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  • 1
    Publication Date: 2020-02-06
    Description: Anaerobic oxidation of methane (AOM) was shown to reduce methane emissions by over 50% in freshwater systems, its main natural contributor to the atmosphere. In these environments iron oxides can become main agents for AOM, but the underlying mechanism for this process has remained enigmatic. By conducting anoxic slurry incubations with lake sediments amended with 13C-labeled methane and naturally abundant iron oxides the process was evidenced by significant 13C-enrichment of the dissolved inorganic carbon pool and most pronounced when poorly reactive iron minerals such as magnetite and hematite were applied. Methane incorporation into biomass was apparent by strong uptake of 13C into fatty acids indicative of methanotrophic bacteria, associated with increasing copy numbers of the functional methane monooxygenase pmoA gene. Archaea were not directly involved in füll methane oxidation, but their crucial participation,likely being mediators in electron transfer, was indicated by specific inhibition of their activity that fully stopped iron-coupled AOM. By contrast, inhibition of sulfur cycling increased 13C-methane turnover, pointing to sulfur species involvement in a competing process. Our findings suggest that the mechanism of iron-coupled AOM is accomplished by a complex microbemineral reaction network, being likely representative of many similar but hidden interactions sustaining life under highly reducing low energy conditions.
    Type: Article , PeerReviewed
    Format: text
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  • 2
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    In:  Geological Society Special Publication 227: 101-115.
    Publication Date: 2007-10-08
    Description: Attachment zones couple the rheological layers of lithosphere. In wrench settings, attachment zones accommodate the transition from relatively continuous wrenching at depth to discrete strike-slip faulting of rigid blocks in the upper crust. Strain is controlled by a component of wrench shearing as well as a component of horizontal shearing associated with the differential displacement of finite-width rigid blocks. Strain modelling of wrench attachments predicts high lateral and vertical strain gradients and specific foliation patterns showing antiforms and funnel-shaped synforms. Lineations are shallowly plunging and oriented close to the direction of wrenching. Shear sense reverses across the vertical axial surfaces of synforms and antiforms. In transpression and transtension attachments developed during low-angle oblique convergence or divergence, the pattern of foliation and lineation is similar to that produced in wrench attachments. Transpression attachments display gradients in the shape of the finite strain ellipsoid, from flattening at the base to strongly constrictional beneath the rigid blocks, owing to the increased effect of the horizontal shear component. Conversely, transtension attachments show constriction at the base changing to flattening beneath the rigid blocks. The location of this fabric change within attachment zones is insensitive to finite displacement and angle of convergence or divergence, and therefore should be one of the most robust criteria to identify transpression and transtension attachments. In general, the component of coaxial flow that characterizes transpressional and transtensional systems decreases upward through attachment zones, due to the increased role of the horizontal simple shear in the finite vorticity. These strain and kinematic gradients are a robust result of attachment modelling and can be used as indicators of attachments developed in wrench, transpression, or transtension.
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  • 3
    Publication Date: 2003-01-01
    Description: The Molucca Sea Collision Zone in eastern Indonesia is the site of an orthogonal collision between two active subduction systems. Both the Halmahera subduction zone, to the east, and the Sangihe subduction zone, to the west, have subducted oceanic lithosphere of the Molucca Sea Plate, which has now been completely consumed. Both volcanic arcs were active since the Neogene and provide a means of probing the element fluxes through the two systems. The geochemistry of Neogene and Quaternary lavas from each volcanic arc is compared to constrain changes in the mass fluxes through the systems and the processes controlling these fluxes at different times during their history. Both arcs show increased evidence for sediment recycling as the collision progressed, but for contrasting reasons. In Halmahera this may represent an increased sediment flux through the arc front, while in Sangihe it may simply reflect a greater opportunity for melting of sediment-fluxed portions of the mantle wedge. In both cases the change in arc geochemistry can be related to the evolving architecture of the particular subduction zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite into the mantle wege.
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  • 4
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    In:  Geological Society Special Publication 231: 299-314.
    Publication Date: 2007-10-08
    Description: The discrete-element method (UDEC -- Universal Distinct Element Code) was used to numerically model the deformation and fluid flow in fracture networks under a range of loading conditions. A series of simulated fracture networks were generated to evaluate the effects of a range of geometrical parameters, such as fracture density, fracture length and anisotropy. Deformation and fluid flow do not change progressively with increasing stress. Instability occurs at a critical stress and is charzacterized by the localization of deformation and fluid flow usually within intensively deformed zones that develop by shearing and opening along some of the fractures. The critical stress state may be described in terms of a driving stress ratio, R = (fluid pressure -- mean stress)/1/2 (differential stress). Instability occurs where the R ratio exceeds some critical value, RC, in the range - 1 to -2. At the critical stress state, the vertical flow rates are characterized by a large increase in both their overal magnitude and degree of localization. This localization of deformation and fluid flow develops just prior to the critical stress state and may be characterized by means of multifractals. The stress-induced criticality and localization displayed by the models is an important phenomenon, which may help in the understanding of deformation-enhanced fluid flow in fractured rock masses.
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  • 5
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    In:  Geological Society Special Publication 231: 257-267.
    Publication Date: 2007-10-08
    Description: Extended research over two decades reveals more than 20 distinct fracture episodes in the Beer Sheva syncline. This paper focuses on eight fault-joint systems that differ from each other in their genetic affiliation and/or their geometric relationship and fracture properties. Two systems are linked to burial, whereas six others relate to various syntectonic-uplift associations. Joint sets within these systems are categorized into three, pre-, syn- and post-fault groups. Correspondingly, synfault early uplift and post-fault early uplift events can be distinguished from prefault and synfault late uplift events. Water drainage may be considerably improved along certain fault-joint systems. Accordingly, in formulating fracture-network models the particular distribution of fault-joint systems and their properties need to be taken into consideration.
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  • 6
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    In:  Geological Society Special Publication 231: 153-182.
    Publication Date: 2007-10-08
    Description: Concepts of differential geometry are reviewed, and it is demonstrated through examples that the main joint surface, rib marks and hackle of a joint may be described using parametric representations such that the first and second fundamental forms fully characterize these surfaces. Other useful quantities are the unit normal vector, the principal normal curvatures, and the Gaussian and the mean curvature. Sufficiently close to any point on a surface the shape is planar, parabolic, elliptical or hyperbolic. The surface of a joint in chert and another in siltstone were scanned and the resulting data analysed. Although the main joint surface of the chert sample is approximately planar, it is composed of low-amplitude undulations with elliptical and hyperbolic forms. The unit normal vector does not vary by more than about 3.4{degrees} over this surface, which is consistent with the threshold angle for the initiation of hackle based on laboratory experiments. An individual hackle is found to be approximately helicoidal in shape, but only in the breakdown zone. Rib marks on the siltstone sample have distinct and similar morphologies, with a concave base and convex peak. Field and laboratory campaigns designed to test hypothese about the geometry of joints should use the principles and tools of differential geometry.
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  • 7
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    In:  Geological Society Special Publication 231: 285-297.
    Publication Date: 2007-10-08
    Description: Poles from line samples of systematic joint sets scatter about a mean pole because joints are neither perfectly planar nor parallel, and because measurement instruments are imprecise. Definition of a single joint set can be based solely on its orientation distribution and this distribution is assessed using two statistical parameters: square root of the circular variance (approximately equal to the standard deviation {sigma} for two-dimensional (2D) data) and cone of confidence ({alpha}95 for 3D data). The distribution for joints generated in the absence of tectonic deformation is well clustered with {sigma} = 1.7{degrees} and {alpha}95 = 0.48{degrees} based on a bootstrap sample of 50. Jointing associated with various fold styles show less clustering: the kink of a fault-bend fold ({sigma} = 6.1{degrees} and {alpha}95 = 1.7{degrees}), basement-cored anticline ({sigma} = 3.5{degrees} and {alpha}95 = 1.5{degrees}), regional joint set transected by a basement-cored anticline ({sigma} = 5.2{degrees} and {alpha}95 = 1.8{degrees}) and a buttress anticline ({sigma} = 4.3{degrees} and {alpha}95 = 1.7{degrees}). Jointing associated with local faulting tends to show even less clustering: a Cretaceous marl ({sigma} = 8.3{degrees} and {alpha}95 = 2.4{degrees}) and a glauconitic sandstone ({sigma} = 8.6{degrees} and {alpha}95 = 2.2{degrees}). The latter sample was drawn from two overlapping joint sets, indicating that distribution data greater than {alpha}95 = 2.2{degrees} may signal overlapping joint sets.
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  • 8
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    In:  Geological Society Special Publication 231: 11-24.
    Publication Date: 2007-10-08
    Description: Opening-mode fractures in clinker and opal-CT chert spheroids form by growth and coalescence of pores, and are associated with extensive textural and compositional changes in the host material. Extensive inelastic deformation outside the immediate vicinity of fracture tips characterizes these fracture processes as ductile. Fracture formation in clinker is concurrent with high-temperature combustion alteration of diatomaceous mudstone. Fracture formation in chert spheroids is associated with the opal-CT to quartz transition in the same host material during early marine diagenesis. In both cases, growth of elongate pores is attributed to the combined effects of diffusive-fracture growth and flow by solution-precipitation creep. Pore growth and coalescence occur preferentially ahead of fracture tips along two directions oblique to the mean macroscopic fracture direction. This growth process, referred to as side-lobe damage, is interpreted to reflect the shear-stress dependence of pore growth by solution-precipitation creep. The tendency for oblique fracture growth is suppressed by global stress and strain-boundary conditions forcing the fracture along a characteristic zig-zag propagation path that is macroscopically perpendicular to the loading direction. These examples of ductile fracture demonstrate that macroscopic fracture formation is not uniquely associated with damage processes by microfracture at low-temperature brittle' subsurface conditions. Instead, fracture is a deformation process that can occur due to various inelastic-deformation mechanisms under diverse crustal environments, which include high-temperature conditions.
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  • 9
    Publication Date: 2007-10-08
    Description: North American and Pacific spore-pollen records show a major extinction event at the Cretaceous-Tertiary (K-T) boundary, and abrupt changes are similarly found in many marine organisms world-wide. In contrast, records from the Old World reveal little evidence of terrestrial vegetational change across the boundary. In order to improve the characterization of changes across the K-T boundary, palynological assemblages from two sections in the southern Pyrenees have been evaluated. The abundance and diversity of trilete fern spores are high in Maastrichtian samples and show a statistically significant decrease during the Danian. The fern spike' of low-diversity spores found elsewhere is not recorded in the Pyrenean region. Minor replacements of taxa across the K-T boundary are also noted, as well as an increase in inaperturate gymnosperm pollen in the Danian. Comparing our two examined sections with one another reveals important differences in angiosperm pollen composition.
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  • 10
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    In:  Geological Society Special Publication 231: 315-324.
    Publication Date: 2007-10-08
    Description: The mechanism for structural damage during incipient slip on joints within the Melechov Granite, Czech Republic, changes with the misalignment of the joint's mesotopography, largely a plumose surface morphology. Prior to slip, the joint surfaces are well mated so that contact area is organized on a microscopic scale. During the first phase of slip, diffusion-mass transfer is the active deformation mechanism between the sliding surfaces of the joints, as indicated by the extensive growth of crystal-fibre lineations characteristic of slickenside surfaces. After slip of the order of 1 cm or more, the mesotopography becomes mismatched and the contact area is reorganized to form indentation pits aligned on the ridges of hackle plumes. Indentation pits, that are testimony to a brittle process, are generated by the excavation of Hertzian ring cracks that propagate under contact loading of a brittle substrate. The depth of the indentation pits increases with contact width, suggesting that indentation creep is active. Following indentation along Hertzian ring cracks the slip mechanism transforms to a frictional abrasion. The distribution of indentation track lengths is consistent with laboratory wear grooves generated during earthquake-like stick-slip sliding. The elliptical shape of the indentation pits indicates a gradual decrease in contact area, a process that is consistent with a slip-weakening mechanism during a stick-slip cycle.
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  • 11
    Publication Date: 2007-10-08
    Description: A knowledgeable choice for a stage boundary stratotype is dependent upon obtaining high-resolution stratigraphic data. Detailed analyses conducted for the two potential Turonian-Coniacian stage boundary stratotypes that were considered at the Second Cretaceous Stage Boundary Symposium provide both positive and negative insights for consideration. The Salzgitter-Salder Quarry in central Germany (which was recommended by the symposium) contains abundant bivalve fossils, including the recommended boundary datum: the lowest occurrence of the inoceramid bivalve Cremnoceramus deformis erectus. Foraminifera are also abundant, but extensive diagenetic recrystallization seriously degrades nannofossil and palynomorph recovery and limits the potential of the section for stable isotope stratigraphy and radiometric dating. Furthermore, palaeoenvironmental analysis indicates that much of the Salzgitter stage boundary interval has resulted from allochthonous sedimentation, indicating that the well-developed lithological cyclicity between limestone and marlstone that occurs in the section is largely autocyclic. The orbital cyclostratigraphic potential of the section is therefore also in question. The Wagon Mound outcrop in northeastern New Mexico, USA, has good recovery and biostratigraphic control for all three microfossil groups, but the base of C. deformis erectus occurs above the section, by definition placing the section entirely in the Upper Turonian Well-preserved ammonites and inoceramid bivalves are also recoverable in over half of this section. Facies have not been recrystallized and represent continuous autochthonous sedimentation with sharply defined lithological cyclicity between limestone/marlstone couplets on a fine stratigraphic scale. In addition, a number of bentonites with proven datability occur in the section. Thus the bio- and chemostratigraphic dating potential, as well as the radiometric dating potential, of the section are good. However, much of the section is composed of carbonaceous, dysoxic facies with abnormal marine micro- and macrofossil assemblages, limiting study of the stratigraphic or palaeoecological trends leading up to the boundary. The absence of the datum at Wagon Mound is puzzling, because microfossil biostratigraphy suggests that the section is substantially coeval with the Salzgitter-Salder section. The C. deformis erectus datum may thus be diachronous. Until the suitability of the recommended boundary datum is addressed, a reasoned choice of a section for the boundary stratotype is not possible. In any case, the absence of C. deformis erectus and the abnormal facies in the lower part of the Wagon Mound section, and the extensive diagenesis and partly allochthonous nature of the Salzgitter-Salder section, are serious enough problems to warrant rejection of both sections as stratotypes.
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  • 12
    Publication Date: 2007-10-08
    Description: Palynological analysis of the Centinela Formation, exposed in the foothills of the Patagonian Andes, has revealed the presence of pollen, dinoflagellate cysts, and chlorococcalean and prasinophycean algae. These groups are here reported from the Centinela Formation for the first time. Sporomorph and dinoflagellate cyst assemblages suggest a Late Oligocene and Early Miocene age. These results coincide with a 87Sr/86Sr age close to the age of the Oligocene-Miocene boundary obtained from the lower part of the section. Palynological information from the Centinela Formation permits correlation with Upper Oligocene and Lower Miocene units cropping out along the Atlantic Patagonian coast. Assemblages from the lower part of the section suggest that the beds were deposited under marine, near-shore palaeoenvironmental conditions with a strong continental influence. In the middle part of the section, high dinoflagellate cyst ratios coincide with a maximum flooding surface recorded in the Centinela Formation. Towards the top of the Centinela Formation, the sporomorph assemblages reflect the development of vegetation adapted to coastal environments, which agrees with the sparse occurrence of marine palynomorphs. A new dinoflagellate species, Hystrichostrogylon sulcatum, is proposed. This species appears to range across the Oligocene-Miocene boundary and is particularly abundant in the lowest Miocene.
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  • 13
    Publication Date: 2007-10-08
    Description: Organic-walled dinoflagellate cysts from Eocene-Oligocene transitional deposits have been studied in a section at Leluchow, Flysch Carpathians, Poland. The Eocene-Oligocene boundary, as based on dinoflagellate cyst distribution, is placed in the upper part of the Leluchow Marl Member. The main biostratigraphic events associated with this boundary interval are the highest occurrence of Areosphaeridium michoudii and Areosphaeridium diktyoplokum, and the lowest occurrence of Wetzeliella gochtii. Distinct changes in dinoflagellate cyst assemblages and palynofacies across the Eocene-Oligocene boundary at Leluchow imply a drop in relative sea-level within the Carpathian flysch basin that might correlate with a major eustatic fall during the earliest Oligocene. A drop in sea surface temperature is recognized prior to the Eocene-Oligocene boundary, and evidence is presented for an increase in nutrient level and decrease in salinity within the photic zone during the earliest Oligocene.
