bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proterozoic geochronology and tectonic evolution of southern Africa
Authors: Hanson R. E. 
Published: April 2008

Abstract
The Precambrian foundation of southern Africa consists of Archaean cratonic nuclei surrounded by belts formed during three separate Proterozoic orogenic episodes. Crust that formed or was reworked at 2.05–1.8 Ga is represented by orogenic belts (e.g. Kheis-Magondi, Ubendian-Usagaran) that partly wrap the ancient craton margins or form extensive basement in younger belts. Orogenic belts formed at 1.35–1.0 Ga record arc magmatism and collisional events during assembly of the Rodinia supercontinent. The Namaqua-Natal Belt defines a major convergent plate boundary active at this time along the southern margin of the Archaean Kaapvaal Craton, and the western part of this belt is inferred to link with a largely buried, NE-trending orogen present in the Kalahari region. Orogenesis in the same time frame farther north is recorded by the Kibaran and Irumide Belts, which are separated by the Palaeoproterozoic Bangweulu Block but are inferred to have undergone a linked tectonic evolution. East of the Irumide Belt, extensive Mesoproterozoic arc crust occurs in Malawi and Mozambique, although strong Neoproterozoic overprinting of the arc rocks makes their original relations unclear. Breakup of Rodinia is signalled by widespread Neoproterozoic alkaline and bimodal magmatism associated with rift zones which, in some cases, evolved into major ocean basins. Subsequent amalgamation of Gondwana led to collisional orogenesis culminating at 575–505 Ma in the Mozambique and West Congo-Kaoko-Gariep-Saldania Belts along the present eastern and western margins of southern Africa. Coeval deformation in the interconnecting, transcontinental Damara-Lufilian-Zambezi Orogen may reflect destruction of linked rifts and narrow ocean basins driven by farfield stresses from the collisional plate margins.
Middle Jurassic to Cretaceous extensional tectonics and sedimentation in the eastern external zone of the Betic Cordillera
Authors: Fernández-Fernández E. , Jabaloy A. , González-Lodeiro F. 
Published: April 2008

Abstract
In the External Zones of the eastern Betic Cordillera, two sets of Mesozoic highangle normal faults can be observed, one with ENE-WSW strikes and the other with N-S strikes. Both sets of faults generate half-grabens and grabens, infilled with wedge-shaped and lens-shaped formations deposited during the Late Jurassic to Early Cretaceous. The relationships of these formations indicate progressive tilting of the hanging walls during deposition of the rocks. The largest basins are related to the ENE-WSW faults.
The rocks of Middle Jurassic age, which predate the faulting stage, are shallow-marine oolitic limestones. The Lower Cretaceous Fardes Formation shows evidence of deposits closer to the carbonate compensation depth (CCD). This evidence indicates that normal faulting was related to very significant thinning of the continental crust.
Palaeomagnetic studies in the area demonstrate the existence during the Miocene of clockwise and counterclockwise rotations with vertical axes. Restoring the faults to their original orientation, the present-day ENE-WSW faults and their main basins had original N-S strikes, while the N-S faults originally had WNW-ESE strikes.
This extensional stage occurred at the same time as the rifting of Iberia and North America, the opening of the Gulf of Biscay and the aborted rifting of the Iberian chain.
Evolution of the southern margin of the Donbas (Ukraine) from Devonian to Early Carboniferous times
Authors: Mccann T. , Saintot A. , Chalot-Prat F. , Kitchka A. , Fokin P. , Alekseev A. 
Published: April 2008

Abstract
A Devonian-Early Carboniferous succession comprising thick clastic and carbonate sediments with interbedded volcanics was examined along the southern margin of the Donbas fold belt, Ukraine. Following initial rifting and subsidence, a continental (fluvial, lacustrine) succession was established. This first phase of synrift activity (Eifelian) was accompanied by the extrusion of basalts. In Late Givetian-early Famennian times, half-graben development was pronounced and a series of E-W-trending half-grabens were formed, along with coeval volcanic activity. Subsequent basin subsidence led to the establishment of a broad marine carbonate platform across the region (Late Famennian-Tournaisian-early Viséan). Renewed uplift led to partial exposure and karstification of the platform. This was accompanied by trachyte intrusion and extrusion. The overlying chert-rich unit was probably deposited under lacustrine conditions, although a shelf environment has also been suggested. Renewed tectonic activity along the main basin-bounding fault resulted in the synsedimentary deformation of this unit.
Precise tracing of exhumation and provenance using
40
Ar/
39
Ar geochronology of detrital white mica: the example of the Central Alps
Authors: Von Eynatten H. , Wijbrans J. R. 
Published: April 2008

