Current channelling and three-dimensional effects detected from magnetotelluric data from a sedimentary basin in Sierras Pampeanas, Argentina     

C. Pomposiello  A. Osella  A. Favetto  C. Sainato  P. Martinelli  & C. Aprea 《Geophysical Journal International》1998,135(2):339-350

Aquifer-bearing intermontane sedimentary basins of the Sierras Pampeanas in the northwest of Argentina are in general very deep and narrow and contain economically important deposits of Tertiary sediments. This paper presents the results of a study to characterize the sedimentary basin bounded to the west by Sierra de Famatina and to the east by Sierra de Velasco, where an electromagnetic sensing technique, the magnetotelluric (MT) method, was applied. 12 MT sites were deployed along a 30  km E–W transect. Some of the data collected were used to derive a 2-D resistivity model of the basin. The model shows a subsurface trough with a thick (approximately 8  km) sedimentary sequence above it. Anomalous behaviour of the E–W electric-field component ( E _y ) was detected in the period range 1–100  s, where the amplitude of this component was below the instrumental noise level. The cause of this anomaly is not known, but it might be due to the presence of an embedded conducting body between 8 and 10  km, which would give rise to N–S current channelling.  相似文献   

Development and erosion in the Brazilian Amazon: A geochronological case study     

Dr. Bruce Forsberg  Dr. Jose Marcus Godoy  Dr. Reynaldo Victoria  Dr. Luiz Antonio Martinelli 《GeoJournal》1989,19(4):399-405

A ²¹⁰Pb chronology of sedimentation in a small floodplain lake in the Jamari river basin (Rondonia, Brazil) provided insight into the relationship between development and erosion in the Brazilian Amazon. Positive correlations between increased sedimentation in the lake and levels of deforestation and mining in the Jamari basin suggested a major increase in erosion associated with these activities. This increase in erosion could diminish agricultural yields in the basin and significantly reduce the useful life of a hydro-electric plant recently built on the river.  相似文献   

Spatial and temporal variations in soil chemistry on the Amazon floodplain     

Reynaldo L. Victoria Dr.  Luiz A. Martinelli  Jeffrey E. Richey Dr.  Allan H. Devol Dr.  Bruce R. Forsberg Dr.  Maria N. G. Ribeiro 《GeoJournal》1989,19(1):45-52

Soil samples were collected on the floodplains of the Amazon River and its principal Brazilian tributaries during dry, early rising water, and early falling water periods. The concentrations of basic cations and pH in these alluvial soils were always higher than those in the more common terra firme soils while the concentrations of aluminum were generally lower. Among the alluvial soils, those from the main channel floodplain were generally higher in basic cations and pH, and lower in aluminum than those from the tribuary floodplains. The concentrations of basic cations in soils along the main channel floodplain decreased downstream. No significant difference was found in the levels of basic cations, pH, or aluminum between sampling periods.  相似文献   

Subsidence rates in the Po Plain, northern Italy: the relative impact of natural and anthropogenic causation   总被引：1，自引：0，他引：1  

E. Carminati  G. Martinelli 《Engineering Geology》2002,66(3-4):241-255

The central-eastern Po Plain in northern Italy is a rapidly subsiding sedimentary basin that hosts about 30% of the Italian population and 40% of Italy's total productive activities. Subsidence rates range from 0 to −70 mm/year, the maximum occurring in synclinal areas at the Po Delta and near Bologna, the minimum located at the top of buried, probable tectonically active anticlines (Mirandola–Ferrara). We show that modern subsidence is at least an order of magnitude higher than due solely to long-term natural processes. This implies that most subsidence in the Po Plain has been induced by human activities. As previously noted, we suggest that the main factor controlling modern subsidence is water withdrawal, which was particularly intense during the second half of the 20th century, coinciding with accelerating economic growth. We also evaluate the impact of rapid subsidence on floods in low areas by comparing subsidence velocity maps with flood maps. This shows that there is a clear-cut correlation between flood frequency and rapid subsidence. In contrast, few floods occurred in low subsidence areas, which generally correspond with the top of buried anticlines. We finally note that the anthropic-caused increase in subsidence has now greatly increased the potential for additional floodings.  相似文献   

Post-seismic relaxation and earthquake triggering in the southern Adriatic region   总被引：1，自引：0，他引：1  

Marcello Viti  Francesca D'Onza  Enzo Mantovani  Dario Albarello  Nicola Cenni 《Geophysical Journal International》2003,153(3):645-657

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Modelling electromagnetic responses of 2-D structures due to spatially non-uniform inducing fields. Analysis of magnetotelluric source effects at coastlines     

Patricia Martinelli  Ana Osella 《Geophysical Journal International》2003,155(2):623-640

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Notes on fossil remains from the Early Cretaceous Lohan Cura Formation, Neuquén Province, Argentina     

Agustín G. Martinelli  Alberto C. Garrido  Analía M. Forasiepi  Ernesto R. Paz  Yamila Gurovich 《Gondwana Research》2007,11(4):537-552

In this contribution, we describe an association of fossil remains collected in the locality of Cerro de Los Leones, approximately 8 km southwest of the town of Picún Leufú, Neuquén Province, Argentina, from different levels of the Albian Cullín Grande Member, Lohan Cura Formation. The fossils include pelecypodan (Neocorbicula dinosauriorum, Neocorbicula pehuenchensis, and genus indet.) and gastropodan (Physa wichmanni) molluscs, a mesoeucrocodylian, possible pterosaurs, theropods, and sauropods. The sedimentary environment at Cerro de los Leones is characterized by fluvial deposits corresponding to a sandy meandering fluvial system. The most fossiliferous levels (located in the lower part of the exposed sequence) were developed in a distal flood plain and flood basin areas. Sedimentological and paleopedological features suggest semi-arid conditions during the deposition of the Cullín Grande Member. Despite the fragmentary nature of the specimens described here, the new information provided from the Albian assemblages of the Lohan Cura Formation at the Cerro de Los Leones locality provides a broader panorama of the composition of terrestrial faunas during the Early Cretaceous in Patagonia.  相似文献   

