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ABSTRACT Standard hydrological methods have been used to evaluate the water balance of a Central American river basin located in Costa Rica, for the purpose of appraising its water resources potential. Estimates are made of the present utilization of water by each major sectorial user, and a comparison of demand and supply is presented that enables the determination of the degree of present utilisation of water resources. 相似文献
2.
Exposure age dating and Equilibrium Line Altitude reconstruction of an Egesen moraine in the Maritime Alps, Italy 总被引：1，自引：0，他引：1
PAOLO ROBERTO FEDERICI DARRYL E. GRANGER MARTA PAPPALARDO ADRIANO RIBOLINI MATTEO SPAGNOLO ANDREW J. CYR 《Boreas: An International Journal of Quaternary Research》2008,37(2):245-253
Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10 Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10 Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas. 相似文献
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Compositional Layering and Syn-eruptive Mixing of a Periodically Refilled Shallow Magma Chamber: the AD 79 Plinian Eruption of Vesuvius 总被引：4，自引：1，他引：3
CIONI RAFFAELLO; CIVETTA LUCIA; MARIANELLI PAOLA; METRICH NICOLE; SANTACROCE ROBERTO; SBRANA ALESSANDRO 《Journal of Petrology》1995,36(3):739-776
A detailed study of the pyroclastic deposits of the AD 79 ‘Pompei’Plinian eruption of Vesuvius has allowed: (1) reconstructionof the thermal, compositional and isotopic (87Sr/86Sr) pre-eruptivelayering of the shallow magma chamber; (2) quantitative definitionof the syn-eruptive mixing between the different magmas occupyingthe chamber, and its relationships with eruption dynamics; (3)recognition of the variability of mafic magma batches supplyingthe chamber. During the different phases of the eruption 25–30%of the magma was ejected as white K-phonolitic pumice, and 70–75%as grey K-tephri-phonolitic pumice. The white pumice resultsfrom the tapping of progressively deeper magma from a body (T= 850–900%C) consisting of two distinct layers mainlyformed by crystal fractionation. The grey pumice results fromsyn-eruptive mixing involving three main end-members: the phonolitic‘white’ magmas (salic end-member, SEM), mafic cumulates(cumulate end-member, CEM) and a crystal-poor ‘grey’phono-tephritic magma (mafic end-member, MEM), which was nevererupted without first being mixed with ‘white’ magma.Evidence is provided that mixing occurred within the chamberand was characterized by a transition with time from physicalmixing at a microscopic scale to chemical hybridization. TheMEM magma had a homogeneous composition and constant 87Sr86Srisotopic ratio, possibly as a result of sustained convection.No unambiguous liquidus phases were found, suggesting that theMEM magma was superheated (T = 1000–1100C); its verylow viscosity was a main cause in the establishment of a physicaldiscontinuity separating the white and the grey magmas. Thewhite-grey boundary layer possibly consisted of a multiply diffusiveinterface, periodically broken and recreated, supplying thephonolitic body through mixing of moderate amounts of fractionatedgrey melts with the overlying white magma. The presence of alarge overheated mass indicates the young, growing stage ofthe AD 79 chamber, whose main engine was the periodic arrivalof hot mafic magma batches. These were characterized by K-tephriticto K-basanitic compositions, high temperatures (>1150C),high volatile contents (20–25% H2O +Cl+F+S), low viscosities[(1+2 102 poises)] and relatively low densities (2500–2600kg/m3). The birth of the Pompei chamber followed the repeatedarrival of these batches (on average characterized by 87Sr/86Sr070729)into a reservoir containing a tephriticphonolitic, crystal-enriched,magma, a residue from the preceding ‘Avellino’ Plinianeruption (3400 BP).In fact, about half of magma ejected duringthe AD 79 eruption could have been inherited from pre-Avellinotimes. KEY WORDS: Vesuvius; magma chamber; magma mixing; compositional layering phonolites; magma supply; potassic magmas
*Correponding author 相似文献
4.
DEFORMATIONAL BEHAVIOURS OF ALLUVIAL UNITS DETECTED BY ADVANCED RADAR INTERFEROMETRY IN THE VEGA MEDIA OF THE SEGURA RIVER,SOUTHEAST SPAIN 
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This work presents the stratigraphy and facies analysis of an interval of about 2500 m in the Langhian and Serravallian stratigraphic succession of the foredeep turbidites of the Marnoso‐arenacea Formation. A high‐resolution stratigraphic analysis was performed by measuring seven stratigraphic logs between the Sillaro and Marecchia lines (60 km apart) for a total thickness of about 6700 m. The data suggest that the stratigraphy and depositional setting of the studied interval was influenced by syndepositional structural deformations. The studied stratigraphic succession has been subdivided into five informal stratigraphic units on the basis of how structurally controlled topographic highs and depocentres, a consequence of thrust propagation, change over time. These physiographic changes of the foredeep basin have also been reconstructed through the progressive appearance and disappearance of thrust‐related mass‐transport complexes and of five bed types interpreted as being related to structurally controlled basin morphology. Apart from Bouma‐like Type‐4 beds, Type‐1 tripartite beds, characterized by an internal slurry unit, tend to increase especially in structurally controlled stratigraphic units where intrabasinal topographic highs and depocentres with slope changes favour both mud erosion and decelerations. Type‐2 beds, with an internal slump‐type chaotic unit, characterize the basal boundary of structurally controlled stratigraphic units and are interpreted as indicating tectonic uplift. Type‐3 beds are contained‐reflected beds that indicate different degrees of basin confinement, while Type‐5 are thin and fine‐grained beds deposited by dilute reflected turbulent flows able to rise up the topographic highs. The vertical and lateral distribution of these beds has been used to understand the synsedimentary structural control of the studied stratigraphic succession, represented in the Marnoso‐arenacea Formation by subtle topographic highs and depocentres created by thrust‐propagation folds and emplacements of large mass‐transport complexes. 相似文献
6.
