bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation structures from the toes of active accretionary prisms
Authors: MALTMAN ALEX J.
Published: December 2007

Coring of sediments in active accretionary prisms by the Ocean Drilling Program (ODP) has revealed a wide variety of deformation features. The structures throw light on processes associated with accretion and the drainage of water-saturated sediments during active deformation. However, some of these structures are rarely described from ancient rocks, partly because they are not well preserved, but perhaps also through the descriptions being scattered among literature not widely read by geologists. This article provides a synopsis of the structures and their implications, based on sediment cores recovered from the five accretionary prisms most recently targeted by the ODP.

Deformation bands are roughly planar, bedding-oblique zones of displacement that vary from resembling faults to being kink like or ductile-shear zone like. They can provide information on bulk strain geometries and dewatering regimes. Narrow zones of faulting (some including grain breakage) are common, and can grade into planar bands of breccia. Scaly fabric results from microscopic zones of flattening which become supplanted by shear-induced rotation and intensification into C–S bands. Surfaces associated with shear in the above structures commonly bear lineations, which even in these incompletely lithified materials can be used for stress tensor analysis. Hydraulic breccia is thought to be an indicator of
in-situ
overpressuring without shear. Web structure involves cataclasis of sand under high pore pressures and can occur at surprisingly shallow levels of burial. Sediment-filled veins may be an indicator of palaeoseismicity. All these structures have hydrological implications and record fluctuating histories of overpressuring and localized fluid flow during deformation.
Tectonostratigraphy of the Glen App area, Southern Uplands, Scotland: anatomy of an Ordovician accretionary complex
Authors: OGAWA YUJIRO
Published: December 2007

The stratigraphy and structure of the Glen App coastal area, northwestern Southern Uplands, are characterized by structural repetition of both chaotic and coherent units of the Middle Ordovician (Caradocian) Tappins Group. The chaotic unit, the Currarie Formation, comprises blocks, including basalt, chert and terrigenous sedimentary rocks, set in folded and in places sheared red to grey siliceous mudstone. The coherent unit is turbiditic, and is divided into the Dalreoch Formation in the north and the Corsewall Formation in the south. The former is characterized by inclined, isoclinal folds and thrusts, whereas the latter shows a homoclinal dip, although both are largely overturned northwards. Small-scale duplexes are observed within the coherent turbidites of the Dalreoch Formation and chaotic units. Larger duplexes, identified on the basis of mapping, are oriented at an oblique angle to the general trend of regional structures. The chemistry of basalt blocks within the Currarie Formation shows a within-plate type, suggesting an origin as seamounts.

The tectono-stratigraphy of the area is interpreted as the result of accretion of a substantial seamount at a subduction zone during Mid-Ordovician time. Thrust interleaving of chaotic and coherent units is inferred to have taken place in and above the décollement zone, while thick turbidite beds without strong folding were probably preserved below the décollement and emplaced below a large-scale nappe. Interpretation of the Glen App area as part of an accretionary complex confirms that an ocean basin remained open in part of the Iapetus system, at least until Caradocian times.
Sequential architecture and cyclicity in Permian desert deposits, Brodick Beds, Arran, Scotland
Authors: FREDERIKSEN K. S. , CLEMMENSEN L. B. , LAWÆTZ H. S.
Published: December 2007

This study of ancient desert deposits (Permian Brodick Beds) tests the possibility that cyclicityin these interbedded aeolian, fluvial and lacustrine deposits was orbitally controlled. The 740 m thicksuccession of desert deposits forms one sequence which can be divided into three genetic units. A majordeflation surface forms the basal sequence boundary and represents a drop in base-level (groundwatertable). On top of the sequence boundary are rather uniform aeolian dune and sand-sheet sediments (Unit1) formed in an erg during low base-level with increasing rates of base-level rise. They are followed byinterbedded aeolian dune, aeolian sand-sheet and flood-reworked aeolian sediments (Unit 2) representingerg margin deposits formed during increasing rates of base-level rise. The uppermost part of the sequenceis composed of gravel sheets (Unit 3) representing alluvial fan deposition during a high base-level withdecreasing rates of base-level rise. The succession is cyclic, and spectral analysis of sedimentary andgeochemical parameters reveal cycles with a thickness of 25.7–29.3 m, 34.5 m, and 64.5 m, and fieldworkreveals cycles of 155 m and 675 m. These sedimentary cycles are thought to reflect climatic oscillations. The lack of detailed time control makes it diffcult to link these climatic fluctuations to orbital cycles, although the detected cyclicity matches well with Milankovitch theory.
Geochemistry, single zircon ages and Sm–Nd systematics of granitoid rocks from theGóry Sowie (Owl Mts), Polish West Sudetes: evidence for earlyarc-related plutonism
Authors: KRÖNER ALFRED , HEGNER ERNST
Published: December 2007

Granitoid gneisses as well as their migmatitic and anatectic derivates were investigated from theGóry Sowie (Owl Mts) Massif of SW Poland in the central West Sudetes. The gneisses and migmatites aretectonically interlayered with paragneisses, and experienced several consecutive tectono-metamorphicevents. Geochemically, the granitoid gneisses are calc-alkaline and similar to orogenic granite suites, whichtherefore lends support to a subduction-related origin.

