bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology and geochemistry of bitumen vein deposits at Ghost City, Junggar Basin, northwest China
Authors: Parnell John , Ansong Geng , Jiamo Fu , Guoying Sheng
Published: May 2009

Veins of solid bitumen occur in Cretaceous sandstones at the northwest margin of the Junggar Basin, China. The bitumen has a low aromaticity and a composition comparable to gilsonite. The bitumen contains abundant steranes and terpanes, and β-carotane, although most n- and i- alkanes have been removed, which is characteristic of the local crude oil. The sterane and triterpane maturity parameters show that the bitumen, local crude oil, and source rocks are all mature. Bitumen–wallrock relationships suggest that the host sandstone was not completely consolidated at the time of emplacement of the bitumen veins, although bitumen emplacement was a relatively late diagenetic event. The burial history for the northwest Junggar Basin shows that hydrocarbon generation from the assumed upper Permian source rocks commenced in late Triassic/early Jurassic times and suggests that rapid hydrocarbon generation may have resulted in overpressure contributing to the bitumen emplacement.
Thermal maturation of the Lower Palaeozoic strata of northern Greenland from conodont colour alteration index (CAI) data: implications for burial history and hydrocarbon exploration
Authors: Armstrong H. A. , Smith M. P. , Aldridge R. J. , Tull S. J.
Published: May 2009

Conodont colour alteration data for the Lower Palaeozoic strata of the North Greenland carbonate platform indicate a pattern of increased thermal maturity northwards within the Franklinian Basin. There is little variation in values through the Canadian–Llandovery (Lower Ordovician–Lower Silurian) interval at any given locality. A simplified thermal model for the platform suggests that the predominant control of conodont colour alteration and thermal maturation was maximum depth of burial, which occurred during the mid- to late Silurian. A preliminary integrated scheme for conodont and organic thermal maturity indicators can be compiled from the data now available from North Greenland.
Mineralization, antiforms and crustal extension in andesitic arcs
Authors: Mitchell A. H. G. , Carlile J. C.
Published: May 2009

The distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.
Neoproterozoic sedimentation on the northeast margin of Laurentia and the opening of Iapetus
Authors: Soper N. J.
Published: May 2009

Very thick shallow water sedimentary sequences were deposited in Neoproterozoic time along the future margins of Laurentia. On the eastern margin these include the Eleonore Bay and Hecla Hoek sequences of Greenland and Svalbard; these are described and their geotectonic context briefly reviewed. They present both geotectonic and geodynamic problems: why did subsidence continue for some 300 Ma prior to the opening of Iapetus, and how could 15–20 km of sediment be accommodated in an ensialic environment?

Prolonged slow stretching appears to have affected the eastern margin of Laurentia while the western (Cordilleran) margin progressed through the rift-drift transition as the Pacific opened. It is proposed that expansion of the Pacific was associated with both the convergence of Proto-Gondwanan continental terranes during the Pan-African orogeny (the extended SWEAT hypothesis) and also the maintenance of very slow extension rates on the future Iapetus margin. The strain-hardening effect of slow stretching may have been inhibited by a continuous basin-fill of juvenile heat-producing Grenville detritus. The onset of subduction in the Pacific freed up this margin; major rifting took place between East Greenland and possibly the Tornquist margin of Baltica in Vendian time, followed by the opening of northern Iapetus.
Chemostratigraphy of predominantly siliciclastic Neoproterozoic successions: a case study of the Pocatello Formation and Lower Brigham Group, Idaho, USA
Authors: Smith Loren H. , Kaufman Alan J. , Knoll Andrew H. , Link Paul Karl
Published: May 2009

Isotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The δ13C values of these carbonates are distinctly negative ( −5 to −3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive δ13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excursion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Namibia, and exceeds the magnitude of any post-Varanger δ13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post-Sturtian successions in western North America and elsewhere.
Basement–cover relationships in the Shaftesbury area of the Wessex Basin, southern England
Authors: Evans D. J. , Chadwick R. A.
Published: May 2009

In the northwestern part of the Wessex Basin of southern England, interpretation of seismic reflection and recently released borehole data provides detailed information of the major unconformity at the base of the sedimentary-fill. Seismic mapping of the top of Variscan basement reveals a concealed, faulted, dome-like Palaeozoic basement culmination or structural ‘high’ lying within the larger Cranborne–Fordingbridge High, southwest of Shaftesbury. This structure profoundly affected the deposition of the overlying Permo-Triassic sequence. The culmination, composed of Carboniferous Limestone, lies to the south of northwards-throwing, basement-controlled, syn-sedimentary faults which form the southern margin of the Mere Basin. In this area, the main phase of faulting occurred during Permo-Triassic times with little or no faulting during the Jurassic. Triassic strata onlap the basement culmination which was overstepped and finally submerged in late Triassic times. The structure has much in common with the basement ‘highs’ at Bruton and in the Mendips and provides further evidence for the existence of such features close to the main lines of Mesozoic faulting within the Wessex Basin. It is considered that differential subsidence related to syn-depositional normal faulting was the dominant factor controlling development of the highs. The simple infilling of a pre-existing post-orogenic topography played a minor role.
Non-marine arthropod traces from the subaerial Ordovician Borrowdale Volcanic Group, English Lake District
Authors: Johnson E. W. , Briggs D. E. G. , Suthren R. J. , Wright J. L. , Tunnicliff S. P.
Published: May 2009

