Isotopes du milieu et circulations dans les aquiferes du sous-sol Vénitien     

Giancarlo Bortolami  Jean-Charles Fontes  Costanzo Panichi 《Earth and Planetary Science Letters》1973,19(2):154-167

L'enfoncement de la plaine de Venise, quel'on peut estimeràprès de 1 cm/an sous le site historique, est liéàla surexploitation des nappes artésiennes profondes. L'investigation hydrogéologique est rendue délicate par la nature de l'aquifère composéde plusieurs centaines de mètres de dépo?ts quaternaires continentaux et marins. Au sein de ce complexe les nappes se superposent en un système multicouche artésien. L'étude du régime de ces nappes aétéentrepris par les moyens géochimiques et isotopiques (oxygène 18, deuterium, tritium, carbone 13 et carbone 14).Les teneurs en isotopes stables montrent l'existence de deux familles d'eaxu profondes attribuablesàune recharge “froide” (δ¹⁸O= ?10 et ?12‰). Ces eaux sont nettements différentes de celles des nappes phréatiques (δ¹⁸O ? ?8‰). Les apports profonds peuvente?tre respectivement liés aux bassins des rivières préalpines Brenta et Piave (δ¹⁸O ? ?10‰) d'une part et au paléocours de l'Adige, fleuve alpin d'autre part. Les eaux alpines ont un gisement limitéàl'aplomb de la lagune etàla partie sud-ouest de la plaine. Les eaux de type préalpin occupent le reste de la plaine, c'est-à-dire plus grande partie.La détermination des vitesses d'écoulement pose le problème de la validitédes temps estimésàl'aide des teneurs en¹⁴C.Les teneurs en¹³Célevées des eaux alpines montrent clairement que les activités en¹⁴C de celles-ci ne sont pas significatives par suite d'unéchange avec l'aquifère ou d'une surcharge en carbone ancien dissous.Pour les eaux qui viennent du domaine préalpin, on observe dans les zones de recharge de fortes teneurs en³H: 85à120 UT alliéesàdes activités relativement faibles en¹⁴C (60à70%). Les teneurs en¹³C indiquent que le carbone dissous n'a pas subi d'échange avec l'aquifère. La discussion de l'ensemble des données suggère que la circulation est rapide dans la zone de recharge oùl'alimentation en eaux d'altitude se faitàpartir d'infiltrations en provenance du réseau hydrographique ou (et) du système karstique des préalpes. Dans les parties basses de la plaine les vitesses sont faibles et décroissent, vers l'Est ou en profondeur, de 3 m/anà1 m/an. Il est possible qu'une rupture dans l'intensitédes vitesses d'écoulement interviennent dans la partie occidentale de la plaine sous l'effet d'une discontinuitésédimentologique majeure (limite occidentale des dépo?ts marins).  相似文献   

The Loci of Satellite Positions: A Constellation Design Approach     

Giancarlo Lucarelli  Raffaele Picone  Salvatore Troisi 《Celestial Mechanics and Dynamical Astronomy》1998,70(1):59-73

In special cases in which satellite constellations can be described by a limited set of parameters, a correlation between the latter and the constellation characteristics (i.e. shape and kinematics of the satellite configurations) has been investigated. Such cases may be a useful starting point for designing more complex constellations in order to achieve better the desired performances. Therefore, this proves to be one way to fix an initial set of parameters once the desired behaviour of the constellation has been established on the basis of the operational purposes required. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Analysing the influence of upslope bedrock outcrops on shallow landsliding     

Paolo Tarolli  Marco Borga  Giancarlo Dalla Fontana 《Geomorphology》2008,93(3-4):186-200

A model for the prediction of topographic and climatic control on shallow landsliding in mountainous terrain is enhanced to analyse the impact of upslope rocky outcrops on downslope shallow landsliding. The model uses a ‘generalised quasi-dynamic wetness index’ to describe runoff propagation on bare rock surfaces connected to downslope soil-mantled topographic elements. This approach yields a simple enhanced model capable of describing the influence of upslope bedrock outcrops on the pattern of downslope soil saturation. The model is applied in both diagnostic and predictive modes to a small catchment in the eastern Italian Alps for which a detailed inventory of shallow landslides in areas dominated by rocky outcrops is available. In the diagnostic mode, the model is used with satisfactory results to reproduce the pattern of instability generated by an intense short-duration storm occurred on 14 September 1994, which triggered a large percentage of the surveyed landslides. In the predictive mode, the model is used for hazard assessment, and the return time of the critical rainfall needed to cause instability for each topographic element is determined. Modelling results obtained in the predictive mode are evaluated against all the surveyed landslides. It is revealed that the generalised quasi-dynamic model offers considerable improvement over the non-generalised quasi-dynamic model and the steady-state model in predicting existing landslides as represented in the considered landslide inventory.  相似文献   

