bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geology, geochronology and chemical evolution of the island of Pantelleria
Authors: Civetta L. , Cornette Y. , Crisci G. , Gillot P. Y. , Orsi G. , Requejo C. S. 
Published: May 2009

AbstractPotassium–argon dating, field relations, geochemical and strontium-isotope compositions are reported for the island of Pantelleria (Strait of Sicily, Italy). These data support the following model for the genesis and evolution through time of the volcanic system: the peralkaline rocks originated from mantle-derived parental magmas; the trachytic magma differentiated in a low pressure magma chamber by crystal–liquid fractionation. This process led to a chemically zoned magma chamber tapped at different levels by successive eruptions. During low-pressure differentiation the 87Sr/86Sr ratios of some of the most evolved Sr-poor rhyolitic magmas increased from 0.703 up to 0.708 by contamination with crustal material.The chemical variation displayed by the products of each of the defined eruptive cycles in the last 50000 years suggests an open system behaviour of the magma chamber which is episodically refilled by more mafic parent magma, differentiated at high rate and episodically erupted.
Zoning in highly alkaline magma bodies
Authors: Wolff John A. , Storey Michael 
Published: May 2009

AbstractWe present chemical data on magmatically heterogeneous pyroclastic deposits of late Quaternary age erupted from zoned magma systems underlying Tenerife (Canary Islands), Sao Miguel and Faial (Azores), and Vesuvius. The most fractionated magmas present at each centre are respectively Na-rich phonolite, trachyte, and K-rich phonolite. Within any one deposit, chemical variation is either accompanied by changes in the phenocryst assemblage (petrographic zonation) or is largely manifested in trace element abundances, unaccompanied by any petrographic change (occult zonation). Zoning is analogous to that in calc-alkaline systems where the most fractionated products are high-silica rhyolites. When a range of magma types are considered, a correlation emerges between roofward depletion of trace elements (especially REE) in the zoned system and compatability of those same trace elements in the accessory phenocryst phases present. Thus, allanite- or chevkinite-bearing rhyolitic systems are light-REE depleted roofwards, the sphene-bearing Tenerife system is middle-REE depleted roofwards, the melanite-bearing Vesuvius system is heavy-REE depleted roofwards, while the Azores systems, which lack these phases, display roofward REE enrichment. Therefore, the behaviour of trace elements may in each case be explained by fractionation of observed phenocryst assemblages. The resemblance between features of zoned magma systems and published work on the dynamic consequences of cooling saturated aqueous solutions prompts us to suggest that sidewall crystallization and consequent boundary-layer uprise to form a capping layer at top of the system may be a plausible mechanism for the generation of both petrographic and occult zonation. Reverse zoning occurs among the first-erupted tephra of some deposits, demonstrating that the most highly differentiated magma available is not always the first to be tapped during an eruption from a zoned system.
Ediacaran events: boundary relationships and correlation of key sections, especially in ‘Armorica’
Authors: Jenkins R. J. F. 
Published: May 2009

AbstractThe transitional interval between the Adelaidean and Ediacaran systems in the central Flinders Ranges, South Australia, comprises mainly basinal sediments, with some tuff beds (Bunyeroo Formation) and a widespread thin dolomite bed which apparently evidences a brief regressive episode (base of Wonoka Formation). Body imprints of metazoans, trace fossils and probable faecal pellets are present at various levels in the Ediacaran succession. Comparable assemblages occurring in key successions in southern Africa, northern Russia, Siberia, Newfoundland and England promise a global biostratigraphy. One Ediacaran body fossil occurs in the Yangtze Gorges section, China. Analysis of abundant late Precambrian radiometric data for the present North Atlantic margins suggests that the Ediacaran may be dated between about 590 Ma and ~ 545–540 Ma.
A note on the Birchi Beds, Lower Jurassic, at Lyme Regis, Dorset
Authors: Palmer C. P. 
Published: May 2009

