bluuebunny/crossref_metadata_2025_split huggingface dataset:
A wide-angle reflection profile across the Iceland-Faeroe Ridge
Authors: Makris Jannis , Lange Knuth , Savostin Leo , Sedov Vladimir 
Published: April 2008

Abstract

A wide-angle reflection profiling (WARP) survey was carried out in July 1993 across the Iceland-Faeroe Ridge in the North Atlantic. Sleeve guns were employed as energy source and ocean bottom seismometers (OBS) used to observe the seismic energy. Results of the first evaluation show that the crust below the Iceland-Faeroe Ridge is stretched continental, with an average thickness of 23 km at its central part. Towards the NE end of the profile, the transition to oceanic crust of the Norwegian Basin has been identified. The upper crust has
P
-wave velocity (
V
p
) values which range between 5.8 and 6.3 km/s, while the lower crust is more homogeneous with
V
p
values between 6.7 and 7.0 km/s. The upper crust, excluding sediments and volcanics, is about 6 km thick at the crest of the ridge and thins with increasing water depths to the northeast and southwest. The lower crust can be separated from the upper part by a first order discontinuity, a
P
i
P
reflector, that has been identified in several travel-time sections.
P
-wave velocities below the Moho have values of approximately 7.9 km/s.
Beyond the turbidite paradigm: physical models for deposition of turbidites and their implications for reservoir prediction
Authors: Kneller Ben 
Published: April 2008

Abstract

The simple physical models which are popularly used to describe deposition from turbidity currents are based on the notion of unidirectional waning flow, resulting in the familiar Bouma sequence (Ta-e) or its high-density counterpart, the Lowe sequence (S1-3). Most geologists working on turbidite successions know only too well how wide is the range of facies which do not fit into the standard facies models. The application of simple equations of motion shows that deposition can occur beneath flows that are steady or even waxing. The various combinations of different spatial and temporal accelerations produce markedly different vertical and lateral variations in the resulting turbidite. On these grounds alone, we should expect not one but at least five basic types of sequence in turbidite beds, for which likely candidates can be found in many deep water clastic systems. This has important implications for deposit geometry, gradients in reservoir properties, and geological interpretation and correlation of well cores. Since many basins are confined,
a priori
reasoning tells us to expect interactions between turbidity currents and topography, producing anomalous intrabed vertical sequences, multiple current directions and locally enhanced deposition. Flume experiments with radially spreading scaled sediment gravity flows demonstrate how the geometry of sandstone deposits may be controlled by topography. Interactions between the flow and topographic features are dependent upon the shape and orientation of the obstacle, and upon its size relative to the height of the flow. Some of the results are counter-intuitive, and may have significant impact on location of reservoir sands around basin-floor and marginal topography.
A classification scheme for shale clasts in deep water sandstones
Authors: Johansson Melissa , Stow Dorrik A. V. 
Published: April 2008

Abstract
Shale clasts are widespread in turbidites and associated facies of all ages. They may yield important information regarding the depositional process of the host sandstone and its specific environmental setting. Previous work has tended to generalize the variety of shale clasts that exist and no comprehensive classification has yet been developed. The scheme proposed here is a descriptive classification based on the nature and arrangement of shale clasts within mainly structureless sandstones. Twelve types of clasts are recognized on the basis of the clast’s position in the bed and/or characteristic features, and these have been grouped according to whether they have been derived from either basal erosion or disturbance (Group A), flow modification (Group B) or post-depositional disturbance (Group C). These clasts have also been organized into characteristic assemblages which are thought to be indicative of particular depositional environment. The classification scheme when used in association with facies analysis can provide an additional tool for core investigations, contributing to the understanding of permeability barriers and relevant architecture.
The onset of interaction between the hydrosphere and oceanic crust, and the origin of the first continental lithosphere
Authors: De Wit Maarten J. , Hynes Andrew 
Published: April 2008

