bluuebunny/crossref_metadata_2025 huggingface dataset:
The preservation of fossil leaves in Cretaceous volcaniclastic rocks from Alexander Island, Antarctica
Authors: Jefferson T. H.
Published: May 2009

Leaf compression fossils are abundant within the lower Cretaceous part of the Fossil Bluff Formation in southern Alexander Island, Antarctica. They occur in lacustrine laminated siltstones with a high volcaniclastic component. During zeolite facies metamorphism of the rocks, breakdown of clay minerals, volcanic glass and calcic plagioclase generated new mineral phases. The growth of these minerals was concentrated within and around leaves: finely disseminated oxide of titanium crystallized within the organic material, a thin film of chlorite was precipitated around leaves and silica, calcite and laumontite grew disruptively between leaf cuticles. Despite relatively low levels of organic maturation the structure of the leaf cuticles was destroyed and the only details which survived were those preserved as impressions in the chorite film.
A thermokarst phenomenon on a terrace of the River Wey near Farnham, Surrey, England
Authors: Fisher P. , Rolls J. D.
Published: May 2009

Palaeochannels developed in a terrace of the River Wey are described. Their morphology, relationship with the underlying Folkestone Sands, and the character of associated superficial deposits all suggest that the channels are examples of thermokarst phenomena, probably of Devensian age.
Partial melting of feldspathic quartzite around late Caledonian minor intrusions in Appin, Scotland
Authors: Platten I. M.
Published: May 2009

Granophyre patches on the sites of former sedimentary feldspars in the feldspathic Appin Quartzite show that partial melting took place in the inner parts of the aureoles of late Caledonian minor intrusions. Mobilization of the melt and refractory quartz residue as a thixotropic suspension is shown to result in the formation of veins and breccias. Textures are related to the wetting of quartz/quartz grain bounderies by the eutectic melt and the later growth of crystals during cooling. From the presence of high (β) quartz coexisting with melt, minimum contact temperatures are estimated as 780°C, showing that some convective circulation of magma took place.
Pyroxene accumulation in spinifex-textured rocks
Authors: Campbell I. H. , Arndt N. T.
Published: May 2009

Natural pyroxene spinifex-textured rocks, free of olivine, may have MgO contents as high as 15%. If these rocks are allowed to crystallize in the laboratory under equilibrium conditions, olivine is the liquidus phase at 1350°C and pyroxene does not appear until the temperature has fallen to 1180°C. A similar problem is encountered in high MgO komatiites. If spinifex-textured and aphyric komatiites from Munro Township are plotted on an MgO-CaO-Al2O3 diagram, olivine control is evident until the MgO content of the melt falls to 15%. At this point the liquid trend moves away from the CaO-MgO boundary, indicating the crystallization of pyroxene. If a high MgO komatiite is crystallized in the laboratory under equilibrium conditions, pyroxene does not appear until the MgO content of the liquid reaches 9%. It is suggested that experimental and natural systems behave differently because pyroxene has crystallized metastably in the natural system under conditions of extreme supercooling. The early metastable crystallization of pyroxene can only affect the liquid trend if the spinifex zone contains a cumulate component.
Evidence for an incipient early Caledonian (Cambrian) orogenic phase in southwestern Norway
Authors: Furnes H. , Austrheim H. , Amaliksen K. G. , Nordas J.
Published: May 2009

Summary. Quartz-keratophyres from an ensimatic island arc on Bømlo, southwest Norwegian Caledonides, resting on the Lykling ophiolite, have yielded a Rb/Sr whole rock age of 535 ± 46 Ma. This Cambrian age, which is a minimum age of formation for the ophiolite, indicates an early phase of subduction, corresponding with the orogenic activity known from northern Norway, i.e. the Finnmarkian. Before Middle Ordovician time, the ophiolite and ensimatic arc had been obducted onto continental crust and deformed, as they are unconformably overlain by a volcanic complex of subaerial rhyolites and andesites which have yielded Rb/Sr whole rock ages of 464 ± 16 and 468 ± 23 Ma respectively.
Rapid estimation of porosity and mineral abundance in backscattered electron images using a simple SEM image analyser
Authors: Pye K.
Published: May 2009

Image analysis is rapidly becoming an integral part of scanning electron microscopy. A number of analogue and digital image analysis systems of varying sophistication are now commercially available for the SEM. This paper illustrates how one such relatively simple system, the IMAS image analyser manufactured by Cambridge Technology, can be used to obtain rapid quantitative estimates of porosity and mineral abundance in backscattered electron images of polished rock sections.
The Pusgillian Stage in Wales
Authors: Price David
Published: May 2009

On the basis of previous work in Northern England and in Southern Scotland the Pusgillian Stage is in turn related to the stratigraphical ranges of selected trilobite species and to the standard graptolite zonal scheme. Thus characterized it can be recognized in rocks of ‘shelly’ facies at localities in the northwest, southeast and south-central Berwyn Hills of North Wales and possibly in the Llandeilo area of South Wales, but does not seem likely to be developed in any rocks of graptolitic facies in Wales.
Interpretation of the Middle Jurassic ammonite genus Spiroceras
Authors: Howarth M. K. , Melville R. V.
Published: May 2009

The taxonomy of the Middle Jurassic ammonite genus Spiroceras Quenstedt, 1856, is critically assessed. It is found that the genus was originally proposed conditionally without any included species, and the type species is Spiroceras bifurcatum Hyatt, 1900, by subsequent monotypy. A neotype is now designated for that species, because Hyatt's figured holotype is lost.
Obruchevella from the early Cambrian Meishucun Stage of the Meishucun section, Jinning, Yunnan, China
Authors: Xueliang Song
Published: May 2009

