bluuebunny/crossref_metadata_2025 huggingface dataset:
Palaeoweathering profiles developed on the Iberian Hercynian Basement and their relationship to the oldest Tertiary surface in central and western Spain
Authors: Ballesteros E. Molina , Talegón J. García , Hernández M. A. Vicente
Published: April 2008

On the southwest border of the Duero Basin the Hercynian basement of the Iberian Peninsula is fossilized by a siderolithic sedimentary cover whose thickness increases progressively eastward. Two different palaeoweathering mantles have developed in this zone. From west to east, these mantles are progressively separated in the vertical sense. Whereas the lower mantle affects the Hercynian basement to a depth of > 18–20 m, being fossilized eastward by the siderolithic cover, the upper mantle affects both the Hercynian basement to the west and the siderolithic cover to the east to a depth of
c
. 3–5 m.

Mineralogical, petrographic and geochemical techniques have shown that the lower mantle shows an upward destruction of the parent minerals with the development of new 2 : 1 phyllosilicates (smectite-like minerals) in the middle levels of weathering and an enrichment in 1:1 phyllosilicates in the upper levels. By contrast, the higher weathering mantle shows important palaeosol features, an enrichment in CT opal, oxyhydroxides mobilizations and occasional concentrations of alunite dated at 58–67 Ma.

A planation surface appears related to the uppermost of these mantles, its remnants now uneven owing to the Alpine tectonic phases. Eastward, the Tertiary sediments of the Duero Basin unconformably fossilize the remnants of this palaeosurface.
The geochemistry of Indian bole horizons: palaeoenvironmental implications of Deccan intravolcanic palaeosurfaces
Authors: Widdowson M. , Walsh J. N. , Subbarao K. V.
Published: April 2008

Deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode. In these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces. The current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events.

The bole horizons normally rest on top of altered basaltic lavas. Both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements, such as aluminium and iron, are closer to fresh basalt than laterite. Nevertheless, these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed. A chemically distinctive nature for some boles can be demonstrated from chondrite normalized REE plots and, in these instances, strontium and neodymium isotopic compositions demonstrate that the fine-grained bole material is derived from a chemically distinct source. In addition, thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts. It is therefore suggested that many Deccan boles are in fact weathered pyroclastic material, and that the pyroclastic content of the basaltic succession may be greater than previously supposed. A significant pyroclastic input during the Deccan eruptions has important palaeoenvironmental implications for the fate of late Cretaceous flora and fauna in peninsular India.
Remote sensing for mapping palaeosurfaces on the basis of surficial chemistry: a mixed pixel approach
Authors: White Kevin , Drake Nick , Walden John
Published: April 2008

Palaeosurfaces are often characterized by distinctive surficial material compositions; for example, iron oxide in lateritic surfaces in India or calcium carbonate in calcreted surfaces in Africa. The chemical constituents of interest often play a significant part in the induration, and hence the preservation, of palaeosurfaces. Furthermore, these components often have distinct spectral reflectance characteristics, enabling them to be detected from multispectral remote sensing systems. However, traditional image processing techniques, such as classification, are inappropriate for mapping such phenomena, which usually exhibit a gradually-varying distribution. In studies of palaeosurface development, the requirement is for data that provide quantitative estimates of the surficial material composition (i.e. the proportions of a given component, such as iron oxides, within an image pixel). Algorithms based on compositional analytical techniques can be applied to unmix the pixel spectral response into estimates of the proportions of the image components (such as vegetation, iron oxides, etc.) within each pixel of an image. The resulting fraction maps provide a powerful technique for mapping palaeosurfaces and analysing their development. This paper demonstrates how these techniques have been applied to studies of Quaternary piedmont surfaces in the Tunisian Southern Atlas.
Orogeny through time: an overview
Authors: Burg Jean-Pierre , Ford Mary
Published: April 2008

As an introduction to a diverse set of papers on orogenic studies we present a personal overview of the most notable developments in orogenic studies since the 1960s. The impact of new techniques such as deep reflection seismic profiling, geochronology, analogue and numerical modelling is discussed. The major geodynamic models and concepts which have stimulated orogenic studies in recent years are also considered.
Rheology of the lithosphere in space and time
Authors: Ranalli Giorgio
Published: April 2008

