bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropy of magnetic susceptibility (AMS): magnetic petrofabrics of deformed rocks
Authors: Borradaile Graham J. , Jackson Mike 
Published: April 2008

Abstract

For 40 years magnetic anisotropy has provided successful geological interpretations of magnetic ellipsoid orientations; in contrast the interpretation of anisotropy magnitudes is far more convoluted. This is due to complexities at various levels within rocks, including different physical magnetic responses of different minerals, grain-scale magnetic anisotropy, the anisotropy of interacting ensembles, the mineralogical constitution of rocks and the processes and mechanisms that align minerals in nature. The chief factors determining the magnetic fabrics of tectonized rocks include: mineral-physics properties, crystal symmetry, mineral-abundances, tectonic symmetry and crystal orientation-distribution, strain
or
stress, kinematic history and certain tectono-metamorphic processes (e.g. diffusion, crystal plasticity, dynamic recrystallization, particulate flow, neomineralization). AMS ultimately provides an integrated record of some combination of these factors. Subfabrics due to distinct processes or events may be expressed in different mineral and/or grain-size fractions, and are superposed in the conventionally observed AMS. Their discrimination may be achieved by various laboratory techniques such as magnetization and torque measurements in weak and strong applied fields, anisotropy of ARM and IRM, gyroremanence, Rayleigh magnetization, chemical leaching. However, under limited circumstances, statistical approaches such as differential analysis, tensor standardization, symmetry of confidence regions for the principal axes may partly isolate different subfabric orientations.
Anisotropy of magnetic susceptibility in the Montes de Toledo area (Hercynian Iberian Belt, Spain) and its petrostructural significance
Authors: Gil-Imaz A. , Barbero L. 
Published: April 2008

Abstract
Anisotropy of magnetic susceptibility data are presented for samples from the anatectic complex of Toledo and the Mora batholith. The units located at the axial part of the Central Hercynian belt are separated by an important listric fault. Anatectic granites (Layos granite), epizonal granites (Mora granite) and, to a lesser extent, high-grade metamorphic rocks and metasediments are considered in this work in order to characterize their magnetic fabric and determine their structural significance in the framework of a large-scale extensional deformation of Late Variscan age. Samples from the Layos granites (footwall) show a magnetic lineation compatible with the stretching related to ductile shear deformation of the Toledo shear zone, which was responsible for the exhumation of the anatectic complex. During the exhumation, the folding of a previous metamorphic foliation in the anatectic complex took place, which is also recognized from the magnetic pattern of the minimum susceptibility axes of Layos granite. On the contrary, the magnetic fabric of the epizonal Mora granites (hanging wall), which intruded at the beginning of the extensional Late Variscan tectonics, mainly reflects magmatic processes.
Relationships between magnetic and structural fabrics revealed by Variscan basement rocks subjected to heterogeneous deformation—a case study from the Kłodzko Metamorphic Complex, Central Sudetes, Poland
Authors: Kądziałko-Hofmokl M. , Mazur S. , Werner T. , Kruczyk J. 
Published: April 2008

Abstract
The Kłodzko Metamorphic Complex comprises a number of thrust units, consisting of meta-igneous and metasedimentary rocks of the Variscan basement of the Sudetes, NE Bohemian Massif. The thrust sheet stack rests upon unmetamorphosed Nowa Ruda ophiolite and is unconformably overlain by Frasnian-Fammenian sediments. The studied rocks underwent six deformation events, scattered in time between the Middle Devonian and Late Carboniferous. The multiphase deformation produced a steep foliation that consistently trends WNW-ESE and a mineral lineation plunging to the ESE at a shallow to moderate angle. The results of the AMS study show that, despite the complex structural evolution, all the studied rocks bear a similar magnetic fabric mirroring the principal structural directions. This relationship between magnetic and structural fabrics is apparent in all tectonic units irrespective of the considerable variations in strain rate and metamorphic grade. This suggests a rather low dependence of magnetic anisotropy on the changing conditions and intensity of deformation.
Development of magnetic fabrics during hydrothermal alteration in the Soultz-sous-Forêts granite from the EPS-1 borehole, Upper Rhine Graben
Authors: Just Jana , Kontny Agnes , De Wall Helga , Hirt Ann M. , Martín-Hernández Fatíma 
Published: April 2008

