bluuebunny/crossref_metadata_2025_split huggingface dataset:
Late Cenozoic crustal extension and basin formation in west Turkey
Authors: Seyitoǧlu Gürol , Scott Barry 
Published: May 2009

AbstractIt is proposed that north–south crustal extension and related sedimentary basin formation commenced in the early Miocene. This extension is believed to be related to a spreading of a thickened crust as a result of Palaeogene compression. That such spreading commenced virtually immediately after the cessation of this compression is considered to be due to the high thermal profile of the crust in that area at the end of the Palaeogene.
Superimposed extensional tectonics in the Argana Triassic formations (Morocco), related to the early rifting of the Central Atlantic
Authors: Medina Fida 
Published: May 2009

AbstractThe first Mesozoic beds in the western Atlas (Morocco) are the Triassic redformations of the Argana valley. The present study was carried out in order to determine the tectonic pattern, especially in the lowermost formations, related to the rifting of the Central Atlantic and to the creation of the Atlas trough. The main results are: (1) from the stratigraphic point of view, the lowermost formation (the Ikakern Formation) is probably of early Triassic age; (2) the sediments of this formation were deposited in an ENE–WSW trending basin affected by northward-tilted blocks delimited by almost pure normal faults; (3) this basin, whose trend was oblique to the younger Atlantic rift, represents a failed branch of the Atlas trough; (4) the “Atlantic stage” corresponds to the creation of a NNE-SSW trending basin superimposed on the first, and the sediments were, in this area, tilted to the west by a major end-Triassic extensional event, just before the extrusion of the basalts.
A newWorthoceras(Ammonoidea, Cretaceous) from Hungary, and remarks on the distribution ofWorthocerasspecies
Authors: Bujtor L. 
Published: May 2009

AbstractA new species of the genusWorthocerashas been recognized in material from a borehole (Bóly-1) in southern Hungary.Worthoceras pygmaeumsp. nov. co-occurs with typical Upper Albian (Stoliczkaia disparZone) ammonites. It seems likely that the genusWorthocerasarose in early late Albian times in North America and migrated eastward (Europe). During the Cenomanian it reached the southern margin of Tethys (Madagascar, India). It reached its most widespread distribution in Turonian times (from North America to New Zealand) and then became extinct. Beside the increasing area and growing dimensions, the strengthened sculpture is characteristic of theWorthocerasevolution.
Rift formation in the Gökova region, southwest Anatolia: implications for the opening of the Aegean Sea
Authors: Görür N. , Sengör A. M. C. , Sakinü M. , Akkök R. , Yiğitbaş E. , Oktay F. Y. , Barka A. , Sarica N. , Ecevitoğlu B. , Demirbağ E. , Ersoy Ş. , Algan O. , Güneysu C. , Aykol A. 
Published: May 2009

AbstractThe time of the onset and the nature of the extension in the Aegean area have been problematic owing to the confusion of neotectonic replacement structures with neotectonic revolutionary structures. This paper concerns two rift systems of different ages and orientations in the Gökova region of southwestern Anatolia. The first system has a northwest—southeast trend with a Middle to Upper Miocene infill, whereas the second system is orientated in an east—west direction and filled with Plio-Quaternary rocks. Structural and palaeomagnetic data indicate that the first system originally had a north—south trend, and then bodily rotated anticlockwise to its present orientation before the end of the Miocene. Both the orientations and the structural patterns of these cross-cutting rift systems suggest that they resulted from two different and successive tectonic régimes. Regional geology suggests that the generative régime of the older system was characterized by north—south compression and related to the palaeotectonic evolution of southwestern Anatolia, whereas that of the younger system is characterized by north-south extension and relates to the neotectonic evolution of this region. This inference contradicts, at least in southwestern Anatolia, some recent claims that the extensional tectonics and the related rift formation in the Aegean region began in the early Miocene, with the alleged demise of the compressional palaeotectonics during the late Oligocene, but is consistent with older views that placed the onset of north—south extension into the later middle Miocene. The formation of the Aegean Sea seems to be the result of these two complicated and contrasting, succesive tectonic regimes that have affected this region since middle Miocene times.
A global Chitinozoa biozonation for the Silurian
Authors: Verniers J. , Nestor V. , Paris F. , Dufka P. , Sutherland S. , Van Grootel G. 
Published: May 2009

