bluuebunny/crossref_metadata_2025 huggingface dataset:
Cambro-Ordovician strata in Ny Friesland, Spitsbergen and their palaeotectonic significance
Authors: Swett K.
Published: May 2009

Field and petrologic investigations of Cambro-Ordovician strata in Ny Friesland, Spitsbergen reveal a stratigraphic, sedimentologic, and diagenetic history for those rocks that bear striking similarities to coeval strata in central East Greenland, northwest Scotland and western Newfoundland. Parallels between these presently widely separated areas include: stratigraphic sequence (including enigmatic gaps), sedimentary structures, faunal assemblages, trace fossils, geochemical anomalies, and diagenetic sequences. It seems inescapable that the Cambro-Ordovician successions in Ny Friesland, central East Greenland, northwest Scotland, and western Newfoundland were developed on a once contiguous shelf on the margin of the lapetus Ocean. A tentative sequential tectono-sedimentological facies model of the ‘North Atlantic Geosyncline’ extending in time from late Proterozoic to the opening of the Atlantic Ocean is proposed to explain the empirical data. Slow closure of the lapetus basin, simultaneously involving transgression of the ‘North American’ plate and subduction of lapetus oceanic crust beneath a Euro-Balto-Scandinavian plate, followed by collision of the two continental plates, in turn followed by reopening along the approximate collision boundary appears to explain the observed relationships. This palaeotectonic/sedimentologic model is subject to further testing. The lithostratigraphic scheme is further refined.
‘Basalt fingers’ – origin of columnar joints?
Authors: Kantha L. H.
Published: May 2009

Thermal stresses due to contraction during cooling have been widely accepted as the origin of columnar structures in certain igneous rocks. It is proposed that these highly ordered structures could be the result of a double-diffusive convective process in the melt during cooling, a process analogous to salt fingers observed in the laboratory and the oceans. Salt fingers are driven by appropriate differences in heat and salt content at the top and bottom of a stably stratified water column. In molten basalts, temperature and chemical-compositional differences between the top and bottom of a stagnant melt could drive highly regular columnar ‘finger’ motions in the melt. When solidification takes place eventually, cracks due to contraction during cooling would then have preferred paths of propagation into the interior from the surface along the junctions of adjacent ‘basalt fingers’ giving rise to columnar jointing. Morphological evidence supporting the finger hypothesis is cited and useful ways of gathering further field data that would shed some light on the validity of the hypothesis are suggested. For the benefit of geologists not familiar with double-diffusive processes, an up-to-date review of these flow phenomena is included.
Gas pipes in Eocambrian volcanic breccias
Authors: Duyverman H. J. , Roobol M. J.
Published: May 2009

Eocambrian volcanic breccias of angular dacite and andesite clasts at Wadi Fatima, Kingdom of Saudi Arabia, contain perfectly preserved gas pipe structures. Only the latter identify them as lithic-rich, pyroclastic flow breccias of Pelean type. Without the gas pipes it would not be possible to identify them as pyroclastic and different from epiclastic breccias originating as mudflows, lahars or avalanches. The pyroclastic flow breccias constitute a minor component of the volcanic Fatima Group dominated by pumiceous water deposited sediments and subaerial welded tuffs.
The age relationship of igneous activity and continental break-up
Authors: Scrutton R. A.
Published: May 2009

The ages of igneous rocks formed at the time of continental break-up indicate that crustal separation begins at, or shortly after, the peak of igneous activity. The present study summarizes and lends support to the conclusions of previous authors on the temporal relationship of igneous activity and continental break-up.
Fluvio-lacustrine cyclothems from the Oligocene of Hampshire
Authors: Daley B.
Published: May 2009

Each fluvio-lacustrine cyclothem may include the following lithotypes (in ascending order): (a) irregularly laminated silts and muds; (b) regularly laminated muds and silts; (c) muds with or without molluscan partings and bands; (d) colour mottled muds. Each cycle reflects a change from flowing water conditions (fluvial) to non-flowing water conditions (lacustrine), culminating in some cases with the formation of marsh. Each lithotype is thought to represent the environmental changes which resulted from the silting up of inter-channel depressions on a flood plain. Successive cyclothems possibly reflect renewed flooding following an increase in river level during more pluvial periods.
The median surface: a new type of trend surface
Authors: Hall A.
Published: May 2009

A conventional trend surface is symmetrically placed between the observed values of a dependent variable. The proposed median surface is symmetrically placed between the ranks of the observed values. The use of a median surface is illustrated by its application to the distribution of silver in a granodiorite stock.
Significance of pebble and mineral lineation in the Chamba syncline of Punjab Himalaya, Himachal Pradesh, India
Authors: Thakur V. C. , Tandon S. K.
Published: May 2009

A pebble lineation has been produced as a result of the first phase deformation that formed the Chamba syncline and the associated slaty cleavage. The lineation indicates the principal direction of maximum elongation of the finite tectonic strain ellipsoid of the first phase deformation and lies nearly normal to the axial direction of the Chamba syncline. The mineral lineation and the long axes of deformed crinoid ossicles show paralelism to subparallelism with the pebble lineation. The second and third phases of deformation, which are characterized by open style folds and associated crenulation cleavage, appear to be of weak magnitude and have not modified the orientations of pebble lineation.
An unusual occurrence of quartz and amorphous silica at Carmean, Moneymore, Co. Antrim
Authors: Preston J.
Published: May 2009