Stratigraphy, chronology, and sedimentology of ignimbrites from the white trachytic tuff, Roccamonfina Volcano, Italy     

Bernardino Giannetti  Giancarlo De Casa 《Journal of Volcanology and Geothermal Research》2000,96(3-4)

We describe the stratigraphy, chronology, and grain size characteristics of the white trachytic tuff (WTT) of Roccamonfina Volcano (Italy). The pyroclastic rock was emplaced between 317 and 230 Ma BP during seven major eruptive events (units A to G) and three minor events (units BC, CD, and DE). These units are separated by paleosol layers and compositionally well-differentiated pyroclastic successions. Stratigraphic control is favored by the occurrence at the base of major units of marker layers. Four WTT units (1 to 4) occur within the central caldera. These are not positively correlated with specific extracaldera units.The source of most of the WTT units was the central caldera. Units B and C were controlled by the western wall of the caldera, whereas units D and E were able to overcome this barrier, spreading symmetrically along the flanks of MC. The maximum pumice size (MP) of units increases with distance from the caldera, whereas the maximum lithic size (ML) decreases. MP and ML of the marker layer of unit D (MKDa–MKDp) do not show any systematic variations with respect to the central caldera. In contrast, the thickness of surge MKDa decreases with distance from the source, and MKDp accumulates to the north of MC probably controlled, respectively, by mobility-transport power and by wind blowing northwards.The grain size characteristics of the WTT deposits are used for classifying the units. There is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units. Large variation of components in subunit E1, with repetitive alternation of pyroclastic flow to surge through fallout vs. surge deposits, suggests that the process of eruption took place in a complex or piecemeal fashion.Pumice concentration zones (PCZ) occur at all WTT levels on the volcano, but they are much thicker and pumice clasts are much larger within the central caldera. These were probably originated by the disruption of lava (flow or dome) to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava. Local basal PCZ are, in some cases, similar to the lapilli-rich “layer 1P” that has been described elsewhere, and may have been deposited from currents transitional between pyroclastic surge and flow. Other basal PCZ formed in response to small undulations in the substrate, or can be originated by fallout. Lenticular PCZ within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts, some of which were buried by subsequant pyroclastic flows.Lithic concentration zones (LCZ) also occur at various stratigraphic height within the extracaldera ignimbrites, whereas intracaldera LCZ are absent, probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent. LCZ at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients (a segregation process). Coarse LCZ and coarse lithic breccias (LB), that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas, are interpreted to be the result of slugs of lithic-rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths. These LCZ become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows (desegregation processes).  相似文献   

A baroclinic coastal trapped wave event in the Gulf of Naples (Tyrrhenian Sea)     

Paola de Ruggiero  Ernesto Napolitano  Roberto Iacono  Stefano Pierini  Giancarlo Spezie 《Ocean Dynamics》2018,68(12):1683-1694

In this study, a baroclinic coastal trapped wave, with period ~?4.5 days and cross-shore scale ~?3 km, is identified in the outputs of a very-high-resolution ocean circulation model of the Campania coastal system (central Tyrrhenian Sea; including the Gulfs of Salerno, Naples, and Gaeta). The outputs are from a simulation spanning June 2003, a month in which the surface winds were always weak, except for a strong northeasterly wind event that lasted 1 day (20 June). This event is found to generate a strong upwelling along the Campania coasts, whose relaxation—virtually free, because of the weakness of the winds—produces coastal current fluctuations that propagate to the north, spanning the three gulfs. The dynamics (analyzed with a focus on the Gulf of Naples) is found to share important features with baroclinic Kelvin waves in a two-layer model, such as the sharp cross-shore decrease of the perturbation amplitude and the vertical reversal of the long-shore current velocities. The simulated phase speed, cross-shore extension, and wavelength of the perturbation are also close to those obtained using a two-layer approximation of the dynamics. Moreover, the propagation described by the models is shown to be compatible with current measurements that were made in June 2003 at the southern entrance of the Gulf of Naples. Experimental implications related to the specific oceanographic problem are finally discussed, and an experimental strategy—inspired by our modeling approach—aimed at identifying the phenomenon is proposed.  相似文献   

