bluuebunny/crossref_metadata_2025 huggingface dataset:
Gravity modelling of the lherzolite body at Lers (French Pyrenees); some regional implications
Authors: Anderson Helen J.
Published: May 2009

Lherzolites outcrop throughout the North Pyrenean Zone of the Pyrenees and are everywhere associated with metamorphosed carbonates. It has been suggested that heat from the cooling of the lherzolites was responsible for the high temperature metamorphism of the carbonates. A gravity survey reported here shows that the volume of the lherzolite body at Lers is approximately 0.8 km3. The maximum volume of carbonates that such a body could metamorphose is 3.2 km3. This latter value is so much less than the volume of carbonates inferred from field mapping that the lherzolite body cannot have been the sole source of heat for metamorphism of the carbonates.

It has been suggested from seismic data that there is a step in the Moho beneath the North Pyrenean Fault in the central Pyrenees. Gravity anomalies reported here show that either the step is less than 10 km high or that the density contrast is very low at the base of the crust in the Pyrenees.
A complete arc-trench system recognized in Gondwana sequences of the Antarctic Peninsula region
Authors: Smellie J. L.
Published: May 2009

Prior to Late Triassic–Early Jurassic times, the geological history of the Antarctic Peninsula region was dominated almost entirely by Gondwana sequences that together comprised a major arc-trench system. Subduction complex, trench-slope-break and fore-arc basin sedimentation can all be recognized, and deposition was at least partly on early Palaeozoic or older continental crust. The only evidence for a contemporaneous magmatic arc situated in the Antarctic Peninsula at this time consists of patchy occurrences of metavolcanic rocks, possibly representing the frontal edge of the arc, and the major outcrop area of these rocks is believed to lie under the broad shallow continental shelf E of the Antarctic Peninsula. This is contrary to most current hypotheses in which a marginal basin, presumably floored by oceanic crust, is thought to crop out close to the E coast of the Antarctic Peninsula. However, the complete absence of substantial outcrops of pre-Jurassic volcanic rocks anywhere in eastern Antarctica and South Africa, which are the closest and most likely places in which these should exist, supports the new proposal. Moreover, the identification of back-arc elements of the arc-trench system (foreland fold-thrust belt and retro-arc foreland basin) in eastern Antarctica and South Africa greatly strengthens the likelihood of the arc cropping out in the area suggested.

Towards the end of the Triassic and during the Early Jurassic Periods, an intense diastrophic event, or culmination of events, of orogenic magnitude occurred (Gondwanian orogeny), causing substantial redistribution of the pre-existing elements of the arc-trench system. In particular, all the fore-arc sequences were strongly deformed, some possibly for the first time (e.g. in the fore-arc basin), and became firmly accreted to the continental margin. Moreover, the magmatic foci migrated trenchwards to intrude the deformed rocks in the Antarctic Peninsula. Because many of the plutons were emplaced synkinematically, they often closely resemble ‘basement’ gneisses. The distinction between these rocks remains a serious problem in the Antarctic Peninsula and it can be solved only partially by radiometric dating.
Low grade and very low grade regional metabasic Ordovician rocks of Llŷn and Snowdonia, Gwynedd, North Wales
Authors: Roberts B.
Published: May 2009

Metabasic assemblages belong to the prehnite-pumpellyite and greenschist facies. The isograds pumpellyite-in, pumpellyite-out/clinozoisite-in and biotite-in have been mapped, and divide the area into four metamorphic zones. Field and petrographic evidence indicate that the metamorphic crystallization was largely syn-and immediately post-tectonic, viz. end-Silurian to Devonian. The use of published Schreinemakers' bundles indicates that most of the prehnite-pumpellyite-bearing assemblages formed at high grades within the facies and that the greenschist facies rocks crystallized in the higher pressure field. As the amount of calcite increases so diagnostic Ca–Al silicates are reduced and eventually eliminated from assemblages. Contrary to recent claims, the evidence indicates that the Gwna Group and the Gwyddel Felsitic Beds of Llŷn were metamorphosed prior to the Arenig.
Microfabric, mineralogy and early diagenetic history of the Whitby Mudstone Formation (Toarcian), Cleveland Basin, U.K.
Authors: Pye K. , Krinsley D. H.
Published: May 2009

The Whitby Mudstone Formation in northeast England contains three shale facies (normal, restricted and bituminous) which have previously been differentiated on the basis of sedimentary structures and faunal assemblages. This paper shows that the three facies can also be differentiated by mineralogical, geochemical and microtextural criteria determined using BSEM, EDXRA, XRD and XRF. The bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite, calcite and dolomite. The weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite. The normal facies shales are very weakly laminated and contain siderite in addition to pyrite. The geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon-rich sulphidic, carbon-poor sulphidic and very carbon-poor sulphidic respectively.
Thermal structure of crystallizing magma with two-phase Convection
Authors: Morse Stearns A.
Published: May 2009

