Non‐impact origin of the crater‐like structures in the Gilf Kebir area (Egypt): Implications for the geology of eastern Sahara     

Letizia ORTI  Mario DI MARTINO  Marco MORELLI  Corrado CIGOLINI  Enrico PANDELI  Alessandra BUZZIGOLI 《Meteoritics & planetary science》2008,43(10):1629-1639

Abstract— Several small crater‐like structures occur in Gilf Kebir region (SW Egypt). It has been previously suggested that they could be the result of meteoritic impacts. Here we outline the results of our geological and geophysical survey in the area. The proposed impact origin for these structures is not supported by our observations and analyses, and we suggest an alternative interpretation. The crater‐like structures in Gilf Kebir area are likely related to endogenic processes typical of hydrothermal vent complexes in volcanic areas which may reflect the emplacement of subvolcanic intrusives.  相似文献   

Horizontal cladding panels: in-plane seismic performance in precast concrete buildings   总被引：1，自引：1，他引：0  

Andrea Belleri  Mauro Torquati  Alessandra Marini  Paolo Riva 《Bulletin of Earthquake Engineering》2016,14(4):1103-1129

The paper investigates the in-plane performance of horizontal precast reinforced concrete cladding panels, typically adopted in one-storey precast industrial and commercial buildings. Starting from in-field observations of cladding panels failures in recent earthquakes, the seismic performance of typical connections is evaluated by means of experimental tests on full-scale panels under quasi-static cyclic loading. The failure mechanisms highlight the vulnerability of such connections to relative displacements and, therefore, the need to accurately evaluate the connections displacement demand and capacity. An analytical model is developed to describe the force–displacement relationship of the considered connections and compared to the experimental results. In order to determine the seismic vulnerability of such connections and provide design recommendations, linear and nonlinear analyses are conducted taking as reference a precast concrete structure resembling an industrial precast building. The results of the analyses show the importance of a correct estimation of the column’s lateral stiffness in the design process and how an improper erection procedure leads to a premature failure of such connections.  相似文献   

The Pliocene‐Quaternary wedge‐top basins of southern Italy: an expression of propagating lateral slab tear beneath the Apennines     

Alessandra Ascione  Sabatino Ciarcia  Valentino Di Donato  Stefano Mazzoli  Stefano Vitale 《Basin Research》2012,24(4):456-474

In recent years, contrasting seismic tomographic images have given rise to an extensive debate about the occurrence and implications of migrating slab detachment beneath southern Italy. One of the most pertinent aspects of this process is the concentration of the slab pull force, and particularly its surface expression in terms of vertical motions and related basin subsidence/uplift. In this study we focused on shallow‐water to continental, Pliocene‐Quaternary basins that formed on top of the Apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain (Apulian Platform). Due to the thick‐skinned style of deformation controlling the Pliocene‐Pleistocene stages of continental shortening, a high degree of coupling with the downgoing plate appears to characterize the late tectonic evolution of the southern Apennines. Therefore, the wedge‐top basins analysed in this study, although occurring on the deformed edge of the overriding plate, are capable of recording deep geodynamic processes affecting the slab. Detailed stratigraphic work on these wedge‐top basins points to a progressive SE‐ward migration of basin subsidence from c. 4 to c. 2.8 Ma over a distance of about 140 km along the strike of the Apennine belt. Such a migration is consistent with a redistribution of slab‐pull forces associated with the progressive lateral migration at a mean rate in the range of 12–14 cm y^–1 of a slab tear within the down‐going Adriatic lithosphere. These results yield fundamental information on the rates of first‐order geodynamic processes affecting the slab, and on related surface response.  相似文献   

Tectonics,sea-level changes and palaeoenvironments in the early Pleistocene of Rome (Italy)     

Domenico Cosentino  Paola Cipollari  Letizia Di Bella  Alessandra Esposito  Costanza Faranda  Guido Giordano  Elsa Gliozzi  Massimo Mattei  Ilaria Mazzini  Massimiliano Porreca  Renato Funiciello 《Quaternary Research》2009,72(1):143-155