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  • 14
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    In:  Geological Society Special Publication 231: NP.
    Publication Date: 2007-10-08
    Description: This volume is a state of the art look at our understanding of joint development in the crust. Answers are provided for such questions as the mechanisms by which joints are initiated, the factors controlling the path they follow during the propagation process, and the processes responsible for the arrest of joints. Many of the answers to these questions can be inferred from the geometry of joint surface morphology and joint patterns. Joints are a record of the orientation of stress at the time of propagation and as such they are also useful records of ancient stress fields, regional and local. Because outcrop and subsurface views of joints are limited, statistical techniques are required to characterize joints and joint sets. Finally, joints are subject to post-propagation stresses that further localize deformation and are the focus for the development of new structures. ... This 250-word extract was created in the absence of an abstract.
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  • 15
    Publication Date: 2007-10-08
    Description: This chapter documents the fracture process associated with the early cooling stage of felsic magma. Characteristics of pre-exhumation joints include their spatial distribution in granite bodies, their fracture surface morphology, and geological and petrological evidence for the depth of fracture initiation. These characteristics allow inferences about the depth and the time of joint origin in the South Bohemian Pluton. The intrusion levels of currently exposed granites of the pluton were 7.4 km in the northern part and 14.3 km in the southern part. Within the northern Mrakotin Granite (Bor[s]ov) early NNE joints propagated while the granite was at a temperature near the solidus, and, in part, magma was still being injected, post-dated by thin granite dykes along NNE joints. Evidence for the pre-exhumation initiation of these joints comes from the geochronological dating of these late-granite dykes (1-2 cm thick) at 324.9 Ma in age, which were creating their own rupture in the rock. The timing of the pluton emplacement at 330-324 Ma and the cooling ages of 328-320 Ma have been given by previous studies. From fluid inclusions within the late-granite dykes that occupy joint surfaces, the trapping depth of the analysed inclusions was calculated to be 7.4 km. Near the solidus H2O separates during the crystallization of anhydrous phases. The associated increasing H2O pressure can initiate the first cracks and can generate a small portion of new granitic melt, which forces the cyclic fracture propagation together with mobile, low-viscosity residual melt' input into the fracture. The determination of the intrusion level and time at which the dykes began cooling provide evidence for the joint initiation at a depth of 7.4 km, which was connected with the level and process of final emplacement and early cooling of the Mrakotin Granite long before the main exhumation. At the earliest, the erosion of the upper rock pile, 7.4 km in thickness, started significantly after generation of the early joint sets. The NNE-trending joints are persistent in orientation throughout the South Bohemian Pluton, but the joint-surface morphology varies in all subplutons and occupies all sections of the stress intensity v. crack-propagation velocity curve (Wiederhorn-Bahat curve).
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  • 16
    Publication Date: 2007-10-08
    Description: This chapter focuses on the evolution of fractures during the inversion of the Bristol Channel Basin, and examines the lateral and vertical consistency of the resulting fracture network within the alternating Liassic limestones and shales. The study has two principal aims. The first is to determine the reliability of fracture systems deduced using more limited data from less well-exposed regions or unexposed regions sampled only by drilling, and the second is to assess whether the fractures are linked to a regional stress field or are the result of a local stress field controlled by the geometry and mechanism of formation of a fold. The joint patterns were studied using a combination of scanline and window sampling, and the results indicate that there are considerable variations in the fracture systems between adjacent limestone beds and also lateral variation within the same bed. Although there is little doubt that the independent development of fracture patterns in adjacent limestone beds is facilitated by the intervening shale horizons, which allow them to become mechanically decoupled, the reasons for these variations are still unclear.
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  • 17
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    In:  Geological Society Special Publication 231: 117-128.
    Publication Date: 2007-10-08
    Description: Hydrofractures are extension fractures generated by internal fluid overpressure (net or driving pressure): they include dykes, veins and many joints. The growth of a hydrofracture depends primarily on the mechanical properties of the host rock and the overpressure of the hydrofracture. Field observations show that in heterogeneous and anisotropic rocks, many hydrofractures change their apertures on passing through layers with different mechanical properties. Alternatively, hydrofractures may become arrested at contacts (and other discontinuities) between layers. We present boundary-element models on hydrofracture arrest and aperture variation that focus on the effects of abrupt changes in Young's modulus in layered reservoirs. The results show that, for internal fluid pressure as the only loading, high tensile stresses concentrate in the stiff layers. When approaching a stiff layer, the hydrofracture tip becomes sharp and narrow, and would normally continue its propagation through that layer. By contrast, soft layers suppress the tensile stresses associated with the hydrofracture tip and blunt the tip itself. Without a nearby weak, subvertical discontinuity that could open up, the hydrofracture tends to become arrested on meeting with a soft layer. When fluid over-pressure is the only loading, the aperture of a hydrofracture is normally larger in soft layers than that in stiff layers, which may lead to flow channelling in a layered reservoir.
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  • 18
    Publication Date: 2007-10-08
    Description: The Catskill Delta Complex of western New York State contains fractured Upper Devonian black shales throughout a 300 km-transect from the more distal, somewhat shallower, deposits of the western region of the state eastward to more proximal and more deeply buried deposits. Each black shale unit grades upward into organically lean grey shale and abruptly overlies another grey shale unit. Within each black shale-grey shale sequence, ENE-trending vertical joints, interpreted to be hydraulic fractures, are best developed (i.e. more closely and uniformly spaced) in the organic-rich shale. Moreover, the density of ENE joints diminishes up-section through each black shale unit, as does the total organic carbon (TOC) content. While ENE joints are less well developed outside the black shale intervals, joints that formed during the Alleghanian orogeny (NW-trending) are found throughout the Upper Devonian shale sequence. Both sets are best developed in black shales in the distal delta sequence, whereas in more proximal deposits the Alleghanian joint sets are best developed in grey shales. Moreover, the density of ENE joints within each stratigraphic level of the black shale exceeds that of Alleghanian joints at the same level, except in the deepest black shale where Alleghanian joints are locally best developed at the top of the black shale interval. The preferential jointing of black shale units in the Appalachian Plateau reflects an extended hydrocarbon generation history. In the distal delta, hydrocarbon generation began when black shale was close to or at maximum burial depth (c. 2.3 km) during the Alleghanian orogeny with the propagation of a NW joint set and continued through post-Alleghanian uplift of the Appalachian Plateau when the ENE joints propagated. In the proximal delta deposits ENE joints propagated before the onset of Alleghanian deformation suggesting that the base of the Upper Devonian section was buried to thermal maturity by progradation of the Catskill Delta Complex before the advent of Alleghanian sedimentation.
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  • 19
    Publication Date: 2007-10-08
    Description: Between the Median Tectonic Line (MTL) and the Japan Sea, the western Chugoku region of SW Japan is cut by a series of N45{degrees}E first-order faults and oblique (N60{degrees}-N170{degrees}E) second-order faults. This fault network, probably formed during Late Cretaceous-Palaeocene times (70-60 Ma), defines a regional block structure. Pre-Plio-Quaternary kinematical indicators suggest left-lateral motion along the first-order faults and right-lateral motion along some of the second-order faults. Geomorphological evidence and earthquake focal mechanisms indicate that Plio-Quaternary slip senses are opposite to Pre-Plio-Quaternary ones. The overall fault pattern is geometrically and kinematically similar to patterns obtained by experimental modelling of simple shear deformation distributed at the base of a brittle layer analogue over its entire width. This similarity suggests the possibility of a mid-crustal, flat-lying partial attachment zone which could have controlled the formation of the western Chugoku fault network in Cretaceous to Palaeocene times. The zone, presently inactive, could correspond to the proto-MTL', a low-angle fault recently imaged by seismic reflection studies and whose trace approximately coincides with the present-day MTL. Reactivation of the system occurred twice after its formation: firstly in Miocene times, during the opening of the Japan Sea and concomitant clockwise rotation of the entire SW Japan arc; and secondly in Late Pliocene to Quaternary times, after a shift of the relative direction of convergence between the Philippine and Eurasia plates. Unlike the first reactivation, the second reactivation led to an inversion of the sense of slip along the faults.
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  • 20
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    In:  Geological Society Special Publication 236: 411-422.
    Publication Date: 2007-10-08
    Description: A petrographic study was conducted on a suite of bottom ash samples from 28 municipal solid waste incinerators in Switzerland. Chemical and mineralogical analyses of bottom ash from waste combustors with comparable technology show similar major oxide composition. A significant decrease of SiO2 was observed in comparison to the chemical composition of bottom ash from 10 years ago. In contrast to major oxide contents, heavy metal concentrations vary significantly in the bottom ash samples, but without any correlation to the type of input waste or plant operating conditions. Similar types and contents of crystalline phases were observed in all samples. The content of newly formed melilite increases with decreasing bulk Si/Ca ratio, indicating that the type of Ca-Mg-Al-silicates crystallizing during incineration and cooling follow petrogenetic rules. A considerable recycling potential for ferrous and non-ferrous metals was identified in the bottom ash. Optimized mechanical metal separation technologies could reduce the waste volume, heavy metal content, H2 production, and exothermic reactions of the bottom ash in landfills and might be economically viable.
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  • 21
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    In:  Geological Society Special Publication 236: 499-513.
    Publication Date: 2007-10-08
    Description: Heat pumps extract heat energy from a low-temperature source and transfer it to a higher temperature sink, usually via a closed loop of volatile refrigerant' fluid in a compression/expansion cycle. They can be efficiently used for space heating (and cooling), extracting heat from seawater, rivers, lakes, groundwater, rocks, sewage, or mine water. Electrical energy powers the heat pump's compressor. The ratio of total heat output to electrical energy input, called the coefficient of performance, typically ranges from 3.0 to 6.0. The use of mine water for space heating or cooling purposes has been demonstrated to be feasible and economic in applications in Scotland, Canada, Norway, and the USA. Mine water is an attractive energy resource due to: (1) the high water storage and water flux in mine workings, representing a huge renewable enthalpy reservoir; (2) the possibility of re-branding a potentially polluting environmental liability as a green' energy resource; and (3) the development of many mine sites as commercial/industrial parks with large space heating/cooling requirements. The exothermic nature of the pyrite oxidation reaction (> 1000 kJ/mol) implies added benefits if closed-loop systems can harness the chemical energy released in mine-waste tips. An appreciation of geochemistry also assists in identifying and solving possible problems with precipitation reactions occurring in heat pump systems.
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  • 22
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    In:  Geological Society Special Publication 236: 529-543.
    Publication Date: 2007-10-08
    Description: Colloid formation is discussed as a possible pathway for the radionuclide release from a nuclear waste repository. An assessment of the colloid relevance on radionuclide migration requires insight into the possible colloid generation mechanisms, their stability and mobility under given groundwater conditions. In various experiments dedicated to the investigation of nuclear waste form behaviour in contact with groundwater, colloidal species are observed mainly for the tri- and tetravalent actinides even in rather high ionic strength solutions where destabilization of colloids is expected. Experimental evidence of laboratory and field studies suggests colloid instability in saline groundwater with time. Groundwater of low ionic strength and high pH enhances colloid stability, as demonstrated in various laboratory and field experiments. The results of an in situ colloid characterization study at the Aspo hard rock laboratory in Sweden are discussed as an example. The mechanism of radionuclide interaction with colloids and notably the reversibility of the radionuclide-colloid binding are other key issues of colloid studies. Kinetic stabilization of the radionuclide binding to colloids may lead to a considerable enhancement of the colloid-mediated radionuclide migration. Substantial kinetic inhibition of actinide dissociation from humic colloids has been established by studying the behaviour of natural humic colloid borne U, Th and rare earth elements. Such behaviour might be explained by the incorporation of these elements into inorganic nanoparticles stabilized by humic coating. Spectroscopic evidence for the occurrence of actinide incorporation into colloidal structures is briefly discussed and the importance of considering the kinetics involved in all kinds of colloidal processes is emphasized. The enhanced migration of tri- and tetravalent actinide ions has been observed recently in various in situ dipole tests at the Grimsel hard rock laboratory in Switzerland. Such experimental findings underline the necessity of further studies on the colloid influence on actinide mobility. Moreover, an improved understanding of colloid-rock interaction mechanisms is required, which is essential for the description and prediction of colloid filtration processes.
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  • 23
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    In:  Geological Society Special Publication 233: 17-28.
    Publication Date: 2007-10-08
    Description: In northern Europe numerous industrial point sources of CO2 surround the North Sea Basin, which contains a number of viable underground sequestration opportunities. These include injection into depleted oil and gas fields and into major regional aquifers; the latter probably offering the greatest ultimate storage potential. At the Sleipner gas field, CO2 is being injected into the Utsira Sand, a large saline aquifer. More than 6 Mt of CO2 have currently been injected, with a projected final target of about 20 Mt. Time-lapse seismic reflection data are being used to monitor the operation and have provided clear images of the CO2 plume and its development with time. Moreover, CO2 volumetrics derived from the seismic data are consistent with the well injection figures. In conjunction with reservoir simulation studies, time-lapse seismic monitoring seems, therefore, to offer an effective means of predicting the future growth, migration and dispersion of the CO2 plume. Another important aquifer, the Bunter Sandstone, stretches from Britain to Poland. In the UK sector alone, the pore volume in structural closures is equivalent to about 350 years' worth of current CO2 emissions from UK power generation. Industrial CO2 sources in northern Europe are well placed to exploit these major subsurface reservoirs and European countries are technically very well equipped to use and develop this emerging technology.
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  • 24
    Publication Date: 2007-10-08
    Description: Geological complexities such as variable permeability and structure (folds and faults) exist to a greater or lesser extent in all subsurface environments. In order to identify safe and effective sites in which to inject CO2 for sequestration, it is necessary to predict the effect of these heterogeneities on the short- and long-term distribution of CO2. Sequestration capacity, the volume fraction of the subsurface available for CO2 storage, can be increased by geological heterogeneity. Numerical models demonstrate that in a homogeneous rock volume, CO2 flowpaths are dominated by buoyancy, bypassing much of the rock volume. Flow through a more heterogeneous rock volume disperses the flow paths, contacting a larger percentage of the rock volume, and thereby increasing sequestration capacity. Sequestration effectiveness, how much CO2 will be sequestered for how long in how much space, can also be enhanced by heterogeneity. A given volume of CO2 distributed over a larger rock volume may decrease leakage risk by shortening the continuous column of buoyant gas acting on a capillary seal and inhibiting seal failure. However, where structural heterogeneity predominates over stratigraphic heterogeneity, large columns of CO2 may accumulate below a sealing layer, increasing the risk of seal failure and leakage.
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  • 25
    Publication Date: 2007-10-08
    Description: The numerous CO2 reservoirs in the Colorado Plateau region of the United States are natural analogues for potential geological CO2 sequestration repositories. To understand better the risk of leakage from reservoirs used for long-term underground CO2 storage, we examine evidence for CO2 migration along two normal faults that cut a reservoir in east-central Utah. CO2-charged springs, geysers, and a hydrocarbon seep are localized along these faults. These include natural springs that have been active for long periods of time, and springs that were induced by recent drilling. The CO2-charged spring waters have deposited travertine mounds and carbonate veins. The faults cut siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge, generally thought to be barriers to fluid flow. The geological and geochemical data are consistent with these faults being conduits for CO2 moving to the surface. Consequently, the injection of CO2 into faulted geological reservoirs, including faults with clay gouge, must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere.
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  • 26
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    In:  Geological Society Special Publication 234: NP.
    Publication Date: 2007-10-08
    Description: This book gives an up-to-date overview of the physical geology of sub-volcanic intrusions. Topics covered in this wide-ranging volume include important aspects of the field geology and physical volcanology of sills, laccoliths and sub-volcanic complexes, magma-sediment interaction and numerical and experimental studies aimed at quantifying more precisely the emplacement mechanics of high-level magmatic intrusions. Provocative papers ask whether laccoliths and high-level sills are forming today, and question the nature of the relationship between high-level intrusions and contemporaneous volcanic activity. Several contributions also deal with the more applied aspects of high-level magma emplacement and 3D seismic imaging of sill and laccolith complexes as relevant to the hydrocarbons industry. It is hoped that with the publication of this volume a consensus will emerge that will help to advance our understanding of the more important physical factors governing the emplacement of high-level intrusions in the continental crust, along with their wider geotectonic implications.