Cavities in Cretaceous chalk, Co. Antrim, contain spongy silica. SEM photographs show minute doubly terminated quartz crystals trapped in fibrous mats of amorphous silica. The absence of both opal diffraction lines and a globular structure indicate the prior existence of gelatinous silica which prevented settling of the suspended quartz crystals. Drying and shrinkage of the gel produced the spongy deposit.
The occurrence of the Ordovician brachiopod Heterorthis alternata (J. de C. Sowerby) in the topmost Onnian of the type Caradoc area
Authors: Harper D. A. T.
Published: May 2009

The orthidine brachiopod Heterorthis alternata (J. de C. Sowerby 1839) is here recorded from the River Onny Cliff Section at an horizon high in the Onnia superba Zone of the Onnian Stage. Previously it had only been recorded from rocks of Upper Longvillian, Marshbrookian and Actonian age of South Salop and of Upper Caradoc age of Morocco.
Age, palaeomagnetism and chemistry of melilite basalts in the Southern Cape, South Africa
Authors: Duncan R. A. , Hargraves R. B. , Brey G. P.
Published: May 2009

Post-Karroo melilite basalts intrude Cretaceous and older sedimentary units in the Cape Province, South Africa. K-Ar ages determined from 4 occurrences range from 63–75 Ma b.p. (Late Cretaceous to earliest Tertiary) and are significantly older than alkaline intrusions to the 5, on the Alphard Bank. These igneous intrusions may be part of a linear trend that connects young oceanic volcanism at Bouvet Island with Cretaceous kimberlitic activity in southern Africa. This lineament nearly parallels the Walvis Ridge and a hot spot model for its origin is examined.
Ephemeral sedimentary structures formed during Aeolian deflation of beaches
Authors: Carter R. W. G.
Published: May 2009

Structures formed during wind deflation of poorly sorted beach sediments have rarely been described in the literature. However, a number of distinct forms exist including capped pedestals, asymmetrical ‘tear’ structures and scoured or impacted crusts. All these phenomena result from differential spatial erosion of the beach surface by wind, caused by textural or compositional variations. Ephemeral structures are indicative of rapidly changing geomorphological conditions and their presence may also exert control over continuing aeolian processes.
On Hill-slopes.
Authors: Lake Philip
Published: May 2009

Some time before the war I examined the profiles, or longitudinal sections, of several rivers, with the object of ascertaining whether they tended towards any particular curve. The method of examination was similar to that employed by Professor O. T. Jones in his interesting paper on “The Upper Towy Drainage System”, but the data were obtained from maps and were not so exact as his. Some rivers showed a very close approximation to a catenary for the greater part of their course, but this was not the case with all. My final conclusion was that there is no general curve towards which all river-profiles tend the form is influenced by the rate at which the volume of the river increases downwards. No sufficient data, however, were available in the case of any river for the exact application of a general theory which was in my mind, and such approximations as were possible were too rough to be of any real value.
Strain and shape analysis from the deformed pyrites with a note on their preferred orientation
Authors: Sen R. , Mukherjee A. D.
Published: May 2009

From the distribution and orientation of final axial ratios of deformed elliptical pyrites and boudins, initial distributions are determined. A strain ellipse is then reconstructed using the shape factor grid. The long axis of the strain ellipsoid represents the trend of regional fold axis (the fold is of flexural slip type). The dimensional orientation (elongation) of the pyrites and the boudins is referred to the homogeneous strain components in the fold. Petrofabrics of the pyrite cubes indicate that they have a preferred orientation.
Chemical petrology and K–Ar ages of the Lewisian gneisses of Rona, near Skye, Scotland
Authors: Holland J. G. , Lambert R. ST J.
Published: May 2009

The average chemical composition of the biotite–gneisses of Rona is very close to that of similar gneisses in the Laxford area, and nearly as close to those of the Torridon area. The biotite–gneisses of Rona are slightly richer in Li, Ba and Zr, slightly lower in Mg and Sr and have a higher Fe2O3/MgO ratio than their mainland counterparts. Biotite mineral ages of 1400 m.y. and hornblende mineral ages of up to 1750 m.y. indicate a similar late-metamorphic history to that of the mainland Laxford assemblage.
Revision of the stratigraphic position of cynodonts from the upper part of the Karroo (Gondwana) System in Lesotho
Authors: Turner B. R.
Published: May 2009

Cynodonts from two localities in Lesotho have been assigned by earlier workers to the Triassic Molteno beds of the upper part of the Karroo (Gondwana) System. These are important inasmuch as they were thought to represent the only evidence of reptilian remains in an otherwise barren sequence and may help to bridge the palaeontological gap in this part of the Karroo succession. Critical examination of both localities during the course of a regional analysis of the Molteno basin showed discrepancies in stratigraphic interpretation. These discrepancies are pointed out and the stratigraphy revised as a result of which the cynodonts can no longer be assigned to the Molteno beds; one is in the underlyingCynognathuszone (confirmed by further finds of typicalCynognathuszone reptiles) and the other is in the Red beds above. At the Tsoaning River locality a pebble conglomerate resting on an eroded surface provides a good local marker for the base of the Molteno. The implications of this with respect to the fossil flora and fauna at these localities are briefly discussed.
Quantitative petrography of mafic dikes from the central Bighorn Mountains, Wyoming
Authors: Heimlich R. A. , Gallagher G. L. , Shotwell L. B.
Published: May 2009

