bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-pressure experiments and the varying depths of rock metamorphism
Authors: Schreyer Werner 
Published: April 2008

Abstract

Hutton’s visions of 1785 included burial and metamorphism of rocks and their reincorporation into the continental crust. As a result of changing environmental conditions, mainly of pressure (
P
) and temperature (
T
), rocks change their mineral assemblages during metamorphism. High-pressure experimentation has now provided geoscientists with quantitative data on the behaviour of rock systems under varying
PT
conditions, so that depths of burial or subduction and pathways of exhumation can be reconstructed, and the metamorphic histories of rocks can be used to gauge the internal dynamics of our globe during geological time. An important prerequisite is the knowledge of the states of chemical equilibrium as a function of
P, T
and rock composition. Several simple chemical model systems are chosen here to demonstrate characteristic mineralogical and petrological behaviour during metamorphism and to identify some important and unusual minerals that typify high- or ultrahigh-pressure metamorphism taking place at depths of up to 150 km, e.g. the dense forms of carbon (diamond) and of SiO
2
(coesite). Low-pressure metamorphism within the normal (∼35 km) crust of the Earth, on the other hand, is typified by less dense minerals such as tridymite or cordierite. In this way, deep and very deep subduction of former rocks of the Earth’s crust was recognized. This required new geodynamic concepts involving the participation of crustal materials in the overall secular convection processes within the Earth’s mantle.
Preliminary investigations into the acquisition of remanence in archaeological sediments
Authors: Batt C. M. 
Published: April 2008

Abstract
Investigations of magnetic remanence, anisotropy of magnetic susceptibility and magnetic mineralogy of sediments from over 30 depositional environments within British archaeological excavations are compared with archaeological evidence provided by excavation and analysis of associated artefacts and ecofacts. The sites include canals, wells, river floods, ditches, moats and estuarine deposits. A comparison of the magnetic and archaeomagnetic determinations allows the characterization of those deposits that appear to retain a record of the past magnetic field and are therefore datable by comparison with the UK archaeomagnetic calibration curve. Most water-lain sediments have a measurable magnetization, but finer grain sizes tend to have higher intensities, although there is no relationship between depositional environment and intensity of magnetization. The sediments with a higher organic content have a lower consistency index probably as they were more likely to have been bioturbated. Although the magnetic fabrics did not always correspond to the expected ‘primary depositional style’, almost all sites seemed to have directions of remanence that corresponded well to the dates indicated by the archaeological evidence.
Viscous remanent magnetization of high thermal stability in limestone
Authors: Borradaile Graham J. 
Published: April 2008

Abstract

Undisturbed Mesozoic limestones of eastern England show univectorial magnetizations of high thermal stability that appear, on first inspection, to be primary geological remanences. However, viscous remanent magnetization (VRM) of anomalously high thermal stability is an alternative possibility. VRM acquired elsewhere in laboratory experiments, or in a few hundred years as in the examples studied here, may require unblocking temperatures >300°C to demagnetize. Normally, such demagnetization temperatures are required to remove only very ancient geological remanences. The classical ‘conglomerate test’ of palaeomagnetism fails to discriminate between a VRM and a primary remanence. Any lithology sensitive to VRM will yield a negative result, suggesting that the remanence is secondary. However, tests of physical phenomena that caused multiple reorientations of clasts, at rotation rates comparable with the viscous remagnetization rate, provide a more suitable field test for VRM. In this study, these latter kinds of test reveal that some
in situ
Mesozoic limestones of eastern England have VRM, despite stability to temperatures >300°C. The high thermal stability VRM of the bedrock must have been acquired in the last 0.7 Ma, since the last geomagnetic reversal. Two new field tests detected the viscous nature of the high stability remanence. The first was a ‘debris flow test’, in which limestone blocks spin slowly with respect to the geomagnetic field. The blocks record variably tilted or helicoidal, multicomponent vectors. The second was a ‘masonry test’, in which samples of limestone from buildings of known age were exposed to the geomagnetic field for known periods, up to 1600 years in this study. This shows that unusually stable VRM may be common in carbonates. Finally, the masonry test permits an empirical estimate of viscous remagnetization rates over hundreds of years. This established chronometric curves that date ground disturbances of geotechnical or geomorphological interest, and archaeological features of unknown age.
Diagenesis and remanence acquisition in the Lower Pliocene Trubi marls at Punta di Maiata (southern Sicily): palaeomagnetic and rock magnetic observations
Authors: Dinarès-Turell J. , Dekkers M. J. 
Published: April 2008

