Proceedings of the Workshop,Bridging the Gap II: Effect of Target Properties on the Impact Cratering Process     

Robert Herrick  Gordon Osinski  Elisabetta Pierazzo 《Meteoritics & planetary science》2008,43(12):1915-1916

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A Global Inventory of Burned Areas at 1 Km Resolution for the Year 2000 Derived from Spot Vegetation Data     

Kevin Tansey  Jean-Marie GrÉgoire  Elisabetta Binaghi  Luigi Boschetti  Pietro Alessandro Brivio  Dmitry Ershov  StÉphane Flasse  Robert Fraser  Dean Graetz  Marta Maggi  Pascal Peduzzi  JOsÉ Pereira  JoÃo Silva  AdÉlia Sousa  Daniela Stroppiana 《Climatic change》2004,67(2-3):345-377

Biomass burning constitutes a major contribution to global emissions of carbon dioxide, carbon monoxide, methane, greenhouse gases and aerosols. Furthermore, biomass burning has an impact on health, transport, the environment and land use. Vegetation fires are certainly not recent phenomena and the impacts are not always negative. However, evidence suggests that fires are becoming more frequent and there is a large increase in the number of fires being set by humans for a variety of reasons. Knowledge of the interactions and feedbacks between biomass burning, climate and carbon cycling is needed to help the prediction of climate change scenarios. To obtain this knowledge, the scientific community requires, in the first instance, information on the spatial and temporal distribution of biomass burning at the global scale. This paper presents an inventory of burned areas at monthly time periods for the year 2000 at a resolution of 1 kilometer (km) and is available to the scientific community at no cost. The burned area products have been derived from a single source of satellite-derived images, the SPOT VEGETATION S1 1 km product, using algorithms developed and calibrated at regional scales by a network of partners. In this paper, estimates of burned area, number of burn scars and average size of the burn scar are described for each month of the year 2000. The information is reported at the country level. This paper makes a significant contribution to understanding the effect of biomass burning on atmospheric chemistry and the storage and cycling of carbon by constraining one of the main parameters used in the calculation of gas emissions.  相似文献   

Late Barremian to early Aptian calcareous nannofossil paleoceanography and paleoecology from the Ocean Drilling Program Hole 641C (Galicia Margin)     

Fabrizio Tremolada  Elisabetta Erba  Timothy J. Bralower 《Cretaceous Research》2006,27(6):887-897

Calcareous nannofossil assemblages at Site 641C (Galicia Margin, North Atlantic) were investigated in order to determine changes in fertility and temperature of surface waters. Taxa such as Zeughrabdotus spp. <3.5 μm, Biscutum constans, Discorhabdus rotatorius and Diazomatolithus lehmanii, which thrived in higher fertility conditions, are particularly abundant across the CM0 interval as opposed to those with oligotrophic affinities such as Watznaueria spp. and Nannoconus spp., which are generally reduced in abundance. The abundances of nannoconids are much lower than those observed in Tethyan sections, indicating higher fertility conditions. Slumpings and low recovery prevent the identification of the onset of the “nannoconid crisis”, but a sharp drop in nannoconid abundances, observed prior to the CM0 interval, correlates with the “nannoconid decline” observed in several Tethys sections.The normalized ratio between low and high fertility taxa (Fertility Index) was used to characterize the nannofossil assemblages in terms of productivity changes. The highest values of the Fertility Index were observed across magnetic chron CM0. The paucity of cold water taxa such as Seribiscutum spp. and Repagulum parvidentatum suggests warm water conditions throughout the deposition of upper Barremian–lower Aptian sediments on the Galicia Margin.  相似文献   

Melt- versus fluid-induced metasomatism in spinel to garnet wedge peridotites (Ulten Zone, Eastern Italian Alps): clues from trace element and Li abundances     

