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81.
Benoît Caron Roberto Sulpizio Giovanni Zanchetta Giuseppe Siani Roberto Santacroce 《Comptes Rendus Geoscience》2010,342(6):453-466
We present in this work a tephrostratigraphic record from a sediment piston core (JO 2004) from Lake Ohrid. Five tephra layers were recognised, all from explosive eruptions of southern Italy volcanoes. A multidisciplinary study was carried out, including stratigraphy, AMS 14C chronology and geochemistry. The five tephra layers were correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra layers already known in the central Mediterranean area. The oldest is from Pantelleria Island (P11, 131 ka BP). Other three tephra layers are from Campanian volcanoes: X6, Campanian Ignimbrite-Y5 and SMP1-Y3 (107, 39 and 31 ka BP respectively). The youngest tephra layer corresponds to the FL eruption from Etna Volcano (3.4 ka BP). In three cases these recognitions confirm previous findings in the Balkans, while two of them were for the first time recognised in the area, with a significant enlargement of the previous assessed dispersal areas. 相似文献
82.
Yves Noel Raffaella Demichelis Fabien Pascale Piero Ugliengo Roberto Orlando Roberto Dovesi 《Physics and Chemistry of Minerals》2009,36(1):47-59
The structure and vibrational spectrum of boehmite have been investigated at the quantum-mechanical level with the CRYSTAL
code, using a Gaussian-type basis set and the B3LYP Hamiltonian. Three space groups are considered in this study: Cmcm, Cmc21, P21/c. Cmcm turns out to correspond to a transition state, whereas Cmc21 and P21/c are minimum energy structures. The difference among them is the position of H atoms only, the Al-O frame being essentially
the same. Harmonic frequencies at the Γ point have been computed. The comparison between calculated and experimental frequencies
shows a good agreement for the Al-O part of the spectrum (under 790 cm−1). For the Al-OH bending modes (800–1,300 cm−1) an absolute differences of 50–100 cm−1 is observed; for the OH stretching modes (3,200–3,500 cm−1) it increases to 120–200 cm−1: anharmonicity is large because OH groups are involved in strong hydrogen bonds. 相似文献
83.
Frezzotti Maria Luce; Ferrando Simona; Dallai Luigi; Compagnoni Roberto 《Journal of Petrology》2007,48(6):1219-1241
Minerals, fluid inclusions and stable isotopes have been studiedin ultrahigh-pressure (UHP) OH-rich topazkyanite quartzitesfrom Hushan (west of Dongai), in southern Sulu (China). Thequartzites underwent a metamorphic evolution characterized bya peak stage (3·5 GPa and 730820°C) with theanhydrous assemblage coesite + kyanite I, followed by an earlynear-isothermal decompression stage (2·9 GPa and 705780°C)with growth of kyanite II, muscovite, and OH-rich topaz, andby decompression-cooling stages, represented by paragonite (1·9GPa and 700780°C) and pyrophyllite (0·3 GPaand 400°C) on kyanite (I and II) and OH-rich topaz, respectively.These rocks may exhibit unusually low 18O and D values acquiredbefore undergoing UHP metamorphism. Five distinct fluid generationsare recognized. Type I: concentrated peak solutions rich inSi, Al, and alkalis, present within multiphase inclusions inkyanite I. Type II: CaCl2-rich brines present during the growthof early retrograde OH-rich topaz. Type III, IV, and V: lateaqueous fluids of variable salinity, and rare CO2 present duringamphibolite- and late greenschist-facies conditions. A numberof conclusions may be drawn from these relationships that havean effect on fluid evolution in deeply subducted continentalrocks. (1) At a pressure of about 3·5 GPa alkalialumino-silicateaqueous solutions, with compositions intermediate between H2Ofluid and melt (H2O > 25 and 50 wt %) evolved from quartzites,probably generated by dehydration reactions. (2) During earlydecompression stages, at the transition from UHP to high-pressure(2·9 GPa) conditions, brines of external origin withhigher water contents (82 wt % H2O) initiated the growth ofOH-rich topaz and muscovite. (3) The subsequent decompression,at P <2 GPa, was defined by a limited circulation of NaClaqueous fluids, and CO2 infiltration. Overall, fluid inclusionsand stable isotopes highlight a metamorphic fluidrockinteraction characterized by internally derived intermediateaqueous solutions at UHP, followed by infiltration of Cl-richbrines with higher water activities. KEY WORDS: ultrahigh-pressure metamorphism; OH-rich topaz; fluid inclusions; stable isotopes; supercritical liquids 相似文献
84.
