bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mounded shallow gas sands from the Quaternary of the North Sea: analogues for the formation of sand mounds in deep water Tertiary sediments?
Authors: Brooke Candace M. , Trimble Tim J. , Mackay Tom A. 
Published: April 2008

Abstract
Shallow gas-bearing sand mounds have been clearly defined by a recent three-dimensional seismic survey and are believed to result from large-scale remobilization of conventionally deposited sand. This concept has been invoked by recent workers to explain the formation of mounded sand geometries in Tertiary turbidite reservoirs of the Forth-Gryphon area northern North Sea. However, the idea has been slow to gain acceptance due to the unconventional mechanism and lack of analogues.
In the Fisher Bank Basin area of the central North Sea unusual mounded gas anomalies have been recognized in the shallow subsurface at depths between 450 and 550 m subsea, most commonly occurring above deeply buried highs. Originally mapped as linear features on two-dimensional seismic data, three-dimensional seismic has revealed a circular to ovoid mounded geometry. The identification of fault zones extending up to this mounded horizon from deep in the section in an area where Upper Jurassic source rocks are gas mature may suggest a possible mechanism for mound formation. We propose here that gas has migrated to shallow levels along fault conduits into a conventionally deposited sand, and that this has resulted in sediment liquification. The movement of gas results in entrainment of sand grains towards subtle highs in the upper surface. Post-depositional processes thus result in the creation of a mound by withdrawal of sand from the flank areas and redeposition towards the centre of the feature.
Permeability heterogeneity within massive Jurassic submarine fan sandstones from the Miller Field, northern North Sea, UK
Authors: Prosser D. J. , McKeever M. E. , Hogg A. J. C. , Hurst A. 
Published: April 2008

Abstract
Analysis of high density (5 cm sample spacing) probe permeameter data has been used to evaluate some of the basic controls on permeability heterogeneity in the Miller Field. Probe permeameter data generally show good correspondence with conventional core-plug permeability data gathered at 25 cm spacings, but record a higher frequency of permeability variation than can be resolved using conventional sampling strategies. Comparison of probe permeameter data gathered from four lithofacies recognizable in core has allowed assessment of their reservoir quality and quantification of their internal permeability heterogeneity. Geostatistical analysis of the permeability data using semivariograms suggests permeability correlation structures and periodicities are related to the frequency of sedimentary phenomena visible within core. In particular, a relationship exists between permeability correlation structure and average bedform or fining upward unit thickness, i.e. the vertical scale at which individual lithofacies packages are stacked. Geostatistical analysis of high sample-density probe permeameter data demonstrates the usefulness of permeability data gathered at more than the conventional 25 cm spacings used for core plugs. High density probe permeameter data can yield important measures of the representative geological ‘structures’ which could form the basis of geologically realistic two-phase flow upscaling.
Crustal growth, surface processes, and atmospheric evolution on the early Earth
Authors: Eriksson Kenneth A. 
Published: April 2008

Abstract
Evolution of the atmosphere between 3.9 and 1.8 Ga can be related to changes in physical, chemical and biological surface processes. Changes in surface processes, in turn, took place in response to growth of continents. Growth of stable continents favoured expansion of epeiric seas and resultant increase in oxygen productivity. Prior to 2.6 Ga, continents probably comprised less than 10% of the Earth’s crust and, as a consequence, physical sedimentation and volcanism, and chemical and biological sedimentation took place mainly in oceanic and island-arc settings. Following major crustal growth at 2.6 Ga, surface processes became dominated by widespread stromatolite growth and iron and manganese precipitation in vast epicontinental seas.
Prior to 2.6 Ga, oxygen was consumed mainly in ocean-crust alteration. Following growth of large continents, the ocean crust oxygen reservoir decreased in scale freeing oxygen for the second major reservoir, namely reduced iron and manganese. Only after oceanic sinks were utilized did oxygen escape to the atmosphere. This was taking place on a large scale by 1.8 Ga at which time the atmosphere had an oxidation state necessary for formation of continental red beds and palaeosols.
Archaean ecology: a review of evidence for the early development of bacterial biomes, and speculations on the development of a global-scale biosphere
Authors: Nisbet E. G. 
Published: April 2008

