bluuebunny/crossref_metadata_2025_split huggingface dataset:
FTIR remote sensing of fractional magma degassing at Mount Etna, Sicily
Authors: Burton M. , Allard P. , Murè F. , Oppenheimer C. 
Published: April 2008

Abstract

The chemical composition of volcanic gas emissions from each of the four summit craters of Mount Etna was measured remotely in May 2001, using a Fourier transform infrared (FTIR) spectrometer operated on the upper flanks of the volcano. The results reveal constant HCl/HF ratio but distinct SO
2
/HCl and SO
2
/HF ratios in the emitted gases, which, in the light of melt inclusion data for Etna basalts, can be interpreted in terms of escape of gases from partially, and variably, degassed magma at different depths beneath the summit. Gases released from the three main summit craters (Bocca Nuova, Voragine, and Northeast) had an identical composition, controlled by bulk degassing of a single magma body that had previously lost
c.
25% of its original sulphur. The similar gas composition at all three main craters suggests that these are connected to a central conduit system that branches at relatively shallow depth. Measurements of the bulk volcanic plume on the same day,
c.
7 km downwind, show that degassing from these craters dominated the total gas output of the volcano, and that no significant chemical evolution occurred within the plume over a time-scale of
c.
12 min. Weaker gas emissions from the Southeast crater were comparatively depleted in SO
2
(SO
2
/HCl and SO
2
/HF ratios a factor of two lower), implying that this crater is fed either by a separate conduit or by a branch of the central conduit whose geometry favours solubility-controlled volatile fractionation. Still lower SO
2
/HCl and SO
2
/HF ratios measured for residual degassing of a lava flow erupted from the Southeast crater verify the lower solubility and earlier escape of sulphur compared to halogens at Etna. Fractional magma degassing is also implied by strong chemical contrasts between the bulk volcanic plume and fissure gas emissions measured during the July-August 2001 flank eruption. These results highlight the ability of FTIR spectrometry to detect fine spatial and temporal variations in magma degassing processes, and thereby constrain models of shallow plumbing systems.
Changes in stratospheric composition, chemistry, radiation and climate caused by volcanic eruptions
Authors: Grainger R. G. , Highwood E. J. 
Published: April 2008

Abstract

The primary effect of a volcanic eruption is to alter the composition of the stratosphere by the direct injection of ash and gases. On average, there is a stratospherically significant volcanic eruption about every 5.5 years. The principal effect of such an eruption is the enhancement of stratospheric sulphuric acid aerosol through the oxidation and condensation of the oxidation product H
2
SO
4
. Following the formation of the enhanced aerosol layer, observations have shown a reduction in the amount of direct radiation reaching the ground and a concomitant increase in diffuse radiation. This is associated with an increase in stratospheric temperature and a decrease in global mean surface temperature (although the spatial pattern of temperature changes is complex). In addition, the enhanced aerosol layer increases heterogeneous processing, and this reduces the levels of active nitrogen in the lower stratosphere. This in turn gives rise to either a decrease or an increase in stratospheric ozone levels, depending on the level of chlorine loading.
Environmental impacts of tropospheric volcanic gas plumes
Authors: Delmelle P. 
Published: April 2008

Abstract
Recent studies suggest that the environmental effects of volcanic gas emissions in the lower troposphere have been underestimated. This chapter first briefly summarizes the techniques available for characterizing tropospheric volcanic gas plumes, including the composition and fluxes of emitted gases and aerosols, as well as their atmospheric dispersion. The second part documents the contribution of gas emissions from degassing craters to the composition of the atmosphere, including effects from dry and wet deposition chemistry. The third section deals with the detrimental impacts on vegetation, soils, and groundwater in relation to passive degassing activity. Improved understanding of the impacts of volcanic degassing on the atmospheric and terrestrial environment will require: (1) systematic two-dimensional and three-dimensional measurements of tropospheric volcanic plumes, (2) development of general physical and chemical models to describe the fate of volcanic gases and aerosols during transport in the troposphere, and (3) investigation of the response of diverse ecosystems to volcanogenic air pollution.
Occurrences of hydrocarbons in and around igneous rocks
Authors: Schutter Stephen R. 
Published: April 2008

