bluuebunny/crossref_metadata_2025_split huggingface dataset:
The link between metamorphism, volcanism and geotectonic setting during the evolution of the Andes
Authors: Aguirre L. , Levi B. , Nyström J. O. 
Published: September 2007

Summary

A low-grade, non-deformational, regional metamorphism ranging from burial to ocean-floor type characterizes the Andean range. Longitudinal variations exist, coinciding with changes in the chemistry of the volcanic suites involved, both trends being controlled by the geotectonic setting. The study of Cretaceous volcanic rocks in Colombia, Peru and Chile indicates that: (i) ocean-floor metamorphism (high-
T
gradients) correlates with tholeiitic volcanism in marginal basins where the continental crust was eliminated or extremely attenuated; (ii) burial metamorphism (low- to moderate-
T
gradients) correlates with calc-alkaline to shoshonitic volcanism in ensialic, aborted, marginal basins with moderate thinning of the continental crust. The metamorphism in the Andes, which is characterized by a counter-clockwise
P-T-t
path, started during the initial stages of basin formation and preceded the orogenic activity, contrary to the development in compressional geotectonic settings.
The structural evolution of the Brent Province
Authors: Yielding Graham , Badley Michael E. , Roberts Alan M. 
Published: September 2007

Abstract

The structural evolution of the Viking Graben has been the fundamental control on the deposition of the Brent Group and on the development of trapping geometries. Major crustal extension in the early Triassic caused tilting of basement fault blocks, which can still be clearly seen at the basin margins. By the mid-Triassic a post-rift thermal-subsidence basin was established. Local fault control on Brent Group deposition indicates the onset of a second period of crustal extension, although the main control on subsidence at this time was still thermal relaxation following Triassic rifting. Extension during deposition of the Brent was of only
c.
1% magnitude.

The second period of extension increased in magnitude following Brent deposition and peaked during the late Jurassic, creating the main structural traps for Brent Province oil and gas. Footwalls to major normal faults were uplifted and eroded. The amount of uplift on a given fault-block can be predicted using quantitative models (flexural and domino models). Subsidence in the adjacent half-graben generally outpaced sedimentation, leading to deep-water basins into which footwall material could collapse. On all but the largest fault-blocks it is likely that footwall uplift rates were low compared with erosion rates, and so footwall crests would have been degraded faster than they would have been uplifted above sea-level. Flushing by meteoric water during the late Jurassic is therefore expected only on the largest fault-blocks (e.g. Snorre, Gullfaks).
Brent Group: sequence stratigraphy and regional implications
Authors: Mitchener B. C. , Lawrence D. A. , Partington M. A. , Bowman M. B. J. , Gluyas J. 
Published: September 2007

Abstract
Previous published models for the stratigraphic evolution of the Middle Jurassic (Aalenian—Bathonian) Brent Group and its equivalents rely largely upon lithostratigraphy, with few reliable time lines for correlation across the Northern North Sea basin. To rectify this a new, largely well-based, multi-disciplinary regional study was undertaken, combining detailed biostratigraphic and sedimentological data from more than 450 wells across the whole of the Northern North Sea basin.
A basin-wide sequence stratigraphy for the Middle Jurassic has been developed, comprising two tectono-stratigraphic units (J20, Aalenian—Late Bajocian and J30, latest Bajocian—Middle Callovian), subdivided into five sequences: J22 (Aalenian), J24 (Early Bajocian), J26 (Early—Late Bajocian), J32 (latest Bajocian—Late Bathonian) and J34 (latest Bathonian—Middle Callovian). The tectono-stratigraphic units developed in response to large scale (second order) tectonic processes: pre-rift thermal uplift (J20) and the onset of rifting (J30), whilst sequence development was controlled by a combination of changes in basin subsidence, sediment supply and eustatic sea level.
A series of palaeogeographic and isopach maps outline the basin evolution and sedimentary response for each sequence. They describe a progressive basinward shift of the J22 and J24 depocentres in response to the thermal uplift; by the end of J26, sediment supply could not keep pace with increased basin subsidence caused by the crustal extension. J32 and J34 represent the first periods where active rifting can be clearly identified in the North Sea basin, with the development of tilted fault block geometries in the East Shetland Basin and Bruce—Beryl Embayment. Continued extension and rifting in these areas led to the development of an overall retrogradational system which extends through to the latest Jurassic.
The study provides a model for North Sea basin evolution and a predictive sequence stratigraphic framework within which the local lithostratigraphy can be resolved and basin potential evaluated.
The fate of feldspar in Brent Group reservoirs, North Sea: a regional synthesis of diagenesis in shallow, intermediate, and deep burial environments
Authors: Glasmann J. Reed 
Published: September 2007

