bluuebunny/crossref_metadata_2025 huggingface dataset:
A Caradoc Failed-Rift within the Ordovician Marginal Basin of Wales
Authors: Campbell S. D. G. , Howells M. F. , Smith M. , Reedman A. J.
Published: May 2009

The dolerite and basalt intrusions within the Lower Palaeozoic sequence of northwest Wales are largely restricted to the outcrop of Ordovician strata. Their distribution and close association with known volcano-tectonic structures were controlled by a tectonic framework of deep-seated fractures. In central and northern Snowdonia, volcanism during Caradoc times was related to the evolution of a fracture-controlled trough. An increase in the extensional stress across the trough with time is reflected in the progressive increase in basaltic magma movement during the volcanic cycle. The trough represents an attempted rift in the lithospheric plate, which failed to create an ocean basin and was subsequently aborted.
Fractionation in a zoned monzonite pluton: Mount Dromedary, southeastern Australia
Authors: Smith I. E. M. , White A. J. R. , Chappell B. W. , Eggleton R. A.
Published: May 2009

Mount Dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the Dromedary igneous complex in southeastern New South Wales. The pluton exhibits a striking arrangement of petrographically, but not always chemically, distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre. The rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship. Minor compositional discontinuities between zones, together with observed and inferred minor intrusive zone boundaries, suggest that each zone has to some extent evolved independently. Negative Eu anomalies in REE abundance patterns show that some of the zones have been affected by fractionation of feldspar, but complementary accumulates are not found at the present levels of exposure. The pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and/or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma. The parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust.
A new 14C age for the Oruanui (Wairakei) eruption, New Zealand
Authors: Wilson C. J. N. , Switsur V. R. , Ward A. P.
Published: May 2009

The Oruanui eruption was the largest known outburst of Taupo volcano, New Zealand, and is among the larger Quaternary eruptions documented. The eruption deposits are variously known as the Oruanui, Wairakei, Kawakawa Tephra, or Aokautere Ash formations, and represent a bulk volume probably exceeding 500 km3. Four new 14C age determinations on carbonized vegetation in the non-welded Oruanui ignimbrite are combined to give a conventional age of 22590±230 yr b.p. Compared with the previously accepted figure of 20000 yr b.p., this new age resolves the anomaly of apparently older 14C ages being obtained from a demonstrably younger New Zealand deposit, and strengthens correlation of this eruption with an Antarctic ice-core acid anomaly. The trace of this eruption has great potential as a time-plane marker in the Antarctic just prior to the last glacial maximum. The close similarity in ages between the Oruanui and a comparable sized eruption (Ito/Aira-Tn) in Japan suggests that this period of activity may represent the best chance of resolving any linkages between large-scale explosive silicic volcanism and climate changes.
Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics
Authors: Alavi Mehdi , Mahdavi M. A.
Published: May 2009

Several rock stratigraphic successions, metamorphosed and non-metamorphosed, are found to be similar and/or identical with each other across the so-called ‘Main Zagros Thrust’. Stratigraphic successions form thin allochthonous sheets carried from northeast to southwest by numerous low-angle thrust faults of either ductile to brittle-ductile type or brittle type. Similarities in lithic and faunal characteristics of the stratigraphic units and in the style of structural deformation across the ‘Main Zagros Thrust’ imply that either the suture between the Afro-Arabian and Iranian lithospheric plates is not located in the Nahavand region or, if it is, it must be buried under several thrust sheets.
New records of Devonian plants from southern Victoria Land, Antarctica
Authors: McLoughlin S. , Long J. A.
Published: May 2009

An assemblage of fossil plants is here recorded from the Middle Devonian Beacon Heights Orthoquartzite and overlying Aztec Siltstone (Taylor Group), of the Cook Mountains and Skelton Névé regions, southern Victoria Land, Antarctica. The Beacon Heights Orthoquartzite exposed in the southern Cook Mountains yielded specimens of the lycopods Haplostigma lineare, Malanzania sp., and Archaeosigillaria sp. cf. A. caespitosa. The Aztec Siltstone flora contains Praeramunculus alternatiramus and H. lineare.
Silurian conodont-based correlations between Gotland (Sweden) and Saaremaa (Estonia)
Authors: Jeppsson L. , Viira V. , Männik P.
Published: May 2009

Correlations between the Silurian successions of Gotland and the East Baltic are based on the narrowest stratigraphic units that can be distinguished in both areas. In order further to increase precision, true ends of ranges in measured sections have been used instead of ‘pooled’ formational faunas, where outcrops and collections permit. Some previous correlations are confirmed. In other cases, there are considerable changes both in levels of correlation and in precision. The major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards. At least some of these gaps decrease in magnitude southwards in Estonia. Gaps at these levels are also noted on Gotland, although they are small and probably do not extend across the island. The patterns through time of deposition (during secundo episodes) and gaps (during primo episodes) agree very well with what can be predicted from a model of oceanic and climatic cyclicity.
Turbidite to storm transition in a migrating foreland basin: the Kendal Group (Upper Silurian), northwest England
Authors: King Louisa M.
Published: May 2009