The historical site of the Monte Mario lower Pleistocene succession (Rome, Italy) is an important marker of the Pliocene/Pleistocene boundary. Recently, the Monte Mario site was excavated and restudied. A spectacular angular unconformity characterizes the contact between the Monte Vaticano and the Monte Mario formations, which marks the Pliocene/Pleistocene boundary. Biostratigraphical analyses carried out on ostracod, foraminifer, and calcareous nannofossil assemblages indicate an Early Pliocene age (topmost Zanclean, 3.81–3.70 Ma) for the underlying Monte Vaticano Formation, whereas the Monte Mario Formation has been dated as early Pleistocene (Santernian, 1.66–1.59 Ma). Palaeomagnetic analyses point to C2Ar and C1r2r polarity chrons for the Monte Vaticano and the Monte Mario formations, respectively. The Monte Mario Formation consists of two obliquity-forced depositional sequences (MM1 and MM2) characterized by transgressive systems tracts of littoral marine environments at depths, respectively, of 40–80 m and 15–20 m. The data obtained from foraminifer and ostracod assemblages allow us to reconstruct early Pleistocene relative sea-level changes near Rome. At the Plio/Pleistocene transition, a relative sea-level drop of at least 260 m occurred, as a result of both tectonic uplift of the central Tyrrhenian margin and glacio-eustatic changes linked to early Pleistocene glaciation (Marine Isotope Stage 58).  相似文献   

Abiotic and Biotic Links Work Two Ways: Effects on the Deposit at the Cliff Foot Induced by Mechanical Action of Date Mussel Harvesting (<Emphasis Type="Italic">Lithophaga lithophaga</Emphasis>)   总被引：1，自引：0，他引：1  

Alessio Rovere  Stefano Bellati  Valeriano Parravicini  Marco Firpo  Carla Morri  Carlo Nike Bianchi 《Estuaries and Coasts》2009,32(2):333-339

The existence of linkages between ecological and geomorphological processes and the influence of human activities both on the biota and on geomorphology is well known for terrestrial environments, while it has been seldom reported for submerged ones. A survey in the Noli-Bergeggi area (NW Mediterranean Sea) has been carried out to test the hypothesis that the harvesting of Lithophaga lithophaga has an impact not only on the hammered rock, but also on the sediments at the cliff foot. Size and roundness of pebbles have been measured at different stations and statistical analyses have been used to test the differences between impact and control situations. Results show a dependence of the roundness of pebbles on the date mussel harvesting, indicating a decrease both of the roundness index and of its variability at the cliff foot in impacted sites. Conclusions stress the biogeomorphological nature of this activity, not limited to the present location.  相似文献   

New algorithms for shoreline monitoring from coastal video systems     

Nico Valentini  Alessandra Saponieri  Matteo Gianluca Molfetta  Leonardo Damiani 《Earth Science Informatics》2017,10(4):495-506

Video systems have become widely used all around the world in coastal monitoring strategies, allowing both high temporal and spatial sampling frequency, with low logistic and costs efforts. The present paper deals with a new tool for coastal images processing, aimed at the automatic shoreline detection and data analysis. The tool is composed by a shoreline detection routine implemented in a web-application, addressed at images processing (i.e. shoreline extraction and geo-rectification), data analysis and sharing results about beach actual state and shore evolution in quasi-real time. The Shoreline Detection Model (SDM) is based on a new algorithm, implementing image-processing procedures, which allows extracting the sea/land boundary from automatic segmented Timex images. The SDM calibration and validation has been performed on different coastal images derived from a video monitoring system installed at Alimini (Lecce, IT) in 2005, by comparing automatic shoreline contours with the manual detected ones. Moreover, in December 2015, new video monitoring systems were installed in South Italy (Porto Cesareo and Torre Canne, Apulia region), at sandy beaches affected by erosion phenomena. The application of the SDM on images recorded by the new systems has allowed testing the model feasibility at sites characterized by different morphological features and geographical exposition. The present describes in detail the SDM algorithm and the image processing procedures used. The results of the model calibration and validation performed at Alimini and the tests performed at Porto Cesareo on first images are reported.  相似文献   

Can plankton communities be considered as bio-indicators of water quality in the Lagoon of Venice?   总被引：4，自引：0，他引：4  

Bianchi F  Acri F  Aubry FB  Berton A  Boldrin A  Camatti E  Cassin D  Comaschi A 《Marine pollution bulletin》2003,46(8):964-971