Arthropod trace fossils are described from the Borrowdale Volcanic Group, a sequence otherwise devoid of faunal evidence. Two forms, both made by the same probably myriapod-like organism, are assigned to the ichnogenera Diplichnites and Diplopodichnus. The lithologies preserving the trace fossils are non-marine and may have been deposited in a freshwater lacustrine environment; some of the traces were probably made in temporarily emergent conditions. The change from one form of trace to the other reflects drying out of the substrate. The trace fossils probably record some of the earliest freshwater arthropods, before the widespread colonization of land by the group.
Sedimentology of the Permian Radok Conglomerate in the Beaver Lake area of MacRobertson Land, East Antarctica
Authors: Fielding C. R. , Webb J. A.
Published: May 2009

The mid- to Upper Permian Radok Conglomerate, the lowermost formation of the Permo-Triassic Amery Group, crops out in the Beaver Lake area of the northern Prince Charles Mountains, East Antarctica. Outcrop is confined to a north-south elongate, fault-bounded corridor interpretedas a remnant of a continental extensional basin formed during Late Palaeozoic times. This basinforms a small part of the much larger Lambert Graben, a major continental rift system. The RadokConglomerate consists of interbedded conglomerates, argillaceous sandstones, siltstones, and minor, thin carbonaceous siltstones and coals. Textural, petrographic, palaeocurrent and other data suggestlocal derivation from Precambrian massifs to the immediate west, during a period of fault activity.The unit is a minimum of 400 m thick, the base being unexposed, and grossly fines upward. It isabruptly overlain by quartzo-feldspathic sandstone-dominated rocks of the Upper Permian Bainmedart Coal Measures. Seven recurrent lithofacies have been recognized with the Radok Conglomerate, and are interpreted as the products of poorly-confined stream flow, sheet flow and sediment gravity flow processes, suspension fallout in shallow standing water, and organic sediment accumulation in peat-forming wetlands. The unit as a whole is interpreted as having accumulated as a coarse alluvial apron along the western margin of a ?graben extensional trough. Similar, though poorly exposed, facies are exposed on the eastern margin of the basin and may reflect similar depositional systems. Towards the top of the Radok Conglomerate, typical Radok lithologies are interbedded with quartzo-feldspathic sandstones derived from the south, precursors of the overlying Bainmedart Coal Measures. Interference between transverse (Radok) and axial (Bainmedart) drainage is possibly related to progressive infilling of extensional topography, thereby allowing axially flowing rivers to avulse increasingly into the Beaver Lake region from the main Lambert Graben.
The durations of Silurian graptolite zones
Authors: Hughes Richard A.
Published: May 2009

Recently published radiometric data show the duration of the Silurian Period to be approximately 32 Ma, significantly longer than previous estimates. Radiometric and graphic correlation studies demonstrate considerable variation in the durations of the four Silurian epochs: approximately 13 Ma for the Llandovery, 4 Ma for the Wenlock, 5 Ma for the Ludlow and 10 Ma for the Přídolí. Using this new geochronological data, figures for average graptolite zone duration are presented for each epoch, ranging from as little as 0.44 Ma in the Wenlock, to 1.43 Ma in the Přídolí. The figures provide a refined subdivision of the Silurian timescale, of value to studies which use Silurian graptolite zones to calibrate geological processes.
Lower Devonian calmoniid trilobites from the Argentine Precordillera: new taxa of the Bouleia Group, and remarks on the tempo of calmoniid radiation
Authors: Edgecombe Gregory D. , Vaccari Norberto E. , Waisfeld Beatriz G.
Published: May 2009

New calmoniids from the Lower Devonian Talacasto Formation in the Precordillera of San Juan, Argentina, extend the stratigraphic and geographic ranges of a clade including Bouleia Kozlowski, 1923 and Parabouleia Eldredge, 1972. The new genus Talacastops accommodates the Lochkovian T. zarelae sp.nov. from the Talacasto Formation and a closely related species from western Bolivia (Talacastops sp.nov. A). The diagnosis of Parabouleia is broadened to include P. eldredgei sp.nov., from Lochkovian strata in the lower part of the Talacasto Formation. Calmoniids from below the Scaphiocoelia Assemblage Zone display morphological disparity that rivals later occurrences, and do not conform to a model of gradual transformation of an acastomorph ancestor. Stratigraphic range extensions based on correction for ghost lineages imply a high diversity within Calmoniidae very early in the Devonian.
Structural setting and timing of hydrothermal veins and breccias on Hurd Peninsula, South Shetland Islands: a possible volcanic-related epithermal system in deformed turbidites
Authors: Willan Robert C. R.
Published: May 2009

