bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biomarker maturity profiles in the Inner Moray Firth Basin and implications for inversion estimates
Authors: Pearson Michael J. , Duncan Alasdair D. , Duncan Alasdair D. 
Published: April 2008

Abstract
The thermal stress (maturity) of Oxfordian to Kimmeridgian rocks in 13 Inner Moray Firth wells and at outcrop has been assessed using sterane and hopane isomer ratios. Significant depth profile displacements between the maturity trends for the Beatrice suite, other groups of Inner Moray Firth wells and a Viking Graben calibrant well are considered to be partly due to differences in uplift during Tertiary inversion and partly to varying palaeo-thermal gradients. Present day temperature plots are used to measure cooling from biomarker-derived maximum temperatures and hence to obtain approximate estimates of inversion.
Consideration of errors in cooling estimates allows the limits of uplift to be constrained. Relative uplift between Inner Moray Firth fault blocks is likely to be subject to fewer estimation errors than absolute uplift (inversion) with respect to the Viking Graben. 12/26-1, the most uplifted well on the Central Ridge, is estimated to have experienced between 400 and 700 m of uplift relative to 12/24-1, the least uplifted in the Smith Bank Graben, although for other wells relative uplift is not always related to present-day structural elevation. Inversion (absolute uplift) of the Smith Bank Graben is probably at least 150 m although the error in this estimate is large. Inversion of well sections in the Beatrice Field is thus estimated to have been around 400 m.
The development of the Ivanhoe, Rob Roy and Hamish Fields, Block 15/21A, UK North Sea
Authors: Currie Susan 
Published: April 2008

Abstract

The Ivanhoe, Rob Roy and Hamish Fields development in southern block 15/21 has been producing oil from Upper Jurassic age sandstones since mid-1989. The two reservoir horizons, historically within the Field models referred to as a ‘Supra Piper’ and a ‘Main Piper’ unit, but now correlated to sandstones in the Piper and Sgiath Formations respectively, comprise shallow marine sandstone facies deposited as part of the progradation of the Piper and Scott delta systems across UKCS quadrant 15. The reservoir has been modelled using a 3D seismic survey shot in 1984 and a sub-regional database of about 20 wells. Through the first five years of field life reservoir performance has been consistently good. In 1985, at Annex B time, the estimate for combined Ivanhoe and Rob Roy Fields STOIIP was 146 × 10
6
bbls. The Annex B total combined reserves figure of 88 × 10
6
bbls for Ivanhoe and Rob Roy was produced by 1994. Both geoscience and reservoir engineering models for the fields have been revised since the Annex B submission. The latest revision resulted in a substantial increase in the estimated initial oil in place figure for the fields. This paper summarizes the initial development of the Fields, subsequent reservoir modelling and the production history during the first five years of field life.
Shale lamination and sedimentary processes
Authors: O’Brien Neal R. 
Published: April 2008

Abstract
Lamination is a common feature of shale and other argillaceous rocks. The type of shale lamination provides an important clue in identifying sedimentary processes when combined with other geological evidence. Presented here is an overview of some common lamination signatures in shale and the sedimentary processes responsible for their formation. Macro-and microfabric and textures of Proterozoic, Palaeozoic, and Mesozoic shales from various sedimentary environments are revealed by X-radiographs, thin-section photomicrographs, and scanning electron microscope micrographs. Characteristic fabrics associated with the following sedimentary processes are presented: (1) bottom flowing currents produce features of fine to thick laminae (approx 0.5–1.0 mm thick) in association with small-scale features of crossbedding, ripple marks, cut and fill and flame structures; (2) deposition from low-density bottom currents and turbidity currents leaves a fabric signature of graded bedding; (3) suspension settling is shown by alternating very fine (<0.5 mm thick) non-graded silt and clay laminae; (4) microbial mats are recognized by wavy lamination.
Tales of 1001 varves: a review of Santa Barbara Basin sediment studies
Authors: Schimmelmann Arndt , Lange Carina B. 
Published: April 2008

