bluuebunny/crossref_metadata_2025 huggingface dataset:
An update on British Tonsteins
Authors: Spears D. A. , Lyons P. C.
Published: April 2008

Tonsteins are thin mudstone beds composed of kaolinite that formed from the alteration of volcanic ash in coal-forming environments. In the Coal Measures of Britain, tonsteins have been recognized as volcanic in origin based on bedform, volcanic textures, field relationships with other volcanics, distinctive volcanic minerals and an igneous geochemistry. The sharp contacts, together with a contrasting composition with adjacent sediments and lateral continuity, are diagnostic of an altered air-fall volcanic ash. Passage into less altered volcanics and into a K-bentonite have both been shown in Britain. A more direct determination of volcanic origin is possible from the identification of volcanic minerals, whole-rock geochemistry and analyses of silicate melt inclusions in volcanic minerals such as
β
quartz. Once a volcanic origin is established the stratigraphic value of a tonstein is enhanced. Immobile trace elements in tonsteins also provide information on the tectono-magmatic setting of the parent volcano. Two tonstein groups are identified in the Coal Measures of Britain, one formed from basic (basaltic) ash of local origin and the other from acid (rhyolite or rhyodacite) ash, probably associated with distant Plinean or ultraplinean eruptions at a destructive plate margin to the south or southeast.
Coals of Greece: distribution, quality and reserves
Authors: Koukouzas C. , Koukouzas N.
Published: April 2008

Greek coals occur in a number of sedimentary basins and range in age from Eocene to Quaternary. The petrographic data indicate a wide variation in petrographic and chemical composition. The rank ranges from the transition zone peat-lignite to subbituminous. There are no deposits of hard coal in the country. Lignite constitutes the most abundant type of coal in Greece and the most important of the Greek lignite deposits formed during the Pliocene and Pleistocene in shallow lakes and marshes of closed intramontaine basins (Ptolemais, Florina, Drama in Macedonia, northern Greece and Megalopolis in Peloponnesus, southern Greece). The proved lignite reserves are currently estimated at 6750 Mt, excluding the 4300 Mm
3
of ‘Phillipi’ peat in Macedonia. There, 58% (about 3900 Mt) is considered to be economically recoverable. The probable and possible reserves are estimated to be of the order of 4000 Mt. The Kozane-Ptolemais-Amynteo-Florina basins in Macedonia contain most (about 64%) of the nation’s coal resources. These lignites, which are all already being exploited, have a very low calorific value (at Ptolemais-Amynteo, 1400 kcal kg
−1
; at Megalopolis, 900 kcal kg
−1
) and high ash and low sulphur contents. The lignite production for 1992 was over 54 Mt. the greatest centres of lignite production are in Macedonia, at the opencast mines of Ptolemais and Amynteo, and in Peloponnesus, at the opencast mine of Megalopolis. The vast majority (98%) of the extracted lignite is used for electricity generation and feeds power plants which have a total capacity of 4533 MW. The lignite-based power plants account for more than 720f the total electricity generation of the country. Today, through detailed geological exploration and evaluation, efforts are being made to locate and develop other lignite deposits throughout Greece.
European Community energy policy: import dependency and the ineffectual consensus
Authors: Wright Philip
Published: April 2008

The lack of an effective European Community (EC) energy policy is discussed in the context of the different degrees and kinds of energy import dependency faced by the different member states. The way in which these contrasting energy economies have impinged on the evolution of EC energy policy, rendering it largely ineffectual, is then explored over the period 1974 to 1992.

The general theme is illustrated by focusing on the evolution of EC policy towards the coal industry, identifying how it has been impotent in the face of national government policies and perverse in terms of its recent outcomes. This argument is supported by data comparing the productivity performances of the different EC coal industries.
Unusual enrichment of U, Mo and V in an Upper Cretaceous coal seam, Hungary
Authors: Tomschey Otto
Published: April 2008

The Late Cretaceous coal basin of Ajka lies in the Bakony Mountains, Transdanubia, Hungary, above Triassic-Jurassic dolomites-limestones and/or Upper Cretaceous calcareous marly sediments. The concentrations of U, Mo and V are unusually high (U = 80 ppm, Mo = 138 ppm and V = 600 ppm on average in ash). Analyses were carried out to determine the trace metal concentrations in the various solid phases within the coal rock and the results compared with the U, Mo and V contents of fly ash from the mine-mouth thermal power plant.
Origin and distribution of sulphur in the Neogene Beypazari Lignite Basin, Central Anatolia, Turkey
Authors: Whateley M. K. G. , Tuncali E.
Published: April 2008

During the Miocene a number of fault-bounded basins developed in Central Anatolia, Turkey. These basins were filled initially with coarse clastic material. Upward fining of the clastics during basin-fill, with an increase in the amount of clay and carbon content, led to the development of relatively shallow limnic basins in which extensive peat deposits accumulated. One such basin at Çayirhan, near Beyparazi, contains thick laterally extensive lignite seams. These lignites are characterized by their high sulphur content (up to 8.20n an air-dried basis). It is suggested that hydrothermal processes are responsible for the increased sulphur contents of the Çayirhan lignites, resulting from sulphate and sulphide precipitation. The mineral matter contains ubiquitous zeolites. The presence of heulandite in the first seam and analcime in the second seam may be a result of depth-temperature control on the distribution of zeolites in the lignite; but these differences are more probably the result of variations in the chemistry of the circulating fluid. Study of the sulphur content reveals three types of sulphur distribution, namely, vertical variation within individual seams, variation between seams and lateral variation across the basin. The first two are related to variations in the chemistry of the mineral matter in the lignite, and the last is probably related to structural/topographic control of the mire at the time of formation.
Fossil indicators of nutrient levels. 1: Eutrophication and climate change
Authors: Brasier M. D.
Published: April 2008