Abstract

Single-grain
40
Ar/
39
Ar dating of detrital white mica from Oligocene to Miocene (31–13 Ma) sediments of the North Alpine Foreland Basin in Switzerland reveals three prominent age clusters indicating cooling of the source rocks below 350–420°C in Carboniferous, Early Permian, and Tertiary times. Precise calibration of sedimentation age throughout the study area enables the thermal evolution of the hinterland in space and time to be precisely traced. Palaeozoic mica ages are documented in all samples and are used as additional provenance indicators. Tertiary mica ages are restricted to sediments younger than 21 Ma, and are only found in central and western drainage systems. Tertiary micas document progressively increasing average cooling rates up to 34–41°C/Ma in the source area (Lepontine Dome), between 21 Ma and 14 Ma. The observed cooling rates and the time-span for rapid cooling in the source area (between 19 and 14 Ma) agree with thermal models derived from currently exposed rocks of the Lepontine metamorphic dome. This study proves that detrital mica geochronology is a robust tool for deciphering the thermal histories of ancient orogens which are no longer exposed today.
A case study of hydrocarbon transport along active faults and production-related stress changes in the Monterey Formation, California
Authors: Chanchani Sneha K. , Zoback Mark D. , Barton Colleen 
Published: April 2008

Abstract
Recent field studies show that critically stressed faults, that is, faults that are close to frictional failure in the current stress field, serve as conduits for fluid flow. Similarly, geological field studies of the low permeability siliceous shales in the Monterey Formation, California, clearly indicate that faults influence hydrocarbon transport. We report here a study of the Antelope Shale, a low permeability siliceous shale hydrocarbon reservoir in the Buena Vista Hills field in the southern San Joaquin Valley to determine the influence of the stress state on the relative hydraulic conductivity of the fractures and faults present in the subsurface. Because production has both lowered reservoir pressure and the horizontal stresses, it was necessary to “restore” the reservoir stress state to initial conditions in order to identify correctly the most highly productive intervals. This analysis demonstrates that prior to production, faults in the reservoir were active in a transitional reverse/strike-slip faulting stress state, consistent with regional tectonics. Initial production rates in the field were 2000 barrels of oil per day, principally from intervals where critically stressed faults were encountered.
From seismic data to core data: an integrated approach to enhance reservoir characterization
Authors: Hesthammer Jonny , Fossen Haakon 
Published: April 2008

Abstract
Integrated structural analyses of seismic and various well data are necessary to optimize hydrocarbon reservoir characterization. However, there are many published examples from the oil and gas industry where single data types are analysed but not integrated. This may lead to erroneous interpretations and drainage strategies. As illustrated by an example from the area around well 34/10-B-12 in the North Sea Gullfaks Field, integrated structural interpretation should typically utilize all available seismic surveys, well log correlation data, dipmeter data and core data. Interpretation of seismic data helps in the understanding of large-scale structural and stratigraphic geometries. Time-lapse (4D) seismic helps to identify changes in reservoir properties caused by injection and production. Well log correlation data are used to document variations in zonation thickness caused by sedimentological or structural changes. Dipmeter data tie observations of bedding orientation from seismic data to subseismic scale. Core data represent the most detailed (millimetre to metre scale) data available and can yield information on rock properties as well as sedimentological and (micro)structural features. Small-scale deformation structures such as deformation bands and fractures can typically be identified and characterized. In addition, it is possible from unorientated cores to find the orientation of bedding and deformation structures. This information is compared to observations from dipmeter data, well log correlation data and seismic data to improve the interpretation.
Well 34/10-B-12 is a hanging wall injector near one of the large-scale faults in the Gullfaks Field. Several 3D seismic surveys are available from the area, as are standard well log data, dipmeter information and cores. Together, the data range from millimetre to kilometre with some overlap between the data types. Through integrated analysis, pitfalls such as interpreting any linear feature on timedip attribute maps as faults has been avoided. Also, a geometric relation between core-scale and seismic-scale faults has been established, and it has been possible to relate small-scale and large-scale structures in a model which is consistent with all the available data.
Microseismic monitoring of geomechanical reservoir processes and fracture-dominated fluid flow
Authors: Jupe Andrew J. , Jones Robert H. , Wilson Stephen A. , Cowles John F. 
Published: April 2008

Abstract
Microearthquakes (microseismic events) are induced during hydrocarbon and geothermal fluid production operations in naturally fractured reservoirs. They typically result from shear-stress release on pre-existing faults and fractures due to production/injection induced perturbations to the effective stress conditions. These stress changes may be due to reservoir depletion, flooding or stimulation operations. Over a number of years it has been shown that microseismic monitoring has the potential to provide valuable time-lapse 3D information on the geomechanical processes taking place within a reservoir. These processes include the distribution of fluid flow and pressure fronts within naturally fractured systems, production-related compaction and the reactivation of faults. With the advent of permanent reservoir monitoring systems (e.g. intelligent wells) microseismic monitoring has the potential to become a practicable means of time-lapse imaging of hydrocarbon reservoir processes remote from production/injection boreholes. This paper illustrates some of the ways in which microseismic monitoring can contribute to the development and management of hydrocarbon reservoirs through the presentation of examples from both hydrocarbon and geothermal reservoirs.
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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract

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

Abstract

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

Abstract

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.