bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of 3D Visualization Techniques to Unravel Complex Fault Patterns for Production Planning: Njord Field, Halten Terrace, Norway
Authors: Dart Chris , Cloke Ian , Herdlevær Åge , Gillard Dominique , Rivenæs Jan C. , Otterlei Cecilie , Johnsen Eivind , Ekern Anders
Published: April 2008

In this paper we demonstrate the benefits of 3D seismic visualization techniques for fault interpretation where the structural geology is complex and the seismic data quality is often poor. Production from the Njord field is strongly influenced by a complex pattern of segmented and linked extensional faults. The current interpretation of the well test data and production history is that the faults form barriers to fluid flow, reducing oil production, and limiting effective gas injection and pressure support. Drilling results demonstrate that geometrical uncertainties remain in the seismic interpretation. An additional problem is that currently available commercial reservoir modelling technology cannot easily handle a very complex fault pattern, making simulation grid construction difficult. Accurate well placement and production forecasting requires that fault geometries and properties are suitably represented in the reservoir simulation model. 3D visualization of depth-scaled volumes and depth-converted interpretations helped to decide how to best simplify the fault geometry for simulation, and compare automatically generated geological model components against seismic interpretations and data. The reservoir simulation model runs resulted in the identification of a number of well targets. 3D visualization techniques were then used to predict faults and structures that the proposed well trajectories may intersect.

Supplementary material:
The nineteen movies referred to in the article are available at
https://doi.org/10.6084/m9.figshare.c.4784667
Integrated Use of 3D seismic in field development, engineering and drilling: examples from the shallow section
Authors: Austin Bryn
Published: April 2008

Examples from exploration acreage and field developments across the glaciated Northwest European Continental Shelf and Slope demonstrate the usefulness of conventional three-dimensional (3D) seismic data to spatially image geological features. Compared to previous grid-based two-dimensional (2D) seismic this allows fundamentally more confident identification, mapping and prediction of geotechnical conditions which is important to ensure safe, efficient engineering and drilling operations. Whilst of immense benefit, the paper argues that the 3D seismic data often do not meet the full expectations, particularly in terms of critical vertical resolution and accurate depth prediction requirements. To illustrate the limitations, direct comparison is made between conventionally acquired 3D and HiRes 2D seismic data. Whilst industry funding to support innovative HiRes 3D seismic acquisition remains sparse, much can be achieved by the careful integration and interpretative calibration of the 3D and HiRes 2D seismic datasets. Three field development case studies illustrate this. Short offset trace correction and reprocessing of the 3D seismic data followed by limited, target specific HiRes 2D seismic, calibrated where possible with drilling or other geological data, is an optimal cost-effective approach.
Improved Drilling Performance through Integration of Seismic, Geological and Drilling Data
Authors: Stewart S.A. , Holt J
Published: April 2008

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
The sedimentology of the Swedish Alum Shales
Authors: Thickpenny A.
Published: April 2008

The middle and upper Cambrian (and locally lowermost Tremadoc) Alum Shale Formation of Scandinavia and the Baltic Sea area outcrops from Finnmark in north Norway to Bornholm in the south, and from Estonia westwards to the Oslo region. The Formation is generally underlain by shallow water sandstones but is locally unconformable on Precambrian continental basement; it is overlain by shallow marine glauconitic, phosphatic limestones.

Detailed examination of borehole cores and some quarry sections from several of the Swedish Lower Palaeozoic outliers indicates the occurrence of five lithofacies: (1) Black laminated mudstone, rich in organic carbon, suggesting extreme anoxic conditions; (2) organically banded mudstone showing more variable organic input: (3) grey mudstone, laminated or unlaminated and lacking significant organic matter, suggesting more oxic conditions; (4) bituminous, fossiliferous limestone concretions also indicative of more oxic conditions, possibly above wavebase; and (5) glauconitic siltstones and sandstones, graded and transported, and quartz rich siltstones, mostly transported. Pyritic laminae may also occur within any of the above mudstone lithofacies. Sedimentation rates for some of the above facies are estimated and show values comparable with modern pelagic sedimentation, the lowest occurring within the bituminous limestones and progressively increasing to interlaminated black and grey mudstones. The sedimentation rates in combination with the lithological variation suggest less extreme reducing conditions in the middle Cambrian compared with the upper Cambrian, a factor important in the control of Uranium and other trace element anomalies found within the upper Cambrian.
Deep-water fine-grained sediments: facies models
Authors: Stow D. A. V. , Piper D. J. W.
Published: April 2008

