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571.
Jos Vicente Prez-Pea Jos Miguel Azan Antonio Azor Paola Tuccimei Marta Della Seta Michele Soligo 《Geomorphology》2009,106(3-4):206-218
The landscape evolution in Neogene intramontane basins is a result of the interaction of climatic, lithologic, and tectonic factors. When sedimentation ceases and a basin enters an erosional stage, estimating erosion rates across the entire basin can offer a good view of landscape evolution. In this work, the erosion rates in the Guadix–Baza basin have been calculated based on a volumetric estimate of sediment loss by river erosion since the Late Pleistocene. To do so, the distribution of a glacis surface at ca. 43 kyr, characterised by a calcrete layer that caps the basin infilling, has been reconstructed. To support this age, new radiometric data of the glacis are presented. The volume of sediment loss by water erosion has been calculated for the entire basin by comparing the reconstructed geomorphic surface and the present-day topography. The resulting erosion rates vary between 4.28 and 6.57 m3 ha− 1 yr− 1, and are the consequence of the interaction of climatic, lithologic, topographic, and tectonic factors. Individual erosion rates for the Guadix and Baza sub-basins (11.80 m3 ha− 1 yr− 1 and 1.77 m3 ha− 1 yr− 1 respectively) suggest different stages of drainage pattern evolution in the two sub-basins. We attribute the lower values obtained in the Baza sub-basin to the down-throw of this sub-basin caused by very recent activity along the Baza fault. 相似文献
572.
573.
574.
In this paper the Marine Fish Community Index (MFCI) for the assessment of ecological status of marine environment is proposed. The MFCI was divided into 4 typologies: Rocky subtidal; shallow, intermediate and deep soft-bottoms. Based on the typical community associated to each typology and the DPSIR analysis performed, a set of metrics were selected and tested through a multiple correlation matrix (Pearson’s coefficient) and the core ones included in the index. The MFCI was applied in all typologies and the scores obtained with each metric were analyzed. In order to test the robustness of the MFCI the final ecological value of each zone was recalculated by removing successively one metric at a time. The MFCI showed a sensitive and robust response in the ecological status assessment. Since it incorporates both functional and structural community information, the MFCI can be useful in the context of the Marine Strategy Framework Directive as well as in other contexts of conservation and sustainable management of the marine environment. 相似文献
575.
Ian A. Simpson Erika B. Guttmann Jonathan Cluett Alexandra Shepherd 《Geoarchaeology》2006,21(3):221-235
The creation of anthropic sediments, traditionally referred to under the blanket term midden, through the utilization of settlement waste materials in domestic settlement construction was first recognized during early excavations at the Orcadian Neolithic site of Skara Brae (V.G. Childe, 1931a; 1931b). Prior to the present study there has been no systematic attempt to identify the nature of these sediments at Skara Brae, whose likely occupation dates between ˜3100 and 2500 B.C., or to assess whether different materials were incorporated into construction or varied with different phases of site formation. The opportunity to begin addressing these issues arose with the location of undisturbed sediment samples held in storage since the last site excavations of 1972–1973 (D.V. Clarke, 1976). Ten thin sections were manufactured from these samples, representing earlier and later phases of Neolithic settlement at Skara Brae. Observations using thin‐section micromorphology, supported by total phosphorus and particle‐size distribution analyses, suggest that both earlier and later settlement phases show accumulation of household waste dominated by fuel residues. These wastes may have been used to help stabilize wind‐blown sand deposits during the later settlement phases. In addition, the use of clay material tempered with household waste is associated with wall construction. Animal manures are only evident in anthropic deposits on the edge of the main settlement site where composting may have been taking place, and there is no evidence for their use in site construction. The authors conclude by drawing attention to possible diverse uses of anthropic sediments in settlement construction at other Neolithic settlements in Orkney. © 2006 Wiley Periodicals, Inc. 相似文献
576.