Abstract
Data on the occurrence of hydrocarbons in and around igneous rocks show them to be global in extent, occurring in over 100 countries worldwide. While this list is not exhaustive, it is possibly the first of its kind to be published, and will serve as a useful source of reference for those wishing to embark on further study.
Fracture formation and evolution in crystalline rocks: Insights from attribute analysis
Authors: McCaffrey K. J. W. , Sleight J. M. , Pugliese S. , Holdsworth R. E. 
Published: April 2008

Abstract
Fractures are ubiquitous in crystalline rocks and control the strength and geophysical and fluid transport characteristics of the Earth’s upper crust. A quantitative description of fracture attributes may constrain models of fracture formation and evolution. In this study, fracture attributes collected from one-dimensional samples across exposures of typical crystalline rocks show comparable variability in fracture size and spacing to sedimentary rocks. Vein thickness and fracture aperture data show predominately power-law distributions. Vein and fracture spacing data are best described by exponential distributions with negative slopes and appear to vary with composition in intrusive rocks. The fracture systems exhibit a range of anti-clustered to clustered patterns, and densities are an order of magnitude higher for joints compared to veins. Fracture clustering data can be used in conjunction with the spatial distributions to provide information on the controlling processes of fracture spacing. We suggest that exponential spacing distribution is produced as a sampling effect for both periodic-spaced and clustered fracture sets. In the examples given here, thermal stress-related joint patterns are distinguishable from tectonic-related fractures in plutonic rocks and fracture density and clustering is increased towards a major reactivated basement fault.
Quantitative characterization of fracture apertures using microfocus computed tomography
Authors: Vandersteen K. , Busselen B. , Van Den Abeele K. , Carmeliet J. 
Published: April 2008

Abstract
Microfocus X-ray computed tomography (μCT) was used as a tool to determine the apertures of a fracture in a cylindrical sample of crinoidal limestone. After scanning, artefacts were removed from the images. Phantom objects were used to establish a calibration relationship between real fracture apertures and fracture aperture measurements on the μCT images. The performance of different procedures for quantitative fracture determination was examined. The calibration relationship was then used to determine the fracture apertures in a naturally fractured sample. A comparison of the μCT technique and a microscope technique shows a good agreement between their results.
Direct imaging of fluid flow in fault-related rocks by X-ray CT
Authors: Hirono T. , Takahashi M. , Nakashima S. 
Published: April 2008

Abstract
Faults profoundly affect patterns and rates of fluid flow and solute transport in the geological environment. They may act as conduits, barriers or combined conduit-barrier systems. In order to elucidate the relationship between fluid flow properties and deformation mechanisms of fault-related rocks, we applied X-ray CT during laboratory permeameter measurements for direct imaging of fluid flow during permeability testing. A KI solution, which has high X-ray attenuation values, was used as a contrast medium for the advection imaging. Three-dimensional fluid flow distributions were measured for the studied fault-related rocks. Fault zones characterized by independent particulate flow as deformation mechanism act as conduits for fluid flow, whereas cataclastic fault zones act as barriers.
Evaluation of local porosity changes in limestone samples under triaxial stress field by using X-ray computed tomography
Authors: Karacan C. O. , Grader A. S. , Halleck P. M. 
Published: April 2008

Abstract
The character of reservoir rocks is uncertain and variable at the depths where they are subjected to different tectonic forces and pressure changes due to drilling, well stimulation and production operations. The stress- and time-dependent deformation of the porous structure is expected to change the behaviour of the most important properties of the rock, such as porosity and permeability, which in turn changes the reservoir production predictions.
In this study, we demonstrate the use of X-ray computed tomography (CT) to investigate the porosity and permeability changes of Cordova Limestone samples during deformation in a triaxial cell. The experiments were performed in a specially designed X-ray transparent triaxial test cell, which enables applying stress as well as making flow measurements. Because the presence and value of confining pressure changes the deformation behaviour of the rock, different constant confining stresses were applied to the samples to change the deformation regime. As the axial load was increased, samples were scanned at different locations to determine the stress-dependent local changes in porosity. Absolute permeability during the deformation was also measured.
Results show that the stress condition applied to the porous medium changes the rock and fluid transport properties, compared to measurements taken without stressing the sample. X-ray CT enabled the local porosity changes to be quantified, to locate compaction bands and places where shear location occurs, and to evaluate how the inner structure of the rock changes during different modes of deformation.
Monitoring void ratio redistribution during continuous undrained triaxial compression by X-ray computed tomography
Authors: Thomson P. R. , Wong R. C. K. 
Published: April 2008