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  • 27
    Publication Date: 2007-10-08
    Description: Monitoring is a key component of the development and operation of nuclear waste repositories, and some of the underlying considerations and lessons learned can benefit projects involving the geological storage of CO2. Before reviewing the general monitoring objectives for nuclear waste repositories, the key differences between nuclear waste disposal and CO2 storage projects are emphasized. The philosophy underlying monitoring after closing/sealing a repository is discussed. Important aspects of this philosophy include the need to collect adequate baseline data representative of the unperturbed site, and the desire to engender public confidence, but not at the expense of compromising the protective barriers of the repository itself. Pre-operational and operational monitoring provide important data that feed into safety assessment calculations, either as input data or as information that can be used to confirm, and/or refine, predictions. Using a specific example of a deep (geological) repository, monitoring experience at the WIPP site in New Mexico is discussed, focusing on methods and techniques that are relevant to CO2 sequestration projects. Such monitoring includes geotechnical (characterization of the evolving behaviour of underground facilities), groundwater (quality and quantity), environmental (impacts on ecosystems), and subsidence (to support subsidence predictions for the WIPP site located in bedded salt formations).
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  • 28
    Publication Date: 2007-10-08
    Description: Over the past 10 years, investigations into the characteristics of the high molecular weight hydrocarbon (HMWHC) fraction in crude oils and, to a lesser extent, source rock extracts have continued to reveal novel information concerning the distribution of hydrocarbons >C40. The major impetus for this work has come from the fact that HMWHCs can cause significant production problems in certain geographical regions and particularly deepwater frontier areas. Since these HMWHCs appear to be ubiquitous in crude oils, the primary questions that need to be addressed are: what are these compounds, where do they come from, and how do they affect physical properties of oils? Here, we review our work over the past decade and discuss the significance of these results and their potential application to reservoir and production problems involving paraffins and asphaltenes. It was commonly believed for many years that only oils derived from source rocks containing higher plant source material would have a high paraffin content. However, it is now abundantly clear that oils derived from lacustrine and marine source rocks also contain relatively high concentrations of higher molecular weight hydrocarbons. In addition to developing methods for the qualitative and quantitative separation of HMWHCs from asphaltenes, progress has been made in identifying individual components of the high molecular weight fraction. This fraction is not a simple mixture of n-alkanes but a complex mixture of seven or eight homologous hydrocarbon series, each with significantly different physical properties. A knowledge of these structures is important in predicting crude oil properties such as cloud point and pour point. Series identified to date include alkylcyclopentanes, alkylcyclohexanes, alkylbenzenes and various branched hydrocarbons. In summary, since the 1970s most of the geochemical research emphasis has been placed on compounds below C40. Whilst compounds above C40 may not have the same degree of structural specificity as the traditional biomarkers, the amount of information available from these compounds could be extremely beneficial in the long term, particularly for reservoir characterization and production purposes and other problems involving high molecular weight hydrocarbons.
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  • 29
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    In:  Geological Society Special Publication 236: 579-594.
    Publication Date: 2007-10-08
    Description: Although glass corrosion resistance has been tested with laboratory methods for decades, investigators are now just beginning to understand the reaction phenomena at or close to saturation with respect to the rate-limiting phase(s). Near saturation, the phenomena that govern element release rates include alkali-hydrogen (species) exchange, differential reactivity of phase-separated glass, and accelerated corrosion rates due to precipitation of key secondary phases. These phenomena were not anticipated by early models of glass dissolution and are incompletely quantified in current rate representations. This review discusses the two over-arching models for glass reactivity, diffusion and surface reaction control, and demonstrates the importance of glass reactivity in terms of glass composition and micro-heterogeneity of the glass. Our conclusion is that surface reaction control best describes the release of elements to solution, but that models based on current interpretations of transition state theory (TST) must be modified to account for reported anomalies in behaviour near saturation.
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  • 30
    facet.materialart.
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    In:  Geological Society Special Publication 236: 619-639.
    Publication Date: 2007-10-08
    Description: The combustion of coal around the world for power generation produces huge volumes of fly ash. In Europe alone this amounted to about 40 Mt in 2000 of which less than 50% was utilized. The waste ends in lagoons, ash mounds, and landfill sites. Coal ashes have high concentrations of many trace elements, some of which are of environmental concern. Although the origin of elements in coals is not considered in this chapter, other aspects of the geochemistry are, and in particular the location of elements within the coal as this influences the behaviour of elements during combustion. During combustion many elements are volatile and are concentrated on the surfaces of the ash particles. Analyses of input coal and combustion residues from Eggborough power station (UK) demonstrate retention of the majority of elements in the solid combustion products, and analyses of size-fractionated fly ash have enabled the percentage surface association to be calculated, which for elements such as As and Mo is considerable. A consideration of the general leaching behaviour leads to the conclusion that it is the surface-associated elements that are most susceptible to leaching in the aqeous environment. The pH is an important control on trace element mobility in water, and in leachates from fly ash ranges from 3.3 to 12.3. High-sulphur coals generate acidic leachates, but not exclusively as the laboratory and field data demonstrate in case studies on UK coals. Batch and column leaching tests on fly ashes are reviewed and data presented for fresh fly ash and weathered fly ashes from two UK mounds dating back 17 and 40 years. The weathered ashes do have lower leachate concentrations than the fresh ash, but in spite of their ages they would not be considered to be inert. The batch leaching tests are of value in simulating high liquid-to-solid ratios encountered in ash lagoons, whereas the column leaching tests relate more closely to ash mounds. Finally, the results of field studies are reviewed and data presented for samples from boreholes in the two ash mounds. Analyses of the ash and extracted porewaters demonstrate depth-related changes due to reaction of the ash with the infiltrating water and whether or not equilibrium was established. Calculations demonstrate that the porewaters achieve saturation with respect to gypsum at depth in the boreholes. Infiltration over the years has led to detectable changes in the concentrations of some of the major elements in the bulk ash, such as Ca, and this enables realistic infiltration rates to be calculated. However, there are not comparable changes in the concentrations of the trace elements in the ash because the rate at which elements are being removed in solution is not sufficiently great.
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  • 31
    Publication Date: 2007-10-08
    Description: Reservoir geochemistry can throw light on the origin of petroleum reservoir fluidheterogeneities at a variety of spatial and temporal scales. This information can be usedto understand the formation and performance of petroleum accumulations, and is avaluable tool for exploration, development and productionstrategies. Key topics covered in this book include: analyticalmethods for the determination of fluid compositionalheterogeneity; physical, chemical and numerical models forinterpreting compositional differences in terms of basin historyand reservoir connectivity; and application case studies. There is now a significant potential for a new wave ofdevelopment focused on component concentrations and amore evolutionary chemical model of reservoired petroleum.When coupled with integrative utilitarian reservoir charge/mixing/production numericalmodels, reservoir geochemistry can provide one of the most significant advances inexploration and production during the 21st century.
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  • 32
    Publication Date: 2007-10-08
    Description: The evolution of the petroleum systems in the Tampen Spur area, with main focus on the filling directions of the northern part of Snorre field, was addressed through 2D basin modelling (Petromod V. 4.5 and 7.0). The geochemical classification of the petroleum populations in the area represented the framework for considering the different kitchen areas and migration systems. Results from the basin modelling support, in general terms, the previous geochemical classification and petroleum families in the region. However, a separate well-defined main kitchen area for the Snorre Field was deduced opposed to the multiple kitchen areas having contributed to the filling as proposed in the literature. Our conclusions are based on the quantitative evaluation of the different proposed kitchen areas and the timing and extent of petroleum generation. Modelling of petroleum generation was performed using asphaltene kinetics determined on petroleum asphaltenes from Snorre oils. This approach was chosen in order to avoid problems associated with the kinetic variability encountered in the Draupne formation. The petroleum asphaltene kinetics was used to delineate the extent of the kitchen area, which reached the time/temperature conditions necessary for the generation of the analysed oil phase. The results thus differ from conventional oil window approximations as we utilize kinetic source rock parameters in the migrated oil for tracing out the generative basin. Three 2D lines crossing the main kitchen areas were modelled in this study. The models were calibrated to data from eight wells, consisting of measured vitrinite reflectance, corrected well temperatures and pore pressure. Three main kitchen areas were considered; one to the west and northwest of Snorre field, one directly to the north (More basin) and one to the east of the field (34/5 kitchen). Modelling suggests that the kitchen area to the west and northwest of Snorre is largely immature and that the volume of potentially generated petroleum is too small to fill the Snorre structure. In the northern kitchen area, the seismic indicated very thin upper Jurassic deposits, which reaches oil window maturities only at a relatively large distance from the structure. The modelling also demonstrated problems related to the filling of the Snorre structure from the More Basin. The combined effect of a thin source rock, which implies a regionally large drainage area to fill the structure, and the large distance to the mature kitchen, lead to the conclusion that the More Basin did not contribute significant volumes of petroleum to the Snorre field. In contrast, the kitchen area east of Snorre Field (the 34/5 kitchen) proved in the modelling to be mature and volumetrically large enough to account for the entire filling of the Snorre Field.
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  • 33
    Publication Date: 2007-10-08
    Description: There is considerable diversity in petroleum type within the Judy and Joanne Fields of the Central Graben. Superficially, the three major reservoir systems can be considered to contain the following fluid types: gas-condensates in the Pre-Cretaceous, undersaturated black oils in the Chalk and gas-condensates in the Palaeocene. Reality is, however, quite different. This paper presents the results of several geochemical studies undertaken in the area; oil/condensate analyses to identify differences in maturity and source input, a pressure data review, high resolution GC fingerprinting, strontium isotope analyses to investigate reservoir connectivity/compartmentalization, and 2D basin modelling to determine the timing and extent of petroleum expulsion and migration. These components have been synthesized to produce a composite petroleum charge model which adequately explains the differences observed. This, in turn, enables an assessment to be made of the likely impact, if any, on field development. Furthermore, the petroleum charge model can be applied to predict the charge risk, fluid type and likely petroleum-water contacts in untested parts of the field and in the immediate vicinity. The results of recent development wells are reviewed in the light of the charge model. Subsequent reservoir geochemistry studies have confirmed the validity of the model and highlight additional applications for reservoir management.
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  • 34
    Publication Date: 2007-10-08
    Description: The Magnolia Field in the deepwater northern Gulf of Mexico is a Plio-Pleistocene age mixed phase reservoir whose fluids are not in compositional equilibrium. Fluid heterogeneities have arisen principally due to (1) variations in maturity of the source rock from which the hydrocarbons were derived, (2) the extent to which biogenic methane has been incorporated into the fluids and (3) phase fractionation effects. These influences express themselves both in terms of bulk fluid properties such as gas/liquid ratio, API gravity and saturation pressure and minor compositional attributes such as hydrocarbon gas isotopic composition and gasoline range molecular ratios. Significant compositional variations that cannot be ascribed to gravitational fluid segregation occur within reservoirs that are demonstrably in pressure communication. These variations challenge the notion that hydrocarbon fluid mixing is geologically instantaneous and underscore the importance of testing assumptions regarding compositional equilibria in conjunction with reservoir studies. Although the state of disequilibrium impedes compartmentalization assessments at Magnolia, it provides both opportunities for fluid property and phase predictions and potentially a development setting in which geochemical surveillance techniques may be profitably employed.
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  • 35
    Publication Date: 2007-10-08
    Description: The ultimate fate of CO2 injected into saline aquifers for environmental isolation is governed by three interdependent yet conceptually distinct processes: CO2 migration as a buoyant immiscible fluid phase, direct chemical interaction of this rising plume with ambient saline waters, and its indirect chemical interaction with aquifer and caprock minerals through the aqueous wetting phase. Each process is directly linked to a corresponding trapping mechanism: immiscible plume migration to hydrodynamic trapping, plume-water interaction to solubility trapping, and plume-mineral interaction to mineral trapping. In this study, reactive transport modelling of CO2 storage in a shele-capped sandstone aquifer at Sleipner has elucidated and established key parametric dependencies of these fundamental processes, the associated trapping mechanisms, and sequestration partitioning among them during consecutive ten-year prograde (active-injection) and retrograde (post-injection) regimes. Intra-aquifer permeability structure controls the path of immiscible CO2 migration, thereby establishing the spatial framework of plume-aquifer interaction and the potential effectiveness of solubility and mineral trapping. Inter-bedded thin shales, which occur at Sleipner, retard vertical and promote lateral plume migration, thereby significantly expanding this framework and enhancing this potential. Actual efficacy of these trapping mechanisms is determined by compositional characteristics of the aquifer and caprock: the degree of solubility trapping decreases with increasing formation-water salinity, whereas that of mineral trapping is proportional to the bulk concentration of carbonate-forming elements, principally Fe, Mg, Ca, Na and Al. In the near-field environment of Sleipner-like settings, 80-85% by mass of injected CO2 remains and migrates as an immiscible fluid phase, 15-20% dissolves into formation waters, and less than 1% precipitates as carbonate minerals. This partitioning defines the relative effectiveness of hydrodynamic, solubility, and mineral trapping on a mass basis. Seemingly inconsequential, mineral trapping has enormous strategic significance: it maintains injectivity, delineates the storage volume, and improves caprock integrity. Four distinct mechanisms have been identified: dawsonite [NaAlCO3(OH)2] cementation occurs throughout the intra-aquifer plume, while calcite-group carbonates [principally (Fe,Mg,Ca)CO3] precipitate via disparate processes along lateral and upper plume margins, and by yet another process within inter-bedded and caprock shales. The coupled mineral dissolution/precipitation reaction associated with each mechanism reduces local porosity and permeability. For Sleipner-like settings, the magnitude of such reduction for dawsonite cementation is near negligible; hence, this process effectively maintains initial CO2 injectivity. Of similarly small magnitude is the reduction associated with formation of carbonate rind along upper and lateral plume boundaries; these processes effectively delineate the CO2 storage volume, and for saline aquifers anomalously rich in Fe-Mg-Ca may partially self-seal the plume. Porosity and permeability reduction is most extreme within shales, because their clay-rich mineralogy defines bulk Fe-Mg concentrations much greater than those of saline aquifers. In the basal caprock shale of our models, these reductions amount to 4.5 and 13%, respectively, after the prograde regime. During the retrograde phase, residual saturation of immiscible CO2 maintains the prograde extent of solubility trapping while continuously enhancing that of mineral trapping. At the close of our 20-year simulations, initial porosity and permeability of the basal caprock shale have been reduced by 8 and 22%, respectively. Extrapolating to hypothetical complete consumption of Fe-Mg-bearing shale minerals (here 10 vol.% Mg-chlorite) yields an ultimate reduction of about 52 and 90%, respectively, after 130 years. Hence, the most crucial strategic impact of mineral trapping in Sleipner-like settings: it continuously improves hydrodynamic seal integrity of the caprock and, therefore, containment of the immiscible plume and solubility-trapped CO2.
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  • 36
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    In:  Geological Society Special Publication 228: 355-382.
    Publication Date: 2007-10-08
    Description: Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.
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  • 37
    Publication Date: 2007-10-08
    Description: This volume summarizes the results of recent research on the Ontong Java Plateau (OJP) in the western Pacific Ocean (Fig. 1). The plateau is the most voluminous of the world's large igneous provinces (LIPs) and represents by far the largest known magmatic event on Earth. LIPs are formed through eruptions of basaltic magma on a scale not seen on Earth at the present time (e.g. Coffin & Eldholm 1994; Mahoney & Coffin 1997). Continental flood basalt provinces are the most obvious manifestation of LIP magmatism, but they have oceanic counterparts in volcanic rifted margins and giant submarine ocean plateaus. LIPs have also been identified on the Moon, Mars and Venus, and may represent the dominant form of volcanism in the solar system (Head & Coffin 1997). The high magma production rates (i.e. large eruption volume and high eruption frequency) involved in LIP magmatism cannot be accounted for by normal plate tectonic processes. Anomalously hot mantle often appears to be required, and this requirement has been a key consideration in the formulation of the currently favoured plume-head hypothesis in which LIPs are formed through rapid decompression and melting in the head of a newly ascended mantle plume (e.g. Richards et al. 1989; Campbell & Griffiths 1990). Eruption of enormous volumes of basaltic magma over short time intervals, especially in the subaerial environment, may have had significant effects on climate and the biosphere, and LIP formation has been proposed as one of the causes of mass extinctions (e.g. Wignall 2001). Several issues ... This 250-word extract was created in the absence of an abstract.
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  • 38
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    In:  Geological Society Special Publication 235: 349-366.
