bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture networks on the Belluno syncline, a fault-propagation fold in the footwall of the Belluno thrust, Venetian Alps, NE Italy
Authors: Zampieri D. , Grandesso P.
Published: April 2008

The Belluno syncline is a structure located in the Venetian fold-and-thrust belt in the Italian Southern Alps. This SSE-vergent chain mainly developed during the Neogene as a back-thrust belt of the Alps deforming the northern margin of the Adria plate. The syncline is asymmetric in shape, with a steep backlimb, as the forelimb of the paired Monte Coppolo Anticline; it is the result of fault-propagation folding during the development of the underlying Belluno thrust. In plan view the Belluno thrust shows a prominent curvature interpreted as reactivation of inherited Mesozoic extensional structures. The hinge of the Belluno syncline presents a similar curvature. Rocks cropping out in the syncline core are Upper Chattian to Langhian fine-grained molassic sediments, mainly siltstones and marls.

Most fractures on the Belluno syncline have formed at high angles to bedding. The dominant fracture trends are subparallel and orthogonal to the fold hinge. Sometimes these fractures show plumose structures revealing extension (Mode I) fracture mechanism and therefore they are referred to as longitudinal (
bc
) joints and cross (
ac
) joints respectively. Other fracture trends oblique to the hinge line are found in measurement stations located on limbs distant from the fold hinge. They are referred to as oblique (shear) fractures. Throughout the western part of the Belluno syncline the fracture network maintains a roughly symmetrical distribution with respect to the fold hinge, suggesting a development in association with folding.
A new method for smoothing orientated data and its application to stress data
Authors: Müller B. , Wehrle V. , Hettel S. , Sperner B. , Fuchs K.
Published: April 2008

Smoothing algorithms provide a means of identifying significant patterns in sets of orientated data, eliminating local perturvations within the observations and predicting patterns of orientated data in places which lack observations. Here we present the smoothing of orientation data with a distance-related method of data weighting as an alternative to previous weighting algorithms. The data weighting and smoothing method presented here in theory and practice is developed on the basis of a statistical smoothing algorithm. The method can be applied to orientation data of 180° periodicity such as maximum horizontal tectonic stresses (
S
H
) as compiled in the World Stress Map database. Our smoothing algorithm enables discrimination between local (<250 km of lateral extent) and regional (
c.
250–5000 km of lateral extent) stress fields, and allows comparison of
S
H
with other directional data such as fault trends or strain data. We present smoothed stress maps for northeastern America, the Himalayas and western Europe. By varying the scale and smoothing parameters we illustrate their influence on the accuracy and smoothness. We give recommendations for the appropriate choice of these parameters.
Simulation of water and gas flow in fractured porous media
Authors: Al-Khlaifat Abdelaziz L. , Arastoopour Hamid
Published: April 2008

The porous media considered in this paper belong to gas reservoirs characterized by a low-permeability matrix, combined with a high-permeability fracture system. The transient, three-dimensional, two-phase numerical model is presented for simulating the simultaneous flow of gas and water through porous and fractured media. The specific problem to which the numerical simulation is applied assumes a single horizontal fracture perpendicular to the flow direction in a quite small geometry. The equations solved treat both fluids as incompressible and immiscible. Accounted for are the effect of capillary pressure and relative permeability. Technically, the finite volume approach is used to discretize the equations. The set of discretized and linearized equations is solved using the IPSA (inter-phase slip algorithm) method. The results of this study indicate that the multi-layer reservoir provides better estimates of post-fracture performance compared to a more conventional, single-layer reservoir description.
Finite strain variations along strike in mountain belts
Authors: Hindle D.
Published: April 2008

In order to quantify finite strain from displacement fields derived from structural restorations in mountain belts, a simple technique using triangular elements (based on the finite element technique) is presented. This adequately describes the discontinuous displacement of a fold-thrust belt, whilst overcoming the difficulties posed by discontinuities which are integrated across appropriate elements for the purpose of strain calculation. The technique has been applied to two fold-thrust belts at contrasting scales, the Central Andes and the Neuchâtel region of the Jura mountains (Switzerland). In both cases, structural restorations have produced the finite displacement fields thought to be involved in their generation. Subsequent calculation of strain variation along strike shows that there is a strong relationship between first-order structure (the scale of major fold axes) and the trends of axis orientations. In spite of the contractional setting of both belts, strong along-strike extension is predicted but this is always in the context of a generally parallel to slightly convergent displacement field, and such extensions are generally related to differential shear accommodated on strike-slip or tear faults. Most elements showing along-strike extension are nevertheless predicted to undergo tectonic thickening. Second-order structures (faults necessary to accommodate local predicted deformation) are also calculated and the enormous difference between slip directions on small-scale faults and the regional ‘far field’ displacement direction is demonstrated. This is thought to be important when trying to infer large-scale tectonic information from very small-scale structures found in the field.
A four-year study of shear-wave splitting in Iceland: 1. Background and preliminary analysis
Authors: Volti T. , Crampin S.
Published: April 2008