Abstract

The Variscan, magnetite-bearing Soultz-sous-Forêts granite is found between 1420 and 2230 m of the EPS-1 borehole situated in the Upper Rhine Graben (France). Our study focuses on the changes of magnetic properties that occur during the progressive hydrothermal alteration and fracturing of the Soultz granite after emplacement. The magnetic susceptibility (κ) of the granite is between 10 and 80 × 10
−3
SI, and suggests that ferrimagnetic minerals are the primary carrier. During cooling and later tectonic and hydrothermal overprints, including the formation of the Rhine Graben, the granite was deformed under brittle conditions and partially altered by hydrothermal fluids. Along with this fluid activity, oxidation of magnetite to hematite occurred and reduced κ (< 1 × 10
−3
SI). AMS analysis on oriented samples documents the history of progressive transformation from primary magmatic fabric to tectonic fabric during hydrothermal alteration and faulting. The fresh granite with multidomain magnetite grains shows sub-horizontal magnetic foliations and randomly oriented magnetic lineations within the foliation plane. This fabric is similar to the magmatic fabric reflected by biotite. Transformation of the magnetic fabric started with localized magnetite oxidation along NW-SE oriented micro-cracks, which are probably associated with a late-magmatic alteration (stage I). Elongated and co-aligned magnetite relics within the newly formed hematite caused a well-defined NW-SE trending magnetic lineation and steeper magnetic foliation. Later alteration associated with intense brittle deformation (stage II) initially adopted this magnetic fabric, but intense cataclasis destroyed it. The geometry and orientation of magnetic fabric clearly indicate a hydrothermal alteration, which relates to the acting tectonic stresses in the post-emplacement history of the Soultz granite.
An introduction to prior information derived from probabilistic judgements: elicitation of knowledge, cognitive bias and herding
Authors: Baddeley Michelle C. , Curtis Andrew , Wood Rachel 
Published: April 2008

Abstract
Opinion of geological experts is often formed despite a paucity of data and is usually based on prior experience. In such situations humans employ heuristics (rules of thumb) to aid analysis and interpretation of data. As a result, future judgements are bootstrapped from, and hence biased by, both the heuristics employed and prior opinion.
This paper reviews the causes of bias and error inherent in prior information derived from the probabilistic judgements of people. Parallels are developed between the evolution of scientific opinion on one hand and the limits on rational behaviour on the other. We show that the combination of data paucity and commonly employed heuristics can lead to herding behaviour within groups of experts. Elicitation theory mitigates the effects of such behaviour, but a method to estimate reliable uncertainties on expert judgements remains elusive.
We have also identified several key directions in which future research is likely to lead to methods that reduce such emergent group behaviour, thereby increasing the probability that the stock of common knowledge will converge in a stable manner towards facts about the Earth as it really is. These include: (1) measuring the frequency with which different heuristics tend to be employed by experts within the geosciences; (2) developing geoscience-specific methods to reduce biases originating from the use of such heuristics; (3) creating methods to detect scientific herding behaviour; and (4) researching how best to reconcile opinions from multiple experts in order to obtain the best probabilistic description of an unknown, objective reality (in cases where one exists).
Sensitive dependence, divergence and unpredictable behaviour in a stratigraphic forward model of a carbonate system
Authors: Burgess Peter M. , Emery David J. 
Published: April 2008