Abstract
Three new profiles (LCM, PMD and CMD) through the lower Cochiti polarity zone allow comparison of the effects of weathering and diagenesis on the magnetic properties of the Lower Pliocene Trubi marls. These marls have been well dated, by means of astronomical calibration, and are of particular interest in terms of polarity zonation and regional tectonics. The freshest exposures (LCM profile) carry a remanence associated with pyrrhotite, which is particularly enhanced in some grey layers. This is the first time that pyrrhotite has been documented as the main remanence carrier in these marls. Previously, single-domain (SD) magnetite was recognized as the fundamental ferromagnetic phase. The mean characteristic remanent magnetization (ChRM) direction from the LCM record does not show the expected 30–35° clockwise rotation found in other studies, nor does it record the normal Cochiti interval (i.e. the sampled interval is entirely reverse polarity), suggesting a relatively late origin for the natural remanent magnetization (NRM). Standard rock magnetic techniques are used to investigate the nature of the magnetization in the three laterally equivalent profiles at Punta di Maiata. The entire dataset seems to be better explained by a complex diagenetic history involving a multistage redox history that invokes a ‘late’ anoxia event. The previously postulated iron migration model was put forward for the ‘suboxic situation’ and does not take into account the presence of magnetic sulphides, which are clearly demonstrated in the zone under study. The ‘extended diagenetic model’ inferred here proposes a pathway that accounts for most of the new observations. The salient feature is the postulated existence of a diagenetic phase that has altered the original NRM in some areas (dissolution of magnetite) resulting in a later-stage acquisition of chemical remanence that does not date to the timing of deposition of the sediments. The extension and the detailed mechanisms by which such a process has taken place deserve further research. None the less, the present investigation accounts for previously unrecognized features in the Trubi marls from Sicily and outlines how intricate the nature of the mechanisms contributing to the blocking of remanence in sediments can be.
The isolation of diagenetic groups in marine sediments using fuzzy
c
-means cluster analyses
Authors: Urbat Michael , Dekkers Mark J. , Vriend Simon P. 
Published: April 2008

Abstract

The evaluation of large rock magnetic datasets may benefit from the application of multivariate statistical methods. The combined use of fuzzy
c
-means clustering (FCM) and non-linear mapping (NLM) have considerable merit over conventional multivariate techniques and appear to provide a more logical choice. An example of the method of identification and characterization of early diagenetic effects on marine sediments is given using samples drilled at Ocean Drilling Program (ODP) Site 904. This confirms the clusters previously identified more laboriously by multi-variable analyses and detects clusters (diagenetic, detrital, etc.) that may only be recognized by the consideration of an array of rock magnetic data. In another example of a complex diagenetic signal the link is expanded between two papers on a long piston core (KC-01B) from the Calabrian Ridge (Central Mediterranean), where FCM and NLM provide a clue as to why the record of the lower Jaramillo Subchron is delayed in this core.
Remanence acquisition and magnetostratigraphy of the Leman Sandstone Formation: Jupiter Fields, southern North Sea
Authors: Turner P. , Chandler P. , Ellis D. , Leveille G. P. , Heywood M. L. 
Published: April 2008

Abstract
The Leman Sandstone Formation, which forms part of the unfossiliferous Rotliegend sediments in the Jupiter Fields, has been cored at various location in the southern North Sea. Samples from the finer-grained sediments have measurable remanences that were classified into four main types. Some of these characteristics can be related to the petrological features that demonstrate that they are likely to have originated during deposition or very early diagenesis. This allows the age of the sediments to be determined using magnetostratigraphy, indicating that the sediments are of post-Kiaman age as they contain both normal and reversed polarities. This magnetostratigraphy can also be used to determine different rates of deposition in different areas.
Diagenesis in platform carbonate rocks: a palaeomagnetic study of an upper Triassic-lower Jurassic section, Tata (Hungary)
Authors: Márton Emő 
Published: April 2008

