bluuebunny/crossref_metadata_2025 huggingface dataset:
Ophiolites and their modern oceanic analogues
Authors: Parson L. M. , Murton B. J.
Published: April 2008

Conventional studies of oceanis structure and evolution are inevitably hampered by the difficulties with sampling the crust in the third dimension. Remote sensing of surficial structure, topography and morphotectonics has become easier and of higher resolution with the advent of more sophisticated techniques such as GLORIA long range sidescan sonar, as well as multibeam swath bathymetric mapping systems. Subsurface studies, however, have enjoyed less of this progress, and although deep drilling, electromagnetic surveys and deep seismic techniques still provide some measure of understanding below the seafloor, these data are few and relatively widely spaced. The integration of studies of ophiolite, therefore, can offer the marine community the benefits of a vast body of knowledge with regard to deeper structure and crustal compositions, which is unattainable in the deep sea. In turn, many of the regional and detailed structures which have been recently identified in active mid-ocean spreading systems, such as ridge segmentation patterns and ridge axis discontinuities, now form a significant contribution to recent studies of ophiolite complexes. The complementary work of the two schools is clear and ripe for development.
Ridge axial segmentation in the Oman ophiolite: evidence from along-strike variations in the sheeted dyke complex
Authors: MacLeod C. J. , Rothery D. A.
Published: April 2008

Evidence from along-strike variations in the sheeted dyke complex shows that the spreading axis at which the Oman ophiolite formed was segmented by first- and/or second-order discontinuities, most probably propagating rifts and overlapping spreading centres. We identify at least four, possibly up to seven, of these discontinuities along the
c.
500 km ridge-parallel length of the ophiolite, but recognize no unequivocal transform fault structures. We show that the discontinuities in the sheeted dyke complex can be related to aspects of segmentation previously deduced from mantle flow fabrics and deep crustal structure, and conclude that the Oman palaeo-spreading axis was segmented on a scale of 50–100 km, comparable with that of a modern fast-spreading axis such as the East Pacific Rise.
Geochemical control on the evolutionary history of the Ballantrae Complex, SW Scotland, from comparisons with recent analogues
Authors: Smellie J. L. , Stone P.
Published: April 2008

A combination of geochemical and field investigations of the Ballantrae Complex allows some control on the relative timing of events in its tectono-magmatic history. In particular, the presence of boninitic lava and hyaloclastite confirms an oceanic, supra-subduction zone origin for this early Ordovician ophiolite assemblage. Boninite eruption was preceded by a substantial phase of late Tremadoc island-arc volcanicity and the boninitic units themselves are interbedded with early Arenig primitive island-arc tholeiites. Various supra-subduction zone extensional processes have been invoked to explain boninite occurrences in recently active oceanic island arcs; interarc rifting as a precursor to marginal basin formation is preferred as a model for the Ballantrae Complex. Evidence to support this preference is drawn from the early to mid-Arenig part of the Complex where sandstones derived from mature volcanic arc lavas are conformably overlain by tholeiitic lavas erupted in a back-arc basin; a possible analogue is seen in the active Bransfield Strait marginal basin. Thus, an evolutionary sequence can be envisaged for the Ballantrae Complex which begins with the establishment of an oceanic island arc where supra-subduction zone extension led to the genesis of boninitic lavas. Next, as extension continued, a marginal basin developed wherein sandstones derived from the arc lavas were deposited and tholeiites of ocean island type were erupted. Imbrication of the back arc sequence and accretion of the ophiolite terrane was initiated in the late Arenig by arc-continent collision.
Influence of the partial melting regime on the formation of ophiolitic chromitite
Authors: Roberts Stephen
Published: April 2008

The mantle sequence of the Vourinos ophiolite is composed of a highly depleted peridotite. Indices of depletion including the MgO content of the whole rock (40 wt% MgO), the CaO and Al
2
O
3
contents of the orthopyroxene (<3.00 and 1.5 wt% respectively) and the Cr# value (100Cr/(Cr + Al)) of the spinels (54–80) all indicate a high degree of depletion, consistent with the removal of one or more melt fractions. The extensive chromite mineralization of the mantle sequence also shows a highly restricted chemistry with all but one chromite segregation falling in the range Cr# 75–82. By comparing the geochemistry of the Vourinos mantle sequence with other depleted (Semail) and more fertile mantle (Appenine) sequences, it can be shown that the melting of increasingly depleted residua results in chromium-rich magmas due to the
D
Cr
peridotite-melt
of 1 or less. These chromium-rich magmas undergo extensive olivine plus spinel fractionation and result in chromium-rich chromite segregations partly due to the chromium content of the liquid but also to the relatively high silica content of the magmas concerned. Although chromite mineralisation is unlikely to be taking place within the ocean basins at the present time, modern oceans do contain evidence of sites of likely former chromite mineralisation within the oceanic crust.
Peridotite intrusions emplaced in the fossil suprasubduction zone environment of Cyprus
Authors: Laurent Roger
Published: April 2008