Abstract
It is usually implied that void ratio of a soil specimen is homogeneous and unchanging during an undrained triaxial test. In this study, X-ray computed tomography was used to measure void ratio redistribution during undrained triaxial compression of a cohesionless soil sample. A specially designed triaxial apparatus was used to scan the same sample at different axial strain levels, while the axial loads and confining pressures were maintained. Significant variation in sample void ratio was observed at the end of consolidation and sample uniformity was found to increase with increasing axial strain. The process of void ratio redistribution can be effectively illustrated in void ratio-effective stress space.
The use of X-ray computed tomography in the investigation of the settlement behaviour of compacted mudrock
Authors: O’Neill M. A. , Goodwin A. K. , Anderson W. F. 
Published: April 2008

Abstract
The material used in the restoration of opencast coal mines is made up predominantly of mudstone particles ranging in size from less than 60 μm to more than 60 mm nominal diameter. Post-compaction settlements are mainly sub-divided into short-term ‘collapse’ and long term ‘creep’ components, both of which can be very large and often significantly reduce the development potential of restored opencast sites. As the mechanics of these movements are poorly understood at present, X-ray computed tomography (CT) was used to investigate the fundamental nature of particulate interactions within specimens of backfill undergoing long-term creep settlement.
The preliminary results from a series of CT analyses of a number of large scale specimens are presented. Different CT procedures were used and an indication for best practice for scanning of large samples has been found. Qualitative interpretation of the images obtained to date is presented in terms of fill structure, particulate changes during settlement and effects of arching. Indications are that particle breakage is a less significant mechanism than previously thought, and that local collapse of voids, particle sliding and particle rotation are the dominant mechanisms. Quantitative data to be extracted from the images may lead to a probabilistic approach to the prediction of settlement. This possibility is noted, as is the potential for the wider use of CT in geotechnical engineering.
The Vocontian clastic dykes and sills: a geometric model
Authors: Parize O. , Friès G. 
Published: April 2008

Abstract
Distal Aptian-Albian deep water channelled massive sands of the Vocontian Basin (SE France) are often associated with sand injections. The Bevons and Rosans areas in the Vocontian domain present probably the most spectacular outcrops showing complex networks of clastic sills and dykes injected into a thick marly/limy succession. Most injections are found in the channel banks, fed laterally from sandy channels. The sills are up to 10 metres thick in the vicinity of the connection with the channel feeder; they thin out and die into marls 2 or 3 kilometres away from it. Most dykes are injected from the sills rather from the channel itself: a few small dykes can be found under the channel fill. They are most abundant within a few hundred metres of the channel. Today, injections extending downwards from sills have up to 275 metres vertical extent, whereas injections extending upwards from sills never reach the contemporaneous palaeo-sea floor. Ptygmatic folding of the dykes by mechanical compaction indicates the amount of local post-injection compaction of shale and clearly shows that sand injection occurred prior to burial. Outcrop mapping shows that channel bank fracturing is contemporaneous with channel infilling. This is evidence of early syn-depositional injection of the sandy material. Vocontian clastic injections provide good geometrical analogues to deep offshore clastic injectite networks and the opportunity to better understand genetic processes.
Deformation structures in Plio- and Pleistocene sediments (NW Bohemia, Central Europe)
Authors: Bankwitz P. , Bankwitz E. , Bräuer K. , Kämpf H. , Störr M. 
Published: April 2008

