bluuebunny/crossref_metadata_2025_split huggingface dataset:
The sedimentology of a Middle Jurassic lagoonal delta system: Elgol Formation (Great Estuarine Group), NW Scotland
Authors: Harris J. P. 
Published: April 2008

Summary
Deposition of N-S prograding lagoonal deltas took place in two separate extensional basins (Sea of the Hebrides and Inner Hebrides Basins) of different size and hence wave energy. Salinity of water in the basins varied spatially and temporally from marine to fresh-brackish. The reduced salinities were controlled by diminished connections with the open sea together with copious run-off from a hilly hinterland with a subtropical seasonal climate. Sections in N Trotternish, S Trotternish, Raasay (Sea of the Hebrides Basin) and Strathaird (Inner Hebrides Basin) represent three different styles of delta sedimentation corresponding to different salinities and basinal energy regimes (waves and tides). In N Trotternish, marine macrofaunas and microfloras occur in a wave-tide interaction delta system in which tidal currents controlled distributary-channel and mouthbar hydrodynamics and high wave energies generated beach-ridge sediments at the delta shoreline. In S Trotternish and Raasay, probable brackish-marine salinities and a deeper basin are reflected in buoyant mouth-bar hydrodynamics. In Strathaird (Inner Hebrides Basin) probable fresh-brackish salinities correspond to a fluvial-dominated delta recording friction-dominated mouth-bar hydrodynamics. This lobate delta is characterized by low angle offshore inclined bar-front sandstones. In the Inner Hebrides Basin, the Elgol Formation delta reaches a depositional limit between Strathaird and Eigg. The N-S transition from marine to fresh-brackish salinities records the gradual establishment of a non-marine depositional system (which is maintained throughout the rest of the Great Estuarine Group) during progradation of the Elgol Formation delta.
Facies associations and sand-body geometries in the Ness Formation of the Brent Group, Brent Field
Authors: Livera S. E. 
Published: April 2008

Summary

The Brent Group in the Brent Field contains over 1000 × 10
6
bbl of recoverable oil in a simple gently dipping half-graben structure. It is 243 m (800 ft) thick and represents a sequence amplified by synsedimentary fault-block subsidence close to the axis of the Viking Graben. On a regional scale the depositional model is of a major shoreface and coastal sequence, the Rannoch and Etive Formations, underlying the partly time-equivalent shallow lagoonal to emergent delta-plain deposits of the Ness Formation. However, more localized and detailed sedimentary modelling is required to predict reservoir geometries and production behaviour, particularly in the Ness Formation.

The Ness Formation is the largest reservoir-bearing unit in the Brent Field, being up to 160 m (525 ft) thick. Five main facies associations form reservoir-quality rock: varied channel sandstones, fluvial sheet sandstones, major mouth bars, lagoonal shoals (which are usually associated with, and capped by, thin beaches) and lagoonal sheet sandstones. These associations make up 50%–60% of the sand-rich sequence and are embedded in the non-reservoir facies associations: lagoonal mudstones, emergent flood-plain mudstones and allochthonous and autochthonous coals. The coals are often field wide in extent. Within the amplified Ness Formation the most important environments were the lagoonal deltas which were wave and fluvial dominated with minor tidal influence. As a result of this importance the sand bodies produced by these deltas are subjected to a more detailed description in this paper. Wave energies were sufficient to redistribute large amounts of sediment and indicate significant fetch in the brackish lagoons diluted by major freshwater input.
Sand-body geometries are very variable, reflecting both localized controls on sediment distribution, particularly immediately above the compacting shoreface pile, and more regional effects including coarse-sediment supply, basinal processes and fault-block subsidence. The dominant controls on sedimentation resulted in regular drowning events on the delta plains and had a significant impact by producing a strongly layered reservoir.
Coal reviewed: depositional controls, modern analogues and ancient climates
Authors: Haszeldine R. S. 
Published: April 2008

Summary

Ancient economic coals usually contain more than 90% organic matter and less than 1% sulphur. Sedimentological reconstructions show the interbedded clastics to be fluvial-plain, deltaic, barrier coastline, estuarine or alluvial-fan deposits. However, bases of coal beds unconformably transgress these various facies, and coals only rarely pass laterally into clastic facies. Thus coal-forming peats
post-dated
the underlying clastic sedimentation and most coals did not form in deltas. Local coal thicknesses can be controlled by compaction of underlying sediment, syndepositional faulting, or basement structure.