Quartz veins and vein-breccias in a greywacke-shale sequence of ?Carboniferous-Triassic age were previously regarded as mesothermal silicified fault breccias, and related to an adjacent Eocene granodiorite pluton. New mapping of vein assemblages and textures, and their structural and cross-cutting relationships, demonstrates that the steeply dipping, sheeted, epithermal-textured vein array was hydraulic in origin and possibly Cretaceous in age. The main vein and breccia swarm trends for 14 km NNE along-strike and 2 km across-strike, cutting large irregular areas of silicified and brecciated sandstone, and patchy areas of pyritic, propylitic and K-feldspar alteration. Angular vein fabrics and hydraulic disruption textures indicate wedging by hydrothermal solutions, hydraulic rupture, brecciation and fragment transport, followed by open-space precipitation, in veins generally < 15 cm thick and breccias up to a few metres thick. Hydrothermal quartz, chlorite, calcite and chalcedony predominate, with variable amounts of chalcopyrite, galena, sphalerite and pyrite. Epidote, arsenopyrite, K-feldspar and andradite garnet are conspicuous in places. Breccias were pre-and syn-mineralization, whereas mineral precipitation was pre-, syn- and post-breccia formation. Hydrothermal activity was simultaneous with extensional faulting, striking NNE, and accompanied by intrusion of dacitic dykes. There followed conjugate shearing on east- and ESE-striking faults, intrusion of high-level tonalite stocks, and several phases of basaltic andesite dyke intrusion. These hypabyssal rocks were probably coeval with the Antarctic Peninsula Volcanic Group dominating Livingston Island, dated between 130 and 75 Ma. Minor copper and iron sulphide-bearing veins occur in adjacent volcanic and hypabyssal intrusive rocks. The Hurd Peninsula veins may, therefore, form part of a volcanic-epithermal hydrothermal system (adularia-sericite-quartz type), of Cretaceous age, rather than a porphyry-related system of Eocene age.
Faunal transport within event horizons in the British Upper Silurian
Authors: Underwood Charlie J.
Published: May 2009

Many marine fossil concentrations are considered the result of episodic sedimentological events, and in particular those due to storms. Most storm or tempestite concentrations are identified as autochthonous or parautochthonous assemblages created by a variety of winnowing processes within shallow water environments. In contrast, samples described here from both a ‘shelf’ and a ‘basinal’ setting within the Ludlow (Upper Silurian) succession of the Welsh Basin reveal the presence of a biota transported by tempestite activity into a setting dominated by a more offshore biota. Tempestite horizons from within an ‘outer shelf’ mud dominated setting include shelly lenses with a transported fauna abounding in gastropods, tentaculitids and atrypid brachiopods, the background sediment being rich in graptolites, cephalopods and small strophomenid brachiopods. Within the ‘basinal’ area, distal tempestites range from minor siltstone layers to thicker bioclastic limestone lenses. The siltstones are largely graptolitic (dominated byBohemograptus), with some small brachiopods, whilstSaetograptus colonusis the only common graptolite in the limestones, which also contain a fauna of broken brachiopods and bryozoa. The transport of assemblages distally into a variety of settings represents a potential source of error in palaeoecological analysis. Transported assemblages may, however, provide evidence of the composition of both benthic and pelagic shallower water faunas no longer knownin situ.
Halokinetic initiation of Mesozoic tectonics in the southern North Sea: a regional model
Authors: Allen M. R. , Griffiths P. A. , Craig J. , Fitches W. R. , Whittington R. J.
Published: May 2009

The North Dogger Fault Zone is located at the northern margin of the UK Southern North Sea Basin, at the edge of the mobile Zechstein Supergroup, and was particularly active during late Triassic and early Jurassic times. It resembles geometrically, and is related tectonically to, the Dowsing Fault Zone which was initiated in late Scythian time along the southwestern edge of the mobile salt. It is proposed that both of these basin-bounding fault systems were initiated in response to the buoyant growth of salt swells in the centre of the Southern North Sea Basin. Passive folding of the Triassic strata over the swells, which accommodated the shape changes caused by halokinesis, led to extension on the fault zones at the edge of the mobile Zechstein salt.
The last stages of dinosaur faunal history in Europe: a succession of Maastrichtian dinosaur assemblages from the Corbières (southern France)
Authors: Le Loeuff Jean , Buffetaut Eric , Martin Michel
Published: May 2009

We report the discovery of a dinosaur assemblage in the non-marine Late Maastrichtian of the Corbieres region of southern France; this allows the reconstruction of the succession of dinosaur faunas during the Maastrichtian in western Europe. An Early Maastrichtian fauna dominated by titanosaurid sauropods was replaced by a Late Maastrichtian assemblage dominated by hadrosaurs. This important faunal replacement seems to coincide with environmental changes (documented by sedimentological and palynological evidence) which have been linked to a marine regression during the Maastrichtian. This suggests that sea-level changes influenced the evolution of dinosaur faunas in Europe during the Late Cretaceous, but were not sufficient to cause the final extinction of dinosaurs, for which other causes must be sought.
Magmatic and solid state deformation partitioning in the Ox Mountains granodiorite
Authors: McCaffrey Kenneth J. W.
Published: May 2009

