bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic properties of sediments deposited in suboxic-anoxic environments: relationships with biological and geochemical proxies
Authors: Vigliotti L. , Capotondi L. , Torii M. 
Published: April 2008

Abstract

Several studies of the rock magnetic properties of sediments deposited in suboxicanoxic environments show that bacterial degradation of organic matter leads to selective dissolution of magnetite with a decrease in magnetic mineral concentration and an increase in magnetic grain size. This study of upper Quaternary sediments from both marine and lacustrine environments shows many similarities, although diagnetic processes appear to be enhanced in the marine sediments. When the remanence is controlled by fine-grained materials, the magnetic susceptibility can be considered a leading indicator of such changes, and the coercivity parameters, such as
S
ratio and
B
0 cr
, are also useful discriminants suggesting when antiferromagnetic minerals become more important in intervals characterized by reductive diagenesis. Generally, magnetic properties show close correlations with other environmental indicators: diatoms and foraminiferal concentrations and compositions and geochemical properties. This suggests that the magnetic analyses are very sensitive to environmental variations and provide powerful tools for monitoring past depositional and diagenetic environments.
Diagenesis and remanence acquisition in the Cretaceous carbonate sediments of Monte Raggeto, southern Italy
Authors: D’Argenio B. , Ferreri V. , Iorio M. , Raspini A. , Tarling D. H. 
Published: April 2008

Abstract

Lower Cretaceous limestones and dolomites drilled at Monte Raggeto, north of Naples, show a hierarchical organization in cycles, bundles and superbundles, similar to that found in other Cretaceous shallow-water carbonate rocks exposed in the Southern Apennines. These cycles have been interpreted as being caused by the influences of planetary orbital perturbations of the Earth (precession, obliquity), with the bundles and superbundles being considered to represent the short- and long-term eccentricity orbital cycles, respectively. The palaeomagnetic properties of an 88 m core (corresponding to a total interval of
c.
3.2 Ma with a rock accumulation rate averaging 1 cm per 360 ± 16 years) were determined at 2 cm intervals. These show the same spectral periodicities as for the sedimentary properties determined at 1 cm intervals, but there are no correlations between these sedimentological and palaeomagnetic sets of data, when analysed on the scale of the bore-core. An example is given of a 15.50 m length of the bore-core, comprising a single superbundle corresponding to one of the long eccentricity terms, and including eight elementary cycles (each topped by a brief emersion episode) grouped in three bundles. These shallow marine carbonate sediments underwent very early diagenesis accompanied by marine cementation in the pore spaces at or immediately below the water-sediment interface in the same way as in modern-day tropical-subtropical environments. During brief emersions at the top of each cycle, meteoric early diagenesis also occurred. All non-carbonate grains that were present in the original sediment, including ferromagnetic ones, are likely to have been cemented in during these very early phases of diagenesis. It is concluded that the studied interval provides a model of the diagenetic evolution of the whole core, where the early diagenesis controlled the locking-in of a nearly continuous record of the geomagnetic field behaviour for the the entire core. Thus depositional, diagenetic and palaeomagnetic properties can be used in conjunction to provide detailed information on the environmental variations and geomagnetic field behaviour during the evolution of this stratigraphic sequence at an ultra-fine resolution, as 1 cm of rock is equivalent, on average, to 360 ± 16 years.
Microfossil diachronism in southern Norwegian North Sea chalks: Valhall and Hod fields
Authors: Bergen J. A. , Sikora P. J. 
Published: April 2008