The rheology of the lithosphere is a factor of primary importance in the kinematics and dynamics of mountain belts. This paper attempts to clarify the role of rheology in orogenesis, by applying simple physical principles to the analysis of tectonic processes. The emphasis is on broad generalizations leading to order-of-magnitude estimates. Since the rheology of lithospheric materials is strongly dependent on temperature, the discussion opens with a review of continental and oceanic geotherms and an assessment of their reliability. Then the brittle (frictional) and ductile (high-temperature creep) properties of the lithosphere are considered. In the brittle field, particular attention is paid to the problem of fault reactivation, which is shown to be more likely in extensional than in compressional regimes. In the ductile field, a summary of creep parameters for the most common lithospheric materials is presented. The central concept of rheological profiles (strength envelopes), essential to the estimation of the depth variations of lithospheric rheology, is discussed with reference not only to its applicability but also to its limitations (a two-dimensional example from the Canadian Cordillera is given). Processes related to the rheological properties and layering of the lithosphere — gravitational collapse in thickened and softened crust, tectonic inversion following the detachment of a lithospheric root, lower crustal ductile flow with consequent relaxation of Moho topography — are analysed semi-quantitatively, mainly to show that they are indeed likely to be important players in geodynamics. Finally, in a brief Archaean detour, some possible important differences between present-day and Archaean oceanic lithosphere are examined, and the conclusion is reached that in all likelihood plate tectonics, although at different rates, has been the main agent of orogenesis during most of the history of the planet.
Geodynamic evolution of the Proterozoic Mount Isa terrain
Authors: O’Dea M. G. , Lister G. S. , Maccready T. , Betts P. G. , Oliver N. H. S. , Pound K. S. , Huang W. , Valenta R. K. , Oliver N. H. S. , Valenta R. K.
Published: April 2008

The Proterozoic Mount Isa terrain records the effects of four periods of intraplate tectonism. The
c
. 1870 Ma Barramundi Orogeny was characterized by a massive felsic magmatic event, and global correlations suggest a physical link between Australia and Laurentia at this time. Thereafter, the terrain underwent an extensional history spanning 200 Ma involving repeated episodes of rifting, post-rift subsidence and associated depositional and magmatic phases. This protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25 km above attenuated continental crust. Rifting was interrupted prior to the formation of ocean crust by the compressional Isan Orogeny (1590–1500 Ma). The Isan Orogeny was synchronous with low-pressure high-temperature metamorphism and widespread metasomatism. In the waning stages of shortening, the Mount Isa terrain evolved into a wrench system characterized by an extensive network of strike-slip faults. The current level of exposure in this terrain provides spectacular examples of superimposed rifts, basin inversion, and wrench geometries developed at middle to upper crustal levels.
Climatic cyclicity and accommodation space in arid to semi-arid depositional systems: an example from the Rotliegend Group of the UK southern North Sea
Authors: Howell John , Mountney Nigel
Published: April 2008

The arid to semi-arid, continental deposits of the Permian Rotliegend Group of the UK southern North Sea (SNS) provide an ideal opportunity to test and further the concepts of sequence stratigraphy in fully non-marine depositional systems. Although these depositional systems are detached from the effects of sea-level change, cyclic fluctuations in the climatic regime result in variations in the vertical facies successions laid down. The effects of increasing or decreasing aridity upon depositional processes are considered. Climatic cycles, bounded at the point of lowest aridity are defined. These climatic cycles have been correlated between different, co-existent depositional environments. This enables depositional systems, such as those present in the Rotliegend, to be considered chronostratigraphically. The application of these concepts to an extensive data set illustrates that, whilst the internal architectures of sedimentary cycles are controlled by the depositional processes and their positions within the basin, the thickness of the cycles directly reflects the rate of accommodation creation.
The Penarth Group-Lias Group succession (Late Triassic-Early Jurassic) in the East Irish Sea Basin and neighbouring areas: a stratigraphical review
Authors: Warrington Geoffrey
Published: April 2008

Small, widely separated outliers of latest Triassic and Early Jurassic rocks in and around the East Irish Sea are preserved in the hangingwall blocks of faults that were active during post-Pliensbachian-pre-Cenomanian times. The successions preserved in the outliers comprise the Penarth and Lias groups, in typical facies and with characteristic microfloras and macrofaunas, and are vestiges of a formerly extensive cover of those rocks to the northwest of their main outcrops in England. The Penarth Group, of Rhaetian (Late Triassic) age, comprises the Westbury Formation and the succeeding Lilstock Formation; the latter is represented largely, or entirely, by the Cotham Member. Lias Group successions preserved in the outliers include, above the basal (‘pre-planorbis’) beds, of latest Triassic age, Early Jurassic beds ranging in age from Hettangian (
planorbis
Zone) to Pliensbachian (
spinatum
Zone) and are considerably thicker than their correlatives in eastern England, indicating that subsidence was slower there than in western Britain in Hettangian, Sinemurian and Pliensbachian times.
The Mesozoic and Tertiary history of the Irish Sea
Authors: Cope John C. W.
Published: April 2008

Uplift centred on the Irish Sea in latest Cretaceous times accompanied by a locally raised geothermal gradient is supported by apatite fission track analyses from the area, the outcrop patterns of the Mesozoic rocks of England and the positive gravity anomalies over the whole of the Irish Sea region. This conclusion allows more precise modelling of the history of the region and the lost Mesozoic cover can be reconstructed, with varying degrees of certainty, by combining the results of extrapolation from existing land and submarine outcrops and subcrops, with the amount of cover lost. Stratigraphical considerations suggest the occurrence of both Late Cimmerian and latest Cretaceous inversions of the Irish Sea area. Following rapid erosion of the central part of the domed area in the Palaeogene, alluvial plain sedimentation was established over the Irish Sea region, developing around valleys cut through the Mesozoic sediments of the area. Deflation of the dome and accompanying faulting allowed the sea to enter the area, initially primarily through St George’s Channel in the early Oligocene and into the whole of the basin in Neogene times.
Clastic sabkhas and diachroneity at the top of the Sherwood Sandstone Group: East Irish Sea Basin
Authors: Thompson Jillian , Meadows Neil S.
Published: April 2008