Two groups of mafic dikes occur within a terrain of metasomatic granitic rocks and quartzofeldspathic gneiss in the central Bighorn Mountains of Wyoming. The younger group consists of dolerite dikes which possess ophitic, subophitic, hypidio morphic-granular and microporphyritic textures. Mineralogically, the dolerites consist primarily of plagioclase (average An 54), augite (average Ca: Mg: Fe = 41: 43: 16) and uralite. The older dikes are metadolerites which possess granoblastic margins that grade into interiors characterized by relict subophitic and locally, porphyriti texture. Dike margins consist of fresh plagioclase and hornblende primarily. Interiors are principally clouded plagioclase (average An 46), augite (average Ca: Mg: Fe = 39: 54: 7) and uralite and/or hornblende. Textural, mineralogic and chemical data indicate that the meta-dolerites were derived from an earlier generation of mafic dikes comparable to the unmeta-morphosed dolerites in the area. The dikes were metamorphosed under low amphibolite facies conditions during the last regional metamorphic event which affected the country rock. During their metamorphism, minimal amounts of water from the country rock facilitated the total recrystallization of the metadolerite margins and the complete or nearly complete replacement of pyroxene by hornblende in the margins. In general, dike interiors underwent no textural changes other than partial destruction of the original subophitic plagioclase–pyroxene relationship as the pyroxene was replaced peripherally by hornblende. This process was accompanied by diffusion of calcium from the plagioclase to form the hornblende, and by diffusion of iron from the augite to cause the clouding of adjacent plagioclase.
Virgellar meshworks and sicular spinosity in Llandovery graptoloids
Authors: Rickards R. B. , Koren' T. N.
Published: May 2009

Orthograptus obuti sp.nov. and Orthograptus insectiformis Nicholson are shown to exhibit a complex proximal meshwork developed from a much-divided virgella which closely resembles retiolitid clathrial and lacinial networks. The virgellar meshworks tend to enclose the rhabdosome, at least for the first few thecal pairs, and may support a tenuous periderm. This kind of virgellar complexity is contrasted with a newly discovered form of sicular spinosity represented by the species Glyptograptus (Pseudoglyptograptus) tabukensis sp.nov. and G. (P.) rhayaderensis sp.nov
Mechanical production of metamorphic banding—a critical appraisal
Authors: Shelley D.
Published: May 2009

The mechanical process for producing foliation (banding) in metamorphic rocks, as proposed by Schmidt (1932), is shown to be inadequate. Examples in the literature ascribed to the mechanism are insufficiently supported and the metallurgical analogy for the process is found to be false. A possible restatement of a mechanical process by analogy with particle interaction effects during the laminar flow of suspensions is discussed. Evidence from metamorphic rocks indicates, however, that the modified mechanical process cannot be responsible for common metamorphic layering.
Descriptive microstructural terminology for high-grade metamorphic tectonites
Authors: Collerson K. D.
Published: May 2009

In high-grade regionally metamorphosed tectonites three varieties of micro- structures are recognized, namely (1) granoblastic, (2) granoblastic elongate, (3) anastomosing. Relative and absolute grain size, combined with grain boundary shape, provide the basis for their description. This microstructural classification is directly applicable to granulite facies and transitional granulite to amphibolite facies rocks and avoids some of the shortcomings inherent in previous terminologies.
The Ordovician Graptolite GenusParaglossograptusMu
Authors: Rickards R. B.
Published: May 2009

The lacinia inParaglossograptusMu is shown to consist of four ladder-like networks which are independent of each other and have no direct connection with spinose thecal apertural processes. The lacinial networks are positioned at the corners of the quadrangular rhabdosome as inParaglossograptus? sp. of Whittington & Rickards, which is described here asParaglossograptus proteus(Harris & Thomas).Paraglossograptus etheridgei(Harris, 1924), the important Ordovician zone fossil, together withP. typicalisMu andP. latusHsü, are considered junior synonyms ofReteograptus tentaculatusJ. Hall, 1865.P. tentaculatus(J. Hall, 1865), is regarded here as the type species ofParaglossograptusMu. Detailed comparisons are made betweenP. tentaculatusand the stratigraphically youngerP. proteus(Harris & Thomas), and withGlossograptus holmiBulman, a species in some ways intermediate betweenParaglossograptusandGlossograptusEmmons.
Turbidite origin of some laminated mudstones
Authors: Piper David J. W.
Published: May 2009

Many deep water marine muds, including lower Palaeozoic mudstones from Britain, have thin graded beds in which mud and silt laminae alternate, with the silt becoming finer and less abundant upwards. Of the known deep-sea depositional processes, turbidity currents are the most likely cause of such graded laminated beds. The lamination may be produced by alternating cohesive and granular bed conditions. Much more careful examination of laminated fine grained terrigenous sediment is needed.
A revised method of contouring stereograms using variable curvilinear cells
Authors: Denness B.
Published: May 2009

A method of contouring pole distributions on Equal Area stereograms is presented; the advantage of this method is a combination of speed, convenience and maximum accuracy.
An outline of the stratigraphy and palaeontology of the Ordovician rocks of Central Portugal
Authors: Mitchell W. I.
Published: May 2009

Well-preserved brachiopod faunas collected from four Ordovician horizons range in age from Upper Llanvirn to Lower Caradoc. The generically restricted Upper Llanvirn and Lower Llandeilo assemblages are associated with diagnostic graptolites. In contrast the Upper Llandeilo and Lower Caradoc assemblages are more diverse and correlate well with faunas from the more precisely dated Chrustenice Substage in Bohemia. Two new brachiopod genera Apollonorthis and Cacemia are described.
A contribution to the geology of the western margin of the Afar Depression, Ethiopia
Authors: Brooks D. J.
Published: May 2009