In the twenty-first century, around 200 notable dam and reservoir failures happened worldwide causing massive fatalities and
economic costs. In order to reduce the losses, managers usually define mitigation strategies identifying flooding area due
to dam break by using standalone hydrodynamic models and then importing the results within a GIS to perform risk analysis.
This two-step procedure is time expensive, error prone due to export/import requirements and not user friendly. For this reason
with this work, a new numerical model for the solution of the two-dimensional dam break problem has been implemented in the
GRASS GIS with a GIS-embedded approach. The model solves the conservative form of the 2D shallow water equations using a finite
volume method; the intercell flux is computed by one-side upwind conservative scheme extended to a two-dimensional problem.
The newly developed GIS module, among others outputs, allows to derive maximum intensity maps that can be directly used for
risk assessment. Finally, the model has been (1) tested against two standard synthetic problems referenced in literature showing
differences in estimated water depth of 2, 3 and 15% and (2) verified against official flooding map of an existing dam (Verzasca)
detecting 75% of similarity. The problem formulation, the new GRASS module and its validation is presented. 相似文献
85.
Prof. Dr. Roberto Malaroda 《International Journal of Earth Sciences》1964,53(1):41-57
Riassunto Nell'Autoctono sedimentario delle Alpi Marittime è stata individuata una formazione tipica, sfuggita agli autori precedenti benchè molto caratteristica ed abbastanza estesa. Si tratta perloppiù di calcari, più o meno arenacei, che contengono ciottoli di porfido quarzifero, di rocce migmatiche e di rocce sedimentarie. Ciò porta a modificare lo schema paleogeografico tradizionale ammettendo una emersione del nucleo del Massiccio dell'Argentera nel Cretaceo superiore.
In the autochtonous sedimentary beds of Alpi Marittime a typical formation is found; it is very peculiar and extends over a wide area, but until now it was unknown. The most common lithotypes represented in it are limestones with variable amounts of arenaceous material and containing pebbles of rhyolites and of migmatitic and sedimentary rocks. From these rock types a new paleogeographic scheme is strongly suggested, one in which there was the emersion of the central Argentera Massif during the late Cretaceous time.
Zusammenfassung In den autochthonen sedimentären Einheiten der Meeralpen wurde eine typische Formation entdeckt, die bis jetzt von früheren Verfassern vernachlässigt wurde. Es handelt sich meistens um mehr oder weniger sandige Kalke, die Gerölle von Quarzporphyren und von migmatischen und sedimentären Gesteinen enthalten. Das führt dazu, das bisherige paläogeographische Bild durch das Auftauchen des Kerns vom Argentera-Massiv in der Oberen Kreide abzuändern.
Résumé Dans l'Autochtone sédimentaire des Alpes-Maritimes a été découverte une formation typique, qui a échappé aux auteurs précédents, quoique étant bien caractéristique et suffisamment répandue. Il s'agit normalement de calcaires, plus ou moins gréseux, qui contiennent des galets de rhyolites, de roches migmatiques et de. roches sédimentaires. Cela conduit à modifier le schéma paléogéographique traditionnel en reconnaissant une émersion du noyau du Massif de l'Argentera dans le Crétacé supérieur.
. , .相似文献
86.
The precipitation/replacement of Ca‐phosphate is a complex process that commonly takes place during the early diagenesis in marine sediments. The unusual occurrence of shallow marine, early diagenetic phosphatic deposits associated with glassy tuffs in the Neogene Gaiman Formation, in the Chubut Province, Patagonia, Argentina, constitutes a good case example for the study of replacement and precipitation of Ca‐phosphate on an unstable substrate. Isocon diagrams illustrate that chemical changes during glass diagenesis include gains in loss on ignition and Ca, and losses of K. These changes are the result of glass hydration during sea water–glass interaction, together with adsorption and diffusion of ions into the bulk shard; combined, these represent an incipient process of volcanic glass replacement by Ca‐phosphate. Subsequent early diagenetic P enrichment in the pore solutions led to phosphate precipitation, associated with pitting on the glass shards and pumice. The associated development of a reactive surface promoted the incorporation of P and Ca into their margins. Lastly, precipitation of calcium phosphate filled the vesicles and other open cavities, inhibiting further glass dissolution. The high porosity and reactivity of the volcanic glass provided an appropriate substrate for phosphate precipitation, leading to the development of authigenic apatite concretions in the volcanic‐glass bearing strata of the Gaiman Formation. This research is of significance for those concerned with marine phosphatic deposits and sheds light on the processes of early diagenetic phosphate precipitation by replacement of an atypical, unstable substrate like hydrated volcanic glass. 相似文献
87.