AbstractA global Chitinozoan biozonation for the Silurian Period is proposed. Each biozone is an interval range defined by the first occurrence of an index species, selected from well-defined species with a relatively short biostratigraphic range. To be included in the scheme, index species must have been recorded from at least two major Silurian palaeocontinents where usable Chitinozoa assemblages have been studied, that is, Avalonia—Baltica (which had already undergone collision by the Silurian), Laurentia, Gondwana and Southern China. Seventeen biozones are identified with seven in the Llandovery: thefragilis, postrobusta, electa, maennili, alargada, dolioliformisandlongicollisbiozones; four in the Wenlock: themargaritana, cingulata, pachycephalaandlycoperdoidesbiozones; three in the Ludlow: theelongata, philipiandbarrandeibiozones; and three in the Přídolí: thekosovensis, elegansandsuperbabiozones. Chronostratigraphic calibration is partly provided by reference to the range of the appropriate Chitinozoa index species in the global stratotype sections and points (GSSP) of the Silurian series, e.g. in Bohemia (Czech Republic) for the Přídolí and the Welsh Borderland in England for the Ludlow and part of the Wenlock. When this information was not available, independent biostratigraphic control was provided by calibration with graptolite biozones or in a few cases, conodont or trilobite biozonal schemes. The index and most characteristic species of each biozone are illustrated and their total stratigraphie range provided.
Pan-African charnockite formation in Kerala, South India
Authors: Choudhary A. K. , Harris N. B. W. , van Calsteren P. , Hawkesworth C. J. 
Published: May 2009

AbstractSm-Nd mineral ages of gneisses and associated granulites from the Ponmudi incipient charnockite locality (South India) indicate that granulite metamorphism occurred at, or shortly after, 558 Ma. Proterozoic ages recorded by garnet separates reflect a detrital age or an earlier metamorphic event preserved by inclusions within garnet. The age of post-metamorphic uplift (440–460 Ma) is constrained by Sr isotope equilibration between biotite and plagioclase. Since charnockite formation and subsequent uplift north of the Palghat-Cauvery shear zone had terminated by earliest Proterozoic time, these results confirm two distinct periods of granulite formation in South India and suggest that the Palghat-Cauvery shear zone represents the boundary between two blocks of strongly contrasting geological histories. Both incipient charnockite formation and subsequent uplift at Ponmudi may be correlated with the tectonothermal evolution of the Highlands Group in Sri Lanka. The similarity between Nd and Sr model ages for charnockites and gneisses from Ponmudi indicates that no significant Rb-Sr fractionation has occurred during the crustal history of these incipient charnockites. Pb isotopic ratios suggest that Th-U ratios were fractionated during charnockite formation at about 500 Ma. In contrast to charnockites found north of the Palghat-Cauvery shear zone, fractionation of U-Pb during the Archaean did not occur in the Ponmudi granulites.
Oxygen and carbon isotope stratigraphy of early Cambrian carbonates in southeastern Newfoundland and England
Authors: Brasier M. D. , Anderson M. M. , Corfield R. M. 
Published: May 2009

AbstractCarbonate rocks have been sampled through predominantly siliciclastic sediments above the Precambrian-Cambrian global stratotype level in southeastern Newfoundland to assess their potential for oxygen and carbon isotope stratigraphy. Comparable successions were sampled at Nuneaton and Comley in England. Greatly depleted δ18O signals are attributed to widespread thermal alteration during deep burial and granitic intrusion, including within the stratotype region. Carbon isotope ratios appear to have been less affected and these are described from nine sections. A provisional, composite δ13C curve is based on non-ferroan, pink nodular and bedded micrites. Several δ13C excursions occur in the fossiliferous Bonavista Group and allow the position of the Tommotian-Atdabanian boundary to be identified. Chemostratigraphic correlation of the new Precambrian-Cambrian boundary stratotype may, however, prove difficult because of the lack of suitable, well-preserved carbonates. The search must begin for a comparable reference section allowing global correlation of the boundary level using chemostratigraphy as well as biostratigraphy.
The numerical age of the Devonian-Carboniferous boundary
Authors: Claoué-Long J. C. , Jones P. J. , Roberts J. , Maxwell S. 
Published: May 2009