Abstract
Feldspar dissolution is an important process affecting the reservoir quality of Brent Group sandstones in the northern North Sea and shows a strong relationship to reservoir temperature and pore water chemistry. In low temperature, brackish, shallow to moderately buried reservoirs (2400–3700 m, reservoir temperature less than 100–120°C) feldspar is generally a major detrital component whose abundance is affected by local variations in facies, extent of early meteoric leaching, and kaolinitization. In deeply buried Brent reservoirs (3700–4700 m) where present burial temperatures exceed 130–140°C detrital K-feldspar is absent and sandstones are characterized by major illitization of early formed kaolinite, precipitation of fibrous illite, extensive quartz cementation, and variable albitization. K-feldspar dissolution apparently supplied elements necessary for illitization, which, according to K-Ar evidence, occurred during early Tertiary burial, associated with initial stages of hydrocarbon accumulation and brine migration. Illite K-Ar ages are unaffected by feldspar contamination in deep reservoirs and the narrow range of measured ages for widely ranging illite size-separates indicates that the major dissolution/illitization reaction was a geologically rapid process. In contrast, illite K-Ar ages from shallow and intermediate-depth reservoirs range from Palaeocene to Early Miocene and often have considerable size dependency due to small amounts of feldspar contamination in coarser fractions. Variable contamination and its effect on measured K-Ar ages often precludes establishing the history of illitization and a well-defined relationship to hydrocarbon accumulation in intermediate-depth reservoirs. Although some feldspar is dissolved during early burial history by low temperature circulation of meteoric water, only deeply buried Brent reservoirs are characterized by the complete diagenetic removal of feldspar; however, the secondary porosity generated by late dissolution is of little benefit to reservoir quality because accompanying cementation results in major loss of permeability.
Open and restricted hydrologies in Brent Group diagenesis: North Sea
Authors: Haszeldine R. Stuart , Brint J. F. , Fallick A. E. , Hamilton P. J. , Brown S. 
Published: September 2007

Abstract

Diagenetic cements in the mid Jurassic Brent Group sandstones of the North Sea have been studied in the Thistle, Murchison, Dunlin and Alwyn South (3/13a-1) oilfields. Volumetrically important cements start with early siderite, kaolinite and calcite, and continue to later kaolinite, ankerite, quartz and illite. The mineralogies of early siderites and calcites are homogeneous in formations with different depositional porewaters. Carbonate concretions nucleated on biotite grains, and their carbon supply was very local and facies controlled. Strontium was derived from dissolution of silicates and shell debris and
87
Sr/
86
Sr rapidly became homogeneous in different formations. Oxygen was derived from meteoric water and was homogeneous throughout, even in marine deposits. These data suggest an open-flow system with uniform meteorically-derived pore fluids and local ion supply throughout the sandstones.

Diagenetically later ankerite formed below 1.1 km and shows mineralogies which are less homogeneous, with
87
Sr/
86
Sr variable. Cement ions could all have been very locally supplied from within the formation. Late kaolinite could also have been formed locally from feldspars within the formation. The exception to this was quartz cement, its large volumes indicating import across formations or from outside the Brent. Fluid inclusions in quartz show abnormally hot temperatures equating to 80–100°C at 2.2 km. These can be interpreted in two ways. First to indicate a large circulation of hot evolved meteoric water within the basin. This would have been induced by tensional fracturing of the crust related to the final phase of North Atlantic rupture in the Palaeocene and Eocene. However, fluid inclusion temperatures within quartz overgrowths show a systematic increase of temperature with present-day burial depth, suggesting that these temperature records could have been reset, and are now too hot. If these temperature data are rejected, a second interpretation is possible. The δ
18
O isotopic signatures show that late diagenetic silicates and carbonates could have grown in meteoric water, unmodified in its δ
18
O value, in a normal geothermal gradient. Illite grew in a slowly flowing fluid, which rapidly evolved to todays δ
18
O values, as individual groups of pores attempted to equilibrate with the rock around them Oil accumulation halted diagenesis and was permitted by buoyant trapping as this porewater system became stagnant.
Coalbed methane in the USA: analogues for worldwide development
Authors: Murray D. Keith 
Published: September 2007