AbstractThe varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off California has been studied extensively by sedimentologists, micropalaeontologists and geochemists during the past four decades. The Santa Barbara Basin is the only basin in the California Borderland Province that exhibits laminations for most of the Holocene. These sediments are essential to further our understanding of climate in that they provide a rare oceanic record of climate change with high resolution. In this overview of the complex and multidisciplinary Santa Barbara Basin sediment research, we briefly introduce the reader to the various analytical approaches and present a comprehensive collection of literature references.
Oligocene laminated limestones as a high-resolution correlator of palaeoseismicity, Polish Carpathians
Authors: Haczewski Grzegorz 
Published: April 2008

Abstract
Thin intercalations of laminated coccolith limestones in a series of flysch and black shales define a regional marker horizon in the Oligocene strata of the Outer Carpathians. Distinctive sequences of laminae in the coccolith limestones have been correlated over distances of up to 240 km and across major facies zones. The correlated succession of laminae provided the basis for correlation of intercalated turbidites. The successions of laminae are disturbed at all studied localities by erosional gaps, intercalations of non-laminated limestone and deformation of some intervals of the laminated sequence. The disturbances themselves have been precisely correlated between three major nappes of the Outer Carpathians. The characteristics of the disturbances and their long-distance continuity indicate their seismic origin. The coccolith ooze at the top of the sediment column was firm and its simultaneous disturbance over large areas required earthquakes of magnitudes above 6.5. Laminated pelagic limestones provide a precise chronostratigraphic framework for long-distance correlation of seismic and other events recorded within their sequence.
High-resolution sedimentology and micropalaeontology of laminated diatomaceous sediments from the eastern equatorial Pacific Ocean (Leg 138)
Authors: Pearce R. B. , Kemp A. E. S. , Baldauf J. G. , King S. C. 
Published: April 2008

Abstract

Scanning electron microscope (SEM)-based analyses of the laminated diatom oozes encountered during Leg 138 reveal three major laminae types. The first lamina type is composed of multiple layers of approximately 20 μm thick diatom mats, which form laminae dominated by assemblages of the pennate diatom, . More than one variety/subspecies of
T. longissima
occurs within these laminae (referred to as the
T. longissima
Group). The second lamina type is composed of a mixed-assemblage of several species of diatoms (centric and pennate varieties), calcareous nannofossils, and subordinate quantities of radiolarians, silicoflagellates and foraminifera. The third lamina type is dominated by an assemblage of nannofossils and minor amounts of those fossil components mentioned above. This last form of lamination is compositionally similar to the background sediment type, foraminifer-nannofossil ooze (F-NO). Two lamina associations occur within the laminated intervals; the first comprises of alternations of
T. longissima
Group and mixed-assemblage laminae (average thickness is approximately 6 mm) and the second is composed of
T. longissima
and nannofossil-rich laminae (average thickness is approximately 3.5 mm). The arrangement of laminae probably originates from the deposition of multiple layers of 20 μm thick mats from one mat-flux episode. The much thinner nannofossil-rich laminae are interpreted to represent periods of more ‘normal’ deposition between mat-flux episodes. The occurrence of several varieties/subspecies of
T. longissima
within individual mat layers is consistent with observations of
Rhizosolenia
diatom mats in the modern world ocean.
Bathymetric segmentation and faulting on the Mid-Atlantic Ridge, 24°00′N to 24°40′N
Authors: Allerton Simon , Searle Roger C. , Murton Bramley J. 
Published: April 2008

Abstract
This investigation of valley-wall faulting and its relationship to bathymetry focuses on the first two segments north of the Kane Fracture Zone. The valley-wall faults imaged by deep-towed sidescan sonar show aspects common to continental normal faults, and a similar erosional pattern, from a fresh fault surface, through eroded, talus covered scarps, to scarps draped with pelagic sediments. The first, southernmost segment is a symmetric graben at the segment centre, and an asymmetric half-graben at the northern end. The second, northern segment is an asymmetric half-graben for its entire length. The gross morphology is reflected in the faulting style, with multiple small faults at the symmetric graben, and one or two large faults on the eastern wall, defining the asymmetic half-graben. This difference in faulting style may reflect differences in depth to the brittle-ductile transition, with asymmetry occurring when the brittle-ductile transition is deep and brittle faults can cross the axial valley, locking faults on the other side. A gross estimate of horizontal strain accommodated by the valley-wall faults correlates well with valley-floor bathymetry, suggesting that bathymetric segmentation is partially due to tectonic thinning at segment ends.
The response of ridge-crest hydrothermal systems to segmented, episodic magma supply
Authors: Haymon Rachel M. 
Published: April 2008

