bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Drilling Performance through Integration of Seismic, Geological and Drilling Data
Authors: Stewart S.A. , Holt J 
Published: April 2008

Abstract
Unexpected incidents leading to lost time when the rig is on location cause unplanned cost to the hydrocarbon industry of over one billion dollars annually. Processing and interpretation of 3D seismic data usually focuses on reservoir levels. But from a drillers perspective, geological features of the overburden are often more significant than those at reservoir level, since over 90% of the well is typically spent drilling the overburden, coping with a wider variety of challenges than those associated with the reservoir itself. 3D seismic data defines overburden tectonostratigraphy, the framework of a geological model that can be used in well planning to reduce geological uncertainty, surprises and expense along the whole well track. Many technologies applied in reservoir modelling are equally valid in defining overburden features relevant to well planning. The overburden 3D volume can be populated with key parameters for well design, such as pore pressure and geomechanical attributes, though the complexity of the model will often be restricted by well cost and perception of drilling risk. The role of 3D seismic data in forming the tectonostratigraphic framework of multi-attribute, kilometre-scale Earth models, is illustrated here by a number of examples where model sophistication has been scaled to match project requirements. Overburden Earth models also provide a framework where several 'academic' research themes, for instance 3D fault geometry, can be put into a commercial context. Construction of overburden models for well planning has also highlighted a number of future geological research areas that could have a significant impact on drilling performance. Some of these, such as hydraulic properties of fault systems, are highlighted here.
Protolith ages of eclogites, Marun-Keu Complex, Polar Urals, Russia: implications for the pre- and early Uralian evolution of the northeastern European continental margin
Authors: Glodny J. , Pease V. , Montero P. , Austrheim H. , Rusin A. I. 
Published: April 2008

Abstract

Single zircon U-Pb dating by ion microprobe and Pb-evaporation techniques, combined with Sr-Nd isotopic and geochemical data, constrain the pre- and early Uralian evolution of the Marun-Keu eclogite-facies metamorphic complex. Polar Urals, Russia. The complex is interpreted as a part of the Early Palaeozoic East European passive margin, subducted, metamorphosed and exhumed during Uralian arc-continent collision. In the Marun-Keu complex, a variety of meta-igneous and metasedimentary rocks documents different evolutionary stages of the northeastern margin of Baltica. Both the oldest, polystage detrital zircon population, which is 570 to 700 Ma in age, and the dominant zircon population in an island arc-type magmatic suite (
c.
550 Ma) are related to the Neoproterozoic Timanian orogeny, which resulted in continental growth of northeastern Europe by accretion of juvenile oceanic and island arc material. A distinct magmatic event at
c.
490 Ma is documented in zircons from metagranites, and is interpreted as evidence for incipient post-Timanian rifting which finally led to formation of both the Proto-Uralian ocean and the Early Palaeozoic East European passive margin. A convergent setting was re-established in Silurian times, culminating in Uralian arc-continent collision by east-dipping subduction of the East European passive margin. Metamorphic zircon ages reflect the collision event at 360 to 355 Ma.
Melt percolation beneath a spreading ridge: evidence from the Semail peridotite, Oman
Authors: Gregory R. T. 
Published: April 2008