Single zircon Pb–Pb evaporation ages suggest that the gneiss precursors were emplaced between 473 and488 Ma, and most samples analysed contain zircon xenocrysts with minimum ages between 1124 and2620 Ma. An early phase of high-grade metamorphism is documented by an age of
c.
440 Ma for ananatectically derived granite. Two late Variscan granites have an age of
c.
333 Ma. Nd isotope systematicssuggest variable involvement of crustal material in the generation of the granitoids.

We speculate that the Góry Sowie Massif was part of Avalonia in early Palaeozoic times, derived fromthe northwestern margin of Gondwana, probably northern South America. Granitoid emplacement in theOrdovician took place along a Japan-type active continental margin while Avalonia drifted towardsBaltica and the Tornquist Ocean was consumed. Collision with Baltica occurred in mid-Silurian times. Our data are compatible with an active magmatic arc extending from southern England to thesoutheastern Sudetes in Cambrian and Ordovician times.
Tourmaline in a sub-Cambrian palaeosol on the Proterozoic Lewisian rocks of NW Scotland
Authors: FERGUSON L. K. , FALLICK A. E. , ALLISON I.
Published: December 2007

Tourmaline, not hitherto recorded in Lewisian rocks of Sutherland, nor reported as a secondary mineral in Precambrian palaeosols, occurs in a late Proterozoic, sub-Cambrian palaeosol in NW Scotland. From field and petrological criteria, the tourmaline is secondary and peculiarly associated with the alteration profile. Hence, it formed either during weathering or later in the profile’s history. A minor constituent of the palaeoregolith immediately below the unconformity, the tourmaline mostly occurs as sub-millimetre, radiating, acicular aggregates and is schorl in composition. Black, tourmaline+quartz veinlets cross-cut the profile. Stable isotope and fluid inclusion data suggest that the tourmaline formed from surface-derived fluids at
c.
110ºC. It is concluded that boron was adsorbed onto precursor illitic clays of the soil profile during the Cambrian marine transgression. Thus the tourmaline formed subsequently after burial under the sedimentary pile, probably during the Caledonian orogeny, when temperatures were high enough to allow its formation at suitable sites of nucleation, e.g. adjacent to biotite. Its peculiarity as a palaeosol phase is due to the combination of a marine transgression over an exposed, permeable illitic soil and underlying regolith, followed by increase in temperature suffcient to allow the tourmaline to form.
Direct dating of mylonite evolution: a multi-disciplinary geochronological study from the Moine Thrust Zone, NW Scotland
Authors: FREEMAN S. R. , BUTLER R. W. H. , CLIFF R. A. , REX D. C.
Published: December 2007

Rb–Sr dating of sub-closure temperature, syn-deformationly crystallized white micas from the Moine mylonites (Knockan and Dundonnell), has yielded ages which vary from 437 Ma to 408 Ma. Morphological and major element analyses of the micas indicate that all the micas within the analysed samples were (re)crystallized during the Moine Thrust shearing. The ages yielded are therefore interpreted as marking the end of crystal plastic deformation associated with shearing on the Moine Thrust. The variation in ages between samples is significantly greater than the individual analytical errors and may be a product of strain localization within the shear zone. Alternatively it may indicate flow of strontium-rich fluids derived from outside the shear zone implying that feldspars may act as potentially unreliable initial isotopic reservoirs even in very high strain samples within the greenschist-facies shear zones. However, the Rb–Sr age are internally consistent and compatible broadly with existing geological and geochronological data for the region suggesting that even if the feldspars have not acted as perfect initial isotopic reservoirs the resulting errors were minimal. The general cessation of ductile deformation at
c
. 430 Ma probably dates the general initiation of imbrication within footwall to the Moine Thrust. The age of 430 Ma is therefore likely to be a time of significant brittle displacement on the underlying Ben More Thrust. K–Ar dating of the (re)crystallized Moine mylonite micas yielded anomalously old ages in comparison to Rb–Sr values as a result of incorporation of excess Ar during shearing. The degree of incorporated excess Ar decreases away from the base of the shear zone into the hanging wall, becoming indiscernible at
c
. 1.5 km structurally above the base of the shear zone. The distance (
c
. 1.5 km) may represent the distance that fluid can have flowed out of the shear zone during deformation.
Mineralogy, sulphur isotope geochemistry and the development of sulphide structures at the Broken Spur hydrothermal vent site, 29°10’N, Mid-Atlantic Ridge
Authors: BUTLER I. B. , FALLICK A. E. , NESBITT R. W.
Published: December 2007

A large collection of hydrothermal sulphides from the Broken Spur hydrothermal vent site, including representative samples of mound sulphide materials, has been characterized using optical mineralogy and sulphur isotope analysis. Young mound sulphides from Broken Spur have a pyrrhotite-dominated mineralogy unusual for bare ridge vent systems. However, pyrrhotite is metastable and is ultimately converted to iron disulphides. Mature sulphides are indurated, recrystallized and contain abundant quartz. Sulphide mound materials are developed by three major processes: (i) coalescing of chimney structures; (ii) accumulation of talus from mass wasting and (iii) precipitation and growth in response to hydrothermal flow. Progressive maturation of mound materials is by modification of primary textures, development of mineralogical zoning and replacement of metastable phases. Sulphur isotope analysis of 35 mineral separates returned δ
34
S values of – 0.5 to +3.2‰. These values are similar to those previously measured for Broken Spur and Snakepit, but are distinctly
32
S enriched compared to the TAG active mound and some Pacific sites. Seawater entrainment and sulphate reduction within the subsurface feeder zone below Broken Spur mounds do not appear to be important processes at Broken Spur, in contrast to the TAG active mound.
Episodic magmatism and diverse plutonic products within the Thverartindur central volcanic complex at the former Icelandic plate margin
Authors: SOESOO ALVAR
Published: December 2007