The uppermost Windermere Supergroup (Kendal Group) of northwest England records the passage from Wenlock and lower Ludlow deep water ‘flysch’ deposits to upper Ludlow and Přídolí shallower water ‘molasse’ deposits within an evolving foreland basin. An upwards progression is preserved from oxygen-poor basin-slope turbidite deposits through more oxygenated, bioturbated dilute density flow deposits, to storm and wave-influenced sediments. The storm-influenced sediments display hummocky cross-stratification, aSkolithosichnofacies, shelly lags, and symmetrical wave ripple cross-lamination. Convolute lamination increases in magnitude and frequency in the upper part of the sequence, apparently nucleated above ripple crests. Tropical hurricanes probably controlled storm deposition, as suggested by late Silurian palaeogeographic reconstructions. Structures in the heterolithic muddy siltstones suggest deposition in a lower energy, wave-influenced setting. Mud-drapes, short wavelength symmetrical ripples and multi-directional ripple cross-lamination are common. The Kendal Group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry, bounded to the northwest and northeast by topographic slopes. As well as a temporal trend, facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through Ludlow and Přídolí time, probably ahead of a rising mountain front to the north. The increase in pre-lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert.
Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales
Authors: Young T. , Martin F. , Dean W. T. , Rushton A. W. A.
Published: May 2009

Lithostratigraphic units of early to late Cambrian age established by T. C. Nicholas in 1915 in the St Tudwal's Peninsula are revised. They comprise, in ascending order: Hell's Mouth Formation (> 190 m); Trwyn y Fulfran Formation (37 m);Cilan Formation (400 m); Ceiriad Formation (40 m seen); Nant-y-big Formation (> 110 m seen); Maentwrog Formation (in part, 50 m seen, an estimated 250 m concealed); Ffestiniog Flags Formation (in part,c. 120m seen). The ‘calcareous grit’ at the top of Nicholas's Nant-pig Mudstones spans the unconformable boundary between the Nant-y-big and Maentwrog formations. Previously described limestone clasts in the ‘grit’ are probably erosional remnants of anin situbioclastic limestone bed; their contained trilobites include genera and species found in the Andrarum Limestone (late Middle Cambrian) of Scania, Sweden. Acritarchs are documented and compared particularly with those from eastern Newfound-land. Those from the highest part of the ‘calcareous grit’ includeCymatiogaleasp. and are of late Cambrian age. One new species,Heliosphaeridium? llynenseMartin, comes from the lower part of the Nant-y-big Formation (middle Middle Cambrian), where it appears a little earlier than theAdara aleaBiozone.
A search for shocked quartz grains and impact ejecta in early Silurian sediments on Gotland, Sweden
Authors: Schmitz Birger , Jeppsson Lennart , Ekvall Johan
Published: May 2009

All bentonite and bentonite-resembling layers thicker than a few millimetres from a 120m-thick Early Silurian sequence on Gotland, Sweden, were searched for shocked quartz grains of comet or asteroid impact origin. Although more than 200000 quartz grains from 86 bentonite samples were studied, not one single grain with multiple planar shock features was found. The studied sequence represents sedimentation during a period of about 2 million years. Impact frequencies, estimated from the cratering record and astronomical observations, indicate that during a 2-myr- period on average 20 comet or asteroid bodies larger than 0.5 km in diameter strike the Earth. The number of smaller impacting bodies is many times higher. In the light of this high frequency of impacts, the absence of any shocked-quartz-bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small- and medium-scale impact events.

The results also show that shocked quartz in general is absent or extremely rare in volcanic ash. This strengthens the case for an impact-related origin of shocked quartz grains in the Cretaceous–Tertiary boundary days.
Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust?
Authors: Gibbons Wes , Murphy J. Brendan
Published: May 2009

The Clarke Head fault megabreccia was produced within a major Late Palaeozoic transcurrent structure (the Minas fault system) which separates the displaced Meguma terrane of southern Nova Scotia from rocks more typical of the Avalon Superterrane. A large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy (2-pyroxene + garnet + plagioclase) and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone. Whole rock geochemistry reveals the granulite protolith to have been a continental, within-plate mafic magma transitional between theoleiitic and alkaline. The original geochemical signature has survived strong dynamic recrystallization at granulite grade. Well-preserved REE abundances testify to a lack of metasomatic fractionation during high grade shearing under water-absent conditions. Sm—Nd data indicate that the basic granulite has a TDM age of c. 1 Ga. Isotopic comparisons with adjacent areas reveal similar TDM ages both north and south of the Minas fault system. The high grade clast may be typical of the lower crust in Nova Scotia and is thought to offer a rare window into the deep crust of the Avalon Superterrane in North America.
Phosphatized soft tissues in bivalves from the Portland Roach of Dorset (Upper Jurassic)
Authors: Wilby Philip R. , Whyte Martin A.
Published: May 2009

Phosphatized soft tissues are preserved in abundance in the trigoniids (Bivalvia) Laevitrigonia gibbosa and Myophorella incurva from the Portland Roach (Upper Jurassic) of Dorset. Cellular structures are preserved and fossilization is almost exclusively the result of a dense coating of mineralized microbes. Phosphatized soft tissues are restricted entirely to those trigoniids whose valves remained tightly closed after death. Only in these specimens was sufficient phosphorus concentrated by the decay of their most ‘labile’ soft tissues to trigger the precipitation of apatite in and around microbes infesting their more ‘refractory’ soft tissues. The absence of fossilized soft tissues in the rest of the fauna implies that phosphatization was very taxon-specific.
The Kunene complex, Angola/Namibia: a composite massif-type anorthosite complex
Authors: Ashwal Lewis D. , Twist David
Published: May 2009