Giorgio Rivalenti Maurizio Mazzucchelli Vicente A.V. Girardi Riccardo Vannucci M. Adelaide Barbieri Alberto Zanetti Steve L. Goldstein 《Contributions to Mineralogy and Petrology》2000,138(4):308-325
Spinel–peridotite facies mantle xenoliths in Cenozoic alkali basalts of the Pico Cabuji volcano (Rio Grande do Norte State,
Northeast Brazil) and the adjacent South Atlantic oceanic island of Fernando de Noronha are studied for: (1) the information
they provide on the composition of the lithospheric component in the erupted basalt geochemistry, and (2) to check the effects
of the Fernando de Noronha plume track on the mantle lithosphere. Xenoliths from Pico Cabuji are protogranular lherzolites
and porphyroclastic harzburgites recording average equilibrium temperatures of 825 ± 116 and 1248 ± 19 °C, respectively. Pressure
in the porphyroclastic xenoliths ranges from 1.9 to 2.7 GPa (Ca-in-olivine geobarometer). Both groups show major element chemical
variation trends in whole-rock and Ti and HREE (Er, Yb) variations in clinopyroxene consistent with fractional melting and
basalt extraction. REE (rare earth element) profiles of clinopyroxenes vary from LREE (La, Ce) enriched (spoon shaped) to
LREE depleted in the protogranular group, whereas they are slightly convex upward in most porphyroclastic clinopyroxenes.
HFSE (Ti and Zr) negative anomalies are in general modest in the clinopyroxenes of both groups. Xenoliths from Fernando de
Noronha have textural variations similar to those of Pico Cabuji. Protogranular and porphyroclastic samples have similar temperature
(1035 ± 80 °C) and the pressure is 1–1.9 and 2.3 GPa, respectively. Whole-rock chemical variation trends overlap and extend
further than those of Pico Cabuji. The trace element profiles of the clinopyroxenes of the porphyroclastic xenoliths are enriched
in La up to 30 × PM and are smoothly fractionated from LREE to HREE, with deep, negative, Zr and Ti anomalies. The geochemical
heterogeneities of the xenoliths from both localities are interpreted in terms of reactive porous percolation. The porphyroclastic
xenoliths from Pico Cabuji represent the lower part of a mantle column (the head of a mantle diapir, at the transition conductive–adiabatic
mantle), where OIB infiltration triggers melting, and the protogranular xenoliths the top of the mantle column, chromatographically
enriched by percolation at a low melt/rock ratio. This interpretation may also apply for Fernando de Noronha, but the different
geochemical signature recorded by the clinopyroxenes requires a different composition of the infiltrated melt. Nd and Sr isotopes
of the Pico Cabuji porphyroclastic clinopyroxenes (143Nd/144Nd= 0.51339–0.51255, 87Sr/86Sr=0.70275–0.70319) and of Fernando de Noronha (143Nd/144Nd=0.51323–0.51285, 87Sr/86Sr=0.70323–0.70465) plot on distinct arrays originating from a similar, isotopically depleted composition and trending to
low Nd–low Sr (EMI) and low Nd–high Sr (EMII), respectively. Correlation of the isotope variation with geochemical parameters
indicates that the isotopic variation was induced by the metasomatic component, of EMI type at Pico Cabuji and of EMII type
at Fernando de Noronha. These different components enriched a lithosphere isotopically similar to DMM (depleted MORB mantle)
at both localities. At Fernando de Noronha, the isotopic signature of the metasomatic component is similar to that of the
∼ 8 Ma old lavas of the Remedios Formation, suggesting that this is the age of metasomatism. At Pico Cabuji, the mantle xenoliths
do not record the high 87Sr/86Sr component present in the basalts. We speculate that the EMII component derives from a lithospheric reservoir, which was
not thermally affected during mantle metasomatism at Pico Cabuji, but was mobilized by the hotspot thermal influence at Fernando
de Noronha. This interpretation provides a plausible explanation for the presence of distinct metasomatic components at the
two localities, which would be difficult to reconcile with their genetic relationship with the same plume.
Received: 12 June 1999 / Accepted: 13 December 1999 相似文献
577.
A rotating annular flume (RALF) has been constructed at the Center of Coastal and Land-Margin Research (CCALMR) to study the biogeochemistry of sediment–water interfaces. The flume was designed to allow for evolving, integrated measurements of physical, chemical, and biological parameters, as often as possible in a real-time, computer-controlled mode. Several numerical models have or are being developed/applied to provide a virtual representation of the flume, with the dual objective of assisting the design of experiments and of assessing our level of understanding of processes and process interactions. We will concentrate here on the characterization of the flow in the flume, a basic but interestingly complex problem. The operational challenge is to minimize secondary circulation and lateral variability of shear stress, factors that prevent the flume flow to match the idealized concept of an endless channel flow. Satisfactory minimization of these factors can be achieved by allowing both the top and the bottom rings of the flume to rotate in contrary directions, a concept introduced by earlier research efforts and verified in RALF via Acoustic Doppler Velocimeter (ADV) measurements and 3D numerical modeling. Once logistics (e.g., in the form of the size of the ADV's sampling volume and of the vertical discretization of the numerical grids) are appropriately handled, observations and model results show good agreement. This agreement legitimates the use of the model as a design and investigative tool, in particular to define optimal rotation ratios of the top and bottom rings. The ratios that minimize secondary flow and lateral variability of shear stress are distinct. This is a logical (generating mechanisms are different) but often not recognized aspect of the operation of annular flumes. 相似文献
578.
