1,720,993 research outputs found
PRIMI RISULTATI DELLA CAMPAGNA OCEANOGRAFICA PALEOCLIGE 1999 (BOCCHE DI BONIFACIO – ARCIPELAGO DI LA MADDALENA)
No full textVengono riportati i primi risultati della campagna oceanografica PALEOCLIGE 1999 (Paleoclimatologia e Paleogeografia) basata su acquisizione di profili sismici in alta risoluzione Sub Bottom Profiler-Chirp.
La spedizione e stata effettuata nell'estate 1999 nell'area delle Bocche di Bonifacio e all'interno del Parco Nazionale di La Maddalena utilizzando la motovedetta MVCP452 della Guardia Costiera.
II posizionamento GPS differenziale è stato effettuato dai tecnici dell'Istituto Nazionale di Oceanografia e di Geofisica Sperimentale di Trieste (OGS), contemporaneamente sono stati acquisiti dati sedimentologici mediante benna e immersioni subacquee utilizzando i mezzi della BLON (Base Logistica Operativa Navale del Corpo Forestale e di Vigilanza Ambientale della Regione Sardegna).
La presente nota, anche mediante il supporto di un poster, illustra le caratteristiche sismostratigrafiche dei sedimenti di fondo dell' intera area investigata.
L' interpretazione delle linee sismiche consente di riconoscere sequenze sedimentarie poggianti su un basamento acustico, corrispondente al basamento cristallino sardo, strutturato durante l'orogenesi Ercinica.
Esso risulta sempre ben risolto e caratterizzato da un andamento molto irregolare con presenza di depressioni tra gli alti strutturali che hanno consentito la formazione di bacini di riempimento sedimentario.
Al di sopra del basamento, dal basso verso l'alto, si osservano delle sequenze sedimentarie sia stratificate che caotiche di probabile origine continentale e delle sequenze sedimentarie di origine marina.
Queste sono caratterizzate da spessori variabili da meno di un metro a più di 30 m.
Gli orizzonti sono in alcune zone suborizzontali e subparalleli tra loro, in altre mancano di continuità laterale e formano delle lenti sedimentarie.
E' stata inoltre rilevata la presenza di incisioni in corrispondenza del fondo mare e all'interno delle sequenze sedimentarie, interpretabili come paleoalvei fluviali. Vi sono inoltre corpi sedimentari (mound) caratterizzati da una geometria interna "hummocky".
Le successioni stratigrafiche sono compatibili con gli eventi paleoambientali e paleoclimatici riferibili alla finestra temporale Pleistocene-Olocene.
Queste testimonianze sono inquadrabili nella fase del minimo glaciale Wurm e nella fase di risalita del mare olocenico che ha invaso le coste a rias in oggetto.
I dati esaminati e l'interpretazione in alta risoluzione digitale hanno consentito di definire gli spessori delle coperture sedimentarie (aree chiave del Golfo di Arzachena, Palau, Porto Liscia e area tra l'isola di Spargi e di La Maddalena) e delle principali geometrie dei bacini
ACOUSTIC FACIES AND MORPHOLOGIES OF THE HOLOCENE DEPOSISTS WITHIN THE LA MADDALENA ARCHIPELAGO (BOCCHE DI BONIFACIO – NW SARDINIA, ITALY)
No full textThis work presents new results of palaeoenvironmental interests from the area of La Maddalena archipelago, the southern part of the Strait Bonifacio between the islands of Sardinia and Corsica. The data have been acquired in the frame of a cooperation program in marine geology researches between the Universities of Cagliari and Trieste.
The data consist of about 250 nautical miles of echographic profiles acquired with Chirp technology in water depths not greater than – 60 m using two motorvessels provided with a differential GPS positioning system.
The profiles have been correlated with 150 bottom samples collected by means of grab samplings and scuba divings.
The sedimentological, paleontological and isotope geochemical content of the analyzed samples provided an interpretative link with the palaeoclimatic and palaeoenvironmental events of the late Pleistocene to Holocene.
The very high Chirp resolution signal, despite a penetration limited to about ten metres in the sandy sediments of the area, allows the recognition of the sedimentary deposits and their related morphologies linked to the Versilian transgression.
These deposits lie over a non-reflective bed-rock characterized by an irregular topography corresponding to the Sardinia pre-Carboniferous granitic basement.
Dikes and lodes, typical of the cristalline basements,are arranged along N-S and W-E, with subordinate NE-SW and NW-SE trends that control the morphostructural and hydrographic pattern of the entire region. During the Würmian sea level low stand the hydrographic network was overdeepened into the cristalline basement. The successive Holocenic sea level rise drowned the palaeocoastlines and caused the sedimentary infilling of the previous hydrographic network with the deposition of the sedimentary bodies illustrated in this work.