    Publication Date: 2007-10-08
    Description: Dolomudstones of the Pekisko Formation in western Canada form small but important oil and gas reservoirs. The reservoirs are irregularly shaped bodies 1 km or so wide and commonly 5-8 m thick. Porosity development within the dolomudstones is a complex function of sedimentation, early facies-selective dolomitization and later telogenetic leaching of calcareous components. The carbonate sediment precursor of the dolomudstone, interpreted from relict textures preserved in chert nodules, was a microwackestone with abundant silt-sized skeletal fragments. Dolomudstone reservoirs are comprised of dolomudstones, calcareous dolomudstones, and subordinate interbedded dolowackestones and dolograinstones. Some dolomudstone reservoirs are contained entirely within grainstones. Others are capped by tight fenestral lime mudstone that has been dolomitized locally. Dolomitization has been most intense within the centres of these reservoirs, and dolomudstones grade laterally into calcareous dolomudstones. The association of facies indicates that microwackestones were deposited in subtidal intershoal and lagoonal environments on an inner ramp. Grainstone shoals provided a broad barrier that absorbed wave energy seaward of the lagoon. Fenestral lime mudstones accumulated in peritidal environments in restricted areas of the inner ramp, landward of the lagoon. Dolomitization is interpreted to have been early and selective to the microwackestone facies because it retained permeability or was reactive during early burial. Dolomitizing fluids were most probably derived from overlying formations and made their way downwards through spatially separated conduits. The Pekisko Formation was exposed and sculptured at several Jurassic-Early Cretaceous unconformities. During these times, sandstones and shales were deposited in solution cavities developed within the dolomudstones. Concomitant leaching of calcite increased porosity of the dolomudstone reservoirs.
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  • 39
    Publication Date: 2007-10-08
    Description: This study focused on a set of shallow subvolcanic bodies, mainly laccoliths and sills, that intruded the Upper Permian-Lower Triassic sedimentary sequence of the central Southern Alps, in the area of Montecampione (Val Camonica, Italy). These intrusions represented a shallow magmatic reservoir probably associated with Triassic volcanism. Based on a detailed stratigraphic reconstruction, this paper presents results dealing with the evaluation of the emplacement depth, the estimated volume of the subvolcanic bodies, a description of their geometries, and their relation to the host rock and response of the sedimentary units to the intrusions. The emplacement depth was estimated using the thickness of the sedimentary overburden at the time of emplacement, and by applying simple equations involving laccolith dimensions. The results are comparable, and support an average emplacement depth of about 1300 m. The minimum volume of the intrusions was obtained using a GIS, and is about 1 km3. Concerning the relationship between the intrusive bodies and the host rock, we observed that sills are mainly emplaced into the Servino Formation, while the laccoliths are emplaced near the contact between the Verrucano Lombardo and the Servino Formation. The two sedimentary units show a different response to the intrusion: the Verrucano Lombardo always appearing fractured and tilted, while the Servino Formation shows a range of deformation patterns, from light ductilization at the contact, to folding, brecciation and foliation. These different responses reflect the mechanics of emplacement and geometry of the intrusions, and local heterogeneities in the host rock. Both units show a local thermal effect close to the contact.
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  • 40
    Publication Date: 2007-10-08
    Description: The present volume represents a series of papers arising from a conference on The Geometry and Petrogenesis of Dolomite Hydrocarbon Reservoirs' held at the Geological Society of London on 3-4 December 2002. More than 70 dolomite enthusiasts gathered in the largest specialist meeting since the bicentennial conference, in Ortisei in 1991, honouring the first description of the mineral by the French Engineer Deodat de Dolomieu (1750-1801). The proceedings of the latter meeting, sponsored jointly by the International Association of Sedimentologists (IAS) and the Society of Economic Paleontologists and Mineralogists (SEPM), were subsequently published in IAS Special Publication 21 edited by Purser et al. (1994). As the title indicates, the focus of the meeting reported here was on the implications of the various processes and products of dolomitization for hydrocarbon exploration. This is by no means a trivial issue, where an estimated 80% of North American and many Middle and Far Eastern reservoirs are in rocks affected by dolomitization. As in any meeting of this kind, the weight of emphasis lies with the contributors. Sessions were devoted to Early Dolomites, Burial Dolomitization, Fractures and Reservoir Quality, the Geometry of Dolomite Bodies, Petrophysics and a variety of case histories. Although a polite accord was maintained throughout the conference discussion raised the blood pressures of at least some delegates. In keeping with the diversity of views on the origins of dolomites, there was a schizoid disconnection between those driven by curiosity; art for arts sake', and those with clear economic objectives, with fanatics and ... This 250-word extract was created in the absence of an abstract.
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  • 41
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    In:  Geological Society Special Publication 236: NP.
    Publication Date: 2007-10-08
    Description: This book provides incentives for further development of sustainable fuel cycles through a novel and interdisciplinary approach to an Earth science-related topic. The main focus is on geochemical concepts in immobilizing, isolating or neutralizing waste derived from energy production and consumption. The book also addresses the issue of using some types of energy-derived waste as alternative raw materials. Moreover, it highlights research on how certain wastes can be used for energy production, an increasingly important aspect of modern integrated waste management strategies. The main objectives are to: (a) identify the most serious environmental problems related to various types of power generation and associated waste accumulation; (b) present strategies, based on natural analogue materials, for the immobilization of toxic and radioactive waste components through mineralogical barriers; (c) discuss modern procedures for reuse of waste or certain waste components; and (d) review the importance of geochemical modelling in describing and predicting the interaction between waste and the environment.
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  • 42
    Publication Date: 2007-10-08
    Description: Subvolcanic intrusions in sedimentary basins cause strong thermal perturbations and frequently cause extensive hydrothermal activity. Hydrothermal vent complexes emanating from the tips of transgressive sills are observed in seismic profiles from the Northeast Atlantic margin, and geometrically similar complexes occur in the Stormberg Group within the Late Carboniferous-Middle Jurassic Karoo Basin in South Africa. Distinct features include inward-dipping sedimentary strata surrounding a central vent complex, comprising multiple sandstone dykes, pipes, and hydrothermal breccias. Theoretical arguments reveal that the extent of fluid-pressure build-up depends largely on a single dimensionless number (Ve) that reflects the relative rates of heat and fluid transport. For Ve 〉〉 1, explosive' release of fluids from the area near the upper sill surface triggers hydrothermal venting shortly after sill emplacement. In the Karoo Basin, the formation of shallow (〈 1 km) sandstone-hosted vents was initially associated with extensive brecciation, followed by emplacement of sandstone dykes and pipes in the central parts of the vent complexes. High fluid fluxes towards the surface were sustained by boiling of aqueous fluids near the sill. Both the sill bodies and the hydrothermal vent complexes represent major perturbations of the permeability structure of the sedimentary basin, and are likely to have long time-scale effects on its hydrogeological evolution.
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  • 43
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    In:  Geological Society Special Publication 236: 1-5.
    Publication Date: 2007-10-08
    Description: Energy has played a key role in the development of civilizations around the globe. Since prehistoric times, Man has depended on energy sources for heating and cooking purposes. The main energy source at that time was wood, and wood burning continues to be of utmost importance in certain parts of the world. The need to secure energy sources has a direct interaction with the environment. Throughout history, this interaction has been detrimental to the environment, as documented, for example, by early deforestation in the Mediterranean area, where the growth of civilizations was linked to deforestation (Thirgood 1981). Today, the environmental impact resulting from energy production and consumption is more visible and more pronounced than ever before, as Man tries to satisfy an ever-growing energy demand. In the year 2001, the total world consumption of primary energy amounted to [~]426 billion GJ (EIA 2003), an increase of more than 15% compared to 1992. By assuming a world population of 6.1 billion people in 2001, the per capita energy consumption is approximately 70 GJ. This figure, however, represents a global average only, and pronounced differences exist for various regions. Figure 1 demonstrates, for example, that in North America the per capita consumption of primary energy is four times greater than the global average, and nearly twice that of Western Europe. On the other hand, the per capita consumption in Africa is merely a third of the global average. This extreme geographical disparity in energy consumption is mirrored by the data for CO2 ... This 250-word extract was created in the absence of an abstract.
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  • 44
    facet.materialart.
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    In:  Geological Society Special Publication 234: 229-232.
    Publication Date: 2007-10-08
    Description: Seismic volume visualization techniques demonstrate that saucer-shaped sill complexes consist of a series of radiating principal flow units rising from an inner saucer and fed by principal magma tubes. Such flow units contain smaller scale secondary flow units, each being fed by a secondary magma tube branching from the principal magma tube. This pattern is repeated down to scales of approximately 100 m with successively smaller flow units being fed from magma tubes repeatedly branching from higher order tubes. The data demonstrates that each sill complex is independently fed from a centrally located point source, that sills grow by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature. These features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening.
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  • 45
    Publication Date: 2007-10-08
    Description: The Nagra/PSI Chemical Thermodynamic Data Base is a critical selection of thermodynamic data used to support performance assessments for planned radioactive waste repositories in Switzerland. For this purpose, the data base is focused on actinides and fission products, but also includes additional data for major elements occurring in common groundwaters. Recently, a peer-reviewed update was carried out (from data base version 05/92 to 01/01) involving major revisions for most actinides and fission products. Altogether, more than 70% of the data base contents have been revised. Most of the thermodynamic data for U, Np, Pu, Am, and Tc were adopted from the reviews by the NEA TDB project. In contrast, data for Th, Sn, Eu, Pd, Al, as well as the solubility and metal complexation of sulphides and silicates, were extensively reviewed. Less effort was put into the review of data for Zr, Ni, and Se as these elements are currently being reviewed in Phase II of the NEA TDB project. The data for metal complexation with organic ligands from data base version 05/92 were not included in this update. They will be reconsidered in a future update, after completion of the NEA TDB Phase II review of organic ligands. The chemical consistency of the selected data was checked with empirical rules related to the periodic properties of the elements and with correlations based on charge/size relations. As a result of the update, major gaps in the data base could be identified, especially with respect to missing carbonate complexes. In some systems, for example, Th(IV)-H2O and U(IV)-H2O, conflicting experimental data cannot be described by a unique set of thermodynamic constants and a pragmatic approach closely reproducing measured solubility data was chosen for application to performance assessment. The electronic version of the Nagra/PSI Chemical Thermodynamic Data Base 01/01 and information concerning its full documentation is available on the PSI web site.
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  • 46
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 236: 595-606.
    Publication Date: 2007-10-08
    Description: Cement has found wide usage in the stabilization of heavy-metal-containing wastes as cement minerals can substantially reduce heavy metal solubility as a result of precipitation, adsorption to the surfaces and incorporation. The solubility of some heavy metal cations is limited by the precipitation of hydroxides, while that of some oxyanions is limited by the formation of Ca salts. Only ions that are sufficiently soluble in basic media will be incorporated in or sorbed to hydrated cement minerals to a significant degree. Heavy metal cations may sorb quite strongly to calcium silicate hydrate (C-S-H). The cations diffuse into the C-S-H particles where they are probably sorbed to the silicate chains. Pure phases of oxyanion-substituted ettringite (3CaO{middle dot}Al2O3{middle dot}3(CaSO4){middle dot}32H2O, an AFt phase) and monosulphate (3CaO{middle dot}Al2O3{middle dot}CaSO4{middle dot}12H2O, an AFm phase) phases and solid solutions with SO42- and OH- have been synthesized. Some thermodynamic data are available for the pure phases. For most elements an approximate range of solubility has recently become known. However, it is not possible to predict solubility from the available data.
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  • 47
    Publication Date: 2007-10-08
    Description: Anaerobic processes have only recently been recognized as an important mechanism in the biodegradation of crude oils. They are normally invoked to explain extensively biodegraded oils with little or no possibility of contact by oxygenated waters from an active aquifer. This work with Kuparuk Field indicates that early stages of anaerobic biodegradation can be subtle and easily missed, yet have economic impact. Kuparuk River Field, North Slope of Alaska, comprises two reservoir intervals: vertically stratified and imbricated lower shoreface sandstones (A sands), and overlying shallow marine sandstones with complex permeability structure (C sands). The vertical and lateral distribution of viscous oil (less than 20{degrees} API) shows a strong relationship to structure and faulting in the Kuparuk Field. Multiple mechanisms for the origin of tars and viscous oils can be proposed, including early aerobic biodegradation, anaerobic biodegradation, inorganic oxidation and gas deasphalting. This geochemical study, integrated with stratigraphic, structural and production data, was undertaken to help understand the origin and distribution of tar and viscous oil in the field. Obvious depletion of n-alkanes and other paraffins, classically regarded as indicative of early biodegradation, is not observed in examined samples. However, Kuparuk viscous oils show slight to extreme selective depletion in long-chain alkyl aromatic (LCAA) hydrocarbon families (e.g. alkylbenzenes and alkyltoluenes). This is interpreted as indicative of an early stage of anaerobic microbial degradation that likely destabilized the oil to promote subsequent precipitation of asphaltenes as tar. Depletions in LCAAs in core samples in the field are linked to decreased hydrocarbon/nonhydrocarbon ratio and to an increase in the high molecular weight (>C50+) components of Rock-Eval 6 pyrolysates. Using a calibration curve constructed from oil Rock-Eval 6 pyrolysis, the API gravity of core oil plus bitumen can be estimated. Tar-plugged formations with depleted LCAAs have estimated API gravities <8{degrees}. Portions of the Kuparuk reservoir with higher iron content tend to show greater depletions in LCAA. Anaerobic biodegradation is likely mediated by dissimilatory iron-reducing bacteria. Biodegradation likely destabilizes the oil with respect to asphaltene precipitation such that later arrival of petroleum leads to tar in the reservoir. Increased tar and depleted LCAAS correspond to intervals with lower productivity indices, thus indicating a significant impact on petroleum producibility.
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  • 48
    Publication Date: 2007-10-08
    Description: Dolomite and dolomite reservoirs are common in Ordovician and middle to upper Permian carbonates in the Permian Basin' area of the SW United States. Scattered, but significant, dolomite reservoirs also occur in the Silurian and Devonian. In the middle to upper Permian, platform and shelf-top carbonates were dolomitized, while limestones in slope and basinal environments were not. Most dolomitization of Ordovician and Permian carbonates occurred in evaporated seawater shortly after deposition (reflux dolomitization). Most dolomitizing brines apparently formed in tidal flat and restricted lagoonal environments in the platform and shelf interiors, and on depositional highs near shelf and platform margins. More than 26 billion barrels of oil have been produced from the Permian Basin, with most of that oil coming from Palaeozoic (mainly Permian) dolomites. Permian Basin dolomites have very heterogeneous porosity and permeability on a wide range of scales. Field-scale (km-scale) variations in porosity are commonly related to position in the original dolomitizing system. Porosity generally increases away from the apparent source of the dolomitizing brines because a greater volume of dolomite was precipitated in proximal parts of the dolomitizing system than in the distal parts; hence, porosity is greater in dolomites in the basinward parts of fields. Most Permian Basin dolomite reservoirs are structural traps with stratigraphic enhancement of closure by loss of porosity and permeability towards the shelf or platform interior. Many traps were formed by compactional drape over the same features that created highs during deposition. Hence, the structurally highest parts of many fields have the poorest porosity and permeability because they coincide with proximal parts of the original dolomitizing system. The most porous, permeable and productive dolomites are on the basinward flanks of structures, and often near the oil-water contact. Dolomite reservoirs in the Permian Basin are quite variable. Ultimate oil recoveries from these fields range from 〈1000 barrels to 2 billion barrels, with the largest fields in shallow middle Permian (San Andres/Grayburg) reservoirs. Reservoir depths range from 1500 to more than 14 000 ft (500-4300 m). Average porosities for fields are 1-21%, with porosities generally decreasing with depth. Average permeabilities are 1-1000 mD. Many deeper reservoirs have high permeability related to fractures in karstified Ordovician reservoirs. Recovery efficiencies are 10-65% of the original oil in place, with higher recovery efficiency associated with larger pores and higher permeabilities.