Abstract

The upper Triassic platform carbonate rocks at Tata are penetrated by three generations of neptunean dykes and cut by strike-slip faults connected to the platform’s break-up in early Jurassic time. These platform carbonate rocks are conformably overlain by lower Jurassic pelagic carbonate rocks, with a clear change in sedimentation type at the Triassic-Jurassic boundary. Openings within the Triassic platform, including bedding-conformable cavities and
Megalodon
shells, are filled with Jurassic material showing late ‘diagenetic’ features with respect to the Triassic platform facies. The Triassic platform carbonate rocks were examined in a 10m high outcrop and in a 200m core, which commenced 40 m below the surface. The Triassic rock commonly has a weak initial natural remanent magnetization (NRM) and diamagnetic susceptibilities, in both outcrop and within the core, and has the same kind of magnetic mineralogy as in the ‘diagenetic’ material and stratified Jurassic rock, but the magnetic mineral content is higher in the Jurassic materials. The core has mixed polarity, whereas the Triassic outcrop and Jurassic materials have only normal polarity. The overall mean palaeomagnetic direction for the core is similar to those in two large quarries of similar age in the same area (the Gerecse Hills), but differs significantly from the overall mean directions of both the Jurassic ‘diagenetic’ material and the Jurassic beds, which are practically identical to each other. Some sites and individual samples in the Triassic outcrop carbonate rocks show Jurassic directions, but others show remagnetization circle distributions between this Jurassic direction and the present-day Earth’s magnetic field. These observations suggest that the remanence of the latest Triassic time was reset during the early Jurassic diagenesis, but this was not associated with chemical changes as the mineralogies in all groups are the same.
The influence of dolomitization on the magnetic properties of Lower Palaeozoic carbonate rocks in Estonia
Authors: Shogenova Alla 
Published: April 2008

Abstract

The low-field magnetic susceptibility and saturation isothermal remanent magnetization of Estonian Lower Palaeozoic carbonate core and outcrop samples were studied, together with their chemical composition. Dolomites of different age and genesis were found to be of different chemical composition and different magnetic properties. The dolomitization of the Lower and Middle Ordovician sequences is diagenetic and is represented by widespread dolomitized layers as well as dolomitization associated with tectonic disturbances. All studied dolomites have an increasing total iron content. In Upper Ordovician and Silurian dolomites this increase is not enough to change magnetic properties significantly. In the rocks, sampled from a fracture zone and from a dolomite layer of the Väo Formation in the Middle Ordovician sequence and another widespread, several metres thick dolomite layer of the Volkhov stage from the Lower Ordovician sequence, the magnetic susceptibility of dolomites was found to be several times higher than that of limestones of the same age. Changes in magnetic susceptibility were found to be associated with substitution of Fe
2+
for Mg
2+
in the crystalline lattice of dolomites.
Alteration of magnetic properties of Palaeozoic platform carbonate rocks during burial diagenesis (Lower Ordovician sequence, Texas, USA)
Authors: Haubold Herbert 
Published: April 2008

Abstract
Palaeomagnetic and sedimentological investigations of samples from two sections of correlative Iapetan platform carbonate rocks from Texas, USA, were made to test whether their magnetic properties reflect diagenetic alteration associated with regional and local tectonism. The Honeycut Formation (Llano Uplift area, central Texas), in close proximity to the late Palaeozoic Ouachita orogenic belt, exhibits a distinct correlation between magnetization intensity, magnetization age (direction) and lithofacies. Mudstones preserve their weak primary Early Ordovician magnetization, whereas dolo-grainstones carry a strong Pennsylvanian magnetization residing in authigenic magnetite. Fluid migration associated with the Ouachita Orogeny has been focused in lithofacies with high permeability and caused dolomite recrystallization and pervasive remagnetization. Magnetization intensity trends covary with fluid/rock ratios. However, aquitards were either not affected or less affected by these fluids. Unlike the Honeycut Formation, permeable rocks of the El Paso Group (Franklin Mountains, west Texas) carry only a non-pervasive Pennsylvanian magnetization. Therefore, a larger percentage of El Paso Group samples retain a primary Early Ordovician signature. This area is further removed from the Ouachita front, and, thus, the influence by Pennsylvanian orogenic fluids was less pronounced.
The role and value of ‘high-impact biostratigraphy’ in reservoir appraisal and development
Authors: Payne S. N. J. , Ewen D. F. , Bowman M. J. 
Published: April 2008

