bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geological prior information and its applications to geoscientific problems
Authors: Wood Rachel , Curtis Andrew 
Published: April 2008

Abstract

Geological information can be used to solve many practical and theoretical problems, both within and outside of the discipline of geology. These include analysis of ground stability, predicting subsurface water or hydrocarbon reserves, assessment of risk due to natural hazards, and many others. In many cases, geological information is provided as an
a priori
component of the solution (i.e. information that existed before the solution was formed and which is incorporated into the solution). Such information is termed ‘geological prior information’.

The key to the successful solution of such problems is to use only
reliable
geological information. In turn this requires that: (1) multiple geological experts are consulted and any conflicting views reconciled, (2) all prior information includes measures of confidence or uncertainty (without which its reliability and worth is unknown), and (3) as much information as possible is quantitative, and qualitative information or assumptions are clearly defined so that uncertainty or risk in the final result can be evaluated. This paper discusses each of these components and proposes a probabilistic framework for the use and understanding of prior information.

We demonstrate the methodology implicit within this framework with an example: this shows how prior information about typical stacking patterns of sedimentary sequences allows aspects of 2-D platform architecture to be derived from 1-D geological data alone, such as that obtained from an outcrop section or vertical well. This example establishes how the extraction of quantitative, multi-dimensional, geological interpretations is possible using lower dimensional data. The final probabilistic description of the multi-dimensional architecture could then be used as prior information sequentially for a subsequent problem using exactly the same method.
Stratal patterns and lithofacies of an intact seismic-scale Carboniferous carbonate platform (Asturias, northwestern Spain): a virtual outcrop model
Authors: Verwer Klaas , Kenter Jeroen A. M. , Maathuis Ben , Della Porta Giovanna 
Published: April 2008

Abstract
Among the more challenging questions in geology are those concerning the anatomy of sedimentary bodies and related stratal surfaces. Though significant progress has been made on the interpretation of depositional environments, little systematic data are available on their dimensions and geometry. With the recent advances in computer power, software development and accuracy of affordable positioning equipment, it has now become possible to extract high-resolution quantitative data on the anatomy of sedimentary bodies. In Asturias, northwestern Spain, aerial photography provides continuous 2-D cross-sections of a seismic-scale, rotated to vertical, carbonate platform margin of the Early Carboniferous. Digital elevation models, orthorectified aerial photographic imagery and ground verification of stratal surfaces generated the elements that are required to reconstruct the true dimensions, angular relationships of bedding planes and the spatial distribution of facies units in this platform margin. Along with biostratigraphy this provides sufficient constraints to estimate rates of progradation, aggradation, growth and removal of sediments in the slope environment. Here we present a methodology to create outcrop models and integrate complementary types of data that provide new insights in sedimentology that were previously unattainable.
Lithospheric structure of the Canadian Shield inferred from inversion of surface-wave dispersion with thermodynamic
a priori
constraints
Authors: Shapiro N. M. , Ritzwoller M. H. , Mareschal J. C. , Jaupart C. 
Published: April 2008

Abstract

We argue for and present a reformulation of the seismic surface-wave inverse problem in terms of a thermal model of the upper mantle and apply the method to estimate lithospheric structure across much of the Canadian Shield. The reformulation is based on a steady-state temperature model, which we show to be justified for the studied region. The inverse problem is cast in terms of three thermal parameters: temperature in the uppermost mantle directly beneath Moho, mantle temperature gradient, and the potential temperature of the sublithospheric convecting mantle. In addition to the steady-state constraint, prior physical information on these model parameters is based on surface heat flow and heat production measurements, the condition that melting temperatures were not reached in the crust in Proterozoic times and other theoretical considerations. We present the results of a Monte Carlo inversion of surface-wave data with this ‘thermal parameterization’ subject to the physical constraints for upper mantle shear velocity and temperature, from which we also estimate lithospheric thickness and mantle heat flux. The Monte Carlo inversion gives an ensemble of models that fit the data, providing estimates of uncertainties in model parameters. We also estimate the effect of uncertainties in the interconversion between temperature and seismic velocity. Variations in lithospheric temperature and shear velocity are not well correlated with geological province or surface tectonic history. Mantle heat flow and lithospheric thickness are anti-correlated and vary across the studied region, from 11 mW/m
2
and nearly 400 km in the northwest to about 24 mW/m
2
and less than 150km in the southeast. The relation between lithospheric thickness and mantle heat flow is consistent with a power law relation similar to that proposed by Jaupart
et al.
(1998), who argued that the lithosphere and asthenosphere beneath the Canadian Shield are in thermal equilibrium and heat flux into the deep lithosphere is governed by small-scale sublithospheric convection.
In situ
seismic investigations of fault zones in the Leventina Gneiss Complex of the Swiss Central Alps
Authors: Ciese R. , Klose C. , Borm G. 
Published: April 2008

Abstract
Underground seismic tomography investigations have been carried out in the Faido access tunnel of the Gotthard Base Tunnel, Switzerland. Velocity measurements were made over a total length of 2651 m of the adit with the tunnel seismic prediction system, ISIS (Integrated Seismic Imaging System). ISIS provides high-resolution seismic imaging, using an array of rock anchors equipped with 3D-geophones.