A four-year study of seismic shear-wave splitting in Iceland was designed to seek temporal variations before earthquakes. Shear-wave splitting is observed routinely in Iceland whenever shear-waves arrive within the shear-wave window of seismic stations, and whenever adequate data are available, temporal and spatial variations in shear-wave splitting are observed before both earthquakes and volcanic eruptions. Shear-wave splitting is caused principally by the stress-aligned fluid-saturated microcracks and pore throats in almost all
in situ
rocks. Fluid-saturated microcracks are the most compliant elements of the rock mass, and changes in splitting can be directly interpreted and modelled as the effects of changing stress on the microcrack geometry in the rock mass often at considerable distances from the immediate earthquake source zone. Such changes were found and are reported in Part 2 of this study. This chapter presents the background, preliminary observations, and analysis of shear-wave splitting in Iceland.
Modelling the influence of tectonic compression on the
in situ
stress field with implications for seal integrity: the Haltenbanken area, offshore mid-Norway
Authors: Skar T. , Beekman F.
Published: April 2008

Exploration for hydrocarbons in overpressured domains is often considered high risk because of the possibility of seal failure and fluid leakage due to natural hydraulic fracturing. Several of the wells drilled in highly overpressured reservoirs on Haltenbanken, offshore mid-Norway, have proved to be devoid of hydrocarbons suggesting that ineffective seals are the cause of exploration failure. However, recent petroleum discoveries within this area demonstrate that fluid pressure is not the ultimate control on entrapment of hydrocarbons. We investigate the way in which far-field tectonic compression may have influenced the
in situ
stress conditions on Haltenbanken, and assess whether tectonic stresses also may facilitate local fracturing of the seal by reducing the retention capacity (minimum horizontal stress-fluid pressure).

We have approached the problem by applying a finite element model. The elasto-plastic model assumes two-dimensional plane-strain and is constrained from geological and geophysical data. The results show that: (1) contrasts in the rock’s mechanical properties across discontinuities (e.g. sediment interfaces) cause rapid shifts in stress magnitudes; (2) the differences in stress magnitudes across such discontinuities can be subdued or enhanced under increased horizontal compression; and (3) structurally controlled variations in vertical displacements produce local concentrations of highs and lows in the stress field. The combined result of these three factors is that the magnitude of horizontal stress may vary quite considerably within spatially restricted areas. The implication of these predictions in terms of hydrocarbon preservation potential in highly overpressured regions is that rapid shifts in minimum horizontal stress magnitudes can reduce the retention capacity and therefore facilitate natural hydraulic fracturing.
Volcanic eruption detection by the Total Ozone Mapping Spectrometer (TOMS) instruments: a 22-year record of sulphur dioxide and ash emissions
Authors: Carn S. A. , Krueger A. J. , Bluth G. J. S. , Schaefer S. J. , Krotkov N. A. , Watson I. M. , Datta S.
Published: April 2008

Since their first depolyment in November 1978, the Total Ozone Mapping Spectrometer (TOMS) instruments have provided a robust and near-continuous record of sulphur dioxide (SO
2
) and ash emissions from active volcanoes worldwide. Data from the four TOMS satellites that have flown to date have been analysed with the latest SO
2
/ash algorithms and incorporated into a TOMS volcanic emissions database that presently covers 22 years of SO
2
and ash emissions. The 1978–2001 record comprises 102 eruptions from 61 volcanoes, resulting in 784 days of volcanic cloud observations. Regular eruptions of Nyamuragira (DR Congo) since 1978, accompanied by copious SO
2
production, have contributed material on approximately 30% of the days on which clouds were observed. The latest SO
2
retrieval results from Earth Probe (EP) TOMS document a period (1996–2001) lacking large explosive eruptions, and also dominated by SO
2
emission from four eruptions of Nyamuragira. EP TOMS has detected the SO
2
and ash produced during 23 eruptions from 15 volcanoes to date, with volcanic clouds observed on 158 days. The EP TOMS instrument began to degrade in 2001, but has now stabilized, although its planned successor (QuikTOMS) recently failed to achieve orbit. New SO
2
algorithms are currently being developed for the Ozone Monitoring Instrument, which will continue the TOMS record of UV remote sensing of volcanic emissions from 2004 onwards.
Rainwater and ash leachate analysis as proxies for plume chemistry at Soufrière Hills volcano, Montserrat
Authors: Edmonds M. , Oppenheimer C. , Pyle D. M. , Herd R. A.
Published: April 2008

Chloride and sulphate concentrations in rainwater and water-soluble leachates from volcanic ash samples track the compositions of gas emissions at the Soufrière Hills Volcano, Montserrat, from 1996 to 2001. There are both systematic spatial and temporal variations in the chloride/sulphate ratio (expressed as the equivalent HCl/SO
2
mass ratio) in rainwater and ash leachates. Temporal variations reflect changes in eruption rate and eruptive style. Mass ratios of HCl/SO
2
in ash leachates correspond closely with those obtained by open-path Fourier transform infrared (OP-FTIR) spectroscopy, and reflect changes in volatile emissions throughout the eruption. Both leachate and OP-FTIR spectroscopic analyses show mass ratios of HCl/SO
2
> 1 during dome growth, and HCl/SO
2
< 1 during non-eruptive periods.