M. Scambelluri  J. Hermann  L. Morten  E. Rampone 《Contributions to Mineralogy and Petrology》2006,151(4):372-394

The peridotite bodies of the Ulten Zone (Upper Austroalpine, Italian Eastern Alps) are enclosed in Variscan migmatites and derive from a mantle wedge environment. They display the progressive transformation of porphyroclastic spinel peridotites (T=1,200°C; P=1.5 GPa) into fine-grained garnet–amphibole peridotites (T=850°C; P=3 GPa). Detailed bulk-rock and mineral trace element analyses of a sample suite documenting the entire metamorphic evolution of the peridotites revealed several stages of metasomatism. The spinel peridotites derive from a depleted mantle that became enriched in some large ion lithophile element (LILE) and light rare earth elements (LREE). The same signature pertains to clinopyroxene and orthopyroxene, indicating that this metasomatic signature was acquired at the recorded temperature of 1,200°C. Such a temperature is considerably above the wet peridotite solidus and hence the metasomatic agent must have been a hydrous melt. Moreover, the Li-enrichment of the spinel-facies pyroxenes (up to 24 ppm Li) reflects disequilibrium distribution after exchange with a presumably mafic melt. ^cpx/opx D _Li=3–7 and ^cpx/ol D _Li=2.7–8 indicate that the spinel-facies clinopyroxene hosts higher Li amounts than the coexisting minerals. LREE fractionation, variable LREE enrichment, LILE enrichment with respect to HFSE (average clinopyroxene Pb _N /Nb _N =16–90) in spinel lherzolites can be related to chromatographic effects of porous melt flow. The significant enrichment of pyroxenes from the spinel lherzolites in Pb, U and Li indicates that the metasomatic melt was subduction-related. All these features suggest that the spinel lherzolites formed a mantle wedge layer percolated by melts carrying recycled crustal components and rising from a deeper source of subduction magmas. The garnet + amphibole peridotites equilibrated at temperatures well below the wet solidus in the presence of an aqueous fluid. Bulk-rock trace element patterns display pronounced positive anomalies in Cs, Ba, Pb and U and moderate enrichment in Li, indicating addition of a crustal component to the mantle rocks. Amphibole hosts most of these trace elements. Clinopyroxene displays high LILE/HFSE (Pb _N /Nb _N =300–600), low Ce/Pb (1.4–2.7 in garnet-facies clinopyroxene compared with 2.6–24.5 in the spinel-facies one) and variable LILE and LREE enrichments. The coupled increase of modal amphibole, Sr and Pb, together with positive Pb–Sr and Pb–U correlations, further indicate that incompatible element influx in these samples was fluid-mediated. In the garnet-facies samples, amphibole and, interestingly, olivine have similarly high Li concentrations as clinopyroxene, leading to ^cpx/amph D _Li=0.7 and ^cpx/ol D _Li=0.7–0.8, the latter being up to ten times lower than in the spinel-facies rocks. Due to its high modal abundance, olivine is the main host of Li in the garnet–amphibole peridotites. The observed metasomatic features provide evidence for the infiltration of an aqueous fluid in the mantle wedge above a subducting slab. This fluid most likely derived from subducted crustal rocks that underwent partial melting. Successive retrograde re-equilibration during exhumation of the garnet peridotite is accompanied by garnet and clinopyroxene breakdown and amphibole formation. This process produced minor changes, such as an increase of HREE and Li in amphibole, and an increase of Li in olivine. The general trace element signature remains essentially unchanged during retrogression and further hydration, indicating that fluids with a similar composition to the one present at the garnet–amphibole peridotite formation, were responsible for increased amphibole formation. The combined evidence from the metamorphic and metasomatic evolution indicates that the peridotites experienced first corner flow in a mantle wedge, followed by subduction and finally entrapment and exhumation within a crustal slab. During their entire history the Ulten peridotites were percolated first by melts and then by aqueous fluids, which added recycled crustal components to the mantle wedge.  相似文献   

Occurrence of minor toxic elements in volcanic-sedimentary aquifers: a case study in central Italy     

Raffaella Vivona  Elisabetta Preziosi  Benoît Madé  Giuseppe Giuliano 《Hydrogeology Journal》2007,15(6):1183-1196

The occurrence of minor toxic elements (arsenic, vanadium and fluoride among others) in the volcanic aquifers of central Italy, with concentrations often above the national standards for drinking waters, has been recognized since the 1970s. However, these groundwaters are still often used for human consumption. With the aim of providing insight into the water–rock interaction processes, as well as into the evolution of arsenic and other elements, water-sampling campaigns where undertaken within a 100 km² area at the eastern margin of the Viterbo region, where volcanites overlie an alluvial aquifer complex. The samples were analysed and geochemical modelling was applied to characterize the thermodynamic state of the waters. The results indicate the existence of direct relations among arsenic, vanadium and fluoride concentrations and of their inverse relationship with calcium concentration. An evolution scheme of groundwater composition from the upstream volcanic aquifer to the downstream sedimentary aquifer is also discussed. Two hypotheses are proposed which justify the observed decrease of the cited minor element concentrations, i.e. dilution processes and/or precipitation of fluorapatite, which can include in its structure small amounts of these elements. The precipitation hypothesis is supported by modelling results.  相似文献   

