| 461. |
- Ketzer, João Marcelo
(författare)
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Diagenesis and Sequence Stratigraphy : an integrated approach to constrain evolution of reservoir quality in sandstones
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diagenesis and sequence stratigraphy have been formally treated as two separate disciplines in sedimentary petrology. This thesis demonstrates that synergy between these two subjects can be used to constrain evolution of reservoir quality in sandstones. Such integrated approach is possible because sequence stratigraphy provides useful information on parameters such as pore water chemistry, residence time of sediments under certain geochemistry conditions, and detrital composition, which ultimately control diagenesis of sandstones. Evidence from five case studies and from literature, enabled the development of a conceptual model for the spatial and temporal distribution of diagenetic alterations and related evolution of reservoir quality in sandstones deposited in paralic environments. Diagenetic alterations that have been constrained within the context of sequence stratigraphy include: (i) formation of kaolinite and intragranular porosity, and mechanical infiltration of clay minerals in sandstones lying at variable depths below sequence boundaries, (ii) formation of pseudomatrix and cementation by calcite, dolomite, and siderite in lag deposits at parasequence boundaries, (iii) cementation by kaolinite, pyrite, and calcite in sandstones lying in the vicinity of parasequence boundaries with coal deposits, (iv) formation of glaucony in condensed interval at parasequence boundaries, transgressive and maximum flooding surfaces, (v) formation of berthierine in fluvial-dominated deltaic deposits of the highstand systems tract, (vi) cementation by calcite in bioclastic sandstones of the transgressive systems tract, and (vii) formation of kaolinite in fluvial deposits of the lowstand systems tract. The distribution of such alterations put important constrains for the pattern of burial diagenesis (e.g., formation of chlorite, illite, quartz), related evolution of reservoir quality in sandstones, and distribution of baffles and barriers for fluid flow in the context of sequence stratigraphy.
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| 462. |
- Medvedev, Sergei
(författare)
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Thin sheet approximations for geodynamic applications
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin sheet approximations are widely used in geodynamics because of their potential for fast computing of 3D lithospheric deformations using simple numerical techniques. However, this simplicity imposes limits to boundary conditions, rheological settings and accuracy of results. The thesis argued here is that thin sheet approximations are powerful tools in geodynamic modelling and their current limitations are not necessary. To support this thesis the following theoretical investigations are provided:previous approximations are classified and their restrictions and advantages are discussed;scaling analysis of balance of forces is performed for application of an asymptotic technique based on the thickness/width ratio; two steps in the asymptotic analysis results in exact balance of forces integrated through the thickness of the thin sheet;the model is based on creep rheology although rheological variations are possible.Fundamental rebuilding of thin sheet approximation on the basis of higher order analysis expands the low order asymptotic background of previous approaches and results in the new Extended Thin Sheet Approximation (ETSA). This ETSA includes a set of 2D equations expressing the integrated balance of forces and rules for reconstruction of 3D stresses and velocities.The new approach retains the simplicity of numerical techniques requited for thin sheet approximations, while broadening their geodynamic applications because of the following points:special investigations found no limitations to possible boundary conditions;the unification behind ETSA allows significant rheological stratification in thin sheets;ETSA demonstrated it's potential by modelling the development of lithospheric instabilities in conditions that were not tractable to previous thin sheet approximations;comparisons with exact analytical solutions demonstrate high accuracy of ETSA.These conclusions are supported by examples of analytical investigations based on the ETSA and analyses of analogue models and field observations. The new computer code, SIMPLE, based on the ETSA, was designed using the simplest numerical techniques to model deformations in a lithosphere with strong rheological layering.
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| 463. |
- Nilsson, Patrik W.
