The geology of the Suldal Sector, southwest Norway, comprises exposures from three orogenic periods; the Telemarkian, Sveconorwegian and Caledonian. Telemarkian (~1500 Ma) basement rocks are interpreted to be the oldest crust in the region; these are intruded by Sveconorwegian granitoid intrusions (~1070-930 Ma). Crystalline nappe units overlie the Mesoproterozoic basement, and from reconnaissance U-Pb dating and zircon hafnium isotopes, are believed to comprise slices of the Mesoproterozoic Norwegian continental margin. The Telemarkian basement comprises meta-plutonic/volcanic lithologies that represent the deformed upper crustal section of a continental arc - the Suldal Arc; U-Pb dating suggests this arc was active from ~1520 to 1475 Ma. Whole-rock geochemistry and hafnium and oxygen isotopes measured in zircon, suggest that arc magmatism recycled older continental crust (20-50% contribution) that had been mixed with mantle-derived material in the lower crust; the older crustal component comprised late-Palaeoproterozoic sedimentary material derived from the Fennoscandian continent. During the arc’s evolution, dehydration of mafic source magma induced by heat from magmatic underplating, and subsequent melting of dehydrated crust enhanced by asthenospheric upwelling, allowed for the intrusion of iron-enriched tholeiitic magmas. The Suldal arc and by extension, the Telemarkia terrane, represent the last stages of continental crust formation within a retreating accretionary orogen that was active since ~1.8 Ga. Based on whole-rock geochemistry, U-Pb, hafnium and oxygen isotopes in zircon, Sveconorwegian granite suites formed between 1.07 and 0.92 Ga, and are largely derived from ~1.5 Ga mafic lower crust with a limited contribution of juvenile mantle-derived material. The geodynamic setting of granitic magmatism evolved from supra-subduction, to overthickened crust, to thinned crust with possible lithospheric delamination. The varying geochemistry of the granite suites (I- to A-type) is controlled not by geodynamic setting, but dominantly by water content in the magma source. Sveconorwegian deformation in the Suldal Sector is bracketed between ~1069 and ~1047 Ma by intrusions of the Storlivatnet plutonic complex.

The Snake River Plain of north-western U.S.A. was the site of voluminous, bimodal, hotspot volcanism in the Miocene. Between c. 12.7-6 Ma silicic volcanism produced an association of deposits so different to typical Plinian and ignimbrite deposits elsewhere it has been termed Snake River (SR)-type. The Cassia Mountains of southern Idaho contain SR-type ignimbrites produced from complex and dynamic magmatic plumbing systems involving multiple magma chambers which gave rise to multiple compositional populations of clinopyroxene that mixed during eruption and were deposited together. The Cassia Mountain ignimbrites become progressively more mafic up-succession in terms of whole rock, glass, feldspar and clinopyroxene compositions, reflecting decreasing time available for fractional crystallisation, as supported by geochronology. Two Cassia Mountain ignimbrites are among three newly discovered ‘super-eruptions’ defined on the basis of phenocryst, glass and whole rock compositions; magnetic polarity; 40Ar/39Ar geochronology; oxygen isotopes; and field data. Erupted volumes range between 640 and 1200 km3, amongst the largest recorded. Intercalated within the Cassia Mountain succession is a newly discovered deposit representing the first recorded explosive, rhyolitic phreatomagmatic eruption from the central Snake River Plain. The fine-grained, non-welded deposit has similar whole rock, glass, oxygen isotope and magmatic temperature characteristics to the surrounding welded ignimbrites, so the unusual deposit facies are interpreted as representing interaction of rising rhyolitic magma with near-surface water. During SR-type volcanism, lavas and ignimbrites of similar chemistry were erupted within a short time. Water contents of melt inclusions were low in both ignimbrites and lavas, consistent with the anhydrous mineralogy and high inferred magmatic temperature. Volatile contents of the magmas (as recorded by the melt inclusions) did not control eruptive style. The intense rheomorphism which characterises SR-type ignimbrites appears to be due to high emplacement temperatures rather than enhanced halogen contents.

Petrophysics traditionally uses Archie’s equation to estimate the amount of hydrocarbons initially in place. This relies on the increase in resistivity when non-conductive hydrocarbons replace conductive saline fluids in the pore space. However, if clay minerals are present in sufficient abundance, they can lower the resistivity to such an extent as to compensate for the increase in resistivity caused by the presence of hydrocarbons. The study reservoir (A), of the Berkine Basin, Algeria, is an example of this “low resistivity contrast”. No discernable change in the resistivity between the water-bearing and the hydrocarbon-bearing sections of the sandstone reservoir results in a continuous overestimation of the water saturation. Chlorite is a known cause of “low resistivity contrast” and is prevalent throughout the study reservoir sandstones. The low cation exchange capacity of chlorites means known shaly-sand models do not apply. Therefore it is necessary to develop an alternative method for estimating saturation in the study reservoir. To understand where the resistivity may be most affected the distribution of the chlorite within the reservoir must be determined. Detailed analysis of the sedimentary data identified a link between the chlorite-rich sandstones and the upper shoreface depositional environment. Discriminant statistical analysis of the log data was successful in identifying the upper shoreface, chloritic sandstones from the lower shoreface sandstones and offshore mudstones. This provided a classification scheme to identify the chlorite-rich intervals from log data in uncored wells. Analysis of capillary pressure curves, with respect to the depositional environments, identified a strong correlation between the chlorite occurrence and core-based petrophysical characteristics. This allowed for Leverett-J saturation height functions to be developed for the upper shoreface, chlorite-rich sandstones and lower shoreface sandstones. Transformation of these Leverett-J functions to the wireline log scale allowed saturation estimations to be calculated that account for the chlorite presence and don’t require the resistivity measurement.