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  • 49
    Publication Date: 2007-10-08
    Description: A number of polyphase or single-phase ceramic waste forms have been considered as options for the disposal of nuclear waste in geological repositories. Of critical concern in the scientific evaluation of these materials is their performance in natural systems over long periods of time (e.g., 103 to 106 years). This paper gives an overview of the aqueous durability of the major titanate host phases for actinides (e.g., Th, U, Np, Pu, Cm) and important fission products (e.g., Sr and Cs) in alternative crystalline ceramic waste forms. These host phases are compared with reference to some basic acceptance criteria, including the long-term behaviour determined from studies of natural samples. The available data indicate that zirconolite and pyrochlore are excellent candidate host phases for actinides. These structures exhibit excellent aqueous durability, crystal chemical flexibility, high waste loadings, and well-known processing conditions. Although both pyrochlore and zirconolite become amorphous due to alpha-decay processes, the total volume swelling is only 5-6% and there is no significant effect of radiation damage on aqueous durability. Hollandite also appears to be an excellent candidate host phase for radioactive Cs isotopes. Brannerite and perovskite, on the other hand, are more prone to alteration in aqueous fluids and have a lower degree of chemical flexibility. With the exception of hollandite, many of the properties of these potential host phases have been confirmed through studies of natural samples.
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  • 50
    Publication Date: 2007-10-08
    Description: Natural geological accumulations of carbon dioxide occur widely throughout Europe, often close to population centres. Some of these CO2 deposits leak, whereas others are sealed. Understanding these deposits is critical for selecting and designing underground storage sites for anthropogenic CO2. To provide confidence that the potential risks of geological CO2 storage are understood, geologists are required to predict how CO2 may behave once stored underground. Natural CO2 accumulations provide a unique opportunity to study long-term geochemical and geomechanical processes that may occur following geological storage of anthropogenic CO2. In addition, natural CO2 springs and gas vents can provide information on the mechanisms of gas migration and the potential effects of CO2 leakage to the surface. This paper provides a description of some natural, European CO2 occurrences. CO2 accumulations occur in many basins across Europe. In addition, volcanic areas and seismically active areas allow CO2-rich fluids to migrate to the near surface. Many of these occur in areas that have been populated for hundreds and thousands of years. Stratigraphic traps have allowed CO2 to accumulate below evaporite, limestone and mudstone caprocks. Comparisons between reservoir sandstone and equivalent nearby sandstones that contain no CO2 indicate that reservoir sandstones may experience increased secondary porosity development through feldspar dissolution. Where fracture reactivation allows CO2-rich fluids to migrate, limited self-sealing may take place through calcite precipitation. Gas migration experiments indicate that, due to geochemical interactions, fine-grained seals would be able to trap smaller volumes of CO2 compared to, for example CH4. In natural systems most leakage from depth occurs along fractures and is typically extremely localized on a metre-scale.
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  • 51
    facet.materialart.
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    In:  Geological Society Special Publication 233: NP.
    Publication Date: 2007-10-08
    Description: Carbon dioxide (CO 2) is the main compound identified as affecting the stability of the Earth's climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change. Geological storage of CO 2, or the injection and long-term stabilization of large volumes of CO 2 in the subsurface in saline aquifers, in existing hydrocarbon reservoirs or in unmineable coal seams, is one of the more technologically advanced options available. A number of studies have been carried out and are reported here. They are aimed at understanding the safety, physical and chemical behaviour and long-term fate of CO 2 when stored in geological formations. Until efficient, alternative energy options can be developed, geological storage of CO 2, the subject of this volume, provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy.
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  • 52
    Publication Date: 2007-10-08
    Description: The growing emissions of greenhouse gases, especially CO2, are seen worldwide as one of the major causes of climate change. International treaties like the Kyoto Protocol are supposed to contribute to reducing the emission of greenhouse gases. Underground sequestration has the potential to play an important role in keeping large volumes of CO2 from escaping into the atmosphere in the short term. The first case of industrial scale CO2 storage in the world (close to one million tonnes per year since 1996) is taking place at the Sleipner underground CO2 storage site in the North Sea offshore Norway. Careful monitoring of the behaviour of the storage facility is required to establish its safety. To this end, two time-lapse seismic surveys have been acquired; the first repeat survey was completed in October 1999 and the second in October 2001. The presence of CO2 beneath thin intra-shale layers within the reservoir has caused significant changes both in reflection amplitudes (up to a factor 10) and in travel time (more than 40ms) through the CO2 plume (the velocity push-down effect). Some aspects of the interpretation of these time-lapse seismic surveys will be presented here.
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  • 53
    facet.materialart.
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    In:  Geological Society Special Publication 233: 225-234.
    Publication Date: 2007-10-08
    Description: Over the past decade, oil and gas producers in the Alberta basin have been faced with a growing challenge to reduce atmospheric emissions of hydrogen sulphide (H2S) that is produced from sour' hydrocarbon pools. Since surface desulphurization is uneconomic, increasingly operators are turning to acid-gas disposal by injection into deep geological formations. Acid gas, a mixture of hydrogen sulphide and carbon dioxide (H2S and CO2), is the by-product of sweetening' sour hydrocarbons. Although the purpose of the acid-gas injection operations is to dispose of H2S, significant quantities of CO2 are also being injected because it is uneconomical to separate the two gases. The acid-gas injection operations in the Alberta basin represent an analogue to geological sequestration of CO2. Large-scale injection of CO2 into depleted oil and gas reservoirs and into deep saline aquifers is one of the most promising methods of geological sequestration of CO2, and in this respect it is no different from acid-gas disposal operations. However, before implementation of greenhouse-gas geological sequestration, a series of questions need to be addressed; the most important ones relate to the short- and long-term fate of the injected CO2. Thus, the study of the acid-gas injection operations in Alberta provides the opportunity to learn about the safety of these operations and about the fate of the injected gases, and represents a unique opportunity to investigate the feasibility of CO2 geological sequestration.
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  • 54
    facet.materialart.
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    In:  Geological Society Special Publication 236: 169-209.
    Publication Date: 2007-10-08
    Description: Ever since the commencement of industrial-scale coal mining (in northeast England around 1600), substantial environmental impacts have been recorded as arising from both the mined voids and from the wastes left behind at the surface. In the early days of coal mining, complaints about such impacts were strident, as the newly established industry adversely affected long-established agricultural interests. When the coal trade had come to dominate regional economies in mining districts, its negative impacts came to be accepted as a necessary byproduct of the generation of coal-based wealth. It has only been since large-scale mine closures began to take place in the major coal-mining economies of the developed world during the last few decades that the negative impacts of coal mining have once more been deemed unacceptable. The environmental impacts arising from coal mining activities are fundamentally attributable to the exposure of reduced earth materials (especially coal, pyrite, siderite, and ankerite) to the oxidizing power of the Earth's atmosphere. The consequences range from the spontaneous combustion of coal to the release of acidic waters from pyrite oxidation. A typology of the known impacts arising from mine voids and wastes in coal mining districts has been developed, which recognizes many subcategories of impacts under five major headings: air pollution, fire hazards, ground deformation, water pollution, and water resource depletion. A robust understanding of geochemical processes is key to understanding how these impacts arise, and to developing sustainable mitigation strategies. The application of the newly developed typology is illustrated using the case of the Shilbottle Coalfield (Northumberland, UK). Although few demonstrable impacts have arisen in the categories of air pollution, fire hazards, or ground deformation, major problems of water pollution have required both preventative and remedial interventions. For the flooded underground voids, these took the form of a pump-and-treat system, whereas emissions of leachates from surface spoil heaps have necessitated the installation of an innovative hybrid' passive treatment system, comprising a permeable reactive barrier, oxidation ponds, and a wetland. Inverse geochemical modelling has clarified the linkages between the various types of water encountered in the coalfield, providing a baseline geochemical understanding upon which future investigations of remedial system sustainability can be based.
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  • 55
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 236: 223-246.
    Publication Date: 2007-10-08
    Description: The generation of electricity by thermal conversion of coal results in significant volumes of solid waste. Most of these materials are disposed of in surface impoundments near coal-fired power plants or in active coal mines. Disposal rates vary from country to country. In the USA, 60-70 wt% of these materials are disposed. Although these materials rarely meet the definition of hazardous, leachate tests on some coal ash have shown them capable of producing elevated concentrations of some regulated metals. As a result of the well-documented environmental concerns posed by coal combustion, and the disposal of coal combustion products (CCPs), a large body of research has focused on characterizing the mechanisms of mobilization and attenuation of trace elements in coal and its ash. However, groups opposed to coal combustion or unregulated disposal of ash overlook the value of these materials as well-proven replacements for aggregate, cement, or soil in numerous engineering and agricultural applications. An extensive body of knowledge has been gathered describing the variability and versatility of these materials. It has been shown that proper utilization or management of ash requires a good understanding of its chemical, physical, and mineralogical properties. This chapter is intended to provide a broad overview of the chemistry and mineralogy of coal, and the combustion products that are formed when coal is burned.
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  • 56
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 236: 247-262.
    Publication Date: 2007-10-08
    Description: Pulverized coal combustion ash is an important source of strategic materials in the USA. Bottom ash is used as a source of aggregate for use in concrete and masonry units (blocks). It is processed primarily to improve its grading. A top size is removed and the finest sizes are removed via wet or dry screens. Pyrite and rock may also be present with the ash. These materials can be removed by spiral concentrators and jigs. In some cases high-quality/high-value lightweight aggregates are produced from stored bottom ash. Fly ash is used as a pozzolanic additive to Portland cement concrete. In addition to partially replacing the cement, it contributes substantially to the durability of the concrete. The advent of low-NOx burners and selective catalytic reduction (SCR) supported ammonia injection has altered the character of the fly ash, particularly the Class F, low-Ca type, by generally increasing the amount of unburned carbon. This contaminant adsorbs air-entrainment reagents and can decrease the resistance of the concrete to freeze-thaw damage. Over the past decade several technologies and approaches have been developed to remove the carbon from the fly ash, including: air classification; electrostatic separation; and fluidized-bed combustion. Other approaches such as microwave heating also show promise. Froth flotation has been successfully applied to wet ash. The amount of ash that is beneficiated has increased to a current level of about 1 million tons per year in the USA, which is expected to grow in time due to the need for predictable materials with constant characteristics. The primary environmental advantage of ash beneficiation is that it enables the use of combustion ash that would otherwise be disposed as waste. High-quality, consistent products can be generated, thus increasing the usefulness and acceptance of these processed products in both traditional and emerging markets. By doing so, the amount of ash that is utilized will be increased, thus reducing the amount of ash that is disposed, while conserving other resources such as aggregate and sand for other uses not applicable to combustion ash.
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  • 57
    Publication Date: 2007-10-08
    Description: By comparing felsic laccolith complexes prominent in the Late Palaeozoic Ilfeld-, Saar-Nahe-, and Saale basins in Germany, a characteristic pattern related to transtensional tectonics is revealed. In contrast to the central magma feeding systems recognized so far for laccolith complexes, individual units of the Late Palaeozoic Central European complexes apparently were fed synchronously by numerous feeder systems arranged laterally in a systematic pattern. The Ilfeld Basin is a small strike-slip pull-apart basin in the SE of the Hartz Mountains cogenetic with a neighbouring rhomb horst -- the Kyffhauser. The Ilfeld Basin represents a frozen-in' early stage of laccolith complex evolution, with small isolated intrusions and domes emplaced within a common level at the intersections of intra-basinal Riedel shears. In the Saar-Nahe basin, numerous medium-sized felsic subvolcanic to subaerial complexes emplaced at a common level have been recognized (Donnersberg-type laccolith complex). The magmatic evolution of the Halle Volcanic Complex in the Saale Basin culminated in the more or less synchronous emplacement of voluminous porphyritic laccoliths within different levels of a thick pile of Late Carboniferous sediments (Halle-type laccolith complex). Laccoliths in the Halle area might consist of several laccoliths typical of the Saar-Nahe Basin according to outcrop pattern and host sediment distribution. The above-mentioned three post-Variscan Central European basins are characterized by a dextral transtensional tectonic regime, leading to a model for laccolith-complex evolution:1 Initial lithosphere-wide faulting forms pathways for magma ascent. 2 Supracrustal pull-apart leads to the formation of a transtensional basin. 3 Continued transtension gives way to decompressional melting of the mantle lithosphere, especially if fertilized by previous magmatic activity, as in the Variscan orogen. The mantle melts rise into the lower crust to differentiate, mingle or cause anatexis. 4 The melts homogenize and start crystallizing in a mid- to upper-crustal magma chamber tapped during tectonic episodes. 5 The resulting SiO2-rich magmas ascend along major transtensional faults into thick sedimentary basin fill. The amount of transtension and the amount of melt rising from the lithospheric mantle have a major influence on the type and size of the laccolith complex to be formed. Additionally, the presence of a mid- to upper crustal magma chamber is a prerequisite for the formation of the Donnerberg and Halle type laccolith complexes.
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  • 58
    Publication Date: 2007-10-08
    Description: During Late Palaeozoic times, andesite magmas intruded a 100-m thick sequence of Late Carboniferous lacustrine to alluvial siliciclastic rocks, sandwiched between folded Namurian sediments at the base and a thick, partly welded rhyolitic ignimbrite sheet at the top, in the Flechtingen area. An intrusive complex, comprising of two main sills up to 200 m thick and over 20 km in lateral extent, was formed (the Flechtingen Sill Complex, or the lower andesites', previously interpreted as lava flows). In the supposed feeder area the andesitic magmas locally pierced the ignimbrite seal, forming isolated pipes and domes (the upper andesites'). Thickness variations of the sills suggest ponding of the andesite magma within former depositional troughs and syn-emplacement deformation of the host sequence with the formation of swells, basins and fault-bounded grabens at the top of the sills. Locally, thin failed' sills are present. In places, sill margins show domains of flattened and aligned vesicles and planar, sharp contacts to the host sediments. However, in many outcrops and drill cores the sill margins consist of variable andesite breccias and peperties. These fragmental rocks reflect auto- to quench-clastic brecciation of chilled andesite magma (in situ breccias and perlite), variable magma-sediment interactions and later breciation by hydrothermal fluids.
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  • 59
    Publication Date: 2007-10-08
    Description: Fracture geometries and fracture-sealing characteristics in dolostones reflect interactions among mechanical and chemical processes integrated over geological timescales. The mechanics of subcritical fracture growth results in fracture sets having power-law size distributions where the attributes of large, open fractures that affect reservoir flow behaviour can be accurately inferred from observations of cement-sealed microfractures and other microscopic diagenetic features, which are widespread in dolostones. Fracture porosity is governed by the competing rates of fracture opening and cement precipitation during fracture growth and by cements that post-date fracture opening. Combined analysis of structural and diagenetic features provides the best approach for understanding how fracture systems influence fluid flow. We review previous work and integrate new data on fractures and diagenetic features in cores from the Lower Ordovician Ellenburger and Permian Clear Fork formations in West Texas, and the Lower Ordovician Knox Group in Mississippi, together with outcrop samples of Lower Cretaceous Cupido Formation dolostones from the Sierra Madre Oriental, Mexico, in order to illustrate our approach.
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  • 60
    facet.materialart.
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    In:  Geological Society Special Publication 235: 193-232.
    Publication Date: 2007-10-08
    Description: Oil is present in the Upper Jurassic Arab A and Arab C carbonates of the Al Rayyan Field. The Arab A consists of porous limestone with thin units of tight dolomite at the top and bottom. Two reservoir intervals can be distinguished, separated by a slightly less permeable unit. The upper reservoir consists of stromatolites and cross-bedded peloidal-grainstones, whereas the lower reservoir consists predominantly of ooliticgrainstones. The less permeable unit comprises moderately cemented, cross-bedded peloidal-grainstones. Higher porosity and permeability generally occurs in the coarser grained, cross-bedded grainstones, where pores are mostly primary and intergranular; lower permeability is characteristic of grainstones with moderately developed early cement. Porosity is enhanced at some levels by the presence of leached intragranular pores, but these have little effect on permeability. The Arab C is strongly stratified and completely dolomitized. Three reservoir intervals can be recognized, separated by less permeable layers of poorer quality rock. The upper reservoir consists of partially leached and moderately cemented, cross-bedded bioclastic-peloidal-grainstones. Porosity is high because of the presence of leached intragranular pores in addition to primary intergranular pores but permeability is relatively low because of the presence of early cement. The main reservoir comprises loosely compacted and lightly cemented, cross-bedded peloidal-grainstones. Porosity is lower than that in the upper reservoir because leached intragranular pores are generally absent, but permeability is higher because cementation is relatively light. The lower reservoir is made up of peloidal-grainstones and coarse-grained bioclastic-grainstones. The upper and main reservoirs are separated by a thick interval of relatively tight, thinly bedded, strongly cemented peloidal-grainstones, whereas the main and lower reservoirs are separated only by a thin bed of tight, nodular anhydrite. The pore types and cements observed in the Arab C are similar to those of the Arab A, but dolomitization has resulted in an enhancement of permeability and capillary pressure properties compared to those of the Arab A. Thus, the overall water saturation of the Arab C is lower than that of the Arab A, and the displacement pressures and irreducible water saturations are also significantly lower than those of Arab A carbonates.