Two-phase packets of crystals plus liquid form rapidly at a magma contact having a high thermal contrast with its surroundings. The packets can detach from an upper contact and settle rapidly with respect to crystal settling or turbulent stirring velocities. They carry crystals and supercooling downward and act as heat sinks for crystallization of floor cumulates. Evolution of picritic magma toward neutral buoyancy and overturn into overlying basalt magma proceeds most efficiently with two-phase convection. Sinking of hot bronzite-laden liquid into cooler anorthositic liquid destroys the liquid stratification within a day or so. Two-phase convection rarely yields crystal mush thicknesses suitable for compaction of cumulates, which occurs only for a narrow window of cooling rates. Two-phase convection leads to cool, thin boundary layers above and below hot interior magma and may tend to prevent or control turbulence. The critical timing and scale of two-phase layer detachment need further study.
Lower Palaeozoic stratigraphy in the southern and central Amanos Mountains, south central Turkey
Authors: Dean W. T. , Monod O. , Günay Yilmaz
Published: May 2009

Formations of Cambrian and Ordovician age originally identified by the letters A to E in the southern Amanos Mountains are reviewed using lithostratigraphic units known from the western Taurus Mountains and south-eastern Turkey. The youngest Cambrian rocks in the southern Amanos belong to the Sosink Formation and their age, based on trilobite evidence, ranges from theBadulesiaZone to theSolenopleuropsisZone of the Middle Cambrian; they are overlain unconformably by conglomerates dated as Triassic? by means of plant fossils. Ordovician rocks – Seydişehir Formation (approx. Arenig) and Bedinan Formation (Caradoc in part) – are exposed further north, in the central Amanos. The unusual position of the allochthonous ophiolites, which rest in part directly upon Lower Palaeozoic rocks, is discussed.
The Newer Granite problem: a geotectonic view
Authors: Soper N. J.
Published: May 2009

The Siluro–Devonian suite of granitic plutons in the British Caledonides known as the Newer Granites, together with their associated extrusive rocks, represent one of the most extensively researched examples of calc-alkaline magmatism apparently related to orogeny. Although recent chemical studies have credibly interpreted some of the Scottish intrusions and volcanic rocks as part of a continental-margin magmatic arc generated by the subduction of lapetus oceanic lithosphere beneath Laurentia, insurmountable problems of distribution and timing arise when attempts are made to relate the magmatic activity as a whole to a traditional two-plate collision model for the orogeny.

Newer Granite magmatism is here discussed in the context of more mobilistic models for the post-Grampian evolution of the British Caledonides which involve E–W closure between Laurentia and Baltica, terminated by collision in the Silurian, followed by the northward accretion of Gondwana-derived terranes in the early Devonian. The former produced the Main Caledonian tectonometamorphism of the Northern Highlands of Scotland, the latter the Late Caledonian deformation of the slate belts in the paratectonic Caledonides. These models imply much more complex convergence geometries which can, in principle, account for the whole Newer Granite suite as a series of subduction-generated magmatic arcs overlapping in space and time.

The model proposed involves three late Caledonian magmatic arcs in addition to the Ordovician ‘Borrowdale arc’ which is not considered in this paper. One is related to Laurentia–Baltica convergence with westward subduction beneath the Scottish sector of the Laurentian margin in the Ordovician and Early Silurian, which generated the early members of the Newer Granite suite in the Highlands; a second is related to northward Silurian–early Devonian subduction at the Solway Line, which generated the younger Newer Granites and volcanic rocks north of the Highland Border; and a third, related to northward accretion of the Armorican terrane in early Devonian time, produced intrusive and extrusive magmatism as far south as Southeast Ireland and the English Midlands.
The succession of small shelly fossils (especially conoidal microfossils) from English Precambrian–Cambrian boundary beds
Authors: Brasier Martin D.
Published: May 2009

Small shelly fossils, especially conoidal microfossils, have potential for biostratigraphic correlation of Precambrian–Cambrian boundary rocks where evolutionary successions of taxa can be recognized. A succession of hyoliths, brachiopods and species of Sunnaginia, Torellella, Eccentrotheca and Rhombocorniculum can be recognized in the Home Farm Member of Nuneaton and/or the Comley Limestone of Shropshire, England. Revised ranges of taxa are given and Sunnaginia neoimbricata n.sp., S. parva n.sp., S. angulata n.sp., Eccentrotheca grandis n.sp. and several new records are described from Nuneaton and Comley. The similarity in the sequence of small shelly fossils in England and Siberia indicates that a correlation can be achieved between the two areas. It is suggested that the lower Tommotian to lower Atdabanian correlates with the Hartshill Formation of Nuneaton, of which the condensed Home Farm Member spans the mid Tommotian to lowest Atdabanian, while the upper Atdabanian to lower Botomian correlates with the condensed Comley Limestone of Shropshire.
Petrography of trench sands from the Nankai Trough, southwest Japan: implications for long-distance turbidite transportation
Authors: De Rosa R. , Zuffa G. G. , Taira A. , Leggett J. K.
Published: May 2009

Twenty-three samples of Quaternary sands from Deep Sea Drilling Project (DSDP) Leg 87 Sites 582 (trench axis) and 583 (lowermost terrace of uplifted trench sediments in the accretionary prism) off Shikoku show a 70–80% volcanic component in the terrigenous grain population. This component comprises 30–40% neovolcanic grains, among which basic and intermediate types are present in roughly equal proportions, and 60–70% palaeovolcanic grains, which are predominantly of acidic composition. No volcanic terrane occurs, in the hinterland of the Shikoku portion of the Nankai Trough, and the first such rocks to the east (up the very slight depositional slope of the Nankai Trough axis) are not encountered for more than 500 km. These, occupying the Izu Peninsula and the majority of the Tokai drainage basin to the north, are Neogene and Recent volcanics which are of comparable variability to the volcanic grains in the sands off Shikoku.