The first onsets of the compressional and shear waves were used for tomographic inversion. Two-dimensional seismic-velocity models reveal a disturbed zone between 2 and 3 m inward from the tunnel wall, characterized by strong variations from 3500 to 5800 m s
−1
in compressional wave velocity
V
P
, and from 2000 to 3000 m s
−1
in shear-wave velocity
V
S
. High-velocity zones correspond to quartz lenses, and low velocities mainly indicate fractured rock. Beyond the excavation disturbance zone, the variations in seismic velocities are generally smaller. The tomographic image of the rock mass also revealed two major fault zones composed of cataclastic shear planes surrounded by wider fracture zones. These structural characteristics are also useful for the prediction of cataclastic zones at other sites.
Integration of electrical and optical images for structural analysis: a case study from ODP Hole 1105A
Authors: Haggas S. L. , Brewer T. S. , Harvey P. K. , Macleod C. J. 
Published: April 2008

Abstract
A significant problem with basement core data acquired by the Ocean Drilling Program (ODP) is that it is unorientated with respect to grid north and in those cores with < 100% core recovery the data may also be inaccurately located within the borehole. In order for structural data from basement cores to be of any real value, the recovered core must firstly be accurately located and orientated. Here, we develop methods for core reorientation and accurate location within a borehole that integrates wireline borehole electrical images with whole-core digital images. Azimuthal orientation and location of individual core pieces allows for the detailed interpretation of structural data, including fabrics and fractures and reorientation of other spatially anisotropic properties of core, such as palaeomagnetism.
ODP Hole 1105A is one of a pair of holes drilled on the Atlantis Bank in the SW Indian Ocean, which penetrate sections of the lower ocean crust. Hole 1105A was drilled to a depth of 158 metres below sea-floor (mbsf), with core recovery of 83% and the vast majority of the recovered material being represented by gabbroic rocks.
Zones of crystal-plastic deformation occur throughout the core, but overall their frequency increases downhole. In the deformed zones, the gabbros are transformed into equigranular or porphyroclastic gneissose textured rocks, characterized by very prominent planar fabrics. These localized deformation zones relate to the early exhumation history of the lower crust in an environment similar to core-complex formation in continental regions.

Using a combination of digital core and formation microscanner (FMS) images, it is now possible to fully orientate structural features in a borehole and so map the oxide gabbro and crystal-plastic deformation zones in Hole 1105A. From the analysis of the crystal-plastic fabrics, the majority appear to dip southwards, with a few (
c
.5%) dipping to the north. This would suggest that the major exhumation surfaces in this hole are represented by southward-dipping structures, formed at high temperatures during unroofing of the Atlantis Bank.
The interpretation of thermal neutron properties in ocean floor volcanics
Authors: Brewer T. S. , Harvey P. K. , Barr S. R. , Haggas S. L. , Delius H. 
Published: April 2008

Abstract
Using near-complete chemical analyses, computed thermal absorption cross-section values (σ) are calculated for ocean-floor basalts from ODP Holes 896a and 1179D. Comparison with nuclear measurement of σ, demonstrates that this computational method is valid and clarifies the interpretation of σ in ocean-floor basalts. Boron, lithium and the rare-earth elements are important controls on the σ-values, and, of these, the distribution of the rare-earth elements is controlled by primary magmatic processes, whereas the distribution of boron and lithium is strongly influenced by secondary low-temperature alteration processes. Consequently, computed σ-values can be used to discriminate between various basalt types and to identify areas of secondary alteration.
Following calibration of the ‘fresh basalt’ signature, it is possible to interpret log derived neutron absorption measurements of a sample (Σ-values), which, when integrated with other log responses, allow the distribution of alteration within a drilled section to be mapped. Examples from ODP Hole 801C demonstrate the potential of this technique.
Microstructure, filtration, elastic and thermal properties of granite rock samples: implications for HLW disposal
Authors: Petrov V. A. , Poluektov V. V. , Zharikov A. V. , Nasimov R. M. , Diaur N. I. , Terentiev V. A. , Burmistrov A. A. , Petrunin G. I. , Popov V. G. , Sibgatulin V. G. , Lind E. N. , Grafchikov A. A. , Shmonov V. M. 
Published: April 2008