Both phosphorus and nitrogen are elements essential to life. Availability of these biolimiting nutrients therefore exerts a major control on the carbon cycle through ocean productivity, bringing about changes in ocean-atmosphere chemistry and climate. This review begins with a brief account of the biological importance of phosphorus and nitrate to the cell, and introduces current terminology relating to the interlinked carbon-nutrient cycles in the oceans. Nitrate-limited, eutrophic ecosystems are associated with modern upwelling zones, characterized by high rates of delivery of new phosphorus, high rates of new primary production and export production. Fossil indicators include high accumulation rates of biogenic silica, apatite, baryte and organic matter, plus non-spinose, smaller planktonic foraminifera. Examples from biomineral chemistry include indications of high Ba/Ca, high Cd/Ca and increased differences between δ
13
C in planktonic and benthic foraminiferal test calcite. Such eutrophic indicators are shown to have peaked during glacial phases in the Quaternary, supporting a model in which Milankovitch-related reductions in solar isolation influenced the availability of nutrients, increasing primary productivity and lowering the levels of atmospheric carbon dioxide.
Modelling of vapour-liquid-liquid equilibria of CO
2
-crude oil mixtures
Authors: Jørgensen Marianne , Stenby Erling H.
Published: April 2008

At temperatures close to the critical temperature of carbon dioxide, some crude oils form three phases when mixed with CO
2
. The objective of this work was to investigate whether the three-phase behaviour of CO
2
-crude oil mixtures can be predicted with the Soave-Redlich-Kwong equation of state. In the description of the C
7+
-fraction, a previously described characterization method was applied. In this characterization procedure, the critical properties and the acentric factor of single carbon number groups within the plus fraction are estimated on the basis of measurable physical properties. By comparison of experimental and calculated data, it is shown that no, or very little tuning of the EOS parameters is necessary to obtain representative predictions of three-phase regions. In addition it is demonstrated how too severe tuning leads to very erroneous results in the simulation of phase diagrams. Finally, it is shown how the described method fails to predict the three-phase region of a very heavy oil with a small three-phase region at the given temperature.
A new approach to oil rim development
Authors: Zakirov S. N. , Shandrygin A. N. , Romanov A. S.
Published: April 2008

Recovery factors for oil rims are usually low. This paper deals with the possibility of improving the recovery efficiency by means of various combinations of water and/or gas injection. These cases are evaluated both experimentally and by mathematical simulation. The best results are obtained by simultaneous injection of water and gas. The recovery depends on the water-gas injection ratio.
Commercial polymer injection in the Courtenay Field, 1993 update
Authors: Putz A. , Pedron B. , Bazin B.
Published: April 2008

The Courtenay reservoir has an elongated shape and lies at a depth of 600 m. With an oil viscosity of 40 cP, fresh formation water and a temperature of 30°C, conditions are favourable for polymer injection. In July 1989 a project was started with 18 producers forming three adjacent polygons (pore volume 640 000 m
3
) and four injection wells. A 900 ppm polyacrylamide solution diluted with field water was injected at a total rate of 380 m
3
/day. With 84% of pore volume injected, the project has now reached a mature stage and the polymer concentration is being tapered off. The total production of oil confirms original expectations, and the operation is profitable.

Oil bank build-up has been observed in 14 production wells. An additional 265 000 bbl or 6.6% of pore volume has been already recovered in addition to the extrapolated primary recovery, for a polymer/oil ratio of 1.16 kg/bbl. With a total cost of $12/bbl the project is clearly profitable.

Simulation of the project performance with a 3D, three-phase simulator including polymer and tracer options resulted in a good match of total oil production. However, for most wells the actual amount of polymer produced is lagging behind the values predicted by the simulator.

Detailed analysis of the polymer produced by well CY 55 confirmed that no degradation had occured.
Devonian precessional and other signatures for establishing a Givetian timescale
Authors: House Michael R.
Published: April 2008

Palaeozoic radiometric dates are so isolated and crude as to offer little numerical precision in stratigraphy. In a Givetian sequence of pelagic micrites in the Montagne Noire of southern France there is a succession of small-scale microrhythms which appear to represent precessional signatures. Correlations can be made with other sections in the Tafilalt of southern Morocco and, for the late Givetian, in the Marble Cliff Beds of north Cornwall. Now that the IUGS has approved boundaries defining the upper and lower limits of the Givetian it is possible to estimate the number of putative precessional signatures for the whole Givetian and, using the calculation of periods for these in the Devonian, to estimate the duration of the Givetian and its conodont zones independantly from radiometric dates.

