1,720,982 research outputs found
Does compaction-induced subsidence control accommodation space at the top of prograding carbonate platforms? Constraints from the numerical modelling of the Triassic Esino Limestone (Southern Alps, Italy)
Full text linkThe demise of the high-relief, steep-slope, prograding Ladinian-Early Carnian carbonate platforms of the
Esino Limestone (Central Southern Alps of Italy) is marked by subaerial exposure of the platform top
associated with different erosional (mainly karst-related), depositional and diagenetic processes (Calcare
Rosso). The exposure-related deposits consist of three major facies associations: 1) residual soils with
thin lenses of conglomerates with black pebbles, and, locally, weathered vulcanites; 2) chaotic breccia
lenses irregularly distributed in the uppermost part of the Esino Limestone carbonate platform, interpreted as collapse breccias in karstic setting: 3) inter-supratidal carbonate cycles with dissolution and
development of paleosols and tepee structures.
Facies distribution follows the sub-environments of the underlying Esino Limestone. Facies 1 and 2
typically characterize the core of the platform, covering the underlying inner platform facies. Facies 3
instead develops toward the edge of the platform, above reef-upper slope facies of the prograding facies
of the Esino Limestone. The thickness of facies 3 decreases toward the core of the platform. Facies distribution reflects differences in the accommodation space and sedimentary processes from the rim
(highest accommodation, favouring the deposition of peritidal-supratidal carbonates) to the core
(reduced accommodation, causing pedogenesis and karstification) of the carbonate system.
The observed thickness changes may be controlled by different factors: 1) syndepositional tectonics, 2)
subsidence induced by magmatic activity or 3) differential subsidence controlled by the stratigraphic
architecture of the Esino Limestone platform and adjoining basins. As evidence of tectonics was not
observed and the presence of volcanic bodies is only documented tens of km away from the study area,
the scenario involving the creation of accommodation space by compaction of the basinal sediments
(resedimented, fine-grained calciturbidites) during the progradation of the carbonate platform is here
investigated. Numerical modelling was performed to verify the compatibility of compaction-induced
subsidence with the observed depositional architecture. The models were built to simulate the architectural evolution of the platform by progressively adding layers from deepest to shallowest, while
compacting the underlying sediments, in order to evaluate compaction-induced subsidence (and accommodation space for the Calcare Rosso) after the deposition of the youngest platform strata. Modelling
results allow us to conclude that the wedge geometry of the Calcare Rosso, deposited on top of the
extinct Esino carbonate platform, can be explained by subsidence controlled by compaction of the basinal
sediments present below the early-cemented, fast prograding platform slope deposits
Multistage Dolomitization in an Early Jurassic Platform (Southern Alps, Italy): insights for the distribution of massive dolomitized bodies
No full textThe Early Jurassic dolomitized carbonates are a hydrocarbon exploration target
in Northern Italy. Of these carbonates, the Liassic Albenza Formation platform
and the overlying Sedrina Formation shelf were studied to define a pervasive
dolomitization model and to shed light on dolomite distribution in the subsurface.
Field work, as well as analyses of well cores, stable isotopes, trace
elements and fluid inclusions, was carried out on the outcropping thrust belt
and sub-surface deformed foreland of the Southern Alps. Petrographic
analyses showed a first, pervasive, replacement dolomitization phase (D1)
followed by volumetrically less important dolomite cement precipitation
phases (D2, D3 and D4). The d18O values fall between )8Æ2& and 0Æ1& Vienna-
Pee Dee Belemnite with the more depleted samples belonging to dolomite
cement-rich dolostones; the d13C ranges from 2Æ6& to 3Æ7& Vienna-Pee Dee
Belemnite. Analysis of trace elements showed different Fe and Mn contents in
the sub-surface and outcropping dolostones, and a higher Fe in the younger
dolomite cements. An increase in the precipitation temperature (up to 130 C
from fluid inclusion data) and a decrease in diagenetic fluid salinity (from sea
water to brackish) are observed from the first pervasive replacement dolomite
to the dolomite cement phases. Field observations indicate that, in the Albenza
Formation, dolomitization was limited to palaeohighs or faulted platform
margins in the Early Jurassic carbonates. The pervasive replacement phase is
interpreted based on a ‘compaction model’; the formation fluids expelled from
compacting basinal carbonates could have funnelled along faults into
permeable palaeohighs. The high homogenization temperature of the
dolomite cements and decreased salinities indicate precipitation at great
depth with an influx of meteoric water. These data, along with the thermal
history, suggest that the dolomite cements precipitated according to the
‘tectonic squeegee’ dolomitization model. The dolomite precipitation
temperature was set against the thermal history of the carbonate platform to
interpret the timing of dolomite precipitation. The dolomite precipitation
temperatures (90 to 100 C) were reached in the studied formations first in the
thrust fold belt (Early Tertiary, 60 Ma), and then in the foreland succession
during the Late Tertiary (10 Ma). This observation suggests that the dolomite
precipitation fronts moved southwards over time, recording a ‘diagenetic
wave’ linked to the migration of the orogenic system. Observations suggest that
the porosity increased during the first phase of replacement dolomitization
while the dolomite cementation phases partially occluded the pores. The distribution of porous dolomitized bodies is therefore linked to the
‘compaction dolomitization’ model
Analysis and interpretation of a Multistage dolomitization in an Early Jurassic platform: iinsights for the distribution of massive dolomitized bodies (Southern Alps, Italy)
No full textThe paradox of the end Permian global oceanic anoxia
No full textGeochemical results argue against global anoxia as a or the cause for the end Permian mass extinction. Instead, they suggest that the water column was oxic and sometimes the sediment pore water was suboxic, which is the norm. Anoxia, if present, may reflect local conditions developed in deep water settings, but that have to be supported by concrete and direct evidence
The influence of petrography, mineralogy and chemistry on burnability and reactivity of quicklime produced in Twin Shaft Regenerative (TSR) kilns from Neoarchean limestone (Transvaal Supergroup, South Africa)
No full textThis study evaluates the influence of chemical, mineralogical and petrographic features of the Neoarchean limestone from the Ouplaas Mine (Griqualand West, South Africa) on its burnability and quicklime reactivity, considering the main use as raw material for high-grade lime production in twin shaft regenerative (TSR) kilns. This limestone consists of laminated clotted peloidal micrite and fenestrate microbial boundstone with herringbone calcite and organic carbon (kerogen) within stylolites. Diagenetic modifications include hypidiotopic dolomite, micrite to microsparite recrystallization, stylolites, poikilotopic calcite, chert and saddle dolomite replacements. Burning and technical tests widely attest that the Neoarchean limestone is sensitive to high temperature, showing an unusual and drastically pronounced sintering or overburning tendency. The slaking reactivity, according to EN 459-2 is high for lime burnt at 1050 °C, but rapidly decreases for lime burnt at 1150 °C. The predominant micritic microbial textures, coupled with the organic carbon, are key-factors influencing the low burnability and the high sintering tendency. The presence of burial cementation, especially poikilotopic calcite, seems to promote higher burnability, either in terms of starting calcination temperature, or in terms of higher carbonate dissociation rate. In fact, the highest calcination velocity determined by thermal analysis is consistent with the highest slaking reactivity of the lower stratum of the quarry, enriched in poikilotopic calcite. Secondly, locally concentered dolomitic marly limestones, and sporadic back shales negatively affects the quicklime reactivity, as well. This study confirms that a multidisciplinary analytical approach is essential for selecting the best raw mix for achieving the highest lime reactivity in TSR kilns
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
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
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