Mudstones are of considerable scientific and economic importance as they are the dominant sedimentary rock type, forming the main repository of Earth history and having significance to numerous aspects of petroleum exploration and production, and many other industries. This study investigated the sedimentological characteristics of 150 diverse mudstone samples. The novel integration of grain size analysis combined with petrographic observations lead to a framework in which six mudstone grain size distribution (GSD) types are defined. The grain size types proposed are remarkably consistent in their form and characteristics and can be understood in terms of well constrained physical processes of deposition. The basis for this definition reflects largely the relative contributions of a flocculated, clay-rich component and an unflocculated silt/sand-rich grain size component. Integration of grain size data, pore size data and petrographic observations suggests a critical division between: (a) flocdominated mudrocks whose structure is supported by the clay matrix; and (b) silt-rich mudrocks whose structure is supported by a silt/fine sand framework. Floc-dominated mudrocks with clay matrix support develop low permeabilities and become very good capillary seals at relatively shallow depths. In contrast, silt-rich mudrocks with framework support only become low permeability units and very good capillary seals at much greater levels of compaction. The framework proposed here can form the basis of predictive flow and seal capacity models for mudrocks. A combined PCAcluster analysis approach to the grain size based classification of mudstones showed that of the six types defined in Chapter 2, types 1 — 4 (floc — silt mixtures) were consistently partitioned from types 5 — 6 (silt or sand rich mixtures). An attempt was made to quantify the distribution of key pore parameters, such as mean pore size, by grouping the data to reflect the matrix (grain size types 1 — 4) and framework (grain size types 5 — 6) support regimes and dividing into 5% porosity bins. The statistical distribution of pore network properties could not be verified, principally due to a combination of sparse sample numbers and highly variable nature of this data. This work illustrates that variability in mudstone pore size distributions is not constrained solely by lithology (support regime) and porosity, and thus that other factors must be taken into account if their evolution during compaction is to be understood.

For this study, spatial and size distributions of normal faults and associated tensile fractures were directly measured in deformed sedimentary rocks in three extensional regions: Kimmeridge Bay and Kilve in the UK and the Maltese Islands. The collected data allow i) quantifcation of regional extension at different scales, ii) determination of the relative importance of large and small structures, iii) quan- tifcation of the spatial heterogeneity of brittle extension, iv) comparison of scaling laws for veins and faults belonging to the same extension event, and v) analysis of the evolution of brittle damage in space and time. Multiple scan-lines of different length and resolution were collected in each study area to record the entire extension-related deformation. In order to quantify the heterogeneity of fracture and strain distributions, a new method of spatial analysis has been developed. The method is based on a non-parametric comparison of the cumulative frequency and extension with that for a uniform distribution and pro- vides a measure of heterogeneity based on both the position and the displacement of individual fractures sampled along a linear traverse. Seismically observable extension is found to scale with total extension in the three study areas, obeying a power-law relationship. The proportion of the total extension that is resolved in seismic refl ection data systematically increases with increasing strain. This means that seismic data signifcantly underestimate the total extension at low strains but record most of the total extension in higher strain regions. Heterogeneity analysis carried out for the three study areas shows that i) hetero- geneities of the distributions of fractures and strain in an area can differ signifcantly, ii) heterogeneities are strongly dependent on lithology and mechanical heterogeneity, and iii) heterogeneities evolve with increasing strain. At Kimmeridge Bay, both veins and faults display power-law scaling, but do not form part of the same distribution. Veins and faults along the Kilve-Lilstock section conform to a single power-law distribution. At the Maltese Islands fault-frequencies conform to power-law scaling, but yield a higher scaling exponent in lower-strain zones than in higher-strain (damage) zones. The platform carbonates at the Maltese Islands take up early extension by randomly distributed small-scale faulting. The layered and mudstone-rich rocks around Kim- meridge Bay respond to low strain by distributed ("ductile") deformation in the shales and by randomly distributed or anti-clustered veining in the stiffer carbonate beds. In inter-bedded carbonates and shales along the Kilve-Lilstock section, early extension is highly localised in narrow zones of faults and associated damage, pre- serving large portions of virtually unfractured rock in between. A tensor method has been developed which permits three-dimensional strain analy- sis from line-data. The results of this analysis show that one-dimensional estimates of extension generally are good approximations of the maximum principal strain and that deformation in most sampled sections conforms to pure-shear, plane-strain conditions. Fold-structures associated with normal faults are explained as due to superimposed "normal drag" within the process zone and slip-related "reverse drag" within the damage zone of a (propagating) normal fault.