Graphical correlation techniques are used to establish a time framework for the Givetian and this is used to estimate the duration of zones in relation to the preliminary precessional scale, and hence to estimate their duration in real time. Biological changes and sedimentary events can similarly be constrained against a scale for the Givetian. It is suggested that such techniques, using a stage for a base, is likely to be useful long before continuous orbital forcing timescales (OFT) can be established. It would be a start in eliminating present crude estimates of the length of stages based on the false presumption that zones within them are of equal duration. Given boundaries, defined internationally by IUGS at Global Stratotype Section and Points, such OFT scales would enable events and zonal durations to be given in relation to OFT graphic composite scales and on the basis of estimated precessional signatures.
Cyclostratigraphy, Quo Vadis?
Authors: Fischer Alfred G.
Published: April 2008

Climatic oscillations forced by orbital variations left their imprint not only on Pleistocene ice regimes, as postulated by Croll (1875,
Climate and Time in their Geological Relations
, Appleton, New York) and by Milankovitch (1941,
Belgrade, Serbian Academy of Science
,
133
), but also on the sedimentary record as postulated by Gilbert (1895,
Journal of Geology
,
93
, 515–533), and not only in glacial times but also, and particularly sharply, in times of greenhouse climates. The amenable facies are those characterized by relatively continuous sedimentation, though in carbonate platforms interruptions constitute the Milankovitch signal. The recording mechanisms include variations in biogenic components and biotic activity, and direct expressions of physical and chemical sedimentation.

So far, cyclostratigraphy has largely remained a demonstration of principle. Applications to geochronology are in their beginnings. The chronological refinement promised by cyclostratigraphy demands quantities of stratigraphic data orders of magnitude beyond those of conventional stratigraphy. Progress in application will therefore depend on combining automated scanning devices (well logs, core and sample logging techniques of various sorts) capable of providing simple variation graphs of long sedimentary sequences, with detailed paleontological and magnetostratigraphic studies. The existence of the cycle hierarchy will provide some protection against chronological errors induced by cryptic gaps in the record, as will the reproduceability of results in distant sequences and different facies, and the possible finger-printing of individual cycles by magnetic character.
Fractionation of pyrrolic nitrogen compounds in petroleum during migration: derivation of migration-related geochemical parameters
Authors: Li Maowen , Larter S. R. , Stoddart D. , Bjorøy M.
Published: April 2008

Analysis of a range of crude oils and source rocks appears to indicate that primary and secondary oil migration has a strong impact on the distribution of pyrrolic nitrogen compounds in reservoired petroleum. The migration effects controlling the composition of pyrrolic nitrogen compounds recognized tentatively in this study include (a) the relative enrichments of alkyl carbazoles to alkylbenzocarbazoles, (b) nitrogen-shielded isomers to nitrogen-exposed isomers, and (c) higher homologues to the lower homologous species. A suite of molecular migration parameters based on chemical compositions of pyrrolic nitrogen compounds in crude oils have been proposed. If substantiated in more case history studies, these parameters are potentially useful in petroleum population mapping.
Detailed geological studies of hydrothermal fields in the North Atlantic
Authors: Krasnov S. G. , Cherkashev G. A. , Stepanova T. V. , Batuyev B. N. , Krotov A. G. , Malin B. V. , Maslov M. N. , Markov V. F. , Poroshina I. M. , Samovarov M. S. , Ashadze A. M. , Lazareva L. I. , Ermolayev I. K.
Published: April 2008

Sidescan sonar and TV/photo surveys, TV-controlled sulphide grab sampling and sediment sampling have been carried out at the TAG and MARK hydrothermal fields of the Mid-Atlantic Ridge during research cruises of the Sevmorgeologija Association, St Petersburg. Detailed mapping of the MARK field (23°N) allowed contouring of the massive sulphide bodies. The largest of them are Cu-enriched and the smallest zincenriched. Sulphides of the TAG field (26°N) active mound appear to be Cu-rich in its central and Zn-rich in its marginal parts. Sampling of the inactive Mir hydrothermal mound of the TAG field revealed an enrichment in Cu in its northern part and an abundance of silica in the south. This mound and especially the north hydrothermal zone, both presently inactive, determined the metal distribution in TAG sediments during the last 10 000–13 000 years. Extensive Cu-rich sulphide deposits were also discovered and sampled near 14°45′N. The dominance of Cu over Zn in mature Mid-Atlantic Ridge hydrothermal deposits, arising at late stages of their formation, can probably be explained by dominant leaching of Cu from basalts at advanced stages of development of the hydrothermal systems and/or by increasing the efficiency of Cu sulphide deposition in the course of formation of the ore body.
Preliminary observations on biological communities at shallow hydrothermal vents in the Aegean Sea
Authors: Dando P. R. , Hughes J. A. , Thiermann F.
Published: April 2008