The layered ultramafic and mafic rocks forming the early plutonic assemblage of the Troodos ophiolite are crosscut by intrusive bodies of poikilitic perioditite. These late intrusions of lherzolitic composition congregate near the base of the crust and rim the diapiric mantle dome (Mount Olympus) of harzburgite which outcrops in the core of the plutonic complex. Their parental magma consisted of extensively melted mantle peridotite with addition of basaltic melt. This mixture or crystal-liquid suspension of high ‘yield strength’ is assumed to have been generated in a mantle diapir within the subduction zone environment. The mantle diapir has reached the base of the Troodos crust, deformed the crust and released crystal mushes resulting in the intrusion of peridotite bodies into the crust.
Evidence for plagioclase-lherzolite intrusion in the Mid-Atlantic Ridge, DSDP Leg 37
Authors: Girardeau Jacques , Mercier Jean-Claude C.
Published: April 2008

From studies of ophiolites, it is thought that plagioclase-peridotites represent a non-negligible constituent of the oceanic lithosphere that reflects magmatism at oceanic ridges. To date, very few of them have been described from the abundant peridotites recovered from oceanic domains at present day oceanic ridges, except from transform faults. However, some plagioclase-lherzolites, interpreted as cumulate rocks, were drilled at Site 334 of DSDP Leg 37 on the Mid-Atlantic Ridge.

These plagioclase-lherzolites display poikilitic textures with oikocrysts of clinopyroxene and interstitial plagioclase that include xenocrysts of strained and partly annealed olivine crystals and subidiomorphic spinels. Petrofabric data for olivine point to a plastic deformation stage for these rocks as they display weak lattice fabrics which may have resulted from high-temperature plastic flow. Mineral compositions bear a strong resemblance to ophiolitic and oceanic rocks interpreted as residues from partial melting, except for clinopyroxenes which show a slight titanium enrichment. It is considered that these plagioclase-lherzolites represent residual harzburgites which have been pervasively impregnated by a melt from which clinopyroxene and plagioclase crystallized. Due to this impregnation episode, the primary structure and chemical composition of olivines were partly modified. It is suggested that these peridotites were locally so sufficiently lubricated by interstitial melt that they behaved as a crystal mush that had intruded the high-level crustal gabbros of the Mid-Atlantic Ridge. Their formation reflects pervasive magma percolation in the upper-most residual upper mantle at the Mid-Atlantic Ridge axis.
The validity of whole-rock geochemistry in the study of the oceanic crust: a case study from ODP Hole 504B.
Authors: Brewer T. S. , Pelling R. , Lovell M. A. , Harvey P. K.
Published: April 2008

Attempts to interpret the geochemistry of the oceanic crust are constrained by the representative nature, quality, and amount of material recovered from an individual site. The most effective sampling method has been that of continuous coring while drilling, although the amount of material recovered from a single hole can vary with depth from 0 to 100%, and is often, though not necessarily, low. Observations suggest there is inevitably a biasing towards the recovery of unaltered material. DSDP/ODP Hole 504B has been successfully drilled in a series of stages and a 1500 m section of the oceanic crust has been sampled. The core recovery in Hole 504B is, however, generally poor; consequently the study of both igneous and alteration processes at this site is limited. An alternative to this scenario is offered by down-hole geochemical (nuclear) measurements. The nuclear responses provide a limited but near-continuous geochemical dataset within this hole. The derived chemo-stratigraphy correlates well with that based upon conventional geophysical measurements. Alteration has played an important role in producing the observed chemical signatures and may partly explain the poor core recovery within the hole. Downhole nuclear measurements in the ocean crust provide a novel geochemical dataset in the study of both primary and secondary processes. This information must be integrated with lithological, petrological and geophysical data to produce the most complete appraisal yet of the oceanic crust.
Peri-collisional extension and the formation of Oman-type ophiolites in the Banda arc and Brooks Range
Authors: Harris R. A.
Published: April 2008

Integration of data from field, geochemistry, and radiometric age investigations of the active Banda arc—Australia collision zone (Banda orogen) and the Jurassic Brooks Range ophiolite provide new constraints for the origin and emplacement of Oman-type ophiolites. These ophiolites are characterized by ultramafic residuals and mafic products that are chemically modified by various degrees of partial melting. The internal structure of the igneous complexes document acute extensional strains. A high temperature metamorphic sole with some continental margin protoliths are locally preserved at the structural base of the massifs. Age relations between the ophiolites, their metamorphic sole, and collisional mountains in which they reside indicate important temporal and spatial associations. Some of these relations are inconsistent with ophiolite genesis in intra-oceanic settings.

Formation of the Savu and Weber basins around the active Banda orogen provide modern analogues of peri-collision extensional processes. These extensional domains are transitional between zones of active supra-subduction zone magmatism (ophiolite genesis) and low-angle overthrusting (ophiolite emplacement). Geochemical data from the volcanic basement of the Savu basin are similar to ‘transitional-type’ ophiolite volcanic suites. Ar/Ar ages, and stratigraphic and structural data from the basin indicate volcanism and forearc extension coincide in time and space with initial collision between promontories of the NW Australian passive margin and the Java trench, suggesting a link between the two processes. Similar age and stratigraphic relations are also documented in the Brooks Range and other Oman-type ophiolites.