(författare)
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The West Ny Friesland Terrane : An exhumed mid-crustal obliquely convergent orogen : by Patrik W. Nilsson
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ny Friesland, in northeastern Svalbard, is the type-area for transpressive orogeny. The West Ny Friesland Terrane (WNT) is composed of a c. 12 km thick basal succession of amphibolite-grade schists and gneisses, previously thought to be the lower of a c. 20 km thick succession of concordant, volcano-sedimentary strata. However, this lower succession is composed of at least five thrust intercalations, where four contain Palaeoproterozoic (c. 1750 Ma) basement gneisses and Mesoproterozoic (or younger) cover sequences. Concordance between the rock units is largely the result of ductile shearing and high Caledonian strain during thrusting. These thrust sheets were assembled sequentially during E-W orthogonal shortening ( minimum c. 80 km) and resulted in a c. 150 km long, N-S trending fold-and-thrust belt, the Atomfjella Antiform, in Ny Friesland, northeastern Spitsbergen. The geometry of this structure, with thinning of some units in the east, suggests that nappe transport was west-directed. Shortening was coupled with increasing grade of metamorphism, and changes in both vertical and lateral boundary conditions during increasing sinistral transpression. This resulted in ductile hinge-parallel elongation of the thrust-stack.Comparison of geochronological and structural data from Ny Friesland with data from the Nordauslandet Terrane (NAT) indicates that these eastern areas differ fundamentally. The Palaeoproterozoic granites in Ny Friesland have no counterparts in Nordaustlandet which is dominated by a Grenvillian-age tectonothermal history. The metamorphic grade is also lower in Nordaustlandet. The NAT Neoproterozoic and Early Palaeozoic strata show affinity with the successions of Central-East Greenland. The Ny Friesland Palaeoproterozoic gneisses are similar in age to the high-grade gneisses and metasediments in North-East Greenland, suggesting a close affinity with these areas. This thesis proposes that the WNT was the result of Caledonian transpressional deformation during collision between Baltica and Laurentia, and that tectonic escape had juxtaposed the WNT and NAT terranes north of Greenland by the end of the Silurian
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| 464. |
- Persson, Katarina Sofia, 1972-
(författare)
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Deformation zones in models and nature
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Field studies encounter several complicating factors not studied in the models. Examples are oblique convergence, heterogeneous materials and thermal softening by intruding magmas. Within the deeply eroded Svecokarelian orogeny, studies in eastern Bergslagen indicate strain accommodation of the N-S orogenic shortening by regional E-W folding and shear along the conjugate Singö Shear Zone and Ornö Banded Series. Rising temperature resulted in migmatites affecting the strain accommodation resulting in decoupling and rotation of folds along one of the deformation zones.Deformation zones developed in convergent orogens have been studied in both analogue models and in nature. These studies have focused on a number of important factors controlling strain accommodation during orogenesis. The models show that the shape of the leading edge of the indenting continent controls whether the initial suture remains active or if an effective indenter develops, the spacing and number of faults, the width of the orogen and the height of the mountains. All these characteristics depend on the rate and spatial distribution of erosion and sedimentation. Erosion decreases the importance of effective indenters and favors shearing on existing faults leading to steeper, longer lived shears bounding narrow orogens. If sediments load the margin (e.g. foreland), the thrusts propagate further outboard widening the orogen. The strain that is accommodated by compaction and shearing along deep décollement and conjugate imbricate shears is episodic in time. This work links episodes of increased rates of erosion and sedimentation to episodes of high uplift rates, i.e. the development of new imbricate thrusts or pop-up wedges.
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| 465. |
- Shebanova, Olga
(författare)
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The High-Pressure Study on the Fe - O System: Thermodynamics and Phase Transitions of Iron Ferrite (FeFe2O4)
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge about the stability of phases and their relationships in the Fe-O system at high pressures and temperatures is essential in implications of the multifarious states of iron oxides for models of the evolution of the Earth. In this respect, the iron ferrite magnetite (FeFe2O4) plays a significant role since it participates in the control of geochemistry of ferric iron, and hence oxygen fugacity in the Earth`s deep interior.High-pressure experiments on Fe3O4 were performed using the diamond anvil cell technique combined with the laser and electrical resistive heating. The approach based on the combination of the synchrotron x-ray diffraction with Raman spectroscopic measurements benefited from the complementarity of the two methods originating from the different sensitivity to a range of structural order. High-pressure transformation of magnetite to a dense polymorph of the CaTi2O4-type structure proceeds via an intermediate step of the decomposition into a mixture of oxides on a microscopic scale. The kinetic hindrance of the reaction of the decomposition effectively prevents a phase separation controlled by diffusion and restricts the formation of the daughter products to locally ordered structures in the strained lattice of magnetite.Thermodynamic analysis of the observed phase transformations along with published results on the elastic properties and pressure-induced transitions of iron oxides has led to the reassessment of the phase diagram of Fe3O4. The pressure - temperature field of its stability with respect to the breakdown to a mixture of oxides FeO and Fe2O3, and to the transition to a high-pressure form, has been accordingly modified.