Coals with more than 1%–2% sulphur are usually overlain within 10 m by marine sediments which provided SO
4
2−
by diffusion. However, most coals contain less sulphur and must be freshwater in origin. Lithotype and spore profiles vertically through coals indicate a characteristic change of peat floras. This resulted from equisites-dominated seat earths, followed by diverse tree-sized vegetation which formed bright coal and lastly by low diversity stunted vegetation which formed dull coal. These features compare well with peats formed in modern ombrogenous blanket or raised bogs. The ancient mires formed in rainwaters (low sulphur), excluded clastic sediments (low ash), had a lateral floral zonation, usually post-dated clastic deposition and occurred inland from the shoreline.

Modern ombrogenous mires are abundant, especially in humid temperate climates. These peats are forming today during a period of long-term climatic cooling in areas with a frequent reliable rainfall. Ancient coals may also have formed during long-term climatic cooling epochs when volcanic CO
2
was being removed from the atmosphere. This could be regarded as a Gaian biosphere maintaining Earth temperatures similar to those of the present day.
Deltaic coals: an ecological and palaeobotanical perspective
Authors: Scott A. C. 
Published: April 2008

Summary
Coals occur widely in deltaic sequences but are rarely of economic quality, being thin, split and with high ash content. Coals with brackish-water influence or overlain by marine rocks tend to have high sulphur values. Not all coals in deltaic sediments formed in swamps or marshes. Peats may form under a wide variety of conditions, and ecological and hydrological interpretations of mire types are essential and should be integrated with facies studies of accompanying clastic sediments. Botanical, physical and chemical data are needed for the interpretation of the coals.
Considerable time may elapse between delta abandonment and the onset of peat formation. Rheotrophic or flow-fed peats may form initially on abandoned delta lobes, but if peat accumulation continues under high rainfall conditions ombrotrophic low ash peats may form as raised bogs. In this case vertical and lateral zoning of the peat (coal) may occur. In any interpretation of the coals based on analogies of modern peats care must be exercised in using ecological data from Recent plant communities, as peat-forming vegetation shows significant changes from the Devonian to Recent.
Fan-delta-lacustrine sedimentation and coal development in the Tertiary Ombilin Basin, W Sumatra, Indonesia
Authors: Whateley M. K. G. , Jordan G. R. 
Published: April 2008

Summary

The Ombilin Basin is a Tertiary intermontane basin situated in the Barisan mountain range of W Sumatra. It covers an area of some 1500 km
2
and is known for the coal resources which have been mined in the Sawahlunto area since 1891. Seismic and borehole data indicate that the basin has been filled with approximately 4600m of middle Eocene to early Miocene sediments. The coal developed early in the basin’s history (middle Eocene). During this study the fan-delta sediments below the oldest seam, the C seam, the seam itself and the sediments immediately overlying the C seam were investigated along the western margin of the Ombilin Basin in the Sawahlunto area.

The oblique convergence of the Indian Ocean plate weith the SE Asia plate created a stress field of the type that can produce a primary dextral wrench fault which in this case is named the Great Sumatran Fault Zone. The Ombilin Basin is a graben-like ‘pull-apart’ basin resulting from localized extension failure and related deformation. The failure and deformation are a function of irregular strike-slip movement along the Great Sumatran Fault Zone during the early Tertiary. Tertiary sedimentation began in the Eocene following graben formation. High basement relief adjacent to the newly formed basin resulted in debris flows and fan-delta formation around the margin of the central lake. Concurrent with the deposition of coarse-grained fan-delta sediments around the basin margins, fine-grained lake sediments accumulated in the basin centre.
Reduction in relief difference between the source area and the basin was associated with an expansion of the lacustrine environment. Shallowing of the lake and a humid tropical climate allowed plant colonization to take place. Peat accumulation was influenced by the underlying fan-delta lobe geometry. In interlobe areas thick sequences of low ash peat accumulated, while central lobe areas through the same interval were sites of continued sediment influx and relatively slow peat accumulation. In these areas high ash coal or carbonaceous shale are laterally equivalent to the low ash coal. A detailed investigation of the character of the coal in the C seam indicates that, while the lateral dispersion of clastic material may play some part in the variation in the ash content of the coal from one place to another, the most significant variable is the rate of accumulation of peat.
Asthenospheric control on magmatism in the ocean basins
Authors: White Robert S. 
Published: April 2008