Peri-collisional extension opens small SSZ ocean basins that may be obducted during or shortly after they form by progressive convergence at multi-plate boundaries. These processes provide a self-perpetuating mechanism for ophiolite genesis and emplacement that accounts for both the similar and diverse aspects of many ophiolites.
The role of Palaeocene magmatism in the tectonic evolution of the Sea of the Hebrides Basin: implications for basin evolution on the NW Seaboard
Authors: England Richard W.
Published: April 2008

Major, trace element and isotope geochemistry of the magmas of the British Tertiary Volcanic Province suggests they rose through the lithosphere in dykes and ponded as sills at the Moho and within the upper crust. In the Sea of the Hebrides basin a linked system of discrete dyke swarms, sills and normal faults record rapid NE-SW extension at the near surface. The presence of a similar system of dykes and sills within the upper crust and at the Moho could have influenced mechanisms of lithospheric extension by dissipating vertical variations in strain laterally, eliminating space problems associated with depth dependant stretching. The addition of large thicknesses of magma to basins along the NW seaboard would have resulted in local burial, but subsidence would be offset by uplift resulting from isostatic effects and thermal expansion of the lithosphere during melting. Heat loss from rising magma would have a negligible effect on the maturation history of the sediments.
Low-temperature effects of the Skye Tertiary intrusions on Mesozoic sediments in the Sea of Hebrides Basin
Authors: Lewis Cherry L. E. , Carter Andrew , Hurford Anthony J.
Published: April 2008

Fission track analysis of samples from the Sea of Hebrides Basin and surrounding regions demonstrates two very distinct age groups around 50 Ma and 300 Ma, regardless of the stratigraphic age. Apatite fission track results from sediments within 8 km of the Tertiary igneous complex on Skye were totally reset by temperatures >110°C during intrusion of the centres, but now yield ages younger than the granites. Zircon fission track results from the granites also demonstrate ages significantly younger than their hosts. Mean track lengths in apatites of <13.5 µm, and reduced apatite and zircon ages, suggest that temperatures remained elevated throughout the 6 Ma during which intrusive activity occurred, but were hotter within the granite bodies than the surrounding sediments.

Prior to intrusion of the complex, temperatures in the basin sediments presently at outcrop were unlikely to have been higher than 50°C, and beyond the effects of the Tertiary intrusions, age and track length distributions from northern Skye, the Isle of Lewis and the west coast of Scotland illustrate that the area is unlikely to have been buried beneath more than 2 km of sediment at any one time since the end of the Devonian. North of the Highland Boundary Fault, Tertiary uplift and erosion in Scotland is considered to have been between 1–1.5 km. This is consistent with a regional pattern of Tertiary erosion identified across the British Isles, but considerably less than that recognised in Northern England.
The Clare Lineament: a relic transform fault west of Ireland
Authors: Tate Michael P.
Published: April 2008

The Porcupine Seabight Basin is dissected at
c.
51°N by a major ESE-WNW trending structure which separates the Main Porcupine Basin from the Seabight Basin. This structure was initially mapped across the southern boundary of the Rockall Trough, where it was termed the Clare Lineament and interpreted as a Mesozoic precursor to the present-day Charlie Gibbs Fracture Zone. Evidence is presented here for its extension to the eastern margin of the Porcupine Seabight Basin. There it lies to the south of the Iapetus suture zone imaged by deep seismic data west of Ireland, to which it does not appear to be related as had previously been suggested. At the onset of sea-floor spreading during the mid-Cretaceous, the Clare Lineament evolved as an incipient transform fault. It separated volcanism to the north, which produced N–S ridges above attenuated continental crust in the axes of the southern Rockall Trough and Main Porcupine Basin, from the rift-drift transition in the proto-Atlantic rift to the southwest, now occupied by oceanic crust of the Porcupine Abyssal Plain. The Clare Lineament was probably then superseded by the Charlie Gibbs Fracture Zone during the Late Cretaceous.
Synoptic palaeogeography of the Northeast Atlantic Seaway: late Permian to Cretaceous
Authors: Doré A. G.
Published: April 2008

The NE Atlantic rift system was a key element in marine connectivity between the northern (Boreal) and southern (Tethyan) marine realms. Palaeogeographic summary maps in this account emphasize the exploitation of pre-existing basement grain on a regional scale, particularly that of the Caledonian Orogen, in the development of the Mesozoic linked rift systems. Also emphasized are the importance of extension across the rift system during successive tectonic episodes and, as implied by restoration of the stretching, the narrowness of the proto-North Atlantic seaway in the Late Permian — Early Mesozoic.