The identification of early evaporite sulphate cements with a marine isotopic signature within the Ormskirk Sandstone Formation supports previous models of diachroneity at the contact of the Sherwood Sandstone Group and the Mercia Mudstone Group in the East Irish Sea Basin. Basin-wide correlations suggest that, at the onset of transgression, a range of sandflat and aeolian dune environments co-existed on the margins of the basin with marginal marine environments toward the basin centre. One of the major implications of this model is that the high quality aeolian sandstone reservoirs encountered near the top of the Ormskirk Sandstone in the southern parts of the East Irish Sea Basin have no reservoir correlatives in large areas of the basin but can be predicted on the margins.
Fault analysis of the Cheshire Basin, NW England
Authors: Chadwick R. A.
Published: April 2008

The Cheshire Basin forms a segment of the N-S trending English Channel-East Irish Sea rift. The southern part of the basin has classic half-graben geometry, with the Wem-Bridgmere-Red Rock Fault system forming its southeast margin, whereas its northern part is much more symmetrical with much smaller basin margin faults. Fault strikes also show systematic differences between the southern and northern parts of the basin. In the south, dominant NE-SW (Caledonoid) fault-strikes indicate a strong degree of basement control, particularly at the faulted southeast margin. Farther north, numerous faults with N-S strikes constitute the majority of faults within the basin. They are interpreted to have formed perpendicular to the initial basin-forming extension (roughly E-W), and suggest a much weaker basement influence. Fault displacement analysis also reveals a N-S split, with two distinct fault populations showing different fractal (power-law) distributions. In the south, extension was concentrated on the large, dominantly oblique-slip basin margin faults, whereas in the north, extension was distributed on numerous small to medium-sized dip-slip faults. The two fault populations are attributed to a variable degree of basement control. Major reactivated Caledonian basement structures controlled basin faulting in the southern part of the basin, whereas farther north the basin faults developed more-or-less independently of a less faulted, more isotropic basement. Estimates of extension magnitude, incorporating the ‘hidden’ contributions of small faults, indicate local basin extension factors in the range 1.07–1.16 (7–16%). However, because of difficulties in measuring the true heaves of the basin margin faults, these values are likely to be minimum estimates.
Characteristics of fault zones in sandstones from NW England: application to fault transmissibility
Authors: Beach Alastair , Lawson Brown J. , Welbon Alastair I. , McCallum Jean E. , Brockbank Paul , Knott Steven
Published: April 2008

Faults within outcrops of Permo-Triassic sandstones from NW England have been analysed, and their throws and fault zone thicknesses measured. These data were collected in order to provide a basis for estimating fault zone transmissibility. Logarithmic plots of fault throw versus fault zone thickness from the same localities show a positive correlation, and this relationship can be used to estimate fault zone thicknesses from fault throws derived from seismic data within similar successions. By combining fault zone thickness with laboratory-derived measurements of fault zone permeability, we show that fault transmissibilities can be estimated for input into reservoir simulation. These results can be applied to the assessment of seal potential and transmissibility in offshore oil and gas fields reservoired in Permo-Triassic sandstones. Layer thickness has a control on the fault populations, giving rise to separate population slopes for faults contained within a distinctive layer compared with those that extend outwith the layer. If layer thickness effects are not taken into account, extrapolation of a single power law trend may lead to an overestimation of the number of small faults in a population.
Controls on the evolution of the Namurian paralic basin, Bohemian Massif, Czech Republic
Authors: Kumpera O.
Published: April 2008

The Namurian A paralic molasse deposits of the Upper Silesian Coal Basin form erosion remnants of an extensive foreland basin located in the eastern part of the Bohemian Massif. This basin represents the latest stage of development of the Moravian-Silesian Paleozoic Basin (Devonian-Westphalian). The paralic molasse stage of the foreland basin evolved from foreland basins with flysch and with marine molasse. The deposition of the thick paralic molasse (Ostrava Formation) started in the Namurian A. In comparison with other coal-bearing foreland basins situated along the Variscan margin in Europe, this is characterized not only by earlier deposition, but also by a different tectonic setting. It is located in the Moravian-Silesian branch of the Variscan orocline striking NNE-SSW, i.e. perpendicularly to the strikes of more western European foreland basins. In the Viséan and Namurian, the foreland basin developed rapidly under the influence of the western thrustfold belt in the collision zone. The deposition was influenced by contrasting subsidence activities of the youngest and most external trough — Variscan foredeep — and the platform. The Upper Silesian Basin shows therefore a distinct W-E lithological and structural polarity and zonation.
A depositional and diagenetic model for the Eocene Sulcis coal basin of SW Sardinia
Authors: Dreesen Roland , Bossiroy Dominique , Swennen Rudy , Thorez Jacques , Fadda Aurelio , Ottelli Luciano , Keppens Eddy
Published: April 2008