Oceanic spreading, concurrent with Icelandic plume activity during the last 16 million years has created the Icelandic crust. The Tertiary Thverartindur central volcanic complex was located at the Icelandic spreading margin
c.
5–7 Ma ago and reveals evidence for episodic magmatic activity. Intrusive rocks range from ultramafic through olivine- and quartz-tholeiitic gabbros and hybrid rocks to granitic rocks. The mafic intrusions form sill-like bodies with compositions close to those expected for magmatic liquids. Field evidence indicates that episodic emplacement of basaltic magma took place over a considerable time span and confirms the contemporaneous existence of primitive and more evolved mafic magmas. Granitic and ultramafic rocks represent the latest phase of magmatism at a spreading margin. The Thverartindur rocks are depleted in MgO, Ni and Cr, which is compatible with early fractionation of olivine and pyroxene. Calculated parental liquid for this complex is picritic (>18 wt% MgO) and resembles picritic lavas from the Reykjanes Peninsula and western Skye, and dykes from Rum and Mull. The compositions of the Thverartindur high-magnesian dykes, olivine- and quartz-tholeiitic gabbros, and granites can be modelled through decompressional fractional crystallization of this magma. The gabbroic sills are crystallized at low pressure following equilibrium crystallization paths.
Lower crustal and possible shallow mantle samples from beneath the Hebrides: evidence from a xenolithic dyke at Gribun, western Mull
Authors: UPTON B. G. J. , ASPEN P. , REX D. C. , MELCHER F. , KINNY P.
Published: December 2007

A Permian (268 ± 2 Ma) olivine-nephelinite dyke cutting Proterozoic (Moinian) psammites on the west coast of Mull, contains an abundance of xenoliths inferred to be from the lower crust and possibly uppermost mantle. The majority are pargasite pyroxenites grading to hornblendites. Next most abundant are pyroxene granulite orthogneisses. High-grade meta-arenites are also relatively common. Scarce xenoliths and related megacrysts are composed of anorthoclase, ferrosalite, apatite, magnetite and ilmenite (af–cpx–ap–mt–il suite). Scarce kaersutite megacrysts are thought to be derivative from pegmatitic hornblendites. The pargasite pyroxenites are derived from ultramafic protoliths that have experienced recrystallization, modal metasomatism (with introduction of amphibole) and deformation prior to entrainment. Olivines are wholly pseudomorphed but pyroxenes are diopsides (Fs
7.8–9.2
) with up to 12.5% Al
2
O
3
. Plagioclase (An
45.6
) is a rare accessory. Whether the pyroxenite protoliths were upper mantle peridotites or lower crustal ultramafic cumulates is indeterminate.

The mesocratic xenoliths are granulite-facies orthogneisses comprising plagioclase (An
38–22
), augite (Fs
16–22
), pseudomorphed pigeonite (?), magnetite, ilmenite and apatite. Pb/U SHRIMP dating of zircons indicates a crystallization age of 1850 ± 50 Ma for the orthogneisses, suggesting that the Archaean/ Palaeoproterozoic Lewisian gneisses were magmatically underplated by younger Proterozoic (Rhinnian or Ketilidian age) rocks. The pyroxenite and granulite gneiss xenoliths may be coeval fragments of a lower crustal and possibly uppermost mantle sequence. The most evolved of the orthogneisses are two-feldspar quartz diorites containing subordinate sanidine (Or
64–74
). The magmas parental to the postulated underplating intrusion are thought to have been mildly alkaline (transitional) basalts. The metasomatic introduction of amphibole that affected the ultramafic rocks is attributed to pervasive influx of Fe, Ti, K, LREE (etc.)-rich small fraction partial melts from the asthenosphere. The af–px–ap–mt–il megacryst suite, however, appears to represent a distinct younger event involving intrusion of a geochemically evolved vein system within the amphibole pyroxenites. Temperature estimates based on coexisting (a) feldspar and (b) oxide pairs indicate establishment of equilibrium at approximately 800°C, suggesting a geothermal radient of
c
. 27°C km
−1
.
On the emplacement of tabular granites
Authors: ALEXANDER.R. CRUDEN
Published: December 2007

Granites in both crystalline terranes and continental magmatic arcs tend to be circular to elliptical in map view and vary in width from about 3 to 100 km. Available gravity and structural data suggests that many of these plutons are tabular in shape with an average thickness of about 3 km. Ductile structures observed around mesozonal granites indicate that space is created by a combination of lateral and vertical displacements of wall rocks, whereas contact relationships of epizonal plutons imply that only vertical displacements are involved during emplacement. In both settings magma arrives at the emplacement site via one or more vertical feeder zones and flows laterally. With the exception of very high-level epizonal plutons, structural studies suggest that space for many tabular intrusions must be provided mainly by floor-depression (lopolith emplacement) rather than roof-lifting (laccolith emplacement). An emplacement model for this type of tabular granite is proposed which involves progressive depression of the floor of an initially horizontal chamber as it is filled by one or more vertical conduits. A crustal-scale balance in the rates of melt extraction, magma ascent and pluton-filling is required by the model, and transfer of material from the source to the pluton is accommodated by broadly distributed deformation of low strain magnitude. The process is evaluated with end-member cantilever and piston sinking mechanisms. The models predict that large (10–100 km wide), tabular plutons (≤3 km thick) can be emplaced quickly (100 a to 1 Ma) with floor-depression and related wall-rock strain rates similar those expected during tectonic deformation (10
–
10
to 10
–
15
s
–
1
). Bulk strains in the intervening crustal column rarely exceed a strain ratio of 1.5, which is likely to remain undetected in the geological record unless the required deformation is accommodated on discrete structures such as normal faults or shear zones at the base of the pluton.
Tectonics and sedimentary environment of the North Scotia Ridge region revealed by side-scan sonar
Authors: CUNNINGHAM ALEX P. , BARKER PETER F. , TOMLINSON JEREMY S.
Published: December 2007