Satellite imagery provides additional support for the published geology of the eastern escarpment of the Ethiopian plateau. However, of greater interest is that inspection of the imagery reveals aspects of the regional geology that have gone unnoticed. The most obvious are used to extend fault lines discussed by Kazmin & Garland (1973).
Discovery of a Tin-tungsten Mineralization in Northern Khartoum Province, Sudan
Authors: Almond D. C.
Published: May 2009

A primary deposit of tin and tungsten has been discovered in association with granites of the Cambrian (?) sub-volcanic igneous complex at Sabaloka, on the Nile north of Khartoum. Wolfram and cassiterite occur in a stockwork of quartz veins which also contain minor amounts of sulphide minerals. The stockwork centres around a small intrusion of primary greisen lying on the contact of a porphyritic microgranite ring-dyke but the greisen and mineralizing solutions are believed to have originated from a nearby mass of biotite-muscovite granite. The deposit has many features in common with the primary tin veins associated with the Younger Granites of northern Nigeria and other parts of northern Africa.
A Photometric Method for the Determination of Preferred Orientation in Thin Sections of Crystal Aggregates
Authors: Durrance E. M.
Published: May 2009

Photometric recording of the variation in intensity of light transmission by the analyser of a petrological microscope whilst the polarizer is rotating at a rate sufficient to eliminate the periodic output from the photocell as the polars cross and uncross, and a thin section of a crystal aggregate is slowly rotated upon its stage, is found to yield information on the direction and degree of development of any preferred optical orientation that may be present in the section. The theory of the method is considered and an equation derived for the representation of any preferred optical orientation in terms of a direct percentage of areal extent. The direction of the preferred orientation is found to be parallel to the plane of polarization of the stationary analyser when the section is rotated to a position of minimum intensity of light transmission. It is suggested that the method has potential applications in the study of any fabric which is displayed in terms of an optical orientation.
The Cretaceous Volcanic Arcs of Japan
Authors: Lauder W. R.
Published: May 2009

The position of Cretaceous volcanic arcs in Japan may be indicated by outcrops of basic and ultramafic rocks.
Possible higher pressure relics within titaniferous augites in a basic sill
Authors: Gibb F. G. F. , Henderson C. M. B.
Published: May 2009

An unusual type of mottled area is described from titaniferous augites in the Dippin sill, Isle of Arran. These are characterized by abundant magnetite inclusions, irregular embayed outlines and distinctive chemical compositions. The possibility that these are due to zoning, especially sector zoning, is examined and discarded. They probably represent partly resorbed relics of pyroxene which crystallized at depth prior to the emplacement of the sill. As such they could have considerable petrogenetic implications both with regard to the sill itself and to alkaline basic magmas in general.
Lava trees and tree moulds as indicators of lava flow direction
Authors: Lockwood J. P. , Williams I. S.
Published: May 2009

Lava trees and tree moulds are common in many areas where fluid basaltic lava has moved rapidly over forested terrain. Lava trees are formed only by thin flows, but tree moulds are preserved in both thin and thick flows. Both structures may indicate the direction of flow of the lava in which they are preserved. The usefulness of lava trees in this regard is limited to recent flows; tree moulds, however, have been described in rocks as old as middle Tertiary. Features commonly well preserved on the inner walls of moulds indicate the local flow direction. When found in sufficient number, tree moulds provide information on the palaeoslope and vent location.
Archaeocyathid fauna of the lowest fossiliferous levels of Tiout (Lower Cambrian, Southern Morocco)
Authors: Debrenne F. , Debrenne M.
Published: May 2009

The oldest archaeocyathid fauna from Tiout (Anti-Atlas, Morocco) contains 15 species belonging to 11 genera. The following species: Aldanocyathus cribratus, Neoloculicyathus magnus, Coscinocyathus primus, C. secundus, C. fasciola, Tumulifungia marocana, Gordonifungia cowieiare new. The biostratigraphy of this archaeocyathid fauna demonstrates that the lower boundary of the Amouslekian stage should be moved downwards to within the ‘Calcaires Supérieurs’ of the Adoudounian (Assadassian or equivalent Ouneinian). One or perhaps more archaeocyathid and trilobite zones may yet be found beneath this boundary at Tiout. The uppermost ‘Calcaires Superiéurs’ may be dated, on the basis of Archaeocyatha, as equivalent to the Atdabanian stage, but not to the lowest part of it. The underlying fossiliferous horizons should be equivalent to all or part of the lower Atdabanian. The Precambrian–Cambrian boundary in Morocco can be looked for lower in the succession and defined on the basis of other fossil groups.
Silurian fossils from western Spitsbergen
Authors: Scrutton C. T. , Horsfield W. T. , Harland W. B
Published: May 2009

Silurian fossils have been identified from Oscar II Land, western Spitsbergen. They are the first Silurian fossils recorded from Spitsbergen, and throw new light on regional correlations and the dating of Palaeozoic orogenic events in the region.
Emplacement of an epizonal granodiorite pluton λ by vertical block elevation
Authors: Leitch E. C.
Published: May 2009

The Carrai Granodiorite is an intrusive magmatic pluton with steeply dipping margins surrounded by a well-developed contact metamorphic aureole. Emplacement of the body was accompanied by little distortion of neighbouring rocks and involved vertical displacement of pre-existing material. Scarcity of country rock blocks, and the presence of numerous dioritic xenoliths indicate that stoping was unimportant, and the pluton was accommodated in the upper crust by vertical uplift of earlier rocks (‘block elevation’). A close relationship existed between faulting and granodiorite emplacement. Deep shears possibly account for the generation of the linear zone of plutons in which the Granodiorite is located.
A note on the sulphurization of Fe-Tremolite
Authors: MacRae N. D. , Grant M. , Kullerud G.
Published: May 2009