Abstract
Segmented, episodic magma supply and cracking models, advanced to explain ridge-axis discontinuities and along-strike variability, have provoked a recent shift in mid-ocean ridge crest hydrothermal models. Segment-scale and time-series observations of hydrothermal vents and plumes along fast and intermediate spreading centres reveal a close coupling between magma supply and hydrothermal fluxes. Based on the premise that magma supply exerts a primary control on hydrothermal processes, a new paradigm of segmented hydrothermal circulation has arisen featuring independent temporal evolution of hydrothermal systems along individual ridge segments. This paradigm explains observed segment-to-segment variations in the chemical composition of vent fluids and plumes (‘chemical segmentation’). Hydrothermally active segments can be classified, independently of spreading rate, into two types that represent end-members for the coupling of hydrothermal and magmatic processes: magma-rich segments and magma-starved segments. Along magma-rich segments, magma intrudes to shallow depths where water:rock ratios are high. Seafloor vent distribution tends to be magmatically controlled along dyke-induced fissures. Along magma-starved segments, intrusion is at greater depth, and deep cracks (usually faults) are required to transport water to and from the heat source. Water:rock ratios are low and vent locations are influenced by crustal permeability structure, as well as heat source location. Although both segment types can occur at any spreading rate, magma-rich segments are more common at faster spreading rates, and magma-starved segments are more typical at slow spreading rates.
Influence of axial segmentation on hydrothermal circulation at fast-spreading ridges: insights from Hess Deep
Authors: MacLeod C. J. , Manning C. E. 
Published: April 2008

Abstract
The evolution of oceanic hydrothermal systems depends heavily upon the origin, timing and spatial distribution of permeability near the magmatic heat source. At fast-spreading ridges, where permanent magma chambers are inferred, permeability in the plutonic portion of the crust is generated during cooling by time-, strain-rate- and temperature-dependent fracturing, which propagates downwards through the crust as the rocks cool and move off-axis. At major axial discontinuities, however, where magmatism may be intermittent and tectonism plays an important role, the controls on hydrothermal alteration are likely to be more complex.
Gabbros exposed at Hess Deep and sampled by the Ocean Drilling Program during Leg 147 provide the first insights from direct observation into the structural and metamorphic evolution of the lower crust near axial discontinuities. Early amphibolite-facies deformation and alteration are related to cooling, fracturing, and hydrothermal fluid flow within several kilometres of the East Pacific Rise axis. Later, dense fracturing and limited alteration occurred in the greenschist facies as the gabbros were transported into the deformation field at the ‘tectonic tip’ of the westward-propagating Cocos-Nazca ridge.
Although this is only one example of the possible influences of axial segmentation on hydrothermal circulation, and may represent a comparatively simplified view of other natural systems, given the potential variations in strain and strain rate coupled with the possibility of reheating events associated with renewed magmatism, we suggest that the multi-stage structural and metamorphic evolution of the Hess Deep plutonics may be a good analogue for the cooling history of the lower crust at other fast-spreading ridge axial discontinuities.
Hydrothermal activity and segmentation in the Magnitogorsk-West Mugodjarian zone on the margins of the Urals palaeo-ocean
Authors: Zaykov V. V. , Maslennikov V. V. , Zaykova E. V. , Herrington R. J. 
Published: April 2008