Abstract
An integrated late Cretaceous calcareous microfossil framework for the southern Norwegian chalks is presented based on detailed study of 13 wells (many with core) and circum-North Sea outcrops, in addition to many cosmopolitan events recognized in reference sections in Tunisia, North America and Europe. Previous biozonations for the North Sea chalks: (1) lack the biostratigraphic resolution needed in production geology; (2) are largely founded on benthic foraminifera and acme events; (3) fail to recognize numerous stratigraphic discontinuities within the North Sea chalks; and (4) are poorly calibrated. Application of this new integrated framework cautions towards the use of certain acme and benthic foraminifera events as chronostratigraphic horizons both within the basin and from the basin into circum-North Sea outcrops. An additional complicating factor is palaeogeographic segregation between low and high latitudes, which intensified during the middle Campanian and became problematic within the North Sea basin itself during the late Maastrichtian. A final consideration is redeposition, which can lead to erroneous correlations between wells, but may also affect reservoir quality. Established North Sea biozonations have not recognized this primary palaeoenvironmental signal and massive redeposition across major lithostratigraphic units, which has resulted in the correlation of diachronous facies rather than isochronous horizons. This could lead to complications in operational applications, such as biosteering.
Towards a stable and agreed nomenclature for North Sea Tertiary diatom floras — the ‘
Coscinodiscus
’ problem
Authors: Bidgood M. D. , Mitlehner A. G. , Jones G. D. , Jutson D. J. 
Published: April 2008

Abstract
Diatoms are one of the most useful microfossil groups to be found in Tertiary (particularly Palaeogene) sequences of the North Sea subsurface for their biostratigraphic utility, especially where other mineralized-walled microfossil groups (e.g. foraminifera, calcareous nannoplankton, etc.) are absent. An example from one offshore borehole (Shell UK; 29/25-1) is given. However, their further use in biostratigraphic and sequence correlation is hampered by the lack of any stable nomenclature applied to their taxonomy. The numbers of so-called ‘in-house’ taxa are legion with duplication of forms almost inevitable. Few of these many and varied taxa are directly comparable between these schemes, and this leads to almost inevitable confusion for exploration, production and development geoscientists trying to correlate between the various schemes.

One stratigraphically important and familiar diatom taxon (
Coscinodiscus
sp. 1) is formally described in this paper as
Fenestrella antiqua
(Grunow) Swatman. In the example shown here it is demonstrated that four forms, previously identified as four independent taxa in open nomenclature (with distinctive stratigraphic ranges), are in fact separate manifestations of the life habitat of this one single species. It is hoped that through an awareness of the biological complexity of these forms, and their relationships to morphology, a stable taxonomy will eventually arise. It is furthermore hoped that this will lead to a stimulus in the study of the biostratigraphic and palaeoenvironmental applications of this important microfossil group to exploration, production and development geoscience.
Biosignals from the EA Field, Nigeria
Authors: Van Der Zwan C. J. , Brugman W. A. 
Published: April 2008

Abstract
The EA Field study was undertaken to determine reservoir connectivity across growth faults. In this high subsidence area, conventional biostratigraphy does not have sufficient resolution to provide a production-scale time frame. Consequently, a new tool had to be developed which would provide such accuracy. This new high-resolution correlation tool, Biosignals, is based on the relationship ‘pollen-parent plant-ecology’. Pollen, thus related, have been grouped into ‘vegetation’ zones, which have been logged per well and summarized on saw blade diagrams. Sequences of vegetation zones could be recognized, showing an upward trend from spore dominated, via swamp, rain forest, savanna to montane.

A number of potential regional time lines could be recognized: (1) a climate curve; (2) a change from the freshwater alga
Pediastrum
to the brackish water alga
Botryococcus
; and (3) the top of frequent fungi.

Based on this study the following conclusions may be drawn: (i) vegetational stacking patterns reflect fourth-order sequence stratigraphy; (ii) Biosignals suggest the tidal channels in well EA-13 to be lowstand deposits, although many of them belong to truncated sequences (only lowstand systems tract (LST) and transgressive systems tract (TST) preserved); (iii) on a third-order scale, the sandy middle part of the sequence (EA-1, 6000–6500 feet) correlates with dry climatic conditions and to low eustatic sea level. The two regionally extensive maximum flooding surfaces correlate with humid climatic intervals and eustatic high sea level; and (iv) the new high-resolution correlation tool provides a detailed biostratigraphical subdivision, within the existing conventional biozonation, and thus enables correlation of reservoir bodies across growth faults.
Deformational controls on the dynamics of fluid flow in mesothermal gold systems
Authors: Cox Stephen F. 
Published: April 2008