Abstract
Preliminary estimates of coalbed gas in the major coal-bearing basins of the world range from approximately 3000 trillion cubic feet (TCF) to more than 12000 TCF (85-340 trillion cubic metres, TCM). The successful development of this important energy resource will largely depend on the judicious transfer of the coalbed methane (CBM) technology developed in the USA during the past two decades. Innovative field research has been conducted primarily in the San Juan and Black Warrior basins. Projects have involved co-operative efforts between the Gas Research Institute, federal and state geological surveys, academia, both large and small oil companies and private consultants. As a result, significant improvements have been made in many aspects of CBM technology, including: (1) dynamic openhole cavitation completions; (2) advanced hydraulic stimulation procedures; (3) enhanced ultimate coalbed gas recovery using the injection of nitrogen or carbon dioxide into the coalbed reservoir; (4) improved reservoir simulation parametric techniques; and (5) seismic methods to predict areas of optimum reservoir permeability. The appropriate applications of this rapidly developing technology to the complex and varied conditions that exist in other coal-bearing basins throughout the world is expected to lessen significantly the risks inherent in the successful commercialization of coalbed gas in a number of countries.
Geological controls on coalbed prospectivity in part of the North Staffordshire Coalfield, UK
Authors: MacCarthy F. J. , Tisdale R. M. , Ayers W. B. 
Published: September 2007

Abstract

Westphalian coal seams in the Kinetica/Taurus exploration licence EXL 282, which covers part of the North Staffordshire Coalfield, are estimated to contain over 5.6 × 10
10
m
3
of initial coalbed gas in place. In the evaluation of coalbed gas prospectivity in the licence area, data from the coal and the oil and gas industries were used to map coal occurrence, coal rank, the gas content of coal seams, gas in-place, structure, face cleat and
in situ
stress.

The North Staffordshire Coalfield is structurally and stratigraphically complex. Westphalian strata occur in a SSW plunging synclinorium that is highly segmented by faults with displacements as great as 500 m. These faults may either be barriers or conduits for fluid migration. The maximum
in situ
horizontal compressive stress is generally oriented NNW, subparallel to face cleats and some faults, which may favour openness and transmissivity of those fractures. In the southern part of the licence area, intraformational unconformities occur in the Westphalian. Total coal thickness is greatest (more than 40 m) and coal rank is highest (medium-volatile bituminous) in the northern part of the licence area, coincident with the greatest thickness of Westphalian strata. Predictably then, gas content and initial gas in-place per unit area are greatest in the northern part of the licence area, coincident with the occurrence of thick, high rank coals. In this area, initial gas in-place is estimated to exceed 4.0 × 10
8
m
3
per km
2
in some areas. Although gas resource trends have been identified, production rates of coalbed gas can only be established through well testing.
Cleat mineralization of Upper Permian Baralaba/Rangal Coal Measures, Bowen Basin, Australia
Authors: Faraj Basim S. M. , Fielding Chris R. , Mackinnon Ian D. R. 
Published: September 2007