Summary
Asthenospheric processes exert a dominant control over the volume and distribution of magmatism in oceanic basins. In particular, the temperature of the asthenosphere controls the amount of melt and hence the volume of igneous crust produced at rifted continental margins and oceanic spreading centres. Changes of as little as 100–150°C in the asthenosphere temperature cause massive differences in the thickness of the igneous crust.
Where the asthenosphere wells up passively during rifting, such as at continental margins and oceanic spreading centres, partial melt is produced by adiabatic pressure release. Continental rifts near hot-spots are often emergent above sea level, with considerable extrusive and intrusive magmatism, whilst those away from hot-spots subside gently without volcanism. Oceanic spreading centres are fed by sublithosphere feeders that generate spreading cells typically 40–80 km long which operate independently of one another. At the intervening fracture zones, where the magma supply from the adjacent feeder is least, the crust thins, sometimes to less than 1 km.
Hot-spots are fed by mantle plumes. The partial melt and resultant surface volcanism comes from the rising plume which is only 100–200 km wide. The broad surrounding topographic swells, 1000–2000 km across, are dynamically supported by the mushrooming head of abnormally hot mantle beneath the lithosphere.
Strontium, neodymium and lead isotope characteristics of the Granadilla Pumice, Tenerife: a study of the causes of strontium isotope disequilibrium in felsic pyroclastic deposits
Authors: Palacz Z. A. , Wolff J. A. 
Published: April 2008

Summary

The Granadilla Pumice deposit, the product of a single explosive eruption of phonolitic magma, exhibits stratigraphically systematic internal compositional variations interpreted as the result of fractionation of the observed phenocryst assemblage in the pre-eruptive magma body. Whole-rock
87
Sr/
86
Sr data exhibit a consistent profile, with the most differentiated compositions having the most radiogenic strontium. The resultant
87
Sr/
86
Sr versus 1/Sr mixing line has a positive slope, suggesting the addition of a relatively radiogenic strontium component to the existing strontium concentration profile. There is no significant systematic variation, however, in neodymium or lead isotopes. Separated alkali feldspar phenocrysts have
87
Sr/
86
Sr values of 0.7031–0.7032, identical with Tenerife mafic magmas; the strontium isotopic variation is restricted to the complementary glasses. The more radiogenic component in the glasses is only partially removed by acid leaching and has a strontium isotope ratio of about 0.707, deduced from analysis of the leachant. Strong acid leaching, accompanied by up to 25% sample dissolution, results in greater, but not complete, loss of the more radiogenic component, with a good correlation between pre- and post-leaching glass isotopic compositions. These relationships cannot be easily explained by either post-eruptive alteration or contamination of the magma chamber with high-
87
Sr/
86
Sr country rock. The data are instead consistent with a model of interaction between vesiculating magma and hydrothermal fluids with high
87
Sr/
86
Sr, immediately before and/or during explosive eruption, involving limited diffusion of strontium from the fluid into bubble walls before quenching of the magma to form glassy pumice. This process may be common during large explosive eruptions, and we suggest that whole-rock strontium isotope variations found in strontium-poor felsic pyroclastic deposits may not reflect purely magmatic processes, even though they closely mimic plausible magmatic variations.
Axial volcanism on the East Pacific Rise, 10–12°N
Authors: Thompson G. , Bryan W. B. , Humphris S. E. 
Published: April 2008