Thec. 15000 km2,c. 2 Ga Kunene complex of southern Angola and northern Namibia is one of the world's largest occurrences of anorthositic rocks, rivalled only perhaps by the Lac St Jean massif of the Grenville Province in Quebec. We report here the results of a detailed field and laboratory study of a 100 km2area in the northern part of the complex. Coarse grained (av. 1–2 cm) anorthosite and leucotroctolite are the predominant rock types, although colour index varies between 0 and 50, averaging about 10. Ultramafic rocks are totally absent. Typical mineralogy is: plagioclase (An57–76) + olivine(Fo64–71) + orthopyroxene(En65–74) + clinopyroxene ± Fe—Ti oxides ± apatite. Textures are dominantly massive, although weak, impersistent, magmatic lamination with nearvertical dip and unsystematic strike is also present. Other magmatic features include plagioclase and orthopyroxene megacrysts, block structure, mortar texture, and anorthositic dykes. Metamorphic effects are minimal or absent. All of these attributes are similar to those found in typical massif-type anorthosites. Since comparable features are present over large areas elsewhere in the complex, we suggest that Kunene should be considered analogous to a large, composite, massif-type anorthositic intrusive complex, rather than to a large, single or composite mafic layered intrusion such as Bushveld, as has been previously suggested or assumed. This interpretation is supported by satellite imagery, which shows the outlines of several individual anorthositic plutons, one of which clearly encompasses our field area.
Magnetic remanence in the Chalk of eastern England: an unusually resistant VRM?
Authors: Borradaile Graham J.
Published: May 2009

A single component, natural remanent magnetization (NRM) is carried largely by pseudosingle domain magnetite in the Cretaceous Lower Chalk and Red Chalk of eastern England. The Red Chalk also records the same direction in haematite. Most of the ferro-magnetic minerals occur as primary clastic or early diagenetic grains. A stable remanence component is resistant to demagnetization, and is carried by both magnetite and haematite. Nevertheless, it has a steep inclination close to the present Earth's field and it is too steep for the previously reported palaeolatitude of these rocks at the time of sedimentation. A postglacial slump breccia scatters the ChRM but also provides some evidence of viscous, partial magnetic overprinting during slumping. Despite its resistance to thermal and alternating field demagnetization the characteristic remanent magnetization (ChRM) is probably a young Bruhnes epoch viscous remanent remagnetization (VRM).
Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite
Authors: Gallagher V. , O'Connor P. J. , Aftalion M.
Published: May 2009

The Croghan Kinshelagh alkali granite intrudes a cleaved volcano-sedimentary sequenceon the border of counties Wicklow and Wexford in southeast Ireland. U-Pb dating of zircons fromthe granite indicate a mid-Caradoc emplacement age of 454 ± 1 Ma. The Duncannon Group hostrocks form the southwestern end of the Avoca Volcanic Belt, a Mid-Ordovician (Caradoc) sequenceof acid and intermediate lavas and volcaniclastics. Dolerite dykes intrude the granite; elsewhere in theregion dolerites are generally associated with volcanic rocks. The main, Dl deformation within theDuncannon Group rocks is manifest as a steep Dl cleavage generally regarded as a product of LateCaledonian regional deformation in southeast Ireland. The Croghan Kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the Caradoc volcanic rocks; relativelyhigh Th, Y, Nb and REE contents set it apart from any other known granite type in southeastIreland. Together with the geochemical evidence, the age determination of 454 Ma indicates that theCroghan Kinshelagh granite was generated and emplaced during Ordovician volcanism in southeastIreland. Volcanism was closely followed by penetrative deformation and emplacement of the granite.The intra-Ordovician deformation may have been a consequence of closure of the Iapetus Ocean ormore localized events such as accretion on the hanging wall of the subduction zone. The age of theCroghan Kinshelagh granite provides an important datum for Ordovician volcanism and subductionin southeast Ireland.
The Cenomanian-Turonian Boundary Event in northern Spain
Authors: Paul C. R. C. , Mitchell S. , Lamolda M. , Gorostidi A.
Published: May 2009

A sparse but moderately diverse nannoflora is recorded through the Cenomanian-Turonian Boundary Event (CTBE) at Menoyo, Spain and allows recognition of the late CenomanianEiffellithus turriseiffeliiZone and the early TuronianQuadrum gartneriZone, as well as five significant nannofossil bioevents associated with the CTBE. Carbon isotopes record a modest excursion which lasted 250–270 thousand years (ka) in three phases, buildup (105 ka), plateau (126 ka) and recovery (42 ka). Acid insoluble residue values imply that sea level rose through the buildup phase, indicated by a reduction in the accumulation rate of siliciclastic sediment. However, oceanic productivity apparently declined through the CTBE, indicated by reduction in accumulation rates of total carbonate and intact coccoliths to less than a quarter of their initial values. These patterns are very similar to those found through the CTBE at Dover, England and reflect widespread not local effects. A combination of lithological changes, seven key bioevents, and details of the δ13C curve, allows us to suggest a bed-by-bed correlation through the CTBE between Dover and Menoyo, demonstrating the practicality of cyclostratigraphy for international correlation at a precision of ± 10 ka. Graphic correlation produces a straight line fit despite wide fluctuations in sediment accumulation rates at both localities. This can only occur if changes were in phase and of similar magnitudes at both localities, again suggesting widespread, perhaps global, control.
First post-Triassic temnospondyl amphibians from the Shan-Thai block: intercentra from the Jurassic of peninsular Thailand
Authors: Buffetaut Eric , Raksaskulwong Lertsin , Suteethorn Varavudh , Tong Haiyan
Published: May 2009