Well-preserved, silicified Obruchevella from the earliest Cambrian (Meishucun Stage) sequence from Meishucun section in Yunnan Province, China contains distinct cross-partitioning. This suggests that this helically coiled microfossil represents the remains of an oscillatorialean cyanophyta. Obruchevella is a microfossil that exhibits a variety of form that may be produced through degradation. Obruchevella identified in the Meishucun section includes O: parva, O. parvissima, O. delicata, O. meishucunensis and several other morphs which are yet to be identified.
Silurian volcanism in the central Welsh Borderland
Authors: Sanderson R. W. , Cave R.
Published: May 2009

This study of Silurian volcanism considers three small intrusions near Bishop's Castle, Salop, as possible volcanic feeders. Acid magma intrusive into Silurian calcareous siltstones has resulted in microgranite dykes, hornsfelsed country rock and metasomatized breccia. The intrusions are of late Wenlock age or younger, but they are relatable to other Wenlock igneous rocks in the area, and are in contrast to nearby Carboniferous basaltic rocks.
Basement blocks and tecto-sedimentary evolution in the Pyrenees during Mesozoic times
Authors: Peybernès Bernard , Souquet Pierre
Published: May 2009

The Alpine tectonics in the Pyrenean Range is controlled by motions of basement blocks (High Primary Range, North Pyrenean blocks). These blocks belong to different tectonic units; they are amygdaloid, wedge-shaped, squeezed at their roots, upthrust and displaced with their cover (detached or not) in a convergent shear zone between the European and Iberian plates. These basement blocks are distributed within isopic (isofacial) units with diachronous terrigenous prisms. The stratigraphical analysis of their Mesozoīc cover reveals their relative position during the Mid-Cretaceous continental break-up which induced the separation of the two previously joined plates.
A geometrical approach to percolation through random fractured rocks
Authors: Rivier N. , Guyon E. , Charlaix E.
Published: May 2009

The permeability of rocks fractured by random, planar cracks, is expressed as a classical bond percolation problem on a random lattice, by Voronoi partition of space. The percolation threshold is determined as a function of the statistical characteristics of the cracks, or of their traces on an arbitrary face of the rock, by using an empirical quasi-invariant of percolation theory.
Hybridization and the petrogenesis of composite intrusions: the dyke at An Cumhann, Isle of Arran, Scotland
Authors: Kanaris-Sotiriou R. , Gibb F. G. F.
Published: May 2009

The composite dyke at An Cumhann, Arran consists of a central unit of quartz-feldspar porphyry flanked by narrow marginal dolerites containing xenocrysts of quartz, plagioclase and alkali feldspar identical to the phenocrysts in the porphyry. The chemistry of the marginal dolerites indicates that they formed by the crystallization of a hybrid magma produced at depth by the incorporation of the porphyritic acid magma in a basic liquid. During the intrusion of the hybrid magma, flow caused a differential distribution of the xenocrysts across the initial basic dyke. Subsequent intrusion of the quartz-feldspar porphyry magma along the still unconsolidated centre of the basic dyke produced the wide central unit. A similar origin is proposed for other composite intrusions of the same type in the region. Whilst it is unlikely that the coexistence of the highly contrasting magmas necessary for the formation of these intrusions is entirely coincidental there is little likelihood that the two liquids were related as members of the same fractionation series.
Zonation, mixing and eruption of silica-undersaturated alkaline magma: a case study from Tenerife, Canary Islands
Authors: Wolff John A.
Published: May 2009

The mineralogy and petrology of banded pumice clasts from a mixed-magma non-welded ignimbrite on Tenerife, Canary Islands, is described. Phenocrysts, which frequently show signs of resorption, are grouped into three assemblages in mutual disequilibrium; these assemblages were originally precipitated by alkali basalt magma (assemblage 1, titanaugite + olivine + calcic plagioclase + high-Mg Fe–Ti oxides), trachyandesitic magma (assemblage 2, salite + kaersutite + sodic plagioclase + hauyne + medium-Mg Fe–Ti oxides) and phonolitic magma (assemblage 3, aegirine-augite + biotite + sodic sanidine + sodalite + nepheline + sphene + low-Mg magnetite) respectively. Phenocryst types (e.g. clinopyroxene, feldspar) which are common to two or all assemblages are compositionally distinctive in each. The excess silica content of nepheline in assemblage 3 indicates a temperature of 770 °C for phonolitic magma, while Fe–Ti oxides and clinopyroxene-ilmenite give temperatures of 915 °C and 907 °C respectively for the trachyandesite. Assemblage 1 and 2 phenocrysts are set in mafic glass; assemblage 3 phenocrysts are only found in a matrix of salic (phonolitic) glass. Analyses of the volumetrically dominant phonolitic glass define a compositional trend consistent with fractionation of assemblage 3 phenocrysts. Analyses of the mafic glass scatter about a straight-line trend produced by mixing of phonolitic liquid with homogeneous intermediate (trachyandesitic) magma. These relations are interpreted as the result of two distinct magma mixing events, consequent on the invasion of a stably zoned magma chamber containing phonolitic liquid stratified above denser trachyandesitic magma, by intruding basaltic magma. High Ca content of assemblage 1 plagioclase suggests precipitation of the basaltic phenocrysts under locally high partial pressure of water. The preferred model involves, in chronological sequence: (i) generation of a differentiated phonolitic cap above trachyandesitic magma, through wall crystallization and boundary-layer uprise of phonolite; (ii) pooling, convective heat loss, and partial crystallization of dense, hydrous alkali basalt magma injected into the chamber and forming a liquid layer beneath the trachyandesitic magma; (iii) volatile saturation of the residual basalt liquid through crystallization, consequent buoyant uprise into, and efficient mixing with, trachyandesite; (iv) eruption of chamber contents and partial mixing of the mixed basalt–trachyandesite with phonolite, although the precise relative timing of eruption and the second mixing event is not known.
Cretaceous-Palaeogene sub-basaltic and intrabasaltic sediments of the Kangerdlugssuaq area, Central East Greenland
Authors: Higgins A. C. , Soper N. J.
Published: May 2009