AbstractThe chronic repetition of a small graphical error, initiated by H. B. Woodward and depicting the Birchi Beds (Lower Jurassic) dipping beneath Lyme Regis, needs rectifying since, by implication, it leads to a gross stratigraphical and structural error amounting to about 21 m (70 ft) at Lyme Regis, Dorset.
Graptolite ultrastructure: evolution of descriptive and conceptual terminology
Authors: Rickards R. B. , Dumican L. W. 
Published: May 2009

AbstractGraptolite ultrastructural studies using SEM and TEM are now more than a quarter of a century old and have reached the stage of routine procedure where material of suitable preservation is to hand. (Specimens may be chemically isolated from the rock or, in SEM and STEM studies, may be retained in the matrix.) Description of ultrastructural elements has evolved from the purely empirical to a conceptual/biological classification following (a) the recognition of the role of collagen fibrils in skeletal construction, and (b) the realization that at least two models of skeletal secretion are possible, each essentially opposed to the other. In this paper old terminology is explained with reference to current practice and the latter is tabulated and referred to the increasing number of described ultrastructural elements. Some of the outstanding problems of interpretation are outlined; and a set of concise, in some cases revised, ultrastructural definitions is given together with illustration, where appropriate, of the ultrastructural element defined.
Geochemical evolution of the Jarawa Younger Granite complex and its related mineralization, northern Nigeria
Authors: Imeokparia E. G. 
Published: May 2009

AbstractThe Jarawa Younger Granite complex is composed of high silica alkali granites that were emplaced 161 Ma ago. The granites are characterized by high contents of Rb, Li, F, Sn, Nb, W above normal low-Ca granitic rocks and have typical S-type characteristics that are indicative of a substantial component of crustal melt.Mineralization in the complex is associated with the biotite granite which was emplaced as a sheet-like body at relatively shallow depth and occurs as disseminations and as greisen lodes and veins.Chemical studies of the granites have shown that the biotite granite represents a highly fractionated rock that crystallized from a residual magma from which the hornblende-biotite granite had previously crystallized. However the biotite granite is characterized by steep gradients in some minor and trace elements that apparently indicate that liquid-state differentiation and/or volatile complexing processes made significant contributions to their differentiation. Enrichment of Th, Li, Rb, Sn, W and Nb may be more closely linked to roofward migration of F.
Fossil Mediterranean molluscs as sea-level indicators
Authors: Richards G. W. 
Published: May 2009

AbstractIntertidal molluscs are known to occur in similar positions or zones on shores throughout the world. However, little is known about the extent to which these distributions are preserved in the fossil record. This study attempts to define the relationship to present sea level of live and dead intertidal molluscs in the Mediterranean, and utilizes this information to interpret the position at which Quaternary shorelines were formed.The preservation of zonation patterns in the fossil record is affected by post-mortem transport, breakage and burial of the shell material. To take account of such taphonomic changes, experimental studies of shell transport and burial under waves and unidirectional currents were made, and the distribution of dead molluscs on modern shores were compared with live distributions. It proved possible to predict the frequency with which certain species were deposited on the modern shore and, by analogy, the likelihood of their preservation in the fossil record. Thus death assemblages in fossil shorelines can be accurately related to past sea levels.
Reconnaissance potassium–argon geochronology of the Suregei–Asille district, northern Kenya
Authors: Fitch F. J. , Hooker P. J. , Miller J. A. , Mitchell J. G. , Watkins R. T. 
Published: May 2009

AbstractPotassium–argon dating of 44 samples of basalt lavas and pantelleritic ignimbrites provides a provisional chronology for the 1900-metre thick Cenozoic succession of the Suregei–Asille district, northeast of Lake Turkana. Volcanic rocks of the Asille Group range in age from late Oligocene (Chattian) to late Miocene (Tortonian). Data obtained from conventional K–Ar total-rock analysis of basalt samples are appraised statistically to indicate the presence of three periods of enhanced volcanism centred around 27, 17 and 11.5 Ma. Equivalent ages obtained from the pyroclastic pantellerites by conventional K–Ar total-rock analysis and 40Ar/39Ar analysis of sanidine concentrates indicate that basic and acid eruptions were closely spaced in time. Continental tholeiite flood lavas belonging to the Gombe Group are of Pliocene age, but are difficult to date precisely because of their young ages and relatively high atmospheric contamination occurring as a result of the secondary alteration in the ubiquitous glass mesostasis. Those ages involving least atmospheric correction are considered most reliable, and are closely similar for the Chen Alia and Harr formations at around 4.85 Ma, although later flood eruptions may have occurred to the south and west of the Suregei–Asille district at about 3.85 Ma.
Panjal Trap chemistry and the birth of Tethys
Authors: Bhat M. I. , Zainuddin Syed M. , Rais A. 
Published: May 2009