Detailed sedimentological, mineralogical and petrographical analysis of closely spaced cored boreholes has enabled the development of a revised depositional model for the early Eocene coal-bearing Produttivo Formation of the Sulcis Basin. The deposition of autochthonous-hypautochthonous palustrine-lacustrine coals and associated carbonates was interrupted episodically by sedimentation of allochthonous lithocalcirudites and lithocalcarenites. The latter clastics display characteristic upward shoaling tidal flat sequences related to marine incursions. This interpretation is in contrast to the previously accepted fluvial origin of the detrital episodes. The coarse basal transgressive lag deposits consist of various carbonate intraclasts, dolosparite, grains consisting of calcite cement and euhedral-subhedral evaporite-bearing quartz grains. Combined stable isotope and cathodoluminiscence analysis has revealed a complex diagenetic history for the clastic deposits. The potential extrabasinal or intrabasinal provenance of the clasts, in particular the origin of the evaporite relicts, is discussed. The subtropical-tropical coastal marshes of the Florida Everglades (USA) are proposed as a possible modern analogue for the subbituminous Sulcis coals.
Chemical characteristics, mineralogical composition and rank of high sulphur coking coals of Middle Miocene age in the Gökler coal field, Gediz, Turkey
Authors: Karayigit A. I. , Whateley M. K. G.
Published: April 2008

Most Miocene coals in Turkey are of subbituminous to lignite rank. The Gökler coal field in the western part of Turkey contains mainly high sulphur coals of bituminous rank. The chemical characteristics, mineralogical composition and rank of high sulphur coking coals of Middle Miocene age in the coal field are investigated for the first time. A total of 46 channel and core samples were collected from underground mine workings and from boreholes drilled in the coal field.

The results of the proximate analyses as well as total sulphur analyses and calorific values on an air-dried basis show on average 1.2% moisture, 22.9% ash, 34.6% volatile matter, 6.9% total sulphur contents and 5850 kcal kg
−1
calorific value. X-ray powder diffraction studies of the coal samples on an air-dried basis show quartz, pyrite and calcite to be the dominant minerals; kaolinite, hydromuscovite, dolomite, gypsum, iron sulphate hydrate and rarely illite/smectite and feldspar constitute the remainder. Secondary calcite in random fractures surfaces of the coals is especially abundant in samples obtained from an area adjacent to the fault zones. The mean random reflectance values (%Rr) of telocollinite vary between 0.50 and 0.95%. These values show that the rank can be determined as a high volatile bituminous stage. In addition, these coals can form isotropic coke. Fluorescence intensities of sporinite are weak to very weak. The mean random vitrinite reflectance values within the coal field generally increase towards southern parts of the coal field. It is thought that this increase can be related to the recent hydrothermal antimony mineralization in the southeastern parts of the coal field.
Comparison of structures derived from mine workings and those interpreted in seismic profiles: an example from the Kačice deposit, Kladno Mine, Bohemia
Authors: Opluštil Stanislav , Pešek Jiří , Skopec Jiří
Published: April 2008

Five seismic profiles across the Kačice coal deposit were reinterpreted and compared with observations in mine galleries. The comparison shows that approximately 80% of normal faults with displacement exceeding 5 m detected on the seismic profiles really exist. In contrast, in only two cases have mine workings shown faults (vertical displacement 10–15 m) that have not been identified by seismic measurements. Discrepancies may be mostly explained by: (i) misinterpretation of the fault with slope of the presedimentary palaeorelief accompanied by differential compaction; (ii) virgation of faults and misinterpretation of a fault zone composed of several small faults individually below the detection limit but whose aggregate displacement is detected, giving the appearance of a single fault; (iii) faults which die away toward the overburden indicating synsedimentary movements in the deposit.
Improvements in direct coal liquefaction using beneficiated coal fractions
Authors: Barraza J. , Cloke M. , Belghazi A.
Published: April 2008

Beneficiated coal fractions from Point of Ayr coal (North Wales) were liquefied in order to determine their effect on conversion, product and metal distribution in coal extract solutions. The coal fractions were obtained in a dense medium cyclone separation unit, using aqueous solutions of Ca(NO
3
)
2
, as medium, of relative density 1.26. The original coal and the coal fractions were liquefied in an autoclave with hydrogenated anthracene oil (HAO) as solvent. Liquefaction results show an improvement in conversion for the overflow fractions over the feed coal, together with a shift in the net product distribution toward higher oils content and lower asphaltenes and preasphaltenes material in the liquid products. A marked decrease in the proportion of Al, Mg, Mn and Si was found in the extracts using overflow coal. However, Ti and Ca, which are deactivating elements of the hydrocracking catalyst used to upgrade the coal liquids, increased their proportion.
Coalbed methane migration in and around fault zones
Authors: Boardman E. L. , Rippon J. H.
Published: April 2008