Hydrothermal vents, at depths varying from the littoral zone to water depths of 115 m, have been explored around the islands of Milos and Santorini in the Hellenic Volcanic Arc. The biota were surveyed by scuba divers and with a remote operated vehicle as well as by soft-bottom sampling with grabs and corers. No species specific to hydrothermal areas were found at any of the sites investigated. Animals in the immediate vicinity of the vents belonged to opportunistic species, such as the polychaetes
Capitella capitata, Microspio
sp. and
Spio decoratus
. The nassariid gastropod
Cyclope neritea
was the dominant macrofaunal species found in the bacterial mat areas at Milos which overlay hot brine seeps. At all rocky hydrothermal sites deeper than 35 m water depth the echiuran
Boniellia
cf.
viridis
was observed. Around the periphery of the seeps the meiofaunal community was dominated by the nematode
Onchlaimus camplyoceroides
. Few nematodes were found in the centre of the hydrothermal brine areas. At Santorini the bacteria at the venting sites were dominated by iron bacteria, whereas at Milos large globular sulphur bacteria,
Achromatium volutans
, covered the hydrothermal brine seeps. Unlike deep-sea vents, little of the biomass production was due to symbiotic associations between animals and chemoautolithotrophic bacteria, although a few stilbotnematine nematodes were found at the periphery of the brine seeps at Milos. Macrofaunal biomass reached a maximum of 80 g m
−2
around the vents, compared with ≥c 500 g m
−2
at hydrothermal vents elsewhere. Much of the bacterial biomass appeared to be exported from the sites.
Lipid characteristics of hydrothermal vent organisms from 9°N, East Pacific Rise
Authors: Rieley Gareth , van Dover Cindy L. , Hedrick David B. , White David C. , Eglinton Geoffrey
Published: April 2008

Lipid compositions are reported for three distinctive deep-sea hydrothermal vent invertebrate species collected around 9°N East Pacific Rise:
Riftia pachyptila
Jones, a vestimentiferan tubeworm;
Bathymodiolus thermophilus
Kenk and Wilson, a mussel; and
Halice hesmonectes
Martin
et al.
, an amphipod crustacean. The lipid compositions of all these organisms were dominated by components characteristic of diets based on bacteria, with only very minor contributions from carbon derived from the oceanic photic zone. In all the organisms studied, large abundances of n-7 fatty acids, polyunsaturated fatty acids with unsaturations separated by more than one methylene bond, and sterol distributions dominated by cholesterol were observed. Branched fatty acids were generally of low abundance, whereas polyunsaturated fatty acids separated by single methylene groups were either absent, as in the case of
R. pachyptila
, or in very low abundance, as in the case of
B. thermophilus
and
H. hesmoncetes
. Monounsaturated fatty acids were the most abundant component of
R. pachyptila
lipids, whereas non-methylene interrupted fatty acids were particularly abundant in the lipids of
B. thermophilus
(up to 450f total fatty acids). The lipids of
H. hesmonectes
were dominated by storage lipids (e.g. wax esters). Stable carbon isotope analyses of individual sterols from the organisms examined allow specific sources to be proposed for these biochemicals. The δ
13
C values of sterols from
R. pachyptila
were consistent with
de novo
biosynthesis, whereas that of cholesterol from
B. thermophilus
corresponded to that from marine phytoplankton. The δ
13
C values of sterols from
H. hesmonectes
fell into two different groups and suggest that at least two distinct sources of sterols are available to these crustacea in the vent ecosystem, one of which derives from phytoplankton. Overall, the combination of the interpretation of lipid structure and distribution with compound specific isotope analyses can lead to valuable insights into trophic relationships within the deep-sea hydrothermal ecosystem.
Hyperthermophilic enzymes: biochemistry and biotechnology
Authors: Cowan Don A.
Published: April 2008

Deep submarine hydrothermal vent habitats have already proved to be rich sources of novel hyperthermophilic micro-organisms, most of which belong to the third super-kingdom, the Archaea. These organisms, many of which survive at temperatures at or above 100°C, contain novel macromolecules and metabolic systems which represent a vast resource for fundamental molecular and physiological studies, and for potential exploitation in biotechnology. The one guaranteed property of enzymes isolated from extremely thermophilic micro-organisms is their thermostability. Resistance to heat denaturation also ensures resistance to a number of other denaturing influences (detergents, organic solvents). This characteristic of hyperthermophilic enzymes is the most likely basis for the development of new biotechnological applications. The ability of thermostable enzymes to function in non-aqueous and mixed-phase solvent systems is a particularly useful property. Only a limited number of hyperthermophilic enzymes have found application in specialist biotechnological applications. Hyperthermophilic DNA polymerases and other DNA-modifying enzymes have already contributed significantly to the development of recombinant DNA technology and gene-based diagnostics. Other hyperthermophilic enzymes have obvious potential in the growing area of biotechnology, whereas more distant but no less exciting possibilities lie in those archaeal enzymes which are wholly novel to these organisms.
Basin inversion in the Gulf of Suez: implications for exploration and development in failed rifts
Authors: Knott S. D. , Beach A. , Welbon A. I. , Brockbank P. J.
Published: April 2008