The North Scotia Ridge is a series of islands and submarine ridges extending 2000 km from Tierra del Fuego to South Georgia in the western South Atlantic. The ridge forms the elevated northern tectonic margin of the Scotia Sea, and accommodates E–W sinistral strike-slip motion at the South American–Scotia plate boundary. Existing studies have shown that the northern flank of the North Scotia Ridge is a large and continuous accretionary prism, formed during presumed mid–late Cenozoic N–S convergence. In this study, we present long-range side-scan sonar (GLORIA) images and seismic reflection profiles which show the structural style of the accretionary prism for the first time. The youngest accreted sediments show a uniform fabric of initial deformation (symmetric–gently asymmetric folds of 1–4 km wavelength), which has been subsequently disrupted at shallower depths by additional shortening and uplift. Between 52
º
45'W and 50
º
30
'
W, the deformation front is exposed at the sea floor, and the Falkland Trough retains the appearance of an active convergent margin. Elsewhere, however, the deformation front is buried beneath younger, undeformed drift sediments indicating that convergence has ceased. GLORIA sonographs also show geological features consistent with current-control of sedimentation, non- deposition, and erosion beneath the Antarctic Circumpolar Current. In particular, this study describes current-influenced sedimentation in the Falkland Trough, and steep-sided, eroded depressions and diffuse slope-parallel fabric on the elevated Falkland Plateau.
Genesis of tectonic inversion structures: seismic evidence for the development of key structures along the Purbeck–Isle of Wight Disturbance
Authors: UNDERHILL JOHN R. , PATERSON SUSAN
Published: December 2007

The interpretation of a densely spaced and well-calibrated seismic grid sheds new light on the development and evolution of key regional and local structures in the Wessex Basin. The results help to resolve long-standing controversies concerning the tectonic significance of apparently anomalous outcrop patterns and the role of important, local ancillary structures with respect to the major monoclinal folds with which they are associated. Although the structures are entirely consistent with the effects of contractional reactivation (tectonic inversion) of normal faults, the subsurface data demonstrate the role that original extensional fault segmentation and associated relay ramps had on original depositional patterns, subsequent inversion geometries and resultant outcrop patterns. As well as illustrating regional controls on the formation of structures, the new seismic-based interpretations enable a reassessment of the Lulworth Crumple and the Ballard Down Fault. The Lulworth Crumple is interpreted as a parasitic fold complex generated by internal folding of the inverted, incompetent syn-rift fill in the immediate hanging wall to the Purbeck Fault, a reactivated major normal fault. The Ballard Down Fault’s origin is interpreted to result from the formation of a local, late-stage ‘out of the syncline’ reverse fault which propagated southwards and upwards through a Chalk succession. As the Chalk had already been rotated to form the northward-dipping steep limb of the Purbeck Monocline at Ballard Down, the structure cuts down stratigraphically. The results stress the importance of understanding the nature of original extensional fault geometries and the competence of the sedimentary units incorporated in folds in gaining a full understanding of the genesis and evolution of structural styles in inverted basins.
Geochronology and geochemistry of a Mesozoic magmatic arc system, Fiordland, New Zealand
Authors: MUIR R. J. , IRELAND T. R. , WEAVER S. D. , BRADSHAW J. D. , EVANS J. A. , EBY G. N. , SHELLEY D.
Published: December 2007

The Median Tectonic Zone in Eastern Fiordland, SW New Zealand, comprises a tectonically disrupted belt of Mesozoic magmatic arc rocks related to subduction along the palaeo-Pacific margin of Gondwana. New ion microprobe (SHRIMP) U–Pb zircon ages confirm that the bulk of the plutonic rocks in eastern Fiordland range from Mid-Jurassic to Early Cretaceous (168–137 Ma) in age. Carboniferous age granitoids occur in SW Fiordland, along the western side of, and within the zone. Triassic plutonic rocks appear to be restricted to the eastern side of the zone. The Mid-Jurassic–Early Cretaceous igneous rocks (collectively referred to as the Darran Suite) are cut by several plutons of Na-rich granitoid (Separation Point Suite) that give ages of
c.
124 Ma, slightly older than equivalent rocks in the NW part of the South Island. Early Cretaceous granulite facies orthogneisses (126–119 Ma) in western Fiordland (Western Fiordland Orthogneiss) are considered to be the lower crustal equivalent of the Separation Point plutons.