Cretaceous-Palaeogene sediments of the Kangerdlugssuaq area on the continental margin of Central East Greenland were deposited in an embayment of an extensive pre-NE Atlantic shelf sea. Pre-Sparnacian sediments are thin (150 m), incomplete and of siliciclastic type, formed in shallow marine waters. Sparnacian times saw the onset of vigorous basaltic vulcanicity, marking the initial rifting episode between Greenland and Eurasia. Uplift immediately prior to the vulcanicity is evidenced by an unconformity at the base of the Sparnacian, above which basement-derived arkosic sandstones and conglomerates are followed by about 1.5 km of coarse volcaniclastics, basaltic flows of dominantly picritic composition, pro-grading hyaloclastite wedges and thin siltstones with abundant organic detritus. Very rapid subsidence accompanied this early phase of vulcanicity, maintaining the top of the pile close to sea level and allowing the deposition of a further kilometre of waterlain tuffs in the embayment. Sedimentation extended northwards and eastwards on to basement rocks at this period, with the formation of a non-marine sequence which includes coals.

The overlying plateau tholeiites overlap the earlier volcanics; their depositional area was extremely extensive along the East Greenland margin and bears no relationship to the Kangerdlugssuaq sedimentary embayment, although their thickest development, 4 km or more, was attained in that region. Eruption rate of the pile exceeded subsidence for a period and it is dominantly subaerial.

This sequence of events is compared with the similar history of sedimentation and basaltic vulcanicity on the west coast of Greenland, and it is inferred that just as the East Greenland sequence records the initiation of spreading between Greenland and Rockall-Faeroe at anomaly 24−25 time, so that of West Greenland marks the propagation of the Labrador Sea spreading axis through the Davis Strait into Baffin Bay at anomaly 26−27 time.
A marine fauna from the Dartmouth Beds (Lower Devonian) of Cornwall
Authors: Evans K. M.
Published: May 2009

A brachiopod fauna is described from a marine horizon within the Dartmouth Beds at Bull Cove, Cornwall. The fauna indicates a Middle or Late Siegenian age and aspects of the palaeoecology are discussed. The Lower Devonian succession of south Devon and north Cornwall is discussed and the terms Meadfoot facies and Standon facies are proposed to replace the Meadfoot Beds and Staddon Grits of the old terminology.
Structural and photogeological evidence for the boundaries to an East Arabian' block
Authors: Hancock P. L. , Al-Khatieb S. O. , Al-Kadhi A.
Published: May 2009

Computer-enhanced Landsat images reveal a 65 km arcuate lineament linking the concealed fault zone beneath Wadi Al-Batin to the central Arabian graben and trough system. Detection of the link allows a continuous 1000 km arc of faults and troughs cutting the Mesozoic-Cenozoic rocks of the Arabian Shelf to be recognized. The arc, here called the East Arabian fault zone, is interpreted as forming the western and southern boundaries of the East Arabian block, a tectonic unit underlying at least 200 000 km2 of the Arabian Peninsula.

Stratigraphical relationships within the 560 km central Arabian graben and trough system demonstrate that its faults were active during the late Cretaceous-early Palaeogene, movements ceasing when the Red Sea began to open and the Arabian subplate was established. The principal hydrocarbon fields of the Arabian Peninsula lie within the boundaries of the East Arabian block.
On polygenetic myrmekite
Authors: Phillips Evan R.
Published: May 2009

A brief review of Becke's (1908) replacement and Schwantke's (1909) exsolution models for myrmekite genesis and further consideration of the morphology and spatial distribution of myrmekite as outlined by Phillips (1974) lead to the conclusion that both hypotheses have a place in explaining the origin of myrmekite. The Schwantke model is generallybest applied, for example, to high-level undeformed massive granitoids and the Becke model to deformed metamorphic rocks. The latter hypothesis and a third model involving interaction between exsolution and replacement (Ashworth, 1972) may be used especially to explain the association of muscovite and myrmekite in rocks whose mineral assemblages have undergone retrograde modification, involving either redistribution of Na, Ca and K by local metasomatic reactions among the mineral grains, or metasomatic change of bulk rock composition.
Revision of the Dinantian stratigraphy of the Craven Basin, N England
Authors: Fewtrell M. D. , Smith D. G.
Published: May 2009

