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111.
Stephen Edward Lewis Robert A. Henderson Gerald R. Dickens Graham A. Shields Simon Coxhell 《Mineralium Deposita》2010,45(6):599-620
A significant resource of vanadium and molybdenum exists near Julia Creek, Australia, where the middle Cretaceous organic-rich
Toolebuc Formation lies between 0 and 25 m of the surface. We present and discuss a comprehensive geochemical study of the
Toolebuc Formation and its enclosing stratigraphy near Julia Creek to understand this ore deposit. V and Mo contents in fresh
facies are strongly associated with total organic carbon (TOC) contents, but not with Al or CaCO3; this suggests that V and Mo were originally concentrated in the organic fraction. However, chemical extractions using H2O2 indicate that Mo was originally concentrated in pyrite. The data also suggest that V was mobilised from organic matter during
early diagenesis and became associated with clays as little V was extracted by H2O2 in the fresh samples. TOC contents in the Toolebuc Formation were removed during weathering, residually enriching trace metals
including V and Mo, and as a result, the TOC relationship with V and Mo disintegrates. With weathering, both V and Mo predominantly
became associated with iron oxide/hydroxide phases (and possibly other unidentified phases) as these elements in the weathered
facies were highly soluble in the sodium citrate–sodium dithionite digestion. Large shale-hosted V and Mo deposits such as
Julia Creek offer a potentially viable alternative to the currently mined magnetite-hosted deposits. A thorough understanding
of the formation and host mineral phases for V and Mo of these shale deposits, however, is critical to ensure that these valuable
metals can be feasibly extracted. 相似文献
112.
113.
J.Michael Moldowan Wolfgang K. Seifert Edward Arnold Jon Clardy 《Geochimica et cosmochimica acta》1984,48(8):1651-1661
Two C28H48-pentacyclic triterpanes were isolated from Monterey shale. X-ray crystallography of a crystal containing both compounds proved their structures as 17β,18α,21α(H)-28,30-bisnorhopane and 17β,18α,21β(H)-28,30-bisnorhopane. Several differences are found between 28,30-bisnorhopanes and the regular hopanes. Unlike the regular hopane epimers, for practical purposes the three epimeric 28,30-bisnorhopanes [17α,21β(H)-, 17β,21α(H)-, and 17β,21β(H)-]cannot be distinguished by their mass spectra. Special conditions are needed to separate them by gas chromatography. The diagenetically first-formed epimer is thought to be 17α,21β(H)- because it predominates in immature shales. The order of thermodynamic stability is 17β,2lα(H) < > 17α,21β(H) > 17β,21β(H), and all three epimers are present in petroleum. 25,28,30-Trisnorhopanes can be analyzed in similar fashion and are found to have similar thermodynamic characteristics. The percent of the ring D/E cis epimer of 28,30-bisnorhopane and/or 25,28,30-trisnorhopane is a useful maturation parameter similar to the 20S/20R sterane ratio. Evidence indicates 25-demethylation of 28,30-bisnorhopane to 25,28,30-trisnorhopane during advanced stages of biodegradation. Hence, percent ring cis 25,28,30-trisnorhopane has an application to maturation assessment in heavily biodegraded oils. 相似文献
114.
Jeremy C. Ely Chris D. Clark Richard C. A. Hindmarsh Anna L. C. Hughes Sarah L. Greenwood Sarah L. Bradley Edward Gasson Lauren Gregoire Niall Gandy Chris R. Stokes David Small 《第四纪科学杂志》2021,36(5):946-960
Palaeo-ice sheets are important analogues for understanding contemporary ice sheets, offering a record of ice sheet behaviour that spans millennia. There are two main approaches to reconstructing palaeo-ice sheets. Empirical reconstructions use the available glacial geological and chronological evidence to estimate ice sheet extent and dynamics but lack direct consideration of ice physics. In contrast, numerically modelled simulations implement ice physics, but often lack direct quantitative comparison with empirical evidence. Despite being long identified as a fruitful scientific endeavour, few ice sheet reconstructions attempt to reconcile the empirical and model-based approaches. To achieve this goal, model-data comparison procedures are required. Here, we compare three numerically modelled simulations of the former British–Irish Ice Sheet with the following lines of evidence: (a) position and shape of former margin positions, recorded by moraines; (b) former ice-flow direction and flow-switching, recorded by flowsets of subglacial bedforms; and (c) the timing of ice-free conditions, recorded by geochronological data. These model–data comparisons provide a useful framework for quantifying the degree of fit between numerical model simulations and empirical constraints. Such tools are vital for reconciling numerical modelling and empirical evidence, the combination of which will lead to more robust palaeo-ice sheet reconstructions with greater explicative and ultimately predictive power. 相似文献
115.
Acta Geotechnica - A constitutive model is developed to describe the stress–strain–time behavior for decomposing municipal solid waste (MSW) within a critical state soil mechanics... 相似文献
116.
Milatz Marius Hüsener Nicole Andò Edward Viggiani Gioacchino Grabe Jürgen 《Acta Geotechnica》2021,16(11):3573-3600
Acta Geotechnica - Gauging the mechanical effect of partial saturation in granular materials is experimentally challenging due to the very low suctions resulting from large pores. To this end, a... 相似文献
117.