The minor component of sedimentary, metamorphic and plutonic grains in the Leg 87 sand samples can be matched with the basinal clastic ophiolitic Shimanto and Chichibu terranes and the high-pressure metamorphic Sambagawa terrane which border the Nankai Trough fore-arc along southwest Japan. This detritus also most likely derives from the Tokai drainage basin, where the easternmost outcrops of the above-mentioned terranes occur, because most sediments deriving from Shikoku and the Kii regions are ponded in terraced fore-arc basins or in basins on the lower slope. Only three major submarine canyons debouch into the floor of the Nankai Trough. The easternmost of these, the Suruga Trough, taps the volcanic Izu/Tokai hinterland, and is therefore the conduit for most sand fed to the trench off Shikoku.
An early Late Cambrian trilobite faunule from Kashmir
Authors: Jell P. A.
Published: May 2009

An early Late Cambrian trilobite faunule of fewer than 20 specimens and includingMonkaspissp. cf.M. serrataMong, ?Blackwelderiasp. andCyclolorenzellasp. is recorded from the Trahagam Formation near the village of Trahagam in Hundwara Tehsil, Kashmir, India. The faunule occurs in green shales and provides the first unequivocal Late Cambrian date for sediments in Kashmir; Kashmiri fossil faunas previously ascribed Late Cambrian ages by Reed are now considered Middle Cambrian.
On the thermo-tectonic evolution of Northern England: evidence from fission track analysis
Authors: Green Paul F.
Published: May 2009

The limited amount of fission track data previously available in Northern Britain has shown unexplained Cretaceous ages in the Southern Uplands and Lake District. Apatite fission track analysis has been applied to 23 samples from Caledonian intrusive bodies, to further investigate these ages. Fission track data of sphene has been carried out on seven samples and zircon in one sample.

Apatite fission track ages vary from a maximum of 278 ± 12 Ma in the Cheviot Granite, down to ages of ∼ 60 Ma in the Carrock Fell region, with intermediate ages of ∼ 140 Ma in the Eskdale Granite and ∼ 80 Ma in the Shap Granite. This variation in fission track age is accompanied by changes in the distribution of confined fission track lengths. Samples with the youngest ages (∼ 60 Ma) have long, narrow distributions (mean length > 14 μm; standard deviation ∼ 1 μm) typical of samples which have had all pre-existing tracks erased by elevated temperatures, and subsequently cooled rapidly so that all tracks now observed have formed at low temperatures. As ages increased from 60 Ma, a component of shorter tracks becomes more dominant, representing tracks which have been shortened at elevated temperatures. Thus ages greater than 60 Ma are ‘apparent ages’, representing a partial overprint of a pre-existing track record, while the ∼ 60 Ma ages record a total resetting at this time.

The heating responsible for the observed fission track annealing may be due to residence at temperatures in the range 70–125 °C over many tens of Ma, or to a short lived heat pulse perhaps associated with the Tertiary igneous province of the northwest. In either case, uplift and erosion on a scale of kilometres at ∼ 60 Ma ago is necessary to produce the observed pattern of fission track parameters. This uplift may be related in some way to basin inversions, also on a kilometre scale, known to have taken place at around the Late Cretaceous/Early Tertiary to the southeast (Cleveland, Sole Pit and Broad Fourteens Basins). No previous evidence of such uplift in Northern England has been reported, and the study reported here highlights the unique potential of apatite fission track analysis for the detection of mild thermo-tectonic events, often in areas where no other evidence exists.
Observations onAstiericeras astierianum(d'Orbigny, 1842) (Cretaceous Ammonoidea)
Authors: Kennedy W. J.
Published: May 2009

Astiericeras astierianum(d'orbigny, 1842) is redescribed, the type material illustrated for the first time and the range of intraspecific variation and striking sexualdimorphism documented. Previous suggestions that the early ontogeny ofAstiericerassupports derivation fromDouvilleicerasde Grossouvre, 1894 of the Douvilleiceratinae are in error: the genus and species are distinctive at the earliest diameters seen and ornament gives no clue to affinities. The sutural formula is that characteristic of some Douvilleicerataceae, however, to which superfamily the species is assigned, as the only member of the family Astiericeratidae Breistroffer, 1953. It is thus a scaphitoid heteromorph, derived from normally coiled immediate ancestors that are themselves recoiled derivatives of an original heteromorphic stock.
Fossil plants of the Severn Coalfield and their biostratigraphical significance
Authors: Cleal C. J.
Published: May 2009

The Carboniferous fossil plants from the Severn Coalfield are described for the first time. They indicate a late Westphalian D age for these strata (Lobatopteris vestitaBiozone) and are clearly similar to floras reported from the Forest of Dean Coalfield. There is also evidence that they can be correlated with the Grovesend Beds in the eastern part of the South Wales Coalfield. It seems that the start of sedimentation in the Forest of Dean and Severn coalfields is related to Leonian (late Hercynian) earth movements.
The Lower Eastern Layered Series of Rhum
Authors: Faithfull John W.
Published: May 2009