The palaeogeographic maps document a sequence of tectonic events leading to the break-up of Pangea. Block-faulting in the mid-Permian enabled marine conditions to penetrate southwards from the Boreal Sea to the Zechstein and Bakevillia Seas of NW Europe, although no link with the Tethyan realm can be documented. The Triassic was characterized by intense differential movement and sediment accumulation. Sporadic marine ingressions took place into the NE Atlantic and North Sea basins. However, no throughgoing connection between marine tracts in the Barents Sea and Tethys was established until the Early Jurassic, when a series of transgressions brought widespread marine conditions and faunal unification between north and south. In the Middle Jurassic, regional uplift in the central North Sea, and probably in the NE Atlantic rift system, ran counter to an overall transgressive regime, suggested by regional sea-level curves and by overstepping of the East Greenland and Mid-Norwegian basin margins. These restrictions re-established acute provinciality between the Boreal and Tethyan realms. Marine connections were restored by intense rifting and transgression in the Late Jurassic, but the evolution of a complex seaway with major land barriers in the earliest Cretaceous saw a return of marine provinciality. Transgressions associated with probable ocean floor development to the southwest (Rockall Trough, Hatton-Rockall Basin) and northwest (Canada Basin) of the study area in the Albian and Late Cretaceous finally established an open seaway through the NE Atlantic rift. Massive subsidence in the Faeroes Trough and Mid-Norwegian basins, and dextral shear along the Barents Sea margin, were precursors to final crustal separation in the Early Tertiary.
Decision making under risk in the mining industry: a risk appraisal case study
Authors: Walduck G. P.
Published: April 2008

The concepts of risk and uncertainty in investment are defined and their relevance explained. The nature of the uncertainty of a number of parameters employed in investment appraisal is described. Risk modelling in computer-assisted evaluations using Monte Carlo simulation is illustrated by means of a case study involving a brief and comparatively simple analysis. The study points to the possibility that a superficially attractive investment can become unattractive when risks are assessed, but conditions under which the reverse may be true are pointed out. The importance of results interpretation and presentation is high-lighted.
Waste disposal, data collection and quarry design
Authors: Allington Ruth , Walton Geoffrey
Published: April 2008

This paper outlines important data that must be collected as a basis for successful quarry design. In particular, it focuses on waste materials; how and in what quantities they will arise and why planning for their handling, storage and disposal must be an integral part of the design at all stages. Difficulties that arise when waste is underestimated or ignored are noted and design methods to avoid these pitfalls are described.
A case history of pre-extraction site investigation and quarry design, Cliffe Hill Quarry, Leicestershire
Authors: Barrett W. L.
Published: April 2008

A brief history of the reasons leading up to the initiation of this project is followed by a description of the geographical location and geological significance of the chosen site.

An initial phase of test pitting produced evidence which warranted a follow-up phase of continuous flight auger drilling along existing tracks. This work in turn indicated that serious exploration at great expense was warranted and a relatively powerful, brand new, drilling rig, capable of both coring and drilling through substantial thicknesses of overburden, was purchased. Several years of drilling, much of it on a 50m grid, subsequently proved the existence of a viable quantity of resource beneath an acceptable depth of overburden. Simultaneous testing of the core samples for a range of physical properties (as per BS 812) indicated the materials to be of acceptable quality for the anticipated markets, including rail ballast for high speed tracks. The drilling information was supplemented by a limited amount of geophysical work, mainly employing a shallow seismic refraction technique.

Initial quarry planning studies indicated that a viable reserve could be generated by stripping overburden to a depth of 40 m around the periphery, and a planning application for areas of quarrying and overburden disposal was submitted. After considerable discussion and some modification, permission was granted, subject to a large number of conditions. Phased overburden stripping will ultimately involve several million cubic metres. This site will be subject to a full investigation as required by Section 9 of the Mines & Quarries (Tips) Regulations and this will determine the angles of safety for both the cut slopes and the deposited overburden.

Preliminary configurations for the quarry, in terms of face heights, batter angles and bench widths were determined from geotechnical logging of the cores, the results of which were subsequently augmented by detailed mapping of the early exposures created. Full site investigations were also carried out for the location of load bearing structures.
Development of a field computer data logger and its integration with the DATAMINE mining software
Authors: Onions R. I. , Tweedie J. R.
Published: April 2008

The paper outlines the reasons for, and the development of, a field data logging system for sand and gravel exploration. It covers the selection of hardware and the development of the software which make up the system.

The use of this system by the geologist/drilling assistant in the field as site investigation progresses is described together with the method of producing borehole logs without further keying in of data.

The progress towards integration of data derived from the field computer, laboratory and the MOSS survey system is outlined as is the use of these data by the DATAMINE package for reserve modelling and assessment, and production of resource and working plans. An evaluation of the time and costs saved using this integrated approach to data gathering, storage and processing in the investigation is made.

The aim of the paper is to show how computers can be used in the extractive industry, from the initial stages of on-site logging to the production of final working plans, to reduce the number of points at which errors can be introduced, thus increasing accuracy of reports and reducing the time and costs involved.
The application of DATAMINE in kaolin resource management
Authors: Howe J. H.
Published: April 2008

The computerized reserve evaluation system developed in house for ECCI’s UK kaolin operations served well from 1981 to 1987 but, with an evolving data base and increasingly more sophisticated demands placed upon it, its limitations became ever more apparent.

It was clear that to maintain the system and develop it at the required pace was not feasible. Therefore the decision to replace it with a proprietary system was taken and DATAMINE was installed in July 1988.