Abstract
Coupling between deformation processes and rock permeability is a major factor influencing fluid migration and fluid-rock interaction during the formation of mesothermal lode gold systems in mid- to upper crustal regimes. The evolution of permeability during deformation is controlled by a dynamic competition between deformation-induced porosity creation processes and porosity destruction processes. Localization of deformation in faults and shear zones leads to flow localization, with large scale flow systems forming when active faults and shear zones link to create percolation networks. Broad regions of fluid focusing develop around the upstream segments of active shear networks and fluid discharge regions develop in the downstream parts of these systems.
The architecture of flow within shear networks is influenced by the relative proportions of backbone, dangling and isolated structures within the network. Connectivity in the network may increase with growth of the shear network, but is expected to continually change as the locus and intensity of deformation changes. The typical distribution of mesothermal lode deposits within crustal scale shear networks indicates that mesothermal systems might develop most efficiently in networks that are close to the percolation threshold, i.e. with most flow occurring along a flow backbone forming only a small part of the total shear network. Dangling elements adjacent to the backbone, particularly in the downstream (discharge) parts of the system, provide some of the best potential for gold deposition by fluid-rock interaction processes.
Contrasting styles of fluid flow are expected between the seismogenic and aseismic regimes of the shear- or fault-hosted hydrothermal systems associated with mesothermal lode gold formation. Below the seismic-aseismic transition, creep processes can lead to near-steady state permeabilities and produce continuous fluid flow regimes. In the seismogenic regime, large cyclic changes in fault permeability, fluid pressures and fluid flux occur during the seismic cycle, and lead to fault-valve behaviour and episodic fluid flow. The seismogenic regime allows for a richer variety of gold deposition processes than is generally available in the aseismic regions of hydrothermal systems associated with lode gold formation.
Thrust-fracture network and hydrothermal gold mineralization: Witwatersrand Basin, South Africa
Authors: Jolley S. J. , Henderson I. H. C. , Barnicoat A. C. , Fox N. P. C. 
Published: April 2008

Abstract
This paper examines the geometry and genesis of a mineralized thrust-related fracture system, developed at a major rheological interface between Witwatersrand sediments and Ventersdorp volcanics in the Witwatersrand Basin of South Africa. At the Elandsrand Gold Mine, the conglomeratic Ventersdorp Contact Reef, which separates these successions, is imbricated by kilometre-wide zones of minor thrusts containing ultracataclastic fault rocks associated with hydrothermal fluid flow. Several sets of fractures are intimately associated with the imbricates, which link to underlying kilometre-scale thrusts. The fractures provided a linked fluid flow pathway and structural sites for precipitation of gold within the Ventersdorp Contact Reef, carrying >900f observed gold, with the remaining 100ccupying post-diagenetic matrix corrosion spaces within a few 100 µm of fractures. The relatively rigid volcanics deformed into low-amplitude kilometre-wavelength flexures, centred on the imbricate zones and underlying kilometre-scale thrusts. These major structures controlled the thrust-fracture system formation along the Ventersdorp Contact Reef-lava contact. Three progressive stages of structural evolution were identified: (1) layer-parallel shear across the contact, with stratigraphy-focused shallow fracture formation; (2) propagation of a kilometre-scale thrust towards the contact, leading to kilometre-scale flexure of the volcanics, with layer-parallel shearing in the limbs producing steep fractures and minor thrusts; (3) propagation of the major thrust along the contact, imbricating the sediments with shallow fracture formation in ramps.
Adularia-sericite gold deposits of Marmato (Caldas, Colombia): field and petrographical data
Authors: Rossetti Piergiorgio , Colombo Fabrizio 
Published: April 2008