The majority of the Darran Suite rocks are I-type, hornblende-bearing calc-alkaline igneous rocks, most likely derived from melting in the mantle wedge above a subducting slab of oceanic lithosphere. In contrast, the Separation Point-type plutons are Na-rich, alkali-calcic granitoids with high concentrations of Sr (typically >500 ppm and up to 1000 ppm) and low concentrations of Y (≤5 ppm) and heavy REE (<10 times chondritic). Isotopic compositions are primitive, with
87
Sr/
86
Sr initial ratios of
c.
0.7038, and å
Nd
values of
c.
+3 at 120 Ma. Their geochemistry is consistent with melting of a mafic protolith of garnet amphibolite mineralogy. Mafic Darran Suite rocks have the appropriate chemical and isotopic compositions to generate the Western Fiordland Orthogneiss and the higher level Separation Point type plutons. We suggest that the sudden appearance of large volumes of Na-rich magma during the Early Cretaceous was triggered tectonically, perhaps by thrusting of the Median Tectonic Zone arc beneath western New Zealand. Melting of basal arc underplate at depths of >40 km would then have generated Na-rich granitoids, leaving residues of garnet + clinopyroxene + amphibole.
The origin of Proterozoic massif-type anorthosites: evidence from interactions between crustal xenoliths and basaltic magma
Authors: DEMPSTER T. J. , PRESTON R. J. , BELL B. R.
Published: December 2007

Plagioclase-rich reaction zones occur around numerous aluminous crustal xenoliths within a suite of Palaeogene sub-volcanic basic sheets on the Isle of Mull, NW Scotland. The xenoliths consist of a glassy core, containing mullite needles, generated from the melting of pelitic source rocks. Thick plagioclase mantles grew at the interface between the aluminous liquid and the enclosing basaltic magma and provide a high-level analogue for the petrogenesis of Proterozoic massif-type anorthosites. Similar interactions between mantle-derived basic magmas ponded at the base of the crust and relatively Al-rich lower crustal lithologies would result in the precipitation of large volumes of plagioclase. Anorthosite massifs were then emplaced at higher crustal levels as crystal-rich mushes within relatively juvenile Proterozoic crust. The model negates the need to crystallize large volumes of mafic minerals prior to the production of plagioclase-saturated liquids, and also accounts for the significant influence of crustal sources on the isotopic signatures of all members of the anorthosite suite.
Late Quaternary evolution of the upper reaches of the Solent River, Southern England, based upon marine geophysical evidence
Authors: VELEGRAKIS A. F. , DIX J. K. , COLLINS M. B.
Published: December 2007

Geological evidence suggests that during the Late Quaternary, a river system (the Solent River) drained a large part of central Southern England. Its upper reaches flowed in a west-east direction, flanked to the south by a Chalk ridge (the Purbeck-Isle of Wight Chalk Ridge). Today, only part of the upper reaches of the river's tributary channels remain, as the area was inundated during the Flandrian Transgression, forming an embayment system (Poole and Christchurch Bays). In order to map the offshore buried channels of the upper reaches of the Solent River an extensive set of shallow-marine geophysical data was analysed and interpreted. The results of this investigation show that the Solent River system was disrupted irreversibly by southerly capture of its upstream section before the Flandrian Transgression. This disruption was the result of the fluvial breaching of the southern barrier of the system (the Purbeck-Isle of Wight Ridge) at three points, probably during Late Devensian time. Poole Bay was first to be submerged during the transgression. The estuaries which resulted from the drowning of the fluvial palaeovalleys of Poole Bay were infilled with transgressive facies sequences which have been preserved within the buried palaeovalleys. In contrast, Christchurch Bay was submerged at a later time, but because of the abrupt manner of its inundation, no transgressive facies have been preserved within its buried palaeovalleys.
Small-scale (<5.0 m) vertical heterogeneity in mudstones: implications for high-resolution stratigraphy in siliciclastic mudstone successions
Authors: MACQUAKER J. H. S. , HOWELL J. K.
Published: December 2007

48 mudstone samples, from the Peterborough Member, Oxford Clay Formation, have been analysed to determine the small-scale vertical and lateral lithofacies variability in this succession. The samples were collected every 0.15 m from Saxon and King's Dyke brickpits (Whittlesey, Peterborough, UK) over a short vertical interval (15 m). The sampled interval spans the
obductum
to the
grossouvrei
Subzones of the Callovian (Upper Jurassic). Lithofacies present were described using combined field logging, optical and backscattered electron optical techniques.

The succession predominantly comprises silt-rich mudstones, with subordinate clay-rich mudstones, shell-beds and shell-pavements. The individual units are variously composed of detrital clay, quartz, pyrite, calcite with minor apatite, kaolinite and glauconite. In some units millimetre-scale upward-fining couplets are present; elsewhere, the original bedding structures have been destroyed by bioturbation. Comparison of successive thin sections reveals that upward-coarsening is present on a metre-scale and that shell-enriched units are located close to the tops of these upward-shoaling units. Comparison of samples collected laterally on a 0.01–1.0 m scale from the same level (3.0 m below the top of Bed 14) indicates that there is lateral lithofacies variability.

The small-scale (0.001 m) couplets are interpreted to be beds deposited by waning flow currents. Significant breaks between these depositional events allowed a dysaerobic infauna to colonize the sediment. The metre-scale upward-coarsening intervals which are capped by shell-enriched units are interpreted to be parasequences.