The Gulf of Suez (Clysmic) rift is a classic and well documented extensional province and has many similarities to the North Sea rift to which it is often compared. New structural mapping and fault analysis in western Sinai have shown that post-rift crustal shortening and inversion occurred across the Gulf of Suez, demonstrated by the presence of reverse faults formed as a result of overturning of normal faults, widespread sub-horizontal hydraulic fractures due to vertical stretching, low-angle thrusting and associated folding in the hangingwalls of normal faults, and steepening of bedding dips adjacent to basement stress risers, in some cases overturning stratigraphy. These features show the effect that superposition of inversion on extensional structures has on the geometry of the bedding in footwalls and hangingwalls. Observations and data from outcrop can be used to assist in the interpretation of similar structural relations in the North Sea, where post-rift contraction is also seen. Recognition of inversion-related structures is important in exploration, appraisal and development of North Sea reservoirs, for example, in estimating palaeobathymetry of Late Jurassic depocentres, in constructing cross-sections for reservoir zonation, and in evaluating fault seal and reservoir compartmentalization. Shortening in the Gulf of Suez occurred immediately after rift failure and was probably a gravity-driven process. Similar processes may have occurred in other failed rifts.
Quantification of Tertiary exhumation from sonic velocity data, Celtic Sea/South-Western Approaches
Authors: Menpes Robert J. , Hillis Richard R.
Published: April 2008

Sonic velocities from the Danian Chalk, the Upper Cretaceous Chalk, the Lower Cretaceous Greensand/Gault Clay, and the Triassic Mercia Mudstone were used to quantify apparent exhumation (i.e. amount of missing section) in the Celtic Sea/South-Western Approaches (southern Irish, south-western United Kingdom, and north-western French continental shelves). Analysis of all four of these stratigraphic units yield similar results. Since it is unlikely that sedimentological and/or diagenetic processes are responsible for similar amounts of overcompaction in the chalks, shaly sandstones and shales analysed, burial at depth greater than that currently observed is the most likely cause of overcompaction (anomalously high velocities). The use of lithologies other than shales in maximum burial-depth/exhumation studies is thus validated. The consistency of results from units of Triassic to Danian age suggests that Tertiary exhumation was of sufficiently great magnitude to mask any earlier Mesozoic periods of exhumation, and that the maximum Mesozoic-Cenozoic burial-depth in the Celtic Sea/South-Western Approaches was attained prior to Tertiary exhumation.

The recognized inversion axes of the Brittany Basin, South-West Channel Basin and North Celtic Sea Basin are highs in apparent exhumation, however highs in apparent exhumation of approximately 1 km also occur in the uninverted St. Mary’s and Plymouth Bay Basins, and on the margins of the Armorican and Cornubian Platforms and the Pembroke Ridge. Tertiary exhumation was regional and not restricted to inversion axes, and thus had a thick-skinned origin. Heterogeneous lithospheric compression is the geodynamic model preferred to account for the regional exhumation of the Celtic Sea/South-Western Approaches. The identification of regional exhumation of approximately 1 km has important implications for modelling thermal maturation in the Celtic Sea/South-Western Approaches, with source rocks previously believed to be immature shown to be potentially mature for oil generation.

When corrected for exhumation, the post-rift sequence in the Celtic Sea/South-Western Approaches area shows relatively little localization over the syn-rift Jurassic-Lower Cretaceous sequence, suggesting that during basin formation, the lower lithosphere, thermal re-equilibration of which controls post-rift subsidence, did not experience localized thinning on the scale of the syn-rift basins.
The inversion history of the northeastern margin of the Broad Fourteens Basin
Authors: Hooper Robert J. , Goh Leng Siang , Dewey Fiona
Published: April 2008

The Broad Fourteens Basin experienced a long and complicated developmental history, involving extension, salt tectonics, inversion and subsidence, that began in the Triassic and continued into the middle Tertiary. Inversion in our study area on the northeast margin of the basin was accommodated not only by backward expulsion of the basin-fill (creating a series of northeast-vergent thrusts and related lobate folds) but also reactivation of basement faults. Restorations indicate that the basin-fill did not behave independently of the basement during inversion. At least 2200 m of inversion-related basement uplift must have occurred at the basin margin in addition to backward expulsion of the basin-fill. The most important factors controlling the final ‘inversion style’ appear to be the pre-inversion structural configuration of the margin and the resolved inversion direction.
Extensional tectonics in the Jeanne d’Arc Basin, offshore Newfoundland: implications for the timing of break-up between Grand Banks and Iberia
Authors: Driscoll Neal W. , Hogg John R. , Christie-Blick Nicholas , Karner Garry D.
Published: April 2008

Using seismic reflection and exploratory well data from the Jeanne d’Arc basin, offshore Newfoundland, we examined the link between unconformity generation and the onset of seafloor spreading between the central Grand Banks and Iberia. A prominent unconformity developed across the entire basin, previously interpreted as a ‘break-up’ unconformity, is reinterpreted as a late Barremian/early Aptian rift-onset unconformity on the basis of the stratal geometry and lithofacies. The rotation and divergence of seismic reflectors above this unconformity attest to differential subsidence documenting an episode of extension and block rotation within the basin at this time. Our seismic sequence analysis suggests that rifting and block rotation continued in the Jeanne d’Arc basin until at least late Aptian/early Albian time.