New work on the sedimentology and palaeontology of the classic area of the ‘basinal’ facies of the Carboniferous Limestone requires that a formal lithostratigraphic framework be established to rationalize the existing system of local rock units and regional lithofaunal ‘groups’ and ‘series’. Five formations, based on the existing ’groups‘ in the Clitheroe area, are defined for the whole Craven Basin outcrop. They are, from the base, the Chatburn Limestone Formation, the Clitheroe Limestone Formation (which includes the ’reef-knolls’ of the Clitheroe area), the Worston Shale Formation, the Pendleside Limestone Formation (to include the knolls of the Craven reef belt) and the Bowland Shale Formation. The chronostratigraphy, in terms of the six British Dinantian Stages, and a provisional micropalaeontological biostratigraphy are outlined.
Volcanic pebbles in Pleistocene gravels of the Thames in Buckinghamshire and Hertfordshire
Authors: Green C. P. , Hey R. W. , McGregor D. F. M.
Published: May 2009

The incidence of volcanic pebbles in the gravels of the middle Thames basin is noted. The detailed petrography of volcanic clasts at two sites is described and found to be broadly similar to that of material from sites in East Anglia, thought to be of Welsh origin. The frequency of volcanic pebbles in the two areas is also similar. This evidence suggests that volcanic material was brought into East Anglia via the ancestral Thames.Records of volcanic rocks in the drift deposits of the upper Thames basin provide additional evidence of this route.
Age of the Cedarberg Formation, South Africa and early land plant evolution
Authors: Gray J. , Theron J. N. , Boucot A. J.
Published: May 2009

The first occurrence of Early Paleozoic land plants is reported from South Africa. The plant remains are small, compact tetrahedral spore tetrads. They occur abundantly in the Soom Shale Member of the Cedarberg Formation, Table Mountain Group. Marine? phytoplankton (sphaeromorphs or leiospheres) occur with the spore tetrads in all samples. Rare chitinozoans are found in half the samples. Together with similar spore tetrads from the Paraná Basin (Grayet al.1985) these are the first well-documented records of Ashgill and/or earlier Llandovery land plants from the Malvinokaffric Realm, and from the African continent south of Libya. These spore tetrads have botanical, evolutionary, and biogeographic significance. Their size in comparison with spore tetrads from stratigraphic sections throughout eastern North America, suggests that an earliest Llandovery age is more probable for the Soom Shale Member, although a latest Ordovician age cannot be discounted. The age of the brachiopods in the overlying Disa Siltstone Member has been in contention for over a decade. Both Ashgillian and Early Llandovery ages have been proposed. The age of the underlying Soom Shale Member based on plant spores and trilobites (earliest Llandovery or latest Ashgillian) suggests that the Disa Siltstone Member is also likely to be of Early Llandovery age, although the distance between the Soom Shale Member spore-bearing locality and rocks to the south yielding abundant invertebrate body fossils at one locality is great enough to permit diachroneity.
Randomness in the pattern of ‘mass extinctions’ and ‘waves of origination’
Authors: Hoffman Antoni , Ghiold Joe
Published: May 2009

‘Mass extinctions’ and ‘waves of origination’ are defined as peaks in the average probability of family extinction and origination per geologic stage, respectively. A simple neutral model is proposed, assuming only that the average probabilities of family extinction and origination have varied independently and had equal chances of going up and down from one stage to another. As a null hypothesis, this model is not rejected by the available palaeontologic data on marine animal and nonmarine invertebrate families in the Phanerozoic. The only discrepancy between the model and the empirical pattern is due to a systematic bias introduced by Fossil-Lagerstätten. The alleged periodicity of Late Phanerozoic mass extinctions follows inevitably from the model.
The Cenomanian hiatus in the Southern Benue Trough, Nigeria
Authors: Amajor L. C.
Published: May 2009

Basal Turonian Ezeaku Sandstone ridges along the Cenomanian hiatus in Afikpo area contain sandstone pebbles, cobbles, and boulders randomly distributed in nearly all the coarsening upward subfacies of the host units. Contacts with the host sandbody are sharp and, in places, lined with solution grooves. Generally, the angular to subrounded clasts have their 2 mm rims ferruginized, are fine to coarse grained and very strongly bioturbated. They are compositionally and texturally more similar to the adjacent Albian Asu River Group sandunits. These characteristics suggest an extrabasinal origin for these marine sandstone clasts. Albian Asu River Group sediments uplifted by the Cenomanian deformation are the most likely source. The general absence of similar clasts towards the eastern palaeostrandline where the primary Cretaceous source rocks lay is consistent with the interpretation. The remarkable parallelism between the trend of the clast outcrops and the axis of the Santonian anticlinorium (NE–SW) suggests the same axial direction for both tectonic phases.
An application of the second derivative as a tool in tectonic analysis in the Qattara Depression area, Egypt
Authors: El-Hussaini A. , Youssef M. , Ibrahim H.
Published: May 2009

The second derivative of gravity anomalies of the Qattara area was analysed and statistically studied for determining the tectonic elements. Zones of zero second derivative were considered as the locations of possible faults. The analysis of a constructed tectonic map portrays the predominance of N45°W, N85°E and N45°E fault trends in addition to less pronounced N15°E and N–S faults. The NW–SE faults are very old and inherited from the basement structures. They acted as first order right-lateral wrench faults during the Alpine tectonism. Second and higher orders of faults, developed as a consequence of these movements, are represented by the N85°E and other less abundant trends. Vertical movements along the existing fault system, in addition to the horizontal displacement, is supported by the analysis of the pronounced anomalies of the second derivative map. The subsurface structural picture of the area is composed of uplifted and downfaulted adjoining blocks.
Conglomerate-hosted copper mineralization in Cretaceous Andean molasse: the Coloso Formation of northern Chile
Authors: Flint S. , Clemmey H. , Turner P.
Published: May 2009

Alluvial fan sediments of the Lower Cretaceous Coloso Formation of northern Chile were deposited during the evolution of a half-graben, arid, intra-arc basin. The sediments were derived from an andesitic volcanic arc and show compositional variation which can be interpreted as an unroofing sequence. Copper mineralization is stratigraphically restricted to the upper 150 m of the sequence in conglomerates of predominantly granodioritic composition. The presence of mineralized clasts at this level indicates the erosion of bedrock mineralization. Lead isotopic signatures of ore sulphide support the sedimentological evidence for derivation of the sediments and metals from an island arc volcano-plutonic complex to the west of the basin.