Abstract

Coals from the Permo-Triassic Bowen Basin have been investigated using a variety of complementary analytical techniques. Face cleat minerals in the studied samples are dominated by authigenic clays, notably pure illite or illite-chlorite mixtures. Butt cleats and joints are dominated by carbonates, mostly calcite with less abundant ferroan calcite, ankerite and siderite. K/Ar ages of cleat-fill illites and one fracture illite-smectite fill indicate three phases of illite formation during the Triassic: (1) an early phase with ages clustered around 244 Ma ago; (2) a second phase about 232 Ma ago; and (3) the latest phase about 219 Ma ago. Thermal modelling of selected boreholes from the study area and other geological data indicate that the first phase of illitization occurred when the coal seams were about 1000 m below the surface and at a temperature of between 70 and 80°C, at a time when the basin was rapidly subsiding. These early illites were stable and retained their 1
M
polytype even after being exposed to temperatures of 150–190°C during maximum burial in the southeastern Bowen Basin. The second phase of illitization (at 232±3) occurred at about the time of maximum burial. The latest phase took place between 223±3 and 212±3 Ma ago and occurred in a wider temperature range (between 170 and 100°C) during a rapid uplift in the Late Triassic. The Bowen Basin area experienced a second cycle of subsidence that commenced in the Early Jurassic with the formation of the Surat Basin, which overlies the Bowen Basin and forms part of the Great Artesian Basin system. Regional uplift and erosion in middle Cretaceous times terminated sediment accumulation in the Surat Basin. During the second cycle of burial widespread carbonate mineralization in butt-cleats and joints took place. Calcite fluid inclusions indicate that calcite was precipitated from meteoric water at about 80°C. The widespread carbonate mineralization in butt cleats and the near-absence of carbonates in the face cleats is here attributed to permeability anisotropy, caused by a change in the direction of lateral compressive stress during Jurassic-Cretaceous times relative to that during the Triassic Hunter-Bowen Orogeny.
Characterization of anthracite
Authors: Davidson M. I. , Bryant R. , Williams D. J. A. 
Published: September 2007

Abstract

Examination of the surface properties of anthracite provides information of assistance in the interpretation of
in situ
behaviour and use of the material as a micronized fuel and as an inexpensive support substrate for growth of micro-organisms. The characteristics of anthracite particles (<10 μm) produced by crushing and grinding larger material (obtained from Cynheidre Colliery, South Wales UK) are reported. Mineral particles, liberated from this anthracite matrix, subsequent to radiofrequency-induced plasma (RFIP) oxidation, were found to constitute 2 wt%, 0.6vol% of that matrix. X-Ray fluorescence analysis and analytical transmission electron microscopy of these particles indicated silicon, aluminium and iron to be the predominant electropositive elements present, with calcium the only other element detected at a level greater than 5wt% of the mineral component. X-Ray diffractometry (XRD) of this component indicated that hematite, pyrite, siderite and a variety of aluminosilicate minerals were present in the original matrix.

Mineral particles liberated by RFIP oxidation of the planar (cut) surface of anthracite were initially captured in plastic replica films and thence transferred to carbon films. Electron microscopic examination of these films indicated that mineral particles present in the anthracite matrix possessed diverse chemistries, were submicron in size and suggested their distribution throughout the carbonaceous matrix to be homogeneous.

Estimates of the surface area of <10μm anthracite particles (107 ± 15 m
2
g
−1
) made using nitrogen adsorption/desorption (BET) analysis, were significantly greater than those predicted for non-porous particles of this size. Equilibration of the surface with nitrogen was reached ≈1.2 × 10
4
s after the imposition of changes in pressure. Hysteresis of the adsorption/desorption isotherms was pronounced, suggesting that the material contained 9%
v/v
pores, of which 75% were estimated to be ≈2 nm diameter.

Potentiometric (aqueous, acid/base, batchwise) titration of the material, at a variety of ionic strengths (
I
), indicated long equilibration times between H
+
/OH
−
and the surface (≈3 × 10
5
s). The dependence of the analytical surface charge density (σ
a
) on pH and
I
were found to be significant though small, with points of zero titration (pH
pzt
) in the range 4 < pH
pzt
< 7 which increased with
I
. at pH < pH < 9, σ
a
was virtually independent of
I
, suggesting a point of zero salt effect to be located in this region or that solute ions were unable to penetrate the surface. The range of σ
a
(based on the surface area determined by BET) was found to be small (−7 < σ
a
< 6 μC cm
−2
) and its nature consistent with that of surfaces of minerals shown and identified by electron microscopy and XRD analysis to be present at low concentration within (and exposed at the surface of) the carbonaceous matrix.
Petrological and spectroscopic structural characteristics of Bohemian and Moravian coals and their possible relation to gas proneness
Authors: Sýkorová I. , Novotná M. , Pavlíková H. , Machovič V. 
Published: September 2007