This study examines whether plankton of the Lagoon of Venice could be considered as a bio-indicator of areas subjected to various anthropogenic influences. This study was a two year hydrochemical and biological survey in five areas of the Lagoon of Venice, each with different environmental conditions due to pollution from urban, industrial, thermal and agricultural wastes. Phytoplankton associations did not show any promising species. In the different lagoonal areas, this community was differentiated into its major groups. In contrast, the copepod Acartia tonsa Dana could be considered as a target species in highly eutrophic areas.  相似文献   

Novel decomposition products of chlorophyll-a in continental shelf (Louisiana shelf) sediments: formation and transformation of carotenol chlorin esters     

Nianhong Chen  Thomas S. Bianchi 《Geochimica et cosmochimica acta》2003,67(11):2027-2042

In April 2000, we collected box cores from five stations along a cross-shelf transect on the Louisiana (LA) continental shelf. Novel esters of carotenols and chlorins (carotenoid chlorin esters, CCEs), which are highly specific grazing markers, were identified in surface and deep sediments (>10 cm) from the LA shelf. Chlorophyll-a inventory indicated that CCEs are one of the major decay products of chlorophyll-a in shelf sediments. Abundances of total CCEs (9-18%) in surface sediments along the cross-shelf transect were comparable to the abundance of pheophytin-a, pyropheophytin-a, and total steryl chlorin esters (SCEs). Prior work has identified four CCEs which have dehydrated fucoxanthin/fucoxanthinol as a substitute alcohol of phytol. We report on four newly identified CCEs associated with nondehydrated fuxocanthin/fucoxanthinol esterified to (pyro)pheophorbide-a. These nondehydrated CCEs were generally present in lower concentrations than their dehydrated counterparts, but were detectable by atmospheric pressure chemical ionization (APCI) mass spectrometry coupled with high-performance liquid chromatography (HPLC). We attributed differences between this study and previous work to the time allowed for predepositional decay and grazing processes to occur. The rapid sedimentation of CCEs in the shallow water column (ca. 10 m) on the LA shelf allowed for effective burial of all CCEs compared to the deeper water column regions sampled by previous work. This speculation is supported by the fact that the concentrations of CCEs with nondehydrated fucoxanthin/fucoxanthinol were extremely low in sediments from the site on the outer LA shelf with a deeper (253 m) water column. We also tentatively identified an additional CCE and its isomer as fucoxanthinol didehydrate pyropheophorbide-a ester. We suggest that the formation and transformation of CCEs are primarily controlled by the following three biologically mediated reactions: demethoxycarbonylation, dehydration, and deacetylation. Our laboratory copepod grazing experiment also confirmed that CCEs can be excellent class-specific biomarkers of zooplankton grazing on phytoplankton.  相似文献   

Effects of three oil spill dispersants on marine bacterial populations: I. Preliminary Study. Quantitative Evolution of Aerobes     

Danielle Marty  Armand Bianchi  Claude Gatellier 《Marine pollution bulletin》1979,10(10):285-287

The effects of three hydrocarbon dispersant agents (Corexit 9527, Hydrogamosol LT and OSR LT 126) on the bacterial flora of the marine environment are analysed in 20-square-metre basins filled with lagoon seawater.Four months after the first treatment, oil slicks were no longer visible, whereas the appearance of the untreated reference slick had hardly changed. The treatment of 10-litre crude-oil slicks causes an appreciable and long lasting increase in the bacterial population.  相似文献   

A Systematic Study of the Stability of Symmetric Periodic Orbits in the Planar, Circular, Restricted Three-Body Problem     

Alessandra Celletti  Andrea Chessa  John Hadjidemetriou  Giovanni Battista Valsecchi 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):239-255

We investigate symmetric periodic orbits in the framework of the planar, circular, restricted, three-body problem. Having fixed the mass of the primary equal to that of Jupiter, we determine the linear stability of a number of periodic orbits for different values of the eccentricity. A systematic study of internal resonances, with frequency p/q with 2p 9, 1 q 5 and 4/3 p/q 5, offers an overall picture of the stability character of inner orbits. For each resonance we compute the stability of the two possible periodic orbits. A similar analysis is performed for some external periodic orbits.Furthermore, we let the mass of the primary vary and we study the linear stability of the main resonances as a function of the eccentricity and of the mass of the primary. These results lead to interesting conclusions about the stability of exosolar planetary systems. In particular, we study the stability of Earth-like planets in the planetary systems HD168746, GI86, 47UMa,b and HD10697.  相似文献