The new system has been installed to operate in parallel with the ECLIPSE ground modelling system which has been in operation at ECCI since early 1985 and has made significant impact in the fields of surveying, mapping and of quarry and tip design. At the present time, 900f the Mid Cornwall China Clay region has been mapped using this system and topographic update is readily available in digital format for quick assimilation into DATAMINE, speeding up model construction immeasurably.

The application of DATAMINE is discussed in terms of its role as a tool in resource management and the construction of orebody models for primary kaolin deposits is briefly described. In order that the system could be made more specific to ECCI’s kaolin operations, a series of macros have been developed which essentially customize DATAMINE to ECCI’s specific requirement whilst maintaining total flexibility. These macros are described in broad outline and this serves to illustrate how the system is being applied in this particular situation. The ultimate goal is to provide a comprehensive and flexible overview of ECCI’s kaolin resources in SW England. This overview, coupled with a mineral extraction and debris disposal schedule, is a key component in the cost effective management of ECCI’s mineral business.
The use of three-dimensional surface modelling in the design of mines and quarries
Authors: Norton J.
Published: April 2008

Major changes have occurred in mining practice as a result of the evolution of computer technology. MOSS Systems Limited was one of the first companies to develop and market a system geared to the requirements of mineral extraction operators. The benefits inherent in the use of such a 3D modelling system are described in detail. MOSS analysis techniques can be applied to the 3D model at any stage in the design or subsequent operation of the workings. These techniques include the generation of sections and profiles, volumetric and mass-haul analyses, contouring, and isopachyte analysis. A novel example of the use of MOSS in the optimized design of spoilheap geometry is given.
Coastal upwelling in the modern ocean
Authors: Smith Robert L.
Published: April 2008

During the past decade several major physical oceanographical experiments were performed over the continental margins along the ocean’s eastern boundaries. The studies extended farther seaward than the continental shelf and extended over the seasons. As a result, our understanding of the processes and phenomena associated with coastal upwelling and affecting the ocean farther seaward has increased. The Coastal Ocean Dynamics Experiment investigated the dynamics controlling the currents over a continental shelf exposed to strong upwelling favourable winds; the experiment was more intensive and completely instrumented than any previous shelf experiment. The Coastal Transition Zone experiment investigated the cool ‘filaments’ conspicuous in satellite images of SST off northern California during the coastal upwelling seasons. Associated with the cool filaments are jets along the boundary between the cooler recently upwelled water and the warmer adjacent ocean water; as the jets meander equatorward and offshore (several hundred km), the upwelled water extends over greater distances offshore than previously thought likely. One experiment (SuperCODE) looked at the large alongshore scale, from 35°N to 50°N off the west coast of north America, defined the seasonal cycle, and found that the tendency for subsurface poleward flow over the continental shelf and slope increased at lower latitudes in spite of the increased equatorward mean wind. The ubiquitous poleward currents, usually subsurface over the inner slope and outer shelf, have been observed in all the experiments off the west coasts of the Americas, in spite of equatorward winds. Unlike the jets of the coastal transition zone, the poleward undercurrents are trapped to the continental slope and shelf. The Leeuwin Current Interdisciplinary Experiment took place off Western Australia, the only major eastern boundary without coastal upwelling in spite of strong equatorward winds. The alongshore pressure gradient along the west coast of Australia is large, perhaps because of the free connection to the western Pacific, and dominates the opposing equatorward wind stress, suppressing upwelling and causing poleward flow (the Leeuwin Current) at the surface over the slope and outer shelf.
Variations in the benthic foraminiferal fauna of the Arabian Sea: a response to changes in upwelling intensity?
Authors: Hermelin J. O. R.
Published: April 2008

Results from ODP Leg 117 show that abundance and species composition of the benthic foraminiferal fauna in the northwestern Arabian Sea vary extensively through time. Studies of the Recent faunas from the region show that the distribution of benthic foraminifers is strongly correlated with the depositional environments present, of which some are associated with the OMZ (oxygen minimum zone). The OMZ is a result of strong seasonal upwelling caused by monsoonal winds and the Recent benthic foraminifers that thrive in this specific environment form a characteristic assemblage. Assuming that this relation between this benthic foraminiferal assemblage and OMZ/upwelling conditions were present in the geological past the relative abundance of the species forming that assemblage can be used to reconstruct past changes in the intensity of the monsoonal upwelling and changes in the water circulation pattern in this area.