Abstract
The antiquity of the carbon cycle, which began prior to 3.5 Ga ago, implies that a complex and diverse biosphere has existed for most of the Earth’s history. The earliest living community may have consisted of a variety of chemotrophic bacteria, including both archaea and eubacteria, that existed around hydrothermal systems. It is possible that photosynthesis began in thermophilic bacteria that originally developed infra-red thermotaxis for detecting hot vents, maximizing the chance of survival in the close vicinity of hydrothermal systems. The post-photosynthetic biosphere may have inhabited a set of distinct habitats, including marine littoral, open ocean, terrestrial and hydrothermal biomes. Sequestration of oxidation power, by partitioning into zones of oxidation and reduction, may have allowed an inflationary biosphere to develop, limited ultimately by the availability of crucial nutrients such as phosphorus. Biomes develop and collapse, and, in consequence, selective pressures over time would have created a cooperative, Gaian biosphere.
Zircon geochronology of Archaean felsic sequences in the Zimbabwe craton: a revision of greenstone stratigraphy and a model for crustal growth
Authors: Wilson James F. , Nesbitt Robert W. , Fanning C. Mark 
Published: April 2008

Abstract

U-Pb ion-microprobe (SHRIMP) work on zircon populations from 13 Zimbabwean Archaean felsic rocks are presented and interpreted. Samples were extracted from felsic volcanic sequences from most of the major greenstone belts and represent the first zircon geochronological data from within the greenstone belts themselves. The data demonstrate a Late Archaean volcanicity spanning 250 Ma which began at least 2900 Ma ago and ended at 2650 Ma. The intrusion of extensive granitoid sills of the Chilimanzi suite at
c.
2.6 Ga marks the widespread stabilization of the craton. Based on the new zircon data and a re-evaluation of published mapping, a new stratigraphic subdivision is presented for the Late (<2.9 Ga) Archaean of Zimbabwe. A feature of the stratigraphic model is the cyclicity of magmatism which begins with ultramafic-mafic rocks, progresses through felsic volcanism and ends with a granitoid event. These cycles are repeated at least three or four times in the 250 Ma time span. An important characteristic of the felsic volcanic rocks is that the bulk of the material examined contains inherited, xenocrystic zircons whose ages range from 1000 Ma to 20 Ma older than the host rocks. The oldest xenocrystic zircons (
c.
3.6 Ga) are restricted to volcanic rocks which erupted through the Tokwe segment; itself the only known > 3.3 Ga fragment of Archaean crust in Zimbabwe. These data suggest that the Early Archaean crust is restricted to the Tokwe segment in the south of the country. Since even the oldest of the felsic volcanics (2.90 Ga, Lower Belingwean) have zircons which are 50 Ma older, it is suggested that remnants of earlier cyclic greenstone-granitoid events must underlie the present craton and that all of the currently exposed greenstone belts of Zimbabwe were developed on sialic crust.
Palaeoproterozoic Laurentia-Baltica relationships: a view from the Lewisian
Authors: Park R. G. 
Published: April 2008

Abstract

Using a modified Patchett
et al.
(1978) pre-Grenville fit of Laurentia and Baltica, tectonic information from the Lewisian complex of Britain and from neighbouring Palaeoproterozoic belts of Laurentia and Baltica is reviewed. It is shown that a remarkable consistency in convergence directions existed across the whole region in the period 1.9–1.8 Ga suggesting that the reconstruction used may be correct, and that a common movement pattern can be inferred for the Palaeoproterozoic period within the North Atlantic region.