Quantifying soil characteristics using state of the art equipments is a necessary step in introducing comprehensive constitutive models which can be used in engineering design. Large areas of the Southern UK are covered by Triassic to Eocene mudrocks that were deposited in dissimilar geological environments, and have experienced diverse post depositional histories leading to a range of current natural structures. The aim of this study was to investigate different aspects of the mudrock’s structure and their implication on the mechanical behaviour of these soils. Three mudrocks were chosen and sampled; Oxford, Kimmeridge and Gault Clays. These were to be compared with London Clay which was previously studied at Imperial College by Gasparre (2005), Nishimura (2006) and Minh (2007). High quality block and rotary core samples obtained for these soils were used in two experimental studies carried out by the author and Brosse (2011) as well as for a micro-structure analysis performed by Wilkinson (2011). The author carried out series of tests using triaxial apparatus equipped with bender elements and high resolution displacement transducers. These tests provided the strength envelopes of each soil, undrained stiffness and drained elastic parameters. Oedometer cells were also used to investigate the 1-D compression of each material. These were complimented by ring shear tests and index tests performed on all four mudrocks. Findings of this study highlighted the highly anisotropic behaviour of these soils. No clear correlation was found to relate the anisotropy or any other characteristics of these materials to their geological age or their depth of burial. For Gault Clay, the effects of weathering and root action were investigated and the importance of highly fissured macro-structure of the soils was noted. The results from this study are in good agreement with those from tests carried out by Brosse (2011) using a hollow cylinder apparatus and the micro-analysis carried out by Wilkinson (2011).

The effects of frequency, clay content, clay type, ionic concentration and saturation on the complex impedance of various shaly sandstone rocks have been investigated in a detailed and systematic manner. Synthetic samples have been used, so as to allow full control over clay content, clay type and clay distribution, hi addition, selected outcrop and reservoir samples with varying concentrations of clay were also used. Experimental measurements of complex impedance were made as a function of applied stress and saturation, for samples having differing amounts of clay, over a frequency range from 10 Hz to 2 MHz. In addition, the influence of ionic concentration (salinity) was also investigated. The modulus of impedance for the bulk sample response for fully saturated samples was frequency independent in the frequency range from approximately 10 kHz to 600 kHz. A strong linear correlation between the average complex impedance values and clay content was observed, with clay type influencing the magnitude of impedance. However, the reactance and dielectric constant were strongly frequency dependent. They both exhibited a power law dependency with frequency for the montmorillonite and illite synthetic shaly samples. It was possible to deduce correlations between the exponents from the reactance with clay content, and to a lesser extent clay type. The illite shaly samples usually showed the highest dielectric constant values, with the lowest belonging to the kaolinite samples. All samples showed strong relationships with salinity as the concentration was varied from 60,000 ppm to 15,000 ppm, with the modulus of impedance increasing as salinity decreased. The bulk sample response was frequency independent over all salinity concentrations. The dielectric constant showed increasing values as the salinity decreased, with a power law relationship best fitting the data. As the samples were desaturated, a frequency dependency developed for the modulus of impedance as a ftinction of saturation. As the samples were de-saturated the dielectric values decreased in magnitude. The concept of double layer thickness, and the variation in the cationic exchange capacity (CEC) with brine salinity and clay type, were used to explain the responses observed. Using this concept, the data was modelled using equivalent RC circuit models, and an impedance network model. It was found possible to model the data using combinations of capacitors and resistors.

Karstification of the Carboniferous Limestone of the northern part of the Derbyshire limestone outcrop began to a limited extent prior to deposition of the Namurian, and continued in some areas with the development of a hydrothermal karst system during the mineralisation phases of the Permo-Triassic. Extensive cavernisation by allogenic streams and by percolating meteoric water began after the final stripping of the cover of younger rocks during the late Tertiary, and the cave systems were extended and modified throughout the Pleistocene, A complex series of erosional events, apparently related to successive glacial phases, gave rise to a series of abandoned cave levels in some areas. The cavities produced during the Permo- Triassic were of importance in determining the nature and orientation of the later karst drainage systems. Where such pre-existing cavity systems failed to correspond with the hydraulic gradients of the Pleistocene, bedding controlled tube networks developed at preferred horizons in the limestone, often where a fossil horizon gave a relatively higher primary permeability and an underlying clay 'wayboard' arrested downward percolation. Interbedded impermeable horizons are important in the development of perched groundwater areas. Where such horizons have been breached they often form the upper limits of large caverns, since oxidation of sulphide minerals which they contain has locally increased the aggressiveness of circulating groundwater. The concentration of large cave systems near the margins of the present outcrop suggests that stripping of the cover during the late Tertiary occurred fast, and was completed prior to the establishment of significant hydraulic gradients within the limestone.