The HCl/SO
2
mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate. The HCl/SO
2
ratios in plume-affected rainwater and ash leachates from June and July 2001 correlate positively with increasing rockfall energy, and with increasing eruption rate prior to a dome collapse event. The HCl/SO
2
mass ratios in water-soluble ash leachates and rainwater samples collected at the same time and from the same sites, are linearly correlated, with rainwater HCl/SO
2
ratios systematically two to three times higher than ash leachate ratios. Spatial patterns of rainwater pH, and HCl/SO
2
in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome, and to the typical pattern of dispersion of the plume by tropospheric winds. These results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity, and represents a valuable supplement to volcano surveillance efforts.
The 12 900 years
BP
Laacher See eruption: estimation of volatile yields and simulation of their fate in the plume
Authors: Textor C. , Sachs P. M. , Graf H.-F. , Hansteen T. H.
Published: April 2008

We estimated the volatile emissions of the 12 900 years
BP
eruption of Laacher See volcano (Germany), using a modified petrological method. Glass inclusions in phenocrysts and matrix glasses sampled over the Laacher See tephra profile were analysed by synchrotron X-ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens, sulphur, and water. These data were used to initialize the numerical plume model ATHAM in order to investigate the fate of volcanic gases in the plume, and to estimate volatile masses injected into the stratosphere. The scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice. We found a scavenging efficiency of
c.
5% for the sulphur species, and of only
c.
30% for hydrogen halides, despite their high water solubility. Our simulations showed that the greatest fraction of hydrometeors freeze to ice, due to the fast plume rise and great height of the eruption column. For the dry atmospheric conditions of the Laacher See eruption, the amount of liquid water was not sufficient to completely scavenge HCl and HBr, so that a large proportion could reach the stratosphere.
Illness and elevated human mortality in Europe coincident with the Laki Fissure eruption
Authors: Grattan J. , Durand M. , Taylor S.
Published: April 2008

Volcanic eruptions represent a significant source of volatile gases that are harmful to human health. This chapter reviews and develops current understanding of the human health response to volcanogenic pollution and dry fog events; in particular it explores the health impact of the gases from the Laki fissure eruption, and presents data that point to a significant increase in the national death rate in England coincident with the early phases of the eruption. It is noted that many common symptoms of severe exposure to air pollution can be linked to the dry fog of 1783; these included difficulty in breathing, eye and skin irritation, headaches, loss of appetite and tiredness.
Modelling fracture systems in extensional crystalline basement
Authors: Sanders C. A. E. , Fullarton L. , Calvert S.
Published: April 2008

Using observations from the extensional basin setting in Vietnam, conceptual models were developed to simulate and analyse fracture systems typical of crystalline basement in such structural settings. Information from field observations, seismic surveys and three-dimensional (3-D) structural modelling were integrated and used to build geologically realistic 3-D fracture networks. A major advantage of the method used in this study is that it allows a better understanding of the apparently chaotic fracture networks characteristic of such rocks, and of the processes responsible for fracturing. Several fracture generating processes are discussed and modelled, with emphasis on tectonic fractures and the relation to structural modelling. An example is presented highlighting the differences in fracturing in the hanging wall and footwall during lithospheric extension superimposed on a primary (igneous) cooling fracture network. Results suggest that during flexural uplift, the hanging wall is significantly more deformed than the footwall, implying the former is more prone to fracturing than the footwall for both kinematic and flexural isostatic processes.
Computed tomography in petroleum engineering research
Authors: Akin S. , Kovscek A. R.
Published: April 2008

Imaging the distribution of porosity, permeability, and fluid phases is important to understanding single and multiphase flow characteristics of porous media. X-ray computed tomography (CT) has emerged as an important and powerful tool for non-destructive imaging because it is relatively easy to apply, can offer fine spatial resolution and is adaptable to many types of experimental procedures and flow conditions. This paper gives an overview of CT technology for imaging multiphase flow in porous media, the principles behind the technology and effective experimental design. By critically reviewing prior work using this important tool, we hope to provide a better understanding of its use and a pathway to improved analysis of CT-derived data. Because of the wide variety of image processing options, they are discussed in some detail.
Study of the microgeometry of porous materials using synchrotron computed microtomography
Authors: Jones K. W. , Feng H. , Lindquist W. B. , Adler P. M. , Thovert J. F. , Vekemans B. , Vincze L. , Szaloki I. , Van Grieken R. , Adams F. , Riekel C.
Published: April 2008

