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51.
Kathryn A. Matthews Andréa G. Grottoli James E. Palardy 《Geochimica et cosmochimica acta》2008,72(18):4537-4550
Skeletal cadmium-to-calcium (Cd/Ca) ratios in hermatypic stony corals have been used to reconstruct changes in upwelling over time, yet there has not been a systematic evaluation of this tracer’s natural variability within and among coral species, between depths and across environmental conditions. Here, coral skeletal Cd/Ca ratios were measured in multiple colonies of Pavona clavus, Pavona gigantea and Porites lobata reared at two depths (1 and 7 m) during both upwelling and nonupwelling intervals in the Gulf of Panama (Pacific). Overall, skeletal Cd/Ca ratios were significantly higher during upwelling than during nonupwelling, in shallow than in deep corals, and in both species of Pavona than in P. lobata. P. lobata skeletal Cd/Ca ratios were uniformly low compared to those in the other species, with no significant differences between upwelling and nonupwelling values. Among colonies of the same species, skeletal Cd/Ca ratios were always higher in all shallow P. gigantea colonies during upwelling compared to nonupwelling, though the magnitude of the increase varied among colonies. For P. lobata, P. clavus and deep P. gigantea, changes in skeletal Cd/Ca ratios were not consistent among all colonies, with some colonies having lower ratios during upwelling than during nonupwelling. No statistically significant relationships were found between skeletal Cd/Ca ratios and maximum linear skeletal extension, δ13C or δ18O, suggesting that at seasonal resolution the Cd/Ca signal was decoupled from growth rate, coral metabolism, and ocean temperature and salinity, respectively. These results led to the following conclusions, (1) coral skeletal Cd/Ca ratios are independent of skeletal extension, coral metabolism and ambient temperature/salinity, (2) shallow P. gigantea is the most reliable species for paleoupwelling reconstruction and (3) the average Cd/Ca record of several colonies, rather than of a single coral, is needed to reliably reconstruct paleoupwelling events. 相似文献
52.
Jos M. Marques Paula M. Carreira Maria Rosrio Carvalho Maria J. Matias Fraser E. Goff Maria J. Basto Rui C. Graa Luís Aires-Barros Luís Rocha 《Applied Geochemistry》2008,23(12):3278-3289
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ2H and δ18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit. 相似文献
53.
54.
Flood hazard delineation combining geomorphological and hydrological methods: an example in the Northern Iberian Peninsula 总被引:2,自引:1,他引:1
Flood mapping requires the combination and integration of geomorphological and hydrological-hydraulic methods; however, despite
this, there is very little scientific literature that compares and validates both methods. Two types of analysis are addressed
in the present article. On the one hand, maps of flood plains have been elaborated using geomorphological evidence and historical
flood data in the mountainous area of northwestern Spain, covering an area of more then 232 km2 of floodplains. On the other hand, a hydrometeorological model has been developed (Clark semidistributed unit hydrograph)
in the Sarria River basin (155 km2, NW Spain). This basin is not gauged, hence the model was subjected to a goodness-of-fit test of its parameter (curve number)
by means of Monte Carlo simulation. The peak flows obtained by means of the hydrological model were used for hydraulic modeling
(one-phase, one-dimensional and steady flow) in a 4 km2 urban stretch of the river bed. The delineation of surface areas affected by floods since 1918, as well as those analyzed
subsequent to the geomorphological study, reveals a high degree of reliability in the delineation of the flooded areas with
frequent recurrence intervals (<50 years). If we compare these flooded surface areas with the estimate obtained by the hydrological-hydraulic
method we can see that the latter method overestimates the extent of the surface water by 144% for very frequent recurrence
intervals (>10 years) and underestimates it as the recurrence interval increases, by up to 80% less floodplain for exceptional
events (>500 years). Finally, a management map is put forth combining the most reliable results available by integrating both
methods.
Originally presented at the Sixth International Conference on Geomorphology. 相似文献
55.
Gravitational spreading of mountain ridges displays primary disequilibrium of flysch mountain areas of the Czech Carpathians.