Filipe Neves Aníbal Costa Romeu Vicente C. Sousa Oliveira Humberto Varum 《Bulletin of Earthquake Engineering》2012,10(1):27-44
The earthquake of the 9th of July 1998 that hit in the central group of the Azores archipelago greatly affected the islands
of Faial, Pico and S?o Jorge, reaching a magnitude of Mw 6.2 with the epicentre located about 15km northeast of the Faial
Island. This earthquake allowed the collection of an unprecedented quantity of data concerning the characterisation of the
building stock and the damage suffered by construction. This is the main purpose of this research, consisting essentially
of three main aspects: (i) A detailed characterisation of the building stock, assigning a five category classification, from
old traditional rubble stone masonry to reinforced concrete moment framed buildings; (ii) A detailed damage grade classification
based on the different damage mechanisms observed; and, (iii) A seismic vulnerability assessment of the building stock. The
results of the vulnerability assessment together with the building stock database and damage classification were integrated
into a GIS tool, allowing the spatial visualation of damage scenarios, which is potentially useful for the planning of emergency
response strategies and retrofitting priorities to mitigate and manage seismic risk. 相似文献
579.
María Sahuquillo Maria Rosa Miracle Sara María Morata Eduardo Vicente 《Limnologica》2012,42(4):282-290
In Mediterranean ponds, summer drought enhances seasonality whose intensity varies along topographic and climatic gradients. The alternation of wet and dry periods in rain dependent ponds affects their biogeochemistry and differentiates them from ponds fed by more stable water sources, such as groundwater springs. Superimposed onto this, land use is also a very strong factor of variability. In this study we compared nutrients and organic matter concentrations, in water and in sediment, among different types of Mediterranean ponds based on the source of water, hydroperiod and land use. Forty-three ponds were sampled in Eastern Spain corresponding to five pond types: (1) permanent spring ponds in lowlands, (2) permanent spring ponds in mountains, (3) semi-permanent rain ponds, (4) temporary rain ponds with long hydroperiod and (5) temporary rain ponds with short hydroperiod.The results of this study indicate relevant differences among these pond types. The temporary rain ponds with short hydroperiod are characterized by high turbidity due to suspension of sediment particles rich in phosphorous adsorbed onto them (argillotrophic aquatic systems). They are used for watering domestic sheep that enhance sediment suspension by trampling. Total phosphorous (TP) concentrations in the water are high (like those of hypertrophic lakes), but planktonic chlorophyll a is very low and not correlated with TP, because of the low P-bioavailavility in the water. At the other extreme, we have permanent ponds in lowlands fed by groundwater springs. They are heavily loaded with nitrates due to the surrounding intensive agriculture. In these and other permanent/semipermanent ponds chlorophyll is highly correlated with TP. Sediment characteristics provide a good indication of the hydroperiod, since desiccation has important effects on biogeochemical transformations. A threshold of 5% organic matter (OM) in the sediment separates temporary ponds with a short hydroperiod from those with a long hydroperiod, and a threshold of 8% separates the later from the semi-permanent and permanent ponds. Besides OM reduction, important loss of N occurs during desiccation through mineralization, ammonia volatization and the sequential nitrification/denitrification pathway. On the other hand, the increase of organic P mineralization in dry sediments does not represent a loss of P from the system, since o-P remains adsorbed or bound onto the soil. This leads to a low TN/TP ratio in sediments in temporary ponds with short hydroperiod. These characteristics have to be taken into account when establishing pond typologies and ecological thresholds to assess water quality in these unique aquatic habitats. 相似文献
580.
Alexandra Ivanova Artem Kashubin Niklas Juhojuntti Juliane Kummerow Jan Henninges Christopher Juhlin Stefan Lüth Monika Ivandic 《Geophysical Prospecting》2012,60(5):957-973
More than 50 000 tons of CO2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO2 had been injected. We show here that rather complex time‐lapse signatures of this CO2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow an estimate of the total amount of CO2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO2 storage site using seismic methods. 相似文献