AbstractThe SHRIMP ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the Hasselbachtal auxiliary global stratotype section through the Devonian-Carboniferous boundary in Germany, and a tuff located at a similar biostratigraphic level in Australia. Multiple replicate analyses have yielded indistinguishable ages, and indicate 353.2±4.0 Ma (2σ) as the age of the boundary. Obtaining an age for the boundary in the German reference section depended on the ability of SHRIMP to date a small sample and to target small areas of structurally complex zircons. Future refinements of the age of this boundary may depend on re-analysis of this uniquely placed bentonite, and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons.
Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru
Authors: Räsänen Matti , Neller Ron , Salo Jukka , Jungner Högne 
Published: May 2009

AbstractStill active Sub-Andean foreland deformation is suggested to have syndepositionally modified the fluvial depositional environments in the Peruvian Amazonian foreland basin throughout Neogene-Quaternary time. Modern fluvial aggradation continues to proceed on a large scale (c. 120 000 km2) in two differing depositional systems. Firstly, various multistoried floodbasin deposits are derived from the meandering and anastomosing rivers within the subsiding intraforeland basins. Secondly, in the northern part of the Pastaza-Marañon basin the largest known Holocene alluvial fan-like formation (c. 60 000 km2) composed of reworked, volcaniclastic debris derived from active Ecuadorian volcanoes, has been identified.The widespread, poorly known, dissected surface alluvium (terra firme) which covers the main part of the Peruvian Amazonian foreland basin shows further evidence of long-term foreland deformation, and terraces indicate both the effects of tectonism and Pleistocene climatic oscillations. In northern Peru, the surface alluvium was deposited by a Tertiary fluvial system with palaeocurrents to the west and northwest into the Andean foreland basin. In southern Peru, the respective surficial alluvium was part of a post-Miocene fluvial system flowing northeast into the main Amazon basin. Both systems were gradually abandoned when the eastward migrating Andean foreland deformation led to the more distinctive partitioning of the intraforeland basins, and the modern drainage system was created.
Primitive olivine melanephelinite dykes from the Orkney Islands, Scotland
Authors: Upton B. G. J. , Mitchell R. H. , Longs A. , Aspen P. 
Published: May 2009

AbstractTwo suites of Permian dykes in the Orkney Islands consist of a predominantly ENE trending camptonite suite and a mainly N-to NE-trending suite formerly referred to as monchiquitic. Some of the silica-poor and more magnesium dykes in the latter suite can be more precisely defined as olivine melanephelinites. Within the parochial context of the British Isles, such compositions appear to be unique. The magmas are deduced to have been primitive, small-scale (? < 0.2%) partial melt products of the asthenospheric mantle that have experienced relatively little modification in transit through the lithosphere.
Recycled acritarchs as provenance indicators: implications for Caledonian terrane reconstruction
Authors: Mccaffrey W. D. , Barron H. F. , Molyneux S. G. , Kneller B. C. 
Published: May 2009

AbstractSilurian successions deposited on the margins of the Iapetus Ocean in the English Lake District, Southern Uplands of Scotland and Ireland contain recycled Ordovician acritarchs. These include taxa known only from Avalonia and Gondwana, with other recycled acritarchs possibly derived from Baltica. There is no palynological evidence to indicate that Laurentiaconstituted a source area. The data presented herein suggest that provinciality in derived microfossils may be profitably exploited in provenance studies.
A new post-early Cambrian archaeocyath from Antarctica
Authors: Wood Rachel A. , Evans Kevin R. , Zhuravlev Andrey Yu. 
Published: May 2009

AbstractA new species of archaeocyath sponge, Dictyocyathus neptunensis, is described from the lower third of the Nelson Limestone of the Neptune Range, Antarctica. Based on the presence of the trilobites Nelsonia schesis and Amphoton oatesi, these strata are interpreted to be mid- to late middle Cambrian in age. D. neptunensis shows a branching, low integration modular form and a very simple skeletal type. Such an organization is predicted from known morphological trends within the early Cambrian Archaeocyatha. Specimens are not in life position, and probably form part of a storm deposit. The absence of Dictyocyathus from latest early Cambrian (Toyonian) strata worldwide suggests a convergent nature for this highly simplified skeletal type in archaeocyaths.
Possible forced folding in the Taurus–Zagros Belt of northern Iraq
Authors: Ameen M. S. 
Published: May 2009

