1,721,038 research outputs found
A record of seafloor methane seepage across the last 150 million years
Full text linkSeafloor methane seepage is a significant source of carbon in the marine environment. The processes and temporal patterns of seafloor methane seepage over multi-million-year time scales are still poorly understood. The microbial oxidation of methane can store carbon in sediments through precipitation of carbonate minerals, thus providing a record of past methane emission. In this study, we compiled data on methane-derived carbonates to build a proxy time series of methane emission over the last 150 My and statistically compared it with the main hypothesised geological controllers of methane emission. We quantitatively demonstrate that variations in sea level and organic carbon burial are the dominant controls on methane leakage since the Early Cretaceous. Sea level controls methane seepage variations by imposing smooth trends on timescales in the order of tens of My. Organic carbon burial is affected by the same cyclicities, and instantaneously controls methane release because of the geologically rapid generation of biogenic methane. Both the identified fundamental (26-27 My) and higher (12 My) cyclicities relate to global phenomena. Temporal correlation analysis supports the evidence that modern expansion of hypoxic areas and its effect on organic carbon burial may lead to higher seawater methane concentrations over the coming centuries
Relationships between recent tectonic activity, mud diapirism and slope instability in the Gulf of Squillace (Calabrian Arc, Ionian Sea)
No full textMud volcanism and fluid geochemistry in the Cheleken peninsula, western Turkmenistan
No full textA geological and geochemical study has been carried out to investigate the relationships between major mud volcano structures and deep fluid migration in the Cheleken peninsula, in the South Caspian Basin. The fluid geochemistry allowed the origin and migration of the saline waters and the hydrocarbons to be deduced along with the regional source and reservoir rocks. The emitted waters formed by the mixing of deep highly saline water from the main source rocks of the Maykop Fm with the Caspian-like pore water contained in the Pliocene reservoirs. The water composition is very similar to that emitted by the mud volcanoes in Azerbaijan, allowing comparisons to be done between the reservoirs in the western and eastern sides of the South Caspian Basin. The associated oil is derived from a mixed type II/III kerogen deposited in a sub-oxic marine environment and generated during the early oil window. The oil biomarkers indicate that the source rock is the Maykop Fm., as previously determined for the other areas of the South Caspian Basin.The spontaneous emissions, showing different morphologies, are mainly aligned along normal and transtensive fault systems, which provide effective pathways for rapid fluid ascent from deep reservoirs to the surface
Relationships between recent tectonic activity, mud diapirism and slope instability in the Gulf of Squillace (Calabrian Arc, Ionian Sea).
No full textThe Calabrian arc, is a 200 to 400 km wide accretionary wedge which connects the Southern Apennine chain, to the North, with the Sicilian-Maghrebian chain, to the Southwest. This wedge is still forming, as testified by seismic activity and by recent sea-bottom morphologies including tectonic lineaments, mud volcanoes and deep-incised canyons. In particular, mud volcanoes and mud diapirs show a strict relationship with the Late Pliocene to Recent tectono-sedimentary evolution of the accretionary wedge (Artoni et al, 2009). In order to better understand their origin and evolution, we focused on the Gulf of Squillace. This latter is located in the northern part of the Crotone-Spartivento forearc basin.
The studied area was selected because of the consistent available data base which consists of 10 well logs, 330 km of public seismic reflection lines and about 350 km of higher resolution seismic profiles (Sparker lines “J”, ISMAR CNR, 1971-75). The latter profiles have been extensively analyzed because they clearly show diapiric structures, also having a sea-bottom expression.
In the Gulf of Squillace the reconstructed complex structural setting shows the occurrence of a system consisting of transpressive and transtensive lines oriented WNW-ESE, which has been interpreted as the off-shore prosecution of the Catanzaro-Squillace transcurrent system (Tansi et al., 2007). All the available WSW-ENE seismic profiles show a wide basin which is confined to the South by WNW-ESE system of deep rooted normal faults, dipping to the North, associated with antithetic faults developing in the northern side of the basin. These latter faults flatten on shallower layers, interpreted as Late Miocene clays with intervening clastic gypsum intervals. The displacement along the southern master fault is associated to an increase in sediment accumulation, of Late Pliocene to Recent age, arranged in a growth geometry on the hanging-wall and documenting the fault activity during this period. Mud diapirs are mainly grouped in this sector of the basin, characterized by the increase in sediment thickness. These diapirs, in turn, are bounded by the major faults. The WNW-ESE seismic profiles also evidence another normal fault system oriented SW-NE, dipping toward the basin, which cuts the upper and middle slope of the gulf. These faults account for hundred of meters of displacement and are associated with significant gravitative processes.
In this frame, the occurrence of mud diapirism is related at least to two favorable conditions: 1) overpressure generated by the asymmetric sediment accumulation on the underlying unconsolidated muds and 2) the propagation of the active normal faults system. This activity, in fact, represents the main trigger for fluid and mud rising up to the seafloor. Mud diapirs could be originated from Late Miocene succession, but also from deeper sources.
The progressive extensional deformation associated with mud diapirs significantly influences the morphologic evolution of the slope and of the basin. Deep erosion occurs in canyons, that are aligned along the main faults and in some cases are also laterally bounded by the mud diapirs relief. The retrogressive and landward migration of the canyon heads is also strictly associated to the evolution of normal faults, oriented near parallel to the coastline, and associated to gravitative slope failures
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
Controls on stable isotope signatures in Methane-Derived Authigenic Carbonates: examples from the Northern Apennines, Italy
No full textDispelling 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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