A speculative plate tectonic history for the region between
c.
2.6 and
c.
1.5 Ga is discussed in four stages. (1) 2.6–2.4 Ga: development of conjugate shear-zone systems in the North Atlantic craton. (2) 2.4–2.0 Ga: rifting and dyke emplacement in older cratons; creation of oceanic and intracontinental basins. (3) 2.0–1.8 Ga: subduction at active margins of older cratons with creation of magmatic arcs; collision of cratons accompanied by closure of intra-cratonic basins and accretion of arc terranes. (4) 1.8–1.5 Ga: development of new active margin discordant to the previous ones, with significant changes in convergence direction within the amalgamated continental assembly.
Deformation in the mid to lower continental crust: analogues from Proterozoic shear zones in NW Scotland
Authors: Wynn Timothy James 
Published: April 2008

Abstract
A suite of 1.8–1.7 Ga (Laxfordian), E-W striking, amphibolite-facies shears in the Lewisian of NW Scotland have been mapped across a pre-existing rheological boundary in the Laxford-Scourie area. The rheological contrast is provided by the southern boundary of the NW striking Laxford shear zone (LSZ), which displays complex Proterozoic folding and shearing of relict Archaean granulites. The more competent Archaean gneisses lie to the SW of the LSZ which has been a focus of shearing, amphibolitization and metasomatism from 2.6 to 1.4 Ga. The shears of interest display a second-order, extensional shear band relationship to the LSZ and formed during a phase of sinistral transtensional shearing and granite intrusion at 1.8–1.7 Ga. The second-order shears show displacement variations consistent with their propagation from the strongly foliated, less competent gneisses in the LSZ into the Archaean granulites to the SW.
A map of the Laxford-Scourie area can be regarded as a section through the mid to lower crust as observed on some deep seismic lines such as the BIRPS DRUM line from the north of Scotland. In the Laxford area, the change in geometry of the second order shears from SW to NE, as they curve into the LSZ, is comparable to the curvature of extensional shears in the mid to lower continental crust. Displacement variations indicate that the shear zones may nucleate at the base of the upper/mid crust and propagate up and down dip. Alternatively the shears may nucleate in the mid/lower crust and propagate up dip, becoming steeper as they do so.
Development of the Witwatersrand Basin, South Africa
Authors: Coward Mike P. , Spencer Richard M. , Spencer Camille E. 
Published: April 2008

Abstract
The Witwatersrand basin is a large hinterland basin of Archaean age developed on already consolidated continental crust south of the Limpopo plate margin. It is a flexural basin formed southeast of a major thick-skinned thrust system, modified by a second thrust system to the southeast. Studies of several thousand kilometres of seismic data, together with geophysical modelling and new field data, have allowed the thrusts and their associated hanging-wall uplifts to be mapped and dated, relative to sediments of Central Rand age. The basin subsequently underwent extension on large detachment faults. Associated half-grabens are infilled with growth sequences of Platberg sediments and intermediate volcanics. These grabens were inverted during post-Platberg and post-Transvaal times. Studies of the Witwatersrand Basin allow tectonic models to be developed for the Archaean which can be used to help interpret Cenozoic mountain belts.
Asian analogues for Precambrian tectonics?
Authors: Graham R. H. 
Published: April 2008

Abstract
A non-specialist view is that the Archaean crust comprises either tonalite/greenstone belt associations or gneissic terrains in granulite facies. Archaean crustal remnants lie as undeformed pods between ramifying Proterozoic mobile belts. The cratons themselves may have unconformable remnants of undeformed Proterozoic ‘platform’ sediments.
Coward, Windley and others have already drawn attention to similarities between the accretionary collage which makes Central Asia and the tectonic patterns of the Precambrian. These similarities are developed and amplified in this paper. Central Asian basins such as Tarim, Junggar and their satellites have developed on stretched continental fragments now accreted within the Asian collage. This stretched lithosphere, having been equilibrated and strengthened, now forms resistant kernels around which the surrounding ramifying accretionary deformation belts have been moulded.
Enclosed foreland basins have developed on the continental fragments in response to loading of the adjacent mountain belts, and great thicknesses of mostly Tertiary sediments have accumulated in them. The ‘mobile belts’ which surround the basins have been reactivated by later, distant, collision events with corresponding loading and sedimentation events in the basin.
The Black Sea and South Caspian basins are back-arc small ocean basins incorporated within the collage. They also form resistant kernels around which the mountain chains are moulded.
Deep erosion levels through these systems might provide broad analogues for Precambrian tectonic patterns, i.e. the Black Sea for the tonalite/greenstone belt terrains, the deep levels of Tarim for ‘reworked’ granulite terrains like John Sutton’s homeground of the NW Highland foreland. Sutton and Watson’s two orogenies are manifested as a ductile shear fabric associated with back-arc stretching (Scourian) reworked in zones after a substantial time interval (Laxfordian). Dykes like the Scourie dykes might be associated with stretching and incipient continental separation, and therefore be close in time with the ductile stretching as, arguably, the Scourie dykes are with the late Scourian (Inverian) deformation in Scotland.
The formation of the Strait of Dover
Authors: Gibbard P. L. 
Published: April 2008