The observed small-scale lateral lithofacies variability is interpreted to be a product of small, but significant vertical miscorrelation errors rather that systematic lateral facies changes. These data suggest that producing reliable, bed-scale lateral correlations over distances of more than 1 km in this, and successions like it, will be very difficult.
Glacio-eustatic control on deep-marine clastic forearc sedimentation, Pliocene-mid-Pleistocene (c. 1180–600 ka) Kazusa Group, SE Japan
Authors: PICKERING K. T. , SOUTER C. , OBA T. , TAIRA A. , SCHAAF M. , PLATZMAN E.
Published: December 2007

Glacio-eustasy has been shown to be a primary control on sedimentation in the open ocean and along passive continental margins, but its importance in clastic-dominated deep-marine sequences at active plate margins remains poorly understood. In order to test the relative importance of glacio-eustasy at tectonically active plate margins during times of substantial polar ice, a high-resolution δ
1S
O and δ
13
C record from planktonic foraminifera
(Globorotalia inflata)
was undertaken from the Plio-Pleistocene
(c.
1180–600 ka) Kazusa Group, a forearc basin fill, onland SE Japan. This was combined with a high-resolution study of the magnetic susceptibility, total organic carbon, and %CaCO
3
in order to evaluate the response to any glacio-eustatic changes in continental-margin sedimentary processes. The sections reveal globally recognized glacial-interglacial cycles, with sandy intervals correlating with inferred glacials, suggesting that relative sea-level changes during glacial-interglacial cycles exerted the primary control on sediment accumulation in the deep-marine forearc basin. Cross-spectral analysis of δ
18
O and δ
13
C data from the inter-turbidite hemipelagic and pelagic mudstones reveals Milankovitch control both at precession and eccentricity modes, with a shift in their relative importance at about 900 ka. The results of this study have important implications for stratigraphers and sedimentologists because they show that at times when there is substantial polar ice: (1) the main control on sediment accumulation at active plate margins is glacio-eustatic, and (2) support the sequence stratigraphic paradigm developed from passive continental margins that global sea-level changes exert a primary control on siliciclastic deposition.
Fire ecology of a Late Carboniferous floodplain, Joggins, Nova Scotia
Authors: FALCON-LANG H. J.
Published: December 2007

The facies distribution and palaeobotanical identity of fossil charcoal is described from the Upper Carboniferous (Westphalian A–B) Joggins section, Nova Scotia, in order to examine the fire ecology of early Westphalian floodplains. Three charcoal assemblages are noted. Assemblage (1) consists of channel sandstone bodies, containing beds of calcrete breccia, cordaite logs (up to 3 m long), and coniferopsid wood charcoal. This assemblage records upland coniferopsid forest fires which altered basin hydrology and promoted flooding in downstream floodplain rivers. Assemblage (2) consists of thin (1–8 mm thick) coals containing hollow, sigillarian tree stumps and lepidodendrid and medullosan plant compressions. Fifteen of the 29 stumps observed have a 2–5 cm thick basal layer infilling the stumps, composed entirely of sigillarian charcoal. Sigillarian and medullosan charcoal is also scattered around the outside of these stumps. This assemblage represents fire in lowland peat-forming communities dominated by
Sigillaria
and medullosan pteridosperms. These forest fire profiles were slowly buried in floodplain muds. Assemblage (3) consists of a heterolithic sheet sandstone body containing a 2.5 m high sigillarian tree trunk with an internal, basal trunk deposit of sigillarian charcoal and a lightly charred bark rind. This also records fire in lowland sigillarian forests, but, in contrast to (2), this forest fire profile was buried rapidly in a distributary lobe.
Attenuation and excision of a crustal section during extensional exhumation: the Carratraca Massif, Betic Cordillera, southern Spain
Authors: ARGLES T. W. , PLATT J. P. , WATERS D. J.
Published: December 2007

Extensional dismemberment of the Betic Cordillera during Late Oligocene to Early Miocene time caused attenuation and excision of a crustal section overlying mantle peridotite. An integrated study of metapelites overlying the peridotite sheet in the Carratraca area shows truncation of a typical orogenic cycle of burial and heating by rapid exhumation and late- to post-tectonic, low-pressure metamorphism. Attenuation by a factor of five or more condensed a greenschist to granulite section to 4 km structural thickness.

Initially coaxial attenuation of the sequence, involving formation of a flat-lying foliation and conjugate shear bands, was superseded by non-coaxial deformation concentrated along low-angle, top-to-the-NE, extensional fault zones. These excised parts of the metamorphic section; a 2 km loss was calculated across one fault zone.

Thermobarometry throughout this section demonstrates that the structural attenuation was related to isothermal decompression to low pressures (2-4 kbar) even at the base of the crustal section. A late thermal event largely postdates the ductile stage of attenuation, particularly in the upper part of the section. Thermal modelling implies that this thermal event could not have been produced by the hot peridotite sheet alone. Rapid tectonic exhumation and asthenospheric upwelling are the probable causes, following detachment of material from the base of the lithosphere.
The influence of country rock structural architecture during pluton emplacement: the Loch Loyal syenites, Scotland
Authors: HOLDSWORTH R. E. , McERLEAN M. A. , STRACHAN R. A.
Published: December 2007