Abstract

The small intracratonic Cheb (Eger) Basin in NW Bohemia (Central Europe) is characterized by swarm earthquakes, many mineral springs and mofettes with upper mantle CO
2
degassing and by neotectonic graben and basin structures. Especially in non-lithified Upper Pliocene clay formations of the basin, a variety of deformation patterns is exposed. They include non-tectonic and tectonic activity and comprise faulting and folding from µm- to km-scale. Previously unrecognized N-S- and ENE-striking faults are sites of mantle degassing and seismic activities. Confined-layer deformation and liquefaction structures hint to palaeoseismic events and gas escape activity. Cleavage-like arranged clay mineral plates represent the microfabric of clay within fault zones. For the first time the degassing channels of Upper Mantle fluids/gases through the Pliocene clay sediments can be documented: µm-scale micro-tubes were produced by the opening of Riedel shear planes induced by fault movements.
Gas and fluid injection triggering shallow mud mobilization in the Hordaland Group, North Sea
Authors: Løseth Helge , Wensaas Lars , Arntsen Børge , Hovland Martin 
Published: April 2008

Abstract
During a regional seismic interpretation study of leakage anomalies in the northern North Sea, mounds and zones with a highly chaotic seismic reflection pattern in the Tertiary Hordaland Group were repeatedly observed located above gas chimneys in the Cretaceous succession. The chaotic seismic reflection pattern was interpreted as mobilized sediments. These mud diapirs are large and massive, the largest being 100 km long and 40 km wide. Vertical injections of gas, oil and formation water are interpreted to have triggered the diapirs.
On the eastern side of the Viking Graben, another much smaller type of mud diapir was observed. These near-circular mud diapirs are typically 1–3 km in diameter in the horizontal plane. Limited fluid injection from intra-Hordaland Group sands, through sand injection zones, into the upper Hordaland Group is interpreted to have triggered the near-circular diapirs.
This observed ‘external’ type of mobilization was generated at shallow burial (<1000 m) and should be discriminated from the more common ‘internal’ type of mud diapirism that is generated in deep basins (>3000 m). The suggested model has implications for the understanding of the palaeofluid system, sand distribution, stratigraphic prediction within the chaotic zone, seismic imaging, and seismic interpretation of the hydrocarbon ‘plumbing’ system.
Sinuous pockmark belt as indicator of a shallow buried turbiditic channel on the lower slope of the Congo basin, West African margin
Authors: Gay A. , Lopez M. , Cochonat P. , Sultan N. , Cauquil E. , Brigaud F. 
Published: April 2008

Abstract
Pockmarks on the slope of the Lower Congo Basin are distributed along a meandering band on seafloor coincident with a shallow buried palaeochannel imaged from the 3D-seismic database. Each pockmark originates systematically at the channel-levee interface and the seafloor expression of the palaeochannel’s sinuosity is mimicked by the sinuous trend of pockmarks. 3D-seismic on the slope, calibrated by biostratigraphic data from cores of the Leg ODP 175, indicate a seaward decrease of the sedimentation rate. We suggest that this condition induces a differential loading of the hemipelagic cover over the palaeochannel and propose a model for episodic dewatering of fluids trapped in the buried turbiditic channel. The consequence is a fluid flow caused by a longitudinal pressure gradient along the buried channel. A hydromechanical model proposed for the formation of shallow pockmarks indicates that the sedimentation rate cannot generate the overpressure required for pockmark formation on the seafloor. Therefore, it is suggested that hydrocarbon migration from deeper overpressured reservoirs is added to the pore fluid pressure in the shallow subsurface sediments. Horizontal drainage by the turbiditic palaeochannel and vertical migration along many vertical conduits (seismic chimneys) probably initiated at shallow subbottom depth. It is concluded that these shallow processes have important implications for fluid migration from deeply buried hydrocarbon reservoirs.
Polygonal fault systems on the mid-Norwegian margin: a long-term source for fluid flow
Authors: Berndt Christian , Bünz Stefan , Mienert Jürgen 
Published: April 2008

Abstract
2D and 3D seismic data from the mid-Norwegian margin show that polygonal fault systems are widespread within the fine-grained, Micene sediments of the Kai Formation that overlie the Mesozoic/Early Cenozoic rift basins. Outcropping polygonal faults show that de-watering and development of polygonal faults commenced shortly after burial. On the other hand, the polygonal fault system’s stratigraphic setting, upward decreasing fault throw and the association with fluid flow features that are attributed to de-watering of the polygonal fault systems shows that polygonal faulting and fluid expulsion is an ongoing process since Miocene times.
Soft-sediment deformation in Lake Superior: evidence for an immature Polygonal Fault System?
Authors: Wattrus N. J. , Rausch D. E. , Cartwright J. 
Published: April 2008