Charges of Fe-tremolite, sulphur and water sealed in gold capsules and run at 600°C and 1 kb confining pressure for one month yielded talc, anhydrite, pyrite and quartz as principal mineral phases. It is concluded that in a S-rich environment talc is stabilized rather than diopside by the strong preference of Ca to form anhydrite.
Ecologic significance of post-Palaeozoic green calcareous algae
Authors: Elliott Graham F.
Published: May 2009

The palaeoecologic significance of post-Palaeozoic green calcareous algae is evaluated with what is known of the environments of comparable living algae. Here requirements and tolerances of temperature, bottomsediment, salinity and water-energy may be observed; depth is apparently significant only as it influences these. In the extinct algae, only a minority show clear taxonomic relationship to living algae, in palaeo-environmentsdeduced from independent evidence. Codiaceae and Dasycladales seem to have had environmental preferences like their living descendants, with preferredmicroenvironments in some genera.
Middle Pleistocene drainage in the Thames valley
Authors: Gibbard P. L.
Published: May 2009

Stratigraphical investigations in the Finchley depression (Middlesex depression) are summarized and show that a gravel, laminated deposits and till sequence is present. Compositional study of the gravels indicates that they were derived from S of the present Thames valley. Gravel patches in North Surrey can be subdivided into two terrace fragments formed by a Mole-Wey south bank Thames tributary. The upper unit is correlated with the gravel at Finchley. The lower unit terrace can be shown to grade into the Thames Black Park Terrace Gravel, and the latter is extended through London to Dartford and Chatham. The events leading to the diversion of the Mole-Wey tributary by the Anglian chalky till ice parallel those of the Thames in the Vale of St Albans and suggest that similar events may also have occurred in other S bank tributary valleys to the E.
Mesozoic stratigraphy of Eastern Svalbard: a discussion
Authors: Edwards M. B. , Bjærke T. , Nagy J. , Winsnes T. S. , Worsley D.
Published: May 2009

This paper proposes an alternative to the complex stratigraphical nomenclature introduced in recent descriptions of the stratigraphy of Eastern Svalbard. We believe that the platform nature of the Mesozoic succession in Svalbard enables recognition of individual stratigraphical units over very wide areas. Our principal conclusions are that the Wilhelmøya Formation can be recognized as the upper formation of the Kapp Toscana Group and occurs throughout Eastern Svalbard. It overlies the De Geerdalen Formation on Hopen and Wilhelmøya. The Janusfjellet and Helvetiafjellet Formations can be recognized on Kong Karls Land.
A note on sheath and core structure in the Mull pitchstones
Authors: Drysdale D. J.
Published: May 2009

Sheath and core structure results from secondary hydration and devitrification, initiated at relatively high temperatures during cooling, of the intrusive pitchstone sheets. Less than 0.5% of the water present is an original magma component.
K-Ar ages from the ore deposits and related rocks of the Isle of Man
Authors: Ineson P. R. , Mitchell J. G.
Published: May 2009

Thirty-seven new K-Ar isotopic ages are reported from the Isle of Man. Thirty clay mineral concentrates from vein gouges and altered wallrocks when interpreted with the remaining seven whole rocks and mineral ages indicate that at least five periods of metasomatism have affected the rocks. It is argued that these can be identified with episodes of ore deposition. The earliest phase, N of the Foxdale area, occurred at 310–320 Ma and appears to be the most extensive of the episodes recorded. In the S of the island, mineralization occurred later at c. 285 Ma and again at c. 250 Ma. Minor Triassic activity is expressed by a cross-course on the Foxdale lode, and a single locality displaying Tertiary mineralization was recognized. The conformity of these ages to the general episodic pattern of ore deposition in the British Isles is demonstrated.
Mg–Fe distribution between coexisting garnet and biotite, and the status of fibrolite in the andalusite–staurolite zone of the Mt Lofty Ranges, South Australia
Authors: Fleming P. D.
Published: May 2009

The distribution of Fe and Mg between coexisting garnet and biotite from andalusite-staurolite zone rocks of the Mt Lofty Ranges is briefly discussed. The average value of the corresponding distribution coefficient, and those of some related parameters, are compared with the values proposed by a number of authors as being characteristic of certain metamorphic grades. From these comparisons it is concluded that despite their occurrence in a terrain in which fibrolite commonly occurs, the rocks have probably only experienced P-T conditions corresponding to those of the andalusite phase field, and that fibrolite has formed under similar conditions.
Isotopic age determinations on clay minerals from lavas and tuffs of the Derbyshire orefield
Authors: Ineson P. R. , Mitchell J. G.
Published: May 2009

Episodic hydrothermal mineralization has previously been recognized in the northern section of the Pennine orefield. Igneous rocks from the southern section (the Derbyshire orefield) have yielded isotopic ages, some of which are thought to represent ages of hydrothermal metasomatism (deuteric or subsequent). In order to ascertain whether epicyclic hydrothermal events gave rise to the Derbyshire mineral deposits, samples of highly altered doleritic lava and pumice tuff were collected adjacent to areas of mineralization. Clay-mineral concentrates from 34 samples were dated by the potassium–argon method. The conclusions drawn from these analyses support a hypothesis of repeated hydrothermal alteration of the clay minerals, reflecting at least two episodes of mineralization, one about 270 m.y., the other about 235 m.y. The geo-chronological significance of these and other results is considered.
Two new graptolites from Victoria, Australia
Authors: Thomas D. E.
Published: May 2009