SummaryK2O, TiO2, P205, Zr, Y, Sr and Nb data from the Panjal Traps of Kashmir indicate that the lava erupted in a rift tectonic setting. This is also suggested by the other features of these rocks and volcanic history of the area. The time of eruption represents the initial phase of break-up of the Indian plate from the Siberian plate. This conclusion is in good agreement with the current views on the tectonic evolution of the area.
Rare earth abundances and origin of some Indian lamprophyres
Authors: Paul D. K. , Potts P. J. 
Published: May 2009

SummaryAbundances of rare-earth elements (REE) and Th, Ta, Hf, Sc, Co, Ba determined by instrumental neutron activation analysis show similarity between lamprophyres and other potassic rocks including kimberlite. The Indian lamprophyres have fractionated REE patterns with enrichment of light REE. The light REEs show more variation than the heavy REEs within the group.Lamprophyres occurring in intimate association with the alkaline basalt may be genetically related. The trace element characteristics of the abundant lamprophyre dykes in granitic terrain are unlikely to be generated by assimilation of alkaline basalt by granitic crust. Small amounts of partial melting in mantle pockets enriched in incompatible elements as a result of metasomatic processes would explain the elemental concentration observed in the lamprophyres.
The geology of central Isla Hoste, southern Chile: sedimentation, magmatism and tectonics in part of a Mesozoic back-arc basin
Authors: Andrews-Speed C. P. 
Published: May 2009

SummaryCentral Isla Hoste lies towards the Pacific side of a Mesozoic back-arc basin in southern Chile, behind a magmatic arc represented by the Patagonian batholith. The volcaniclastic sediments on Isla Hoste were derived from the magmatic arc and deposited in the back-arc basin by turbidity currents. These sediments may, in part, overlie mafic volcanic and intrusive rocks. Geochemical and lithologic data are used to suggest an ocean-floor origin for these mafic igneous rocks on central Isla Hoste. The sedimentary and mafic igneous rocks were deformed and uplifted during the middle Cretaceous Andean orogeny. However, the nature of the crust underlying most of the sedimentary rocks in the back-arc basin and the style of deformation in most of this basement are unknown. Therefore the role, if any, of subduction within the back-arc basin during the middle Cretaceous ‘closure’ of this basin is not certain. Post-kinematic intrusions within the back-arc basin are common. These intrusions will confuse attempts to determine by geophysical means the nature of the pre-kinematic basement of the back-arc basin and attempts to outline the present extent of the basin in offshore regions.
The primary crescumulates of the Lizard peridotite, Cornwall
Authors: Rothstein A. T. V. 
Published: May 2009

SummaryPreserved in the deformed peridotites of the Lizard, Cornwall, are relics of intricate primary precipitates of olivine. The mineral compositions of those rocks with an abundance of primary relics are typical of the primary assemblage Lizard peridotite. In detail the olivine primary structures resemble, but are not identical to, the crescumulates described from various layered ultrabasic intrusions. The available evidence shows distinctive specific features in the Lizard crescumulates in the scale and morphology of the structures and in the conditions of growth.
Evidence for glaciation in the Ordovician rocks of western Ireland
Authors: Williams D. M. 
Published: May 2009