The Ox Mountains granodiorite (western Ireland) is situated along the Fair Head—Clew Bay line, a major Caledonian structure. The pluton was emplaced synchronously with respect to deformation on a major strike-slip shear zone system and experienced a pervasive episode of sinistral shear. Remnants of magmatic state deformation such as phenocryst alignments and tiling fabrics are present. An early phase of strain partitioning produced sinistral offsets on internal contacts. These structures were overprinted by a solid state fabric characterized by crystal plastic deformation in feldspar and the operation of recovery processes during quartz deformation indicating temperatures in the range 450–500 °C. A sinistral shear band fabric is ubiquitous and its formation was enhanced by myrmekite production leading to the formation of fine-grained feldspar and quartz. Late deformation partitioning during further pluton cooling produced a conjugate shear zone system containing mylonites. Deformation within the Ox Mountains granodiorite provides important constraints on the nature of late Caledonian age mid-crustal deformation along the Highland Boundary fault. The pluton also provides exceptional examples of the range of structures that may form in a syntectonic pluton.
Slump-fold and palaeoslope orientations in Upper Silurian rocks, North Wales
Authors: Eva S. J. , Maltman A. J.
Published: May 2009

Silurian mudstones and siltstones in the region south of Colwyn Bay, North Wales, contain numerous ‘disturbed beds’, with folds, fabrics, and other features resulting from pre-lithification deformation at or near to the sea floor. Orientation data are presented for slump folds in four areas of Ludlow rocks where the exposure allows three-dimensional measurement. The data show considerable scatter, perhaps reflecting an irregular slope morphology, and the palaeoslope inferred for each of the areas is slightly differently orientated. In general, however, the palaeoslope directions indicate that the slumps moved not eastwards, along the axis of the Denbigh Trough, as most recently suggested, but down the southern flanks of a gentle, intra-basinal swell.
Batyrbay Section, South Kazakhstan, U.S.S.R. – potential stratotype for the Cambrian–Ordovician Boundary
Authors: Apollonov M. K. , Chugaeva M. N. , Dubinina S. V. , Zhemchuzhnikov V. G.
Published: May 2009

The base of the Cordylodus proavus conodont Zone is the most appropriate horizon for the Cambrian–Ordovician Boundary. At Batyrbay the horizon reflects a significant global eustatic event that is marked by distinctive geochemical changes and by drastic changes in the trilobite and conodont faunas. The palaeomagnetic polarities change from reversal to normal just below this horizon.
Geochemistry and tectonic significance of augen gneisses from the southern Menderes Massif (West Turkey)
Authors: Bozkurt E. , Winchester J. A. , Park R. G.
Published: May 2009

The protoliths of mylonitized augen gneisses exposed in the southern sector of the Menderes Massif (West Turkey) are calc-alkaline, peraluminous, S-type, late- to post-tectonic tourmaline- and garnet-bearing, two-mica leucogranites. They cut and post-date the fabrics of the ‘main Menderes metamorphism’ which took place between the early Eocene and early Oligocene and intrude metamorphic basement rocks comprising the so-called ‘Palaeozoic schist envelope’ of the massif. They are themselves cut by an extensive network of tourmaline-rich dykes. Chemical, mineralogical, isotopic and field relations suggest that the granitic protolith crystallized from a boron-rich, water-saturated melt, derived from partial melting of metagreywacke in the lower crust during peak Barrovian-type metamorphism. The protolith was probably emplaced during lateorogenic extensional collapse of the thickened crust in west Turkey during late Oligocene time.
The formation of travertine shrubs: Mammoth Hot Springs, Wyoming
Authors: Pentecost Allan
Published: May 2009

The structure and microbiology of active travertines is described from Canary and Minerva springs, with emphasis on ‘shrubs’ growing in terracette pools. These dendritic growths of aragonite consist of intricately branched sprays containing thousands of radiating needles. Shrub microstructure could be explained by the principle of ‘Keimauslese” and the preferential elongation of sharp protuberances in a rapidly depositing environment.

The shrubs, and other active travertines, contain unicellular and filamentous bacteria. Estimates of total bacteria numbers ranged from 0.6−1.7 × 105 mm−3 but biomass was low, and always less than 1% of the travertine by weight. No evidence was found to indicate that bacteria played a role in shrub growth or morphology, but crystal trapping on bacterial strings may influence travertine fabrics on cascades. The shrubs are considered to have developed by inorganic processes, in hot spring waters supersaturated with aragonite.
The carbon- and oxygen-isotope record of the Precambrian–Cambrian boundary interval in China and Iran and their correlation
Authors: Brasier Martin D. , Magaritz Mordeckai , Corfield Richard , Huilin Luo , Xiche Wu , Lin Ouyang , Zhiwen Jiang , Hamdi B. , Tinggui He , Fraser A. G.
Published: May 2009