Abstract
Although conceptual models of carbonate systems typically assume a dominance of external forcing and linear behaviour to generate metre-scale carbonate parasequences, there is no reason to preclude autocyclic and non-linear behaviour in such systems. Component parts of the carbonate system represented in this numerical forward model are entirely deterministic, but several parts are non-linear and exhibit complex interactions. Onshore sediment transport during relative sea-level rise generates autocyclic quasi-periodic shallowing upward parasequences but model behaviour is sufficiently complex that water depth evolution and parasequence thickness distributions are not predictable in any detail. The model shows sensitive dependence on initial conditions, resulting in divergence of two model cases, despite only a small difference in starting topography. Divergence in water-depth history at one point takes ∼ 10 ka, and for the whole model grid takes ∼ 100 ka. Fischer plots from the two cases show that divergence leads to entirely different parasequence thickness evolution in each case. Chaotic behaviour is a specific type of sensitive dependence, and calculation of trajectory divergence in a 3-D pseudo-phase space indicates that water depth evolution is not truly chaotic. If sensitive dependence, divergence and complex processes generating random products turn out to be common in real carbonate systems, predictions should be limited to elements of the system unaffected by these phenomena, or limited to cases where an element of periodic external forcing over-rides their affects. These results also suggest that increasingly complex and sophisticated stratigraphic forward models are not necessarily going to lead directly to more deterministic predictive power, although they may well be useful sources of statistical data on carbonate strata.
Input uncertainty and conditioning in siliciclastic process modelling
Authors: Tetzlaff Daniel M. 
Published: April 2008

Abstract
Deterministic forward sedimentary process models enhance our quantitative understanding of sedimentary systems. They are also being used increasingly to assist in the reconstruction of the geological past and the inference of the present configuration of sedimentary deposits. Such usage presents the challenge of having to establish the initial and boundary conditions that will cause the model’s output to match present-day observations. This constitutes an inversion problem that can sometimes be handled by traditional optimization methods. Clastic sedimentation models, however, often incorporate complex non-linear relationships that preclude the use of these techniques. The problem must then be handled statistically by relaxing the requirement of honouring exact observations and matching only the spatial variability of the observed deposits. Recent advances in control of non-linear dynamic systems may also shed light on possible solutions to the inversion problem in siliciclastic models. This paper reviews known approaches to problems related to input uncertainty and conditioning, and presents original preliminary results on control of sedimentation models.
Classical logic and the problem of uncertainty
Authors: Pshenichny Cyril A. 
Published: April 2008

Abstract
The uncertainty of knowledge, in contrast to that of data, can be assessed by its probability in the logical sense. The logical concept of probability has been developed since the 1930s but, to date, no complete and accepted framework has been found. This paper approaches this problem from the point of view of logical entailment and natural sequential calculus of Classical logic. It is shown herein that probability can be comprehended in terms of a set of formal theories built in similar language. This measure is compliant with general understanding of probability, can be both conditional and unconditional, accounts for learning new evidence and complements Bayes’ rule. The approach suggested is practically infeasible at present and requires further theoretical research in the domain of geoscience. Nevertheless, even within the framework of existing methods of expert judgement processing, there is a way of implementing logic that will improve the quality of judgements. Also, to reach the state of formalization necessary to use logical probability, techniques of knowledge engineering are required; this paper explains how logical probabilistic methods relate to such techniques, and shows that the perfect formalization of a domain of knowledge requires them. Hence, the lines for future research should be: (1) the development of a strategy of co-application of existing expert judgement-processing techniques, knowledge engineering and classical logic; and (2) further research into logic enabling the development of formal languages and theories in geoscience.
Scale dependence of hydraulic and structural parameters in fractured rock, from borehole data (KTB and HSDP)
Authors: Zimmermann G. , Burkhardt H. , Engelhard L. 
Published: April 2008