A genetic model is proposed in which uneconomic metal concentrations were transported into the basin as detrital phases and released by diagenetic reactions. The precipitation of copper minerals followed authigenic formation of quartz, feldspar, analcime and calcite and also some secondary parosity generation. Copper minerals include the oxychloride atacamite, and the suphides bornite, digenite, djurleite and covellite. Sulphur isotope values for the sulphides are relatively heavy isotope-enriched (δ34S = −3.6 to −12.8‰). Although these results could be interpreted in terms of closed-system bacterial sulphide reduction there is no known occurrence of organic material within the Coloso basin. An alternative explanation involving the mixing of diagenetically derived copper-rich brines and sulphur-rich hydrothermal fluids is proposed to account for the Coloso mineralization.
Graptolites from the type Arenig Series
Authors: Zalasiewicz J. A.
Published: May 2009

The graptolites recovered from the Carnedd Iago Formation of Arenig Fawr, Gwynedd, North Wales are described. They originate from the type section of the Arenig Series and comprise the species Didymograptus aff. simulans Elles & Wood, D. aff. deflexus Elles & Wood, D. cf. praenuntius Törnquist, Azygograptus cf. eivionicus Elles and Tetragraptus reclinatus Elles & Wood.
The parental magma on Rhum: evidence from alkaline segregations and veins in the peridotites from Salisbury's Dam
Authors: Kitchen D. E.
Published: May 2009

Feldspathic peridotites on Rhum contain teschenite segregations and veins. Bulk rock and mineral compositional trends define a path of alkali and iron enrichment related to discontinuous isolation of evolving intercumulus melts. Compositionally zoned and skeletal crystals of actinolite, zircon, apatite, sphene, epidote and chlorite are enclosed by clear analcime, and appear to have grown directly from a water-rich fluid at some undercooling, and below dry equilibrium solidus temperatures. The occurrence of late stage residua with undersaturated alkalirich characteristics in the Rhum ultrabasic complex suggests that the patental magma was alkaline rather than tholeiitic, and had similarities to the Plateau Magmas on Skye.
Certain mechanical aspects in comparative continental rifting with a special reference to the Baikal rift
Authors: Bahat Dov
Published: May 2009

In the Baikal rift fracture initiation, propagation and bifurcation occurred under energy conditions considerably higher than in other continental rifts. The brittle fracture of this rift was strongly influenced by the adjacent Siberian platform. Comparative continental rifting suggests that rift initiation reflects local mantle rather than regional crustal conditions. Three aspects related to fault bifurcation in rifts include intensity and repetition of branching, as well as displacement along branching planes; the three should be distinguished.
Tretaspis radialis Lamont and allied species (Trilobita)
Authors: Price D.
Published: May 2009

Recently discovered specimens from the Portrane Limestone Formation of eastern Ireland are regarded as topotypes of Tretaspis radialis Lament and used to further characterize the species. The features shown by these specimens confirm the close relationship between T. radialis and forms from Zones 2–4 of the Cautleyan Stage of northern England and Wales and allow its differentiation from T. moeldenensis Cave and from another related form of low Rawtheyan age which is here erected as a new species, T. caritus sp.nov.
Discovery of Late Precambrian trace fossils in Jersey, Channel Islands
Authors: Squire A. D.
Published: May 2009

Feeding burrow trace fossils are recorded from the Upper Brioverian of St Ouen's Bay, Jersey. The traces resemble Sabellarites (Dawson) and represent deep water turbidity metazoans of Late Precambrian age, which are unknown in the remaining Brioverian of the Massif Armoricain.
The petrology of the basic and intermediate rocks of upper Swat, Pakistan
Authors: Jan M. Qasim , Kempe D. R. C.
Published: May 2009

A series of metamorphosed (amphibolite facies) basic and intermediate igneous rocks from upper Swat, Pakistan, is described, with seven chemical analyses. The rocks intrude ?Palaeozoic metasediments and are partially bordered by other, later, intrusive and volcanic rocks. The group, now represented by, from S–N, epidote amphibolites, amphibolites, noritic and hypersthene gabbros, and quartz diorites, is considered to be derived from a series of plagioclase hypersthenites, norites, hypersthene gabbros, and hypersthene diorites. Variation diagrams are used to show that the series forms a differentiated sequence; FMA and lime-alkali diagrams suggest that it is similar to the rocks of the Garabal Hill–Loch Fyne area of Scotland. Some of the mineralogy of the group is briefly discussed, with five chemical analyses. A K/Ar age determination gives 67 Ma; thus the rocks probably derive from an early Himalayan (Alpine) tholeiitic basalt magma.
A review of the Triassic vertebrate faunas of Svalbard
Authors: Cox C. B. , Smith David G.
Published: May 2009