The Lower Eastern Layered Series (LELS) comprises approximately units 1–5 of previous workers. Remapping has revealed considerable along-strike lithological variation in the units of the LELS. It is suggested, on the basis of field and geochemical evidence, that two layers formerly regarded as ‘conformable intrusive sheets of fine-grained olivine gabbro’, may be evolved alii valite layers rather than later intrusions. Xenolith suites, in these layers and elsewhere, indicate a component derived from the roof or walls of the magma chamber. Cryptic variation is more extensive in the LELS than in other parts of Rhum: olivine forsterite content varies from 85.6 to 70, and clinopyroxene Mg×100/(Mg+Fe) varies from 88 to 74. Postcumulus effects and subsolidus re-equilibration have altered the initial compositions of the mineral phases. The data are consistent with a model of repeated replenishment by picritic magma, although the replenishing liquids may have been slightly less magnesian than those subsequently available, during the formation of the upper ELS.
Fluid dynamic and geochemical evolution of cyclic unit 10, Rhum, Eastern Layered Series
Authors: Tait Stephen R.
Published: May 2009

Lithological, major element, trace element and Sr isotope data from cyclic unit 10 of the Rhum Eastern Layered Series are presented. The lower 65 metres of the unit are peridotite, subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick. The uppermost 16.5 metres of the unit are allivalite. There are steep geochemical gradients across the peridotite-allivalite boundary in Ni content of olivine and whole-rock Sr isotope composition.

Calculations are presented on the geochemical evolution of a Rhum picritic liquid undergoing olivine precipitation, both when the olivines remain suspended in the residual liquid as they precipitate, and when they are continuously fractionated. Quenched groundmass and olivine compositions from the Rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model. The Rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension; however, replenishment by a highly olivine-phyric basalt is also possible. The peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor.

The lower part of the peridotite is a poikilitic adcumulate; it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines. In the latter stages of adcumulus growth, more Fe-rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re-equilibrate and giving the intercumulus plagioclase a higher Sr isotope ratio than lower down. The olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their Ni content. They also show substantial variation in major element composition laterally within the allivalite. It is suggested that these features are a consequence of postcumulus re-equilibration of olivine with migrating intercumulus magma.
Channelled metasomatism in Rhum layered cumulates – evidence from late-stage veins
Authors: Butcher Alan R.
Published: May 2009

Late-stage veins have been studied in the Rhum layered intrusion as part of a wider investigation into postcumulus processes – in particular, to study compositions of residual liquids and their effects on host cumulates. Studies have concentrated on Unit 10 of the Eastern Layered Series (ELS), though brief investigations have also been made in the Western Layered Series (WLS).

The Unit 10 veins are generally concordant with the layering, although locally they are transgressive with dilational relationships. Two principal types can be recognized: ultrabasic and basic. Detailed microprobe studies have shown that the liquids responsible for the veins have substantially modified the compositions of the cumulus minerals in the wall-rock peridotite up to 1 cm from the vein margin.

The style of veining in the WLS is more complex than in the ELS, and several generations of vein can be identified. Both normal and harrisitic cumulates have undergone localized chemical modification near to the veins. Modification occurs regardless of the vein orientation.

The ELS and WLS veins are geochemically distinct from the numerous gabbro intrusions associated with the layered series, and it is concluded that they represent fractionated intercumulus liquids injected into early formed fractures in the cumulates. The observed chemical modification is explained by a model involving mixing of the intrusive vein melt with trapped intercumulus melt in the adjacent peridotite, followed by diffusion-controlled re-equilibration of the cumulus minerals. This type of highly localized compositional modification along fractures is termed channelled metasomatism.
Marine incursion in Upper Palaeozoic sedimentary rocks of the Oslo Region, Southern Norway
Authors: Olaussen S.
Published: May 2009

The discovery of marine fossils in the Upper Palaeozoic of the Oslo Region suggests a previously unknown marine transgression of probable middle Carboniferous age. The fossiliferous sequence in the Oslo district was probably deposited in a very shallow marine environment as indicated by its fauna, ooids and the strong micritization of the fossils. The discovery of this sequence is consistent with the rift model for the Oslo Rift Zone, and suggests a connection with the Variscan Ocean.
The Pleistocene rocks of the Cayman Islands
Authors: Brunt M. A. , Giglioli M. E. C. , Mather J. D. , Piper D. J. W. , Richards H. G.
Published: May 2009

In the Cayman Islands a core of Miocene and Oligocene crystalline limestones is overlain unconformably by limestones of the Pleistocene Ironshore Formation. Within this Formation five separate depositional environments are recognized. A reef facies contains corals still in their growth position. This reef facies is succeeded by a back reef facies, followed by a lagoonal facies. The lagoonal facies contains a diverse molluskan fauna of 75 species which differs considerably from that found in the present lagoons around the island. Rocks of these facies are overlain in places by ridges of calcarenite, considered to be shoal deposits. Higher ridges which overlie the Tertiary limestones and reef facies rocks are interpreted as beach ridges. It is thought that the Pleistocene sediments were deposited around a gradually subsiding core of Tertiary rocks.
A geological note on the Qir earthquake, SW Iran, April 1972
Authors: McQuillan H.
Published: May 2009