Two temnospondyl intercentra from non-marine middle Jurassic rocks at Mab Ching, in the southern peninsula of Thailand, are the first remains of post-Triassic labyrinthodont amphibians to be reported from the Shan-Thai block. They closely resemble an intercentrum recently reported from the middle Jurassic of the Khorat Plateau of northeastern Thailand, which is part of the Indochina block. Although the Mab Ching specimens are too fragmentary to warrant a precise identification, they confirm that temnospondyl amphibians were widespread on the various Asian continental blocks in the Jurassic.
The base of the Jurassic System: new data on the first appearance of Psiloceras planorbis in southwest Britain
Authors: Hodges Peter
Published: May 2009

Recent collecting in the Lower Lias of localities at St Audrie's Bay, north Somerset, Sedbury Cliff, Gloucester and Lavernock Point, South Glamorgan has yielded Psiloceras planorbis (J. de C. Sowerby) in beds considered by some to be of Rhaetian, Triassic age. These are the earliest records of this ammonite to date in southwest Britain. Evidence is provided of a major facies change at the top of the pre-planorbis beds followed by the diachronous first occurrence of Psiloceras planorbis. These new data have implications for the use of earliest occurrence of Psiloceras planorbis as a chronostratigraphic marker in defining the base of the Jurassic System, and for the definition of the base of the Hettangian Stage in the recently proposed candidate Global Stratotype Section at St Audrie's Bay.
The earliest Ordovician nematophorid graptolites: taxonomy and correlation
Authors: Erdtmann B.-D.
Published: May 2009

The earliest nematophorid (planktic) dendroid graptolites (Family Anisograptidae) are described and revised from several heterofacial facies sections of the Broom Point Formation, Cow Head Group, western Newfoundland (Broom Point North and St Paul's represent medial to upper continental slope, Martin Point and Green Point distal slope environments). Noting potential conodont recycling in the palaeoslope environments of the proximal Cow Head Group sections, graptolites are the only group of fossils that could not have been subject to post-burial transport. The graptolites belong to an informal group of quadriradiate form-species principally representing two originally related but then diverging phyletic groups: pendent Rhabdinopora Eichwald, 1855 and horizontal to sub-horizontal Staurograptus Emmons, 1855; both being stratigraphically within Assemblage Zone I (emended after Cooper, 1979) of earliest Tremadoc or early Ibexian age (top of Cordylodus intermedius to base of C. lindstromi conodont zones). Assemblage I graptolites offer a higher resolution than coeval conodonts and are a better tool for inter-facies correlations both within the Broom Point Formation and with other graptolitic sequences on a global scale. Form-species of quadriradiate Rhabdinopora rustica (such as ?R. praeparabola and R. parabola) and of Staurograptus dichotomus (e.g. ‘Radiograptus’ or ‘Heterograptus’ flexibilis or ‘Aletograptus’) are interpreted as astogenetic morphs, or as phylogenetically descendant variants of these forms. Upon evidence of late astogenetic insertion of dissepiments in Staurograptus and Anisograptus the names ‘Heterograptus’ and ‘Radiograptus’ are placed into junior synonymy, and ‘Aletograptus’ is regarded a junior synonym of Staurograptus because its post-primary dichotomies are merely delayed distally (or omitted) to be observed exclusively in very mature specimens. The Cow Head Group fauna is compared with earliest nematophorids from Oslo, Norway (Naersnes) and Dayangcha, Jilin, China (Xiaoyangqiao), and a new comprehensive ecostratigraphic zonation for early Tremadoc graptolites is proposed.
Techniques for quantitative stratigraphic correlation: a review and annotated bibliography
Authors: Tipper J. C.
Published: May 2009

The development of techniques for quantitative stratigraphic correlation has tended to outstrip their acceptance by practising stratigraphers. To make these techniques more readily accessible and to encourage their use, this paper presents a brief, general review of the problem of quantitative stratigraphic correlation and then shows how, using a natural framework for stratigraphic correlation, the stratigraphic time-series, there can be seen an orderly pattern among them. The annotated bibliography, of almost 400 articles, includes a majority of those references concerned with quantitative stratigraphic correlation, in whatever sense: the scheme of annotation provides a straightforward, albeit subjective indication of the general thrust of each article.
First report of Pan-African Sm—Nd and Rb—Sr mineral isochron ages from regional charnockites of southern India
Authors: Unnikrishnan-Warrier C. , Santosh M. , Yoshida M.
Published: May 2009