Identifications of new material collected by Cambridge expeditions and a new find from Hopen are discussed with reference to earlier work and to the stratigraphic setting. All available generic names relating to Svalbard material are listed systematically. A supplement to the alphabetical index of records (Buchanet al., 1965) is added.
Scapolite compositional change in a metamorphic gradient and its bearing on the identification of meta-evaporite sequences
Authors: Kwak T. A. P.
Published: May 2009

Scapolite occurs in the NE Mt Lofty area of South Australia in rocks of bulk compositions as diverse as sulphide-rich veins, meta dolerite, scapolite (pelitic) schists, calc-silicate rocks and impure marbles. Scapolites analysed from all these rocks show with increasing grade a linear to near-linear change in composition from Me50 and Me66. Some scatter around these values is attributed to local perturbations of fCl/fCo2 in the fluid phase during metamorphism. Sulphur values as SO3 are below the 0.02 level even when scapolite occurs in contact with sulphides in a vein in a small copper mine; here, however, an interpreted FeO value of 2.58 weight % was recorded. The values in this study are comparable with those of Heitanen (1967), and are believed to be representative of products of normal metamorphic fluids evolved from non-evaporitic metamorphic rocks under a greenschist–amphibolite facies gradient; they can thus be used as a standard in assessing the possible significance of meta-evaporites in other areas.
The Ashgill Series near Welshpool, North Wales
Authors: Cave R. , Price D.
Published: May 2009

The name Trawscoed Mudstone Formation is proposed for previously undescribed mudstones cropping-out between the Caradoc Nod Glas Formation (‘Gwern-y-Brain Group’ of Wade, 1911) and the overstepping Rhuddanian Powis Castle Conglomerate Formation some 5 km NW of Welshpool, North Wales. The mudstones have a fauna, dominated by brachiopods and trilobites, which indicates that they are contained within the Cautleyan Stage of the Ashgill Series and suggests deposition in a deep shelf environment.
Layered gabbros in the Eastern Lizard, Cornwall, and their significance
Authors: Kirby G. A.
Published: May 2009

Small-scale igneous layering and lamination have been found in the gabbro of the Eastern Lizard, Cornwall. An origin by gravitational settling of plagioclase and olivine crystals is proposed. Several post accumulation factors have obscured the lateral continuity of these features.Their present orientation suggests that the gabbro has been rotated through approximately 90° about an E—W axis and‘ tops’ to the N. This invalidates the idea of an in-situ ring intrusion but is in keeping with the ophiolite model for the Eastern Lizard.
Breccias.
Authors: Reynolds S. H.
Published: May 2009

Breccias in general have been exhaustively discussed by W. H. Norton, and Bonney has fully described a large number of sedimentary origin. But since these papers were written attention has been drawn to certain fresh types of brecciated rock, and perhaps a briefer account than that in Norton's paper and one referring more particularly to British examples may be of service.
The mineralogical modification of the chemistry of metamorphic rocks
Authors: Leake B. E.
Published: May 2009

It is pointed out, with a few examples, that metamorphic rock compositions can be significantly modified by the stable mineralogy that itself may provoke metasomatic movement, as distinct from externally actuated metasomatism.
Clastic dykes in the Namurian shales of Co. Leitrim, Republic of Ireland
Authors: Brandon A.
Published: May 2009

A description is given of the numerous thin dolomitic sandstone dykes cutting dark marine shales of E1a age in Co. Leitrim. They are almost wholly confined to the Dough–Thur Mountain area, which is cut by the Caledonoid trending Ox Mountain and Belhavel Faults. It is thought probable that movement along one of these faults, possible in E1c times, conferred thixotropic properties to a sand horizon in the marine shales and also produced fractures in the shales up which the sand was intruded.
Stromatoporoid diagenesis: outline of alteration effects
Authors: Riding Robert
Published: May 2009

Elucidation of the effects of secondary alteration on the stromatoporoid skeleton is important for the development of a sound taxonomy of the group. Four stages of progressive alteration in Palaeozoic stromatoporoids are identified and their effects summarized.
Contributions to the Neogene radiometric time-scale from northern Africa
Authors: Vass D. , Badgasarjan G. P. , Bajanik S.
Published: May 2009

Four volcanic rocks from northern Tunisia and a syntectonic granite from northeastern Algeria were dated by the K—Ar method. The stratigraphic position of the dated rocks is determined mainly by their relationship to biostratigraphically calibrated Miocene tectonism. The K—Ar age of the granite, which is younger than latest Burdigalian and older than Early Tortonian, is 16.8 m.y. (*15.8 m.y. calculated with western decay constants). Rhyodacite at 10.9 (*10.4), rhyolite at 8.8 (*8.3), basalt at 7.3 (*6.9) and adesite at 7.0 (*6.7) m.y. are all apparently younger than Lower Tortonian.
A bedded deposit of anthophyllite schist in the Precambrian belt of Nellore, South India
Authors: Rao T. Ramamohana
Published: May 2009

A pure anthophyllite schist occurs as a bedded deposit conformable with garnet-bearing quartz—muscovite, and quartz—chlorite—biotite schists and diopside-bearing caic-silicate rocks in the north-central part of the Nellore Schist Belt. Field and petrochemical studies show that anthophyllite schist has formed from regional metamorphism of Fe-, Mg-rich aluminous sediments aided by metamorphic differentiation due to local kinematic action under amphibolite facies conditions which is the general grade of metamorphism of the Nellore Schist Belt. A pure anthophyllite schist of sedimentary origin reported here is the first of its kind described from any terrain.
The geology of the Vesturhorn Intrusion, SE Iceland
Authors: Roobol M. J.
Published: May 2009