Summary

The East Pacific Rise axis, 10–12°N, consists of three discrete topographic or tectonic units each of which has erupted compositionally distinct magmas. The two major units have an axial bathymetric high, are bounded by transform or overlapping spreading centres and are shown to be discrete volcanoes. One of the units shows systematic variation in magma composition along the rift consistent with injection of lava down-rift and concomitant low-pressure fractional crystallization with distance from the topographic high. Compositional variation within and between magmatic units is largely controlled by fractional crystallization at low and intermediate pressures. The eastern and western limbs of a large overlapping spreading centre at about 11°45′N have compositionally distinct lavas, apparently from separate magma batches. Axial eruptions in the vicinity of a large transform fault (Clipperton Fracture Zone) show a large variation in composition and at least one independent magma injection. Highly fractionated lavas with compositions up to 59% silica are included in these eruptions. One of the axial tectonic units has, in addition to normal tholeiitic eruptions, some lavas highly enriched in incompatible elements such as potassium, titanium, strontium, barium, zirconium and lanthanum. These lavas are also isotopically enriched with respect to
87
Sr/
86
Sr, suggesting that the mantle beneath some portions of the axis is compositionally heterogeneous. The presence of compositionally distinct magma batches, often in close proximity, suggests that magma chambers underlying the East Pacific Rise axis are small and probably intermittent.
Characterization of the St Helena magma source
Authors: Chaffey D. J. , Cliff R. A. , Wilson B. M. 
Published: April 2008

Summary

Combined Sr-Nd-Pb isotope and trace-element data for St Helena are interpreted in terms of changing thermal and chemical fluxes impinging on and interacting with the base of the lithosphere over a period of 6 Ma. The data reveal the existence of two geochemically distinct components in the St Helena source region: (i) a HIMU (high U/Pb) component which has extremely radiogenic lead isotopes (
206
Pb/
204
Pb >20.8) with
87
Sr/
86
Sr and
143
Nd/
144
Nd ratios displaced below the mantle array; (ii) a component with less radiogenic lead and strontium isotopic compositions and more radiogenic neodymium compositions. Coupled trace-element and isotope variations are evident during the activity of each volcano. During shield development an increase in incompatible-trace-element enrichment occurs. This is coupled to a decrease in
143
Nd/
144
Nd, whilst strontium and lead isotope ratios become progressively more radiogenic with time. The time-dependent variations are thought to be consistent with high-level processes occurring at the base of, or within, the lithosphere. A decrease in the signature of the depleted component with time is shown to be the result of a decreasing thermal flux acting on the base of the lithosphere. As a consequence the degree of partial melting of the depleted component (which may reside in the lithosphere or asthenosphere) is reduced, increasing the signature of the HIMU component in the erupted magmas.
Hygromagmaphile element distributions in oceanic basalts as fingerprints of partial melting and mantle heterogeneities: a specific approach and proposal of an identification and modelling method
Authors: Joron J.-L. , Treuil M. 
Published: April 2008

Summary
On the basis of the properties of hygromagmaphile (HYG) elements we propose a specific method of identifying and modelling the evolution of mantle geochemical properties using simple mass balance equations and taking into account a large volume of data obtained for basaltic series belonging to characteristic oceanic domains. This method uses both binary and ternary HYG element ratio diagrams to distinguish between the effects of partial melting and mantle heterogeneity. It is assumed that batch partial melting is the simpler and more suitable process of basaltic magma generation, which produces linear correlations on binary HYG element ratio diagrams. Melting of a homogeneous source is projected on ternary HYG element ratio diagrams as a single point approximating the composition of the mantle source.
We show that basalt HYG element ratios are closely dependent on four main factors, namely the nature of melting (batch partial melting), the degree of partial melting, the composition of the mantle and the mineralogy of the mantle.
Partial-melting trends and complex mantle heterogeneities are clearly indicated by binary diagrams, and a simple and regular suboceanic mantle HYG element array is obtained in ternary diagrams. Taking into account the close relation with isotopic trends, the HYG element array is considered to be the fingerprint of ancient mantle differentiation. It can be reproduced by a simple fractional crystallization process, and mostly excludes a large-scale and intensive chemical mixing process. These results are in good agreement with a marble cake mantle model, limiting convection effects to a mechanical stirring of the upper mantle, but they do not necessitate any recycling of crustal material into the suboceanic mantle.
Evaluation of rare gas data in relation to oceanic magmas
Authors: Fisher D. E. 
Published: April 2008