The onset of seafloor spreading between the central Grand Banks and Iberia is uncertain because of limited marine magnetic and drilling data (ODP & DSDP), and the existence of the Cretaceous magnetic quiet zone along the margin. However, recent studies indicate that magnetic anomaly M0 (118 Ma) is not well resolved north of the Newfoundland Seamounts within the Newfoundland basin and is not present north of the Figueiro fracture zone along the conjugate Iberian margin. This suggests that seafloor spreading between the northern portion of the Newfoundland basin and the northern Iberian margin began after the early Aptian. Given that the cessation of rifting marks the onset of seafloor spreading our seismic sequence analysis indicates that the onset of seafloor spreading in the northern Newfoundland basin, north of the Newfoundland Seamounts, began after late Aptian time.
Thermal histories of Permian and Triassic basins in Britain derived from fission track analysis
Authors: Carter A. , Yelland A. , Bristow C. , Hurford A. J.
Published: April 2008

Permian and Triassic rifting in northern Europe resulted in the deposition and preservation of alluvial sediments within discrete graben structures throughout the UK. The sediments are mostly continental red-bed facies which contain little or no organic materials for vitrinite reflectance palaeotemperature estimation. However, the sandstones commonly contain detrital apatite from which fission track age and track length data can be readily derived, and the elusive low temperature thermal history quantified. Published and new fission track data from over 80 Permian and Triassic sandstones in Britain reveal contrasting thermal histories. Triassic rocks of northwest Scotland have seen only moderate palaeotemperatures (60–75°C), reached during the Mesozoic, in contrast to the Cheshire and Irish Sea Basins which experienced greater maximum palaeotemperatures (80–110°C) during the Late Cretaceous (Lewis
et al.
1992
b
). In southwest England, maximum palaeotemperaturs of 70–80°C (∼95°C in the basin centre at Wytch Farm) were reached during the Lower Cretaceous. The Permian and Triassic sediments of this study indicate that maximum burial is not restricted to the Late Cretaceous and that, in the southwest especially, temperatures peaked much earlier, during the Lower Cretaceous. This implies a significant variation throughout Britain in both Mesozoic cover and its subsequent exhumation.
Dating, correlation and stratigraphy of the Triassic sediments in the West Shetlands area
Authors: Swiecicki T. , Wilcockson P. , Canham A. , Whelan G. , Homann H.
Published: April 2008

Very thick sequences, up to 25 000 ft, of Permo-Triassic sediment are preserved within the Papa and East Solan Basins, in the West Shetlands area. The active margin of this Permo-Triassic basin lay along the West Shetland Spine Fault. Due to severe erosional truncation, the position of the westerly passive margin cannot be delineated. The Triassic basin fill, referred to the Papa Group, has been proven by drilling to be at least 8000 ft thick. A combination of palynological, log and sedimentological analyses have allowed the succession to be informally subdivided into lithostratigraphic units. The oldest, of earliest Triassic age, is the Otter Bank Shale Formation deposited in a coastal/alluvial plain setting. This is gradationally succeeded by the coarse-grained Otter Bank Sandstone Formation comprising sediments derived from the interdigitation of sheetflood, braidplain and aeolian environments of deposition. These represent the initial erosional products derived from the uplifted, rifted basin margin. This major phase of Early Triassic rifting is believed to have taken place during the Scythian. The succeeding Foula Sandstone Formation marks the establishment of predominantly axial braidplain systems, deposited during a period of intermittent but waning tectonic influence during Middle to Late Triassic times. The Papa Group is referred to the New Red Sandstone Supergroup.
Sequences, cycles and other nonsense: are submarine fan models any use in reservoir geology?
Authors: Anderton R.
Published: April 2008

There is no fundamental reason why there should be a relationship between the vertical succession of beds in a submarine fan deposit and their three-dimensional geometry. Parts of some fans behave in such a way that they leave behind sequences that can be used to define bed geometry. However, a significant proportion of the fan sands that are found in hydrocarbon reservoirs were deposited in unstable mid-fan environments that produce chaotic vertical successions. These are best modelled using stochastic techniques.
The liquification and remobilization of sandy sediments
Authors: Nichols Robert J.
Published: April 2008

A number of large, unusually shaped sandbodies have been interpreted from three-dimensional seismic data of hydrocarbon-bearing Tertiary submarine fan deposits of the North Sea. The unusual sandbody shape is considered to have resulted from post-depositional liquification of turbidite deposits. An understanding of liquification processes may therefore be important in delineating reservoir body geometry. The unusual shapes take the form of sheet-like intrusions, either along faults or as dyke and sill complexes, and domes with oversteepened sides. Three processes can cause liquification: (1) fluidization, which results from pore fluid movement; (2) liquefaction, caused by the agitation of grains during cyclic shear stress; and (3) shear liquification which results from the movement of grains during the application of a shear stress across the sandbody. In laboratory experiments each liquification process produces its own style of deformation. Fluid escape and dish structures are produced during fluidization, load structures form during liquefaction, and mass flow structures result from shear liquification. The three liquification processes can interact to create an even greater diversity in deformation style. The active liquification process, or combination of processes, can change in both space and time. In the natural environment it is unlikely that one liquification process will occur independently and therefore most natural liquification must be considered in terms of two or more interactive processes. The large-scale deformation of sandbodies and hence their geometry may vary according to which liquification process or processes are active. In natural systems the sandbody will not deform in isolation from the surrounding material. The rheology of the surrounding material and the nature of the stress field active at the time of deformation will play an important part in controlling the behaviour of the sandbody during remobilization.
Sediment dispersal patterns in a deep marine back-arc basin: evidence from heavy mineral provenance studies
Authors: Browne J. R. , Pirrie D.
Published: April 2008