Geomorphological, paleontological and Sr/Sr isotope analyses of early Pleistocene paleoshorelines to define the uplift of Central Apennines (Italy)     

Marco Mancini  Elisabetta D'Anastasio  Mario Barbieri  Paolo Marco De Martini   《Quaternary Research》2007,67(3):487-501

The eastern border of the Middle Valley of the Tiber River is characterized by several Plio-Pleistocene paleoshorelines, which extend for about 100 km along the western margin of the Central Apennines (Italy). We studied these paleoshorelines by the means of geological and paleontological analyses and new ⁸⁷Sr/⁸⁶Sr isotope analyses. The youngest and uppermost paleoshorelines have been detected and mapped through detailed geologic and stratigraphic surveys, which led to the recognition of nearshore deposits, cliff breccias, alignments of Lithophaga borings, fossil abrasion notches and wave-cut platforms. The altitude of these paleoshorelines decreases almost regularly in the NNW–SSE direction from 480 to 220 m a.s.l. Measurements of the ⁸⁷Sr/⁸⁶Sr isotope ratio have been conducted on corals and mollusks collected from sediments outcropping close to the paleoshorelines. The isotopic dating results indicate numerical values that range between 0.70907 and 0.70910 all over the 100-km outcrop. These results, together with biostratigraphic data, constrain the age of the youngest paleoshorelines to 1.65–1.50 Ma. These paleoshorelines are thus considered almost isochronous, giving an estimated uplift rate of 0.34–0.17 ± 0.03 mm/a moving from NNW to SSE. Shape, length and continuity of the 100-km-long observed movements indicate that the studied paleoshorelines are an important marker of the Quaternary uplift of the Central Apennines.  相似文献   

The Valanginian carbon isotope event: a first episode of greenhouse climate conditions during the Cretaceous   总被引：1，自引：0，他引：1  

Andrea Lini  Helmut Weissert  Elisabetta Erba 《地学学报》1992,4(3):374-384

Lower Cretaceous pelagic carbonates outcropping along the Southern Alps of northern Italy provide a record of Tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle. The carbonate C-isotope stratigraphy established at five selected localities in the Southern Alps allows an accurate picture to be drawn of the duration and amplitude of the Valanginian C-isotope event. δ¹³C values near 1.25–1.50% determined in Berriasian and lower Valanginian sediments are replaced by more pdsitive δ¹³C values near 3% in the late Valanginian. The carbonate C-isotope excursion ends in the early Hauterivian with values fluctuating between 1.5% and 2%. The carbonate C-isotope excursion is accompanied by a positive excursion in the total organic carbon C-isotope curve. The Valanginian C-isotope excursion identified in Tethyan sediments correlates with a C-isotope excursion recorded in the western North Atlantic, in the Gulf of Mexico, and in the Central Pacific (DSDP Sites 534,391,535 and 167). By analogy with the Aptian stage, also marked by a significant positive C-isotope excursion, the time of positive δ¹³C values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments. A warm and humid climate, possiblycoupled with a high atmospheric CO₂ content and a high global sea-level, may have triggered the acceleration of the global carbon cycling. In this case the Valanginian C-isotope event would reflect a first episode of Greenhouse Earth conditions during the Cretaceous.  相似文献   

Advanced numerical modeling of seismic response of a propped r.c. diaphragm wall     

Chiara Miriano  Elisabetta Cattoni  Claudio Tamagnini 《Acta Geotechnica》2016,11(1):161-175

The paper presents some results from a number of dynamic FE simulations carried out to investigate the seismic response of a propped flexible retaining wall in a dry coarse-grained soil, considering two bedrock acceleration time histories as seismic input. Two different soil plasticity models have been considered in this study: an anisotropic hardening, critical-state model for cyclic/dynamic loading of sands and the classical Mohr–Coulomb elastic-perfectly plastic model with nonassociative flow rule. The results obtained allow to highlight the main features of the seismic performance of such type of flexible retaining structures and to evaluate the effects of the constitutive assumptions made on soil behavior on the predicted wall displacements and structural loads.  相似文献   