Abstract
New continental crust forms above subduction zones through the recycling of hydrated oceanic lithosphere. The most efficient process known for oceanic lithosphere hydration takes place at the submerged mid-ocean ridges where the lithosphere is young and warm, and cools through hydrothermal convection. Such mid-ocean ridge hydrothermal interactions were operative at least as far back as 3.5–3.8 Ga. The apparent absence of preserved continental crust older than 4.0 Ga may reflect the absence of hydrothermal interaction before that time. This model requires that prior to about 4.0 Ga mid-ocean ridges stood above sea level. Our calculations show, however, that on a plate-tectonic early Earth with substantially less continent, realistic higher heat flow, and a volume of sea water similar to that of today’s ocean, Archaean mid-ocean ridges would have remained below sea level. Only with a substantial reduction of surface water would Earth have been able to recycle dry oceanic lithosphere, and thus prevent the present day style of continental crust formation.
A 30% reduction of surface water is required to elevate early Earth’s ridges above sea level. This excess water may have been stored in nominally anhydrous minerals of the mantle. Early Earth’s mantle may have released a significant proportion of its initial water only gradually through convective overturn of the oceanic floor. Given realistic ocean-floor creation rates, it would have taken roughly 500 Ma to process the early Earth’s mantle through a MORB generation event if only the upper mantle was involved and considerably longer if whole mantle convection was involved. The inefficiency of water extraction during this process is illustrated by the amount of water apparently present in the source regions for present-day MORB. In this scenario, the Hadean-Archaean transition may mark the time when Earth changed its style of cooling from one dominated by heat exchange directly to the atmosphere to one dominated by heat exchange with the hydrosphere, which still buffers Earth’s heat loss today.
Lode-gold deposits of the Yilgarn block: products of Late Archaean crustal-scale overpressured hydrothermal systems
Authors: Groves D. I. , Ridley J. R. , Bloem E. M. J. , Gebre-Mariam M. , Hagemann S. G. , Hronsky J. M. A. , Knight J. T. , McNaughton N. J. , Ojala J. , Vielreicher R. M. , McCuaig T. C. , Holyland P. W. 
Published: April 2008

Abstract

Although the lode-gold deposits of the Yilgarn block are hosted by a variety of rocks, and their structural style, associated alteration and ore mineralogy are also variable, common parameters suggest that they represent a coherent group of epigenetic deposits, most of which formed during a widespread (500 000 km
2
) and broadly synchronous (2635 ± 10 Ma) hydrothermal event in the closing stages of the Late Archaean tectonothermal evolution of the host granitoid-greenstone terrains. Progressive variations in deposit parameters can be correlated with the metamorphic grade of the enclosing greenstone successions. These systematic variations, combined with evidence for their timing and the
P-T
conditions of their formation, indicate that the deposits form a continuum in which gold deposition took place from < 5 km depth (1 kbar, 180°C) to > 15 km depth (> 5 kbar, 700°C), marking hydrothermal fluid flow and fluid evolution through the middle and upper crust.

The primary ore fluid appears to have been an overpressured, low salinity H
2
O-CO
2
-CH
4
fluid originating from a deep source. Upward fluid advection was strongly channelized along vertically extensive conduits. Although there is a gross regional association between clusters of gold deposits and craton- or greenstone-scale deformation zones, these do not appear to have been the primary fluid conduits, at least during their major phase of structural and magmatic activity. Further, all kinematic types of lower-order structure are mineralized, and the fossil fluid conduits exposed at the mine scale are extremely variable, some with no obvious fault or shear control. A potentially unifying hypothesis that can explain this extreme variability in the nature of the conduits is that fluid flow was focussed into zones of low mean stress in the granitoid-greenstone terrains. This can explain the selective occurrence of gold deposits adjacent to irregular or fault-bounded granitoid contacts in some goldfields, the selective mineralization of competent units (e.g. dolerites) in elongate greenstone belts that contain such units and are oriented sub-perpendicular to the far-field compressive stress, and the lack of mineralization in major, largely planar, shear zones undergoing simple shear. The orientation of the greenstone belts with respect to the far-field compressive stress appears to be a crucial factor in defining the potential for strike-extensive zones of low mean stress. This potentially can explain why granitoid-greenstone belts with a high density of sub-parallel craton- and greenstone-scale deformation zones are most highly mineralized and commonly contain the giant gold deposits which, themselves, are located in geometrically anomalous zones within these greenstone belts.
Global sea-level and the (pen-)insularity of late Cenozoic Britain
Authors: Funnell Brian M. 
Published: April 2008

Abstract
During mid-Pliocene times, Britain was surrounded by warm temperate seas. In the south, these received relatively little clastic input, accumulated mainly biogenic sediments, and appear to have allowed free circulation of marine waters between the North Sea and the Atlantic Ocean, either around or across southern Britain.

In late Pliocene times, commencing at about 2.5 Ma
bp
, the first major global sea-level falls associated with northern hemisphere glaciation occurred. At about the same time, climatic changes appear to have accelerated the rate of headwater extension and bedload transport of the principal rivers flowing towards the southern North Sea. The combination of sea-level fall and progressive deltaic progradation into the southern North Sea converted Britain into a European peninsula.