No description available.

No description available.

Fracture in rock is a major factor that affects the rock's physical properties and it also provides the route for the passage of fluids that can transport potentially hazardous substances and hydrothermal fluids. Assessment of the degree of fracture in rocks is important as they play an essential role in many geomechanical issues (stability of boreholes, stimulation of oil and geothermal reservoirs, the design of civil structures, tunnels and hazardous waste disposals), and in understanding a number of processes in the Earth's crust such as magmatic intrusions, plate tectonics, fault mechanics and sedimentary basins. The fundamental understanding of how seismic waves are altered when they pass through fractured rock are currently poorly understood, hence a comprehensive study is timely. An improved understanding of how fractures affect the physical properties (such as seismic velocity and attenuation) would significantly enhance our ability to predict the fracture state of rock at depth remotely. The main focus of this thesis is to characterize P and S wave velocity, their ratio, shear wave splitting and attenuation and their dependence on the fracture density of the rock. Laboratory experiments were carried out in uniaxial compressive condition to increase microfracture density and hydrostatic confining condition to close microfractures. Experiments were performed on a single rock type (Westerly granite) to keep the mineralogy, chemical composition, and grain size constant. The condition of the microfractures was dry to remove the complexity of saturation and fluid type. Through transmission technique was used to measure P and S wave velocities and spectral ratio technique was used to measure attenuation. P and S wave velocities were measured at 1.5MHz. Attenuation measurements were made in the frequency range of O.8MHz to 1.7MHz. Elastic properties can be measured statically where strain data are recorded and related to stress during slow loading of a specimen, or dynamically, where the elasticity can be calculated from the velocity of P and S waves. In order to understand the elastic properties of the crust at depth using seismology, the relationship between the static and dynamic properties must be known. Increasing-amplitude, uniaxial cyclic loading experiments were carried out to investigate and quantify the effect of microcracking on the elastic properties, and to establish a relationship between static and dynamic measurements. There is a linear relationship between static and dynamic Young's moduli, and a significant discrepancy between the static and dynamic Poisson's ratio. We attribute the differences in the static and dynamic elastic properties to the size distribution of the crack population relative to the amplitude and frequency of the applied stress, frictional sliding on closed cracks during loading/unloading, and the assumption of isotropic elasticity in the sample. Strong stress-dependency exists in the uniaxial compressive and hydrostatic confining conditions due to closure of microcracks. This resulted in: an increase in the P and S wave velocities, their ratio, static and dynamic Young's modulus, and static and dynamic Poisson's ratio; and a decrease in the P and S wave attenuation. The increase of fracture density caused: a decrease in the P and S wave velocities and static and dynamic Young's modulus; a small increase in the dynamic Poisson's ratio and VpNs; and a large increase in the static Poisson's ratio, and P and S wave attenuation. Seismic wave attenuation is more sensitive than seismic wave velocity to closure of microcracks and Increase of microfracture density. The effect of varying crack density on the P and S wave velocities and elastic properties under confining pressure (depth) were quantified. The elastic wave velocities and Young's modulus of samples that have a greater amount of microcrack damage required higher confining pressure to be equal to those of samples with no induced microcrack damage. We found that fractures are completely closed at ~5km (~130MPa) in crystalline rocks. At shallow depth (less than 5km), fracture density affects seismic wave velocities. We observed an overall 6% and 4% reduction in P and S wave velocities respectively due to an increase in the fracture density. The overall reduction in the P and S wave decreased to 2% and 1 % at ~2km. Consequently, assessing the degree of fracture between 2km and 5km using seismic wave velocities may be difficult