FRANCESCO SALVINI ROBERTO DELLA MAGGIORE LUCIANO FORTUNATI FRANCESCO MAZZARINI 《Polar research》1994,13(1):23-33
A model is presented that performs spectral deicing of mixed pixels in satellite images of glaciated areas. The model was tested in Northern Victoria Land, Antarctica. For this region we assumed that pixels could be grouped in two broad categories representing pure ice and pure rock. Naturally mixed ice and rock pixels are present in satellite images; these were recomputed to separate the spectral component related to the rock fraction. We used Landsat TM images as input data and aerial photographs, maps and field surveys as reference data. By making use of sample populations of pixels corresponding to pure ice and to pure rock groundels (i.e. ground elements, the ground portions corresponding to each pixel), we detected the linear correlation between pairs of bands and selected the two most suitable bands. For every pixel falling between the correlation lines of the two categories, the rock fraction in the corresponding groundel was computed. This fractional value was then used to perform the automatic deicing process with which the DNs of the selected mixed pixels were recomputed. In the utilised Antarctic image, this process increases about 2.7 times the number of pixels in the pure rock category, allowing the production of enhanced images and, as a side product, a thematic map of rock percentage in the groundels. 相似文献
7.
Even though sustainable development has been broadly debated, the clean development mechanism (CDM) still lacks sophisticated multi-criteria decision methods for identifying, selecting and assessing CDM project activities from this perspective. Bearing in mind the huge number of CDM projects that are beginning to accumulate as the carbon market gains momentum, and the importance for non-Annex I Parties to keep focused on the sustainability objective, this article aims at developing a tool for prioritizing—within a given group, and once a specific list of sustainable development criteria is agreed upon and given—proposed CDM projects from this sustainable development point of view. We reached the following conclusions: (1) it is important to make a conscious choice of an appropriate way to normalize the sustainability performance data of CDM projects; (2) it is important to make a conscious choice of how to aggregate across multiple attributes; (3) in contrast with conventional multi-criteria assessments, which elicit preferences from a stakeholder panel, preference optimization infers from CDM projects' performance data an optimal set of weights that proponents would choose in order to win a competitive selection process. Such preference optimization methods (a) yield sensible results, simulating a range of decision circumstances, (b) avoid conflict and convey impartiality in situations where competing project proponents are likely to clash over objectionable weightings, (c) avoid cognitive overload when the number of CDM projects and/or indicators is overwhelmingly large, and (d) circumvent time-consuming and costly interviews and surveys. From a policy perspective, the multi-criteria assessment described here can be a powerful tool for prioritizing CDM projects (1) when there is a limited amount of grant funding to certain CDM project candidates, and (2) when the decisionmaking process incorporates the CDM objective of promoting sustainable development, in addition to the objective of helping developed countries to meet part of their reduction obligations as specified in Annex I of the Protocol. 相似文献
8.
KLAAS VERWER GIOVANNA DELLA PORTA† OSCAR MERINO-TOMɆ JEROEN A.M. KENTER‡ 《Sedimentology》2009,56(6):1801-1831
Spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics, external controls and degree of predictability of the facies architecture of shallow‐water carbonate‐platform tops. To quantify the spatial distribution and vertical stacking of lithofacies within an outer‐platform shoal‐barrier complex, integrated facies analysis and digital field technologies have been applied to a high‐relief carbonate platform exposed in the Djebel Bou Dahar (Lower Jurassic, High Atlas, Morocco). The outer platform is characterized by subtidal, cross‐bedded, coarse grainstone to rudstone grading into supratidal, pisoidal packstone‐rudstone with tepees that together formed a 350 to 420 m wide shoal‐barrier belt parallel to the margin. This belt acted as a topographic high separating a restricted lagoon from the subtidal, open marine region. Low‐energy tidal flats developed on the protected flank of the barrier facing the lagoon. Lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model. The outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts. In addition, the spatial heterogeneity was captured in multiple time slices, i.e. during different phases of cyclic base‐level fluctuations. In general, the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top, establishing low‐energy subtidal conditions across the whole platform, and when the accommodation space was filled with tidal flat facies. Heterogeneity increased during deposition of the relief‐building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation. Cycles commonly are composed of a thin transgressive tidal flat unit, followed by coated‐grain rudstone bar facies. Lateral to the bar facies, pisoidal‐grainstone beach deposits accumulated. These bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand. There the bars either graded into supratidal pisoidal facies with tepees (when accommodation space was filled) or were capped by subaerial exposure (due to a sea‐level fall). Modified embedded Markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval (constant depositional mode). Analysis of individual sections did not reveal any ordering, which may be related to the limited thickness of these sections. Composite sections, however, rejected the null hypothesis of randomness. The addition of stratigraphically significant information to the Markov analysis, such as exposure surfaces and lateral dimensions of facies bodies, strengthens the verdict of unambiguous preferential ordering. Through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models, accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation. 相似文献
9.
EMILIANO MUTTI DANIEL BERNOULLI FRANCO RICCI LUCCHI ROBERTO TINTERRI 《Sedimentology》2010,57(3):933-934
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