Paola Sbarra Valerio De Rubeis Emiliano Di Luzio Marco Mancini Massimiliano Moscatelli Francesco Stigliano Patrizia Tosi Roberto Vallone 《Natural Hazards》2012,62(2):425-443
A detailed analysis of the earthquake effects on the urban area of Rome has been conducted for the L??Aquila sequence, which occurred in April 2009, by using an online macroseismic questionnaire. Intensity residuals calculated using the mainshock and four aftershocks are analyzed in light of a very accurate and original geological reconstruction of the subsoil of Rome based on a large amount of wells. The aim of this work is to highlight ground motion amplification areas and to find a correlation with the geological settings at a subregional scale, putting in evidence the extreme complexity of the phenomenon and the difficulty of making a simplified model. Correlations between amplification areas and both near-surface and deep geology were found. Moreover, the detailed scale of investigation has permitted us to find a correlation between seismic amplification in recent alluvial settings and subsiding zones, and between heard seismic sound and Tiber alluvial sediments. 相似文献
88.
Thomas Heymes Patrick Monié Nicolas Arnaud Arnaud Pêcher Jean-Pierre Bouillin Roberto Compagnoni 《Lithos》2010,114(3-4):451-472
This study provides new 40Ar/39Ar geochronological constraints on the age of the Alpine tectonics in the Aspromonte Massif (southern part of the Calabrian–Peloritan belt). This massif exposes the upper units of the Calabride Complex which originated from the European continental margin. The Calabride Complex was incorporated in the Alpine orogenic wedge and then integrated into the Apennines and Maghrebides fold-and-thrust belts. Throughout the Calabride Complex there is evidence for a two stage tectonic history, which remains however rather poorly dated: Alpine nappe stacking is followed by extensional reworking along the former thrust contacts or along new detachment surfaces. Our new ages suggest that exhumation of the uppermost units, which accompanied nappe stacking, probably started at 45 Ma and that the deepest units were almost completely exhumed at 33 Ma. This kinematics probably corresponds to syn-orogenic extension while the end of exhumation is clearly related to the extensional tectonics dated at 28.6 Ma along detachment structures.Our geochronological data reveal a very short lag time between accretional and extensional processes in this part of the Mediterranean Alpine orogenic belt. The direction of extension, when the units are restored to their initial position (i.e. before the opening of the Western Mediterranean basins and the bending of the arc) is NNE–SSW. Such a direction does not fit with the eastward slab-retreat model generally put forward to explain extension in the Western Mediterranean. In contrast, we provide evidence for roughly N–S middle Oligocene extension in the accretionary prism, not previously described in this part of the Mediterranean domain. 相似文献
89.
S. Kersey Sturdivant Robert J. Díaz Roberto Llansó Daniel M. Dauer 《Estuaries and Coasts》2014,37(5):1219-1232
Human development has degraded Chesapeake Bay's health, resulting in an increase in the extent and severity of hypoxia (≤2 mg O2 l-1). The Bay's hypoxic zones have an adverse effect on both community structure and secondary production of macrobenthos. From 1996 to 2004, the effect of hypoxia on macrobenthic production was assessed in Chesapeake Bay and its three main tributaries (Potomac, Rappahannock, and York Rivers). Each year, in the summer (late July???early September), 25 random samples of the benthic macrofauna were collected from each system, and macrobenthic production in the polyhaline and mesohaline regions was estimated using Edgar's allometric equation. Fluctuations in macrobenthic production were significantly correlated with dissolved oxygen. Macrobenthic production was 90 % lower during hypoxia relative to normoxia. As a result, there was a biomass loss of ~7,320–13,200 metric tons C over an area of 7,720 km2, which is estimated to equate to a 20 % to 35 % displacement of the Bay's macrobenthic productivity during the summer. While higher consumers may benefit from easy access to stressed prey in some areas, the large spatial and temporal extent of seasonal hypoxia limits higher trophic level transfer, via the inhibition of macrobenthic production. Such a massive loss of macrobenthic production would be detrimental to the overall health of the Bay, as it comes at a time when epibenthic and demersal predators have high-energy demands. 相似文献
90.
János Kovács Szabolcs Á. Fábián Gábor Varga Karoly Németh Corina Risso Francisco Nullo Gabor Kereszturi Titusz Bugya Szabolcs Á. Fábián Noémi L. Görcs István P. Kovács Bertalan Radvánszky Gabriella Barta Rudolf Musil Alice Ghiselli Marzio Merazzi Andrea Strini Roberto Margutti Michele Mercuriali Rauf Gardashov Daria Gushchina Boris Dewitte Martin Michálek Marián Putiš Christoph A. Hauzenberger Jindřich Šancer Martin Štrejbar Aneta Maleňáková George Migiros George D. Bathrellos Hariklia D. Skilodimou Theodoros Karamousalis 《Central European Journal of Geosciences》2011,3(2):229-229