Shales are highly anisotropic in their mechanical behaviour. The strength of anisotropic shales depends not only on the magnitude of the principal stresses, but also on the bedding plane orientations relative to the principal stresses. In this study, the failure of shales are investigated using triaxial compression and extension tests, while the role of intermediate stress (sigma2) on the strength of anisotropic shale is evaluated using data from new triaxial extension tests, as well as data from the literature. Triaxial compression and extension experiments were made on two organic-rich shales, at different confining stresses and bedding angles (Beta). Examination of post-failure computed tomography (CT) and thin section images for high strength anisotropy shale show that, for large and small values of Beta, the fracture plane follows the angle that is predicted by the Coulomb’s failure criterion for an isotropic material. In the range of angles of roughly 35deg.<Beta<75deg, failure occurs along the bedding plane. Both of these results are consistent with the assumptions of Jaeger’s plane of weakness (JPW) model. However, there exists a transition regime of loading angles lying between about 10deg. and 35deg., wherein the failure surface follows an irregular path that may jump between the bedding plane and the plane defined by the Coulomb criterion. In this regime, the strength of the rock is lower than the strength predicted by JPW model. For the shale with low strength anisotropy, the failure plane angles agree with the predictions of JPW model. The triaxial compression experimental data on shales and several data sets from the literature were fit with both Pariseau’s continuum model for the failure of transversely isotropic materials and JPW model. Comparison of both models show that the Pariseau model provided a better fit for ten of the twelve rocks, whereas the JPW model provided a better fit only for two low strength anisotropy shales. It was noted that all the rocks with a strength anisotropy ratio (SAR) > 2 were fit more closely by the Pariseau model, whereas both shales that were a better fit with the JPW model had SAR < 2. Pariseau’s model is also more robust and accurate than Jaeger’s model when using a reduced numbers of data (i.e., data collected at fewer confining stresses and/or fewer angles). Finally, both the JPW model and Pariseau’s model was applied in the true-triaxial stress regime, in which sigma1 > sigma2 > sigma3. When analysed with Mogi’s experimental data on Chichibu Schist, both models could predict failure under true-triaxial stress conditions. Mogi’s data and the triaxial extension experiments for the two shales shows that an increase in the intermediate stress sigma2 increases the intact rock strength, whereas weak plane failure depends not only on intermediate stress sigma2, but also on bedding plane angle Beta and foliation direction (omega).

No description available.

No description available.

This study deals with the changes in mineralogy and fabric of a suite of mudrocks due to increased induration caused by diagenetic history, and the subsequent controls on geotechnical properties. Burial diagenesis of mudrocks has important implications on their engineering behaviour, in particular the liberation of Si and Ca during illitisation of smectite and mixed layer clay minerals leading to cementation. The objective of the research has been to provide a means of predicting engineering performance of mudrocks from mineralogical composition. A suite of 41 mudrock samples ranging from Cambrian slates to Carboniferous Coal Measures in age and variable diagenetic rank has been sampled and tested. A detailed mineralogical evaluation of the samples was conducted and it was found that the proportion of mixed layer clays and kaolinite decreased with an increase in diagenetic rank of the material, but not necessarily with increasing ages of the samples. The diagenetic histories of the samples was assessed using illite 'crystalinity' and vitrinite reflectance measurement, which indicated that the samples ranged low diagenetic to epizonal in rank. The textures of the samples was studied using back-scattered scanning electron microscope imagery. The novel application of this technique to textural analysis in the field of engineering geology resulted in the diagenetic rank parameter classification scheme being devised. The classification parameter consists of a systematic approach to the evaluation of pore and microfracture distribution, clay mineral orientation and degree of recrystallization, degree of contact of clastic mineral constituent and the degree of cementation. The physical properties of the mudrocks were assessed in terms of bulk index properties, swelling, slaking and strength. In evaluating the test data, it was found that that the principal controls on the durability of indurated mudrocks was the distribution of micro fractures and the mixed layer clay content. With increasing diagenetic rank measured by illite 'crystallinity' determination, the durability of the samples increased due to the development of a more mature rock fabric as seen by the use of back-scatter scanning electron microscope imagery. With increasing diagenetic rank there is a decrease in microfracture distribution due to recrystallization of clay mineral species and subsequent recementation of the sample also due to release of Ca and Si from the conversion of clay mineral species. This process reduces void space, eliminates micro fractures and creates a non expansive clay mineral suite resulting in a durable mudrock less susceptable to swelling and slaking effects. An additional controlling factor on mudrock durability was found to be the presence of calcareous and organic carbon cements. These controls were found to be short term, as seen in natural weathering experiments, where samples of high calcareous and carbonate contents were found to start slaking after a period of 6 to 8 months of exposure, and samples of low carbonate and calcareous content began to degenerate almost instantaneously. The controls of cementation on the durability of mudrocks are eventually broken down due to the effects of air breakage in voids and swelling stress resulting from the expansive clay mineral species present. A range of simple index tests were used to physically characterise the mudrock samples and their potential in determining mudrock durability was evaluated. A mudrock rank durability classification approach is presented which is based on the modified jar slake test, methylene blue adsorption and moisture absorption determination. These index tests were found to correlate strongly with void and microfracture distributions and proportions of mixed layer clays within the samples. This classification approach was tested on the samples in the study and found to be effective in distinguishing between non-durable, moderately durable, and durable mud rocks.