Abstract

Optical and infra-red microscopy, diffusion reflectance infra-red spectrometry and solid-state nuclear magnetic resonance spectrometry (
13
C CP/MAS NMR) were applied to the determination of the degree of coalification and structural characteristics of lignite and bituminous coal from deposits in the Czech Republic. Structural parameters such as the aliphatic and aromatic contents and carbonyl contents of coal and coal macerals could be valuable tools for determination of gas proneness, e.g. the CH
2
/CH
3
ratio derived from infra-red spectroscopy. Aromaticity,
f
a
, determined by
13
C CP/MAS NMR, is shown to be a valuable parameter reflecting the degree of coalification, particularly for low and middle rank coal, thus supplementing data derived from the vitrinite reflectance
R
o
and (H/C)
at
ratio data. The maceral group of huminite/vitrinite mirrored similar changes with increasing coalification degree as the parent coal. The structure of two macerals of the liptinite group, sporinite and cutinite, was investigated for bituminous coal, and the aromatic and oxygen group contents were higher in cutinite than in sporinite.
Minerals and major elements in density-separated coal fractions from Point of Ayr coal, Wales, UK
Authors: Barraza J. , Gilfillan A. , Cloke M. , Clift D. 
Published: September 2007

Abstract
Density separated coal fractions from 1.30 floats to 1.70 sinks of Point of Ayr coal for the particle sizes −3350+2800, −1000+850, −300+212 and −38+20µm, have been studied for major element and mineral content. Low temperature ash residues were analysed using Fourier transform infra-red and X-ray diffraction spectrometry. Major elements (Al, Ca, Fe, K Mg, Mn, Na and Si) were determined in high-temperature ash residues using atomic absorption spectrometry and atomic emission spectrometry. The minerals identified in the samples were kaolinite, illite, montmorillonite, quartz, dolomite, anhydrite, calcite, gypsum, mica, bassanite and interlayer smectite. The study suggests the origin of the minerals, on the basis of their association with the organic or mineral matter fractions, and indicates that there is a correlation between some major elements and mineral distribution in the coal fractions. It is shown that both the organic affinity of the elements and the abundance of specific minerals are related to the particle size.
Mineralogy, geochemistry and pyrite content of Bulgarian subbituminous coals, Pernik Basin
Authors: Kostova Irena , Petrov Ognyan , Kortenski Jordan 
Published: September 2007

Abstract
The mineralogy and geochemistry of Pernik subbituminous coals (coal bed A) and some genetic peculiarities related to the mineral formation were studied. The mineral matter of the coal consists chiefly of pyrite, kaolinite, siderite, quartz and calcite. Other minerals (dolomite, ankerite, plagioclase and some sulphates) are present in minor amounts, some occurring as accessory single crystals. Pyrite is the main mineral in these coals and exhibits a large array of textures and morphology. Isolated and clustered euhedral, bacterial and inorganic framboidal, cluster-like, homogeneous and microconcretional massive, infilling and replacing anhedral, and cleat-filling and fracture-filling infiltrational pyrite types were observed. Four stages of mineralization were distinguished: pyrite-kaolinite, pyrite, pyrite-siderite and sulphate stages. The amount of pyrite present in two sections of coal bed A was determined by quantitative powder X-ray diffraction analysis. The concentrations of 37 trace elements were determined. As, Cu, Co, Ni, Zn, Pb, V Ti, Mo, Rb, Cr and Mn are typomorphic for this coal. On the basis of their relation to organic or inorganic matter, four groups of trace elements were subdivided; and on the basis of cluster analysis four associations were differentiated.
Subsurface correlation of Carboniferous coal seams and inter-seam sediments using palynology: application to exploration for coalbed methane
Authors: McLean Duncan , Murray Iain 
Published: September 2007

Abstract
Palynology has a long history of application in the hydrocarbon exploration and development industry. Palynological methodologies developed for the study of traditional hydrocarbon reservoirs are directly transferable to exploration for coalbed methane. The principal difference in approach relates to the fact that coal seams usually contain abundant palynomorphs, whereas conventional reservoirs (sandstones and carbonates) do not. Work since the 1930s in the onshore British coalfields and work in the offshore southern North Sea Carboniferous basin illustrate that the high-resolution correlation of coal seams is achievable using palynology. The methods lend themselves to studies of coalbed methane reservoir connectivity and correlation. Other applications, such as the identification of coring points and stratigraphic targets, the monitoring of vertical and horizontal drilling and the study of coal seam maturation by spore colour analyses represent standard palynological applications.