A series of measurements of the structure of a variety of porous materials has been made using synchrotron computed microtomography (SCMT). The work was carried out at the Brookhaven National Synchrotron Light Source (NSLS), the Argonne Advanced Photon Source (APS) and the European Synchrotron Radiation Facility (ESRF). The experiments at Brookhaven and Argonne were carried out on bending magnet beam lines using area detectors to obtain CT images based on determination of X-ray absorption coefficients. The work at the ESRF used an undulator beam line, a 13 KeV pencil X-ray beam of 2 µm and an energy dispersive X-ray detector to make tomographic sections of trace element distributions by X-ray fluorescence tomography. Most of the work was done with a pixel/voxel size ranging from 0.002 to 0.010 mm. We examined the structure of unconsolidated estuarine sediments, whose structure is relevant to transport of contaminants in rivers and estuaries. Fluorescent tomography with 2–3 µm resolution was used to ascertain whether or not metals were concentrated on the surface or throughout the volume of a single sediment particle. Sandstone samples were investigated to obtain a set of values describing their microstructures that could be useful in fluid flow calculations relevant to petroleum recovery or transport of environmental contaminants. Measurements were also made on sandstone samples that had been subjected to high-pressure compression to investigate the relation between the microgeometry and the magnitude of the applied pressure. Finally, a Wood’s metal-filled sample was scanned for demonstration of resolution enhancement and fluid flow studies.
Three-dimensional visualization of fractures in rock test samples, simulating deep level mining excavations, using X-ray computed tomography
Authors: Sellers E. , Vervoort A. , Van Cleynenbreugel J.
Published: April 2008

A series of experiments on cubic blocks of quartzite were performed to create fractures with three-dimensional characteristics so that they could serve as verification examples for numerical models that are being developed to analyse the fracture processes around mining excavations. The experiments proved to be very successful for creating 3D fracture patterns that have characteristics similar to those observed underground. The shape and position of the fracture surface is determined by the mining geometry and by the interaction with pre-existing discontinuities. However, variations of the fracture planes within the sample could not be determined from the visual study of the block surfaces. The application of a state-of-the-art medical X-ray computed tomography scanner and the development of automatic surface reconstruction software provided a method of producing a full three-dimensional, digital view of fractures within laboratory test samples. Software was developed to provide an interactive graphical method for studying the scans in three orthogonal planes simultaneously. By contouring below a selected density threshold, three-dimensional images of the fracture surfaces were produced. X-ray computed tomography was found to provide a unique means of visualizing the fractures within rock test samples, which can greatly assist the study of rock fracture processes.
Rock drying tests monitored by X-ray computed tomography — the effect of saturation methods on drying behaviour
Authors: Rousset-Tournier B. , Mazerolle F. , Géraud Y. , Jeannette D.
Published: April 2008

Drying experiments were conducted under controlled conditions (relative humidity, temperature, motionless atmosphere) using Fontainebleau sandstone. X-ray computed tomography images acquired at various stages of the drying show that the location of water in the pore network depends on the method of initial saturation. After capillary absorption, the trapped air, or free porosity, allows the water distribution to be homogeneous and independent of the pore structure. This is because it homogenizes the tensions that apply to the water in the pores, regardless of the pore dimensions. However, this is not the case after a total saturation under vacuum. These differences are visible from the beginning to the end of the drying experiments. These results are important for curators or restorers of the architectural heritage, because they show that before testing a conservation product for stones, the method of saturation of these stones must be considered and attention should be given to the required effect.
Assessment of soil structure using X-ray computed tomography
Authors: Rogasik H. , Onasch I. , Brunotte J. , Jegou D. , Wendroth O.
Published: April 2008

Assessment of soil structure, characterized by complex morphological and functional properties, is difficult because most conventional soil physical investigations are destructive and variable in spatial resolution. The use of X-ray computed tomography, as a non-destructive technique, presents significant progress. It can be used to study soil structure at the millimetre scale, e.g. with a resolution of 0.25 mm in the horizontal direction and 1 mm in the vertical direction for the reported study. The measured Hounsfield Unit (HU) values characterize X-ray attenuation for each volume element of the soil core samples. From HU values, soil physical properties of soil cores or their subunits can be derived. They enable: (i) visual assessment of the soil structural condition through inspection of the X-ray CT images; (ii) 3D visualization of air-filled macropores; and (iii) calculation of the mean dry bulk density and standard deviation of voxel-related HU values for successive slices of soil cores. The degradation of structure of loamy and silty soils by tillage could be assessed by CT through quantification of decreased air-filled porosity, destroyed macropore connectivity, increased dry bulk density and decreased standard deviation of HU values in horizontal slices. Small-scale compactions near earthworm burrows could also be detected.
How sediments become mobilized
Authors: Maltman Alex J. , Bolton Alistair
Published: April 2008