Five main acoustic facies have been distinguished on the echographic profiles. Their correlation with the analysed samples provided the following interpretation:
1 - Bed-rock facies due to the outcropping of the granite and its dikes and/or to quaternary and pre-quaternary consolidated sediments.
2 - Transparent or semi-transparent facies over the bed-rock.
This facies occurs near the coastlines and represent medium to coarse sands deposited over the bed-rock during the late Holocene sea level high stand, i.e.the late 5000 years B.P.
3 - Semitransparent facies with sparse internal irregular reflectors. This facies is found along the northern coast of Sardinia in front of and near the present mouths of the so-called "rias", rivers with torrential regime incised in the granitic basement. This facies would represent palaeo-fluvial and palaeo-deltaic environments developed during the late-Holocene high standing conditions. Thicknesses up to 20 m are observed on some profile near the coast.
4 – Semitransparent to opaque facies over stratified horizontal facies. These are found in water depths generally deeper than -30 m and correspond to very coarse sands deposited over stratified coarse to medium sands. Within the channels between the Sardinian coast and the islands of La Maddalena and Spargi, bottom currents of the Strait of Bonifacio sometimes shape the upper facies into acoustically opaque, upward convex lenses that at least on bottom surface correspond to very coarse biogenic sands and gravels.
The contact with the underlying stratified facies is sometimes of erosional type. There is evidence of weak angular unconformities and channels that have been incised for a couple of metres into the stratified facies and infilled by the overlying semitransparent-to-opaque facies.
We interpret these two superposed facies respectively as the transgressive and the high standing depositions of the Versilian transgressive event.
5 – Very well stratified facies, occuring only in the area of Porto Liscia, Porto Puddu and the inner part of the gulf of Arzachena, represents a fine to very fine sediment deposited in low-to-very low energy environments like restricted or protected bays
Earthquakes and depleted gas reservoirs: Which comes first?
Full text linkWhile scientists are paying increasing attention to the seismicity
potentially induced by hydrocarbon exploitation, so far, little is known
about the reverse problem, i.e. the impact of active faulting and
earthquakes on hydrocarbon reservoirs. The 20 and 29 May 2012 earthquakes in
Emilia, northern Italy (Mw 6.1 and 6.0), raised concerns among the public
for being possibly human-induced, but also shed light on the possible use of
gas wells as a marker of the seismogenic potential of an active
fold and thrust belt. We compared the location, depth and production history
of 455 gas wells drilled along the Ferrara-Romagna arc, a large hydrocarbon
reserve in the southeastern Po Plain (northern Italy), with the location of
the inferred surface projection of the causative faults of the 2012 Emilia
earthquakes and of two pre-instrumental damaging earthquakes. We found that
these earthquake sources fall within a cluster of sterile wells, surrounded
by productive wells at a few kilometres' distance. Since the geology of the
productive and sterile areas is quite similar, we suggest that past
earthquakes caused the loss of all natural gas from the potential reservoirs
lying above their causative faults. To validate our hypothesis we performed
two different statistical tests (binomial and Monte Carlo) on the relative
distribution of productive and sterile wells, with respect to seismogenic
faults. Our findings have important practical implications: (1) they may
allow major seismogenic sources to be singled out within large active thrust
systems; (2) they suggest that reservoirs hosted in smaller anticlines are
more likely to be intact; and (3) they also suggest that in order to
minimize the hazard of triggering significant earthquakes, all new gas
storage facilities should use exploited reservoirs rather than sterile
hydrocarbon traps or aquifers
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
Shallow water sea-floor morphologies around Asinara Island (NW Sardinia, Italy)
No full textSide scan sonar, high-resolution seismic and multibeam data collected off the coast of Asinara Island in the northernmost part of Sardinia have revealed the occurrence of four distinct acoustical patterns that can be related to four main sea-bed types. The four facies represent fine sand (Type A), medium to
coarse sand (Type B), patchy sand cover between basement outcrops (Type C) and a predominantly sandy sea-floor colonized by the seagrass Posidonia Oceanica (Type P). The distribution of the sea-bed types indicates that the study area is characterized by a rather complex morphological setting.
A remarkable physiographic difference exists between the eastern and western sector of the island, with the latter being affected by strong, westerly winds, mainly the so-called ‘‘Mistral’’. The wave climate in this area is dominated by wind waves, which can reach a maximum height of 8m during winter storms.
Sediments are mobilized at water depths greater than 30m from the sea surface during these energetic oceanographic regimes. We infer that dune fields and sand ribbons are deposited by strong offshore flows along the sea-bed resulting as a consequence of wave- and wind-induced onshore water
transport
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
- …