Abstract
New multi-beam sonar and seismic data collected in Lake Superior document the wide-spread development of lake-floor rings in fine-grained lake-floor sediments. The multi-beam images reveal that the rings develop as connected clusters and that individual rings have an irregular polygonal appearance. High-resolution seismic data collected with a 28 kHz echo sounder reveal extensive fracturing and faulting in the glacio-lacustrine sediments below the lake-floor. Displacement on the faults is typically normal with throws of less than 50 cm. Three styles of faulting are recognized: (a) monoclinal flexure; (b) graben-like; and (c) conjugate. Zones of acoustic blanking below the faults may be associated with de-watering and mobilization of the sediments. Lateral thickness variation in some horizons suggests that fault and fracture development is linked with lateral movement of sediment. Piston cores collected near lake-floor rings show well-developed fractures and micro-faults, suggesting that fracturing and faulting occurs on a wide range of scales. The seismic and lithological characteristics of the glacio-lacustrine section are similar to those of sediments in which Polygonal Fault Systems (PFS) have been described. This suggests that the rings in Lake Superior may be the surface expression of PFS in the near-surface sediments.
Outcrop examples of mudstone intrusions from the Jerudong anticline, Brunei Darussalam and inferences for hydrocarbon reservoirs
Authors: Morley C.K. 
Published: April 2008

Abstract
Mudstone intrusions in the Jerudong area represent natural hydraulic fractures developed above an inferred mobile mudstone diapir sourced from the Middle Miocene Setap Formation. Intrusions are manifest as dykes, sills and laccoliths. Intrusion geometries are strongly influenced by pre-existing weaknesses, in particular normal faults. Local inflation of country rock shale units also occurs. Dyke terminations include curved traces, splays and en echelon faults. The wall rocks tend to be smooth, or have numerous small, sub-horizontal ledges (mini jogs). Faults and bedding surfaces cause larger jogs in the dyke trend. Mudstone sills commonly change thickness at normal faults, and inflate the hanging wall so that the normal fault sense of motion is inverted, thrusting and fault bend folding are the result. An exposed mudstone laccolith passes laterally via v-shaped bedparallel intrusions into sandstones. The roof of the laccolith is arched upwards and near the intrusion, the roof is broken up by small and large intrusions. Existing models for diapir rise require the brittle shear strength of the roof sequence to be overcome. The Jerudong outcrops demonstrate diapir rise by hydraulic fracturing and stoping which limits the roof sequence strength to the minimum horizontal stress plus the tensile strength of the country rock or normal fault zones in the roof sequence. The crosscutting mudstone dykes, sills, mudstone intruded fault zones and associated cataclastic deformation form planar permeability barriers that can highly compartmentalize the reservoir rock and significantly reduce the area of reservoir rock that can be effectively produced of hydrocarbons. Intruded mudstones could easily be mistaken for stratified shales when interpreting and correlating well logs.
Remobilization of sand from consolidated sandstones: evidence from mixed bitumen-sand intrusions
Authors: Parnell John , Kelly Jason 
Published: April 2008

Abstract
Some sand in intrusive bodies has an origin in the disaggregation of consolidated sandstones. Evidence from the study of mixed bitumen-sand intrusions includes progressive spalling of individual grains from cemented sandstones and individual sand grains with adhering cements. Both physical forces related to rapid fluid movement and chemical dissolution may contribute to the disaggregation process. Rapid fluid flow due to hydrofracturing of an overpressured sequence is responsible for several examples of sand-bearing bitumen veins. As overpressuring is a widespread phenomenon, disaggregation of lithified sandstones may be more prevalent than hitherto appreciated. Sand may be entrapped in bitumen within vein systems cutting kilometres of stratigraphy. Fluid inclusion data from an example at Bentheim, Germany, shows that cementation of sandstone occurred at high temperatures before sand disaggregation and mobilization.