Geological sediments tend to strengthen during progressive burial but the interplay of porosity and permeability, strain and effective stress gives rise to numerous circumstances in which the strength increase can be temporarily reversed. The sediment becomes capable of bulk movement — sediment mobilization. Most explanations involve overpressuring, which results from additional loading being sustained by pore-fluid that is unable to dissipate adequately, leading to frictional strength reduction. The processes are highly heterogeneous, areally and with depth. The loads can be external (‘dynamic’) and both monotonic (e.g. a rapidly added suprajacent mass) and cyclic (e.g. the passage of waves), internal (e.g. the result of mineral reactions) and hydraulic (e.g. injection of external fluid). The sediments may become liquidized — that is, lose strength completely and behave as a fluid — through temporary fabric collapse (sensitive sediments) because loads are borne entirely by the pore-fluid (liquefaction), or by the grains becoming buoyant (fluidization), typically due to the ingress of externally derived fluids. In response to hydraulic gradients, buoyancy forces and reversed viscosity or density gradients, the weakened sediment may undergo bulk movement, though this requires failure of the enclosing material and sustained gradients. Mobilized but non-liquidized sediments retain some residual strength but can attain large shear displacements under critical state conditions.
Load structures: gravity-driven sediment mobilization in the shallow subsurface
Authors: Owen Geraint
Published: April 2008

Load structures are a type of soft-sediment deformation structure comprising synforms (load casts and pseudonodules) and antiforms (flame structures and diapirs) at an interface. They form in response to unstable density contrasts (density loading) or lateral variations in load (uneven loading) when sediment becomes liquidized or otherwise loses strength. They are here classified into five varieties: simple and pendulous load casts, in which the upper (denser) layer is laterally continuous; and attached pseudonodules, detached pseudonodules and ball-and-pillow structure, in which discrete masses of the upper layer are separated by matrix. Conceptual models demonstrate that there are several possible modes of formation for each type of load structure. One interpretation of the variation of load structure morphology is as a deformation series representing varying degrees of deformation, controlled by the magnitude of the driving force and/or the duration of its effective action. An interpretation of the commonly observed pattern of wide load casts and narrow flame structures is presented in terms of their differential growth. Fluidization has an important influence on the development of load structures and their relationship to other products of sediment mobilization.
Fluidization pipes and spring pits in a Gondwanan barrier-island environment: groundwater phenomenon, palaco-seismicity or a combination of both?
Authors: Draganits E. , Grasemann B. , Schmid H. P.
Published: April 2008

Cylindrical structures, cross-cutting stratification at right angles, occur in the Muth Formation, representing Lower Devonian barrier island arenites of the North Indian Gondwana coast. These structures are up to 1.5 m in height and 0.8 m in diameter, with an internal structure comprising concentric, cylindrical laminae. The pipes, which probably represent water conduits for laminar upward flow of ground water, initiate from relatively thin horizons, with upper terminations formed by spring pits. Thus, the structures in the Muth Formation represent a rarely observed combined occurrence of spring pits and their conduits below. Their formation is explained by rising ground water seepage in a coastal depositional environment that produced a relatively high hydrostatic head, resulting in the formation of springs. The rise in relative sea level might be related to tectonic subsidence caused by tectonic activity linked to the formation of conjugate deformation bands in the Muth Formation. This means, if tectonic activity was involved, it did not form the cylindrical structures by seismic liquefaction directly, but might be responsible indirectly through ground water seepage rise resulting from tectonic subsidence. Due to the little relief in this environment, the sea level rise affected a relatively large area and fluidization structures can be found widespread in distant sections.
Experimental evidence on the role of gas in sediment liquefaction and mud volcanism
Authors: Pralle Norbert , Külzer Michael , Gudehus Gerd
Published: April 2008

Mud volcanoes are structures that are formed through ‘cold volcanism’ and indicate soil liquefaction. Their evolution depends on the structure, state and excitation of fine-grained feeding sediments. The disturbance of the framework of a loose, fine-grained, saturated sediment causes shear deformation leading to a pore fluid pressure increase. Effective stresses are thereby reduced and can vanish; the soil is then totally liquefied. Small amounts of enclosed gas bubbles render the soil compressible and enhance local shearing, pore pressure build-up and structural damage. Liquefield, overpressurized sediments form mud chambers, whose excess pressure is released through cracks and other inherent weak channels caused, for example, by density variations in the overlying strata.