Abstract
This contribution presents preliminary data on the petrographic and mineral—chemical composition of the granitoid and dioritoid core samples of the Itatsky and Kamenny sites in the Nizhnekansky Massif of the Krasnoyarsk Region, in combination with data on structure of their pore space, filtration, elastic, mechanical and thermophysical properties, data necessary to select a site for an underground research laboratory. This laboratory would be a precursor to an underground radioactive waste facility. It was found that the variation of petrophysical properties depends on the degree of metamorphic, hydrothermal—metasomatic and deformational transformations, and differs markedly for two groups of rocks, namely, 1 — granites and granite-gneisses, and 2 — quartz diorites and diorites. Comparative analysis of the data obtained shows that the country rocks of the Kamenny site have a relatively higher degree of heterogeneity in their petrophysical characteristics, than those of the Itatsky site. These results could be applied both to select the preferred site and to make a preliminary estimate of the thermal, hydraulic and mechanical behaviour of country rocks in the vicinity of a prospective underground heat-generating waste repository.
Effect of compositional and structural variations on log responses of igneous and metamorphic rocks. I: mafic rocks
Authors: Bartetzko A. , Delius H. , Pechnig R. 
Published: April 2008

Abstract

Well logging has become a standard method in the oil industry for the investigation of subsurface geology. Accordingly, interpretation techniques have been mainly developed for use in sedimentary rocks, and the log responses of sediments are well known. However, this is not the case for igneous and metamorphic rocks. We present a compilation of log responses for mafic rocks from drill-holes in oceanic and continental basement. The holes cover a variety of mafic rocks: mid-ocean ridge basalt (MORB), gabbro, basalt and andesitic basalt from back-arc basins, flood basalt from large igneous provinces (LIPs), and continental metamorphic rocks. The comparison of log responses shows that rocks from the same geological setting have similar
in situ
physical properties. Differences in physical properties between rocks from different geological settings are mainly related to variations in the structure of the rocks, while variations in composition have only a minor effect on the
in situ
physical properties. In volcanic rocks, variations in fracturing and vesicularity related to cooling of the lava strongly influence log responses. Mafic rocks from continental drill-holes were enriched in radioactive elements during regional metamorphism, resulting in higher values in the total gamma-ray compared to the oceanic rocks.
Investigating glacier-permafrost relationships in high-mountain areas: historical background, selected examples and research needs
Authors: Haeberli Wilfried 
Published: April 2008

Abstract
Investigations on the relationships and interactions between glaciers and permafrost in high-mountain regions have long been neglected. As a consequence, numerous fascinating questions remain open and offer possibilities for highly relevant, innovative and integrative research concerning materials, processes, landforms, environmental aspects and natural hazards. The historical background to this situation is first reviewed, examples are given of some key unanswered questions and two case studies are presented to illustrate the importance of considering the combined effects of glaciers and permafrost, particularly in the context of hazard assessments in high mountains.
Glacier-rock glacier relationships as climatic indicators during the late Quaternary in the Cordillera Ampato, Western Cordillera of southern Peru
Authors: Dornbusch Uwe 
Published: April 2008

Abstract
Mapping of glacial and periglacial features along a 15 km long, north-south trending ridge at the eastern end of the Cordillera Ampato (Fig. 1) has been carried out using aerial photograph interpretation. Over the length of the ridge a distinct change in features from moraines and small rock glaciers in the north to large rock glaciers and a lack of moraines in the south can be observed. It is suggested that this feature change reflects a steep precipitation gradient during the Pleistocene. Comparison with geomorphological mapping — both in the field and from air photographs — in other areas of the Cordillera Ampato and further west shows that this feature change is unique and that its location at the eastern end of the Cordillera is in good agreement with present-day precipitation distribution. This indicates that the general precipitation pattern, and thus the general circulation pattern, during the Pleistocene was very similar to that today.
Kinematics of syneclogite deformation in the Bergen Arcs, Norway: implications for exhumation mechanisms
Authors: Raimbourg Hugues , Jolivet Laurent , Labrousse Loïc , Leroy Yves , Avigad Dov 
Published: April 2008