The fossiliferous section at Meishucun of Yunnan, China, is a candidate stratotype section for the Precambrian–Cambrian boundary. Early diagenetic dolomites and phosphorites have been sampled across the boundary interval here, and in the correlated section at Maidiping in Sichuanand Valiabad in Iran, for comparison of their carbon and oxygen isotopes. This is the first such study that is calibrated by biostratigraphy in the interval from the earliest (pre-Tommotian) skeletal fossils to trilobites. Although negative oxygen isotopes indicate a diagenetic signal in the Zhongyicun Member and basal Badaowan Member phosphorites, two carbon-isotope cycles are clearly present and can be correlated in dolomitic rocks between the two sections. The first appearance datum (FAD) of the earliest skeletal assemblage (zone I, Marker A), FAD of diverse micromolluscs (zone II, Marker B) and FAD of Chinese trilobites (zones IV, V) and Marker C appear at similar points on the carbon-isotope curve in the two Chinese sections. Integrated carbon-isotope and early skeletal fossil biostratigraphy is shown to have the potential to correlate further afield, with sections in Iran, as well as with India, Siberia, Morocco and Australia. We suggest that a distinctive positive excursion provides a global marker for the interval between Marker B and C in China and just below the Tommotian Stage of Siberia.
Revised stratigraphy and relationships of Lower Palaeozoic rocks, eastern Taurus Mountains, south central Turkey
Authors: Dean W. T. , Monod O.
Published: May 2009

Lithostratigraphic terminology is revised for rocks of Ordovician age in the eastern Taurus. The Seydişehir Formation, of late middle Cambrian to early Ordovician age, is shown to be applicable in the eastern and western Taurus as well as in south-eastern Turkey. Near Degˇirmentaş, northeast of Adana, the Seydişehir Formation is overlain, with inferred unconformity, by clastic strata of Ashgill age referred to the Şort Tepe Formation, first defined south of Hakkâri, in the Border Folds of southeastern Turkey. Palaeontological evidence is cited for the early Silurian (Llandovery) age of the unconformably overlying Halityayla Formation farther south, on the coast near Ovacik, where the Şort Tepe Formation is as yet unrecorded. A general model is proposed showing relationships of Cambrian and Ordovician rocks and faunas in southern and southeastern Turkey.
Timing of post–Karoo alkaline volcanism in southern Namibia
Authors: Reid D. L. , Cooper A. F. , Rex D. C. , Harmer R. E.
Published: May 2009

New radiometric age data are reported for alkaline centres in southern Namibia, and are discussed together with published age data in terms of models put forward to account for post-Karoo (Mesozoic–Recent) alkaline magmatism within the African plate. Agreement between K–Ar and Rb–Sr ages indicate emplacement of the Dicker Willem carbonatite in southern Namibia at 49 ± 1 Ma. Alkaline rocks associated with the Gross Brukkaros volcano show a discordant radiometric age pattern, but the best estimate for the age of this complex is 77 ± 2 Ma, similar to that obtained for the neighbouring Gibeon carbonatite-kimberlite province. The Dicker Willem carbonatite is therefore younger than the Luderitz alkaline province (133 ± 2 Ma), and the Gross Brukkaros volcano, but is older than the Klinghardt phonolite field (29–37 Ma). The new age data argue against a distinct periodicity in alkaline igneous activity in southern Africa, thereby ruling out possible controls by episodic marginal upwarping of the subcontinent. Although the available age data do not appear to be consistent with the passage of one or even two hotspots under southern Namibia, it is argued that the surface expression of hotspots under continents may be so large and overlapping that within-plate magmatism attributed to these thermal anomalies need not necessarily be confined to narrow linear belts or show an age progression. The role of hotspots in continental alkaline magmatism is most likely one of melt generation, while local crustal structure probably controls the distribution and timing of eruption. Major tectonic boundaries in the Precambrian basement underlying southern Namibia seem to have controlled the development of Tertiary alkaline centres in that region.
Petrology of ultramafic xenoliths from Madeira island
Authors: Munha J. , Palacios T. , Macrae N. D. , Mata J.
Published: May 2009

Ultramafic xenoliths from Madeira island are divided into dunite/websterite/wehrlite/clinopyroxenite (DWWC) and harzburgite/lherzolite suites; the harzburgite/lherzolite xenoliths show abundant deformational features and are more refractory (Fo = 90–91) than the DWWC suite (Fo = 77–88).

DWWC xenoliths are spinel-bearing olivine ± orthophyroxene cumulates with intercumulus clinopyroxene and rare plagioclase, amphibole and phlogopite. Mineral chemistry and geothermobarometric data indicate that DWWC xenoliths crystallized at 1150–1300 °C from Madeiran alkalic basalts and accumulated in magma reservoir(s) located 36–45 km beneath the island.