Experiments were conducted on small-scale soil columns and on model slopes, using quartz powder as model material. Soil column tests were aimed at determining the influence of gas bubbles with regard to the liquefaction process, whereas model slope tests were targeted at the collapsability of gentle slopes, subject to atmospheric pressure changes. Different initial porosities were achieved through ion content variation. Liquefaction of fine-grained sediments and subsequent volcano evolution could be produced.
Shallow bottom-simulating reflectors on the Angola margin, in relation with gas and gas hydrate in the sediments
Authors: Nouzé Hervé , Baltzer Agnès
Published: April 2008

Acoustic facies interpretation, high-resolution velocity analysis and amplitude
versus
offset modelling have been performed on high resolution seismic data acquired on the West African margin offshore Angola, in water depths of about 2000 m. The area has a complex structural, thermal and fluid-flow setting, in which sediments are affected by salt diapirism and faulting associated with sediment compaction. A discontinuous bottom-simulating reflector (BSR) at a depth of about 200 m below sea floor could mark the base of the gas hydrate occurrence zone, which does not always coincide with the top of the free gas zone. Within the gas hydrate stability zone, a shallow bottom-simulating reflector is observed at a depth of about 75 m below seafloor. This shallow bottom simulating reflector, that is termed ‘sheep back reflector’ (SR), correspond to a small amount of gas being trapped in the sediments. It could mark the top of the gas hydrate occurrence zone, where gas hydrate dissociation may occur. A reversed polarity reflector (R1) is also observed about 25 m below the sea floor. This reflector could correspond to a limit between normally compacted and underconsolidated sediments, possibly related to a permeability change in the sediments. Thus, the occurrence of excess pore pressure generated during gas hydrate dissociation could explain some subsurface sediment mobilization processes.
Mobile shale related deformation in large deltas developed on passive and active margins
Authors: Morley C. K.
Published: April 2008

Understanding the nature of mobile shale deformation in deltas requires appreciation of several critical factors: (1) the tectonic setting (deposition on an active or passive margin); (2) the range of potential structural styles and how to identify them on seismic reflection data; (3) how structural styles evolve with time; (4) how to apply and modify what is understood about salt deformation to mobile shale deformation; and (5) how delta structures influence sedimentation. Differences between active and passive margin settings include: (a) active margins tend to display shorter, higher gradient drainage systems associated with high rates of erosion per unit area when compared with passive margins; (b) active uplift of the hinterland will force delta progradation (not seen on passive margin); (c) uplift causes erosion and re-cycling of older deltaic deposits which can cause comparatively fine grained sandstone reservoirs; and (d) the development of large compression-related folds and thrusts in the shelfal region of deltas on active margins can create areas of active uplift. Consequently, structurally controlled embayments may develop that cause distinct changes in the dominant depositional process (wave, tidal, fluvial) along the margin. On both active and passive margins, growing gravity-driven structures locally create sea floor highs and depressions and create changes in the dip of slopes which influence depocentre location and sediment pathways from the shelf to deepwater. A wide range of mud diapir geometry can be found in deltas. Commonly mud diapirs exhibit reactive, active, passive and collapse features. Some diapirs develop as compressional features seaward of fault bounded depocentres. Also frequently associated with delta provinces are fluid pipes, shale intrusions, fluid fronts and gas clouds. All the overpressure phenomena can produce dimming, or disruption of reflections on seismic reflection data, however the characteristics of the different phenomena are sufficiently diverse that they can frequently be differentiated on good quality data.
Analogue models of delta systems above ductile substrates
Authors: McClay Ken , Dooley Tim , Zamora Gonzalo
Published: April 2008

Delta systems developed above ductile substrates such as overpressured shales and salt have been modelled using layered sand-packs above ductile silicone polymer layers. Gravity spreading of progradational sedimentary wedges produces delta-top and upper delta-slope grabens linked to delta-toe contractional fold-thrust and diapir zones. The delta-top grabens are bound by both regional and counter-regional listric growth faults. A basinward-stepping sequence of regional, counter-regional followed by regional faulting is commonly developed. Polymer pillows and ridges commonly develop in the footwalls of the major listric extensional faults and may evolve into reactive diapirs. Successive progradational loads generate new delta-top or upper delta-slope graben systems on top of older contractional belts where the ductile polymer layer has been thickened significantly. The analogue model results in cross-section show many similarities to examples of natural deltas and differential sedimentary load systems such as offshore Angola, the Niger and Nile Deltas, Kutai Basin, Kalimantan, the Baram delta, Brunei and the Orinoco delta, Columbus basin and offshore Trinidad.
Pliocene to Recent mud diapirism and related mud volcanoes in the Alboran Sea (Western Mediterranean)
Authors: Talukder A.R. , Comas M.C. , Soto J.I.
Published: April 2008

High resolution and multichannel seismic profiles depict the Pliocene to Recent evolution of the mud diapirism in the West Alboran Basin (WAB) and its relationship with the Miocene diapir province that occupies the WAB depocentre. During the early to middle Miocene period of basin extension (16 to 9 Ma), normal faulting triggered the diapirism from mobile overpressured shale containing olistostromes. Plio-Quaternary diapirism evolved as a second main stage of diapiric activity and developed throughout the subsequent contractive tectonic evolution of the basin (9 Ma to Holocene). Mud volcanoes, discovered to the south of the WAB, developed on the flank of Recent diapirs as a consequence of the rise of fluidized sediments through diapiric bodies and/or through fractures connecting with deeper diapirs. During the Pliocene to Recent, some diapirs stopped ascending, leading to the production of collapse structures on their tops due to lateral subsurface mud migration and/or fluid escape. Other cylindrical shaped diapirs continued rising and produced mud volcanoes on the sea floor. All the studied volcanoes seem to be currently inactive. Two major pulses of diapiric rise have been distinguished during the Pliocene to Recent contractive evolution of the basin.
The origin and processes of mud volcanism: new insights from Trinidad
Authors: Deville E. , Battani A. , Griboulard R. , Guerlais S. , Herbin J.P. , Houzay J.P. , Muller C. , Prinzhofer A.
Published: April 2008