By the mid-Quaternary Cromerian stage, the Great European (Ur-Frisia) Delta top was sufficiently moribund, and subject to subsidence, to allow interglacial sea-levels to encroach southwards across it. During the following Anglian Glaciation, impounded glacio-marine or glacio-lacustrine waters appear to have extended southwards, across both the former delta top and the bounding Weald-Artois chalk ridge, into the English Channel.
Subsequently a marine connection between the North Sea and the Atlantic Ocean, via the English Channel, was alternately established and broken, as global sea-level rose and fell (synchronously with interglacial and glacial periods), cyclically converting Britain from island to peninsula and back again.
Insularity and Quaternary vertebrate faunas in Britain and Ireland
Authors: Stuart A. J. 
Published: April 2008

Abstract

Terrestrial vertebrate faunas (mammals, reptiles and amphibians) from the Middle and Upper Pleistocene of Britain, Ireland and adjacent Continental Europe are compared. Problems arise from uncertainties of status and correlation of stages. Evidence of insularity is provided by reduced diversity in (a) Britain
versus
the Continent, and (b) Ireland
versus
Britain. British temperate/interglacial faunas older than the Last Interglacial are very similar to Continental faunas, notably the Cromerian faunas of West Runton, England, and Voigtstedt, Germany. The earliest indications of insularity are in Last Interglacial faunas, in which, for example, pine voles
Pitymys
spp., extinct rhinoceros
Stephanorhinus kirchbergensis
, horse
Equus ferus
and humans, present in equivalent Continental faunas, are absent from Britain. Local extinction of horses and humans is implied. The British Last Cold Stage (Devensian) faunas are very similar to those of the adjacent Continent, indicating unimpeded migration. However, Irish Last Cold Stage faunas are impoverished (absences include woolly rhinoceros
Coelodonta antiquitatis
and humans), indicating no connection from Ireland to Britain. Early Holocene separation of Britain is reflected in the absences of several small vertebrates found on the adjacent Continent. Irish Holocene faunas are much more impoverished, lacking, for example, voles, frogs and snakes, indicating continued isolation from Britain.
Sea-levels and the evolution of island endemics: the dwarf red deer of Jersey
Authors: Lister Adrian M. 
Published: April 2008

Abstract
The dwarfing of red deer on Jersey in the Last Interglacial allows a detailed investigation of the ‘island dwarfing’ phenomenon. Uniquely, the island furnishes normalsized deer in stratified deposits both preceding and succeeding the dwarfing episode. Timing the dwarfing process depends on a number of assumptions about land-sea history, but suggests a maximum duration of 6000 years. The changes in size and body form of the deer are discussed in terms of adaptation, development and evolutionary rate, and are compared with modern analogues.
Deglaciation, Earth crustal behaviour and sea-level changes in the determination of insularity: a perspective from Ireland
Authors: Devoy Robert J. N. 
Published: April 2008

Abstract
Insularity is defined here in terms of the presence or absence of land-bridge connections between adjacent landmasses. The development of a land-bridge depends upon the existence of a special combination of environmental conditions. These are created through the interaction of climate, sea-level and other physical environmental controls, together with changes in palaeogeography. Such factors operate together to produce conditions suitable for a land-bridge over only relatively short time-scales (10 to 100 years). New palaeoenvironmental data about such factors have emerged in recent years from the Irish Sea and from neighbouring regions. These data, derived from a variety of disciplines, have contributed to earlier discussions about the existence here of land-bridge links in the Late Quaternary. Some of this information, particularly that concerning patterns of Earth crustal behaviour, former ice distributions, deglacial history and sea-level changes, is reviewed. An assessment is given of their significance for possible land-bridge operation at this time.
The what, why, when, how, where and who of geological data management
Authors: Giles Jeremy R. A. 
Published: April 2008

Abstract
The variety, form and volume of data available to geologists have increased significantly over the past few decades. It has become essential to use databases (either analogue or digital) to turn this avalanche of data into usable information. A significant percentage of databases that are created do not repay the cost and effort of their creation and can therefore be considered to be failures. The probability of creating a successful database can be increased by careful consideration of a few simple questions. What is the objective that the database will meet? Why is a digital database being considered? When, if ever, will the cost and effort of creating the database be repaid? How will the database be designed and created? Where are the users? And finally, who will be responsible for maintaining the integrity of the database?
Data modelling a general-purpose petroleum geological database
Authors: Chew K. J. 
Published: April 2008

Abstract
Experience gained while modelling a petroleum geological database can be summarized as follows. General-purpose database models should reflect the real world, complete with imperfections, and avoid being application-oriented in design. In geological database modelling it is necessary to separate the recording of descriptive features (empirical data) from that of geological processes (concepts). Detailed analysis reveals that many geological relationships assumed to be inherently hierarchical are in fact many-to-many. Ambiguity and inconsistency in definitions should be avoided, if necessary by adopting a definition at variance with industry norms. Use of generic entities simplifies the modelling exercise and can benefit the end-user.
Magnetic mineralogy of sandstones from the Lunde Formation (late Triassic), northern North Sea, UK: origin of the palaeomagnetic signal
Authors: Hounslow Mark W. , Maher Barbara A. , Thistlewood Laurence 
Published: April 2008