Mineral and whole-rock isotope data for a massive charnockite from Kottaram in the Nagercoil Block at the southern tip of Peninsular India yield Sm—Nd and Rb—Sr ages of 517 ± 26 Ma and 484 ± 15 Ma respectively. The Nd model age calculated for the charnockite isc. 2100 Ma. Our study reports the first Pan-African mineral isochron ages from regional charnockites of Peninsular India, which are in good agreement with the recently obtained ages of incipient charnockites in the adjacent blocks, as well as alkaline plutons within the same block. Our results indicate that the Pan-African tectonothermal event in the granulite blocks south of the Palghat—Cauvery shear zone was regional, with terrain-wide rejuvenation. These results correlate with similar Pan-African tectono-thermal events reported from Sri Lanka and East Antarctica, and have an important bearing on Gondwana reconstructions.
Isotope studies of granitoids from the Bangenhuk Formation, Ny Friesland Caledonides, Svalbard
Authors: Johansson Å. , Gee D. G. , Björklund L. , Witt-Nilsson P.
Published: May 2009

The Caledonian Hecla Hoek succession in Ny Friesland, eastern Svalbard has been interpreted, for many decades, to be a continuous stratigraphic sequence. Early Palaeozoic and Neoproterozoic strata in its upper parts pass more or less conformably down into amphibolite facies rocks (Stubendorffbreen Supergroup) at depth. Recent isotopic age-determination and structural studies have indicated that the Stubendorffbreen succession is tectonostratigraphic and made up of at least three major thrust sheets. This paper provides new data from two meta-igneous units within the succession, the Bangenhuk and Instrumentberget gneisses. Both are granitoid sheets, consisting mainly of red, strongly lineated gneisses of monzogranitic composition; the Bangenhuk unit also contains some lenses of little deformed granitoids, as well as cross-cutting aplite dykes, amphibolitized dolerites and subordinate metasedimentary rocks. The latter are locally cut by granitoids. U—Pb zircon dating of six samples of variably deformed Bangenhuk granitoids, including one cross-cutting aplitic dyke, has yielded ages between 1720 and 1770 Ma, the higher values generally from the less deformed samples. The Instrumentberget gneissic granite yielded an age of 1737+46−41 Ma. These ages are interpreted to date the time of intrusion of the granitoids at around 1750 Ma; the younger ages may have been slightly lowered by Caledonian deformation, particularly those from specimens located close to a major fracture (the Billefjorden Fault Zone) in Wijdefjorden—Austfjorden. U—Pb dating of titanite from the least deformed granitoid also yields comparable Palaeoproterozoic ages; in the more deformed rocks, however, titanites give evidence of Caledonian ductile deformation at c. 410 Ma. The Rb—Sr system of the corresponding whole rock samples has been disturbed and yields an errorchron age of about 1650 Ma and, for some samples, an impossibly low initial Sr ratio. The Sm—Nd system may be more intact and yields initial εNd values of −2 to −3, suggesting some contribution from older crustal material to the granitoid magmas. The results indicate the presence of extensive units of Palaeoproterozoic granitic basement within the Lower Hecla Hoek succession of Ny Friesland, supporting the hypothesis that the latter is composed of tectonically intercalated basement and cover units.
Geochemical character of Neoproterozoic volcanic rocks in southwest Wales
Authors: Bevins R. E. , Pharaoh T. C. , Cope J. C. W. , Brewer T. S.
Published: May 2009

Volcanic rocks of Neoproterozoic age form several fault-related inliers in Wales and the Welsh Borderland. Those in North Wales and the Borderland have been investigated recently, while those in southwest Wales remain little studied. In southwest Wales, basic to intermediate lavas and related volcaniclastic rocks and silicic tuffs in the St David’s area comprise the Pebidian Supergroup, which is intruded by minor basic intrusions, while the Coomb Volcanic Formation, exposed farther east around Llangynog, is composed of basic and silicic lavas and silicic tuffs, intruded by a single dacite sill and numerous dolerite sills. New geochemical data show that both the Pebidian and Coomb basalts have subduction-related characteristics. The Coomb basalts are geochemically similar to those of the Uriconian Group of the Welsh Borderland, while the Pebidian basalts bear a similarity to volcanic rocks recovered from the Bryn-teg Borehole, in the Harlech Dome. Uriconian-type volcanic rocks may underlie much of the Midlands Microcraton, with the Welsh area underlain by volcanic rocks of Pebidian type.
The crystalline units of the High Himalayas in the Lahul–Zanskar region (northwest India): metamorphic–tectonic history and geochronology of the collided and imbricated Indian plate
Authors: Pognante U. , Castelli D. , Benna P. , Genovese G. , Oberli F. , Meier M. , Tonarini S.
Published: May 2009

In the High Himalayan belt of northwest India, crustal thickening linked to Palaeogene collision between India and Eurasia has led to the formation of two main crystalline tectonic units separated by the syn-metamorphic Miyar Thrust: the High Himalayan Crystallinessensu stricto(HHC) at the bottom, and the Kade Unit at the top. These units are structurally interposed between the underlying Lesser Himalaya and the very low-grade sediments of the Tibetan nappes. They consist of paragneisses, orthogneisses, minor metabasics and, chiefly in the HHC, leucogranites. The HHC registers: a polyphase metamorphism with two main stages designated as M1 and M2; a metamorphic zonation with high-temperature recrystallization and migmatization at middle structural levels and medium-temperature assemblages at upper and lower levels. In contrast, the Kade Unit underwent a low-temperature metamorphism. Rb–Sr and U–Th–Pb isotope data point to derivation of the orthogneisses from early Palaeozoic granitoids, while the leucogranites formed by anatexis of the HHC rocks and were probably emplaced during Miocene time.