Paleomagnetic analysis of curved thrust belts reproduced by physical models     

Elisabetta Costa  Fabio Speranza   《Journal of Geodynamics》2003,36(5):633-654

This paper presents a new methodology for studying the evolution of curved mountain belts by means of paleomagnetic analyses performed on analogue models. Eleven models were designed aimed at reproducing various tectonic settings in thin-skinned tectonics. Our models analyze in particular those features reported in the literature as possible causes for peculiar rotational patterns in the outermost as well as in the more internal fronts. In all the models the sedimentary cover was reproduced by frictional low-cohesion materials (sand and glass micro-beads), which detached either on frictional or on viscous layers. These latter were reproduced in the models by silicone. The sand forming the models has been previously mixed with magnetite-dominated powder. Before deformation, the models were magnetized by means of two permanent magnets generating within each model a quasi-linear magnetic field of intensity variable between 20 and 100 mT. After deformation, the models were cut into closely spaced vertical sections and sampled by means of 1×1-cm Plexiglas cylinders at several locations along curved fronts. Care was taken to collect paleomagnetic samples only within virtually undeformed thrust sheets, avoiding zones affected by pervasive shear. Afterwards, the natural remanent magnetization of these samples was measured, and alternating field demagnetization was used to isolate the principal components. The characteristic components of magnetization isolated were used to estimate the vertical-axis rotations occurring during model deformation. We find that indenters pushing into deforming belts from behind form non-rotational curved outer fronts. The more internal fronts show oroclinal-type rotations of a smaller magnitude than that expected for a perfect orocline. Lateral symmetrical obstacles in the foreland colliding with forward propagating belts produce non-rotational outer curved fronts as well, whereas in between and inside the obstacles a perfect orocline forms only when the ratio between obstacles' distance and thickness of the cover is greater than 10. Finally, when a belt collides with an obstacle in the foreland oblique to the shortening direction the outer front displays rotations opposite in sign to oroclinal-type rotations, whereas the internal fronts seem to assume an “oroclinal type” rotational pattern. Furthermore rotation is easier in laterally unconfined models, i.e. when the wedge can “escape” laterally. The results from our models may be useful when compared to paleomagnetic rotations detected in natural arcs. In these cases, our results may allow for better understanding the tectonic setting controlling the genesis of curved mountain fronts, as is the case of the Gela Nappe of Sicily we compare with some of our models.  相似文献   

Deep mid-water bacterial mats from anoxic basins of the Eastern Mediterranean     

Elisabetta Erba 《Marine Geology》1991,100(1-4):83-101

Peculiar pellicles have been recorded in the extant anoxic hypersaline basins of the Bannock area and the Western Strabo Trench (Eastern Mediterranean). Discrete layers of pellicles were found in 29 cores. They are oriented parallel to bedding planes or are folded within the sandy base of turbidites and within slumped sediments. In addition, similar pellicles occur at the surface of or interlocked within gypsum crystals recovered from the Bannock area.

The pellicles are 0.5–3 mm thick and dark greenish-grey in colour. They foliate into very small (<1 mm) undulating and anastomosing microlaminae entrapping abundant biogenic and inorganic particles. The amorphous organic matter of the pellicles is most probably produced by bacterial masses linked to mineralization processes of the organic debris. Anaerobic sulphate-reducing bacteria (Desulphovibrio) are abundant and the presence of methane bacteria is likely.

Detailed analyses with the light microscope and scanning electron microscope yielded differences and similarities concerning ultrastructure, content, abundance and morphotypes of the bacterial pellicles from the Bannock area and the Western Strabo Trench. A consistently well-developed ultrastructure comprising thin microlaminae characterizes the Bannock pellicles, whereas the ultrastructure of the Tyro and Poseidon pellicles is usually not organized. Siliceous microfossils are abundant in samples from both sites, but centrate diatoms prevail in the Bannock pellicles whereas pennate diatoms are overwhelmingly dominant in the Tyro and Poseidon pellicles. Calcareous micro- and nannofossils, together with pyrite framboids, are more abundant in samples from the Bannock area. Bacteria are extremely abundant in samples from the Bannock area and three different morphological types have been distinguished. Only one type of bacteria was commonly observed in pellicles from the Western Strabo Trench basins.

Pellicles form at the normal seawater/brine interface, as substantiated by transmittance profiles and bacteriological investigations. Therefore, the term “deep mid-water bacterial mats” is proposed herein for these peculiar layers.

After bacterial mats grow at the interface, they are included within the sediments by following one of two different paths: (a) when pelagic sedimentation prevails, pellicles sink to the basin floor due to the increasing load of biogenic and inorganic detritus, and (b) under a tectonically active regime, turbidity currents and slumps can disrupt the interface and destroy the floating mats. In the latter case, fragments of pellicles are transported to the bottom within the gravity flows.  相似文献