‘Published Works’ have been removed from the electronic copy of this thesis due to third party copyright restrictions. The full version can be viewed at the University of Leicester Library.

The fluorite deposits of the Southern Pennine Orefield occur in vein fillings and metasomatic replacements. Primary and secondary fluid inclusions define five discrete phases of fluorite mineralization or remobilization. Homogenization temperature ranges for the five events are; (1) 100-171°C; (2) 62-82°C; (3) 65-99°C; (4) 73-106°C; (5) 66-68°C. Little evidence was found of east-west thermal gradients having operated during any of the events. The inclusion types are further characterized by distinctive melting point ranges of ice, hydrohalite or antarcticite. Major element concentrations of the ore fluids have been determined from cation ratios in inclusion leachates modelled in the ternary system NaCl-CaCl2-H20. High Ca/Na ratios in the type 2, 4 and 5 fluids indicate compositions atypical of present-day high salinity formation waters resident in deep sedimentary basins. Mineral solubility data has been used to determine limits for trace anion and cation activities. Ranges for oxygen and sulphur fugacity and pH have also been estimated for mineralizing phases 3 and 4. REE analysis of fluorite and carbonates showed LREE-enriched chondrite normalized patterns with negative cerium and europium anomalies. Total lanthanide abundances are low. Strontium isotope ratios range from 0.7082 to 0.7101 indicating ore fluid interaction with wall rocks enriched in radiogenic strontium with respect to Visean marine carbonates. Muscovite, biotite and K-feldspar can be demonstrated to have been unstable in the ore fluids at 100°C and represent potential fluorine source minerals. Dissolution or alteration of aluminium silicates could have produced fluoride release into the brines. The homogeneity of the inclusion fluids, the uniform REE content of the fluorite and equilibrium mineral textures indicate a non-mixing mechanism of mineralization. An open system, "one pass" model of mineralization with fluorite precipitated as a result of metasomatism of carbonates and possibly limited cooling, and sulphide deposition through pH increase is proposed.

The lithostratigraphy of the Great Estuarine Group is revised by reference to defined type sections of the eight formations (joint publication with J.D. Hudson). Within this framework a series of lagoonal delta and lagoon shoreline depositional models are proposed for the two sandstone dominated formations (Elgol and Valtos). Sedimentation was controlled by brackish, widely fluctuating and locally marine salinities in two elongate basins (Inner Hebrides and Sea of the Hebrides) separated by a slowly subsiding ridge termed the mid-Skye palaeohigh. Low sinuosity rivers of rapidly fluctuating discharge supplied the deltas with sand sourced from the Moinian and Dalradian (probably via the ORS) of the Scottish landmass to the east and tram the Lewisian of the Outer Hebrides landmass to the west. The Elgol Formation represents a fluvial-wave-tide interaction delta in the north of the Sea of the Hebrides Basin Where salinities were marine and shows a southwards transition to a fluvial dominated delta with buoyant mouth bar dynamics. In the Inner Hebrides Basin it represents a fluvially dominated lobate delta system with fresh-brackish salinities controlling friction dominated mouth bar hydrodynamics. The Valtos Formation in the Sea of the Hebrides Basin represents 8 phases of fluvial-wave interaction delta progradation separated by transgressive shell debris beds. The deltas pass laterally into interdeltaic lagoon shorelines and part of the formation represents offshore shell debris sheets and shoals. In the smaller Inner Hebrides Basin the formation represents 6 fluvially dominated lobate delta progradation phases with only minor wave reworking. The identification of genetic relationships between facies allows correlation and the prediction of sand body geometry while the recognition of the overall control of contemporary subsidence rates allows palaeogeographic reconstruction.

The primary aim of this thesis is to provide a comprehensive assessment of the geology of the Southern North Sea Basin during the Jurassic and Early Cretaceous. In order to achieve this the integration of a wide variety of data has been undertaken, including the interpretation of shallow seismic profiles, downhole geophysical log correlation and petrographic descriptions of all available core and seabed sample information from the offshore area. A number of onshore cored borehole sequences were examined in some detail to establish some control points with which to compare the largely uncored offshore successions. [Taken from the thesis Introduction]

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