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  • 61
    Publication Date: 2007-10-08
    Description: Analyses of porosity and permeability are examined from cores drilled in two Miocene carbonate platforms cored by ODP Leg 194, seaward from the Great Barrier Reef, including one site in the Northern Marion Platform (NMP; mostly preserved as limestone) and two sites in the Southern Marion Platform (SMP; mostly dolomitized). The majority of plug samples are from coarse bioclastic facies and their dolomitized equivalents. Dolomitization probably occurred by circulation of normal to slightly modified sea-water. Increasing fabric destruction at greater depth in the SMP may reflect overprinting of multiple dolomitization episodes in older strata, perhaps related to successive cycles of sea-level fluctuation. Both limestones and dolostones show similarly wide variation in porosity and permeability, reflecting extreme metre-scale heterogeneity of lithologies and diagenetic responses. The limestones show poorer porosity-permeability correlation, with generally lower permeability for given porosity compared with the dolostones, but with similar maximum permeabilities. Despite wide textural diversity, the dolostones cluster along a single trend that parallels the ideal relationship described by the Kozeny equation and characteristic of well-sorted sandstones. The low permeability-for-given-porosity of many limestones is explained by the fine grain size of some samples and, in other cases, by isolation of macropores behind mud matrix. Pore systems in the dolostones, however, tend to be dominated by interparticle macroporosiity, consisting of either relict intergranular pores (grainstones with fabric-preserving dolomitization) or intercrystalline pores (fabric-destructive dolostones and packstones with fabric-preserving dolomitization). Although many dolostones have vuggy pore systems, the vugs appear to be effective for fluid flow because they are connected by the enclosing system of interparticle macropores.
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  • 62
    facet.materialart.
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    In:  Geological Society Special Publication 235: 255-300.
    Publication Date: 2007-10-08
    Description: Carbonates in SE Asia range in age from Palaeozoic to Recent, but are most important as reservoirs in the Neogene where they comprise a major target for hydrocarbon exploration (e.g. Batu Raja Formation, South Sumatra, Sunda and Northwest Java basins). Carbonates of pre-Tertiary, Palaeogene and Neogene age all show a strong diagenetic overprint in which dolomite occurs as both cementing and replacive phases associated with variable reservoir quality. This paper reviews published data on the occurrence and types of dolomites in SE Asian carbonates, and considers the models that have been used to explain the distribution and origin of dolomite within these rocks. Pre-Tertiary carbonates form part of the economic basement, and are little studied and poorly understood. Although some, such as in the Manusela Formation of Seram, may form possible hydrocarbon reservoirs, most are not considered to form economic prospects. They are best known from the platform carbonates of the Ratburi and Saraburi groups. in Thailand, and the oolitic grainstones of the Manusela Formation of Seram. The Ratburi Group shows extensive dolomitization with dolomite developed as an early replacive phase and as a late-stage cement. Palaeogene carbonates are widely developed in the region and are most commonly developed as extensive foraminifera-dominated carbonate shelfal systems around the margins of Sundaland (e.g. Tampur Formation, North Sumatra Basin and Tonasa Formation, Sulawesi) and the northern margins of Australia and the Birds Head microcontinent (e.g. Faumai Formation, Salawati Basin). Locally, carbonates of this age may form hydrocarbon reservoirs. Dolomite is variably recorded in these carbonates and the Tampur Formation, for example, contains extensive xenotopic dolomite. Neogene carbonates (e.g. Peutu Formation, North Sumatra) are commonly areally restricted, reef-dominated and developed in mixed carbonate-siliciclastic systems. They most typically show a strong diagenetic overprint with leaching, recrystallization, cementation and dolomitization all widespread. Hydrocarbon reservoirs are highly productive and common in carbonates of this age. Dolomite is variably distributed and its occurrence has been related to facies, karstification, proximity to carbonate margins and faults. The distribution and origin of the dolomite has been attributed to mixing-zone dolomitization (commonly in association with karstic processes), sulphate reduction via organic matter oxidation, and dewatering from the marine mudstones that commonly envelop the carbonate build-up. Dolomite has a variable association with reservoir quality in the region, and when developed as a replacive phase tends to be associated with improved porosity and permeability characteristics. This is particularly the case where it is developed as an early fabric-retentive phase. Cementing dolomite is detrimental to reservoir quality, although the extent of this degradation generally reflects the abundance and distribution of this dolomite. Dolomitization is also inferred to have influenced the distribution of non-hydrocarbon gases. This is best documented in North Sumatra where carbon dioxide occurs in quantities ranging from 0 to 85%. There are a number of possible mechanisms for generating this CO2 (e.g. mantle degassing), although the most likely source is considered to be the widely dolomitized Eocene Tampur Formation that forms effective basement for much of the basin. High heat flows are suggested to have resulted in the thermogenic decomposition of dolomite with CO2 produced as a by-product.
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  • 63
    Publication Date: 2007-10-08
    Description: The late Varican intermontane Saar-Nahe Basin underwent an intensive episode of synsedimentary intra-basinal magmatism, with magmas ranging from tholeiitic basalts to rhyolites. Volcanism began late in the sedimentary history of the basin, after accumulation of about 5000-5500 m of continental sediments. Basic to silicic maar-diatremes formed mostly on hydraulically active faults or fault intersections. Basic to intermediate sills were emplaced at depths between about 2500 m and almost the original surface. Some sills inflated considerably in thickness. Silicic laccoliths intruded in the same depth range. Ongoing volume inflation of some laccoliths led to huge intrusive-extrusive domes, rock falls and probably block-and-ash flows and even to extensive thick lava extrusions. Some domes are composite or show evidence for magma mingling. In the Baumholder-Idar-Oberstein area, lava flows reach a cumulative thickness of 800-1000 m. Outside this thick lava pile, flows are concentrated in several thinner series. Basic to intermediate lava flows were frequently inflated to a thickness of up to 40 metres and were emplaced like thick flood basalts. Silicic tephra deposits are widespread and mostly phreatomagmatic in origin. The specific formation of maar-diatremes, sills, laccoliths and most tephra deposits is related to the uppermost 1500 to about 2500 m of the continental sediments of the basin fill. During volcanism and subvolcanism, these sediments were largely unconsolidated and water-saturated, and thus this soft sediment environment influenced very specifically the emplacement of the magmas in the basin. Inflation of laccoliths in this environment caused slumping and washing away of the updomed unconsolidated roof sediments. Consequently, the effective initial overburden decreased with time by this particular process of unroofing, and, upon further inflation, larger inflating intrusive domes became extrusive.
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  • 64
    Publication Date: 2007-10-08
    Description: The low- and high-field magnetic anisotropy (AMS, HFA) of the Rhenohercynian mudstones and greywackes is compared to the theoretical anisotropy calculated from neutron texture goniometry measurements. The magnetic anisotropy is predominantly carried by the paramagnetic phyllosilicates in the form of chlorite/mica stacks and the ferromagnetic contribution is insignificant. The respective principal directions of the theoretical anisotropy and the AMS and HFA are sub-parallel; magnetic foliation reflects the orientation of the maximal concentration of phyllosilicate basal planes, magnetic lineation is subparallel to the intersection axis of those planes. For the purpose of quantitative comparison, the infrequently used standard deviatoric susceptibility as a measure of the HFA degree is employed. A very good linear correlation of the degree of theoretical anisotropy and the measured AMS and HFA is found. The prolate and oblate shapes of the respective fabric ellipsoids are reasonably well correlated. Neutron texture goniometry justifies the use of the conventional magnetic anisotropy technique for the assessment of the mineral fabric of studied rocks. When compared with other works relating the magnetic anisotropy to the mineral preferred orientation (examined by e.g. U-stage or X-ray texture goniometry) neutron texture goniometry seems to be a preferable and very precise method fabric analysis.
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  • 65
    facet.materialart.
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    In:  Geological Society Special Publication 238: 9-20.
    Publication Date: 2007-10-08
    Description: The anisotropy of magnetic susceptibility (AMS) of rocks is controlled by preferentially oriented magnetic mineral grains that carry AMS and, therefore, it contains information about both the grain susceptibilities and the grain orientations. Under certain conditions, information about the grain orientations can be deduced from the AMS. For a multigrain system composed of identical grains that are magnetically uniaxial (for the grain principal susceptibilities it holds that K1 > K2 = K3, or K1 = K2 > K3), an exact relationship exists between the AMS and the orientation tensor. We investigate the extent to which the theoretical relationships can be used when grains are generally triaxial. The parallelism of the principal directions of the susceptibility tensor and those of the orientation tensor are well preserved in all basic grain configurations. If grain leading axes have polar or girdle distributions and the two other axes have balanced distributions (similar orientation tensors), the parameters of intensity I and shape T based on the eigenvalues of the orientation tensor are well estimated. For unbalanced distributions, formulas are found for possible errors of I and T estimates.
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  • 66
    Publication Date: 2007-10-08
    Description: Most studies of the anisotropy of magnetic susceptibility (AMS) of dykes have assumed that the axes of maximum susceptibility (kmax) should define an opposed imbrication pointing along the direction of magma flow, and that this orientation should be preserved along the dyke. This assumption is partially based on a model predicting the orientation of ellipsoidal particles floating in a moving liquid although the model actually predicts a cyclic movement of the particles that has been overlooked in msot AMS studies without further justification. The consequences of considering the full rotation of the ellipsoidal particles, as actually predicted by the theory, in the expected AMS of dykes are examined in this work. The complete version of the motion of ellipsoidal particles is then incorporated in a model of magma movement that takes into consideration the distribution of shear deformation within the dyke as predicted from the velocity gradient of the moving magma. Results of this model show that both particle elongation and the amount of shear that is sampled will affect the quality of the AMS results. By paying attention to the systematic variations of the AMS predicted by the theory, however, it is possible to devise sampling schemes that can be used to add more confidence to the interpretation of the AMS results. Although based on an idealized scenario of magma movement within a dyke, the model developed here explains satisfactorily the sometimes observed variation of AMS along flow direction in one dyke, and provides a simple explanation for many of the abnormal' magnetic fabrics that have been reported in dyke swarms around the world.
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  • 67
    Publication Date: 2007-10-08
    Description: The low anisotropies of paramagnetic granites, due to magnetocrystalline anisotropy, require a statistical treatment of the anisotropy of magnetic susceptibility (AMS) data when systematic fabric studies are performed. Absence of statistical information on these data makes evaluation of their quality difficult. The statistical significance of magnetic fabric in granites is evaluated in this paper. Jelinek's elliptical confidence angles for the three principal susceptibility axes (E13, E12, E23) of a specimen are used as markers of the quality of the AMS data. Comparing these markers at sample-, site- and massif-scale with the mean AMS axes that result from spherical statistical models helps clarify the reliability of the AMS data. This analysis is presented in detail for the plutons of Veiga and Trives (Spain). It is then applied to seven other massifs from the Pyrenees. We propose the following guides: (1) fabrics with E13 between 10{degrees} and 20{degrees} tend to isotropy; the directional data and the shape parameter should be considered with great care; (2) lineation is not reliable when E12 > 25{degrees}, i.e. when Kmax is almost the same as Kint; (3) similarly, foliation is considered as not reliable when E23 > 25{degrees}, i.e. Kmin does not easily differentiate from Kint. Errors attached to the mean Kmax and Kmin axes should always be produced, thus allowing further interpretation. In Trives and Veiga, perfect' triaxiality cannot be automatically assumed since foliation and lineation could be defined simultaneously in only 53% of the cases. Finally, a minimum of three cores (9 specimens) per site would considerably increase the proportion of reliable orientation data.
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  • 68
    Publication Date: 2007-10-08
    Description: Low-field magnetic and plagioclase fabrics were compared in Mesozoic mafic dykes of the Rio Ceara-Mirim swarm. Coarse titanomagnetites with pervasive ilmenite lamellae constitute the main carrier of the magnetic anisotropy. The hysteresis parameters of the mafic dykes fall in the pseudo-single domain field. The resulting AMS ellipsoid is usually oblate and has a very low anisotropy (<3%). Textures indicate that the oxi-exolution processes and size reduction of the ferrimagnetic domains occurred at subsolidus temperatures on cooling of the dykes. The magmatic fabric was determined by the shape preferred orientation of plagioclase laths. It rarely matches the magnetic fabric. Besides their contrasting shape ellipsoids, prolate and oblate respectively, their corresponding principal directions diverge from each other or exchange their positions depending on the symmetry of the ellipsoids. These discrepancies are attributed principally to small differences in the net shape of Ti-poor magnetite after exsolution of ilmenite and in the inherently oblique fabric of grains with different shapes. These results draw attention to the need to use independent methods to confirm the conclusions about flow fabrics of weakly anisotropic mafic dykes based only in AMS.
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  • 69
    Publication Date: 2007-10-08
    Description: Rock-magnetic properties, in particular anisotropy of magnetic susceptibility (AMS) were investigated in detail for eight sections transecting southwestern and central parts of Siberia. The results obtained indicate that magnetic properties and magnetic fabrics of loess/palaeosol deposits in western and southwestern Siberia depend on superposition of two different mechanisms namely a pedogenic mechanism proposed for Chinese loess and a wind-vigour mechanism for Alaskan loess. The wind-vigour mechanism is predominant in loess deposits and this allows palaeowind directions during glacial periods to be determined. In palaeosols, the balance between both models strongly depends on the geographical position of the section and thus reflects the palaeoclimate. In western Siberia, palaeosols corresponding to OIS 3 have sedimentary magnetic fabric, while the magnetic fabric of palaeosols corresponding to OIS 5 is completely reworked by pedogenesis. Such differences indicate a warmer climate during OIS 5. In central Siberia, separated from the west by the Kuznetsk Ala-Tau mountain ridge, the magnetic properties and AMS of loess/palaeosol sequences agree with Alaskan' type of loess, suggesting a colder and windier climate during the Late Pleistocene. Therefore, the Siberian subaerial realm may be subdivided into two provinces based on the palaeoclimate conditions prevailing during the Late Pleistocene. These climatic provinces remain in the modern climate.
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  • 70
    Publication Date: 2007-10-08
    Description: We have carried out a magnetic fabric study on deformed, clay-rich rocks from the Carboniferous Texas beds and Coffs Harbour Association in order to test the hypothesis of oroclinal bending of the Texas and Coffs Harbour blocks of the southern New England Orogen, eastern Australia. The magnetic susceptibility is dominated by paramagnetic phyllosilicates, with site-dependent contributions from the ferromagnetic minerals pyrrhotite, magnetite and hematite. Pyrrhotite is ubiquitous in the Texas block and in the central part of the Coffs Harbour block, and may be important as an indicator of the grade of low-temperature metamorphism. The magnetic fabric results, in general, show good agreement with structural observations in the Texas and Coffs Harbour blocks. The magnetic foliation is related to the pervasive cleavage associated with accretionary deformation prior to oroclinal bending. The magnitudes of the anisotropy parameters and the plunge of the magnetic lineation indicate an increase in the intensity of deformation from east of the Coffs Harbour orocline towards the Texas orocline. An imprint from oroclinal deformation is suggested by a significant increase in the anisotropy parameter and by the development of steeply plunging magnetic lineations towards the hinges of the Texas and Coffs Harbour oroclines. The Terrica beds from the Early Permian (Allandale) Terrica inlier in the Texas orocline also show another, pre-tilt induced, tectonic imprint. Remanence data from volcanics in the Alum Rock inlier (293 Ma) and magnetic fabric data from this inlier tentatively constrain the onset of oroclinal bending as prior to extrusion of the Alum Rocks, and the completion of bending as post-Terrica beds deposition and pre-Illawarra Reversal (est. 265 Ma).