The mobilized sediments expelled by the mud volcanoes in Trinidad correspond to liquefied argillaceous and sandy material in which the solid fraction is systematically polygenic and originating from several formations (Cretaceous to Pliocene). The mud is notably rich in thingrained quartz that is angular and frequently mechanically damaged related to shearing at great depth, during the sedimentary burial, and/or hydraulic fracturing processes. The exotic clasts are mostly fractured fragments from various formations of the tectonic wedge (mostly Palaeocene to Miocene). The origin of the solid particles of the mud is polygenic, including deep Cretaceous-Palaeogene horizons close to the décollement, and various materials from the stratigraphic pile pierced by the mud conduits. Moreover, the fluids expelled by the mud volcanoes have a deep origin and notably the gas phase is thermogenic methane generated probably below a depth of 5000 m. The effusions occur either during cycles of moderate effusion of mud and fluids (quiescence regime), or during catastrophic events responsible for the expulsion of huge volumes of mud, clasts and fluids (transient regime). Available subsurface data suggest that the deep structure of the mud volcanoes includes: (1) a focused deep conduit at depth in the zone of overpressure; (2) a mud chamber intruding the surrounding formations around and above the top of the abnormal pressure zone; and (3) a superficial outlet leading to the surface vents.
A new scaphognathine pterosaur from the Upper Jurassic Morrison Formation of Wyoming, USA
Authors: Carpenter Kenneth , Unwin David , Cloward Karen , Miles Clifford , Miles Clark
Published: April 2008

A partial rostrum of a new species of scaphognathine pterosaur, distinguished by a thin median crest along its dorsal margin and a deep embayment of the dental margin, is the first identifiable cranial fragment of a pterosaur from the Upper Jurassic Morrison Formation of western North America. By contrast with pterodactyloids, cranial crests are rare in “rhamphorhynchoids” and this is the first record of such a structure. The new material provides fresh insights into the taxonomic diversity of Late Jurassic North American pterosaurs. Based on the ratio of the skull and skeleton of
Scpahognathus
, the fragment represents an individual with an estimated wing span of 2.5 m. Consequently, this is one of the largest “rhamphorhynchoids” found so far. A mandible fragment from the same quarry has closely spaced alveoli, therefore cannot be referred to the rostrum. Its large size indicates another large “rhamphorhynchoid” in the Morrison Formation.
A new species of tapejarid pterosaur with soft-tissue head crest
Authors: Frey Eberhard , Martill David M. , Buchy Marie-Céline
Published: April 2008

Two specimens of a tapejarid pterosaur (Pterodactyloidea, Tapejaridae) are described as representing a new species. Both specimens show evidence for soft tissues preserved in association with a sagittal bony cranial crest. Both specimens are from the Nova Olinda Member Konservat Lagerstätte of the Crato Formation of the Araripe Basin, northeastern Brazil. They represent the second tapejarid species from this formation. Comparisons are made with other crested pterosaurs and comments on the utility and aerodynamics of pterosaurian head crests are made.
Ichnological evidence for quadrupedal locomotion in pterodactyloid pterosaurs: trackways from the Late Jurassic of Crayssac (southwestern France)
Authors: Mazin Jean-Michel , Billon-Bruyat Jean-Paul , Hantzpergue Pierre , Lafaurie Gérard
Published: April 2008

More than 30 well-preserved pterosaurian trackways have been excavated from the site of Crayssac (Lower Tithonian, southwestern France), along with hundreds of isolated imprints. The general pattern of pterosaurian trackways is described and corresponds to the morphology of the ichnogenus
Pteraichnus
Stokes 1957. A crocodilian origin for
Pteraichnus
is rejected. The morphology of the pes and manus prints is described and discussed, and exhibits a great dynamic variability. The three manus digit prints are confirmed as the marks of digits I–III, but the high angle of divarication may reflect strong digit abduction as well as a backward folding of the digit III. The manus gait-width is as much as 3 × the pes gait-width. The narrowest manus trackways corresponds to low-velocity walking in a semi-erect stance, whereas the widest manus trackways corresponds to higher velocity walking (perhaps even running), with a subhorizontal body.
The systematic problem of tetrapod ichnotaxa: the case study of
Pteraichnus
Stokes, 1957 (Pterosauria, Pterodactyloidea)
Authors: Billon-Bruyat Jean-Paul , Mazin Jean-Michel
Published: April 2008