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| 466. |
- Tutti, Faramarz
(författare)
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Experimental Study of some Potassium and Sodium Bearing Aluminosilicates at High Temperatures and High Pressures
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents the results of a high-temperature and high-pressure experimental study of some abundant aluminositicates, which are the main repositories for the two geochemically important elements, sodium and potassium, in the Earth's crust. Phase transitions of end member alkali feldspars and jadeite clinopyroxene are studied at high and ultrahigh pressures corresponding to the conditions between the transition zone and the deep Earth's lower mantle. Thermal expansion, dehydroxylation, and high-temperature structural behaviour of a hydrous phlogopite up to 1100 °C at 1 bar is also presented in this thesis. High-pressure and high-temperature experiments were carried out in externally- and internally-heated Mao-Bell type diamond anvil cells (DAC). Samples in DAC were heated externally at temperatures between 650 and 800 °C, using a resistive graphite heating system. For high-temperatures between 1200 and 2300 °C, a Nd: YAG laser beam was employed. Recovered samples from high pressures and high temperatures were studied by powder X-ray diffraction technique and synchrotron radiation. High- temperature measurements at 1 bar were performed by using a resistive platinum wire acting as a heater and sample holder under the X-ray radiation. The results of DAC experiments show that NaAlSiO4 calcium ferrite-type structure is the only high-pressure modification of albite and jadeite stable at pressures above 23 GPa up to at least 75 GPa in a wide range of temperatures. It is also found that KA1Si3O8 hollandite-type structure, the high-pressure form of orthoclase above 10 GPa, is a stable mineral at pressures up to at least 95 GPa. The new data, therefore, suggest that calcium ferrite- and hollandite-type structures might be the host for sodium and potassium, respectively, in a deep primitive chondritic lower mantle.
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| 467. |
- Isaksson, Simon, 1988
(författare)
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Towards Energy-Efficient Drinking Water Production using Biomimicry
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water is a prerequisite for life and we therefore need pure drinking water to survive. Yet there are more than half a billion people that do not have access to pure drinking water. Water treatment can be performed in many different ways, one of the most commonly used being filtration. As the climate is getting warmer and sources of fresh water are being increasingly contaminated, attention is shifted to the sea in the search for drinking water. Sea water does, however, need to be desalinated before it is usable as drinking water.Desalination is commonly conducted using the process of reverse osmosis (RO), where water is forced to penetrate water-selective barriers in filters. The main issues with reverse osmosis are that the pressure needed to drive the process against the osmotic pressure build-up is significant and that the diffusivity of water through the selectively permeable layer is relatively slow. The energy input needed to run a reverse osmosis process using saline sea water is therefore substantial and the process is mainly performed in large-scale desalination plants. A more energy-efficient solution is needed in order to produce drinking water in a more sustainable manner as well as on a smaller scale.Nature purifies water in a variety of ways such as large-scale water passage through sand and small-scale purification conducted by mussels. The aim of this thesis was to design a water filter using inspiration from nature. The model system of choice was the water transport across the cell membrane, which is present in both animals and plants. This water transport is conducted by transmembrane proteins called aquaporins, and the aim of this thesis was to incorporate aquaporins in a design that could potentially be used for water filtration purposes.This thesis proposes a design where aquaporins are supported by mesoporous silica in order to improve robustness. A straightforward assembly process was developed and the resulting design was evaluated using a range of characterization techniques. The results showed that the mesoporous substrate greatly facilitated the spontaneous rupture and bilayer formation from proteoliposomes. Furthermore, neutron reflectivity data provided evidence of protein–silica intercalation where aquaporins made use of the aqueous pore environment to host their extracellular domains. This behavior is thought to improve the robustness of the system. The proposed water filter design put forward in this thesis will hopefully prove useful in the production of drinking water in the future.
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| 468. |
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| 469. |
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| 470. |
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