Abstract
Over recent years changes in the application of biostratigraphy in the reservoir appraisal and development arena have greatly increased the impact and value of the discipline, giving it a central role in integrated reservoir description. These changes include placing emphasis on local field-scale bioevents to erect a reservoir framework of time slices through which reservoir heterogeneity can be modelled and the application of biosteering to maximize reservoir penetration. In addition, palaeoenvironmentally diagnostic benthonic microfacies are used to model the lateral continuity of intra-reservoir mudstones in an attempt to understand their potential as baffles/barriers to fluid flow. The evolution of this cost-effective methodology is discussed by reference to three Palaeocene turbidite reservoirs from the North Sea UK continental shelf (UKCS); the Donan, Forties and Andrew fields.
Chalk palaeoenvironments and depositional model, Valhall-Hod fields, southern Norwegian North Sea
Authors: Sikora P. J. , Bergen J. A. , Farmer C. L. 
Published: April 2008

Abstract
Palaeoenvironmental analysis in the North Sea chalk is hampered by the prevalence of widespread allochthonous units, intervals of massive reworking of microfossils and an often monotonous lithology of massive chalks of uncertain depositional history. Most difficult of all is devising precise regional biostratigraphic correlations in a complex section with large, but very subtly expressed, disconformities and condensed zones. Facies change quickly both laterally and vertically. Without very precise regional correlations, it is impossible to formulate any detailed palaeoenvironmental model.
Through a multidisciplinary palaeontological approach, employing graphic correlation methodology and a composite standard database, a highly accurate and detailed regional chronostratigraphy was generated. Biofacies recognized within the section were then scaled in absolute time, allowing for more reliable recognition of facies trends at any one time horizon. Biofacies were formulated based upon recovered benthic foraminifera, planktic foraminifera, calcispheres, siliceous microfossils and macrofossil debris.
Biofacies mapping for several higher-order sequences recognized in the Upper Cretaceous chalks has allowed recognition of four major periods of deposition: (1) early Turonian-early Santonian high pelagic productivity and rapid deposition of chalks over a relatively continuous ridge from the Valhall to Hod fields; (2) early Campanian-earliest Maastrichtian deep-water autochthonous chalk deposition off-structure with structural crests mantled by submarine hardgrounds; (3) very heterogeneous autochthonous and allochthonous middle Maastrichtian chalk deposition controlled by local grabens formed from crestal collapse; and (4) widespread sediment flows and redeposition of sediments with crestal shoaling and winnowing in the latest Maastrichtian culminating in crestal erosion of Cretaceous chalks in the early Danian.
High-resolution biostratigraphy and sequence development of the Palaeocene succession, Grane Field, Norway
Authors: Mangerud G. , Dreyer T. , Søyseth L. , Martinsen O. , Ryseth A. 
Published: April 2008

Abstract
A detailed biostratigraphic zonation and sequence stratigraphic framework has been developed for the Grane Field (PL 169), situated in Block 25/11 in the North Sea. The study is focused on the Upper Palaeocene interval, where a high level of chronostratigraphic resolution has been achieved and where the depositional history can be understood in terms of a finite set of depositional cycles and subcycles.

This work documents that the Grane Field reservoir succession, which consists of alternating turbidite sandstones and marine basin plain mudstones, fall within two main biozones, corresponding to a general Late Palaeocene age. The reservoir succession is developed between two regional datums: last stratigraphical common occurrence of
A. gippingensis
and last stratigraphical occurrence of
Isabellidinium? viborgense
. This corresponds to our major cycles T40 and T50, in which the reservoir sands comprise lowstand units filling in local accommodation during stepwise encroachment of the submarine fan system into this area.