The harzburgite/lherzolite xenoliths are composed of olivine + orthopyroxene + spinel ± clinopyroxene ± (rare) phlogopite and display alkali feldspar or clinopyroxenite veins and crystal aggregates. The complex thermal evolution recorded by these xenoliths and the close similarity of clinopyroxene REE contents and calculated fO2 values in both harzburgites and DWWC cumulates are attributed to recent infiltration of the harzburgites by melts trapped or crystallized within the mantle; these features, and the refractory bulk chemistry of the harzburgite/lherzolite suite, support the interpretation that these xenoliths represent depleted oceanic lithosphere variously modified by magmatism associated with the genesis of Madeira island. The association of these upper mantle xenoliths with cumulates crystallized from Madeiran magmas (DWWC) suggests that the harzburgite/lherzolite suite originated in the uppermost mantle above magma storage zone(s), probably near the boundary between the mantle and the overlying oceanic crust.
Stratigraphic and tectonic implications of Triassic conodonts from northwest Peninsular Malaysia
Authors: Metcalfe I.
Published: May 2009

The Chuping Limestone of northwest Peninsular Malaysia, until recently considered entirely of Permian age, has yielded late Triassic (early Norian) conodonts. TheLimestone thus spans the time interval late Early Permian–Late Triassic and is in part equivalent to the Kodiang Limestone (Late Permian–Late Triassic) in Kedah andsimilar limestone sequences in south Thailand and north Sumatra. Early Late Triassic (Carnian) conodonts are also reported from pelagic limestones associated with bedded chertsof the Chert Member of the Semanggol Formation in Kedah. The Chert Member, previously considered of Middle Triassic age, is re-interpreted to represent Early, Middle and early Late Triassic deposition. The Triassic sedimentary rocks of the Malay Peninsula represent three distinct sedimentary regions: a stable shallow marine carbonate complex (ChupingLimestone, Kodiang Limestone), which forms part of an elongate carbonate platform on theSibumasu block; a deep water pelagic/turbidite basinal sequence (Semanggol Formation) which accumulated in either a foredeep basin or an intracratonic pull-apart basin related to strike-slip faulting; and a volcanic-sourced volcaniclastic basinal sequence on the East Malaya block (Semantan Formation and equivalents) which accumulated in either a forearc/intra-arc setting, or in a post-orogenic rift basin.
Hamrat Duru Group: revised stratigraphy of a Mesozoic deep-water passive margin in the Oman Mountains
Authors: Cooper D. J. W.
Published: May 2009

The stratigraphy of the Hawasina Complex is redefined and rationalized to conform with standard stratigraphical nomenclature. Previously proposed tectono-stratigraphical units are abandoned in favour of a system that relies on the lateral correlation of lithofacies between structural units. To this end, the Dibba, Dhera, Wahrah and Al Ayn Formations are incorporated into an expanded Hamrat Duru Group. This group is divided into five formations, the Zulla, Guweyza Sandstone, Guweyza Limestone, Sid'r and Nayid and spans Triassic to Mid Cretaceous (Cenomanian) time. It locally passes up into the syn-orogenic sediments of the Riyamah Member of the Muti Formation. The nomenclature of the deeper-water, chert-dominated formations is left unaltered.
More Arran geology
Authors: Harland W. B.
Published: May 2009

The Geologists& Association has done a valuable service for British geology and for English-speaking geologists outside the British Isles by organizing field excursions and, for or from them, publishing guides. The first GA contribution was a report of a field meeting led by Gregory & Tyrrell (1924). In the 1960s there was a GA series of at least 41 guides covering most field areas in Britain and of these the one by S. I. Tomkeieff (1961) treated Arran. Tomkeieff's guide was brief and was not up to the standard expected of a work concerning this much frequented island. That work may be out of print and this guide appears to be a replacement. McKerrow & Atkins is good value and gives much to think about. Without hesitation, then, the reviewer's advice is that anyone going to Arran should buy it.
Archaean strike-slip faulting and related ensialic basins: evidence from the Pilbara Block, Australia
Authors: Krapez B. , Barley M. E.
Published: May 2009

Archaean sedimentary and volcanic successions in the Lalla Rookh Basin andc. 2950 Ma old Whim Creek Belt in the Pilbara Block, Western Australia, were deposited in basins with roughly the same configuration as their present outcrop. Basins were fault-bounded and developed in an ensialic setting, overlying older (3500 to 3300 Ma old); deformed and metamorphosed supracrustal rocks and granitoids. The basin margin faults are now part of a pattern of strike–slip faults which were active during the later stages of regional batholith emplacement. In both cases, structural patterns and style of basin filling are similar to younger basins related to strike–slip faulting. The Lalla Rookh Basin was dominated by coarse clastic sedimentation, comprising alluvial–fan, braided–stream, fan–delta and lacustrine facies. The Whim Creek Belt contains bimodal volcanics and clastic sediments, which comprise alluvial, subaqueous fanglomerate, submarine-fan and basinal facies. Regional strike–slip faulting and the development of the Lalla Rookh Basin and Whim Creek Belt, in response to externally imposed deformation, records an important step in the cratonization of the Pilbara Block. Late Archaean sedimentary basins, dominated by coarse clastic facies and situated adjacent to major strike–slip faults, in other cratons may have a similar origin.
Extrusive carbonatites: their origins reappraised in the light of new experimental data
Authors: Gittins John , Jago Bruce C.
Published: May 2009

Calcite-rich carbonatites are commonly attributed to calcitization of alkalic carbonatite of Oldoinyo Lengai type. The interpretation arises from the presumption that magmatic crystallization of calcite at atmospheric pressure is not possible. We show that only a small percentage of fluorine, a common element in carbonatite magmas, permits such crystallization, and we argue that most of the calcite in extrusive carbonatites is magmatic. The presence of any more than minor apatite precludes an alkalic carbonatite parentage. While not denying that calcification of alkalic carbonatite can occur, we suggest that it is not generally responsible for the formation of extrusive calcific carbonatites.
Isotopic evidence for the extent of early Proterozoic basement in Scotland and northwest Ireland
Authors: Dickin A. P. , Bowes D. R.
Published: May 2009