A deepening of the lower boundary of the OMZ occurred between 6.5 and 3.0 Ma with a maximum at 5.0 Ma (= more intense upwelling ?). After 5.0 Ma, mixing of more oxygenated outflow water originating in the Red Sea weakened the severity of the OMZ in the interval 200 to 500 m in this part of the Arabian Sea. This mixing became more intense with time, as reflected in the benthic foraminiferal fauna, and today there is a pronounced intercalation of oxygenated water at this water depth and a low percentage of the assemblage associated with the OMZ.
Radiolarian microfauna in the northern California Current System: indicators of multiple processes controlling productivity
Authors: Welling Leigh A. , Pisias Nicklas G. , Roelofs Adrienne K.
Published: April 2008

Radiolaria, as other plankton, appear to be highly tuned to specific oceanographic environments. Thus, in a transitional region such as the eastern North Pacific, where many different water masses are mixed, radiolaria provide very sensitive tracers of these water masses and the currents that carry them. We present the first two years of radiolarian results from the Multitracers sediment trap study across the northern California Current System. Three moorings, positioned along a transect at approximately 130, 280 and 650 km from the coast, sample a wide variety of oceanographic conditions both spatially and temporally. Selected species or species groups are presented along with hydrographic data from the region in order to demonstrate the basic trends in the radiolarian data and illustrate their relationships to fluctuations in their physical environment. Multiple linear regression is used to explore the relationship between radiolarian composition and the export of carbon from this system.

The most important physical process controlling variability in the radiolarian composition along this transect is attributed to variability in the intensity of the southward-flowing California Current. The seasonality of the California Current is clearly reflected by changes in the composition of the radiolarian trap assemblages; very different species dominate this region in summer as compared to winter. In addition to seasonal trends, evidence in both the offshore and onshore environments suggests significant differences between years. This region appears to have been more strongly influenced by cold, subarctic water during the winter of 1988/1989 than during the previous year.

The relationship between radiolarian species abundances and the flux of organic carbon strongly indicates that a number of different oceanographic processes contribute to enhanced productivity at these sites. This has important implications when making inferences from the geological record about past changes in the intensity of upwelling in this eastern boundary current system.
Organic geochemistry as a tool to study upwelling systems: recent results from the Peru and Namibian shelves
Authors: Repeta Daniel J. , McCaffrey Mark A. , Farrington John W. , McCaffrey Mark A.
Published: April 2008

Organic geochemists are currently developing new, molecular-based tools for studying the historical record of coastal upwelling. Several hundred biomarkers, organic compounds with known biological sources, have been identified in sediments underlying the world’s major upwelling systems. Studies completed over the last two decades show that the distribution of many biomarkers in sediments is heavily impacted by the oceanographic and ecological conditions that prevail at the time of sediment deposition. Therefore, these biomakers have the potential to serve as useful palaeoenvironmental indicators. In order to decipher the sedimentary record on the molecular level, a better understanding of early diagenesis, and the coupling between water column biology, chemistry and biomarker distribution in sediments, is needed. Upwelling environments provide excellent sites to conduct such studies. High sediment accumulation rates and good preservation of organic matter in sediments relative to other depositional environments permit high-resolution time-series studies. We summarize here some recent research on early diagenesis, the effect of dysaerobic conditions on biomarker preservation, and the impact of El Nino Southern Oscillation (ENSO) events on the organic geochemical record. We further suggest some specific areas of future research that could substantially enhance our understanding of upwelling environments.
Evidence for aridity-driven dust flux to the northwest Arabian Sea and for decoupling of the dust and upwelling systems
Authors: Krissek L. A. , Clemens S. C.
Published: April 2008

Late Quaternary records of dust grain size, dust flux (mass accumulation rate; MAR) and dust mineralogy from ODP Site 722 on the Owen Ridge, northwest Arabian Sea, have been used to: (1) infer environmental conditions in the continental source areas; (2) determine the spectral response (frequency and phase relationships) of dust MAR and mineralogy to environmental changes associated with global ice volume variations and orbital insolation patterns and (3) evaluate potential associations between the continental (dust) and marine (upwelling) systems over the past 800 ky. The terrigenous dust component is composed of smectite, illite, palygorskite, kaolinite, chlorite, quartz, plagioclase feldspar and dolomite. This is consistent with the composition of source areas currently supplying sediment to the Arabian Sea. An R-mode factor analysis identifies four mineral assemblages: three reflect arid continental source conditions and one reflects more humid conditions. Total dust MAR, two of the three ‘arid’ factor assemblages, and six of the seven minerals associated with the ‘arid’ factors are coherent with the marine isotopic record of global ice volume over at least one primary orbital frequency, with input maxima during glacial (arid) hemicycles. In contrast, wind strength and upwelling intensity indicators exhibit maxima during the interglacial (humid) hemicycles, indicating a decoupling of the continental (dust MAR) and monsoon-driven upwelling systems.
Variation of South Somalian upwelling during the last 160 ka: radiolarian and foraminifera records in core MD 85674
Authors: Caulet Jean Pierre , Vénec-Peyré Marie-Thérèse , Vergnaud-Grazzini Colette , Nigrini Catherine
Published: April 2008