Abstract
The minerals responsible for the magnetic properties of the Late Triassic Lunde Formation have been examined using a combination of magnetic mineral extraction, microscopy and rock magnetic measurements. The magnetic mineralogy is controlled by the depositional environment and the effects of diagenesis, by a process of differential preservation and modification of the original detrital minerals. The magnetic susceptibility and remanence properties of the sediments are strongly influenced by the proportion of silt and clay sized clastic material, which contains most of the magnetic minerals. Paramagnetic minerals, both of depositional origin and produced during diagenesis, are largely responsible for the magnetic susceptibility. A suite of residual ferrimagnetic oxides (chromite and Mn-substituted magnetite) is responsible for the remanence properties in grey sandstones, because most of the originally deposited magnetic Fe-Ti oxides have been removed by reducing conditions during diagenesis. However, a small number of reddened horizons preserve a higher proportion of original detrital Fe-Ti oxides (ferrimagnetic ilmenite, ferrimagnetic chromite and magnetite), although authigenic hematite has replaced most of the original mineralogy in the reddened horizons. Magnetic oxide inclusions in quartz and feldspars are important contributors to the remanence signal, particularly in horizons which have a low content of discrete detrital ferrimagnetic grains, either through diagenetic dissolution, or paucity of the silt and clay fraction. Within the grey sandstones, the Triassic palaeomagnetic signal is carried by magnetite as inclusions in detrital silicates, with a contribution from detrital ferrimagnetic chromite. A model of the effects of diagenesis on the magnetic mineralogy in deeply buried sequences is proposed.
Results from a palaeomagnetic investigation of the Brent Group sediments in wells 34/10–16 and 34/10–17 showing evidence for complete remagnetization of the sediment
Authors: Beyer Claus 
Published: April 2008

Abstract
Cores from wells 34/10–16 and 34/10–17 in the Tampen Spur area, Norway were studied to establish a magnetic polarity stratigraphy for the Brent Group in the area. Approximately 100 samples from each well were treated by traditional thermal and alternating field demagnetization procedures and the apparent polarities determined. Thin sections were studied and scanning electron microscopy carried out with the purpose of verifying a primary origin of the remanent magnetization.
Correlation of the two wells based on the polarity logs was in agreement with the lithoand biostratigraphic correlations. However, the mineralogical analysis did not determine any primary magnetic minerals, although potential remanence carrying diagenetic minerals were observed. This, combined with magnetic data indicating extensive remagnetization of the sediment, lead to the conclusion that the remanent magnetization of these sediments is late diagenetic, probably of Tertiary age.
The results are not encouraging with respect to the use of palaeomagnetism as a chronostratigraphic tool for these sediments. It may, however, be useful for dating diagenetic events and, as a result of the strong secondary magnetization, magnetic orientation techniques can be successfully applied to the core material.
Application of magnetostratigraphy to Brent Group reservoir zonation in the Visund Field
Authors: Hauger Eirik , Veen Paul Van 
Published: April 2008

Abstract

Magnetostratigraphy has been applied to an increasing number of oil fields in the North Sea region with promising results for detailed chronostratigraphic reservoir correlation. However, the magnetization processes in hydrocarbon reservoir successions, and the potential use of magnetostratigraphy for reservoir zonation purposes, are not very well known. Therefore, aspects of these subjects are discussed on the basis of a magnetostratigraphic study of three different wells covering the Middle Jurassic Brent Group at the Visund Field, northern North Sea. Results from scanning electron microscopy and remanent coercivity analysis suggest that the primary magnetization defining the magnetozones in the Brent Group is a combination of detrital remanent magnetization and a chemical remanent magnetization, probably acquired contemporaneously shortly after deposition. Detailed thermal demagnetization has uncovered an important secondary magnetization component in most of the core samples. This magnetization is probably due to cooling of the cores from a reservoir temperature of about 110°C to surface temperature, and it causes the main disturbances in the palaeomagnetic results. Based on analyses of individual core samples, characteristic remanent magnetization components have been defined. The magnetopolarity stratigraphy for the individual wells is based on these components and the results are comparable from well to well. The well correlation covers a rock sequence with a thickness of about 200m, and both magnetostratigraphic and biostratigraphic results have been used in combination with the lithostratigraphy. The acme of
Corollina
represents the most important palyno-event, and the top and bottom of this palynozone is used as the main tie-level for two of the wells. Sixteen additional correlation lines have been derived from the magnetostratigraphic results, six of these considered as tentative. The correlation reveals that the magnetostratigraphic results are facies independent and some of the lithostratigraphic formation lines appear to be diachronous within this deltaic mega-sequence. Although the magnetostratigraphy only provides a relative time framework for the Brent Group, the results are encouraging and suggest the possibility of achieving high resolution chronostratigraphic well correlations for Middle Jurassic reservoir sequences in the northern North Sea area.