Based on a large amount of published data and stimulated by the papers and discussion at the International Workshop on Fine-Grained Sediments held in Halifax, Canada in August 1982, we have attempted a synthesis of deep-water fine-grained sediment facies. Three main facies groups related to depositional processes can be identified: turbidites, contourites and pelagites/hemipelagites. There is a continuum between the different processes and hence a continuum between facies. Nevertheless, it is possible to define several distinct facies models within each of these groups on the basis of sedimentary structures, texture and composition, and to provisionally interpret these in terms of depositional hydrodynamics. Patterns of horizontal and vertical facies distribution can be related to depositional subenvironments. There is much variability within and departure from the facies models we propose, and many interesting and problematic areas of research remain in the quest for better understanding of deep-water fine-grained sediments.
A model of volcanogenic sedimentation in marginal basins
Authors: Carey Steven , Sigurdsson Haraldur
Published: April 2008

Marginal basins adjacent to oceanic island arcs receive volcaniclastic debris from the bordering volcanic arc, back-arc spreading centre, and, to a lesser degree, the remnant arc. The volcanic arc is volumetrically the most important source, with abundant volcaniclastics being produced by explosive subaerial and/or subaqueous eruptions and secondary erosion of the arc complex. Transport of material to the deeper parts of marginal basins occurs by passive settling through the water column or by a variety of sediment gravity flows generated by primary eruptions and secondary remobilization processes. Deposition of arc-derived material at the base of the arc flank produces thick volcaniclastic aprons and results in a marked asymmetry in the accumulation of volcanogenic sediment within basins. The apron facies are complex and not analogous to typical deep-sea fan systems because of the influence of arc volcanism on the nature and delivery of sediment to the deep sea. Back-arc spreading centres supply a small volume of deep-water hyaloclastites and hydrothermally derived volcanogenic sediments which are incorporated into the basal parts of sedimentary sequences. The dispersal and deposition of volcanogenic sediments are profoundly influenced by geological processes associated with marginal basin evolution such as back-arc spreading, faulting, and island-arc splitting.
Geochemical characteristics of basaltic volcanism within back-arc basins
Authors: Saunders Andrew D. , Tarney John
Published: April 2008

Back-arc basins are formed by extensional processes similar to those occurring at mid-ocean ridges. However, whereas the magmas erupted along the major ocean ridges are predominantly LIL element-, Ta- and Nb-depleted N-type MORB, many back-arc basins are floored by basalts transitional between N-type MORB and island arc or even calc-alkaline basalts (viz. enrichment of LIL elements (K, Rb, Ba, Th) relative to HFS elements (Nb, Ta, Zr, Hf, Ti)). On a broad scale, it is possible to relate basalt composition, tectonic setting of the basin, and maturity of the adjacent subduction zone. Thus, the Parece Vela Basin, formed during the earliest stages of the Mariana subduction system, is floored by basalts indistinguishable from N-type MORB, whereas the later Mariana Trough is erupting N-type MORB
and
basalts with calc-alkaline characteristics, commonly in close spatial proximity. The calc-alkaline component is best developed in narrow, ensialic basins such as Bransfield Strait, where the extension is adjacent to mature, continent-based magmatic arcs. This range of compositions, from N-type MORB to calc-alkaline basalt, can be satisfactorily explained only by invoking chemical variations in the composition of the mantle material supplying the back-arc basin crust. Two major processes may be suggested: (i) selective contamination of the mantle wedge by LIL-enriched hydrous fluids, perhaps together with sediments, derived from the descending, dehydrating oceanic lithosphere; and (ii) repeated melt (and incompatible element) extraction during basalt genesis. The former process will enrich the mantle source of back-arc basalts with LIL elements; the latter will deplete the source in all incompatible elements, but the net effect of both processes is to increase the LIL/HFS element ratio of the source regions. Consequently, as the subduction zone matures, the LIL/HFS element ratio of successive back-arc basalts will be expected to increase, from initial N-type MORB ‘background’ values, to ratios more typical of island-arc basalts. The model has implications for mantle dynamics in back-arc regions, because transfer of material from the subducted slab may destabilize the overlying mantle, potentially leading to diapiric uprise when tectonic conditions permit extension.
Characteristics and tectonic significance of supra-subduction zone ophiolites
Authors: Pearce J. A. , Lippard S. J. , Roberts S.
Published: April 2008

Supra-subduction zone (SSZ) ophiolites have the geochemical characteristics of island arcs but the structure of oceanic crust and are thought to have formed by sea-floor spreading directly above subducted oceanic lithosphere. They differ from ‘MORB’ ophiolites not only in their geochemistry but also in the more depleted nature of their mantle sequences, the more common presence of podiform chromite deposits, and the crystallization of clinopyroxene before plagioclase which is reflected in the high abundance of wehrlite relative to troctolite in their cumulate sequences. Most of the best-preserved ophiolite complexes in orogenic belts are of this type.