Indicators of upwelling activity and surface-water productivity for the last 160 ka have been studied in the ‘Marion Dufresne’ core MD 85674 taken off Somalia (3°11, 2 N-50°26, 3 E; 4875 m depth). Quantitative changes in the abundances of radiolarian species which are restricted to upwelling areas (
A. murrayana, C. irregularis, D. infabricatus, L. nigriniae, P. caryoforma, P. crustula
, and
P. minythorax
) were used to monitor the variation of vertical advection of deep water. These changes are compared with those recorded by the stable carbon isotopes of a foraminiferal thermocline dweller,
N. dutertrei
, and with quantitative variations of some planktonic foraminifers (
N. dutertrei, G. bulloides, G. menardii, G. sacculifer
and
G. glutinata
). Taken together, our data indicate that, under the south Somalian gyre, upwelling activity was maximal during transition between isotope stages 6 and 5, isotope stage 3, and transition between isotope stages 2 and 1 (respectively at about 130 ka, 65 to 25 ka, and 15 to 10 ka). These data also suggest that, at least during the last 60 ka, periods of increased activity in the Somalian, Arabian and Peruvian upwelling systems were synchronous.
Peruvian coastal primary palaeo-productivity during the last 200 000 years
Authors: Schrader Hans
Published: April 2008

Two times series of primary palaeo-productivity off the Peruvian coast over the last 200 000 years are presented for Ocean Drilling Leg 112 Sites: Site 681, Hole 681A at 11° and Site 686A, Hole 686A at 13° southern latitude. Estimates of primary palaeoproductivity are based on the transfer function PDU-3 that uses marine planktonic diatom assemblage distribution from surface sediment samples and a ten-year average primary productivity map over the area with a range of 37 to 365 gC/m
2
/year. Primary palaeoproductivity does not follow a simple glacial-interglacial mode; the record is more complex and above average palaeo-productivity occurred in Sites 681 and 686 over the following time intervals: 12 to 28, 60 to 68, and 148 to 160 ka; major increases in productivity were found during peak glaciations, and significant decreases occurred at 8, 24, 72 to 80, 112 to 128, and 160 to 168 ka. The averaged palaeo-productivity curve of 681A and 686A over the last 160 000 years is in inverse phase with the Vostok ice core atmospheric CO
2
indicating that part of the atmospheric CO
2
variations is linked to changes in the biological pump activities of the eastern Pacific boundary current system.
Transfer functions to reconstruct ocean palaeoproductivity: a comparison
Authors: Sarnthein M. , Pflaumann U. , Ross R. , Tiedemann R. , Winn K.
Published: April 2008

Oceanic plankton (export) productivity contributes to the control of glacial-to-interglacial changes in atmospheric CO
2
concentration. The extent of this contribution may be deciphered from global reconstructions of palaeoproductivity. We quantitatively estimate palaeoproductivity over the last 350 000 years in the eastern equatorial Atlantic, using equations based on foraminiferal assemblages and marine organic carbon accumulation rates; and make qualitative estimates using diatom and radiolarian accumulation rates. These proxydata are calibrated to data on modern primary production. When applied to the same set of marine sediment samples, the various reconstruction techniques produce productivity estimates with similar temporal productivity oscillations and a long-term similar absolute productivity level, suggesting that each provides a good signal of productivity changes.
The history of coastal upwelling off Peru (11°S, ODP Leg 112, Site 680B) over the past 650 000 years
Authors: Heinze Peter-Matthias , Wefer Gerold
Published: April 2008

The coarse sediment fraction (>63 μm) and benthic foraminiferal composition of Quaternary sediment cores from ODP LEG 112 Hole 680B (252.5 m water depth) were sampled from the upwelling area off Peru. High-resolution oxygen isotope stratigraphy based on analyses of the benthic foraminifera
Bolivina seminuda
allows a detailed reconstruction of the upwelling history since oxygen isotope Stage 16. Variations in the relative abundances of the benthic foraminiferal species
Nonionella auris, Bolivina costata
, and
Bolivina seminuda
document changes in fertility, which were found to be enhanced during interglacial Stages 1, 3, 5, 7, 9 and 11. Generally, bioturbated sediments are dominated by the genera
Cassidulina, Epistominella, Gyroidina, Trifarina
and
Valvulineria
. These benthic foraminifera are members of the ‘Undercurrent Fauna’, which is commonly associated with sediments that have a high terrigenous detrital component and a low organic carbon content (<3 wt%). These sedimentary deposits are indicative of high near-bottom current velocities of the Peruvian Undercurrent and well oxygenated bottom waters (0.5 to >6 ml/l O
2
). The entire core interval investigated in Hole 680B appears to have been affected by the Peruvian Undercurrent. Generally, undercurrent-dominated sections were found to correspond with glacial oxygen isotope stages.
Evolution of the Izu-Bonin intraoceanic forearc basin, western Pacific, from cores and FMS images
Authors: Pezard Philippe A. , Hiscott Richard N. , Lovell Michael A. , Collela Albina , Malinverno Alberto
Published: April 2008

One of the objectives of Ocean Drilling Program (ODP) Leg 126 was to investigate the origina nd evolution of the Izu-Bonin arc and forearc, both products of the subduction of Pacific lithosphere under the Philippine Sea Plate. Within the forearc basin, a full set of downhole measurements was recorded in two deep holes (792E and 793B). In addition, borehole electrical images were obtained (for the first time in the context of ODP) with the Formation MicroScanner (FMS*).