Abstract
Fundamental understanding of the origin, geometry, extension and scale dependence of fluid pathways in fractured rock is still incomplete. We analysed fracture networks on different scales, based on data from fluorescent thin sections and borehole televiewer (BHTV) images, to obtain geometrical network parameters and to estimate fracture permeability in the vicinity of a mantle plume (Hawaii Scientific Drilling Project, HSDP).
In the depth interval between 814 and 1088 m below sea-level, we observed microfractures in the fluorescent thin sections, and macroscopic fractures in the corresponding BHTV data from the same depth range. Initial modelling of the microscopic network from the fluorescent thin section taken at 1088 m below sea-level gives a clear indication that in this particular case the preferential hydraulic pathways on the microscopic scale are the microfractures in the olivine crystals. This is the only plausible explanation of high porosity (16.6%, based on core measurement), due to the observed vesicles and the corresponding low permeability of 10 µdarcy. Modelling hydraulic flow and calculation of permeability leads to similar values of permeability of 12.3 µdarcy, assuming a mean fracture aperture of 1 µm and an exponential distribution function of the fractures.

Detected structures from BHTV measurements were used to construct a macroscopic stochastic network to simulate the hydraulic flow. We found 337 fractures in the depth section from 783.5 to 1147.5 m below sea-level, which result in a linear frequency of 0.927 m
−1
. Assuming horizontal layers and constant fracture apertures of 100 µm for all structures, leads to a first estimate of permeability of 77 mdarcy (7.7 × 10
−14
m
2
) in this depth section.

In a recent work, we showed that for data from the Continental Deep Drilling Project (KTB), the fracture density versus fracture length follows a power law. First results from the Hawaiian data suggest a similar relationship, despite all of the differences in the lithological conditions between both sites.
Distribution and properties of fractures in and around the Nojima Fault in the Hirabayashi GSJ borehole
Authors: Ito H. , Kiguchi T. 
Published: April 2008

Abstract
A borehole penetrating the Nojima Fault was drilled in 1996, one year after the magnitude 7.2 1995 Kobe earthquake. The major fracture distribution detected by a borehole imaging tool (FMI) in the borehole was compared with the S-anisotropy from aftershocks. The fractures far from the Nojima Fault (more than 50 m) are aligned in an east—west direction, that is, parallel to the tectonic stress direction, whereas the fractures close to the Nojima Fault are normal to the fault. In the fault zone, a fault-parallel fault system was observed over short depth intervals, otherwise the fracture system in the fault zone is random. The fault-normal fracture suggests the complete reduction of the shear stress of the Nojima Fault.
Petrofabric-derived seismic properties of a mylonitic quartz simple shear zone: implications for seismic reflection profiling
Authors: Lloyd G. E. , Kendall J. M. 
Published: April 2008

Abstract

The link between petrofabric (LPO) and seismic properties of an amphibolite-facies quartzo-feldspathic shear zone is explored using SEM/EBSD. The shear-zone LPO develops by a combination of slip systems and dauphine twinning, with
a
-maximum parallel to lineation (
X
) and
c
-maximum normal to mylonitic foliation (
XY
). The LPO are used to predict elastic parameters, from which the three-dimensional seismic properties of different shear-zone regions are derived. Results suggest that LPO evolution is reflected in the seismic properties but the precise impact is not simple. In general, the P-wave velocity (
V
P
) minimum is parallel to the
a
-axis maximum; the direction of maximum shear-wave splitting (
AV
S
) is parallel to mylonitic foliation; and the
V
P
maximum and
AV
S
minimum are parallel to the
c
-axis maximum. The seismic anisotropy predicted is significant and increases from shear zone wallrock to mature mylonite. The P-wave anisotropy ranges from 11 to 13%, fast and slow shear waves’ anisotropies range from 6 to 15% and the magnitude of shear-wave splitting ranges from 9 to 16%. Nevertheless, such anisotropy requires a considerable thickness of rock with this LPO before it becomes seismically visible (i.e. 100s of m for local earthquakes; 10s of m for controlled source experiments). However, reflections and mode conversions provide much better resolution, particularly across tectonic boundaries. The low symmetry and strong anisotropy due to the LPO suggest that multi-azimuth wide-angle reflection data may be useful in the determination of the deformation characteristics of deep shear zones.
Fractured reservoir analysis using modern geophysical well techniques: application to basement reservoirs in Vietnam
Authors: Luthi S. M. 
Published: April 2008