The progression of various types of mass movements is a product of long-term ridge disintegration and is predisposed by the
geological structure of the area and the upper Tertiary-Quaternary morphogenesis of the mountain area. Deep-seated slope deformations
are spatially interconnected by the occurrence of some other types of slope deformations (e.g. debris flows, debris slides,
slumps, rock avalanches, etc.), which pose a considerable risk for the existence of human society. An important causative
factor in these dynamically developing hazardous processes is, among other factors, the way in which land has been used in
the last three centuries. Therefore, the occurrence of various types of slope deformations is studied in terms of their relation
to deep-seated gravitational deformations and in terms of other limiting factors (structural geological, morphological and
climatic factors, manmade impacts, etc.). The paper presents several case studies of slope deformations (Velká Čantoryje Mt,
Lysá hora Mt, Ropice Mt and Smrk Mt) in the area of the Outer Carpathians within the territory of the Czech Republic and also
adverts to some consequences in terms of the socioeconomic structure of the landscape. 相似文献
56.
Vittorio Zanon Fátima Viveiros Catarina Silva Ana Rita Hipólito Teresa Ferreira 《Natural Hazards》2008,45(1):19-31
A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged
over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO2, CO, H2S and CH4) were performed in four study trenches, dug in an area of ∼3 m2, where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column
of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey
to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of
404 ppm CO and 3.4% CO2 originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after
the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block
interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size
of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between
anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not
total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion
process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through
the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented
by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced
observers and, consequently, delay proper action. 相似文献
57.
58.
Biaxial test simulations using a packing of polygonal particles 总被引:1,自引:0,他引:1
The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
59.
Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile 总被引:1,自引:0,他引:1
J. Carrillo-Rosúa S. Morales-Ruano D. Morata A. J. Boyce M. Belmar A. E. Fallick P. Fenoll Hach-Alí 《Mineralogy and Petrology》2008,92(3-4):341-360
Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous
andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E
fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are
pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As
+ Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs
interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up
to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid
inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.%
NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest
the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed
for the formation of the El Dorado deposit.
Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain 相似文献
60.
Summary The Aguablanca Ni-Cu-(PGE) magmatic sulphide deposit is associated with a magmatic breccia located in the northern part of
the Aguablanca gabbro (SW, Iberia). Three types of ores are present: semi-massive, disseminated, and chalcopyrite-rich veined
ore. The principal ore minerals are pyrrhotite, pentlandite and chalcopyrite. A relatively abundant platinum-group mineral
(PGM) assemblage is present and includes merenskyite, melonite, michenerite, moncheite and sperrylite. Moreover, concentrations
of base and precious metals and micro-PIXE analyses were obtained for the three ore-types. The mineralogy and the mantle-normalised
chalcophile element profiles strongly suggest that semi-massive ore represents mss crystallisation, whereas the disseminated ore represents an unfractionated sulphide liquid and the chalcopyrite-rich veined
ore a Cu-rich sulphide liquid. Palladium-bearing minerals occur commonly enclosed within sulphides, indicating a magmatic
origin rather than hydrothermal. The occurrences and the composition of these minerals suggest that Pd was initially dissolved
in the sulphides and subsequently exsolved at low temperatures to form bismutotellurides. Negative Pt and Au anomalies in
the mantle-normalised chalcophile element profiles, a lack of Cu-S correlation and textural observations (such as sperrylite
losing its euhedral shape when in contact with altered minerals) suggest partial remobilisation of Pt, Au and Cu by postmagmatic
hydrothermal fluids after the sulphide crystallisation.
Authors’ addresses: R. Pi?a, L. Ortega, R. Lunar, Departamento de Cristalografía y Mineralogía, Facultad de Geología, Universidad Complutense de Madrid, ES-28040 Madrid,
Spain; F. Gervilla, Facultad de Ciencias, Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada-CSIC, Avda. Fuentenueva, s/n, ES-18002
Granada, Spain 相似文献