Summary
The isotopic compositions of the rare gases measured in oceanic rock samples present stimulating but incomplete information concerning the time and extent of magma degassing processes. Isotopic abundances of gases trapped from suboceanic mantle source regions are related to the depleted/undepleted mantle concepts, while atmospheric or crustal components form an important part of the data set. A reasonable story can be presented for the rare gas component from normal mid-ocean ridge basalt mantle source regions, but oceanic islands and island arc basalts result from more complex sources; the rare gas evidence is not yet sufficiently free of ambiguities and experimental uncertainties to provide a firm constraint to various models.
Geometry and kinematics of inversion tectonics
Authors: Williams G. D. , Powell C. M. , Cooper M. A. 
Published: April 2008

Summary
Positive inversion tectonics involves the reversal of extensional fault movement during contractional tectonics. Basin stratigraphy developed before, during and after extensional fault movements may be described as pre-, syn- and postrift sequences. Growth fault activity may be graphically displayed using thickness changes in stratigraphic intervals from fault footwall to hanging wall. Alternatively, it may be recorded using a hanging wall displacement/distance plot. Contractional reactivation of extensional faults puts progressively older synrift markers into net contraction. The point of change from net extension to net contraction is the null point. Its position in the synrift stratigraphy may be used to quantify the inversion ratio, which is defined as the ratio of contractional to extensional movement. Negative inversion is the reactivation in extension of a significant portion of an existing contractional system. Stratigraphic separation diagrams constructed from geological maps may be used to define the null point of individual faults and to quantify their inversion ratio.
Some geometrical characteristics of inversion
Authors: Hayward A. B. , Graham R. H. 
Published: April 2008

Summary
The inversion of extensional fault systems results in the reversal of slip on the faults and expulsion of the synrift fill. During inversion the beds in the cover sequence shorten before the net extension at the basement level has been cancelled. Shortening of the sedimentary cover generates folding and backthrusting in the still downthrown hanging wall block. Intracratonic inverted basins in different parts of the Alpine Foreland show similar structural geometries with the major extensional faults which controlled basin development reactivated during subsequent compression. We use examples from the Western Approaches and offshore Holland (Broad Fourteens Basin) to illustrate the structural styles developed during inversion. The fundamental control on compressional structural geometry exerted by pre-existing extensional structures is also visible in more complexly deformed orogenic belts, like the Western Alps and the Pyrenees. In these areas inversion also occurs, but more commonly extensional faults which may not have inverted act as an indirect control on the location of ramps, and/or thrust orientation. Seismic data are normally required to establish these effects with certainty. However, as the body of knowledge builds up, it is possible to recognize certain geometrical characteristics which suggest the control of extensional faults in thrust belts. These include footwall shortcuts, out of sequence structures and arcuate thrust-fold traces.
The inverted margin of the French Alps and foreland basin inversion
Authors: de Graciansky P. C. , Dardeau G. , Lemoine M. , Tricart P. 
Published: April 2008

Summary
The whole of the Western Alpine realm can be considered to result from the inversion of the European margin of Ligurian Tethys as a consequence of the collision between Apulia and Europe. The margin was developed due to Tethyan rifting during the Liassic and Middle Jurassic and regional thermal subsidence as the Ligurian ocean was spreading in the Late Jurassic and Early Cretaceous. Coevally, the margin underwent additional stretching in response to North Atlantic rifting. Inversion was initiated by Late Cretaceous times when the Ligurian oceanic crust began to be subducted, with localized obduction, beneath the previously passive margin. The most recent inversion of the Western Alps occurred in the external Molasse basin of Manosque-Digne-Valensole during the Late Miocene and Pliocene. Regions of mild inversion allow useful comparisons to be made with more strongly inverted basins. The geometric characteristics of the inverted basins depend on the lithology, geometry of the extensional structures, orientation of extensional faults with respect to the compressive Alpine stresses and the amount of compression. Comparisons of the external and interal zones suggest that the ductilely deformed thrust sheets may have originated from inverted half-grabens.