First Ar/Ar age of the Ceprano man (central Italy)     

Sébastien Nomade  Giovanni Muttoni  Hervé Guillou  Eric Robin  Giancarlo Scardia 《Quaternary Geochronology》2011,6(5):453-457

The Ceprano calvarium, found in 1994 in Italy and attributed to Homo cepranensis, is one of the most celebrated hominin remains of Europe. It was considered at least 700 ka-old until a recent investigation incorporating magnetostratigraphy and K-Ar ages from the literature assigned to the calvarium an age of ∼450 (+50, −100) ka. Here we pin down the age of the Ceprano calvarium to 353 ± 4 ka (±1σ external) by means of new ⁴⁰Ar/³⁹Ar dating on K-feldspars retrieved from the sediments that hosted the skull. In absence of evidence of reworking, this refined age sinks the conviction that H. cepranensis belonged to human evolution at the Brunhes–Matuyama boundary (c.a. 781 ka). Our refined age indicates that H. cepranensis lived in central Italy probably during the cold period of marine isotope stage (MIS) 10, and that despite his archaic morphology and lack of Neanderthal traits, he was contemporaneous with more advanced species such as H. heidelbergensis.  相似文献   

Drainage network detection and assessment of network storage capacity in agrarian landscape     

Federico Cazorzi  Giancarlo Dalla Fontana  Alberto De Luca  Giulia Sofia  Paolo Tarolli 《水文研究》2013,27(4):541-553

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Joint analysis of Rayleigh- and Love-wave dispersion: Issues, criteria and improvements     

Giancarlo Dal Moro  Fabrizio Ferigo 《Journal of Applied Geophysics》2011,75(3):573-589

Joint analysis of Rayleigh- and Love-wave dispersion is performed with the aim of evaluating how their joint use can improve retrieved vertical V_S profiles. In fact, non-uniqueness of the solution and complex energy distribution among different modes represent problems which, if not properly considered, can eventually lead to ambiguous or erroneous subsurface models.Some tests performed on synthetic datasets show that for the deepest layers the improvements obtained by the joint inversion cannot be considered as fully decisive in terms of ultimate solution of non-uniqueness. Nevertheless joint analysis of dispersive properties of Rayleigh and Love waves reveals as a highly valuable tool able to clarify possible interpretation issues of the single components. Under some stratigraphical circumstances, velocity spectra of Rayleigh waves can in fact be extremely complex in terms of energy distribution among different modes and erroneous interpretations of dispersion curves can thus occur. Beneficial aspects of the joint analysis is shown in the light of possible inconsistencies of the Pareto front, since major interpretative errors can be revealed in the outcomes of the proposed inversion procedure. Two field datasets are analysed also suggesting some improvements in the field acquisition procedures aimed at the acquisition of both Rayleigh and Love waves.  相似文献   

Spectral analysis of Swift long gamma-ray bursts with known redshift     

J. I. Cabrera  C. Firmani  V. Avila-Reese  G. Ghirlanda  G. Ghisellini  L. Nava 《Monthly notices of the Royal Astronomical Society》2007,382(1):342-355

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15–150 keV) of the Swift -BAT detector, the spectral fitting is reliable only for fitting models with two or three parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, two parameters) and cut-off power law (CPL, three parameters) models to the time-integrated spectra of the 47 bursts, and we present the corresponding parameters, their uncertainties and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the  ν f _ν  peak energy E _pk. For these GRBs, we calculate the energy fluence and the rest-frame isotropic-equivalent radiated energy,   E _γ,iso  , as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram   E '_pk  versus   E _γ,iso  . We confirm a significant correlation between these two quantities (the 'Amati' relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high-energy PL index frozen to −2.3, obtaining a rather good agreement with the 'Amati' relation of non- Swift GRBs.  相似文献   

The diffusion kinetics of CO2 in cordierite: an HT-FTIR microspectroscopy study     

Francesco Radica  Giancarlo Della Ventura  Fabio Bellatreccia  Gianfelice Cinque  Augusto Marcelli  Mariangela Cestelli Guidi 《Contributions to Mineralogy and Petrology》2016,171(2):12

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