Geological reconstructions suggest that most SSZ ophiolites formed during the initial stages of subduction prior to the development of any volcanic arc. Evidence from these ophiolites suggests that the first magma to form in response to intra-oceanic subduction is boninitic in composition, derived by partial melting of hydrated oceanic lithosphere in the ‘mantle wedge’. As subduction proceeds, the magma composition changes to island-arc tholeiite, probably because the hydrated asthenosphere of the ‘mantle wedge’ eventually becomes the dominant mantle source. Other SSZ ophiolites formed in the early stages of back-arc spreading following splitting of a pre-existing arc. Nonetheless the more common mechanism for formation of SSZ ophiolites appears to have been
pre-arc
rather than back-arc spreading.
The Ordovician marginal basin of Wales
Authors: Kokelaar B. P. , Howells M. F. , Bevins R. E. , Roach R. A. , Dunkley P. N.
Published: April 2008

The Lower Palaeozoic Welsh Basin was founded on immature continental crust. During late Precambrian-early Cambrian times, volcanism and sedimentation were influenced by NE-SW-trending faults which defined the NW and SE margins of the basin. During the Cambrian, marine sediments infilled a graben and at the end of the Tremadoc widespread tectonism was associated with an island-arc volcanic episode. In the Ordovician this subduction-related activity was succeeded by mainly tholeiitic volcanism related to back-arc extension, with the locus of arc volcanism sited further N, in the Lake District—Leinster Zone of the Caledonides. In Wales, the Ordovician volcanic activity shifted in time and space. In S Wales volcanism persisted from the middle Arenig through the Llanvirn. In N Wales the volcanism can be broadly divided into dominantly pre-Caradoc activity in southern Snowdonia and an intra-Caradoc episode in central and northern Snowdonia. In eastern Wales, including the Welsh Borderland, and in Llŷn, both episodes are represented. In all areas faults greatly influenced both volcanism and sedimentation. Intrusive activity was dominated by high-level emplacement of sills. Granite (
s.l.
) stocks are restricted to central and northern Snowdonia and Llŷn and many were coeval with extrusive volcanism.

Volcanism in the basin was essentially bimodal with voluminous eruptions of tholeiitic basalts with ocean-floor affinities, and of rhyolites. Minor volumes of andesite to rhyodacite resulted from low-pressure fractional crystallization of the tholeiitic basalts. Available evidence suggests that the rhyolites resulted mainly from crustal fusion, although in some instances evolution by crystal fractionation from intermediate magma has been proposed. Calc-alkaline assemblages are petrographically distinct, of minor occurence and, contrary to previous conclusions, are relatively insignificant in the characterization of the tectonic environment of the basin.

Throughout the basin, volcanism was generally succeeded by deposition of black muds and then turbidite-dominated sequences.
The Late Precambrian and early Palaeozoic marginal basin of South China
Authors: Pan Guoqiang
Published: April 2008

An integrated study based on recent geological mapping and encompassing the evolution of sedimentary facies, volcanism, plutonism and metamorphism in the Sinian and early Palaeozoic rocks of SE China has led to a reinterpretation of the area as representing a marginal basin situated at the SE margin of the Yangtze continental plate. The marginal basin comprised an active basin or trough and an inactive or marginal sea. The two parts display different sedimentary facies and tectonic and volcanic histories. It is concluded that in the early stages of evolution magma was derived from the mantle but later magmas were generated mainly in the crust.
Evolution of a Mesozoic passive continental margin: Baër-Bassit (NW Syria)
Authors: Delaune-Mayere M.
Published: April 2008

The Baër-Bassit area comprises imbricate sheets of ophiolities and pelagic sedimentary rocks thrust eastward onto the Arabian platform.

Deep-water sediments were deposited from Late Triassic to Mid-Cretaceous time (Cenomanian/Turonian). Triassic sediments consist of marls and Halobia-bearing limestones. From Jurassic to Cenomanian the deposits were siliceous mudstones, siltstones and cherts.