The main result of the drilling is that the forearc basin formed between 31.0 and 24.0 Ma by separation of a formerly contiguous frontal and outer arc high. The cored material shows a characteristic pattern of volcanogenic input, from turbidites and debris flows produced by volcanism and erosion of surrounding highs. The short rifting period is characterized by high sedimentation rate (300 m/Ma). In this context, the high resolution of FMS images was used to analyze the sedimentary processes associated with the deposition of deep-water volcaniclastics. The images reveal fine details of turbidite sequences that dip at low angles due to recent tectonics.

An FMS-based sedimentary log was calibrated from cores and prepared for each of the two holes, providing continuous bed-by-bed sections and permitting the investigation of trends in bed thicknesses. Palaeocurrent data were obtained from the analysis of ripple marks. During early basin history (30.2 to 29.5 Ma), the main sediment source was located to the east, in the vicinity of the modern outer arc high, with a secondary transport-mode oriented northward, along the basin axis. In the shallower section, emplaced at a lower rate from 28.9 to 27.3 Ma, axial transport from the north dominates a small component of flow from the western margin of the basin.

Initiated by rifting of the arc during the Oligocene time, basin development was followed by periods characterized also by extensional tectonics. Postdepositional extensional deformations such as normal microfaults, conjugate high-angle fractures, and dewatering veinlets were identified in the core and on FMS images. The orientation of the stress field within the arc and forearc was obtained from the analysis of borehole ellipticity. The results confirm models of stress distribution in forearc-arc-back arc regions. In particular, a rotation of the maximum horizontal stress trajectory in the overlying plate was observed, in a direction orthogonal to the plate boundary. In spite of a 90° clockwise rotation of the Philippine Sea plate since Oligocene time, the orientation of the stress field seems to have remained stable with respect to the trench axis over this period.
Automated prediction of sedimentary facies from wireline logs
Authors: Bølviken Erik , Storvik Geir , Nilsen Dag Erik , Siring Erling , Van Der Wel Dirk
Published: April 2008

The problem addressed is whether a computer can be programmed to identify depositional facies from a set of wireline logs. The basic approach is to let the computer learn by itself the patterns to search for by feeding it log signatures that have already been assigned facies labels. Having gone through this training phase, it can make sedimentary predictions from new data. The underlying model is a mathematical formalization of the idea that sedimentary processes have deposited lithological sequences which influence the observed log traces. Stochastic descriptions are used for these relationships. Markov chains link the lithology to the underlying sedimentary facies. The upward transition probabilities of the Markov chain are the main features which discriminate sedimentary facies.

An efficient reconstruction algorithm permits probabilistic restoration of both lithology and sedimentology. This allows the uncertainty of the conclusions to be quantified, and more than one interpretation can be put forward where appropriate. Results of the tests are promising.
Analysis of dipmeter data for sedimentary orientation
Authors: Cameron Gavin I. F.
Published: April 2008

Dipmeter data are logged as a vertical traverse through formations of interest. By analogy to concepts of dip analysis at surface outcrops, not all of the dip data collected by a logging run are of direct relevance to specific interpretation aims. A methodology is required whereby only relevant dip magnitude and azimuth data can be extracted from the mass of logged results. One approach involves the deductive use of log zonation and dip filtering techniques to isolate the dip results that most closely match the geological requirements. Statistical analysis for preferred orientation in the selected dataset gives a result to which clear geological significance can be attached. The principles described can be applied to a variety of sedimentary dipmeter interpretation problems, such as the determination of palaeocurrent directions, considerations of reservoir geometry and preferred bedding orientation.
Stress trajectory determinations in southwestern Ontario from borehole logs
Authors: Yassir Najwa A. , Dusseault Maurice B.
Published: April 2008

This paper reviews the benefits and limitations of the use of four-arm dipmeter logs to detect breakouts, and to estimate horizontal stress trajectories. An example is given from southwestern Ontario, a low seismic risk area, yet one with unusually high horizontal stresses, causing contemporaneous deformations such as pop-ups and tunnel closures. The preliminary results show that the relatively few breakouts detected follow two main trends, approximately N80°E and S80°E. The breakouts often have different orientations within the same well, but do not seem to ‘prefer’ a particular lithology. The data, when compared to other stress measurements, do show a general NE trend for compressive stress, as popularly believed. However, they are as yet too few to make statistically reliable assumptions on the stress state in the area.
Attempts to detect open fractures and non-sealing faults with dipmeter logs
Authors: Bell J. S. , Caillet G. , Adams J.
Published: April 2008

If enough stress-generated breakouts have been identified on four-arm dipmeter logs to map regional horizontal stress trajectories, it may be possible to use anomalous orientations to identify open fractures and non-sealing faults. These act as free surfaces and, if they were oriented obliquely to regional stresses, deflect them locally. This type of analysis is simple to apply and appears to offer a novel way to obtain key information required for optimizing the production of oil and gas. In offshore eastern Canada, the regional stress regime is well established and local deflections appear to be caused by near-by open fractures and non-sealing faults. In the Aquitaine Basin in France the regional stress signature is not homogeneous. Though some anomalous orientations appear to be caused by open fractures and faults, it is clear that many are not. Hence the method may not be applicable everywhere. Possible reasons include differences in the σ
H
:σ
h
ratios of the two areas and the geotectonic settings.