Clinopyroxene of spinel-peridotite mantle xenoliths from Lake Nji (Cameroon Volcanic Line, W Africa): crystal chemistry and petrological implications     

Francesco Princivalle  Gabriella Salviulo  Andrea Marzoli  Enzo M. Piccirillo 《Contributions to Mineralogy and Petrology》2000,139(5):503-508

The crystal chemistry of six clinopyroxenes enclosed in protogranular spinel-peridotite mantle xenoliths from Lake Nji (Cameroon, W Africa) was studied by means of single-crystal X-ray diffraction and electron microprobe. These spinel-peridotite xenoliths are characterised by clinopyroxene contents distinctly higher than those reported by Lee et al. (1996) for spinel-peridotite xenoliths of the same region (19–11% and 15–8% respectively) and by high clinopyroxene/orthopyroxene ratios: 0.7–2.7 (present study) and about 0.4 (Lee et al. 1996). The clinopyroxene crystal chemistry indicates that the xenoliths show the compositional features of a mantle source contaminated by small-volume melts, responsible for the high clinopyroxene content. The protogranular texture of the Cameroon xenoliths (upper portion of lithospheric mantle) testifies that the spinel peridotite and the associated small-volume melts completely re-equilibrated at the spinel-peridotite facies. This is also supported by the petrological and geochemical data of Lee et al. (1996) on the Etinde–Biu Plateau spinel-peridotite xenoliths, which underwent Late Proterozoic–Early Paleozoic enrichment in incompatible trace elements. Received: 6 October 1999 / Accepted: 27 March 2000  相似文献   

On the least action principle in cosmology     

Adi Nusser  Enzo Branchini 《Monthly notices of the Royal Astronomical Society》2000,313(3):587-595

Given the present distribution of mass tracing objects in an expanding universe, we develop and test a fast method for recovering their past orbits using the least action principle. In this method, termed FAM for fast action minimization, the orbits are expanded in a set of orthogonal time basis functions satisfying the appropriate boundary conditions at the initial and final times. The conjugate gradient method is applied to locate the extremum of the action in the space of the expansion coefficients of the orbits. The treecode gravity solver routine is used for computing the gravitational field appearing in the action and the potential field appearing in the gradient of the action. The time integration of the Lagrangian is done using Gaussian quadratures. FAM allows us to increase the number of galaxies over previous numerical action principle implementations by more than one order of magnitude. For example, orbits for the 15 000 IRAS PSC z galaxies can be recovered in 12 000 CPU seconds on a 400-MHz DEC-Alpha machine. FAM can recover the present peculiar velocities of particles and the initial fluctuations field. It successfully recovers the flow field down to cluster scales, where deviations of the flow from the Zel'dovich solution are significant. We also show how to recover orbits from the present distribution of objects in redshift space by direct minimization of a modified action, without iterating the solution between real and redshift spaces.  相似文献   

An operational model to estimate hourly and daily crop evapotranspiration in hilly terrain: validation on wheat and oat crops   总被引：2，自引：1，他引：1  

Gianfranco Rana  Nader Katerji  Rossana M. Ferrara  Nicola Martinelli 《Theoretical and Applied Climatology》2011,103(3-4):413-426

In this paper, we present an operational model to estimate the actual evapotranspiration (ET) of crops cultivated on hilly terrains. This new model has the following three characteristics: (1) ET modelling is based on a Penman?CMonteith (PM) type equation (Monteith 1965) where canopy resistance is simulated by following an approach already illustrated by Katerji and Perrier (Agronomie 3(6):513?C521, 1983); (2) the estimation of ET, by means of the PM equation, is made by using meteorological variables simulated on sloped sites as input; (3) these variables are simulated by using simple relationships linking the variables measured at a reference site on plane to the topographic characteristics of the site (slope, orientation, altitude as difference between reference, and sloped sites). This approach presents two advantages if compared with previously proposed models: Not only computation steps are greatly simplified but also error sources due to the simulation of climatic variables in sloped sites and the ET estimation are well distinguished. This model was validated at hourly and daily scales at four sites cultivated with wheat and oats offering a wide range of slope and orientation values: a reference site on plane, site 1 (9° sloping, NW orientation, 7 m from the reference site in plane), site 2 (6°, SE, 12 m) and site 3 (1°, SE, 18 m). At hourly scale, the new model performed well at all sites studied. The observed slope of the linear relationships between estimated and measured ET values ranged between 0.93 and 1.03, with coefficients of determination, r ², between 0.80 and 0.98. At daily scale, the slopes of the linear relationships between measured and estimated ET for the sites on plane and the sloped sites were practically the same (0.98?±?0.01); however, the coefficient of determination r ² observed in the site on plane was clearly greater (0.98) than that observed in the sloped sites (0.83). The presented analysis does not show any significant systematic effect of topography (slope and orientation of the plots) on the good performance of the proposed model for the ET estimation. Furthermore, we observed that coefficients of determination tend to decrease with the increase in the slope of the site, which translates into increased inaccuracy of the climatic variables simulation, in particular the net radiation, as the slope of the site increases. The proposed model allows to verify the different steps for calculating the fluxes, to identify the eventual sources of error and to make the needed corrections. For this reasons, the proposed model seems to be particularly ??operational??, i.e. a useful tool for estimating fluxes on hilly terrains.  相似文献