SummaryThe Maumtrasna Formation is a thick succession of coarse clastic rocks situated in the South Mayo Trough of western Ireland. Its upperage limit is not defined but it is post-Llanvirn in age and probably Ordovician. Several aspects of the conglomerates within the succession are compatible with the action of a glacial influence during its deposition. New evidence is presented which tends to confirm the glacial hypothesis. 10.7% of garnets separated from the matrix of the conglomerates exhibit chattermark trails. Published accounts of such trails indicate that they are only found in sediments which are glaciogenic or were derived from pre-existing glaciogenic sediments. It is suggested that the Ordovician glacial activity in the South Mayo Trough took the form of a highland glaciation which was maintained, possibly at sub-equatorial latitudes, by a continuous uplift of the source area.
Vendian rocks of the western part of the East European Platform: stratotypic range, boundaries and principles of their establishment
Authors: Makhnach A. S. , Veretennikov N. V. , Shkuratov V. I. 
Published: May 2009

AbstractThe Vendian in a stratotype area in the western part of the East European Platform includes three regional stratigraphic subdivisions: the Vilchanian, Volynian and Valdaian series, which clearly differ in structure and lithology. They are closely interconnected stratigraphically and geochronologically, and form an indivisible Late Baikalian structural stage of the platform sedimentary cover. The upper subdivision, the Valdaian Series, is palaeontologically substantiated and divided into horizons. The Vendian in such a composition has definite boundaries: the upper biostratigraphic, and lower lithostratigraphic ones, and is well correlated with the formations of the same age from other regions.
Sedimentation of the Vendian–Cambrian marine sequence, Poland
Authors: Lendzion K. 
Published: May 2009

AnbstractIn the Lublin area of the East European Platform (southeast Poland) sedimentation of the Vendian–Cambrian marine sequence began in Late Vendian times. Vendian and Cambrian strata occur in sedimentary continuity and their features indicate sedimentation in the tidal zone of a shallow epicontinental sea. The Vendian–Cambrian boundary, drawn on the basis of mainly palaeontological data, passes between theVendotaeniaandSabellidites zones.
Upper Precambrian–Lower Cambrian biota from the northwest of Argentina
Authors: Aceñolaza Florencio Gilberto , Durand Felipe Ramón 
Published: May 2009

AbstractThe principal characters of the biota from Upper Precambrian–Lower Cambrian rocks in the northwest of Argentina are described. It is possible to observe two groups: the trace fossils and the medusoid impressions. At the same time, a regional palaeogeographical analysis is attempted as well as a comparison with outcrops of similar age from the Gondwanaland area and from North America.
Evolution of archaeocyaths and palaeobiogeography of the Early Cambrian
Authors: Zhuravlev Andrey Yu. 
Published: May 2009

AbstractIn the Early Cambrian, there were two peaks of the increase in number of new archaeocyathan genera. These diversification bursts are, perhaps, related to significant changes in Early Cambrian palaeogeography. The first burst at the beginning of the Atdabanian was, perhaps, connected with the initiation of archaeocyathan expansion beyond the Siberian Platform. During the second half of the Atdabanian, closely related archaeocyathan assemblages were established from North Africa to Australia because neither climate, nor geographic isolation could have affected their differentiation in that time. At the end of the Atdabanian and the beginning of the Botomian the number of archaeocyathan genera again increased sharply, and isolated provinces were established. The American–Koryakiyan province was formed in western North America (from Alaska to Sonora) and included the Koryakiya, while the Afro–Siberian–Antarctic province probably extended from North Africa and Western Europe to Siberia, Australia, and Antarctica. The main difference between the regular archaeocyathan assemblages lies in what skeletal elements filled the intervallum. There was a certain stability in the distribution of skeletal elements of high taxonomic rank and an interchangeability of elements of low taxonomic rank.
The stage scale of the Cambrian System
Authors: Spizharski T. N. , Zhuravleva I. T. , Repina L. N. , Rozanov A. Yu. , Tchernysheva N. Ye. , Ergaliev G. H. 
Published: May 2009