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  • 71
    Publication Date: 2007-10-08
    Description: Calcite petrofabrics are sensitive to weak strains, possibly being the most sensitive classical petrofabric indicator. Thus, calcareous sediments may reveal stress trajectories in neotectonic environments. Calcite aligns by crystal-plastic deformation and pressure solution produce corresponding alignments in accessory clay minerals and magnetite (possibly fossil-bacterial). Their alignments are rapidly and precisely detected by anisotropy of low field magnetic susceptibility (AMS) with net magnetic fabrics, which blend diamagnetic contributions from matrix calcite (diamagnetic bulk susceptibility {kappa} [~] -14 {micro}SI), accessory clay minerals ({kappa} = 100 to 500 {micro}SI) and sometimes trace magnetite ({kappa} > 2 SI). Their relative abundances and different anisotropies must be considered in interpreting AMS orientations, nevertheless our study reveals orientation distributions of AMS axes in sub-areas and regions that are sensibly interpreted as palaeostress trajectories in Neogene and Quaternary strata. The AMS axes may be correlated with the orientation of faults, plate-motion vectors and seismic solutions. Large samples (1090 specimens from 419 sites) are treated by different statistical approaches ( standardization') to emphasize or suppress the contribution of subfabrics with anomalous mean susceptibility. A sub-sample of 254 specimens from 219 sites, from different sub-areas was investigated by anisotropy of anhysteretic remanence (AARM), which isolates the orientation distributions of magnetite. Magnetic fabrics are mostly of the L-S kind with the magnetic lineations compatible with gravitational stretching of the sedimentary cover away from the Troodos massif and orthogonal to the principal faults and graben. The L-direction (kmax) shows a smooth variation in orientation, through the sub-areas, directed radially from the Troodos massif and the S-components of the magnetic fabrics are inclined gently to the bedding, compatible with vergence toward the Cyprean Arc to the S and SW of Cyprus.
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  • 72
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 243: 11-24.
    Publication Date: 2007-10-08
    Description: Fracture and vein patterns in the brittle crust of the Earth contain information on the stress and strain field during deformation. Natural examples of fracture and vein patterns can have complex geometries including combinations of extension and conjugate shear fractures. Examples are conjugate joint systems that are oriented with a small angle to the principal stress axis and veins that show an oblique opening direction. We developed a discrete numerical model within the modelling environment Elle' to study the progressive development of fractures in two dimensions. Results show that pure shear deformation alone can produce complex patterns with combinations of extension and shear fractures. These patterns change in geometry and spacing depending on the Young's modulus of the deforming aggregate and the initial noise in the system. A complex deformation history, including primary uniaxial loading of the aggregate that is followed by tectonic strain, leads to conjugate shear fractures. During progressive deformation these conjugate shear fractures may accommodate extensional strain or may be followed by a secondary set of extension fractures. The numerical patterns are consistent with joint, fault and vein geometries found in natural examples. The study suggests that fracture patterns can record complex deformation histories that include primary uniaxial loading due to an overlying rock sequence followed by tectonic strain.
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  • 73
    Publication Date: 2007-10-08
    Description: Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 {degrees}C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate indentation rate and the dry control experiments did not show any measurable deformation. The rate of calcite indentation is found to be inversely proportional to the indenter diameter, thus indicating that the process is diffusion-controlled. The microcracks in the dissolution region under the indenter dramatically enhance the rate of calcite indentation by a significant reduction of the distance of solute transport in the trapped fluid phase. This result indicates that care should be taken in extrapolating the kinetic data of pressure solution creep from one mineral to another.
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  • 74
    Publication Date: 2007-10-08
    Description: Statistical properties of crack-seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks. Crack-seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid. They represent a time-sequence record of an aseismic and anelastic process of rock deformation. The statistical characteristics of several crack-seal patterns containing several hundreds of successive cracks have been studied. Samples were collected in three different areas, gold-bearing quartz veins from Abitibi in Canada, serpentine veins from the San Andreas system in California and calcite veins from the Apennine Mountains in Italy. Digitized pictures acquired from thin sections allow accurate measurement of crack-seal growth increments. All the samples show the same statistical behaviour regardless of their geological origin. The crack-seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation. They differ from other fracture patterns, such as earthquake data, which exhibit power-law correlations (Gutenberg-Richter relationship). Crack-seal series represent a natural fossil record of stress release variations (less than 50 bars) in the crust that show a characteristic length scale, associated with the resistance of rock to effective tension, and no correlation in time.
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  • 75
    Publication Date: 2007-10-08
    Description: An extensive data-set of petrophysical down-hole measurements exists for boreholes drilled into continental crystalline crust. We selected boreholes covering a range of different types of plutonic rocks and gneisses in amphibolite or high-grade metamorphic rocks. According to Serra's concept of electrofacies, a specific set of log responses should characterize one rock type. Here, we concentrate on the detection of compositional variations between rock types. Bulk composition of the protoliths influences the mineralogical composition of the metamorphic rock, and we demonstrate how this impacts on the down-hole measurements. Integration of logging data with geochemical core data and mineralogical descriptions allows the calibration of the log responses to rock types. The relationship of the log responses with core data shows a remarkably good correlation, and diagnostic trends are detected. From the logs, potassium and neutron porosity are particularly helpful in distinguishing different types of gneisses and igneous rocks with respect to their protoliths. The proportions of amphibole/pyroxene, mica + K-feldspar and feldspar + quartz in the rocks seem to control the direction of correlation in a cross-plot, i.e. positive or negative, depending on increasing or decreasing mineral proportions. This is true for all boreholes, and a generalized classification scheme could be developed for these crystalline rocks.
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  • 76
    Publication Date: 2007-10-08
    Description: Problem zones in a sylvinite mine were explored by underground measurements using a set of geophysical methods (geosonar, seismics, georadar, EM methods and geoelectrics), which yield parameter sets for disturbed and undisturbed rock. Underground geo-electrical methods are most suitable for examining humidity content and structures for the transport of brines, although they have to be constrained by wave-propagation methods. Additional laboratory experiments on rock salt samples were carried out in order to provide quantitative evaluation methods. A titration method was used to determine the amount of water. This was applied simultaneously with a four-electrode resistivity measuring system for samples with very high resistivity. These measurements were made on samples at different scales, yielding relationships between water content and resistivity, as well as information about the parameter distribution in larger core samples. Together, the field and laboratory results show that geo-electrics is a suitable method for the detection and evaluation of problem zones of the geological barrier of hazardous waste repositories, and a criterion for the risk assessment based upon resistivity measurements is defined.
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  • 77
    facet.materialart.
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    In:  Geological Society Special Publication 241: NP.
    Publication Date: 2007-10-08
    Description: Often regarded as the Cinderella' of palaeontological studies, palaeobotany has a history that contains some fascinating insights into scientific endeavour, especially by palaeontologists who were perusing a personal interest rather than a career. The problems of maintaining research facilities in universities, especially in the modern era, are described and reveal a noticeable absence of a national UK strategy to preserve centres of excellence in an avowedly specialist area. Accounts of some of the pioneers demonstrate the importance of collaboration between taxonomists and illustrators. The importance of palaeobotany in the rise of geoconservation is outlined, as well as the significant and influential role of women in the discipline. Although this volume has a predominantly UK focus, two very interesting studies outline the history of palaeobotanical work in Argentina and China.
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  • 78
    facet.materialart.
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    In:  Geological Society Special Publication 241: 95-110.
    Publication Date: 2007-10-08
    Description: The need to conserve geological features and palaeontological sites is an increasingly recognized part of conservation policy in many countries. In the USA, Canada and Great Britain this need was emphasized by the discovery in the 19th century of spectacular plant fossils that were in danger of disappearing through overcollecting or through the effects of weathering. People were spurred into action by these all too obvious dangers to save the plant fossils where they had been found as monuments' or records of the past'. The methodology for protection varied from one country to another through differences in both land ownership and legislation. The backgrounds to the discoveries, the reasons for their conservation, and the methods employed for their protection are outlined and discussed. ... This 250-word extract was created in the absence of an abstract.
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  • 79
    facet.materialart.
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    In:  Geological Society Special Publication 241: 1-3.
    Publication Date: 2007-10-08
    Description: This volume concentrates on selected historic aspects of palaeobotany that are, perhaps, hard to find elsewhere. In writing historical accounts it is often of much greater value to provide fresh material concerning little known personages and events rather than re-invent the wheel by going over well-trodden paths more expertly tackled in other works. Therefore we have not endeavoured to include all those who have made substantial contributions to the science, so that there are inevitable gaps and omissions. Instead, we hope that the compilation presented in this volume will be of interest to those who wish to explore some of the byways of our palaeobotanical heritage. A full history of Palaeobotany' has yet to be written, but we hope that this volume may help to spur such future activity. The history of palaeobotany contains fascinating insights into scientific endeavour. In the past it has been too easily dismissed as the Cinderella' of palaeontological studies in which many of the early workers were pursuing personal interests rather than a full-time career. This publication falls into several broad sections with a couple of minor themes occurring throughout. The first two papers serve as an introduction into the early developments of selected aspects of palaeobotany. Wilding briefly examines the work and setting of Robert Plot and Edmund Lhwyd, who laid down foundations for what would eventually become the sciences of palaeontology and Palaeobotany. Torrens looks at the life and work of the Moravian minister, Reverend Henry Steinhauer, who became a disciple of William ... This 250-word extract was created in the absence of an abstract.
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  • 80
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 241: 85-94.
    Publication Date: 2007-10-08
    Description: Baron Achille de Zigno (1813-1892) of Padua published dozens of articles on the early Mesozoic floras from the Venetia region of Italy. His magna opera, however, were the two volumes of the Flora fossilis formationis oolithicae (Volume 1 (1856-1867) and Volume 2 (1873-1885), Padua University Press, Padua). In these he aimed to put the Venetian Jurassic plants in context with what were then considered oolitic floras from around the world. Like many of his contemporaries, his research has been revised both taxonomically and stratigraphically, so that the fossil plants he described from the calcari grigi are now regarded as older than Middle Jurassic. His collection of over 3000 specimens of Italian fossil plants, now kept in the University of Padua, continued to attract researchers during the 20th century from across Europe who used light microscopy to investigate them. Today electron microscopy is being applied to Baron Zigno's specimens that are of importance not only as representatives of a rare Middle Liassic flora but also of value in the palaeobiogeography of the Tethys area in Lower Jurassic times. ... This 250-word extract was created in the absence of an abstract.
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  • 81
    Publication Date: 2007-10-08
    Description: Palaeobotanical studies in the NW of England could be said to originate with Mr William Barton and Charles Leigh in the latter part of the 17th century. These individuals merely noted the existence of fossil plant remains in the Coal Measure deposits around Lancashire. However, it was not until the 19th century before any real studies were carried out on the flora found within the Lancashire Coalfield. The Ravenhead collection is primarily made up of an Upper Carboniferous Langsettian flora, fish and bivalves with some insect remains. The collector was Liverpool Museum volunteer Reverend Henry Hugh Higgins and the collection was made from a railway construction site in 1870. The site exposed two coal seams known as the Upper and Lower Ravenhead Coals. The collection was exhibited at the British Association meeting held in Liverpool in 1870 and at once created a great deal of interest. W. Carruthers remarked upon the fine preservation and the importance of having material where the separate components can now with certainty be shown to be part of the same plant. Higgins published the first paper on the Ravenhead collection in 1871. A year later, museum assistant Frederick Price Marrat produced an extensive paper for the Liverpool Geological Society in which he attempted a more detailed description of the Ravenhead flora. This paper described 58 true and seed fern specimens with variations, nine types that included five holotypes and two syntypes. However, Marrat admitted he found identification of plant remains by relying on external features extremely difficult and Williamson's methods of examining the microstructures of fossilized material were not yet in use. He published a further paper in 1872, listing the Sphenopsids found at the Ravenhead site. The bulk of the Ravenhead collection, including most of the types, survived the May 1941 blitz that virtually destroyed the museum. Unfortunately, all of the Ravenhead display material was lost in the fire. ... This 250-word extract was created in the absence of an abstract.
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  • 82
    facet.materialart.
    Unknown
    In:  Geological Society Special Publication 242: 145-155.
    Publication Date: 2007-10-08
    Description: Phases of activity of four solifluction lobes at an altitude of 750-800 m are dated by tephrochronology at Snaefell, central eastern Iceland (64{degrees}48' N 15{degrees}33' E). The sample includes sorted lobes with tread gradients of 3-11{degrees} and unsorted (turf-banked terraces) in slope-foot locations. Trenches through lobe fronts reveal detailed internal structures picked out by multiple tephra layers. The tephras V1717, V1477, O1362, V870, Hekla-3 (2900 years BP and Hekla-4 (3800 years BP) provide isochronous surfaces of known age whose deformation and disturbance indicate mass movement and/or cryoturbation of the soil cover. Undisturbed soil including the Hekla-3 tephra indicates an absence of solifluction prior to 2900 years BP. Several centuries after Hekla-3, gravel-rich horizons mark wide-spread frost heave and solifluction of hillslopes. Later stabilization of these lobes allowed the accumulation of aprons of aeolian sediment below lee-side risers. These aprons contain in situ mediaeval tephras, dating the inception of solifluction to a considerable time prior to Norse settlement. The likely period of this first phase of solifluction is the Later Bog Period of the Subatlantic, c. 2500-1000 years BP. The aprons are currently being overridden and deformed by solifluction lobes reactivated in the Little Ice Age.
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  • 83
    Publication Date: 2007-10-08
    Description: Fault segments belonging to a fault population can link and interact, eventually forming a single larger fault, and thus affecting the estimation of the maximum expected earthquake. We present throw distribution data along the Quaternary normal faults of the Colfiorito fault system (central Italy), which consists of four main fault segments and where a seismic sequence occurred in 1997-1998. Throw values along the two central overlapping, en-echelon segments (8.5-9.5 km long) were measured on a good stratigraphic marker, by constructing a set of closely spaced geological cross-sections, perpendicular to the fault strike. As these faults are commonly retained active and border Quaternary basins, we compare morphological and geological throws in order to verify the faults neotectonic activity. Geological and morphological throw distributions show good correlation, testifying that recent faulting affected the topographic surface and suggesting that the observed offset completely accumulated during the Quaternary. The throw distribution along the fault segments is asymmetric and reaches maximum values (500-550 m) within the zone of fault overlap, suggesting mechanical interaction between the studied faults. Maximum length-throw correlation suggests that the studied faults grew according to a linear scaling relationship.
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  • 84
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    In:  Geological Society Special Publication 246: 1-21.
    Publication Date: 2007-10-08
    Description: The process of terrane accretion is vital to the understanding of the formation of continental crust. Accretionary orogens affect over half of the globe and have a distinctively different evolution to Wilson-type orogens. It is increasingly evident that accretionary orogenesis has played a significant role in the formation of the continents. The Pacific-margin of Gondwana preserves a major orogenic belt, termed here the Australides', which was an active site of terrane accretion from Neoproterozoic to Late Mesozoic times, and comparable in scale to the Rockies from Mexico to Alaska, or the Variscan-Appalachian orogeny. The New Zealand sector of this orogenic belt was one of the birthplaces of terrane theory and the Australide orogeny overall continues to be an important testing ground for terrane studies. This volume summarizes the history and principles of terrane theory and presents 16 new works that review and synthesize the current state of knowledge for the Gondwana margin, from Australia through New Zealand and Antarctica to South America, examining the evolution of the whole Gondwana margin through time.
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  • 85
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    In:  Geological Society Special Publication 241: 127-135.
    Publication Date: 2007-10-08
    Description: Marie Stopes was unquestionably one of the most remarkable women of the 20th century. The long-term significance of her work in pioneering the defence of women's rights, and in urging the general acceptance of contraception, far exceeds that of her contributions to palaeobotany. Nonetheless, between 1903 and 1935 she published a series of palaeobotanical papers that placed her among the leading half-dozen British palaeobotanists of her time. Her book Ancient Plants (1910; Blackie, London) was a successful pioneering attempt to popularize the subject for a non-botanical audience. Her contributions on the earliest angiosperms, on the formation of coal-balls, and, above all, on the nature and terminology of coal macerals have had a lasting impact on palaeobotanical thought. ... This 250-word extract was created in the absence of an abstract.
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  • 86
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    In:  Geological Society Special Publication 241: 281-292.
    Publication Date: 2007-10-08
    Description: The first records of fossil plants in Argentina were related to the visits of the naturalist-explorers Azara, d'Orbigny, Darwin, de Moussy, Burmeister and Bonpland during the 19th century. The settlement of Burmeister in Buenos Aires in 1862 fostered the arrival of foreign, mostly German, scientists to work in, or closely related to, the School of Sciences in Cordoba. Among them were Stelzner, Brackebusch, Doering, Zuber, Ave-Lallemant, Hautal, Berg, Kurtz and Bodenbender. Fossil plants they collected were studied in part in Europe by Geinitz, Conwentz and Szajnocha, but also received opportune comments by Schenck, Nathorst, Zeiller and Ward. The first Argentine scientists who quoted the presence of fossil plants were Moreno, Lista, Fontana and Aguirre. The record of Tertiary plant remains from Tierra del Fuego by the Romanian explorer Popper and the Swedish Nordenskjold and Dusen completed the palaeobotanical studies in Argentina during the 19th century. ... This 250-word extract was created in the absence of an abstract.