The Vesturhorn Intrusion, exposed over 19 km2 of the south-eastern coast of Iceland, comprises two mafic complexes and a central core of epigranites. The latter can be subdivided into a central area with a flat-lying sheet structure, surrounded and separated from the mafic complexes by a more massive belt called the Transitional Epigranites with variable colour index and containing many rounded-to-angular inclusions and net-veined complexes. The consideration of several lines of evidence suggests that the components were emplaced as magmas in the sequence, first the epigranites with a sheet structure and second the basic complexes. The Transitional Epigranites appear to have originated by the remobilization and local hybridization of the early, sheet-structured epigranites. The relatively large volume of remobilized material and an absence of partially melted zones are considered to result from the early epigranites being still partially molten at the time of emplacement of the mafic complexes, together with a ponding of remobilized material beneath the chamber roof. A final intrusive episode occurred with the emplacement of a body of fayalite—hedenbergite epigranite largely into the Transitional Epigranites, probably after the consolidation of the latter.
Foraminiferid-encrusted ooids: evidence for ancient subtidal algal mats?
Authors: Talbot M. R.
Published: May 2009

Ooids and grapestones from some parts of the Corallian Beds (Oxfordian) contain encrustations of the foraminiferid Nubeculinella. Encrusted layers within ooids clearly reveal lengthy periods when the grains were stationary and not accreting carbonate laminae. It seems likely that during colonisation by the foraminiferids the ooids were immobilised beneath a subtidal algal mat and there are indications that the mats were sufficiently coherent to bind lumps of sediment together during disruption by burrowing organisms.
Evolution of Nigeria's Benue Trough (Aulacogen): a tectonic model
Authors: Olade M. A.
Published: May 2009

The tectonic evolution of Nigeria's Benue Trough has recently been the focus of investigations, especially in relation to continental drift and opening of the South Atlantic Ocean during Cretaceous times. Most of the tectonic models presented for the Benue depression have placed undue emphasis on certain plate tectonic concepts which are inconsistent with the salient geologic features of the trough. A possible model, involving the rise and cessation of mantle upwelling beneath a Cretaceous hot spot, and attendant patterns of doming, rifting, sedimentation, magmatism and tectonism, is proposed for the Benue aulacogen.
Tholeiite from the Cenozoic alkaline volcanic province of Nigeria
Authors: Wright J. B.
Published: May 2009

Bouldery outcrops of coarse-grained olivine-free lava, containing abundant orthopyroxene and clinopyroxene, mostly in glomerophyric aggregates, occur over a small area among the Tertiary to Recent volcanics of the Jos Plateau, Nigeria. This is the only rock of tholeiitic affinity in an otherwise completely alkaline volcanic province. Petrographically it does not greatly resemble tholeiitic occurrences reported from such provinces elsewhere, but that is believed to be due more to a relatively complex crystallization history than to any fundamentally different process of magma generation. It is not regarded as representing a tholeiitic parent for the alkaline lavas of the Jos Plateau region.
Some curious garnet clusters from the Garnetiferous Beds of the Leinster Granite Aureole
Authors: Kennan P. S.
Published: May 2009

Hollow, often ellipsoidal, clusters of small manganiferous garnets are described. They occur as discrete entities in the normal garnet–quartz coticule fabric of the Garnetiferous Beds, an important group of metamorphosed manganese-rich sediments found within the aureole of the Leinster Granite. The clusters are thought to represent small original sedimentary concretions, subsequently completely reconstituted.
The Indus Suture Line, the Himalaya, Tibet and Gondwanaland
Authors: Crawford A. R.
Published: May 2009

Misunderstanding exists about the origin of the Himalaya, Indo-Tibetan relationships and the extent and history of Gondwanaland. The Indus Suture Line is a relic of fracture to the mantle but for a period only represented by the faunas of the ‘exotic blocks’ of the Tibetan Himalaya, i.e. Permian—Late Jurassic. Tibet appears originally to have been part of a plate including India, but submerged while India remained continental. Associated with the fracture extending to the mantle represented now by the Indus Suture Line, shallower subparallel fractures developed within which the Gondwana sediments of the Himalaya were preserved. These, together with the salt at the base of the Tethyan marine sequence, facilitated intra-continental orogeny when, much later, India was affected by vigorous sea-floor spreading and plate movement in the NW Indian ocean after it had become attached to Asia.