Abstract
The northwestern part of Holsnøy island, in the Bergen Arcs, Norway, consists of a granulite-facies protolith partially transformed at depth in eclogite (700 °C, > 19 kbars) and amphibolite (650 °C, 8–10 kbars) facies during the Caledonian orogenesis. Eclogitized zones are mainly planar objects (fractures with parallel reaction bands and cm-to-100 m-scale shear zones). Eclogitic zones are distributed in two sets of orientations and the associated deformation can be described as ‘bookshelf tectonics’. The major shear zones strike around N120 and dip to the North, and show consistent top-to-the-NE shear sense throughout the area.
In the large-scale kinematic frame of Caledonian NW-dipping slab, eclogitic shear zones are interpreted as the way to detach crustal units from the subducting slab and to prevent their further sinking. As the retrograde amphibolitic deformation pattern is similar to the eclogitic one, the detached crustal units started their way up along these eclogitic shear zones. Radiometric ages of eclogitic and amphibolitic metamorphism and their comparison with the chronology of Caledonian orogenesis show that the deformation recorded on Holsnøy occurred in a convergent context. The mechanism we propose can thus account for the first steps of exhumation during collision.
Decoupling and its relation to strain partitioning in continental lithosphere: insight from the Periadriatic fault system (European Alps)
Authors: Handy M. R. , Babist J. , Wagner R. , Rosenberg C. , Konrad M. 
Published: April 2008

Abstract
The Periadriatic fault system (PFS) is an array of late orogenic faults (35-15 Ma) in the retro-wedge of the Alpine orogen that accommodated dextral transpression during oblique indentation by the southern Alpine crust. Decoupling along the leading edges of the southern Alpine indenter occurred where inherited lithological and rheological contrasts were accentuated by lateral thermal gradients during emplacement of the warm orogenic retro-wedge next to the cold indenter. In contrast, decoupling within the core and retro-wedge of the orogen occurred in a network of folds and mylonitic faults. In the Eastern Alps, this network comprises conjugate sets of upright, constrictional folds, strike-slip faults and low-angle normal faults that accommodated nearly coaxial NNE-SSW shortening and E-W extensional exhumation of the Tauern thermal dome. The dextral shear component of oblique convergence was taken up by a discrete, brittle fault parallel to the indenter surface. In the Central and Western Alps, a steep mylonitic backthrust, upright folds, and low-angle normal faults effected transpressional exhumation of the Lepontine thermal dome. Mylonitic thrusting and dextral strike-slip shearing along the steep indenter surface are transitional along strike to low-angle normal faults that accommodated extension at the western termination of the PFS. The areal distribution of poles to mylonitic foliation and stretching lineation of these networked structures is related to the local shape and orientation of the southern Alpine indenter surface, supporting the interpretation of this surface as the macroscopic shearing plane for all mylonitic segments of the PFS. We propose that mylonitic faults nucleate as viscous instabilities induced by cooling, or more often, by folding and progressive rotation of pre-existing foliations into orientations that are optimal for simple shearing parallel to the eigenvectors of flow. The mechanical anisotropy of the viscous continental crust makes it a preferred site of decoupling and weakening. Networking of folds and mylonitic fault zones allow the viscous crust to maintain strain compatibility between the stronger brittle crust and upper mantle, while transmitting plate forces through the lithosphere. Decoupling within the continental lithosphere is therefore governed by the symmetry and kinematics of strain partitioning at, and below, the brittle-to-viscous transition.
Late Quaternary shelf-margin wedges and upper slope progradation in the Gulf of Cadiz margin (SW Iberian Peninsula)
Authors: Lobo F. J. , Dias J. M. A. , Hernández-Molina F. J. , González R. , Fernández-Salas L. M. , Díaz Del Río V. 
Published: April 2008

Abstract
The distribution patterns and internal geometries of recent shelf-margin wedges off the Guadiana River, Gulf of Cadiz margin, were studied in order to discern the effects of varying trends of falling sea-level and lowstand on upper slope progradation. A seismic-sequence stratigraphic analysis was conducted, based on the interpretation of a dense grid of high-resolution seismic profiles.
Five major shelf-margin wedges deposited during late Quaternary sea-level fall and lowstand periods were documented. Most of the studied shelf-margin wedges produce upbuilt-outbuilt upper slopes. The analysis of their internal geometries reveals two distinct types of configuration: the four older shelf-margin wedges are mainly composed of forced regressive deposits developed during stepped sea-level falls. The scarceness of lowstand deposits suggests abrupt sea-level fall to rise transitions; and the most recent shelf-margin wedge shows both forced regressive deposits and low-stand deposits significantly preserved. This architecture probably resulted from the occurrence of a long-lived sea-level lowstand after a prolonged period of gentle sea-level fall.
Two types of shelf-margin wedges have been recognized: wedges with elongate parallel depocentres, laterally constant thickness and uniform seaward shelf-break migration, related to linear source supply and high lateral sediment redistribution during gently falling sea level; and wedges with (multi) lobate depocentres with laterally variable thickness, leading to uneven shelf-break migration during periods of faster sea-level fall, due to delta lobe switching and significant shelf valley incision.