This note outlines some thoughts on the possible significance of the April 1972 Qir earthquake with respect to the geological structure of Fars Province, SW Iran. The area in which the disturbance occurred belongs to a belt of simple folds of the Zagros system. These folds exhibit localized anomalies of structure which are attributed both to renewed movements along deep-seated basement features and to the modifying effects of salt mobility in the subsurface. The absence of surface indications of rupture in the devastated area is puzzling, but the alignment of zones of maximum destruction to buildings suggests a shallow epicentre associated with a concealed N70°W trending thrust fault system. Such seismicity is indicative of the continued activity of the Zagros orogenic movements.
The palaeontology of the Liassic (Lower Jurassic) clay pits at Stonehouse and Tuffley in Gloucestershire
Authors: Palmer C. P.
Published: May 2009

The two pits expose Pliensbachian silty shales and ferruginous limestones and sandstones. Fossils collectedin situare listed and two new morphospecies of fossil bivalve mollusc are described—Hippopodium tuffleyensisandHettangia aperta. A taxonomic discussion is followed by palaeoecological inferences drawn from the essentially bivalve-dominated molluscan fauna. The conclusions indicate that the silty shales were deposited in well oxygenated waters, probably not exceeding 100 m, and the limestones at even shallower depths. Pebbles in the limestones indicate that some erosion preceded each of the limestones in the Margaritatus zone.
Fluviatile fining-upwards cycles and the magnitude of palaeochannels
Authors: Leeder M. R.
Published: May 2009

The bankfull width (w) of modern meandering rivers (sinuosity >1.7) is related to bankfull depth (h) by the equation w = 6.8h1.54. The equation may be used to calculate limits for the bankfull widths of palaeochannels that deposited alluvial fining-upwards cycles. Calculated bankfull widths and measured bankfull widths from epsilon cross stratification are further used to state ranges of values for meander wavelength and mean annual discharge using existing empirical equations. The empirical equations directly relating width/depth ratios to sediment load and sinuosity are shown to be generally valid only for small rivers because of the increase of width/depth ratios as meandering rivers increase in size.
The petrology of the Warsak alkaline granites, Pakistan, and their relationship to other alkaline rocks of the region
Authors: Kempe D. R. C.
Published: May 2009

A suite of Tertiary alkaline porphyritic microgranites and hybrid and peralkaline granite from northwest Pakistan is described, with six rock analyses (five of them new). The microgranites, an earlier group of which some contain garnet, have undergone metamorphism, lacking in the granites. The microgranites are shown to be precisely similar to those from the Shewa–Shahbazgarhi area, for which four analyses (two of them new) are presented, and related to a third group from Tarbela. The mineralogy of the rocks is discussed, with seven new analyses of aegirine, riebeckite, ferrohastingsite and astrophyllite, and X-ray determinations of the feldspar compositions. The granites are considered to be related to the undersaturated syenites and associated rocks of Koga, and a petrogenetic scheme for the alkaline province is presented, with a K/Ar age determination, tentatively deriving the source magma (quartz trachytic) from a Himalayan tholeiite.
Felsic plutonic rocks from the southern portion of the New Caledonian Ultramafic Belt
Authors: Rodgers K. A.
Published: May 2009

Granodiorite stocks were intruded into the alpine peridotites of southern New Caledonia in the Eocene following overthrusting of the ultramafics onto the sialic core of the island. Strong zoning, from mela-diorite to granodiorite, is developed in one pluton and is believed to be the result of assimilation of ultramafic and mafic rocks by the calc-alkaline magma. Evidence in favour of a consanguineous relationship between the felsic and ultramafic rocks is largely circumstantial. In their petrography, mineralogy and chemistry, the rocks show few differences from other felsic plutonics of Tertiary age in the southwest Pacific.
A marginal Late Proterozoic ocean basin in the Welsh region
Authors: Baker J. W.
Published: May 2009

Re-assessment of the idea that the Monian and Longmyndian accumulated along the margin of a palaeo-ocean suggests that Monian sedimentation occurred near the eastern shoreline of a micro-continent. If Monian igneous activity, metamorphism and deformation are attributed to an underlying subduction zone, this must have dipped northwestwards away from a small ocean basin to the southeast. Consumption of this ocean floor brought about collision with the continental shield and simple deformation of the Longmyndian.
Petrology of the alkali syenites of the Mundwara magmatic suite, Sirohi, Rajasthan, India
Authors: Bose M. K. , Gupta D. K. Das
Published: May 2009

The alkali syenites of the Mundwara magmatic suite, Sirohi district, Rajasthan, in north-western India, are chiefly developed in the Musala hill of the complex. They comprise three principal varieties representing different stages of crystallization, viz. nepheline-sodalite syenite, nepheline-barkevikite microsyenite, and nepheline poor leucosyenite. The dominant constituent of these hypersolvus syenites is alkali feldspar, an orthoclase microperthite showing a variable degree of exsolution. The chief mafic mineral is a distinctly green and zoned sodic pyroxene, close to aegirine-augite in composition. A brown calciferous amphibole, identified as a barkevikite, is developed in addition in the microsyenites. Reddish brown biotite of the phlogopite-annite series is common to all the syenites. The petrography and mineralogy of the syenites are discussed, and a comparative study of the Mundwara syenites with similar rocks of the Deccan volcanic province is presented. Chemistry and mineralogy of the syenites of the Mundwara suite suggest that they are related to those associated with the Deccan volcanic province.
An extension of the granophyric quartz-dolerite intrusion of Centre 2, Ardnamurchan, Argyllshire
Authors: Butchins C. S.
Published: May 2009