Summary
Field mapping in the Semail ophiolite complex, southeastern Oman Mountains reveals a thick oceanic crustal section (on average >6 km thick) underlain by a 9–12 km thick upper-mantle sequence consisting of a basal harzburgite-dunite zone overlain by a foliated harzburgite containing concordant layers of dunite (cm-m scale) and olivine orthopyroxenite (cm scale). The harzburgite and the concordant layers are crosscut by discordant dunite bodies (cm-km scale) and by dykes of dunite, websterite, olivine clinopyroxenite, and gabbro (cm-m scale). The sequence and mineralogy of these features are all consistent with the interpretation that both the concordant and discordant layers represent crystallization or reaction products between ascending melts and host peridotite. Dunite is the only volumetrically significant discordant or concordant rock type crosscutting the peridotite representing ∼50% of the basal 3–4 km of the peridotite section and <15% elsewhere. Addition of ∼2 km of mantle dunite to the Semail average crustal composition suggests that the average melt percolating up through the Semail mantle had picritic affinities (PLAG 32, DIOP 16, OL 44, SI 08). Field evidence does not require that the harzburgite be cogenetic with the ascending melts that produced the overlying oceanic crustal section. The extremely depleted character of the Semail harzburgite results from interaction with transient melts in the regime of overall high melt/rock ratio (0.5–0.8) found beneath the fossil late-Cretaceous ridge. The melt/rock ratio is calculated assuming that the basal harzburgite-dunite represented the shallow-level, ‘off-axis’, boundary of the zone of upward magma migration beneath the ridge. The apparently thicker than normal crustal section and the depleted character of the Semail peridotites may suggest that the supply of melt to the Semail ridge system was greater than could be accommodated by spreading in the closing Hawasina ocean basin.
Cryptic variation within the Cumulate Sequence of the Oman ophiolite: magma chamber depth and petrological implications
Authors: Browning P. 
Published: April 2008

Summary
The Cumulate Sequence of the Oman Ophiolite consists of layered mafic and ultramafic cumulates that represent the products of a dynamic, long-lived, crustal magma chamber that underlay a late-Cretaceous spreading ridge. Regional variations in Cumulate-Sequence stratigraphy reflect not only contrasting degrees of mantle fractionation but also contrasting primary magma compositions.
Microprobe data are presented from a 600 m section of modally layered olivine gabbros. Coherent cryptic cyclic variation is shown, with both ‘normal’ and ‘reversed’ geochemical gradients present; these are explained in terms of fractionation, mixing and eruption in an open-system magma chamber. The height of the liquid column required to precipitate the observed cyclic units is calculated to be about 100 m; the implications of this result are discussed.
A contrast between the Fo-An co-variation between olivine and plagioclase in the Oman Cumulate Sequence and that observed for MORB volcanics is noted; this may reflect compositional stratification in spreading-ridge magma chambers or significant differences between the petrogenesis of the Oman ophiolite and MORB.
Petrology of the Upper Pillow Lava suite, Troodos ophiolite, Cyprus
Authors: Malpas J. , Langdon G. 
Published: April 2008

Summary
The recently redefined Upper Pillow Lava suite of the Troodos ophiolite in Cyprus is composed of a series of related rock types: ultrabasic rocks, komatiites, olivine basalts and aphyric basalts, derived from a highly depleted primary melt by dominant olivine fractionation. Differentiation within high-level magma chambers involving approximately 25% olivine fractionation, and subsequent tapping of the resultant magma types explains the field relationships observed.
Evolving metallogenesis at the Troodos spreading axis
Authors: Boyle J. F. , Robertson A. H. F. 
Published: April 2008

Summary
An area of the eastern Troodos Massif has been mapped in detail to identify stages of volcanism, faulting and metallogenesis which could be related to the evolution of the late Cretaceous Troodos spreading axis. The field relations and comparisons with modern spreading ridges suggest the following succession of events. Pillowed and massive flows making up most of the lava volume were erupted on a relatively flat sea floor at the axis of a well-defined median valley. Volcaniclastic sediments accumulated during a hiatus in volcanism. The Mathiati massive sulphide formed in the vicinity of ridge-parallel fractures towards the margins of the rift valley, whilst ferromanganiferous oxide-sediments were deposited in the surrounding area. Normal faulting, at first parallel to the rift axis, then at 30–40° to it, accompanied formation of the rift-valley walls, together with renewed eruption of lavas, equivalent to the Upper Pillow Lavas. Small grabens and half-grabens, which formed during this stage, were fringed with lava talus, then gradually filled, first with ferromanganiferous umbers precipitated from local hydrothermal vents, then, as the spreading axis migrated away, by more hydrogenous metal-oxide sediments and later deep-sea deposits. In Cyprus, metallogenesis persisted from the median valley to the flanks of particular regions of crust. Also the inferred site of formation of the Mathiati sulphide towards the margin of the rift valley differs from that of the known ‘smokers’ which are active closer to the spreading axis.
Possible causes and consequences of upper mantle decoupling and ophiolite displacement
Authors: Spray J. G. 
Published: April 2008