Most of the complicated metamorphic setting is related to polyphase tectonic stacking of the HHC with the ‘cooler’ Kade Unit and Lesser Himalaya during the Himalayan history. However, a few inconsistencies exist for a purely Himalayan age of some Ml assemblages of the HHC. As regards the crustal-derived leucogranites, the formation of a first generation mixed with quartzo-feldspathic leucosomes was possibly linked to melt-lubricated shear zones which favoured rapid crustal displacements; at upper levels they intruded during stage M2 and the latest movements along the syn-metamorphic Miyar Thrust, but before juxtaposition of the Tibetan nappes along the late- metamorphic Zanskar Fault.
Spinel lherzolite and other xenoliths from a dolerite dyke in southwest Donegal
Authors: Gallagher S. , Elsdon R.
Published: May 2009

A highly xenolithic dolerite dyke is described which contains a large number of spinel lherzolite xenoliths. The petrology of the dolerite and the xenolith suite is described and electron probe analyses presented for the mineral phases in one of the spinel lherzolite xenoliths. The dyke geochemistry is consistent with a Permo-Carboniferous age.
The Solund–Stavfjord Ophiolite Complex and associated rocks, west Norwegian Caledonides: geology, geochemistry and tectonic environment
Authors: Furnes H. , Skjerlie K. P. , Pedersen R. B. , Andersen T. B. , Stillman C J. , Suthren R. J. , Tysseland M. , Garmann L. B.
Published: May 2009

Metabasalts of the Upper Ordovician Solund-Stavfjord Ophiolite Complex of the westernmost Norwegian Caledonides, show N-to E-MORB affinity, with high Th/Ta (or Nb) ratios giving evidence of subduction influence. The Solund–Stavfjord Ophiolite Complex is overlain by a heterogeneous assemblage of sedimentary and volcanic rocks, the Stavenes Group, of which the Heggøy Formation of metasandstones and phyllites conformably overlies the metabasalts of the Solund–Stavfjord Ophiolite Complex. The Heggøy Formation contains, in places, abundant metabasalt pillow lavas and minor intrusions, geochemically similar to those of the Solund–Stavfjord Ophiolite Complex, and basic metavolcaniclastites of island arc tholeiite (IAT) composition. This indicates that the Solund–Stavfjord Ophiolite Complex and Heggøy Formation developed in a marginal basin between a continental margin and an active subduction system, for which the present-day Andaman Sea may provide a realistic model. The other magmatic rocks of the Stavenes Group, showing both calc-alkaline and alkaline affinities, are less well time-constrained, but they are thought to represent an advanced stage of the island arc development, and ocean island build-up, respectively.
Upper Ordovician – lower Silurian sequences of the Bohemian Massif, central Europe
Authors: Štorch P.
Published: May 2009

Upper Ordovician – lower Silurian sequences of the Bohemian Massif (in the Moldanubian Zone and Barrandian preserved in the Prague Basin; Rožmitál area; metamorphic ‘islets’ in the mantle of Central Bohemian Pluton; and in the Železné hory area), as well as along the northern margin of the Bohemian Massif in the Saxothuringian and Lugian (= West Sudetian) zones, show evidence of regressive–transgressive facies changes which can be related to glacio-eustatic sea-level fluctuations recognized elsewhere. Glacio-marine diamictites of late Ordovician (Hirnantian) age occur in the Prague Basin and Rožmitál area, and in north Bavaria and Thuringia. They provide evidence of temporary cooling of the region. Facies changes caused by synchronous sea-level changes allow stratigraphic correlation of even the faulted, weakly metamorphosed and biostratigraphically poorly dated sections in the Bohemian Massif. Correlation is based on sections in the Prague Basin in which the changes are best recorded and dated.
Palaeomagnetic and geochemical evaluation of a terrane-linking ignimbrite: evidence for the relative position of the Grampian and Midland Valley terranes in late Silurian time
Authors: Trench A. , Haughton P. D. W.
Published: May 2009

The proposed correlation of Lower Old Red Sandstone dacitic ignimbrites between the Northern Midland Valley and Grampian terranes of central Scotland has been investigated in a combined palaeomagnetic and geochemical study. Statistically indistinguishable late Silurian palaeolatitudes (Grampian terrane 27.0° S±3.5°; Northern Midland Valley terrane 22.9° S± 1.8°), comparable remagnetization histories, a shared ‘normal’ polarity for the primary magnetization and equivalent gyroremanence acquisition, favour correlation across the Highland Boundary Fault. Similar chemistry for biotite phenocrysts further corroborates correlation which was initially made on the basis of a similar field appearance and petrography.