Abstract

At Marmato (Caldas, Colombia), epithermal gold mineralization is associated with volcanic to subvolcanic (dacite to andesite) bodies intruding a late Miocene sedimentary sequence and older basement rocks. Mineralization occurs in dilational veins related to a post-magmatic brittle deformation event, possibly connected with reactivation of the Cauca-Romeral fault system. Within the vein system, a vertical zonation is observed. In the lower part the veins are mainly composed of adularia + pyrite ± quartz ± calcite. In the upper part the dominant assemblage is calcite + quartz + pyrite + sphalerite + arsenopyrite + galena + chalcopyrite, and minor argentite, pyrrhotite, polybasite and freibergite. Data from drill cores show that gold is principally related to the hydrothermal veins and dissemination in the wall rock is of minor importance. Wall-rock alteration around the veins is mainly represented by a strong, often complete, sericitization, with minor silicification. The sericitization post-dates an earlier propylitic alteration event, unrelated to gold deposition. The hydrothermal circulation was characterized by ascent of low salinity fluids with a low CO
2
content focused along a structurally controlled fracture system. Boiling was a major controlling factor in deposition in the lower part of the system, while in the upper part mixing also occurred.
Fluidized hydrothermal breccia in dilatant faults during thrusting: the Colombian emerald deposits
Authors: Branquet Yannick , Cheilletz Alain , Giuliani Gaston , Laumonier Bernard , Blanco Oscar 
Published: April 2008

Abstract
The emerald deposits of Muzo and Coscuez hosted within the western flank of the Colombian Eastern Cordillera formed during thrust tectonics affecting series of lower Cretaceous black shales. An unusual polygenetic breccia fills opened fractures and dilatant sites within thrusts and tear faults. Detailed field and petrographic studies show that the breccia formed during a fluidization process in which a hydrothermal pulp was injected into dilatant sites. Fluidization is synchronous with fault propagation. Multistage brecciation is observed and appears to correspond to successive faulting-fluid flow pulses. The opening of dilatant sites during compressive tectonics and the combination of fluidization and hydraulic fracturing suggests that these pulses may be related to successive build-up and drop of the fluid pressure.
Age of mineralization of carbonate-hosted, base metal deposits in the Rathdowney Trend, Ireland
Authors: Sevastopulo G. D. , Redmond P. 
Published: April 2008

Abstract
The mineralization which resulted in the base metal deposits hosted in carbonates of Lower Carboniferous (Dinantian) age in Ireland is in most deposits younger than their mainly Tournaisian-aged host rocks. The stratigraphical age of mineralization at Navan has been shown to be mostly pre-Arundian in age. In the Lisheen deposit in the Rathdowney Trend, development of massive sulphide mineralization post-dated regional dolomitization of late Tournaisian Waulsortian Limestone. Estimates from fluid inclusion and oxygen isotope data of the temperatures at which dolomitization took place suggests that the depth of burial at the time of dolomitization must have been greater than that achieved by early Arundian time, indicating that mineralization at Lisheen was later, and perhaps substantially later, than at Navan. Mineralization coincided with, or post-dated, maximum downthrow on extensional faults atLisheen; maximum downthrow, therefore, was not attained until after the beginning of Arundian time. If minealization of the Irish deposits, rather than being restricted to a narrow interval of time (Lower Viséan-early Arundian), as has been suggested in recent reviews, continued into the younger parts of the Viséan, later Viséan rocks in Ireland should be considered to be potential targets for exploration.
Constraints on Moho depth and crustal thickness in the Liguro-Provençal basin from a 3D gravity inversion: geodynamic implications
Authors: Chamot-Rooke N. , Gaulier J.-M. , Jestin F. 
Published: April 2008

Abstract
3D gravity modelling is combined with seismic refraction and reflection data to constrain a new Moho depth map in the Liguro-Provençal basin (Western Mediterranean Sea). At seismically controlled points, the misfit between the gravimetric solution and the seismic data is about 2 km for a range of Moho depths between 12 km (deep basin) and 30 km (mainland). The oceanic crust thickness in the deep basin (5 km) is smaller than the average oceanic crust thickness reported in open oceans (7 km), pointing to a potential mantle temperature 30–50°C below normal and/or very slow oceanic spreading rate. Oceanic crust thickness is decreasing towards the Ligurian Sea and towards the continent-ocean boundary to values as small as 2 km. Poor magma supply is a result of low potential mantle temperature at depth, lateral thermal conduction towards an unextended continental margin, and decrease of the oceanic spreading rate close to the pole of opening in the Ligurian Sea. Re-examination of magnetic data (palaeomagnetic data and magnetic lineations) indicates that opening of the Liguro-Provençal Basin may have ceased as late as Late Burdigalian time (16.5 Ma) or even later. The absence of a significant time gap between cessation of opening in the Liguro-Provençal Basin and rifting of the Tyrrhenian domain favours a continuous extension mechanism since late Oligocene time driven by the African trench retreat.
Early Tertiary structural evolution of the border zone between the Pannonian and Transylvanian Basins
Authors: Györfi István , Csontos László , Nagymarosy András 
Published: April 2008