Summary
The possible causes and consequences of tectonic decoupling within the oceanic upper mantle and the subsequent displacement of ophiolites are considered with specific reference to the petrology, chemistry and structure of the basal mantle tectonites of ophiolites and their metamorphic soles. Investigations of the basal peridotites provide information on high temperature-high pressure events that have occurred in the upper mantle and on its mechanical properties at depths <15 km, while metamorphic soles reveal the pressure-temperature regimes operating during and as a direct result of overthrusting. Currently available age data from several well-documented ophiolites reveal that ophiolite igneous crystallization and basal metamorphism are broadly contemporaneous, in keeping with the localized occurrence of granulite-facies sole assemblages. Theories on the formation of sub-ophiolite metamorphic rocks are reviewed and the process of ophiolite inception is reappraised. It is concluded that many ophiolites are tectonically decoupled along the lithosphere-asthenosphere boundary and initially displaced as complete slices of hot, thin, immature lithosphere in close proximity to spreading centres.
Initiation of subduction zones along transform and accreting plate boundaries, triple-junction evolution, and forearc spreading centres—implications for ophiolitic geology and obduction
Authors: Casey J. F. , Dewey J. F 
Published: April 2008

Summary
Most large ophiolite complexes have been interpreted as representing the obducted remnants of oceanic basement of forearc regions. A knowledge of the tectonic setting of ophiolite formation as well as the mechanism of their entrapment within forearc regions is essential to achieve a more complete understanding of the often complicated geology of ophiolite complexes and the tectonic processes that result in their evolution and ultimate obduction. The mechanism of entrapment of an ophiolite complex within a forearc region is intimately related to the mechanisms involved in trench initiation. The most easily documented and apparently likely mechanisms of trench initiation and isolation of oceanic basement within forearcs are: (i) polarity flips along weakened back-arc/island-arc interfaces, and (ii) plate boundary evolution involving the conversion of active transform and accreting plate boundaries into subduction zones. These latter mechanisms of trench initiation are predicted by plate theory to occur by the evolution of transform and accreting plate boundaries upon (usually) gradual and (less often) abrupt changes in their position with respect to the instantaneous pole of relative motion, and by the evolution of certain types of triple junctions that leads to rapid conversion of transform and accreting plate boundaries to subduction zones. These plate boundary evolutionary schemes involve spatially and temporally complex overlap of subduction and plate accretion processes in forearc regions. The overlapping processes occurring during these conversions may result in ‘atypical’ oceanic-crustal magmas that are produced during or soon after sea-floor spreading within the forearc region. These magmas may not resemble typical mid-ocean-ridge basaltic (MORB) compositions. Such ‘abnormalities’ in the petrology of some ophiolite complexes need not necessarily imply that a process other than sea-floor spreading was the dominant plate-boundary process responsible for the generation of these ophiolite complexes. The term ‘island-arc ophiolite’ attached to several ophiolite complexes on the basis of their petrology may not appropriately reflect the dominant plate-boundary process (i.e. sea-floor spreading) and should be used cautiously and only if supported by non-petrologic data (e.g. field observations and structural relationships).
Ophiolites and the tectonic evolution of the Arabian Peninsula
Authors: Coleman R. G. 
Published: April 2008

Summary
Arabian ophiolites mark periods of important tectonic activity. Their petrotectonic evolution gives insights on movements of the Arabian plate through Proterozoic and Phanerozoic times. The upper Proterozoic ophiolite belts in Saudi Arabia and NE Africa indicate that oceanic crust of this age was incorporated within the continental crust during its Precambrian evolution. Recent studies on the Semail ophiolite in Oman reveal that it was emplaced onto the Arabian plate in the Campanian during the closure of Neo-Tethys. An igneous complex of sheeted dykes, layered gabbro, granophyre, and basaltic-rhyolitic lava on the SE margin of the Red Sea represents new oceanic crust formed some 20–24 m.y. ago during the initial opening of the Red Sea when the continental crust became attenuated.
Deep-water fine-grained sediments; history, methodology and terminology
Authors: Stow D. A. V. , Piper D. J. W. 
Published: April 2008