Thomas A. Anderson Erick A. Bestland Lesja Soloninka Ilka Wallis Edward W. Banks Markus Pichler 《Hydrogeology Journal》2017,25(8):2435-2451
High and variable levels of salinity were investigated in an intermittent stream in a high-rainfall area (~800 mm/year) of the Mt. Lofty Ranges of South Australia. The groundwater system was found to have a local, upslope saline lens, referred to here as a groundwater salinity ‘hotspot’. Environmental tracer analyses (δ18O, δ2H, 87/86Sr, and major elements) of water from the intermittent stream, a nearby permanent stream, shallow and deep groundwater, and soil-water/runoff demonstrate seasonal groundwater input of very saline composition into the intermittent stream. This input results in large salinity increases of the stream water because the winter wet-season stream flow decreases during spring in this Mediterranean climate. Furthermore, strontium and water isotope analyses demonstrate: (1) the upslope-saline-groundwater zone (hotspot) mixes with the dominant groundwater system, (2) the intermittent-stream water is a mixture of soil-water/runoff and the upslope saline groundwater, and (3) the upslope-saline-groundwater zone results from the flushing of unsaturated-zone salts from the thick clayey regolith and soil which overlie the metamorphosed shale bedrock. The preferred theory on the origin of the upslope-saline-groundwater hotspot is land clearing of native deep-rooted woodland, followed by flushing of accumulated salts from the unsaturated zone due to increased recharge. This cause of elevated groundwater and surface-water salinity, if correct, could be widespread in Mt. Lofty Ranges areas, as well as other climatically and geologically similar areas with comparable hydrogeologic conditions. 相似文献
118.
Andreas?LüttgeEmail author Edward?W.?Bolton Danny?M.?Rye 《Contributions to Mineralogy and Petrology》2004,146(5):546-565
We use a kinetic model of a metamorphic system to study the effect of competing rates of reaction, fluid injection, and heating on the evolution of the reaction pathway in temperature/composition space at constant pressure. We show that for rocks in contact with mixed volatile (e.g., CO2-H2O) fluids the reaction path may be quite different from what is expected from equilibrium-based petrologic models. Equilibrium-based models, used to understand the development of rock systems undergoing mineral reactions during a metamorphic event, rely on the Gibbs phase rule and only consider stable phases. For constant pressure, the temperature-composition paths follow univariant curves and significant reactions may occur at invariant points. By contrast, the more general kinetic treatment is not constrained by equilibrium, although with the proper competing rates equilibrium is a possible endmember of the kinetic approach. The deviation from equilibrium depends on the competing rates of reaction, heating, and fluid injection. A key element required by the kinetic approach is the inclusion of metastable reactions in the formulation, whereas such reactions are irrelevant for equilibrium-based models. Metastable reactions are often involved in a complex interplay with common prograde stable metamorphic reactions. We present model results for the well-studied CaO-MgO-SiO2-CO2-H2O (CMS) system to show how the system evolves under kinetic control. Our simulations and discussion focus on the behavior of the CMS system under a number of closed and open system conditions. Special attention is paid to closed system behavior in the vicinity of the (first) isobaric invariant point (with Dol, Qtz, Tlc, Cal, and Tr). Also, for open systems with massive fluid infiltration we consider heating rates varying from contact to regional metamorphic conditions. For some geologically reasonable rates of reactions, heating, and fluid injection, our results demonstrate that equilibrium conditions may be significantly overstepped in metamorphic systems. We used overall mineral reactions in this model with rates based on experimental results. Future models could rely on more fundamental dissolution and precipitation reactions. Such an extension would require additional kinetic rate data, as well as mineral solubilities in mixed volatile fluids.Editorial responsibility: J. Hoefs 相似文献
119.
Melt density and the average composition of basalt 总被引:9,自引:0,他引:9
Densities of residual liquids produced by low pressure fractionation of olivine-rich melts pass through a minimum when pyroxene and plagioclase joint the crystallization sequence. The observation that erupted basalt compositions cluster around the degree of fractionation from picritic liquids corresponding to the density minimum in the liquid line of descent may thus suggest that the earth's crust imposes a density filter on the liquids that pass through it, favoring the eruption of the light liquids at the density minimum over the eruption of denser more fractionated and less fractionated liquids. 相似文献
120.
Migmatites from Cone Peak, California, USA and the Satnur-Sangam road, Southern Karnataka, India contain coarser grained orthopyroxene-bearing leucosomes with subordinate biotite in finer grained hornblende-biotite-pyroxene-bearing hosts. At both localities the leucosomes are enriched in quartz and feldspar and have a higher ratio of pyroxene to hornblende + biotite compared to the host rocks. Biotite grains in leucosomes along the Satnur-Sangam road are concentrated at the margins of orthopyroxene grains and have lower abundances of Ti, Fe, and Cl and a higher abundance of F than biotite grains from the host rock. Fluorapatite grains in all rocks from both localities contain monazite inclusions similar to those produced experimentally by metasomatically induced dissolution and reprecipitation. Some fluorapatite grains at both localities are partially rimmed by allanite. The only compositional differences found between fluorapatite grains in the leucosomes and host rocks were higher concentrations of Cl in grains in leucosomes from Cone Peak. The mineralogies of the rocks suggest that the leucosomes formed by dehydration melting reactions that consumed feldspar, quartz, hornblende, and biotite and produced orthopyroxene. Allanite rims at the margins of fluorapatite grains may have formed by the later retrogression of monazite rims formed by incongruent dissolution of fluorapatite in the melt. Biotite grains at the margins of orthopyroxene crystals in the leucosomes from the Satnur-Sangam road apparently formed by retrogression of orthopyroxene upon the solidification of the anatectic melt. A similar high-grade retrogression did not affect orthopyroxene crystals at Cone Peak, indicating that H2O was removed from the crystallizing leucosomes probably in a low H2O activity fluid. Compositional differences between the paleosome and neosomes at Cone Peak are best explained by metasomatic interaction with concentrated brines while elevated Cl concentrations in fluorapatites in the leucosome suggest interaction with a Cl-bearing fluid. Brines may have been responsible for an exchange of elements between the host rock along the Satnur-Sangam road and zones of melt generation now marked by leucosomes, but fluid flow appears to have been less vigorous than at Cone Peak. 相似文献