Heavy mineral provenance studies can aid reservoir description in deep marine depositional systems by providing a clearer understanding of the lateral extent of discrete sediment bodies. In this study the lower Gustav Group (Lagrelius Point, Kotick Point and Whisky Bay formations) of James Ross Island, Antarctica, which was deposited in a deep marine slope-apron-submarine fan complex has been investigated. The Kotick Point and Whisky Bay formations crop out in two separate areas on the west coast of James Ross Island. The provenance of the group has been studied by both standard sandstone petrography and electron microprobe analysis of the heavy minerals’ garnet, pyroxene and Fe-Ti oxides. The sandstones are lithic to arkosic arenites derived from the adjacent Antarctic Peninsula magmatic arc. Although the general source area can be recognized, individual stratigraphical or depositional units cannot be distinguished on the basis of sandstone petrography. However, electron microprobe analyses of the detrital heavy minerals allows a more detailed discrimination of sediment provenance. In particular, analyses of the detrital Fe-Ti oxide minerals show that in the Whisky Bay Formation, the southern outcrop area, contains ilmenite, whilst the northern outcrop area contains titanomagnetite. In conjunction with the available biostratigraphical and palaeocurrent evidence, this can be interpreted in two ways. Firstly, if the two outcrop areas are direct age equivalents then they were derived from separate point sources, and deposited as discrete sediment lobes. Alternatively, if they are not directly time-equivalent, the depositional system may have switched laterally with time, with sediment derived from source rocks of varying composition. Either interpretation has implications for the understanding of the deep marine depositional system. Detrital opaque minerals are commonly source specific and should not be ignored during provenance studies.
Paradigms for the Pilbara
Authors: Trendall Alec F.
Published: April 2008

The Pilbara Craton is a discrete and coherent body of well preserved and exposed early continental crust in the northwestern part of the Australian continent, with a present surface area of about 180 000 km
2
. It has two tectonostratigraphic components: an older ‘basement’ of granite-greenstone terrane, formed between about 3.5 and 2.9 Ga, unconformably overlain by a supracrustal sequence, the Mount Bruce Supergroup, laid down between about 2.8 and 2.4 Ga in the Hamersley Basin. The main body of the craton has retained its integrity since that time, and has undergone only regional uplift, mild metamorphism, and gentle folding. A tendency to interpret the geology of the craton in terms of paradigms, involving a simplistic comparison with other areas thought to be better understood, has impeded the development of independent hypotheses of crustal evolution based on objective integration of observational evidence from within the Pilbara craton itself.
Early Proterozoic mafic dykes in the North Atlantic and Baltic cratons: field setting and chemistry of distinctive dyke swarms
Authors: Bridgwater David , Mengel Flemming , Fryer Brian , Wagner Paul , Hansen Søren Claudius
Published: April 2008

Widespread swarms of basic dykes intruded the Archaean North Atlantic craton (NAC) and the NW Baltic shield between 2.5 and 1.9 Ga. The oldest Mg-rich dykes and sills are 2.4–2.5 Ga and are associated with rift controlled acid and basic magmatism. In SW Greenland the main high-Mg swarms are
c.
2.2 Ga. The high-Mg dykes have high Si, LILE and LREE and are low in Ca, Al, Ti and Nb. Isotopic compositions (Sr, Nd and Pb) demonstrate a high degree of crustal contamination. Individual dykes are remarkably constant in composition but there are large variations between adjacent dykes. Tholeiitic swarms were emplaced at
c.
2.2 Ga in the southern part of the craton in SW and SE Greenland and Labrador. The majority are normal moderately evolved tholeiites with no marked LILE or LREE enrichment, a few c. 2.2 Ga comparatively mafic tholeiitic dykes show a LILE and LREE enrichment. Dense swarms of distinctive Fe-enriched hornblende-bearing tholeiitic dykes (the
c.
2.0 Ga Kangâmiut dykes) intruded the northern part of the NAC in Greenland. Many are composite with intermediate centres. The Kangâmiut dykes were emplaced at depth during shearing in a regional N-S compressional regime and developed metamorphic mineral assemblages at the time of dyke injection. The 1.83 Ga Avayalik dykes from the eastern foreland of the Torngat orogen, northern Labrador show comparable syn-tectonic emplacement and autometamorphic assemblages. Emplacement was controlled by regional sinistral shearing after the first calc-alkaline igneous activity had occurred within the orogen.
The Pleistocene evolution of the Thames and Rhine drainage systems in the southern North Sea Basin
Authors: Bridgland D. R. , D’Olier B.
Published: April 2008

During most of the Middle and Late Pleistocene, global climate was colder than at present. At such times, sea-level was very much lower and the southern North Sea was land, drained by the same rivers that today issue into the sea from Britain and north-west Europe. Evidence from onshore in Britain suggests that the Thames did not drain into the southernmost part of the North Sea Basin until the early Middle Pleistocene; prior to that it flowed across East Anglia and northwards across the area of the present north Norfolk coast. It is thought that the lowland between Kent, East Anglia and the Continent was at this time drained by the ‘Lobourg River’, which arose on the northern flanks of the Wealden ridge and drained northwards into what is now the southern North Sea. The early Medway is thought to have joined this Lobourg River in the area that now lies offshore from southeast Suffolk. It seems that by the early Middle Pleistocene the Thames had adopted this course of the Medway and with it, therefore, the confluence with the Lobourg.