Sheet-like bodies of dolerite with granophyre within the Hypersthene-gabbro on the NE shore of Sanna Bay are shown to be akin to the granophyric quartz-dolerite, and suggest that the latter originally extended for a considerable distance N of its previously mapped limits.
The role of CO2 in alkali rock genesis
Authors: Rock N. M. S.
Published: May 2009

The extreme rarity of alkaline rock suites bearing both calcic plagioclase and magmatic carbonatites is believed to reflect a fundamental bifold division between Gabbroic and Carbonatitic types, plagioclase being present only in the former and carbonatite only in the latter. Alkali basalt magma may be parental to both lineages, the gabbroic lineage deriving from normal differentiation under low CO2 pressure, and the carbonatitic by suppression of plagioclase crystallization under high pressures of CO2, leading through pyroxene fractionation to a ‘secondary parental’ olivine-poor nephelinite magma. Support for this hypothesis is found in evidence for the suppression of plagioclase in CO2-rich alkali basaltic magmas and for the secondary origin of olivine-poor nephelinites, in the nature of xenoliths and cumulates at carbonatite complexes, in Sr isotopic data, and in major and trace element compositions of the magmas. The possible origin of melilitic rocks at carbonatite complexes is also briefly discussed.
Vertical igneous layering in the Ewarara layered intrusion, central Australia
Authors: Goode A. D. T.
Published: May 2009

The Ewarara Intrusion of central Australia contains two vertical fine-banded horizons within a sequence of sub-horizontal ultramafic cumulates. The horizons are arranged in an en échelon pattern adjacent to a steep intrusional contact, and consist of an alternation of two layer types which correspond to the two major lithologies present in the horizontal sequence. The horizons are up to 5 m thick. A number of possible origins, including folding of originally horizontal cumulates, flow differentiation and multiple injection, do not satisfactorily explain the formation of the layering. The most likely origin appears to involve differential viscous flow along the steep contact of an inhomogeneous crystal mush derived from the horizontal layered sequence. This mobilization is related to fresh injections along a feeder zone trending 060µ, the only such zone recognized in the Giles Complex.
The Iglesia Irca intrusion and the role of gas brecciation in the emplacement of the Coastal Batholith of Peru
Authors: Bussell M. A. , McCourt W. J.
Published: May 2009

In the Iglesia Irca intrusion early undifferentiated pulses of granitic magma were emplaced at pressures of approximately 1 kb as narrow dykes of vesicular felsite. These dykes are associated with penecontemporaneous burst breccias and gas breccias and are themselves sometimes brecciated. Subsequently a large dyke of granophyre, representing a more fractionated composition, was emplaced by subsidence and stoping along the line of earlier microbreccias, explosion breccias and felsites. The dyke cooled relatively slowly at low structural levels and retained its volatiles while at higher levels more rapid cooling accompanied the greater escape of volatiles. This resulted in marked potassium enrichment of the upper levels of the dyke and the country rocks of the hanging wall. It is argued that the Iglesia Irca intrusion provides an example of the association of gas brecciation with vesiculating and volatile-rich magma which is atypical of the Coastal Batholith as a whole.
Newly discovered Tremadoc rocks in the Carmarthen district, South Wales
Authors: Cope J. C. W. , Fortey R. A. , Owens R. M.
Published: May 2009

Newly discovered Tremadoc rocks in South Wales are described from outcrops south of Carmarthen. The faunas suggest that both the Clonograptus tenellus and Shumardia pusilla Zones are represented, together with possible higher Tremadoc strata.
Sri Lanka in Gondwanaland and the evolution of the Indian Ocean
Authors: Katz M. B.
Published: May 2009

The present position of Sri Lanka and its past fit in Gondwanaland are investigated in relation to the development of the Indian Ocean. The 3 stages in the evolution of the Indian Ocean are shown to be controlled by fundamental NW, NS, and NE Precambrian lineament directions in Sri Lanka and South India. These older lineaments were rejuvenated in the Mesozoic–Tertiary to form oceanic transform faults which determined the phases of Indian Ocean floor spreading.
The trachybasaltic volcanics of the Adrano area, Mount Etna, Sicily
Authors: Duncan A. M.
Published: May 2009

The Adrano area covers approximately 150 km2 of the tower SW flanks of Mount Etna, Sicily. A wide selection of the rocks that occur on the volcano are represented in the area. Lavas of alkalic affinity form by far the greater proportion of the volcanics in the area, and comprise a trachybasaltic suite of lavas ranging from hawaiite through mugearite to benmoreite. There appears to be no overall progressive variation in the chemistry of these trachybasaltic lavas with time; rather that the parental magma has remained fairly constant in composition. Periodically, however, this parental magma has been able to differentiate into more evolved products. The chemical variation shown by the trachybasaltic lavas can be largely explained by crystal fractionation of augite, olivine, plagioclase and titanomagnetite at moderate to low pressures. Crystal fractionation, however, cannot explain the variation in the alkalis which is thought to be affected by volatile transfer.
Mesopotamia: the Tigris—Euphrates delta and its Holocene Hammar fauna
Authors: Macfadyen W. A. , Vita-Finzi C.
Published: May 2009