One of the characteristics of all operating coalbed methane fields is the considerable variation in producibility success within these fields and even between adjacent wells, suggesting that very site-specific controls are operating. The most likely control in many coalfields is geological structure, particularly faults, which can divide the ground into fluid migration pathways and zones with bypassed, retained gas. Apart from the faulted zone itself adjacent ground will have been subject to dilational or contractional strain, and the strain profiles on either side of the fault will have their own individual permeability characteristics which may be further modified by subsequent burial history. Although any one well will be site-specific, this introductory paper seeks to describe the general ways in which modern understanding of faults and their associated strained ground can contribute to better well spacing and detailed siting and therefore a greater proportion of successful completions.
Exploration history of the offshore Southeast Sumatra PSC, Java Sea, Indonesia
Authors: Wight A. , Friestad H. , Anderson I. , Wicaksono P. , Reminton C. H.
Published: April 2008

The Offshore Southeast Sumatra Production Sharing Contract (PSC) is situated in the Java Sea, just north of Indonesia’s capital, Jakarta. It was the first to produce offshore oil in Indonesia and has so far produced over 0.8 × 10
9
BOE. The crude is low sulphur, waxy and sourced by Oligocene lacustrine shales. Over 200 exploration wells have been drilled from 1970 to the present, with 21 commercial accumulations discovered. Reservoirs are Oligocene to early Miocene in age with around 25% of the reserves in carbonates and 75% in fluvial-alluvial clastics. The main basins, Sunda and Asri, are retro-arc, N-S-oriented, asymmetric half-grabens situated between the stable Sunda Shield and the active volcanic arc on Java island.

This paper describes the acquisition of the area and traces its history from the initial discovery at Cinta-1 in 1970, through the oil price rise and fall of the 1980s, to the discovery of a new productive basin in 1987. Exploration is not only reliant on technological advances and available budgets, so other factors relevant to the history of exploration are also included.
Gravity anomalies and deep structural controls at the Sabah-Palawan margin, South China Sea
Authors: Milsom John , Holt Robert , Ayub Dzazali Bin , Smail Ross
Published: April 2008

The hydrocarbon-rich southeastern margin of the South China Sea is divided by NW-SE lineaments into a series of sharply contrasting segments distinguished by, among other things, abrupt changes in gravity patterns. The Sabah segment is bounded to the SW by the Tinjar or West Baram line and to the NE by the Balabac line at the southwest margin of the Sulu Sea. The most prominent gravitational feature of this segment is the strong freeair gravity low associated with the Sabah Trough which lies about 150 km offshore. Seismic reflection data suggest that loading by prograding sediments and gravity driven thrust sheets has depressed the extended continental crust of the South China Sea below its level of local isostatic compensation, producing the trough as a foreland basin in which sedimentation has failed to keep pace with subsidence. The load masses themselves, supported in part by the rigidity of the underlying crust and lithosphere, are above their levels of local compensation and deep Neogene sedimentary basins lie on the flanks of Bouguer and free-air gravity highs. Gravity values decrease across the Sabah coast so that the Crocker Ranges, including Mt Kinabalu, rest in rough isostatic equilibrium on presumably weaker lithosphere. The free-air gravity anomaly associated with the Sabah Trough is smaller than would have been predicted from the thickness of the water column, suggesting crustal thinning beneath the trough axis. This is not a characteristic of normal foreland basins and can therefore be assumed to predate basin formation. It can be concluded that the NE-SW trending belts of parallel gravity anomaly and geomorphology, of which the Sabah Trough is the most obvious, have been controlled by the pre-existing fabric of the crust and lithosphere of the South China Sea since they are discordant to the Palaeogene geological trends in Sabah. Reconstructions of the Tertiary history of the Sabah segment can be based on this assumption, which also suggests that sediments deposited in rift basins formed during the Palaeogene break-up of the South China margin were the source for much, if not all, of the hydrocarbon reserves of the area.
Reservoir characterization and modelling: a framework for field development
Authors: Archer John
Published: April 2008

This introductory paper seeks to highlight some of the challenges for reservoir simulation modelling that are presented by proper reservoir characterization and by appropriate cross-scaling of petrophysical parameters. The significance of tensorial representation of effective fluid-phase permeabilities is indicted by a number of examples.

In the UKCS (United Kingdom Continental Shelf) an important contribution to increased recoverable reserves is being made by the application of technology and by the reduction of reservoir description uncertainty. Some developments in reservoir simulation are indicated by examples from innovative well technologies: infill drilling locations indicated from enhanced understanding of flow directions; gas injection and gas condensate behaviour; and fractured reservoir performance.