The paper comprises descriptions of a new genus and species of multiramous dichograptid from the Bendigonian (Be 4) and a new species of Tetragraptus from the Lancefieldian (La 2).
Crescumulate layering in a gabbroic body on Seiland, northern Norway
Authors: Robins B.
Published: May 2009

The cumulates and crescumulates in the Crescumulate Zone of the Rognsund gabbro are described. The olivine and olivine-clinopyroxene crescumulates contain large dendritic crystals of olivine due to rapid upward growth from cumulus nucleii on the temporary floor of the magma chamber. Crescumulate growth was accompanied by the bottom accumulation of primocrysts, some of which were enlarged by the normal adcumulus process. The crescumulates are thought to have originated when cumulus crystals sank from a labile environment near the roof of the body into a metastable environment on the floor.
Single whole rock K—Ar isochrons
Authors: Fitch F. J. , Miller J. A. , Hooker P. J.
Published: May 2009

Conventional K—Ar age determinations are frequently discrepant. A major factor is the failure of rocks to conform to the basic simplifying assumptions made in the total fusion method. Many rocks incorporate initial argon with an isotopic composition different from the present atmosphere and others have not remained closed systems.By careful sampling and the application of isochron geochronometry more reliable and geologically acceptable K-Ar ages can be obtained. K-Ar step heating isochrons from Kenyan Miocene volcanic sanidines are used to illustrate the accumulating evidence for the presence in ancient rocks of initial argon with an isotope ratio unlike that of the modern atmosphere. Single whole rock total fusion K-Ar isochrons from the Olduvai basalt, Tanzania and the Upper basalts of Antrim are presented to illustrate a new version of the K-Ar isochron technique. Special circumstance multiple rock K-Ar isochrons from the Belfast section of the Antrim basalts and from an ignimbrite-ash flow unit in Bed I, Olduvai Gorge, are used in a further discussion of the general applicability and usefulness of K-Ar isochrons.
Reinterpretation of ceratitic ammonoids from the Greville Formation, New Zealand
Authors: Furnish W. M. , Glenister B. F. , Kummel B. , Spinosa C. , Sweet W. , Teichert C.
Published: May 2009

Ceratitic ammonoids from the Greville Formation in the Nelson Regional Syncline, South Island of New Zealand, were described as a new genus and species of the Ophiceratidae, Durvilleoceras woodmani, and dated as ‘late Middle Permian’ (Waterhouse, 1973). In fact, Durvilleoceras differs from all known Permian ammonoids in both conch form and sutural pattern, but closely resembles lower Triassic ceratites. Structural and sedimentologic complexities within the Nelson Syncline are such that stratigraphic interpretations are questionable, and the fauna of both the Greville and adjacent formations is sparse. Consequently, we consider that Durvilleoceras is best interpreted as a middle Scythian ceratite of the family Flemingitidae.
Variation in lens packing ofPhacops(Trilobita)
Authors: Fortey R. A. , Morris S. F.
Published: May 2009

Phacops turcoaff.praecedensHaas, from the Devonian (Eifelian) of Morocco, varies in the type of lens packing in the eye. Cubic close packing in trilobite eyes is described for the first time.
A Liassic palaeofault from Dorset
Authors: Jenkyns H. C. , Senior J. R.
Published: May 2009

Evidence is presented for Liassic (Toarcian) faulting at Watton Cliff in coastal W Dorset. This movement is inferred from the abrupt changes in thickness of the Junction Bed and contiguous strata given that the contact with the overlying shale and clay is horizontal. Further evidence for synsedimentary movement is manifested by the presence, in the palaeofault zone, of numerous calcilutite-filled fissures penetrating a coarser, more sandy matrix. These neptunian dykes and sills contain abundant ammonites of the middle to late Toarcian, presumably the time of fault movement. This onshore Jurassic palaeofault broadens the known extent of such features from Sutherland (Brora—Helmsdale Fault) and Yorkshire (Peak Fault) to include southern Britain.
Numerical methods for the reconstruction of fossil material in three dimensions
Authors: Doveton J. H.
Published: May 2009

Distances measured between homologous reference points on fragmentary fossil material can be used to recover a three-dimensional framework by operations of standard matrix algebra. A procedure that combines both linear and non-linear algorithms is described and illustrated in a simple reconstruction of Waptia fieldensis. The approach attempts to provide a modelling process in which a palaeontologist can explore the geometrical consequences of fossil measurements through continuous interaction with programmed reconstructions.
Stratigraphical inversion in the Sulitjelma Area, Central Scandinavian Caledonides
Authors: Boyle A. P. , Griffiths A. J. , Mason R.
Published: May 2009

Major stratigraphical inversions are recognized in two parts of the Sulitjelma area, on the border of Norway and Sweden. In the Otervatn area, inversion is directly demonstrated by way-up structures in pillow lavas of the Sulitjelma Amphibolite Group. The porphyritic amphibolites of the group belong to a penecontemporaneous sheeted intrusive complex which originally underlay the pillow lavas. The other inversion, S of Sorjusjaure, is proposed in order to simplify the stratigraphical succession of the area. The inversions are both thought to belong to the inverted limb of the Gasak Nappe, which is the upper tectonic unit at Sulitjelma. Folding associated with the inversion could cause tectonic repetition of the strata-bound Sulitjelma ore horizon.
Diagenetic concretions from the Ribband Group sediments of County Wexford, Ireland
Authors: Shannon P. M.
Published: May 2009