This paper deals with the systematics of tetrapod ichnotaxa based on footprints. Beyond the consideration of the nomenclatural rules for ichnotaxa in the ICZN, this paper tries to determine how to establish an ichnotaxonomy that reflects the identity of the track-maker (the organism that has made the track) and how to include this ichnotaxonomy in the skeleton-based taxonomy. This leads to the establishment of several criteria, e.g. ichnospecies should be defined on the print morphology and the relative position of the prints (including the variability due to the track-maker’s dynamics), two ichnospecies should represent different species, the ichnospecies and ichnogenus levels are sufficient to discriminate the ichnotaxa and link them to the skeleton-based taxonomy. These ichnotaxonomical criteria are applied to a revision of the ichnogenus
Pteraichnus
Stokes 1957 (Pterosauria, Pterodactyloidea). Only the type species
Pteraichnus saltwashensis
is considered as valid, the pterosaurian origin of
Purbeckopus
is questioned and
Agadirichnus
is highlighted because it could be a senior synonym of
Pteraichnus
. The result of this drastic revision underlines the importance of the proposed ichnotaxonomical principles to avoid the unfounded proliferation of tetrapod ichnotaxa.
Petrology and evolution of the Brezovica ultramafic massif, Serbia
Authors: Bazylev B. A. , Karamata S. , Zakariadze G. S.
Published: April 2008

The tectonomagmatic history of ultramafic rocks in the Brezovica massif (Serbia) involved two separate magmatic stages, as inferred from the mineral and bulk-rock chemistry data and thermal history of the peridotites. In the first stage, a suite of spinel harzburgites was formed during partial melting of the mantle and segregation of tholeiitic melts. During the second stage, these spinel harzburgites were repeatedly heated and affected by percolating melt. This process formed dunites and refractory spinel harzburgies during melt-harzburgite interaction. The melt that segregated from these rocks during the second magmatic stage was of high-Ca boninite affinity. Both magmatic stages occurred in a suprasubduction geodynamic setting at a relatively deep level (25–28 km). In its present position the Brezovica massif has been interpreted as a relic of a suprasubduction-type oceanic lithosphere derived from the Central Dinaridic-Mirdita ocean basin. During eastward emplacement of the Brezovica massif over the underlying olistostrome, the ultramafic rocks were cooled to temperatures around 735 ± 20°C.
Structural and microstructural analysis of a palaeo-transform fault zone in the Neyriz ophiolite, Iran
Authors: Sarkarinejad Khalil
Published: April 2008

The Neyriz ophiolite in SW Iran includes a NNW-SSE-trending, steeply dipping oceanic palaeo-transform fault zone that consists mainly of deformed and sheared gabbros and peridotites. Mylonitic rocks within the fossil palaeo-transform fault display C-, C′- and S-band shear cleavages containing green hornblende- and feldspar-rich bands. Deformed hornblendemantled porphyroclasts have symmetrical tails or σ-type porphyroclast systems, which show clockwise stair-stepping rotation and oblique foliation with asymmetrical complex stripes and wings. These microstructures indicate dextral shearing on the palaeo-transform fault. The
c
-axes of hornblende in high-grade S-C mylonitic rocks exhibit strong lattice-preferred orientation (LPO) patterns with M- and G-type origin. These LPO patterns are asymmetrical with respect to the shear zone foliation and also indicate dextral shearing. The NNW-SSE trend of the palaeo-transform fault is perpendicular to the general NE strike of sheeted dykes and is parallel to the average harzburgite foliation. These observations suggest a noncoaxial shear orientation of mantle flow, which progressively rotated toward parallelism with the fossil fracture zone. This dextral transform fault is inferred to have connected ENE-trending oceanic spreading centre segments in a Neo-Tethyan ocean basin.
The nature of faulting and deformation in the Mineoka ophiolite, NW Pacific Rim
Authors: Takahashi Akiko , Ogawa Yujiro , Ohta Yasufumi , Hirano Naoto
Published: April 2008

A belt of disrupted ophiolitic rocks occurs on the Boso Peninsula (Japan), currently located north of the oblique subduction boundary between the Philippine Sea and North American Plates, under which the Pacific Plate has been subducting westwards. This ophiolitic belt (Mineoka Belt) is composed of mafic-ultramafic rocks together with Tertiary chert and limestone and island-arc volcaniclastic rocks. Our detailed structural studies in and around the basaltic rock bodies within the ophiolite reveal three phases of deformation. The first phase is further divided into three stages, all related to oblique normal faulting associated with extensional tectonics at or near a spreading axis. Fluid pressures appear to have fluctuated in association with faulting and veining during this phase. The second phase of deformation is characterized by thrust-related shear zones with a significant strike-slip component and is probably related to the final emplacement of the ophiolite by oblique subduction-obduction processes. The third and final phase of deformation affected not only the ophiolite but also later terrigenous and island-arc pyroclastic rocks. This deformation involved large-scale transpressional dextral slip on forearc sliver faults, which are still active today.