Tightly clustered Sm–Nd model ages, with an average of 1.96±0.02Ga, for the gneiss complex of Inishtrahull indicate coeval development with the earlyProterozoic gneiss terrane of Islay. The extent of this terrane, largely beneath the Dalradian Supergroup, is argued to be 100×600 km, from northeast Scotland to western Ireland. This is based on the distribution of dated basement in conjunction with Pb, Sr and Nd isotope systematics and inherited zircons in Caledonian granites of the region.
A Cambrian island arc in Iapetus: geochronology and geochemistry of the Lake Ambrose volcanic belt, Newfoundland Appalachians
Authors: Dunning G. R. , Swinden H. S. , Kean B. F. , Evans D. T. W. , Jenner G. A.
Published: May 2009

The Lake Ambrose volcanic belt (LAVB) outcrops as a 45 km long northeast-trending belt of mafic and felsic volcanic rocks along the eastern side of the Victoria Lake Group in south-central Newfoundland. It comprises roughly equal proportions of mafic pillow basalt and high silica rhyolite, locally interbedded with epiclastic turbidites. Volcanic rocks have been metamorphosed in the greenschist facies and are extensively carbonatized.

U-Pb (zircon) dates from rhyolite at two, widely separated localities give identical ages of 513 ± 2 Ma (Upper Cambrian), and this is interpreted as the eruptive age of the volcanic sequence. Primitive arc and low-K tholeiites can be recognized on the basis of major and trace element geochemistry, ranging from LREE-depleted to LREE-enriched. Geochemical variation between mafic volcanic types is interpreted predominantly to reflect contrasts in source characteristics and degree of partial melting; some variation within each geochemical type attributable to fractional crystallization can be recognized. Detailed examination of some samples indicates that the heavy REE and related elements have locally been mobile, probably as a result of carbonate complexing.

The LAVB is the oldest well-dated island arc sequence in Newfoundland, and perhaps in the Appalachian–Caledonian Orogen. Its age requires modification of widely held models for the tectonic history of central Newfoundland. It is older than the oldest known ophiolite, demonstrating that arc volcanism was extant before the generation of the oldest known oceanic crust in this part of Iapetus. It further demonstrates that there was a maximum of approximately 30 Ma between the rift-drift transition which initiated Iapetus, and the initiation of subduction. This suggests that the oceanic sequences preserved in Newfoundland represent a series of arcs and back arc basins marginal to the main Iapetus Ocean, and brings into question whether the Appalachian accreted terranes contain any remnants of normal mid-ocean ridge type Iapetan crust.
New early Triassic Bryozoa (Trepostomata) from Spitsbergen, with some remarks on the stratigraphy of the investigated horizons
Authors: Nakrem Hans Arne , Mørk Atle
Published: May 2009

New trepostomatous bryozoan species, Paralioclema winsnesi sp. nov., Paralioclema mariaholmensis sp. nov. and Paralioclema sp. cf. mariaholmensis are described from the Lower Triassic succession of Spitsbergen. The investigated bryozoan faunas are associated with coarse sandstones, calcareous siltstones and shelly limestones. The bryozoan colonies are mostly well preserved in situ, and show limited evidence of transportation. Some zoarial fragments show bioerosion. The conodont species Neogondolella elongata, Ellisonia triassica, Neospathodus dieneri and Neospathodus svalbardensis extracted from the investigated horizons are Dienerian–Smithian in age.
A U/Pb age for the Sulitjelma Gabbro, North Norway: further evidence for the development of a Caledonian marginal basin in Ashgill–Llandovery time
Authors: Pedersen Rolf-Birger , Furnes Harald , Dunning Greg
Published: May 2009

The Sulitjelma Gabbro in the central Norwegian Caledonides has been dated with the U/Pb zircon/sphene method to 437±2 Ma. Geological relationships as well as trace-element geochemistry and Nd and Sr isotopic compositions suggest that the gabbro and associated dyke swarms and pillow lava formed during the initial stages of back-arc spreading. The age constrains the timing of juxtaposition of an older island-arc terrane and continental-margin lithologies exposed within the Caledonian nappes. The age of the gabbro is similar to that of the Solund–Stavfjord Ophiolite in west Norway, and confirms that spreading-related magmatism and marginal-basin development took place along the margin of Iapetus in late Ordovician–early Silurian times.
Upper Cretaceous (upper Santonian)Boehmocerasfauna from the Gulf Coast region of the United States
Authors: Kennedy W. J. , Cobban W. A.
Published: May 2009