An occurrence of small diagenetic siderite concretions is described. They occur towards the top of a postulated shallowing sequence of cleaved Lower Palaeozoic siltstones and shales. The concretions occur as lenses and aggregates associated with horizontal grazing trails, and also as diffuse bands apparently unrelated to the latter. The concretions are compared with other similar structures described elsewhere, and an origin by diagenetic growth beneath the sediment–water interface in a marine environment is postulated.
Precambrian stratigraphic scale of the USSR
Authors: Keller B. M.
Published: May 2009

A new stratigraphic scale of the USSR Precambrian officially adopted by the All-Union Precambrian Meeting in Ufa (1977) and approved by the National Stratigraphic Committee (1978) is discussed. Archean and Proterozoic have been distinguished in the Precambrian, the boundary between being 2600 Ma. Proterozoic is subdivided into the Lower- and Upper-Proterozoic with the boundary between them 1650 Ma. Riphean and Vendian are distinguished in the Upper Proterozoic. More detailed subdivisions of the Upper Proterozoic are Burzyanian, Yurmatian, Karatavian, Kudashian and Vendian. Lithological and palaeontological characteristics of these subdivisions and their radiometric age are given.
Fission track dates from two Galloway granites, Scotland
Authors: Hurford A. J.
Published: May 2009

Previous radiometric age determinations for the Criffell–Dalbeattie and Cairnsmore of Fleet Newer Granite intrusions are briefly reviewed. Thirteen fission-track dating results are presented for the co-existing accessory minerals sphene, zircon and apatite separated from the two granites. The mean sphene apparent age of 401±10 Ma and single zircon apparent age of 389±26 Ma are interpreted as the age of initial post-intrusion cooling of the granites. Results from apatite are discordant with those of sphene and zircon. Four determinations give a mean Upper Cretaceous apparent age of ∼ 80 Ma which is not readily interpreted. A single apatite determination upon a sample located adjacent to a basaltic dyke yielded a Tertiary age.
The occurrence of large scale kink bands in Campanian chalk at the Gulf of Elat (‘Aqaba) rift zone
Authors: Shirav (Schwartz) M.
Published: May 2009

Three sets of kink bands occur in Campanian chalk, near the coast of the Gulf of Elat. The kink bands can be traced by a system of vertical joints, intersecting the chalk and filled with secondary crystalline calcite. The geometry and the development of these structures are described, suggesting a change of the stress regime during the opening of the rift along the studied area.
Geology of Hopen, Svalbard
Authors: Smith David G. , Harland W. B. , Hughes N. F.
Published: May 2009

Hopen (Hope Island) in the Svalbard archipelago is difficult of access and only recently has reliable geological information become available. Published information is reviewed and combined with new observations.

The island, 37 km long and no more than 2.5 km wide or 370 m high is structurally simple with flat-lying arenaceous strata which are described with three measured sections. Three new local stratal units are defined: Iversenfjellet Formation (325 m, base not seen); Flatsalen Shale Formation (55 m); and Lyngefjellet Sandstone Formation (80 m, top not seen).

From a few ammonite, bivalve, saurian and plant megafossil occurrences and 30 palynomorph taxa (newly recorded) the marine and fluviatile facies range in age from possibly late Karnian, through Norian, Rhaetian and possibly into early Jurassic. The Rhaetian flora, well established palynologically, is the first clear evidence of rocks of this age in Svalbard. Associated Sirenites extends the range of this ammonite and suggests that Svalbard may yield significant new evidence for this span of Earth history.
Ultramafic nodules and their host rocks from Auckland, New Zealand
Authors: Rodgers K. A. , Brothers R. N. , Searle E. J.
Published: May 2009

Ultramafic and mafic nodules are abundant inclusions in Cainozoic alkali basalts at 7 localities in the Auckland Province. Nodule types show a gradation from dunites and pyroxenites through periodotites to eucrites. Bulk chemical variations in the nodules show a wide range in MgO/ΣFeO with a tendency for Al2O3, ΣFeO, CaO and Na2O + K2O to increase as this ratio decreases. These chemical trends, together with published data on the nodules mineralogy and fabric, are consistent with their being interpreted as fragments of the upper mantle.
Epidotic calc-silicates of Arnipol Type—a widely distributed minor sedimentary facies of the Moinian assemblage, Scotland
Authors: Winchester J. A.
Published: May 2009

In the Moinian rocks of Scotland, epidote-bearing calc-silicates, distinct from the commoner garnet-zoisite-bearing calc-silicates, occur at several widely scattered locations. The major element geochemistry of the two types of calc-silicate is very similar, and their somewhat different petrology and trace element geochemistry may be explained by the preservation of grains of detrital epidote and heavy minerals in the epidotic calc-silicates. These grains were concentrated in the original sediment and remained stable under greenschist and epidote-amphibolite metamorphic facies conditions. While the garnet-zoisite bearing calc-silicates may be derived from calcareous marls, the epidotic calc-silicate bands are probably derived from epidotic grits similar to those recorded in the Torridonian.
The stratigraphy of Wilhelmøya and Hellwaldfjellet, Svalbard
Authors: Smith David G.
Published: May 2009