Abstract
The Strait of Dover (Pas-de-Calais) is a narrow sea passage that links the North Sea and the English Channel between Britain and France. Much evidence suggests that the Dover Strait did not exist throughout most of the Pleistocene. Instead, a Chalk barrier was present, formed by the Weald-Artois anticline. Advance of the continental ice-sheet across the North Sea in the Middle Pleistocene Elsterian/Anglian Stage apparently dammed the southern part of the basin and water discharging into it was prevented from reaching the Atlantic to the north. The resulting lake apparently drained by spilling over the barrier and initiated the gap. This scenario is supported by sediments at Wissant, France. This theory contrasts with one, proposed by French geologists, that favours a structural origin.
Overflow from the lake has been interpreted as having been catastrophic. This was invoked to explain the origin of the complex anastomosing system of valleys or channels that occurs on the floor of the Channel cut into bedrock, predominantly of Mesozoic age. These valleys are interlinked to form a drowned drainage system and can also be linked to present rivers that enter the Channel on both the British and French sides. However, it is highly probable that the drowned valley system is multigenetic, resulting from repeated fluvial and marine erosion and deposition rather than representing a single, short-lived event. The valley system probably originated in the late Early to early Middle Pleistocene as a consequence of uplift of the Weald-Artois region.
Once the Dover Strait was formed, the rivers Thames and Scheldt were deflected through the gap and into the Channel River system during periods of low relative sea-level. Subsequently these rivers were probably joined by the Maas and Rhine, diverted by glaciation in the Drenthe Sub-stage (Saalian/Wolstonian Stage). The narrows seem to have been progressively enlarged by marine tidal scour and coastal erosion during high sea-level events.
Raised beaches and sea-levels in the English Channel in the Middle and Late Pleistocene: problems of interpretation and implications for the isolation of the British Isles
Authors: Keen D. H. 
Published: April 2008

Abstract
This paper discusses the problems of the interpretation of the evidence for pre-Holocene high sea-level events and their age in the Strait of Dover and adjacent areas. This review suggests that there is evidence for the isolation of Britain from the continent in Oxygen Isotope Stages 7 and 5. The evidence for isolation in Stage 9 is less certain, and in Stage 11 is rather poor. In Stage 5, at least, isolation may have lasted for as long as 60 000 years.
Insularity and the Quaternary tree and shrub flora of the British Isles
Authors: Bennett K. D. 
Published: April 2008

Abstract
The distribution of trees and shrubs within the British Isles and elsewhere in northern Europe is considered in the light of palaeoecological evidence for Holocene distributions. A small number of species appear to be capable of spreading across any seachannel in the region, and the overwhelming majority are capable of spreading across channel of 10–100 km extent. Thus, there is little evidence that insularity would have been a significant factor in controlling the tree and shrub flora in the present or previous interglacials, and hence the presence or absence of any species cannot be used as evidence or otherwise for isolation. However, there have been significant losses of tree and shrub species from islands during the late Holocene as a consequence of anthropogenic activities. These may be among the more dramatic prehistoric extinctions yet described.
Structuring soil and rock descriptions for storage in geotechnical databases
Authors: Toll D. G. , Oliver A. J. 
Published: April 2008