Within the reservoir interval the zonation is based on the appearance and extinction of species with a regional distribution that also have marked frequency variations. These include
A. gippingensis, P. bulliforme, C. striatum, P. pyrophorum
and
I? viborgense
. In addition, events representing quantitatively marked peaks in the frequency of long-ranging taxa are used for correlation purposes. These events need to be constrained by other events, but are good for local correlations. Examples from the Grane Field include influxes of
Deflandrea denticulata, Cometodinium comatum
and
Subtilisphaera
spp.

The high-resolution biostratigraphy serves as a template for the sequence stratigraphic framework in the study area. Sixteen correlatable zones have been established by linking each of the fossil events to a specific sequence stratigraphic surface. As shown by previous workers, surfaces associated with condensation (regional and subregional maximum flooding surfaces) prove to be the most useful ones for correlating the Tertiary of the North Sea. In addition, some of the biostratigraphic events seem to coincide with transgressive surfaces and sequence bounding unconformities. Application of the sequence stratigraphic framework indicates that several reservoir sand units, which appear correlatable on well logs, actually are of different age. They may therefore contain potential flow barriers, formed in periods of condensation between the lowstand events.
Reservoir biostratigraphy of the Pedernales Field, Venezuela
Authors: Jones R. W. , Jones N. E. , King A. D. , Shaw D. 
Published: April 2008

Abstract
The geographic and geological settings of the Pedernales Field, and its history from discovery to development, are briefly outlined. Biostratigraphy and palaeoenvironmental interpretation, and their impact on integrated reservoir description (IRD) and production geology, are discussed in detail.
Historical and modern vintage micropalaeontological data enable the recognition of a number of ‘zones’ over the reservoir interval. These ‘zones’ are diachronous, although they do have correlative value when integrated into the framework of isochronous tectonostratigraphic sequence boundaries and flooding surfaces identified on seismic sections and well logs. The ‘zones’ and their containing sediments can be tentatively calibrated against global standard biozones and hence sequence boundaries and flooding surfaces on the eustatic sea-level cycle chart.
Micropalaeontological and palynological data also enable the recognition of a number of biofacies interpreted on the basis of modern analogy as indicating a range of delta-top, delta-front and prodelta environments. The principal reservoir is interpreted as having been deposited in a range of delta-top to delta-front subenvironments, the seal in a range of distal prodelta subenvironments.
The ongoing high-resolution biostratigraphic work programme has revealed the existence of a large number of correlatable events over the reservoir interval. Integrated high-resolution biostratigraphic, well log and seismic correlation can be achieved both within and between the compartments of the field.
High-resolution biostratigraphic/biofacies data demonstrate the existence of a bathymetric gradient at the time the reservoir were being deposited. Gravity gliding along the observed gradient provides a possible mechanism for the locally observed section repetition and enhanced reservoir development, and also for the up-dip trapping mechanism.
High-resolution sequence biostratigraphy of a lowstand prograding deltaic wedge: Oso Field (late Miocene), Nigeria
Authors: Armentrout J. M. , Fearn L. B. , Rodgers K. , Root S. , Lyle W. D. , Herrick D. C. , Bloch R. B. , Snedden J. W. , Nwankwo B. 
Published: April 2008

Abstract
High-resolution biostratigraphic analyses provide calibration of both depositional systems and specific depositional environments. Such studies facilitate prediction of reservoir geometry and the lateral continuity of both reservoir sandstones and sealing mudstones. Data from the offshore Nigeria Oso Field are presented as a case study of one late Miocene deltaic depositional system. Within the Oso Field, marine mudstones are recognized as effective top seals across the entire field in contrast to marginal marine to non-marine mudstones which have more restricted distribution and act as intrafield baffles. Three sequence stratigraphic models have been considered: (1) the first is based on biostratigraphic data integrated with core sedimentology; (2) a second model constructed using core sedimentology; and (3) a third based on interpreted regional seismic reflection profiles and well-log data. Integration of all data shows that the lower Oso Field producing interval is interpreted as a lowstand prograding wedge, and the upper interval as a prograding distal transgressive or alternatively distal highstand system tract.