It is widely believed that Anglian/Elsterian ice-sheets caused proglacial ponding in the southern North Sea basin and that a large lake formed, fed by the Thames-Medway and Rhine river systems. It has also been suggested that this lake overflowed to the southwest into the English Channel Basin, breaching the Chalk ridge and initiating a through route via the Strait of Dover, a route that was used by the Rhine-Thames drainage system during all subsequent low-sea-level episodes. Middle and Upper Pleistocene deposits of both the Thames and Rhine systems are preserved in the areas immediately offshore from Britain, The Netherlands and Belgium and can be traced from both sides towards the axial channel of the North Sea Basin, the formation of which was perhaps initiated by the Lobourg River. Although the Rhine’s offshore deposits, in particular, appear to follow a route that heads southwards, towards the Strait of Dover, no sedimentary evidence has yet been found that demonstrates a late Pleistocene fluvial course either through this strait or, conversely, into the North Sea.
Extension of the British landmass: evidence from shelf sediment bodies in the English Channel
Authors: Bellamy Andrew G.
Published: April 2008

Mapping and interpretation of high-resolution shallow seismic and vibrocore sample data from a submerged, infilled valley immediately east of the Owers Bank, at −20 m to −40 m chart datum (CD), eastern English Channel, indicate sediment body formation during multiple cut-and-fill events. Interpretation suggests that these occurred in a combination of diachronous gravel-bed river, peat-land, estuarine and shallow sub-littoral environments with subsequent marine planation (forming ravinement surfaces) and accumulation of a sea-bed sediment veneer. These environments are associated with large-scale relative sea-level and (inferred) climatic changes during the Quaternary which forced subaerial inner continental shelf conditions during cold stages, repeatedly interrupted by interglacial shelf submergence. A model of sediment body formation off the south coast of England, based on the case study findings, shows that subaerial, and not submarine, processes have dominated sedimentary history within present-day, submerged, infilled valleys. Relative to the Quaternary as a whole, global ice-volume is presently unusually low, implying that present eustatic sea-level is unusually high. Subaerial linkage of present-day southern England with the adjacent inner shelf has therefore persisted for most of Quaternary time, with the notion of British insularity applicable to only a relatively small part of the period.
A model of sea-levels in the Irish and Celtic seas during the end-Pleistocene to Holocene transition
Authors: Wingfield Robin T. R.
Published: April 2008

A macroscale model is attempted to accommodate offshore observations indicative of former sea-levels in the Irish and Celtic seas. The indications considered here are those that appear to post-date 12 ka
bp
. Raised beaches at about present sea-level, and formed in the Last Interglacial, are found about these seas. This shows that controls to produce the later sea-level changes have acted to return to about their conditions in the Last Interglacial, and that later permanent tectonic displacements have not been significant. A simple, geometrically based model is developed of the interaction of: glacio-eustasy, from graphs based on coral-reef studies; glacio-isostatic depression with an annular forebulge of equal volume, both contracting through the interval considered; and hydro-isostasy, as an enhancement of the other effects by up to 20%. The best fit of the empirical submarine data suggests that from 12 to 9 ka
bp
relative sea-levels varied from 80 m above, and 160 m below present mean sea-level in the two seas. The resultant sea-level graphs for points from Scotland to Ushant compare with published graphs from eastern North America and northern Europe. Derived maps of palaeocoasts show land-bridges from Britain to Ireland and later to the Isle of Man after 11.35 ka
bp
.
The floristic record of Ireland’s Pleistocene temperate stages
Authors: Coxon P. , Waldren S.
Published: April 2008

The unique flora of Ireland, that includes plants with Atlantic, amphi-Atlantic and Mediterranean affinities, has attracted the attention of many biogeographers. Using a database, this paper compiles the Irish Pleistocene plant fossil record and examines the disappearances of some taxa and the continuity of others. A retreat of some plants to the east since the Tertiary, movement of arctic-alpine species to the north and to the mountains, and the long continuity of Atlantic and amphi-Atlantic taxa, including some not present in Britain, can be identified. The flora of the Irish Middle Pleistocene Gortian temperate stage is examined and its uniqueness, and the long continuity of certain taxa, are discussed. The long record of Atlantic and amphi-Atlantic species, as well as wetland and aquatic taxa, suggests the possibility of proximal refugia for some plants. The implications for
in situ
survival and for migration during and after cold stages are discussed in the light of the compiled fossil record.
Database design in geochemistry: BGS experience
Authors: Coats J. S. , Harris J. R.
Published: April 2008

The Minerals Group of the British Geological Survey (BGS) has been successfully using a relational database for over seven years to hold geochemical and related locational and geological data collected by the DTI-sponsored Mineral Reconnaissance Programme (MRP) since 1972. Operational experience has shown that several problems and deficiencies of the database are the result of the lack of normalization of the original data model. A new data model, derived from analysis of the data collected by the MRP and other geochemical programmes, is presented and solves many of these problems. It is designed to hold all BGS geochemical data for the UK landmass and is currently being implemented. It is presented as a contribution to a wider debate on generalized data models for geochemistry.