The paper aims to provide a framework for the design and modelling of improved hydrocarbon recovery processes.
Polygonal faulting in the Tertiary of the central North Sea: implications for reservoir geology
Authors: Lonergan Lidia , Cartwright Joe , Laver Rod , Staffurth Joe
Published: April 2008

Interpretation of regional two-dimensional seismic surveys and three-dimensional seismic surveys in the central North Sea has demonstrated the existence of a pervasive polygonal network of normal faults affecting Tertiary shale-dominated slope and basin-floor depositional systems. The area affected by the faulting encompasses most areas of hydrocarbon production from Tertiary sandstone reservoirs. The polygonal fault networks were active during sedimentation and early burial. Throws measured on individual faults range from 8 to 100m, with average fault plane dips of 45°. Lengths of individual fault segments range from 80 to 1400m, and average fault spacings range from 100 to 500m. The high density and the polygonal geometry of the faults make seismic interpretation of the Lower Tertiary interval problematic, and can lead to misinterpretation of faults as apparent seismic-stratigraphic features.

The recognition of this fault system has consequences for the development of of fields in Tertiary reservoirs. The remaining hydrocarbon potential in the Lower Tertiary could be considered predominantly to be stratigraphic plays, but the presence of faults active during sedimentation and early burial implies that this play concept is too simplistic, particularly for Eocene reservoirs. The role of both syn-depositional and early-burial normal faulting on original reservoir distribution and post-depositional modification should be considered further. The presence of this fault system may also be important for secondary migration into Lower Tertiary reservoirs from Kimmeridge Clay Formation source rocks. The existence of an interconnected fault and fracture network in the low-permeability mudrocks may have provided an efficient vertical migration pathway for charging isolated lower Tertiary sandstone reservoirs. Finally, the maximum fault throws of between 50 and 100m are large enough to represent potential barriers for lateral communication in sandstone reservoirs where individual sand bodies are commonly 25–100m thick.
Mechanisms for
85
Sr migration through glacial sand determined by laboratory and
in situ
tracer tests
Authors: Williams G. M. , Hooker P. J. , Noy D. J. , Ross C. A. M.
Published: April 2008

Prediction of solute transport based on the laboratory measurement of radionuclide/sediment sorption parameters has been compared with field tracer tests involving the release of
85
Sr and a conservative tracer
131
I into a radially divergent flow field around a recharge well in a confined glacial sand aquifer. Tracer breakthrough was monitored in multi-level sampling installations. Two tests at different imposed rates of groundwater flow were conducted. At average flows up to 5 m day
−1
, the retardation of
85
Sr at a given sampling point was lower than that observed with an average flow rate of 0.5 m day
−1
, suggesting a kinetic control on sorption. Sequential selective leaching was also undertaken to study the geochemical phases responsible for sorption. In a core consisting predominantly of medium sand, approximately 80% of the
85
Sr was present in ion exchange sites, with 12% in the carbonate phase. The remaining 8% was recovered easily by extraction with distilled water. Kinetic data for Sr sorption on sand and silt core material suggested a two-stage process which could be fitted by two empirical sorption/desorption rate constants. These were used to simulate the effect of kinetics of sorption on the breakthrough curves for strontium. The retardation of
85
Sr at the lower flow rate was in relatively good agreement with laboratory values derived from batch sorption experiments lasting several days. At the high flow rate, longitudinal dispersivity α
L
for
85
Sr was larger than that for
131
I, but this discrepancy reduced at the lower flow rate where some convergence to the
85
Sr values was observed. A possible explanation is that at the high flow the opportunity for
131
I diffusion into relatively static porewater was limited; whereas with solutes moving at a lower rate there was a greater opportunity for diffusion into ‘dead end’ pores.
Detection of point sources of contamination by chlorinated solvents: a case study from the Chalk aquifer of eastern England
Authors: Misstear B. D. R. , Rippon P. W. , Ashley R. P.
Published: April 2008

Groundwater contamination by chlorinated solvents such as trichloroethene is of increasing concern in the UK. This paper describes a case study of chlorinated solvent contamination of the Chalk aquifer at a groundwater supply source in eastern England. The investigations comprised two phases: the first phase focused on the extent and nature of the contamination within the main Chalk aquifer (both in the fissures and in the Chalk matrix); and the second phase targeted the sources of contamination through detailed sampling of the unsaturated drift at suspect sites. The volatile nature of the organic contaminants required special hygiene procedures during drilling and sampling to avoid cross-contamination between boreholes, or loss of contaminants in the samples collected. Four potential sources of contamination were identified within an industrialized area about 1 km up hydraulic gradient from the contaminated well. However, the contamination was found to be extremely localized, with closely spaced investigation boreholes at individual sites giving highly varied results. To be successful, investigation boreholes had to target precise locations where these chemicals were known or suspected to have been used or stored. Therefore, a key aspect of the investigation was a solvent usage survey prior to each phase of drilling.
Morphology and sedimentation on the Hebrides Slope and Barra Fan, NW UK continental margin
Authors: Armishaw Julie E. , Holmes Richard W. , Stow Dorrik A. V.
Published: April 2008