Comparisons with the pelagic sediments of the Mamonia Complex (Cyprus) and the Antalya Complex (Turkey) show that the three areas in the East Mediterranean had a similar evolution from Upper Triassic to Lower Cretaceous time. In the Upper Triassic there was continental rifting and formation of oceanic crust in a rift similar to the Red Sea. The opening was more marked in the west than in the east. This was followed by subsidence and sedimentation of siliceous rocks from Jurassic to Lower Cretaceous. Per-alkaline volcanism took place in the Baër-Bassit area at this time. Sedimentation stopped in Hauterivian time in Cyprus, in the Cenomanian/Turonian in Syria, and during Late Cretaceous in Antalya. Sedimentation related to closure of the oceanic basin still remains to be defined.
The Arabian sub-plate during the Mesozoic
Authors: Hirsch F.
Published: April 2008

The Mesozoic facies, distribution, palaeo-zoo-geography and tectonic history of the Levantine and Tauride-Zagride autochthonous and para-autochthonous units, suggest that these areas were part of the Arabian sub-plate and never lay far apart. This would tend to invalidate the hypothesis of an oceanic basin (Mesogea) in the present Eastern Mediterranean during the Mesozoic.
The SW segment of the Antalya Complex, Turkey as a Mesozoic-Tertiary Tethyan continental margin
Authors: Robertson A. H. F. , Woodcock N. H.
Published: April 2008

The SW segment of the Antalya Complex is an assemblage of Mesozoic carbonate platform, margin and ophiolitic rocks which record the formation and tectonic emplacement of a small Mesozoic ocean basin.

The pros and cons of three alternative models in the literature are outlined. The original model was of a linear continental margin of a southerly Mesozoic ocean basin (Dumont
et al.
1972), emplaced in latest Cretaceous and Miocene time as three major nappes. Ricou
et al.
(1975) reinterpreted these nappes as being rooted in a unique northerly Tethys. In the light of knowledge of modern ocean basins, Robertson and Woodcock then developed the concept of a palaeogeographically complex small southern ocean basin in which strike-slip faulting played an important role in both formation (Reuber, this volume) and emplacement (Woodcock & Robertson 1977).

We discuss here a number of important and controversial topics, including the timing of volcanism and ocean crust genesis, the origin of mountain-sized shallow water limestone masses in the allochthon, and the role of strike-slip versus nappe tectonics in the Antalya Complex. An updated version of our palaeogeographical model views the Antalya Complex as an early Mesozoic (Triassic-Jurassic) rift expanded in the Cretaceous by formation of a small ocean basin strongly influenced by strike-slip faulting during both the opening and closing stages.
Geodynamic evolution of Turkey and Cyprus based on palaeomagnetic data
Authors: Lauer J. P.
Published: April 2008

Using all the available palaeomagnetic results tentative reconstructions are given for the past positions of various parts of Turkey. At least two parts were located near the equator in Triassic times, presumably along the south-eastern boundary of the Arabian plate. This implies large-scale continental drift towards the north-west which must be taken into account in interpretations of the Alpine orogeny and the geology of the Eastern Mediterranean.
Structural evolution of the Pelagonian Zone in Northwestern Macedonia, Greece
Authors: Mountrakis D.
Published: April 2008

The pre-Upper Palaeozoic basement of the North Pelagonian zone s.1. consists of two units: the Eastern unit of the Voras Mountains and the Western unit of the Vernon Mountains. These units are two parallel crystalline sequences which have been metamorphosed under similar conditions in the greenschist facies. An Upper Carboniferous granite (302.4 ± 5/15 Ma) intrudes the metamorphic rocks of the Vernon unit. During Upper Palaeozoic time, subsidence of the western Pelagonian margin created a possible slope where a meta-clastic sequence was deposited. The clastic sediments were succeeded by a neritic carbonate cover of Middle Triassic-Jurassic age. In the eastern area of the Pelagonian zone a metamorphic carbonate mass, probably of the Triassic-Jurassic age, has been tectonically emplaced on to the crystalline basement. This carbonate cover has a possible para-autochthonous origin; thrust surfaces, folds and linear structures indicate that it was overthrust from the eastern Pelagonian margin. Two metamorphic events in the North Pelagonian zone are inferred: one pre-Upper Carboniferous which affected the crystalline basement and a second post-Jurassic which affected the Upper Carboniferous granite, the Upper Palaeozoic meta-sediments and the Triassic-Jurassic carbonates.
Pre-Neogene nappe structure and metamorphism of the North Sporades and the southern Pelion peninsula
Authors: Jacobshagen Volker , Wallbrecher Eckard
Published: April 2008