Abstract
Recent geophysical well techniques have significantly improved the analysis of fractured reservoirs. These methods include electrical and ultrasonic scans and, in some cases, optical video images, that provide azimuthal high-resolution images of the borehole wall on which fractures are prominently visible. Additionally, fractures produce reflections and attenuations of the Stoneley wave, a borehole mode recorded by the array sonic wireline tool. A fracture identified with these methods can be individually probed with a new wireline formation tester featuring a dual-packer module that hydraulically isolates it from the surrounding formation. The combination of these techniques can provide information on fracture locations, dip, azimuth, aperture, permeability and fluid content. Seismic data can be used to extrapolate this information away from the wells. A case study on basement reservoirs from offshore Vietnam exhibits foliations, borehole breakouts, hydraulic and tectonic fracturing. Oil production comes from a small number of point entries that correspond to fractures, most of which produce more than 1000 barrels of oil per day. Two intersecting fracture sets were found, which may explain the high sustained production. Properly planned horizontal wells may increase production and decrease the chance of water breakthrough.
Fracture mapping with electrical core images
Authors: Lovell M. , Jackson P. , Flint R. , Harvey P. K. 
Published: April 2008

Abstract
Naturally fractured reservoirs often contain a range of different fracture types and networks; fractures that are relatively permeable and relatively impermeable, unconnected and connected to the part of the fracture network that carries fluid flow, and naturally occurring or drilling induced. Consequently, in terms of their fluid connectivity, fractures may be open or closed, while individual fractures may be isolated or well connected.
We have adapted our approach to imaging sedimentary fabric in the laboratory, where we related electrical core images to properties such as porosity, permeability, grain size and cementation, to enable electrical imaging of fractures in core. Our approach uses similar principles to those employed in down-hole electrical imaging. The results demonstrate an ability to image conductive fractures in fully saturated low-porosity water-bearing core: these fractures being electrically connected from the flat measurement surface through to the outer surface of the core.
Published results for numerical modelling of down-hole electrical imaging tools show the electrical response is related to fracture depth and fracture aperture. Our experimental results on fractured core in the laboratory support these numerical observations, increased current flowing into the fracture as the aperture increases. The finite size of the electrode, however, means that this technique cannot distinguish between a single fracture and smaller groups of fractures intersecting the electrode.
Reactive flow and permeability prediction — numerical simulation of complex hydrogeothermal problems
Authors: Bartels J. , Clauser C. , Kühn M. , Pape H. , Schneider W. 
Published: April 2008

Abstract
Simulating complex flow situations in hydrogeothermal reservoirs requires coupling of flow, heat transfer, transport of dissolved species, and heterogeneous geochemistry. We present results of simulations for typical applications using the numerical simulator SHEMAT/Processing SHEMAT. Heat transfer is non-linear, since all thermal fluid and rock properties depend on temperature. Due to the coupling of fluid density with both temperature and concentrations of dissolved species, the model is well suited to simulate density-driven flow.
Dissolution and precipitation of minerals are calculated with an improved version of the geochemical modelling code PHRQPITZ, which accurately calculates geochemical reactions in brines of low to high ionic strength and temperatures of 0–150°C. Changes in pore space structure and porosity are taken into account by updating permeability with respect to porosity changes due to precipitation and dissolution of minerals. This is based on a novel relationship between porosity and permeability, derived from a fractal model of the pore space structure and its changes due to chemical water — rock interaction.
A selection of model studies performed with SHEMAT completes the review. Examples highlight both density-driven and reactive flow with permeability feedback. With respect to the former, the thermohaline free convection Elder’s problem, and density-driven free convection in a coastal aquifer with geothermal exploitation, are considered. Mineral redistribution and associated permeability change during a core flooding experiment; reaction front fingering in reservoir sandstone; and long-term changes in reservoir properties during the operation of a geothermal installation, are all considered in relation to reactive flow with permeability feedback.