Rapidly deposited Neogene sands and Pleistocene glacigenic sediments originating from NW Britain were transported across the shelf and downslope to the Barra Fan depocentre. In contrast, the Holocene interglacial shelf environment is typified by sediment winnowing, sea-floor polishing and transport of relatively small volumes of sediment along the shelf to the northwest. Interpretation of swath bathymetry, 32 kHz side-scan sonar, 3.5 kHz pinger, sea-bed photography and near-bottom current survey data on the shelf edge and slope provides good morphological evidence for both downslope and alongslope sedimentary processes on this composite slope-front fan. On the northern fan a corrugated shelf edge gives rise to a network of channels on the upper slope, which incise into Pleistocene and older sediments and funnel sediment to middle and lower fan. An underpinning variable topography on the fan bulge originates from major and minor slide masses, sediment creep and debris flows. These are reworked by spatially and secularly variable strong-to-weak bottom currents and redistribute material across and down fan forming transverse and linear bedforms, draped sandy contourite sheets and moulded drifts.
Mechanical properties of terrigenous muds from levee systems on the Amazon Fan
Authors: Marc Audet D.
Published: April 2008

The mechanical stability of channel levees may be an important control on channel avulsion and sediment distribution patterns in submarine fans. Levee stability depends on the shear strength of the levee sediments, which in turn depends on how the sediments are deposited and compacted. Long, continuous sections of levee sediments on the Amazon Fan were recently cored during Leg 155 of the Ocean Drilling Program. The porosity-depth profiles from Sites 939 and 944, situated on the levee of the Amazon Channel, were analysed using a theoretical compaction curve derived from soil mechanics theory. By fitting the theoretical compaction curve to porosity-depth data, estimates of the compression index and the void ratio at 100 kPa effective stress were determined. The compression index of the levee sediments was estimated to be 0.58–0.68. The mechanical parameters of the levee sediments are consistent with published geotechnical data for remoulded clays. Undrained shear strengh data from Leg 155 were analysed using an infinite slope analysis to determine the slope angle for failure as a function of burial depth. The variations in the shear strength measurements were bounded by critical slope angles of 1–3°. The higher bound of 3° tends to be consistent with maximum slopes measured near the levee crest near Site 938 on the Blue channel. The lower bound of 1° appears to be consistent with the slope of the sediment deposit blanketing the slope away from the levee crest. The top 55 m of Site 941, sited in the Western Debris Flow, show a relatively undisturbed, normally compacted porosity profile, even though the sediments show soft-deformation features. In contrast, the core samples between 55 and 68 m show lower porosity values compared with the porosity profile from Site 939. This low-porosity zone was interpreted as a zone of reworked or sheared sediment that could be the failure surface of a translational slide.
The Southeast Greenland glaciated margin: 3D stratal architecture of shelf and deep sea
Authors: Clausen Lene
Published: April 2008

A seismic stratigraphic study of the Upper Neogene and Pleistocene shelf and deep-sea deposits of Southeast Greenland is presented. The depositional environment was controlled by glacial, turbidity current, and contour current processes. Below the mid- and outer shelf a Tertiary sedimentary wedge, as much as 1.7 km thick, is resting on a seaward-dipping volcanic acoustic basement. A lower marine part is separated by a regional unconformity, SB-A, from two seismic sequences of early Pliocene to Pleistocene prograding clinoforms. SB-A is surmised to represent a seaward-dipping palaeo-relief surface, accentuated by modest submarine erosion related to a sea-level lowering. The overlying two Sequences x and y reflect shelf-edge progradation in front of grounded ice during periods of maximum glaciation. The topset beds of the youngest sequence, possibly of Pleistocene age, are characterized by six or more sub-horizontal, landward-dipping internal unconformities, taken to reflect individual glacial cycles of grounded ice erosion. The present-day shelf is overdeepened, landward dipping, and traversed by troughs. These features are characteristic of a shelf sculptured by grounded ice. The position of the transverse troughs, reflecting the positions of former icestreams, seems to have been more or less permanent since the late Neogene. The shelf progradation has been higher in front of the troughs than in front of adjacent banks, resulting in the development of trough-mouth fans (TMF). The strata continue seawards below the shelf break across a crustal monoclinal flexure to the deep sea. Three seismic sequences have been identified within the late Miocene and Pleistocene deep-sea sedimentary succession on the continental rise. They are bounded by unconformities of mid-Pliocene, early Pliocene, and (?) late Miocene ages. The oldest sequence is interpreted as basin floor fans, probably linked to a sea-level lowstand. The two youngest sequences were deposited from interplay of contour and turbidity currents during glacial periods, and they form large sediment ridges on the sea floor, oriented almost perpendicular to the continental rise, nucleated on the older sequence. Inter-ridge channel-levee complexes recognized within the youngest sequence were deposited from turbidity currents. The major turbidity channels are prolongations of the transverse shelf trough-trough-mouth fan systems. A moat zone, at the base of the continental slope, reflects the position of strong modern contour currents. Appreciable contourite deposition did not commence before the early Pliocene, and was probably linked to glaciation of the shelf and onset or intensification of the Labrador Sea Water deep current.
Recent geological processes in the Central Bransfield Basin (Western Antarctic Peninsula)
Authors: Ercilla G. , Baraza J. , Alonso B. , Canals M.
Published: April 2008