Summary
To introduce this collection of papers presented at an international research workshop in Halifax, Canada (1982), we highlight briefly three aspects of deep-water fine-grained sediments that are alluded to throughout the volume but never discussed specifically. These are: (a) an historical outline of the research that has made both possible and necessary the workshop and the volume; (b) a review of the methodology currently used in the study of fine-grained sediments; and (c) an assessment of the state of terminology as applied to this class of rocks.
Sedimentology of the Halifax Formation, Nova Scotia: Lower Palaeozoic fine-grained turbidites
Authors: Stow D. A. V. , Alam M. , Piper D. J. W. 
Published: April 2008

Summary
The Halifax Formation is a several kilometre thick, shale-rich succession that forms part of the (?) Cambro-Ordovician Meguma Group of Nova Scotia. The Meguma sediments were mostly deposited by sediment gravity flows on a prograding marine slope-rise complex of uncertain water depth. Eight separate facies of the Halifax Formation are recognized on a facies continuum from very shaley to very sandy. The two most sandy facies show partial Bouma sequences; the others are best interpreted in terms of a more detailed ‘ideal sequence’ for fine-grained turbidites. Vertical sequences show thinning-upward, thickening-upward and irregular patterns of sandstone and siltstone beds on a large-scale (100–200 m). There is also much wedging, subdivision and amalgamation of these coarse lithologies. Erosional features are locally common at the base of turbidite beds and still more widespread at the top. Slumps and bioturbation are less common. The depositional setting of most of the Halifax Formation is interpreted to be the mid- or upper-fan area of a muddy deep-sea fan, passing upwards into a prograding continental slope.
Contourite or turbidite?: magnetic fabric of fine-grained Quaternary sediments, Nova Scotia continental rise
Authors: Shor A. N. , Kent D. V. , Flood R. D. 
Published: April 2008

Summary

Samples of three piston cores and one gravity core from the Nova Scotia continental rise (depths 4210–4925 m) have been examined to differentiate parallel-to-slope and downslope depositional processes in Quaternary deposits from a region presently influenced by a strong contour current. Measurement of anisotropy of magnetic susceptibility of samples of a red-brown, silt-laminated lutite ‘contourite’ facies shows grain alignments which are consistent with both parallel-to-slope (contour current) flow
and
downslope (turbidity current) flow. We believe that these results provide support for the hypothesis that ‘geologically significant’ contour currents have influenced continental rise deposition during the Pleistocene. However, our observation that both alongslope and downslope alignments are present in lithologically similar units clearly demonstrates the need for studies on the relationship between lithofacies and process in this geological setting.
The sediment texture of contourites in Lake Superior
Authors: Halfman J. D. , Johnson T. C. 
Published: April 2008

Summary
Previous sedimentological studies in Lake Superior indicated that deep water circulation is sufficiently intense in some regions to influence the deposition and erosion of postglacial clay. This is particularly evident off the Keweenaw Peninsula, where 3.5 kHz profiles, side-scan sonar, and cores reveal wavy bedforms and interbedded muds and sands interpreted to be contourites. This region is a good lacustrine analogue to the marine environment, yet is unique in its lack of interbedded turbidites and significant bioturbation.
The sedimentary texture of the core top (< 2 cm depth in core) samples in the region, determined by pipette and sieve analyses, changes from sand (md = 2.2 phi; 220 μm) at the base of the slope, where the currents are strong, to clay (md = 10.8 phi; 0.6 μm), farther offshore, where the currents are weak. Textural analyses reveal a distinct bi-modal distribution of sand and clay populations, with the sand dominating the sediment at the base of the slope, and clay dominating the sediment further offshore. The silt fraction of the sediment samples was analysed by an electronic particle analyser, which detected changes in the particle-size histograms from coarse-grained (md = 4.79 phi; 36 μm) and positively skewed (0.45) distributions to fine-grained (md = 6.06 phi; 15 μm) and negatively skewed (−0.09) distributions, that correlate to the previous sand and clay textures, respectively. There is a down-core increase in grain-size in two piston cores that suggests that bottom currents decreased in intensity from 9500 years ago to the present.
A late Miocene and early Pliocene upper slope-to-shelf sequence of calcareous fine sediment from the Pacific margin of New Zealand
Authors: Ballance P. F. , Gregory M. R. , Gibson G. W. , Chaproniere G. C. H. , Kadar A. P. , Sameshima T. 
Published: April 2008