An upper Santonian fauna dominated by the curved baculitidBoehmocerasRiedel, 1931, occurs as phosphatic moulds in the Tombigbee Sand Member of the Eutaw Formation in Mississippi and Alabama, and also is reworked into the base of the Mooreville Chalk; a similar assemblage is present in the middle part of the Pen Formation of the Big Bend area, Texas. The assemblage is:Pseudoschloenbachia(Pseudoschloenbachia)mexicana(Renz, 1936),Placenticeras syrtale(Morton, 1834),Reginaites leei(Reeside, 1927a),Reginaites exilissp. nov.,Texanites(Texanites) sp. juv. cf.gallicusCollignon, 1948,Texanites(Plesiotexanites)shiloensisYoung, 1963, Texanitinaeincertae sedis, Hyphantoceras(?)amapondense(van Hoepen, 1921).Glyptoxocerasspp.,Boehmoceras arculus(Morton, 1834) andScaphites(Scaphites)leeiReeside, 1927a, form I. The assemblage is referred to the uppermost SantonianTexanites(Plesiotexanites)shiloensiszone of the Gulf Coast sequence. Common occurrence ofScaphites(S.)leeiI andReginaites leeisuggest correlation with the Upper SantonianDesmoscaphites erdmannizone of the U.S. Western Interior; common occurrence ofBoehmoceras arculus(= B.loescheriof European authors) suggests correlation with theMarsupites–granulatazone at the top of the North German Santonian. These data strengthen intercontinental correlation of the Santonian–Campanian boundary sequence. They also provide a biostratigraphic link to a numerical age of 84.2±0.9 Ma from a bentonite at a slightly lower level in the Tombigbee Sand Member of the Eutaw Formation in Mississippi.
Mafic dykes from Øksfjord, Seiland Igneous Province, northern Norway: geochemistry and palaeotectonic significance
Authors: Reginiussen H. , Ravna E. J. Krogh , Berglund K.
Published: May 2009

Mafic dykes from the Øksfjord-Langfjord area were intruded at different stages during the prolonged tectonomagmatic evolution of the Seiland Igneous Province. Field relations, petrography and geochemistry indicate the presence of four dyke generations with alkali basalt composition and one generation of alkaline lamprophyres. The entire dyke suite has geochemical signatures consistent with formation in a within-plate geotectonic environment. Trace elements indicate that the alkali basalt dykes have OIB (ocean island basalt) affinities and we suggest a sublithospheric mantle source. The data support a rift-related origin for the Seiland Igneous Province. Longevity of magmatism in the Seiland Igneous Province (300 m.y.) is difficult to explain within a conventional mantle plume framework. Instead, it is proposed that the intermittent magmatism in the province was predominantly permissive and controlled by lithosphere structure.
Geophysical constraints on the nature of the Highland Boundary Fault Zone in western Scotland
Authors: Dentith M. C. , Trench A. , Bluck B. J.
Published: May 2009

Previously published models of gravity anomalies across the Highland Boundary Fault in western Scotland interpret this structure as a high-angle reverse fault. These gravity anomalies have been re-interpreted in the light of more extensive gravity data now available, and new density data from the Highland Border Complex. The new data suggest that earlier interpretations have overestimated the fault anomaly and used over-simplified density models. New gravity models of the Highland Boundary Fault Zone are presented which show that the interface between the Dalradian and Highland Border Complex dips to the northwest at an angle of about 20°. We interpret the contact between these two formations as a thrust fault. The interface between the Highland Border Complex and the Lower Old Red Sandstone is shown to be vertical as suggested by surface geology, with the latter rocks a few hundred metres thick.
The ichnogenusSchaubcylindrichnus: morphological, temporal, and environmental significance
Authors: Frey Robert W. , George Pemberton S.
Published: May 2009

Schaubcylindrichnus, a distinctive sheaf of arcuate, well lined, congruent dwelling tubes, although poorly known in general, is a good indicator of shoreface depositional settings for many Cretaceous rocks of the United States. Until recently, in fact, it was known only from those rocks; but it has now been recognized in Tertiary rocks of Taiwan, possibly in slightly more distal depositional settings. In addition to its distinctive morphological and environmental significance, the ichnogenus also may have substantial biostratigraphical significance. Further reconnaissance is needed to confirm these seemingly unique distributions, that is, to help explain why the trace fossil so far seems to be restricted to certain Cretaceous rocks in North America and certain Tertiary rocks in Asia.
The Lower Pleistocene stratigraphy of the Ormesby Borehole, Norfolk, England
Authors: Harland R. , Bonny Anne P. , Hughes M. J. , Morigi A. N.
Published: May 2009

The sedimentology, micropalaepntology and palynology of Lower Pleistocene sediments recovered from a borehole at Ormesby St Margaret, near Great Yarmouth, Norfolk, have been investigated. The sediments, consisting of a lower clay facies overlain by an upper predominantly sandy facies, were deposited in inner neritic environments. Micropalaeontological and palynologicalevidence allows comparisons with the nearby Ludham sequence but an unequivocal correlation cannot be made. The Ormesby Borehole sequence includes representatives of the Pre-Ludhamian to Early Pastonian stage interval and the presence of a late Pre-Ludhamian to late Baventian/Pre-Pastonian a hiatus. Foraminiferal faunas matched to grain size analysis are indicative of transportation and considerable post-mortem sorting.