1,720,986 research outputs found
Deformation and fluid flow during orogeny at the palaeo-Pacific active margin of Gondwana: the Early Palaeozoic Robertson Bay accretionary complex (north Victoria Land, Antarctica)
No full textStructural investigations, integrated with X-ray diffraction, fluid inclusion microthermometry and
oxygen-stable isotope analyses are used to reconstruct the deformation history and the palaeo-fluid
circulation during formation of the low-grade, turbidite-dominated Early Palaeozoic Robertson Bay
accretionary complex of north Victoria Land (Antarctica). Evidence for progressive deformation is
elucidated by analysing the textural fabric of chronologically distinct, thrust-related quartz vein
generations, incrementally developed during progressive shortening and thickening of the Robertson
Bay accretionary complex. Our data attest that orogenic deformation was mainly controlled by
dissolution–precipitation creep, modulated by stress- and strain-rate-dependent fluid pressure cycling,
associated with local and regional permeability variations induced by the distribution and evolution of
the fracture network during regional thrusting. Fracture-related fluid pathways constituted efficient
conduits for episodic fluid flow. The dominant migrating fluid was pre-to-syn-folding and associated
with the migration of warm (160–200 C) nitrogen- and carbonic (CO2 and CH4)-bearing fluids. Both
fluid advection and diffusive mass transfer are recognized as operative mechanisms for fluid–rock
interaction and vein formation during continuous shortening. In particular, fluid–rock interaction was
the consequence of dissolution–precipitation creep assisted by tectonically driven cooling fluids moving
through the rock section as a result of seismic pumping. The most likely source of the migrating fluids
would be the frontal part of the growing accretionary complex, where fluids from the deep levels in the
hinterland are driven trough channelization operated by the thrust-related fracture (fault) systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A combined integrated multi-method approach for the assessment of the thermal maturity of sedimentary basins
No full textThe reliable assessment of thermal maturity of sedimentary successions is crucial for the evaluation of hydrocarbon generation/expulsion. Uncertainties in thermal maturity assessment up to 0.2-0.3% of vitrinite reflectance values can occur according to commonly adopted parameters (eg., vitrinite reflectance, Tmax, etc.) especially when exploring Lower Paleozoic shale gas targets that are devoid of vitrinite macerals. This level of uncertainties is not acceptable in thermal modelling and can negatively influence decisions on the development of prospects.
This contribution provides a new methodological workflow to assess thermal maturity of organic matter dispersed in sediments and hosting sedimentary succession to largely reduce such uncertainties.
The multi-method approach consists in combining optical analysis and Raman and FTIR spectroscopy of organic matter dispersed in sediments with X-ray diffraction of the inorganic fine-grained fraction of sedimentary successions.
The four techniques have been systematically compared in diagenesis for the first time. Results are from an about 3000 m deep Cretaceous-Silurian section that shows a regular and highly resolved trend of increasing thermal maturity with depth on the base of spectroscopic and XRD data, and a general agreement among vitrinite reflectance, FTIR quantitative and qualitative indexes, pyrolysis and Raman indexes. Levels of thermal maturity of dispersed organic matter range from immature-early mature stages of hydrocarbon generation in the Cretaceous-Jurassic section to mid-late mature in the Triassic and Silurian units. Moreover, fine grained sedimentary rocks record an increasing trend of thermal maturity from early diagenesis in the Cretaceous-Jurassic section to late diagenesis for the Triassic and Silurian sections
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Sedimentary vs. tectonic burial and exhumation along the Apennines (Italy)
Full text linkWe review the burial-exhumation history of sedimentary units along the Apennines, focussing on paleothermal and thermochronological data derived from organic matter optical analyses, X-ray diffraction of clay-rich sediments, fission-track and (U-Th)/He dating. In the Northern Apennines, burial conditions and timing of exhumation progressively decreases eastwards from the inner towards the outer zones and through the nappes from the lowermost to the uppermost unit. Apart from large outcrops of metamorphic rocks well exposed in Tuscany, most of the rocks of the Northern Apennines reached only diagenetic conditions. In the Central Apennines paleo-thermal and thermochronological data indicate a substantial low sedimentary and tectonic burial testifying minor amounts of orogenic shortening with a prevailing thick-skinned structural style and scarce exhumation when compared to the Northern and Southern Apennines. In the Southern Apennines, thermal indicators record exhumation of sedimentary units in the axial zone of the chain from depths locally in excess of 4 km (Lagonegro Unit and Monte Alpi structure). Apatite fission-track data indicate that exhumation marks the late tectonic stages (younger than 10 Ma) of chain evolution, probably initiating with the buttressing of the allochthonous wedge against the thickening passive margin of Adria microplate. On the other hand, higher structural units (derived from Apenninic platform deformation) show variable amounts of burial along the strike of the chain (increasing from Lucania to North Calabria border). In Eastern Sicily thermal maturity decreases from hinterland to foreland as a result of less severe thermal evolution and/or tectonic loading apart from the Peloritani Mts. in the hinterland that subdued two different phases of exhumation: the first between 35-20 Ma and the second younger than 15 Ma. Accretionary prism made up of Sub-ligurian unit (namely Sicilidi) in the footwall of the Peloritani Mts. mainly exhumed in Burdigalian times (17-19 Ma) from depths of a few kilometers. Frontal thrust stack derived from late deformation of Mesozoic passive margin successions mainly exhumed in Tortonian-Pliocene times from depths of about three kilometers. Syn-orogenic siliciclastics (mainly thrust-top basins) generally show low thermal maturity testifying scarce burial apart from those at the rear of the chain (on top of the Peloritani Mts) that are thermally imprinted by out-of-sequence reactivation in Serravalian times followed by fast exhumation in extensional regime
Modelling of organic and inorganic paleo-thermal indicators to constrain the evolution of the geothermal system of Rosario de La Frontera (La Candelaria Ridge, NW Argentina): a new tool for geothermal exploration
No full textX-ray diffraction of clay grain-size fraction of sediments,
organic matter optical analysis and micro-thermometric study of fluid inclusions are widely used in oil exploration for determining the thermal maturity of sedimentary successions and basin evolution (from tens to hundred million years) by means of thermal modelling (ROURE et alii, 2010). The quantitative investigation of organic matter physico-chemical variations by optical measurements (e.g., vitrinite reflectance), of clay minerals structural and compositional changes (e.g., mixed layer illite-smectite) by X-ray diffraction and of microthermometry recorded by fluid inclusions (e.g., Th and Tm) allows to determine the thermal maturity of sediments, from diagenesis to very low-grade metamorphism, and to constrain the maximum temperatures experienced by rocks (e.g., MAZZOLI et alii, 2008).
As a matter of fact this multi-method approach is much less
applied to detect paleo-temperatures in fossil and active
geothermal systems, despite the validity of the single
techniques has been tested in several case histories of
geothermal interest to characterise modes of fluid-rock
interaction and abnormally high geothermal gradients at
shallow crustal levels (ALDEGA et alii, 2010).
In the last year, we have been fully developing this
integrated methodology to reconstruct the thermal evolution of Rosario de La Frontera active geothermal system (ESPELTA et alii, 1975), located in the Santa Barbara System, in NW Argentina in the foothills of the Cordillera. In this contribution we present the preliminary analytical and modelling results concerning the paleo-thermal conditions recorded by the sedimentary succession cropping out along La Candelaria Ridge that hosts the aforementioned system
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