Abstract
The Magnitogorsk-West Mugodjarian zone is interpreted to have developed as a marginal rift to the main Urals palaeo-ocean. In this zone, seven distinct tectonic segments each with a strike extent between 140 and 220 km have been identified. These segments can be distinguished on the basis of volcanic facies and features of hydrothermal activity. In the three southernmost segments the volcanics comprise basaltic and rhyolite-basalt complexes. The former contain massive sulphides of Cyprus-type and cherty iron-formation whilst the latter contain massive sulphides of ‘Uralian’ type, cherty iron-formation and manganese oxide deposits. In the two central segments rhyolite-basalt complexes are developed associated with giant massive sulphide deposits (Sibay > 100 million tonnes massive sulphides). In the two northernmost segments rhyolite-basalt and andesite-basalt complexes are developed, both associated with cherty iron-formation and manganese oxide deposits. It is proposed that the variations in frequency, size and composition of the metalliferous deposits between the segments are a result of differences in the sequence of Palaeozoic oceanic development. Rifting started during the Eifelian in the south (current position) and in Late Givetian times in the north. This diachronous rifting and tectonic development has influenced the major geological features of the segments.
The hydrothermal imprint on life: did heat-shock proteins, metalloproteins and photosynthesis begin around hydrothermal vents?
Authors: Nisbet E. G. , Fowler C. M. R. 
Published: April 2008

Abstract
Molecular evidence implies that the first living community existed around a hydrothermal system. From this setting, life may have colonized a wide variety of hydrothermal environments. These would have included hydrothermal systems on mid-ocean ridges, around komatiite plume volcanoes, and in a variety of shallow-water settings. Hydrothermal systems on ridge segments may have been crucial in providing habitats to sustain the first communities of life.
The early hydrothermal heritage may now be deeply imprinted in all organic life. Biological processes that use essential metals, especially Fe (typically as 4Fe-4S), Mn, Zn, Cu, Mo, Mg, Se and Ni, may all have hydrothermal descent from reactions that first evolved on a natural hydrothermal metal sulphide substrate, and it is possible that the first supply of P, when life began, was also associated with volcanism. The heat-shock proteins and many important ‘housekeeping’ enzymes of the biosphere, such as urease, hydrogenase, and nitrogenase may all be of hydrothermal origin. Photosynthesis may have originated via infrared phototaxis developed at mid-ocean ridge hydrothermal systems. The modern biosphere may have grown out of bacterial processes originally evolved at mid-ocean ridges.
The thermodynamics of Himalayan orogenesis
Authors: Hodges K. V. 
Published: April 2008

Abstract
Geological and geochemical research in the internal zone of the Himalayan orogen reveal evidence for complex relationships between regional metamorphism, anatexis, thrust faulting and normal faulting in Miocene time. Such interactions share many characteristics with those that define the behaviour of non-equilibrium thermodynamic systems, like chemical oscillators. The internal ordering of such systems arises spontaneously and is maintained by continual exchange of energy with the outside world. Mountain ranges are open thermodynamic systems, equally capable of displaying self-organized behaviour. They accumulate energy through a variety of mechanisms, particularly crustal thickening, but their non-equilibrium structure is maintained through compensating mechanisms of energy dissipation. The simultaneous operation of normal faults and thrust faults in the Himalayan system, ejecting a wedge of middle crust southward from the orogen towards the Indian foreland, was a remarkably efficient method of mass (and therefore energy) dissipation in Miocene time. Research in many branches of science suggests that thermodynamic systems forced far from equilibrium by their boundary conditions may evolve towards establishing the most efficient possible mechanisms for counteracting those conditions. For the Himalaya, one possible explanation for development of a process set characterized by simultaneous normal faulting and thrust faulting, linked through metamorphism and anatexis, is that simple physical erosion alone was inadequate to moderate the extraordinary crustal thickness and topographic gradients that characterized the southern flank of the range in Miocene time. The orogenic system may have adapted to this condition through a new and more efficient mechanism of energy dissipation that required the coordination of a variety of thermal and deformational processes.
Low- to medium-pressure Variscan metamorphism in Galicia (NW Spain): evolution of a kyanite-bearing synform and associated bounding antiformal domains
Authors: Reche J. , Martínez F. J. , Arboleya M. L. 
Published: April 2008