This correlation, together with evidence from provenance studies, suggests that the separation of the Northern Midland Valley and Grampian terranes inferred for the Ordovician period was largely removed by late Silurian times, with scope for relative displacements of the order of only tens of kilometres after Lower Old Red Sandstone deposition.
Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: Geochemical evidence of ensialic marginal basin volcanism
Authors: Merriman R. J. , Roberts B.
Published: May 2009

Metabentonites occur extensively in the Moffat Shale Group of the Southern Uplands of Scotland. At Dob's Linn 135 metabentonite beds, 1–50 cm thick, occur in Ashgill to Llandovery strata, representing an aggregate thickness of 6 m of compacted ash accumulated over approximately 25 Ma. The metabentonites are characterized by relatively high concentrations of trace elements, including Ba, Cs, Hf, Nb, Rb, Ta, Th, U, Y, Zr and REEs, which were inherited from evolved vitric ash. Immobile trace element data indicate that a spectrum of silicic ash compositions accumulated, ranging from subalkaline to mildly peralkaline. In the late Ordovician N. gracilis to G. persculptus biozones, subalkaline ash falls predominated, whereas peralkaline ash falls predominated in the Llandovery (Silurian) P. acuminatus to M. convolutes biozones, giving way to predominantly subalkaline ash falls during accumulation of the M. sedgwickii to R. maximus biozones. Changeovers in the dominant ash types are marked by increased proportions of ash. The magmas from which the ash types evolved were generated in an ensialic arc transitional to a back-arc setting, and involved attenuated sialic crust and mantle characterized by variable depletion in HFS elements. Lithological, petrological and REE characteristics suggest that the Moffat Shale Group is not exclusively pelagic in origin and probably accumulated in a back-arc basin bordering an ensialic arc terrane.
Estimating rates of calcrete formation and sediment accretion in ancient alluvial deposits
Authors: Wright V. P.
Published: May 2009

The use of calcrete horizons as a means of assessing rates of sediment accretion in ancient alluvial sequences is reviewed. Any attempt to use such horizons in quantifying ancient alluvial deposition must appreciate that accurate data on rates of formation of Quaternary calcretes are limited. Such data show considerable variations in the rates and no reliable data exist at all for some calcrete types. The abundance of calcretes in the geological record warrants a new initiative to improve our understanding oftheir origins and rates of formation.
A Cretaceous Neo-Tethyan carbonate margin in Argolis, southern Greece
Authors: Clift Peter D. , Robertson Alastair H. F.
Published: May 2009

The Argolis Peninsula, southern Greece, is believed to form part of a Pelagonian microcontinent located between two oceanic basins, the Pindos to the west and theVardar to the east, in Triassic to Tertiary time. In eastern Argolis, two important units are exposed: (i) the Ermioni Limestones cropping out in the southwest; (ii) the Poros Formation, observed on an offshore island in the northeast, and on the adjacent mainland. Both these units comprise late Cretaceous (Aptian-Maastrichtian) pelagic limestones, calciturbidites, lenticular matrix- and clast-supported limestone conglomerates and slump sheets. However, the Poros Formation is distinguished from the Ermioni Limestones by the presence of bituminous micritic limestones and an increasing proportion of shale up sequence. These successions are deep-water slope carbonates that once formed the southeast-facing passive margin of the Pelagonian platform (Akros Limestone). Beyond this lay a late Cretaceous ocean basin in the Vardar Zone. This ocean was consumed in an easterly-dipping subduction zone in latest Cretaceous (?) to early Tertiary time, giving rise to an accretionary complex (Ermioni Complex). During early Tertiary (Palaeocene-Eocene) time the passive continental margin (Pelagonian Zone) collided with the trench and accretionary complex to the east. As the suture tightened, former lower-slope carbonates (Ermioni Limestones) were accreted to the base of the over-riding thrust sheets and emplaced onto the platform. Farther west, bituminous upper slope carbonates (Poros Formation) flexurally subsided and passed transitionally upwards into calcareous flysch and olistostromes in a foreland basin. These sediments were then overridden by the emplacing thrust stack and themselves underplated. Late-stage high-angle faulting then disrupted the tectonostratigraphy, in places juxtaposing relatively high and low structural levels of the complex.
The Emei Taphrogenesis of the upper Yangtze Platform in south China
Authors: Zhili Luo , Yizhong Jin , Xikui Zhao
Published: May 2009

The Yangtze Platform (Yangtze Palaeoplate) drifted into the area of southern China following late Silurian tectonism. In late Palaeozoic to early Mesozoic time the Yangtze Platform was subjected to strong extensional movements in its southeastern region within Yunnan, Guizhou, Guangxi and Hunan provinces, and along its northwestern margin in the Songpan-Ganzi area. Taphrogenesis (intracontinental extension) began in Devonian times, climaxed with the late Permian eruption of the Emeishan basalts, and ended in mid Triassic times. Therefore, the senior author (LZL) has named this extension the ‘Emei Taphrogenesis’, a phenomenon that was constrained by the neighbouring tectonic units of the Yangtze Platform. The platform has been substantially affected by the early Palaeozoic south China fold zone along its eastern margin, and by the late Palaeozoic opening of the Tethys Ocean on the northwestern margin. This paper delineates the tectonic patterns associated with the Emei Taphrogenesis.
The geology of the western part of the Fintona Block, Northern Ireland: evolution of Carboniferous basins
Authors: Mitchell W. I. , Owens B.
Published: May 2009