In 1957, Hudson, Eames & Wilkins proposed the name of Hammar Formation for a series of sands and silts below the surface alluvium of the Mesopotamian Plains near Basrah, Iraq, which yielded a marine molluscan fauna of Holocene age. This paper shows that deposits yielding a very similar molluscan fauna are present at shallow depths at Amarah and Qurmat Ali, and lists the numerous foraminifera recovered from these deposits. Marine or brackish water conditions are thus shown to have prevailed in recent times over a distance of at least 250 km NW of the present head of the Persian Gulf.
K-Ar age determinations of some Miocene–Pliocene basalts in Israel: their significance to the tectonics of the Rift Valley
Authors: Steinitz G. , Bartov Y. , Hunziker J. C.
Published: May 2009

Thirty samples of Upper Tertiary basalts intruding marine and continental sequences were by the K-Ar method. Four volcanic phases are recorded: (a) 24.8±1.5 Ma of the Raqabat e Na'ame dike in Central Sinai; (b) 20.4±0.7 Ma of basalt intrusions in Central Sinai and the Arava. Some of these are offset by E-W to NE-SW dextral faults of the Central Sinai – Negev Shear Zone; (c) 14.5±0.3 to 4.9±1.3 Ma of basalt flows in the Eastern Galilee and the Coastal Plain; (d) 2.7±0.6 Ma of ‘En Yahav dike. These results contribute to the correlation between Tertiary continental formations from different areas, and put limits on the age of tectonic events, such as folding in the Syrian arc, faulting in the Central Sinai - Negev Shear Zone and shearing along the Jordan Rift.
Comparison of the San Andreas Fault System with the Highland Boundary Fault System of Scotland
Authors: Lambert R. St J. , McKerrow W. S.
Published: May 2009

There are close geometrical and dimensional similarities between the faults in Scotland north of the Highland Boundary Fault and faults in southern California east of the San Andreas Fault. It is argued that the Moine Thrust and Oarlock Fault are equivalents and that the Great Glen Fault and the Rosamund Lineament are also equivalent, implying corresponding senses of movement and that the Highland Boundary Fault originated as a dextral transform. The comparison cannot be extended yet to the terrains to the N of the Oarlock Fault or W of the San Andreas or to the corresponding areas in the Caledonides.
The Arctic Caledonides and earlier Oceans
Authors: Harland W. B. , Gayer R. A.
Published: May 2009

Consideration of the arctic configuration of the Caledonides leads to a distinction between eastern and western geosynclinal belts. The western belt, comprising the East Greenland, East Svalbard and southern Barents Sea Caledonides is postulated to continue northwards into the Lomonosov Ridge, whilst the western Spitsbergen Caledonides are thought to have originated as part of the North Greenland geosyncline which is also thought to continue northwards to form the western part of the Lomonosov Ridge. The eastern Caledonian geosynclinal belt comprising the Scandinavian Caledonides appears to swing eastwards to link with the Timan Chain and possibly the Urals.

The already postulated (‘Proto-Atlantic’) ocean concept is reviewed in the light of the Arctic Caledonides and named Iapetus. Faunal provincialism suggests that the ocean was in existence up to early Ordovician but had substantially closed by mid Ordovician times. Possible relics of the suture marking the closure of this ocean suggest that it lay to the west of the Arctic Scandinavian Caledonides trending NE to latitude 70° N and thence veered eastwards separating the southern Barents Sea Caledonides from those of Arctic Scandinavia, possibly connecting with the northern Uralian ocean. A previous branch of the ocean may have separated East Svalbard and East Greenland as an ocean-like trough. A further (pre-Arctic) ocean may have existed to the north of the North Greenland–Lomonosov Ridge geosynclines. This is named Pelagus.

The closure of these oceanic areas and the deformation of the bordering geosynclines delineates three principal continental plates, namely, Baltic, Greenland and Barents Plates. Their relative dominantly E–W motion up to Silurian times produced compression between the Greenland and both the Baltic and Barents plates but dextral transpression and transcurrence between the latter plates. In Late Silurian to Devonian times an increasing northward component controlled late Caledonian transpression and sinistral transcurrence between the Greenland plate and the combined Baltic and Barents plates.
The significance of primary structures in the Ordovician pillow lava sequence of Western Norway in an understanding of major fold pattern
Authors: Furnes H. , Skjerlie F. J.
Published: May 2009

The present paper deals with the Lower Ordovician–Silurian rocks between Fördefjord and Sognefjord on the western coast of Norway. During the Caledonian orogeny this sequence was subjected to several phases of Silurian deformation, the first of which resulted in the formation of a large-scale anticline (the Stavfjord Anticline), which now occupies part of an overthrust unit. On the basis of ‘way-up’ criteria in the partly well-preserved Lower Ordovician pillow lavas it has been possible to determine with some confidence the geometry of the Stavfjord Anticline, its probable regional extension and the position of the axial plane trace. Arcuate deflections in the trend of this axial plane trace are a result of large-scale refolding, the later fold axes having WNW–ESE trends.
The Eller Beck Formation (Bajocian) of the Ravenscar Group of NE Yorkshire
Authors: Knox R. W. O'B.
Published: May 2009