Abstract

Evidence for different substitution relationships between aluminosilicates in two domains east of the Ollo de Sapo gneiss antiform in Galicia (NW Spain) suggests a high dependence of metamorphic evolution on the local tectonic and granitoid intrusion history. The Vivero pelite belt constitutes a pinched synformal domain located between the Ollo de Sapo antiform to the west and the Lugo dome to the east. Within this synform, black, Alrich Silurian pelites contain kyanite that, along with muscovite, formed pseudomorphically after early pre-D
2
andalusite. Syn-D
2
inversion of andalusite to kyanite indicates an evolution from early, low-
P
to medium-
P
regimes. Locally, near the Vivero transtensional fault, which constitutes the E boundary of the synform new, late post-D
2
pleochroic andalusite grew from staurolite and biotite indicating reinstallment of a new low-
P
regime during and after the D
3
deformation phase, which is related to movement along the fault zone. The Ollo de Sapo domain contains only a high
T
-low
P
series of metamorphic assemblages. The peak assemblage within this domain was cordierite-biotite-K-feldspar-andalusite/fibrolite related to emplacement of a pre- to syn-D
2
swarm of sheet-like peraluminous granitoids located mainly in the core of the antiform. Early pre- to syn-D
2
staurolite-biotite ± garnet, and late sillimanite-staurolite-biotite assemblages present on the west side of the Lugo dome testify to an early stage of nearly isothermal decompression followed by decompression with local heating. Stabilization of late andalusite in the Vivero pelite belt and of sillimanite west of the Lugo dome appear almost synchronous and clearly related to a syn-D
3
thermal peak induced by Upper Carboniferous granitoid intrusion along the Vivero transtensional fault separating both domains.
Low-pressure crustal anatexis: the significance of spinel and cordierite from metapelitic assemblages at Nanga Parbat, northern Parkistan
Authors: Whittington Alan , Harris Nigel , Baker Judy 
Published: April 2008

Abstract

Spinel-bearing domains in high-grade metapelitic rocks from Nanga Parbat represent zones of partial melting during biotite breakdown under vapour-undersaturated conditions. Spinel is essentially of the MgAl
2
O
4
-FeAl
2
O
4
solid solution, and is therefore not stabilized by the presence of trace elements such as zinc, but is restricted to a quartz-absent petrogenesis. A new petrogenetic grid for metapelites has been constructed to allow for both vapour-undersaturated and quartz-undersaturated conditions. This grid contains a quartz-absent invariant point in KFASH that predicts quartz-absent melting will occur in biotite-sillimanite assemblages at low pressures.

A
P–T
pseudosection drawn for bulk compositions with intermediate Fe/Mg ratios shows that at low pressures biotite will break down initially in the presence of quartz, to produce cordierite and K-feldspar and melt. At higher temperatures the quartz-absent reaction will be crossed, and biotite will break down to produce spinel in addition to cordierite, K-feldspar and melt. The sequence of assemblages is biotite-cordierite, biotite-cordierite-spinel, and finally cordierite-spinel. This biotite-absent assemblage is not observed, indicating that the quartz-absent reaction did not go to completion. Limits can be placed on the pressures and temperatures at which the biotite breakdown reaction is crossed, from the coexistence of solid phases and granite melt over a range of water activities. For the Nanga Parbat assemblages, pressures and temperatures lay at about 720°C and 5 kbar at water activity, a

H
2
O

≥ 0.6. These conditions are consistent with a rapidly exhuming terrane, as suggested by isotopic constraints and thermal modelling of the region.
Vesiculation processes in silicic magmas
Authors: Navon Oded , Lyakhovsky Vladimir 
Published: April 2008

Abstract
The physics of vesiculation, i.e. the process of bubble formation and evolution, controls the manner of volcanic eruptions. Vesiculation may lead to extreme rates of magma expansion and to explosive eruptions or, at the other extreme, to low rates and calm effusion of lava domes and flows. In this paper, we discuss the theory of the different stages of vesiculation and examine the results of relevant experimental studies. The following stages are discussed: (1) The development of supersaturation of volatiles in melts. Supersaturation may develop due to a decrease in equilibrium solubility following changes in ambient pressure or temperature or due to an increase in the magma volatile content (e.g. in response to crystallization of water-free or waterpoor mineral assemblages). (2) Bubble nucleation. The classical theory of homogeneous nucleation and some modern modifications, heterogeneous nucleation with emphasis on the nucleation of water bubbles in rhyolitic melts and the role of specific crystals as heterogeneous sites. (3) Bubble growth. The effect of diffusion, viscosity, surface tension, ambient pressure and inter-bubble separation on the dynamics of growth. (4) Bubble coalescence. The theory of coalescence of static foams. factors that may effect coalescence in expanding foams and shape relaxation following bubble coalescence.