Abstract
The paper describes the development of a database for geotechnical information. The database is part of a knowledge-based (expert) system for the interpretation of geotechnical information. It has been implemented using the INGRES relational database management system. A particular feature, unique to the database structure developed, is the ability to store layer descriptions in a structured form. In other database systems these are simply stored as single text fields. A complex structure has been derived which can accommodate the full range of layer descriptions; for example, interbedded soils/rocks within a layer, the variation in description from top to bottom of a layer, and the existence of multiple soil or rock types within a description. The paper presents details of the database tables with examples of how the structured representation is used.
Transfer and SERPLO: powerful data quality control tools developed by the British Oceanographic Data Centre
Authors: Lowry Roy K. , Loch Stephen G. 
Published: April 2008

Abstract
Quality control is a vital component of data management. However, in the current data volume explosion, practising quality control with finite resources presents a very real problem. During 18 years of operation, the British Oceanographic Data Centre has developed a cost-effective quality control strategy.
In this paper we describe the quality control procedures developed with emphasis on two vital components, the transfer system and SERPLO. The transfer system provides the initial interface between external data and the BODC system, combining reformatting with extensive data checking. SERPLO is a powerful, interactive, non-destructive graphical editor. It is shown how the internal development of these systems has dramatically increased the efficiency of the data management operation.
Data management in the National Geological Records Centre
Authors: Bowie R. C. 
Published: April 2008

Abstract
The National Geological Records Centre (NGRC) has collated large collections of borehole records (600 000) manuscript geological maps (50 000) and site investigation reports (19 000) with other collections of original and archive material. The majority of these data are now digitally indexed and searches can be carried out interactively on computer or via a GIS as part of a comprehensive enquiry service.
Magnetic mineral assemblages and magnetic contrasts in diagenetic environments — with implications for studies of palaeomagnetism, hydrocarbon migration and exploration
Authors: Machel Hans G. 
Published: April 2008

Abstract
Magnetic mineral assemblages in diagenetic environments are governed by microbial and inorganic/chemical processes. Empirical evidence and thermodynamic modelling of diagenetic environments ranging from near-surface settings to depths of about 6–7 km suggests that microbial processes are very important in surface and near-surface diagenetic settings, whereas inorganic diagenetic processes dominate in most deeper subsurface diagenetic settings. In all diagenetic environments, molecular oxygen and hydrocarbons are important because they control which types of bacteria can thrive and because they drive various redox reactions via changes in the redox potential.
Iron oxides, such as hematite and goethite, are stable under relatively oxidizing/aerobic conditions. With decreasing redox potential, i.e. under relatively reducing/anaerobic conditions, magnetite and pyrrhotite are the most important stable magnetic minerals, whereas hematite is unstable. Other magnetic minerals, such as greigite, may be important in some instances. Pyrite and siderite are also important because they may form at the expense of magnetic minerals. A significant decrease in the redox potential in diagnetic settings, via the invasion of hydrocarbons during migration or seepage from traps, for example, almost invariability results in diagenetic remagnetization. As a result ‘positive’, ‘absent’ or ‘negative’ magnetic contrasts are generated relative to the total magnetization (or remanence, or susceptibility) before such a decrease, depending on the relative amounts of magnetic to non-magnetic minerals formed and destroyed. Thermodynamic modelling further suggests that magnetic contrasts are more probable and tend to become more ‘positive’ with depth and with proximity to hydrocarbon pools.
Any significant change in the redox potential is likely to cause magnetic contrasts via the formation or destruction of magnetic minerals, thus generating secondary (chemical) magnetization and resetting original detrital or bacterial magnetization. The predicted magnetic contrasts are also likely to form as a result of hydrocarbon migration, and it appears possible to delineate migration timing and pathways by geomagnetic methods. Hence the predicted magnetic mineral assemblages can aid in the interpretation of palaeomagnetic studies, particularly via the recognition and proper interpretation of remagnetization. Magnetic contrasts, measured from the air, at the surface or on drill core, can be used for hydrocarbon exploration in association with other exploration methods.