The late Caledonian Loch Loyal syenites comprise three related, but geographically separate, composite intrusions: the Ben Loyal, Ben Stumanadh and Cnoc nan Cuilean bodies. They were emplaced
(c.
426 Ma) into Moine and Lewisian rocks of the Moine and Naver thrust sheets previously deformed by Caledonian NW-directed folding and thrusting at amphibolite facies metamorphic conditions. The intrusions lie mainly within a zone of large-scale cross-folds in which the regional foliation trends NW-SE at high angles to regional orogenic strike (NNE-SSW). The cross folds are underlain by a broad, ESE-dipping zone of high strain known as the Ben Blandy shear zone. The NW basal contact of the Ben Loyal body dips generally SE and strikes sub-parallel to the foliation in the underlying Ben Blandy shear zone. The higher parts of this syenite, together with those of the Ben Stumanadh and Cnoc nan Cuilean intrusions, form a series of variably coalesced dykes trending NW-SE sub-parallel to the foliation in the pre-existing zone of cross-folds. There is little evidence for significant country-rock deformation during emplacement of the syenites. Minor components of top-to-the-SE extension occurred along the NW boundary of the Ben Loyal body, whilst minor dextral shearing is associated with the emplacement of the NW-SE, vertical sheet-like units that are thought to form the SE part of this intrusion and the other Loch Loyal syenites. Generally contact-parallel magma tic-state deformation fabrics are dominant in most of the intrusions and are thought to reflect limited magma pressure-driven, internal deformation of the igneous bodies during and immediately after emplacement. The geometry of these fabrics and the Loch Loyal syenites as a whole has been directly controlled by the pre-existing structural architecture of the surrounding country rocks. This appears to be a previously overlooked feature of many plutons emplaced at mid- to upper crustal depths below the region influenced by the free surface. The siting and emplacement of the Loch Loyal syenites may have been initially facilitated by late Caledonian gravity-driven extension of the Moine Thrust sheets. Following the initial phase of intrusion, it is also possible that the presence of magma actually promoted further nappe collapse in the adjacent country rocks. There is no compelling reason to link the upper crustal extension observed during emplacement to the genesis of the alkaline magmas in the underlying mantle. The siting and ascent of the syenites at depth may be linked to the presence of steeply-dipping structures in the Lewisian autochthon buried beneath the Moine Nappe.
Magmatic belts in accretionary margins, a key for tectonic evolution: the Tonalite Belt of North Victoria Land (East Antarctica)
Authors: MUSUMECI GIOVANNI
Published: December 2007

Occurring in the Early Palaeozoic palaeomargin of the East Antarctica Craton, the Tonalite Belt of North Victoria Land is a narrow linear magmatic belt up to 200 km long, made up of strongly foliated tonalitic and granodioritic intrusions. They were synkinematically emplaced into the Lanterman-Murchison Shear Zone, a major tectonic structure across which different tectono-metamorphic terranes were accreted during the Late Cambrian Ross Orogeny. The deformational and kinematic features of the intrusions indicate that strain and displacement during terrane accretion were partitioned into oblique thrust, high-angle thrust and strike-slip shear zones. From this it is deduced that a transpressional regime prevailed during Early Palaeozoic deformation and terrane accretion. This and other magmatic belts which exploited major tectonic structures in collisional margins, such as the Coast Plutonic Complex of NW America, are basic keys for understanding deformational processes and kinematic regimes during terrane accretion. Moreover, the occurrence of such types of magmatic belts might be regarded as a reliable indication of large scale strike-slip motion between accreting terranes in an oblique convergent setting.
Rare earth element geochemistry of upper Ordovician cherts from the Southern Uplands of Scotland
Authors: OWEN A. W. , ARMSTRONG H. A. , FLOYD J. D.
Published: December 2007

Caradoc and Ashgill radiolarian cherts and siliceous mudstones from the Southern Uplands preserve primary rare earth element (REE) signatures which are comparable to those of more recent deposits from continental margin settings. This is incompatible with the widely held view of these rocks as open ocean deposits incorporated in an accretionary prism and reinforces the model of deposition on an extensional continental margin. The REE signatures can be used as fingerprints to differentiate between some of the fault-bounded formations within the area. They indicate the provenance of the mud grade siliciclastic material in these distal hemipelagites and are comparable with published REE data on grey wackes in the same successions. This detailed analysis of the REE patterns in Lower Palaeozoic cherts demonstrates the usefulness of this approach in ancient orogens.
Structure and stratigraphy of the metamorphic rocks in part of Northwest County Mayo, Ireland
Authors: Crow Michael John , Max Michael David , Sutton John Stuart
Published: December 2007

A new geological map covering over 1000 square km of
n.w.
Co. Mayo is presented. Metasediments, probably Moine and Dalradian in age, have been deformed and metamorphosed during the Caledonian orogeny together with the pre-Moine Erris Complex (Laxfordian? rocks). The gneissose Erris Complex is commonly preserved except where significant Caledonian reconstitution to schists has occurred. Rocks of the Erris Complex were tectonically emplaced within the metasediments as major anticlinal cores, and as transgressive thrust wedges during the first Caledonian deformation.

A significant structural and metamorphic break occurs across the Corraun Fault which is probably the south-westward continuation of the Leannan Fault of County Donegal.
Pleistocene deposits of Church Stretton (Shropshire) and its neighbourhood
Authors: Rowlands Paul Humphreys , Shotton Frederick William
Published: December 2007

The concealed valley beneath the Church Stretton valley floor is interpreted as water-cut, sloping gently down from north to south and becoming the buried floor of the Marshbrook Gorge. In this were laid down outwash gravels and tills of a valley glacier, which may be interpreted as making two advances separated by a retreat, and which terminated just north of Little Stretton. This glacier carried erratics derived from the Breiddens and Stiperstones, the Trias of Cheshire, the Lake District and the floor of the Irish Sea, an ‘Irish Sea’ assemblage. Deposits above the tills can be dated, by pollen and radiocarbon, as Zones I and II, suggesting a Late Devensian date for the Irish Sea Glacier. During Zone III and, perhaps intermittently, after that until early Zone VI, frost-shattered debris was carried down from the Longmynd valleys on the west, to form three fans across the valley, ponding up marshes from Zone VIa onwards.