On the North Sporades and on the southern Pelion Peninsula, four tectonic units can be distinguished. The lowermost is the Pelagonian Nappe which is a sequence of Permo-Triassic metaclastics and platform carbonates of Middle Triassic to Upper Jurassic age. It is overlain by the Eohellenic Nappe, which consists of a melange with ophiolite bodies and crystalline slices, followed by a series of calc-schists, platy marbles and spilites, and, finally, a flyschoid sequence. Subsequent to the overthrusting of the Eohellenic Nappe in the Early Cretaceous, both nappes were partly eroded and then covered by the meso-autochthonous sediments of Middle Cretaceous to Lower Tertiary age. In the Eohellenic Nappe, as well as in the higher units, blue amphiboles often appear, i.e., magnesio-riebeckite in quartzitic and phyllitic layers and crossite or glaucophane in metabasites. The pelitic layers contain phlogopite and stilpnomelane as well as chlorite and phengite. In meta-radiolarites, spessartine and piemontite have also been found. This association, indicating high pressure during very low-grade metamorphism, contrasts greatly with the albite-biotite-almandine assemblage in the underlying Pelagonian Nappe, which is typical of low-grade metamorphism at more moderate pressures. A geodynamic explanation is proposed.
Neotectonic deformation patterns in the convex-northwards arc of the North Anatolian fault zone
Authors: Barka A. Aykut , Hancock Paul L.
Published: April 2008

The convex-northwards arc of the North Anatolian fault zone between Çerkeş and Erbaa contains structures and landforms permitting right-lateral displacements for several time intervals to be estimated. Within the Pontus Formation (Late Miocene-Early Pleistocene) in basins along the fault zone, an unconformity, representing a time interval from the latest Tortonian to the earliest Pliocene, is interpreted as marking the transformation of the structure from a broad shear zone to a narrow fault belt. Although the amount of displacement during the shear zone phase is unknown the offset of a sedimentary facies boundary in the Lower Pontus Formation of the Havza-Ladik basin demonstrates that since the latest Tortonian there has been 25 km of right-lateral slip. The offset of valleys and ridges suggests that there has been 8 km of Quaternary displacement, about 2 km of it in the late Quaternary and at least 500 m during the Holocene.

Structures in the Pontus Formation indicate that the early history of the western Neogene basins was influenced by regional compression and that the later histories of all basins were dominated by strike-slip displacements. The main active trace is discontinuous, the 2 km-wide belt containing subordinate en échelon faults whose geometry is consistent with development during right-lateral shear.
Pliocene lacustrine sediments in the volcanic succession of Almopias, Macedonia, Greece
Authors: Chorianopoulou P. , Galeos A. , Ioakim Ch.
Published: April 2008

This paper is a geological and palaeobotanical study of the lacustrine sediments occurring in the Voras mountain range NNW of Aridaea, in Western Macedonia, Greece. The sediments are interstratified with Pliocene volcanics from the Almopias volcanic centres. Alternations of chert, pyroclastics, limestone, tuff and breccia overlie a metamorphic basement or trachyandesitic lavas and tuffs.

Analysis of pollen in the lacustrine sediments indicates an Early Pliocene age. The most important species are
Pinus haplostelle, Pinus diplostelle
type, Taxodiaceae, Cupressaceae (
Taxodium, Sequoia
), cf.
Quercus
(
Scabratricolpites microhenrici, Tricolpopollenites henrici
), cf.
Castanea, Symplocos, Nyssa, Liquidambar
and
Tsuga
. Pollen analysis provides important clues to past climates and relief.
Recent shelf clastic sediments
Authors: McCave I. N.
Published: April 2008

Shelf sedimentation in the past 21 years has moved from an essentially descriptive study to one where theory and measurement of sediment transport play an important role in accounting for the distribution of shelf sediments. This paper looks briefly at pre-1960 works then presents a view of the major features of present research on shelf clastics. This is organized under shelf muds, tidal-current-dominated sands and wave-dominated sands. Brief consideration is given to processes of mud and sand transport and deposition prior to a discussion of sediment types and bedforms. Storms are emphasized and their capacity to emplace sand layers on the shelf by wind-driven flows is discussed.