Abstract
The Mid-Hungarian Lineament is the most important tectonic feature of the Intra-Carpathian area. Its evolution is closely related to the Early Tertiary (Palaeogene-Early Miocene) episodes of basin formation. This paper attempts to explain the structural relationships between the Transylvanian Palaeogene Basin and the Mid-Hungarian Lineament. Microtectonic data collected on the field, combined with the available geological and geophysical data point to the following conclusions.

(1)
The first compressional event is probably Early Oligocene in age, and is characterized by σ1 oriented ENE-WSW. We assume that the Oligocene basin is flexural in origin.

(2)
The second phase of compression occurred during Early Miocene times with σ1 oriented NNW-SSE. The last thrust emplacement accounts for the Ottnangian-Karpatian overthrusting of the Alcapa block on top of the Tisza-Dacia block. This deformational phase could have induced large-scale block rotations in both units.

(3)
Late Miocene left lateral faulting occurred along the Dragos-Voda fault system, the effects of which can be traced as far as Hungary. This event most probably corresponds to an eastward escape of the Tisza-Dacia block with respect to surrounding terranes.
Protecting the redox stability of a deep repository: concepts, results and experience from the Äspö hard rock laboratory
Authors: Banwart Steven A. , Wikberg Peter , Puigdomenech Ignasi 
Published: April 2008

Abstract
Redox potential and net reducing capacity are rigorously defined geochemical parameters that provide a framework for assessing the redox-related performance of waste containment in the sub-surface. These concepts are illustrated by performance assessment issues in the geological disposal of spent nuclear fuel, and also by consideration of chromium and tetrachloromethane as illustrative compounds representing other types of hazardous waste. Recent and ongoing research at the Äspö Hard Rock Laboratory, a full-scale prototype repository, provides a case study of the redox-related performance of the geological barrier and its function to protect a deep repository from intrusion of dissolved oxygen. Enhanced recharge during construction of the underground laboratory at Äspö strongly influenced redox conditions in the shallow bedrock. The rapid recharge, caused by tunnel construction through a vertical fracture zone, mobilized organic carbon into the groundwater. Microbial processes were critical to the performance of the shallow bedrock, as a barrier to oxygen intrusion during enhanced recharge, by efficiently scavenging oxidants through intense respiration of the added carbon. Because the study site was mainly exposed bedrock with very little soil cover, this effect may be even more pronounced at potential repository sites with thicker overburden.
The role of sorption onto rocks of the Borrowdale Volcanic Group in providing chemical containment for a potential repository at Sellafield
Authors: Berry J. A. , Baker A. J. , Bond K. A. , Cowper M. M. , Jefferies N. L. , Linklater C. M. 
Published: April 2008

Abstract
The current Nirex design concept for the disposal of intermediate-level and certain low-level radioactive wastes in the UK involves emplacement in a cementitious repository deep underground. A site near Sellafield has been investigated to see if it is suitable. The Nirex Safety Assessment Research Programme includes a study of the sorption of radionuclides on the potential host rock formation, as sorption processes are important mechanisms for retarding radionuclides emanating from a repository. The potential host rock is the Borrowdale Volcanic Group (BVG) which is comprised of tuffs characterized by low porosity and permeability. This paper gives an overview of studies of the sorption of radionuclides, in particular actinides, on BVG rock and includes a description of experimental techniques in use at AEA Technology, the difficulties inherent in working with intact-rock samples of such low porosity and permeability and the use of data from both crushed and intact-rock experiments in performance assessment studies. The main sorbing minerals in the BVG are described, and the study of perturbing influences such as the presence of degradation products from organic materials in the wastes and highly alkaline porewater from the cementitious backfill are also discussed. Illustrative results are presented.