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  • 87
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    In:  Geological Society Special Publication 241: 229-257.
    Publication Date: 2007-10-08
    Description: The year 2001 marked the 150th anniversary of the appointment of William Crawford Williamson to the Chair of Natural History at Owens College, which later became the Victoria University of Manchester. Since 1851 a palaeobotanical presence in Manchester has been continuous, apart from 1940 to 1950. The history of the various incumbents in academic posts and their contributions are charted and discussed. They include Williamson, Weiss, Lang, Stopes, Walton and Watson. Other palaeobotanists associated with Manchester were students, museum staff or incumbents of various ancillary appointments, and there were many distinguished visitors. The total number of students registered for higher degrees is remarkably few, nearly half studying with Watson in the past 20 years. The proportion of women palaeobotanists, counting staff and postgraduate students, is very high. The research output from Manchester includes most British fossil floras, and impressive attention to devising and improving laboratory techniques from Williamson to the present day. There is evidence that palaeobotany in Manchester has been considered an anachronism even from Williamson's time and it now faces extinction in 2005. ... This 250-word extract was created in the absence of an abstract.
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  • 88
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    In:  Geological Society Special Publication 245: 329-346.
    Publication Date: 2007-10-08
    Description: Zones of localized strain are common geological features at all spatial scales, are persistent in time and have important implications for rock strength. Technical advances now allow mechanical tests to be carried out to high strain, and, thus, there is both need and the opportunity to formulate constitutive laws for rocks as their structure (i.e. fabric, texture and mineralogy) changes. This paper reviews some attempts to describe quantitatively the mechanical behaviour of calcite rocks deformed to large strains. To include the effect of evolving structure on strength, three or more interlinked laws are needed: an evolution equation describing the rate of change for each structural variable; a kinetic equation relating mechanical and thermodynamic loading and the structural variables to the rate of strain; and a kinematic equation involving a time integral of inelastic strain rate. Structure variables may be explicitly identified or implicitly determined without identification. Appropriate explicit state variables might include aspects of the dislocation microstructure or the grain size, as are common in studies of plasticity in metals. But because natural tectonic situations are more complex, a much broader class of state variables will be needed. Among these additional variables might be crystal lattice preferred orientation, progress variables for metamorphic reactions, solid-solution chemistry, porosity and pore fluid fugacity.
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  • 89
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    In:  Geological Society Special Publication 245: 347-372.
    Publication Date: 2007-10-08
    Description: This paper examines how crystalline basement thrust sheets can detach in foreland thrust belts, in terms of the deformation mechanisms and rheological evolution of the detachment fault zones. Basement thrust fault zones of the Moine Thrust Belt and the external Western Alps show relatively narrow thrust zones considering the large displacements accommodated. Microscopic examination of fault rocks from these high strain thrust zones show that syntectonic alteration of fractured feldspars to white mica of strong preferred orientation generated ultramylonites deforming by diffusion creep and other viscous deformation mechanisms, similar to documented basement thrust zones in North America. Motivated by these observations coupled with other published examinations of foreland basement thrust zones, and recent developments in crustal hydrology, a conceptual model is proposed to explain basement detachment formation and evolution. Meteoric fluid that percolated into a previously fractured upper crust is drawn into developing fault zones by dilatancy pumping during the early stages of thrust-related deformation. The generation of cataclastic fault rocks with fresh fracture surfaces by microfracturing enhances the rate of fluid-rock interaction. Syntectonic alteration causes a deformation-mechanism transition to phyllosilicate-dominated ductile fault-rock rheologies, resulting in a large ductility contrast between host rock and fault zone that inhibits growth of the zone into the wall rock and weakens the thrust. Deformation becomes focused into these weakened early thrust zones so that they become zones of high strain, preventing the development of other newer fault zones elsewhere. This model explains the detachment and continued sliding of basement thrust sheets on narrow mica-rich zones of high strain in foreland thrust belts, and suggests that reaction weakening of the basement is important in decreasing the strength of the foreland crust in orogenic wedge evolution.
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  • 90
    Publication Date: 2007-10-08
    Description: We interpret the strain and stress fields of the western/central Alpine arc on the basis of 2.5D finite element modelling and a recent seismotectonic synthesis. Models have fixed boundary forces and different crustal geometries, so that they respond to buoyancy forces (variations in gravitational potential energies). The seismotectonic regime, characterized by orogen-perpendicular extension in the high topographic core of the belt and local orogenperpendicular compressional/transpressional deformation in the external zones, appears to be very close to the modelled gravitational regime. Rotation of Apulia has a minor effect on the current strain or stress fields of the Alpine realm. Nevertheless, it could help to explain the orogen-parallel dextral faulting that is observed all along external zones, from the northern Valais to the Argentera external crystalline massif. Our results highlight the consequences for the Alpine realm of ongoing convergence between the African and European plates. Our interpretation is that collision is no longer ongoing and that buoyancy-driven stresses dominate the present-day geodynamics of the western/central Alps.
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  • 91
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    In:  Geological Society Special Publication 246: 275-291.
    Publication Date: 2007-10-08
    Description: The early Palaeozoic Ross Orogen in northern Victoria Land, Antarctica, consists of three major fault-bounded tectonostratigraphic terranes. Their true nature, fartravelled or local part of the accretionary collage, is under discussion. The inboard Wilson terrane (WT) consists mainly of high-grade metamorphic rocks intruded by the calcalkaline magmatic arc of the Ross Orogen. The terrane nature of the WT is doubtful, as it appears more like the leading edge of the East Antarctic craton. The Bowers terrane (BT) comprises a mixed sedimentary-volcanic succession, beginning with volcanic rocks of island-arc character, followed by turbidites, mudstones, conglomerates and fossiliferous Middle Cambrian shallow-water sediments. The whole sequence is capped by a fluvial to deltaic quartizitic series several kilometres thick, with strong continental affinity. The combination of primitive forearc to back-arc volcanics at the bottom and mature continental sediments at the top poses a problem. The outer Robertson Bay terrane (RBT) is made up of a thick turbidite succession which, in one area, contains allochthonous blocks of fossiliferous Tremadocian limestones. All terrane boundaries appear to be distinct fault zones. The WT/BT boundary forms a deep-reaching continent-ocean suture associated with strongly sheared rock units, ultramafic lenses and high-pressure rocks. Coesite in eclogites of the Lanterman Range indicates a depth of burial of around 90 km. A greenschist-facies schist belt marks the BT/RBT boundary. The terranes contain evidence for subduction at an active margin setting as well as for accretion processes along major faults. The present changes of the Cambrian time-scale, such as younging of the base of the Upper Cambrian by about 30 Ma since the 1980s, allow separation of arc formation and later terrane accretion events.
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  • 92
    Publication Date: 2007-10-08
    Description: Basement inliers of high-grade metamorphic rocks within the eastern Colombian Andes record a Grenvillian history. Among them, the Garzon Complex and the Dibulla, Bucaramanga and Jojoncito gneisses were studied using different geochronological methods to produce better correlations in the context of the reconstruction of the Grenville belt and of the supercontinent of Rodinia. The dynamic evolution of all of these units includes a final collisional event with exhumation of high-grade rocks. Such a tectonic history bears strong similarities with the Grenville Province in Canada and seems to confirm that these domains took part in the aggregation of Rodinia. Mesoproterozoic U-Pb zircon ages indicate heritage from magmatic protoliths, and the Sm-Nd model ages, as well as the {varepsilon}Nd values, suggest derivation from an evolved continental domain, such as the Amazonian craton, with some mixing with juvenile Neoproterozoic material. When these continental fragments are correlated with similar terrains in Mexico and the Central Andes, a large crustal fragment is implied; very probably it made up the southern portion of the Grenville belt within Rodinia, which was disrupted when Laurentia separated from Gondwana forming the Iapetus Ocean, leaving behind cratonic fragments that were later accreted to the South American Platform.
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  • 93
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    In:  Geological Society Special Publication 245: 277-290.
    Publication Date: 2007-10-08
    Description: Evaporitic minerals, such as gypsum, within sedimentary sequences play an important role in localizing deformation, especially in thrust tectonics, implying that their strength is generally lower than that of other rocks. To study the rheological and microstructural evolution of gypsum with strain, a set of experiments was performed on natural gypsum samples from Volterra (Italy). To reach high shear strain (up to {gamma} = 5), deformation tests were performed in torsion at 300 MPa confining pressure, at temperatures up to 127 {degrees}C, and at shear strain rates between 10-3 and 10-5 s-1. All samples were studied by optical microscopy, to investigate the evolution of the microstructure with strain, and by X-ray diffraction (XRD) analyses, to determine whether and to what extent gypsum dehydrated during deformation. The shear stress increased with shear strain rate and decreased with temperature. A peak stress was usually reached at {gamma} between 0.5 and 1.5. After the peak, 30-40% of weakening occurred but mechanical steady-state conditions were never reached. The microstructure evolved from a plastic deformation microstructure, where grains changed shape according to the bulk strain imposed, into a recrystallization-dominated microstructure, where grains were more equant. The shear stress sensitivity to strain rate increases with progressive strain, thus a meaningful constitutive flow law can only be determined from experiments in which steady-state flow is eventually reached. These results imply that gypsum in nature will flow plastically at shear stress levels lower than those expected from previous experimental studies due to the strain weakening associated with dynamic recrystallization, which can occur at temperatures even lower than gypsum dehydration.
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  • 94
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    In:  Geological Society Special Publication 247: 231-249.
    Publication Date: 2007-10-08
    Description: Faunal change at the Early-Middle Pleistocene boundary in Europe has long been a topic for discussion. However, analyses of large mammal turnover at this time in Africa have been lacking, largely because of the low number of sites dated to this interval. Recent work, particularly in the last 10 years, has resulted in a much larger published sample of sites and we synthesize these data in this paper. In our multivariate (TWINSPAN) analyses of African and Levantine large mammal faunas we found that localities were subdivided by geographic regions, not by age. There were some small-scale changes with the appearance or extinction of particular taxa, but there was no large-scale turnover such as that seen in Europe. The Levant was included as a possible route for faunal interchange with east Africa, but no similarities were found between these areas. It therefore appears that the modern zoogeographic separation of the Levant and north Africa into the Palaearctic region and sub-Saharan Africa into the African region can be traced back to at least the Early-Middle Pleistocene boundary.
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  • 95
    Publication Date: 2007-10-08
    Description: Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.
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  • 96
    Publication Date: 2007-10-08
    Description: Quantitative analyses of the calcareous nannofossil Reticulofenestra asanoi and related species have been performed on the Early-Middle Pleistocene transition in the Mediterranean Sea (ODP Sites 976 and 963) and Atlantic Ocean (DSDP Hole 610A) in order to improve the understanding of their stratigraphic distributions. Abundance patterns have allowed the identification of the lowest common occurrence (LCO) and highest common occurrence (HCO) of R. asanoi in a short interval below and above the lowest occurrence of Gephyrocapsa sp. 3. Correlation with oxygen isotope stratigraphy at Site 976 places the LCO of R. asanoi at the Marine Isotope Stage (MIS) 34-33 transition and its HCO at the MIS 23-22 transition. At Site 963, the HCO of R. asanoi (estimated age of 0.96 Ma correlated to MIS 25) is regarded as artificially' low, and its highest occurrence (estimated age 0.90 Ma correlated to MIS 23) has therefore been used for bio-chronostratigraphic correlation. The LCO of R. asanoi is estimated at 1.05 Ma at Site 963 and 1.17 Ma at Hole 610A, which suggests correlation to MIS 30 and MIS 35, respectively. These data suggest a possible diachrony for the LCO of R. asanoi.
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  • 97
    Publication Date: 2007-10-08
    Description: This review focuses on the loess-palaeosol record across the Early-Middle Pleistocene transition to show the main structural features in key sections from the Loess Plateau of China via central Asia to Europe. Loess-palaeosol sequences in general demonstrate an impressive coherence with oxygen isotope osillations, providing a high-resolution terrestrial record for stratigraphic subdivision. Accordingly, they are considered useful for detailed climatostratigraphy and correlation. Nonetheless, there are many uncertainties in loess-palaeosol stratigraphic correlation across the Early-Middle Pleistocene transition from region to region within northern Eurasia. The interval between the top of the Jaramillo Subchron and the Matuyama-Brunhes (M-B) Chron boundary is discussed in detail because it embraces suitable horizons for placing the Early-Middle Pleistocene boundary. This interval contains a variable number of loess and palaeosol horizons in sections along the different loess provinces from east to west. A distinctive palaeosol unit just below the M-B reversal can serve as a marker horizon for establishing the Early-Middle Pleistocene boundary. In south Tajikistan, it corresponds to the pedocomplex 10 (PC10) and to palaeosol S8 in the Loess Plateau of China. The base of this soil horizon correlated with the base of Marine Isotope Stage 21 can be considered as a distinctive geological level for recognizing the Early-Middle Pleistocene boundary on the continent.
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  • 98
    Publication Date: 2007-10-08
    Description: A late Early Pleistocene pollen record was obtained from a coastal site in Auckland, New Zealand. A combination of isothermal plateau fission track ages on interbedded tephras, palaeomagnetism, palynostratigraphy and orbital tuning to the marine oxygen isotope record of Ocean Drilling Program Site 677 constrained the age of the topmost 28 m of sediments to c. 1.4-1.0 Ma (Marine Isotope Stages (MIS) 45-28). For this interval a diverse pollen record consisting of mostly extant pollen types shows multiple compositional shifts from a Nothofagus-dominated to conifer-dominated regional vegetation. These shifts are broadly correlated to changes in the marine oxygen isotope record. The inferred climate was moist, temperate, stable, and cooler than at present, but never as cool as the last glacial maximum. A permanent increase in Nothofagus forest in the region after MIS 35 seems to be related to a long-term palaeoclimatic shift that probably included greater temperature extremes between warm and cool stages and decreases in humidity and increased seasonality during cool stages. Although the Patiki pollen record predates the mid-Pleistocene revolution by c. 100 ka, the nature of climate change itself was already in transition, and becoming more similar to the climate regime experienced in northern New Zealand in the Late Pleistocene.
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  • 99
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    In:  Geological Society Special Publication 247: 221-229.
    Publication Date: 2007-10-08
    Description: The end of the Early Pleistocene is intriguing particularly for mammalian palaeontologists. In Eurasia, this interval has a faunal turnover caused by both the evolution and migration of species. It is the time in which the famous end-Villafranchian event' takes place, a phenomenon characterized by a faunal turnover resulting mainly from the migration of larger mammals. The smaller mammal record reveals in particular an important radiation in medium-sized voles. Different Microtus species evolve rapidly from species of the genus Allophaiomys, and various lineages can be observed. This radiation finally leads to the diversity seen today. In eastern Europe, particularly on the Russian Plain and the Taman Peninsula, a number of localities occur where faunal assemblages from well-dated stratigraphic sequences can be analysed. These assemblages show the mid-Pleistocene evolution of rodent faunas within eastern Europe. Identical and synchronous changes in the mammalian faunas are found in other parts of Europe. However, a fauna from Untermassfeld in Germany does not fit this general picture, and serious doubts about its published age must be considered.
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  • 100
    Publication Date: 2007-10-08
    Description: The region of the gold-rich Ashanti belt in southern Ghana was chosen as the subject for a detailed regional thermal modelling study. Geological studies, in addition to laboratory measurements of thermal properties and heat-production rates, allow us to constrain a finite-element thermal modelling. Scenarios intergrating variations of the structure of the crust and various chronological settings were examined. We calculated the thermal regime before and after the thrust tectonism that affected the region during the Eburnean orogeny (2130-2095 Ma), just before ore deposit formation. This gives a new insight into the regional thermal state of the crust before the mineralizing events. To satisfy the thermobarometric observations, the most probable mantle heat flow must be 60 mW m-2, which is at least three times greater than the present-day value. At shallow depths, our results also indicate anomalies of lateral heat flow reaching 25 mW m-2, focused on the margins of each lithological unit, including the Ashanti belt. These anomalies are related to the distortion of the isotherms in the first few kilometres that can be explained mostly by lateral contrasts in thermal conductivity. Such anomalies could be of importance for the mineralizing events, as they would favour fluid circulation locally.
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