AbstractA stage subdivision of the Cambrian System is proposed. In the lower series four stages are distinguished (the Tommotian, Atdabanian, Botomian, Tojohnian); in the middle series, two (the Amga and Maya stages); in the upper series, three (the Ayusakkanian, Sakian, and Aksayan stages). The stratotypes of the stages of the lower and middle series are located on the Siberian Platform, while the stratotypes of the stages of the upper series are found in Kazakhstan (the Maly Karatau). The lower boundary of the Cambrian is drawn along the bottom of the Al. sunnaginicus Zone, the lower boundary of the middle series along the Schistocephalus Zone, and that of the upper series along the Cormagnostus simplex Zone. The Cambrian–Ordovician boundary is not quite clear yet, but it is most likely to be drawn along the bottom of the C. proavus Zone.
Prospectatrix genatenta(Stubblefield) and the trilobite superfamily Cyclopygacea
Authors: Fortey R. A. 
Published: May 2009

SummaryCyclopyge genatentaStubblefield, 1927, is interpreted from new material, and established as the type species of a new cyclopygid genus,Prospectatrix. The morphology ofProspectatrixshows that the cyclopygids and nileids are closely related, and together with the Taihungshaniidae, these families are included in an expanded concept of the Cyclopygacea. The subfamily Ellipsotaphrinae Kobayashi and Hamada, 1971 is excluded from the Cyclopygidae. Pelagic habits arose on at least five separate evolutionary lines among Ordovician trilobites:Prospectatrixlies near the origin of one of these.CremastoglottosWhittard was derived from a robergioid ancestor by forward migration of the eyes.
The Ordovician trilobite fauna of the Great Paxton Borehole, Cambridgeshire
Authors: Rushton A. W. A. , Hughes C. P. 
Published: May 2009

SummaryThe Ordovician trilobite fauna of the Great Paxton Borehole, Cambridgeshire, consists of twelve species including the seven new species;Segmentagnostus stubblefieldi, Trinucleus bicallis, Bergamia artemis, Protolloydolithus salax, Ogygiocaris macrops, Merlinia anxiaandBohemilla tridens. The fauna recalls that from the lower Llanvirn of the Shelve area, Shropshire, but the possibility of an upper Llanvirn age remains.
The Ordovician brachiopods of Cornwall
Authors: Bassett Michael G. 
Published: May 2009

SummaryThe brachiopod fauna of the Gorran Quartzites of south Cornwall is described; it comprises five orthid genera. Three taxa are described under open nomenclature, and one new species is assigned to a new genus (Schalidomorthis stubblefieldi). The fauna supports the Llandeilo age suggested by accompanying trilobites. There is no brachiopod evidence to indicate that the quartzite pebbles of the Triassic Budleigh Salterton Pebble Bed are derived directly from the Ordovician of Cornwall.
Crustal growth of the Antarctic Peninsula by accretion, magmatism and extension
Authors: Storey B. C. , Garrett S. W. 
Published: May 2009

AbstractA subduction-accretion model incorporating new geophysical data is presented to explain the geology of the Antarctic Peninsula from late Palaeozoic to Cenozoic time. According to the model, the peninsula consists of overlapping accretionary, magmatic and extensional regimes that were diachronous across the peninsula and have built the crust to its present form. The crust, which contains a small proportion of sialic basement, was mainly formed by accretionary and magmatic processes and modified to its present shape by extension. The Gondwanide Orogeny for the Antarctic Peninsula is interpreted in terms of the accretionary processes.
Gravity modelling of the lherzolite body at Lers (French Pyrenees); some regional implications
Authors: Anderson Helen J. 
Published: May 2009

AbstractLherzolites outcrop throughout the North Pyrenean Zone of the Pyrenees and are everywhere associated with metamorphosed carbonates. It has been suggested that heat from the cooling of the lherzolites was responsible for the high temperature metamorphism of the carbonates. A gravity survey reported here shows that the volume of the lherzolite body at Lers is approximately 0.8 km3. The maximum volume of carbonates that such a body could metamorphose is 3.2 km3. This latter value is so much less than the volume of carbonates inferred from field mapping that the lherzolite body cannot have been the sole source of heat for metamorphism of the carbonates.It has been suggested from seismic data that there is a step in the Moho beneath the North Pyrenean Fault in the central Pyrenees. Gravity anomalies reported here show that either the step is less than 10 km high or that the density contrast is very low at the base of the crust in the Pyrenees.