AbstractThe folds in the Taurus–Zagros Belt of northern Iraq have generally been considered to be decollement buckle folds. This implies the presence of a decollement horizon at or near the base of the sedimentary cover, the ‘Infra-Cambrian Hormuz Salt’ and a passive role of the Precambrian basement in the tectonic evolution of the folded belt. Structural, stratigraphic, geophysical and remote sensing evidence suggests that forced folding, due to faulting in the basement, has played a significant role in the development of many of the folds in this region. This is clear from the substantial evidence of basement faulting, the lack of any convincing evidence for the presence of an extensive and regional decollement horizon (i.e. the Hormuz Salt) between the basement and the cover rocks, and the geometries of the folds and related mesostructures. The study shows that in the Taurus Foothills Zone, the folds are short, oval in plan shape, and arranged in an en echelon pattern along two sets of dislocation zones in the basement. However, the folds in the Zagros Foothills Zone are longer, linear and arcuate in plan shape. Many of the studied folds show similar features to those observed in the Rocky Mountains, U.S.A.
Magnesian andesites from the island of Skyros, Greece: geochemistry and regional significance
Authors: Pe-Piper G. 
Published: May 2009

AbstractHigh-magnesian andesites outcrop in a subvolcanic complex in the island of Skyros in the central Aegean Sea. Mineralogical indicators of this high-Mg content include bronzite and clinopyroxene phenocrysts, the former with high Cr2O3, and some phlogopite. Plagioclase (oligoclase–andesine) and Fe–Ti oxides were late phases to appear at the liquidus. Whole-rock geochemistry shows trace element features similar to those of subduction-related rocks. Radiometric dating indicates an early Serravallian (middle Miocene) age, approximately synchronous with the onset of post-orogenic rifting and extension of the Aegean Sea. This tectonic setting is consistent with an origin by adiabatic decompression of mantle peridotite previously modified by subduction-related fluids.
A reinterpretation of Scottish ‘hummocky moraine’ and its significance for the deglaciation of the Scottish Highlands during the Younger Dryas or Loch Lomond Stadial
Authors: Bennett Matthew R. , Boulton Geoffrey S. 
Published: May 2009

AbstractThe aim of this paper is to demonstrate that much of the ‘hummocky moraine’ present within the northern part of the LochLomond Readvance ice cap formerly situated in the North West Scottish Highlands may be interpreted as suites of ice-front moraines deposited during active decay. These landforms can be used to reconstruct ice cap decay, whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions. Evidence has been collected from 10803 airphotographs and from detailed field survey. It is presented at three spatial scales.
Graphite geothermometry in low and high temperature regimes: two case studies
Authors: Luque F. J. , Barrenechea J. F. , Rodas M. 
Published: May 2009

AbstractThis paper examines the potential use of the variation of the co parameter of graphite with temperature for geothermometric estimations. Two examples are presented in which graphite geothermometry, at low-and high-temperature conditions, is tested against other widely used geothermometers. The results obtained indicate that, at low-grade metamorphic conditions, the co parameter of graphite is affected by other factors besides the temperature, so graphite geothermometry (based on co) can only be used in such rocks for qualitative estimations. For temperatures above 500 °C, when the fully ordered graphite appears, there is a close correlation between the temperature estimations based on the structural ordering of graphite and from mineral-exchange geothermometry. The temperature calculations based on the co parameter of graphite are not influenced by factors (such as pressure or retrometamorphism) that clearly affect the exchange equilibria. Thus, graphite thermometry is a useful tool, for temperatures above 500 °C.
Geology and petrogenesis of the Straumsvola nepheline syenite complex, Dronning Maud Land, Antarctica
Authors: Harris Chris , Grantham Geoffrey H. 
Published: May 2009