The northern plate boundary was beyond Tibet, on the N side of the Tarim Basin Block, and along the Tien Shan. The Tien Shan present peculiar features, particularly very deep long intramontane depressions such as Issyk Kul in USSR and Turfan-Hami in China, and their stratigraphy shows persistent mobility. The Tarim Basin Block has moved sinistrally relative to Tibet and in Gondwanaland lay near northern Western Australia. The suggested extent of Gondwanaland explains the present lack of continental crust W of Western Australia, now in Tibet, and the intracontinental origin of the Himalaya is consistent with the absence of recent volcanism in an area of considerable seismicity. The association of Tibet with India in Gondwanaland destroys the effectiveness of arguments against continental drift based upon the extension of Indian stratigraphic sequences across the Himalaya. The hypothesis of an enlarged Gondwanaland is given support by recent Chinese discoveries of terrestrial vertebrate fossils of Gondwanic type near the Tien Shan.
The Shell of Devonian Atrypida (Brachiopoda)
Authors: Copper Paul
Published: May 2009

A simple visual method for distinguishing important Devonian atrypid brachiopod taxa, and for separating the Atrypidae and Palaferellidae family-groups is outlined. The thickness, distribution, and repetition of the three layers of impunctate atrypid shell wall differ markedly from one genus to the next and show a general evolutionary trend towards reduction and simplification.
A Review of Wenlock and Ludlow Stratigraphy and Sedimentation in N. W. England
Authors: Furness R. R. , Llewellyn P. G. , Norman T. N. , Rickards R. B.
Published: May 2009

Recent studies in N.W. England have indicated the need for a review of Wenlock and Ludlow (Silurian) stratigraphy. Detailed re-mapping, mainly for the first time since 1872, has modified and more clearly defined the established terminology. Determinations of new graptolite and shelly faunas have resulted in a revision of some earlier work and the establishment of a modern zonal classification for parts of the Wenlock and Ludlow. Lithofacies are broadly summarized and described with comments on some palaeocurrent data.
Seismically-induced load structures in the basal Coal Measures, South Wales
Authors: Weaver J. D.
Published: May 2009

Within the basal Coal Measures between Ystradgynlais and Abercraf a number of liquefaction layers are seen displaying ball and pillow structures. These layers consist of balled-up, ovoid masses of sandstone some 0.25–0.3 m thick and 0.5–0.7 m across. It is considered that they were formed by loading, resulting from the lique-faction of underlying silts, produced by the passage of earthquake shock waves associated with the main fault zone of the Swansea Valley Disturbance. Elsewhere in South Wales, horizons displaying load and slump structures in rocks of Upper Palaeozoic age may have resulted from seismic shock waves caused by contemporary movements along major Variscan fractures.
The 1973 Heimaey Strombolian Scoria deposit, Iceland
Authors: Self S. , Sparks R. S. J. , Booth B. , Walker G. P. L.
Published: May 2009

The 1973 eruption on Heimaey, Iceland, presented the opportunity to study the interaction of the principal factors that control the formation of pyroclastic fall deposits. The grain size characteristics and the dispersal of some of the scoria fall units within the Eldfell Scoria deposit are described and related to observations made on the wind speed and direction, the height of the eruption column, the ‘muzzle’ velocity and the various styles of activity during the first month of the eruption.
A re-evaluation of the blueschist facies
Authors: Wood R. M.
Published: May 2009

The blueschist facies metamorphism has always been one of the most difficult to quantify. This is for two important reasons. Firstly, the temperatures and pressures of the facies tend to be inaccessible to experimental analogues of the blueschist indicator minerals: aragonite, glaucophane, jadeite and lawsonite. Secondly, the conditions of blueschist metamorphism are not typical of the earth's crust. For a rock to be metamorphosed under lower temperatures at a given pressure than those of normal geothermal gradients (considered here as negative deviation metamorphism) requires ‘rapid’ downwarping and reuplifting. The movement during metamorphism, combined with hydration rather than dehydration (a feature of this environment) fails to preserve a single metamorphic culmination and hence the mineralogy and textures of blueschist assemblages may fail to match the conventional phase equilibrium metamorphic model. Thus the simple phase equilibrium interpretative basis of metamorphic petrology is recognized as only a special case of a more general theory of metamorphic chemical/mineral interaction.
Glaucophane Schists of Caledonian age from Spitsbergen
Authors: Horsfield W. T.
Published: May 2009

Glaucophane schists from Oscar II Land in western Spitsbergen are described for the first time. Although lawsonite, aragonite and pumpellyite have not been found, the mineral assemblages correspond generally with glaucophane schist assemblages known from elsewhere. The results of three XRF chemical analyses are presented, and five K/Ar radiometric determinations. The radiometric dating and field evidence both suggest that the glaucophane schists are a result not of the Tertiary orogeny which affected this part of Spitsbergen, but of the earlier Caledonian orogeny.
Microfabrics of a recumbent fold in cross-bedded sandstones
Authors: Yagishita K. , Morris R. C.
Published: May 2009

A thin-section study of the orientation of long-axes of quartz grains was conducted for a similar type fold of overturned cross-bedding in Carboniferous sandstones. Preferred orientation of detrital grains of the fold shows that (a) apparent long-axes of grains are parallel to the axial plane in a plane normal to the fold axis, (b) long-axes of grains in the axial plane are oriented in a high angle to the fold axis, and (c) grains are aligned parallel to the fold axis in a plane perpendicular to the other two directions. From the dimensional orientation of quartz grains in this sample, it is concluded that the overturned fold was made by a shear mechanism immediately following sedimentation in which the original quartz grains were reorientated by small-scale slippage along the shear planes.
Post-cumulus disruption of the Lilloise Intrusion, East Greenland
Authors: Matthews D. W.
Published: May 2009

Field, petrographic and chemical evidence from the cumulates of western Lilloise suggest a substantially higher level of exposure in the cumulus pile than is seen on the E side, due to relative subsistence of the western half of the intrusion. It is suggested that the subsistence started while both cumulus pile and the surrounding basalts were still hot and not fully consolidated. When, later, reactivation occurred, the rocks were in a more cohesive state and ‘syenitic’ magma was available for intrusion as discrete sheets and veins.