The western part of the Fintona Block is divided into four fault-bounded segments that contain red-bed sediments formerly assigned to the Lower Old Red Sandstone.Dating by miospores indicates the presence of deposits of early Devonian age in the Irvinestown Segment, late Viséan–early Silesian age in the Tempo–Lisbellaw Segment, and late Viséan–early Silesian and late Silesian ages in the Milltown Segment. Northward migration of the early Carboniferous marine transgression in the northern part of Ireland coincided with the sequential propagation of back-stepping faults and resulted in the development of diachronous facies belts between late Courceyan and Arundian times. Tectonic uplift, of a possible southwesterly extension of the Tyrone Igneous Complex, gave rise to the deposition of Asbian to Pendleian red-beds to the south of a massif. An interface between these red-beds and contemporaneous marine sediments farther to the south is recognized and dated. A new non-marine basin, containing Brigantian and Pendleian red-beds, also developed to the north of the massif A waterlogged floodplain that developed during Westphalian A times may be coeval with more widespread coal-bearing sequences elsewhere in Ireland. Alluvial fans prograded southwards over this plain during Westphalian B times when faults bordering a northern landmass were reactivated.
Factors controlling the kinetics of crystallization: supersaturation evolution in a porous medium. Application to barite crystallization
Authors: Prieto Manuel , Putnis Andrew , Fernandez-Diaz Lurdes
Published: May 2009

The nucleation of barite has been studied in a system involving the doublediffusion of Ba2+and SO42-in an Na-rich aqueoussolution, through a porous medium. The evolution of the concentration profiles in the medium, which is a column of porous silica gel, has been determined as a function of time by direct chemical analysis of the diffusion-controlled mass transfer. By measuring the pH evolution, a Debye–Huckel treatment of ionic complexing has enabled the supersaturation evolution to be determined. The location of barite precipitation in the column is controlled both by the need to exceed a threshold supersaturation, as well as achieve an ‘equality range’ in which [Ba2+]/[SO42−] is close to unity. The value of the threshold supersaturation is a kinetic parameter and depends on the rate at which supersaturation increases. The experimental system described here has wide application to the study of crystallization phenomena in rocks. Experiments on the effect of additives designed to inhibit nucleation of barite in North Sea oil wells are used to quantify the resultant increase in supersaturation threshold.
Milankovitch cyclicity and the Boom Clay Formation: an Oligocene siliciclastic shelf sequence in Belgium
Authors: Van Echelpoel E. , Weedon G. P.
Published: May 2009

The Boom Clay Formation of northeast Belgium consists of a sequence of alternating, laterally persistent beds of silt and clay. Power-spectral analysis of grain-size variations indicates regular sedimentary cycles with wavelengths of about 100 and 46cm that had periods of 124 and 57 thousand years (ka) or less. The lateral continuity ofthe beds, combined with the regularity and estimated periods of the cycles, suggests an indirect link to the 100 and 41 ka orbital (Milankovitch) cycles. The variations in meangrain size were caused by changing bottom-water turbulence as controlled by storms and/or glacio-eustatic water depth fluctuations. This study confirms that certain marinesiliciclastic sequences can provide proxy-records of palaeoclimatic variance.
Petrogenetic implications of mineral crystallization trends of Troodos cumulates, Cyprus
Authors: Thy P.
Published: May 2009

Hole number CY-4 of the Cyprus Crustal Study Project penetrated the lower sheeted dyke complex, gabbros and ultramafic cumulates of the Troodos ophiolite. The lower part of the drill core sampled a coarse-grained plutonic complex revealing phase and cryptic layering and one major magma chamber replenishment. This magma chamber intruded medium-grained gabbroic rocks showing intricate chemical evolution trends reflecting several magma replenishments. In the upper part of the core, the gabbroic cumulates are intruded by fine-grained dykes, which grade into the sheeted dyke complex and chemically can be correlated with the lavas of the lower pillow sequence. The upper pillow lavas are best correlated with the ultramafic cumulates. A study of coexisting plagioclase (An) and mafic mineral (opx Mg #) compositions in the drill core revealed three main rock types: (1) a primitive group (An95–98, Mg #75–85) represented by the lower, coarse-grained gabbroic and ultramafic cumulates. (2) an intermediate group (An86–95 and Mg #70–78) represented by the upper level gabbroic cumulates, and (3) the lower part of the sheeted dyke complex (An60–80 and Mg #60–70). The plagioclase of the gabbros and ultramafic cumulates have an unusually high An content. Numerical simulation of the expected anhydrous, one atmosphere, crystallization trends show that the Troodos trends cannot be reproduced from known spreading or subduction related glasses. Mineralogical evidence indicates that the extrusives and the cumulate sequences of the Troodos ophiolite are genetically related. Glasses from the extrusives, nevertheless, also fail to reproduce the mineral crystallization trends observed in the plutonics. Attempts to model high PH2O crystallization produced trends more consistent with those observed in the cumulates. The very sodium-poor nature of the plagioclase may therefore mainly reflect high PH2O crystallization. High water content is consistent with the inferred subduction zone basin origin for the Troodos ophiolite.
The Cretaceous—Tertiary boundary in Mangyshlak, U.S.S.R.
Authors: Naidin D. P.
Published: May 2009

Upper Cretaceous carbonate sequences contain omission surfaces, hardgrounds and intercalations of ‘clays’. These ‘clays’ are largely associated with submarine biogeochemical carbonate dissolution that was caused by high biological productivity in the pelagic zone. The Maastrichtian-Danian ‘boundary clays’ probably accumulated during a maximum productivity that led to the exhaustion of nutrients, development of phenomena comparable to present-day red tides, and mass mortality of marine biota. There was a type of ecological break in the seas and oceans at the time of the Maastrichtian-Danian boundary.