Acoustic character of the near-surface geological features in the Central Bransfield Basin, located between the northwestern Antarctic Peninsula and the South Shetland Islands, are products of recent sedimentary, volcanic and oceanographic processes. A platform, between 250 and 750 m water depth, is characterized by a highly rough surface with prolonged and hyperbolic reflections, which are interpreted as a result of ice-sheet grounding that occurred during the last glacial advance and iceberg scouring. Locally, this surface is draped by thin, stratified sediments deposited from suspension during the present interglacial stage. The upper slope shows prolonged and hyperbolic reflections without subbottom returns that form an irregular surface resembling slide scars and slumped material. Futher downslope, sediments become stratified, and individual, chaotic or semi-transparent slump masses occur locally, within the eroded valleys and in inter-valley areas. Basin sediments are defined by stratified, semi-transparent and chaotic deposits that correspond to a variety of mass-transport, volcanic and oceanographic processes. Mass-transport and volcanic processes develop slump masses, turbidite deposits and volcanic edifices of varying characteristics. The activity of slope-parallel bottom currents builds sediment drifts between the volcanic edifices and the base of the Antarctic Peninsula slope.
Late Glacial to Recent accumulation fluxes of sediments at the shelf edge and slope of NW Europe, 48–50°N
Authors: Hall I. R. , McCave I. N.
Published: April 2008

Data were collected on magnetic susceptibility, volcanic tephra abundance, coarse silt mean grain-size, and total and fine inorganic carbon for a suite of cores collected from the NW European Margin between 48 and 50°N. Age models were constructed based on accelerator mass spectrometry (AMS)
14
C dating and stratigraphy based on δ
18
O of foraminiferal carbonate together with correlatable instantaneous marker horizons of the Vedde Ash and the ‘Heinrich’ layers of ice-rafted detritus. Glacial vertical flux over the transect (2200–4500 m) on the open slope of Goban Spur yields an approximately 15 cm ka
−1
deposition rate. This decreases in the Holocene to a present deposition rate of between 3 and 6 cm ka
−1
. Deposition rates within the Porcupine Seabight are in close agreement with those seen at a similar depth on the open slope, whereas enhanced resuspension and sediment focusing leads to an approximate doubling in the depositional rate of hemipelagic sediment found near the base of King Arthur Canyon. Carbonate burial flux shows a maximum in the early part of isotope stage 2, during the deglaciation (17.5 ka to 12 ka) and in the late Holocene. This is seen at depths shallow enough to suggest it is not due to dissolution. It therefore could reflect enhanced productivity. Changes in current speed inferred from the sortable silt component of the sediment suggest slow currents during isotope stage 2 increasing irregularly through to a maximum just before the Younger Dryas, decreasing sharply in the early Holocene, then increasing again in the late Holocene. Rates of deposition at OM-2K follow this pattern fairly well for much of the time, suggesting lateral flux is important. However, during isotope stage 2 there is high flux of sediment with low current speed, suggesting supply from ice-rafting or directly downslope.
Recharge: the key to groundwater pollution and aquifer vulnerability
Authors: Robins N. S.
Published: April 2008

Recharge is pivotal to understanding the processes by which groundwater pollution can occur. It is implicit in the classification of aquifer units according to their vulnerability to pollution. The management of both groundwater resources and of individual groundwater sources cannot sensibly be undertaken without some knowledge of recharge: its quantity, its seasonality and, above all, the different routes through the sub-soil and the unsaturated zone by which it can occur. However, current estimates of recharge, other than on a research site basis, may be poor, both in the UK and overseas. This volume provides a review of current research into these issues; this introductory paper attempts to highlight the thread throughout all of this work which collectively provides the basic information in support of the current and future management of groundwater resources and sources.
Groundwater recharge and pollutant transport beneath wastewater irrigation: the case of León, Mexico
Authors: Chilton P. J. , Stuart M. E. , Escolero O. , Marks R. J. , González A. , Milne C. J.
Published: April 2008

Agricultural irrigation with wastewater is widely established in Mexico. The city of León is the centre of the Mexican tanning industry, and produces wastewater with a significant component of industrial effluent. The city is one of the fastest growing in Mexico and is highly dependent on groundwater for public supply. Much of this is drawn from aquifers around the city, including those beneath the wastewater area. The sources of recharge to these aquifers and the types of pollutants are reviewed. Regionally, groundwater levels are falling as a result of excessive groundwater abstraction but, within the area of wastewater irrigation, groundwater levels are maintained close to the ground surface. Groundwater sampling from existing boreholes, surface geophysics, soil sampling and the drilling of cored investigation boreholes have been able to characterize a body of shallow, polluted groundwater beneath the wastewater area, and contrast this with the regional groundwater quality. The most immediate threat to public supply from pollutants originating in the wastewater is posed by salinity. The predicted consequences of various management options for reducing the impact of wastewater on the quality of deeper groundwater are briefly discussed.