The Welsh till around Marshbrook and southward is ascribed to an earlier glaciation, as yet undated, but associated with glacial gravel terraces on the valley sides and an erosion surface through which the over-deepened Church Stretton valley was cut before the Irish Sea glacier advanced into it. A series of four terraces below the glacial gravels, in the valleys of the Quinny Brook and River Onny, may eventually help to solve the question of the age of the tills of Welsh origin.

In the appendix, palynological detail is given justifying the zonal subdivisions in the organic deposits which lie above and below the fan gravels. It is also suggested that in Zones VIIa and VIIb, the influence of human agricultural activities can be recognized.
The Statistical Reservoir Model: calibrating faults and fractures, and predicting reservoir response to water flood
Authors: Main I. G. , Li L. , Heffer K. J. , Papasouliotis O. , Leonard T. , Koutsabeloulis N. C. , Zhang X.
Published: December 2007

This paper describes the new concept of a ‘Statistical Reservoir Model’ to determine significant well-pair correlations. We solve this conceptual problem using a predictive error filter, combined with Bayesian methods that identify those well pairs that are related to each other with statistical significance, for the Gullfaks reservoir in the North Sea. Significant, long-range, correlations in the whole field are found at an optimal time lag of one month. The correlation function for significantly-correlated well pairs, after normalization for the distribution of available wells, shows a long-range power-law decay that is consistent with a critical-point response at the reservoir scale. A principal component analysis shows a strong correlation with the location and orientation of faults that intersect the main producing horizon. A predictive experiment shows that the model performs very well both in history matching and predictive mode on a time scale of about one month.
The fused fault block approach to fault network modelling
Authors: Hoffman K. S. , Neave J. W.
Published: December 2007

Fault network modelling of complex faulted structures, those containing hundreds or even thousands of faults, can be an extremely difficult and time-consuming process. Although techniques for mapping and modelling faulted structures have been in existence for nearly forty years, asset teams still struggle to create correct portrayals of such complex faulted reservoirs due to the limitations of the commonly used techniques. We have developed a new approach to fault network modelling, using a new concept of ‘fused’ fault blocks. The identification of fault–fault intersections is based not on a manually drawn fault network or table of relationships, but rather is derived from the fault surfaces themselves. The calculated intersection lines are then used to truncate faults against each other. Because the truncation information can be stored with the fault model, this process yields a repeatable and easily updatable fault model. The name of our technique ‘fused fault blocks’ refers to the fact that when a section of a fault is removed, the two fault blocks that had been created by the fault are then fused together, forming a single fault block. The resultant fault model can then be used to create a 3D reservoir grid, one in which the fault geometry has not been compromised, and therefore better reflects the actual structure. The speed of the fault-building process ‘seconds or minutes, even for models with hundreds of faults’ also allows multiple interpretations, placing the emphasis of the fault network building on the evaluation of the interpretation and the effects of compartmentalization, and not on the manipulation of software.
Transport model of the human Na+-coupled l-ascorbic acid (vitamin C) transporter SVCT1
Authors: Mackenzie Bryan , Illing Anthony C. , Hediger Matthias A.
Published: December 2007

Vitamin C (l-ascorbic acid) is an essential micronutrient that serves as an antioxidant and as a cofactor in many enzymatic reactions. Intestinal absorption and renal reabsorption of the vitamin is mediated by the epithelial apical l-ascorbic acid cotransporter SVCT1 (SLC23A1). We explored the molecular mechanisms of SVCT1-mediated l-ascorbic acid transport using radiotracer and voltage-clamp techniques in RNA-injected Xenopus oocytes. l-Ascorbic acid transport was saturable ( K0.5 ≈ 70 μM), temperature dependent ( Q10 ≈ 5), and energized by the Na+ electrochemical potential gradient. We obtained a Na+-l-ascorbic acid coupling ratio of 2:1 from simultaneous measurement of currents and fluxes. l-Ascorbic acid and Na+ saturation kinetics as a function of cosubstrate concentrations revealed a simultaneous transport mechanism in which binding is ordered Na+, l-ascorbic acid, Na+. In the absence of l-ascorbic acid, SVCT1 mediated pre-steady-state currents that decayed with time constants 3–15 ms. Transients were described by single Boltzmann distributions. At 100 mM Na+, maximal charge translocation ( Qmax) was ≈25 nC, around a midpoint ( V0.5) at −9 mV, and with apparent valence ≈−1. Qmax was conserved upon progressive removal of Na+, whereas V0.5 shifted to more hyperpolarized potentials. Model simulation predicted that the pre-steady-state current predominantly results from an ion-well effect on binding of the first Na+ partway within the membrane electric field. We present a transport model for SVCT1 that will provide a framework for investigating the impact of specific mutations and polymorphisms in SLC23A1 and help us better understand the contribution of SVCT1 to vitamin C metabolism in health and disease.