Stratigraphic sections measured at Wilhelmøya and Hellwaldfjellet in eastern Svalbard are described in their entirety in terms of formal lithostratigraphic units for the first time. They include rocks of mid-Triassic to late Jurassic age. The Uleneset Member is newly described and palynological evidence is used to show that it is largely Norian (late Triassic) in age.
Phlogopitization of pyroxenite; its bearing on the composition of carbonatite magmas
Authors: Gittins J. , Allen C. R. , Cooper A. F.
Published: May 2009

Phlogopitization of pyroxenite is common in contact zones between clinopyroxenites and carbonatite dikes of the Cargill ultramafic rock—carbonatite complex near Kapuskasing, Ontario. The most typical development is a mica zone 1–10 cm wide but phlogopite is also developed in a more pervasive manner throughout the groundmass of several types of ultramafic rock. Fenitization is most commonly thought of as a process whereby aegirine and riebeckitic amphiboles are formed in the host rock while feldspar is recrystallized and silica progressively removed. Phlogopitization of pyroxenite can properly be referred to, however, as a type of fenitization. It is clearly related to the intrusion of carbonatite into pyroxenite and is further testimony to the fact that many carbonatite magmas are initially alkalic but lose alkalies to the surrounding rocks and crystallize as calcitic and dolomitic carbonatite with alkali contents restricted to the amounts that could be fixed as micas, pyroxenes or amphiboles. This in turn is controlled by the silica and alumina activity of the carbonatite magma. Abundant evidence for considerable amounts of fluorine in carbonatite magmas suggests that alkalies may be transported into the country rocks as fluorides. It is further suggested that late-stage feldspathization in carbonatite complexes is explained by the abstraction of potassic halide solutions from the crystallizing carbonatite magma. The conclusion seems inescapable that alkali carbonatite magmas, far from being the curiosity thought by many petrologists, are in fact very common during the evolutionary history of carbonatites. The common calcitic and dolomitic carbonatites have not generally crystallized from a magma of the same composition but are the residue remaining after the abstraction of an alkali-rich aqueous fluid. Consequently, there is a need to redesign the experimental phase equilibrium approach to problems of carbonatite genesis in order to take account of the presence of alkalies in most carbonatite magmas.
Ages of Pre-Mesozoic formations of the Lesser Himalaya, Hazara District, Northern Pakistan
Authors: Crawford A. R. , Davies R. G.
Published: May 2009

Three samples of low-grade metamorphic rocks from the Hazara Group, northern Pakistan, analysed as total-rock samples by the Rb—Sr method, give model ages of 765±20 and 950±20 Ma. The results are discussed in terms of the stratigraphy of Hazara, northwestern Iran, and certain other areas.
Bolopora not a bryozoan, but an Ordovician phosphatic, oncolitic accretion
Authors: Hofmann H. J.
Published: May 2009

The supposed cyclostome bryozoan Bolopora undosa Lewis 1926 is reinterpreted as a chemogenic and/or bacteriogenic dubiofossil.
Tidal flat and shallow marine sediments from the Craignish Phyllites, Middle Dalradian, Argyll, Scotland
Authors: Anderton Roger
Published: May 2009

Sediments from 6 localities showing negligible deformation are described from a generally strongly deformed formation of metasediments. The tidal flat facies include decimetre-thick tabular sands, interpreted as the flood tide storm deposits of subtidal to intertidal channels, as well as centimetre to millimetre thick, rippled and laminated sands and silts with gypsum pseudomorphs. The gypsum crystals grew at interfaces where more permeable, overlaid less permeable, sediment and then underwent partial solution before being replaced by ferroan calcite and quartz. The shallow marine facies are centimetre-thick rippled sands interbedded with muds, interpreted as storm sediments.
Gravity tectonics or plate tectonics: example of the Numidian flysch, Tunisia
Authors: De Jong K. A.
Published: May 2009

The Numidian flysch unit is the largest tectonic unit in the western Mediterranean, extending from Gibraltar to southern Italy. Displacement of the unit is supposedly to the S, a result of either gravity tectonics or plate tectonics. Both interpretations have their adherents, and to solve this dilemma the Numidian flysch in Tunisia was studied. Field data indicate surprisingly that the Numidian flysch in northeastern Tunisia (Mogods–Hedil area) did not move at all, which renders the question of the emplacement mechanism irrelevant. In northwestern Tunisia (Kroumiria) the flysch moved presumably only a few km to the S, not 50 km as was thought previously. Analysing this small displacement it appears unlikely that gravity tectonics was of importance because move ment over the fault was probably upward; moreover, sedimentological data do not indicate a high area from which sliding could have occurred. A plate tectonic interpretation cannot explain, however, why flysch movement was spasmodic instead of continuous and contemporaneous with plate movement, or why plate deformation was restricted to the thin flysch unit.
Age limits for the Ubendian metamorphic episode in Northern Malawi
Authors: Dodson M. H. , Cavanagh B. J. , Thatcher E. C. , Aftalion M.
Published: May 2009

The Nyika granite gives a U-Pb zircon age of 1970±30 Ma, which is a minimum age for the high-grade Ubendian metamorphism in Northern Malawi. Cordierite gneisses from the same region yield an Rb-Sr whole-rock isochron age of 1815±260 Ma. Because this age is believed to reflect the high-grade Ubendian metamorphism, the latter cannot be significantly older than about 2100 Ma.
A note on the origin of syntectonic porphyroblasts and their inclusion fabrics
Authors: De Wit M. J.
Published: May 2009

Previous mechanisms of syntectonic growth of porphyroblasts, leading to sigmoidal inclusion patterns, are thought to be based on invalid assumptions. A new mechanism, which involves the formation of extension fractures, is outlined.