the survey area (<longitude 142.60), where mean water depth was relatively shallow (approximately 13 m below MSL) and where sediments were comprised primarily muddy sand to gravelly sand. Seagrass nitrogen and starch content, the most important nutrients for marine herbivores, were significantly correlated with species and with the plant component (above or below ground). For all seagrass species, the above-ground component (shoots and leaves) possessed greater nitrogen concentrations than the below-ground component (roots and rhizomes), which possessed greater starch concentrations. S. isoetifolium had the highest total nitrogen concentrations (1.40±0.05% DW). However, it also had higher fibre concentrations (38.2±0.68% DW) relative to the other four species. H. ovalis possessed the highest starch concentrations (2.76±0.12% DW) and highest digestibility (83.24±0.66% DW) as well as the lowest fibre (27.2±0.66% DW). The high relative abundance (found at 55% of the sites that had seagrass) and nutrient quality characteristics of H. ovalis make it an important source of energy to marine herbivores that forage sub-tidally in the Torres Strait. There were two regions in Torres Strait (north-central and south-western) where sub-tidal seagrass meadows were prevalent and of relatively higher nutritional value. This spatial and nutritional information can be used by local agencies to manage and to protect the ecological, economic and cultural values of the sub-tidal seagrass ecosystems and associated fisheries of the Torres Strait. 相似文献
89.
Multistage Variscan magmatism in the central Tauern Window (Austria) unveiled by U/Pb SHRIMP zircon data 总被引:2,自引:0,他引:2
Roland Eichhorn Georg Loth Rudolf Höll Fritz Finger Andreas Schermaier Allen Kennedy 《Contributions to Mineralogy and Petrology》2000,139(4):418-435
U/Pb SHRIMP ages of nine Variscan leucocratic orthogneisses from the central Tauern Window (Austria) reveal three distinct pulses of magmatism in Early Carboniferous (Visean), Late Carboniferous (Stephanian) and Early Permian, each involving granitoid intrusions and a contemporaneous opening of volcano-sedimentary basins. A similar relationship has been reported for the Carboniferous parts of the basement of the Alps further to the west, e.g. the “External massifs” in Switzerland. After the intrusion of subduction-related, volcanic-arc granitoids (374?±?10?Ma; Zwölferkogel gneiss), collisional intrusive-granitic, anatectic and extrusive-rhyolitic/dacitic rocks were produced over a short interval at ca. 340?Ma (Augengneiss of Felbertauern: 340?±?4?Ma, Hochweißenfeld gneiss: 342?± 5?Ma, Falkenbachlappen gneiss: 343?±?6?Ma). This Early Carboniferous magmatism, which produced relatively small volumes of melt, can be attributed to the amalgamation of the Gondwana-derived “Tauern Window” terrane with Laurussia–Avalonia. Probably due to the oblique nature of the collision, transtensional phenomena (i.e. volcano-sedimentary troughs and high-level intrusives) and transpressional regimes (i.e. regional metamorphism and stacked nappes with anatexis next to thrust planes) evolved contemporaneously. The magmas are mainly of the high-K I-type and may have been generated during a short phase of decompressional melting of lithospheric mantle and lower crustal sources. In the Late Carboniferous, a second pulse of magmatism occurred, producing batholiths of calc-alkaline I-type granitoids (e.g. Venediger tonalite: 296?±?4?Ma) and minor coeval bodies of felsic and intermediate volcanics (Heuschartenkopf gneiss: 299?±?4?Ma, Peitingalm gneiss: 300?±?5?Ma). Prior to this magmatism, several kilometres of upper crust must have been eroded, because volcano-sedimentary sequences hosting the Heu- schartenkopf and Peitingalm gneisses rest unconformably on 340-Ma-old granitoids. The youngest (Permian) period of magma generation contains the intrusion of the S-type Granatspitz Central Gneiss at 271?±?4?Ma and the extrusion of the rhyolitic Schönbachwald gneiss protolith at 279?±?9?Ma. These magmatic rocks may have been associated with local extension along continental wrench zones through the Variscan orogenic crust or with a Permian rifting event. The Permian and the above-mentioned Late Carboniferous volcano-sedimentary sequences were probably deposited in intra-continental graben structures, which survived post-Variscan uplift and Alpine compressional tectonics. 相似文献
90.
Hgbomite, a rare exotic mineral, is found to be associated with the vanadiferous–titaniferous(V-Ti) bearing magnetite bands at Bhakatarhalli, Nuggihalli greenstone belt, western Dharwar Craton, India. We report on a second occurrence of hgbomite from the Dharwar craton in Karnataka, which is the sixth documented occurrence of this mineral from India. We evaluate the chemical characteristics of hgbomite and associated Fe-Ti-minerals in an attempt to identify its formation as a primary hydrothermal mineral in a metamorphosed magnetite layer.We report here the presence of hgbomite as a complex oxide of Fe, Mg, Al and Ti with accessory of Zn, V and Sn. Petrographic studies suggest the(V–Ti) bearing magnetite(Mt) contain spinel, hgbomite, chlorite, martite, ilmenite(Il) and minor amounts of diaspore. The hgbomite displays euhedral to subhedral textures, and is up to 250 μm along the grain boundaries of magnetite and ilmenite. In the samples studied, hgbomite is prismatic, irregular and elongated in shape. The genesis of hgbomite in veins between magnetite and ilmenite implies its precipitation from fluids without involving complicated reactions. Several models were proposed for the formation of hgbomite; however, the subject is still debatable. 相似文献