Summary

Upper Miocene and lower Pliocene sediments at East Cape, North Island, New Zealand, comprise an upwards-coarsening and shallowing sequence. Calcareous sandy siltstones, with coccoliths and about 10% clay, were deposited in upper bathyal depths. Upwards they became sandier, with an increasing ratio of benthic to planktic foraminifera and increasing macrofauna, and grade into fossiliferous very fine silty sands, with many coccoliths and a few percent clay; the sands were deposited in shelf depths of 50 to 100 m. Comparison with modern equilibrium shelves suggests that the shelf sediments were deposited on a storm-dominated, wind- and wave-driven ocean margin characterized by long-period swells and normal wave heights of 1 to 3 m. Clay-size sediment seems to have been winnowed out of all the sediments and transferred to greater depths, apart from a few percent trapped between framework grains. The prolific trace fossil fauna contains several ichnotaxa common to all the sediments; however,
Teichichnus
, a
Zoophycos
-type and a compound
Nereites
type, along with minor forms and non-calcareous tube fossils (cf.
Terebellina
) are confined to the bathyal facies, while
Asterosoma
extends from the shelf facies part way into the bathyal facies. Coccoliths comprise a restricted flora of temperate-water aspect, lacking both deep water and tropical forms. Macrofauna of some 50 species in the bathyal sediments is dominated by thin-shelled Nuculid and Nuculanid bivalves, while some 80 or more species in the shelf sediments are dominated by the thick-shelled bivalve
Cucullea
. Debris-flow deposits in the bathyal facies include both bathyal and shelf sediments; they suggest a shelf-slope topography. Numerous interbeds of graded volcanic sand occur in all the facies studied. They were deposited by air-fall and turbidity currents, are mostly rhyolitic in composition, and were derived from the active New Zealand magmatic arc.
Origin of varve-type lamination, graded claystones and limestone-shale ‘couplets’ in the lower Cretaceous of the western North Atlantic
Authors: Robertson A. H. F. 
Published: April 2008

Summary
The petrography and sedimentary structures of pelagic and hemipelagic sediments in the early Cretaceous interval of the Blake-Bahama Basin reveal a subtle interplay between terrigenous source materials, plankton productivity and diagenesis. Three specific sediment types drilled at Site 534A (Leg 76) of the DSDP are: (1) persistent, fine parallel lamination resembling varves; (2) thin, size-graded nannofossil claystones and ‘black shales’, and (3) ‘couplets’, composed of pale burrowed and dark laminated nannofossil radiolarian carbonates.
The varve-type lamination reflects some combination of fluctuations of terrigenous plant material plus fine clastic input and plankton productivity. Both possibly reflect short periodicity (10s to 100s of years) climatic variations. Lithification took longer in the clay-and organic-rich laminae. Slow compaction then accentuated the lamination. By contrast, purer nannofossil oozes lithified more quickly and now show less compaction. The graded claystones and ‘black shales’ were mostly redeposited by turbidites from within, or near, the oxygen-minimum zone on the upper continental slope. Turbiditic input reduces the need for bottom water anoxicity. The dark-light couplets reflect wetter periods on land averaging 20–60 000 years, during which abundant plant material entered the Atlantic.
Contrary to some recent suggestions, the early Cretaceous Atlantic need not have been poorly circulated and weakly oxygenated. Instead, both short and longer periodicity climatic fluctuations controlled input of mostly land-derived material. High rates of organic matter input, partly turbiditic, produced sub-surface sediment anoxia below a circulating relatively fertile early Cretaceous Atlantic Ocean.