The Eller Beck Formation is a thin marine intercalation in a predominantly non-marine Middle Jurassic sequence of coal measures facies. The formation consists of thin transgressive ironstones and siltstones at the base which are overlain by a thicker regressive sequence of shale passing upwards into sandstone. The close association between changes in the local subsidence pattern and the transgression suggest that the incursion resulted from epeirogenic movement rather than from eustatic rise in sea level or a purely sedimentation-controlled change in delta distributary pattern. Facies distribution was greatly affected by local synsedimentary tectonic movement. Water depths were probably very small throughout, and tidal effects on sedimentation minimal.
The Phillipsinella Parabola—Staurocephalus Clavifrons fauna and Upper Ordovician correlation
Authors: Price D.
Published: May 2009

Horizons characterized by the trilobites Staurocephalus clavifrons and/or Phillipsinella parabola have long been regarded as significant in Upper Ordovician correlation. From time to time this idea has been formalized by the erection of Phillipsinella parabola or Staurocephalus clavifrons Zones or by equating the range of a ‘Phillipsinella parabola fauna’ with Series sub-divisions within the Standard Ordovician succession. At the present time the Phillipsinella parabola-Staurocephalus clavifrons fauna is widely regarded as indicating a Rawtheyan age (Ashgill Zones 5–7).

Recent work by the author, however, together with a review of available evidence from the literature casts grave doubts on the validity of such concepts. It is suggested that in some areas the Phillipsinella parabola-Staurocephalus clavifrons fauna may range at least as low as basal Cautleyan (Ashgill Zone 1).
Plateau phonolite lava flows, Kenya
Authors: Lippard S. J.
Published: May 2009

The Miocene phonolite succession of the Uasin Gishu Plateau comprises seven flows totalling about 600 km3 in volume and covering an area of some 6500 km2. Each flow has a number of recognizable and laterally persistent features which permit it to be recognized over a wide area (thousands of square kilometres). These flows originated within the Rift Valley and flowed westwards for distances of up to 60 km across the marginal plateau area.
Homological variability of archaeocyathans
Authors: Rozanov A. Yu
Published: May 2009

The history of the study of homological variation in the archaeocyathans is reviewed and some morphological details defined. Homological variability is considered at generic and familial level and a new detailed table of the homological series at generic level is presented.
The geology of the Katete carbonatite, Rhodesia
Authors: Lee C. A.
Published: May 2009

The Katete carbonatite is situated in an area of rifting in the NW of Rhodesia. It consists of varieties of carbonatite and of agglomerates. There is little alteration of the surrounding sandstones and there are no associated alkaline rocks. The age of the complex is mid-Cretaceous, which is about the same as the later stages of carbonatite activity in the Rufunsa Valley in Zambia.
A method for the measurement of volume change
Authors: Barr M. , Coward M. P.
Published: May 2009

A method for measuring volume change, which involves combining measurements of the strain ratio with the angle between the surface of no finite longitudinal strain and the principal extension direction in a principal plane, has been used to obtain values for the volume change in two groups of deformed rocks in southern Africa.
The Manubriate Isograptids
Authors: Beavis F. C.
Published: May 2009

The reference of Isograptus manubriatus (T. S. Hall) to the genus Maeandrograptus Moberg by Skevington (1968) is argued to be invalid. A new genus, Pseudisograptus has been introduced to which the manubriate isograptids I. manubriatus, I. hastatus, and I. dumosus are referred.
A contribution to the geology of the Annapurna and Nilgiri Himals, Nepal
Authors: Waltham A. C.
Published: May 2009

Within the Tethyan Zone of Central West Nepal, the Nilgiri Limestone is the dominant unit. The significance of the separation of the Larjung Formation is questioned in the light of new outcrops examined, and the Nilgiri Sandstone is described. Recumbent fold structures are correlated between Annapurna, Nilgiri and Dhaulagiri. Between these mountains the Thakkhola graben faults are continued southwards, and estimates are made of the magnitude of their throws.
Penecontemporaneous folding from the Lower Palaeozoic of the Trondheimsfjord region, Norway
Authors: Roberts D.
Published: May 2009

Occurrences of penecontemporaneous folds of varying style and amplitude are described from low-metamorphic flysch sediments from an area in the Central Norwegian Caledonides. A short discussion of the mode of formation of these folds is presented, and from geometrical considerations it is suggested that, in several cases, both foundering and slumping have contributed to the overall deformation. The significance of the presence of these structures in the stratigraphical sequence is outlined, and the inherent danger of their possible misrepresentation as tectonic folds in higher metamorphic areas is briefly discussed.
Age of the Eycott Volcanic Group and its conformable relationship to the Skiddaw Slates in the English Lake District
Authors: Downie C. , Soper N. J.
Published: May 2009

An earliest Llanvirn age is established on micropalaeontological grounds for the interbedded lava–pelite sequence at the base of the Binsey Volcanic Formation in the northern Lake District. The northern volcanic sequence, here termed the Eycott Volcanic Group, is earlier than, and chemically distinct from, the main Borrowdale Volcanic Group. The evidence precludes a regional unconformity between the Skiddaw Slates and the overlying volcanic rocks, but is compatible with the hypothesis that the vulcanicity occurred in an island arc environment.