AbstractThe 170 Ma Straumsvola nepheline syenite complex in western Dronning Maud Land, Antarctica, is located on the eastern edge of the Penck-Jutul Trough, a major tectonic feature which may be a Palaeozoic-Mesozoic rift system. The 5 km diameter pluton consists entirely of nepheline syenite and can be divided into two volumetrically important units: a relatively structureless outer zone which is overlain by a layered zone. The latter exhibits continuous rhythmic alternations of layers containing different proportions of alkali feldspar to amphibole+Na-rich pyroxene+biotite+nepheline throughout its 350 m thickness. The mafic zone is a volumetrically minor unit which unconformably overlies the layered zone and consists almost entirely of mafic minerals and nepheline. The layered zone shows no systematic stratigraphic variation in major or trace composition or mineral chemistry which is interpreted as being due to a combination of migration of intercumulus liquid and action of deuteric fluids. The remarkably constant thickness of successive layers throughout the layered zone suggests that layering resulted from an internally self-regulating process(es). The layering is defined by changing proportions of alkali feldspar to mafic minerals+nepheline which is consistent with layering being caused by differences in nucleation rate during eutectic crystallization. Dykes associated with the complex show wide-ranging compositions and include both over-and undersaturated types. Low σ18O values of the nepheline syenites (mean 5.9%, n = 9) suggest that the magma from which the nepheline syenites crystallized was mantlederived. Peralkaline microgranite dykes have higher σ18O values (mean 7.3%, n = 4) and it is suggested that they are either undersaturated liquids contaminated by siliceous crust, or derived by partial melting of partly fenitized gneiss. Oxygen isotope ratios of the surrounding gneiss indicate that the intrusion of the nepheline syenite did not cause extensive circulation of meteoric or magmatic hydrothermal fluids.
Deep structure of the Anglo–Brabant massif revealed by seismic profiling
Authors: Blundell D. J. 
Published: May 2009

AbstractDeep seismic reflection profiles over the Anglo–Brabant massif in the southern North Sea reveal reflection patterns throughout the crust that are distinctive and which differ significantly from those observed beneath adjacent areas with Mesozoic basins. Comparisons with reflection profiles from other platform areas suggest that the reflection patterns indicate large-scale structural features associated with compressional tectonics. If so, they may represent thrust structures associated with continental accretion of preferred Caledonian age.
The metamorphic history of the concealed Caledonides of eastern England and their foreland
Authors: Merriman R. J. , Pharaoh T. C. , Woodcock N. H. , Daly P. 
Published: May 2009

AbstractWhite mica (illite) crystallinity data, derived mostly from borehole samples, have been used to generate a contoured metamorphic map of the concealed Caledonide fold belt of eastern England and the foreland formed by the Midlands Microcraton. The northern subcrop of the fold belt is characterized by epizonal phyllites and quartzites of possible Cambrian age, whereas anchizonal grades characterize Silurian to Lower Devonian strata of the Anglian Basin in the southern subcrop of the fold belt. Regional metamorphism in the Anglian Basin resulted from deep burial and Acadian deformation beneath a possible overburden of 7 km, assuming a metamorphic field gradient of 36 °C km-1. Late Proterozoic volcaniclastic rocks forming the basement of the microcraton show anchizonal to epizonal grades that probably developed during late Avalonian metamorphism. Cambrian to Tremadoc strata, showing late diagenetic alteration, rest on the basement with varying degrees of metamorphic discordance. During early Palaeozoic times, much of the microcraton was a region of slow subsidence with overburden thicknesses of 3.3–5.5 km. However, concealed Tremadoc strata in the northeast of the microcraton reach anchizonal grades and may have been buried to depths of 7 km beneath an overburden of uncertain age.
Relationship between metamorphism and structure in the Skiddaw Group, English Lake District
Authors: Fortey N. J. , Roberts B. , Hirons S. R. 
Published: May 2009

AbstractRegional variation of white mica (illite) crystallinity in the Skiddaw Group is set against the structural interpretation of Hughes, Cooper & Stone (1993, this issue) in which early- or pre-Ludlow deformation and slaty cleavage development (S1) were succeeded by southward thrusting and an associated development of S1 and S1 crenulation cleavages, possibly during early Devonian times. Kubier index (KI) values are plotted in relation to geological structure for a major part of the Skiddaw Group, and cross-sections constructed. The pattern is interpreted in terms of three processes: (1) diagenetic to low anchizonal burial metamorphism under a relatively high geothermal gradient during the late-arc stage (early to mid-Silurian) which preceded the orogenic phase and formation of S1; (2) upper anchizonal to epizonal metamorphism due to tectonic thickening and slaty cleavage development during the early to pre-Ludlow orogenic phase following closure of Iapetus; (3) late-tectonic uplift of already metamorphosed rocks by southward-directed movement on the Loweswater, Gasgale Gill and Causey Pike Thrusts possibly during early Devonian time. An analogous interpretation is made for the Skiddaw area, though with the addition of major post-S1 contact metamorphism.