Thermochemically induced transformations in Al-smectites: A Spanish natural analogue of the bentonite barrier behaviour in a radwaste disposal   总被引：1，自引：0，他引：1  

L. Prez del Villar  A. Delgado  E. Reyes  M. Pelayo  J.M. Fernndez-Soler  J.S. Czar  M. Tsige  A.J. Quejido 《Applied Geochemistry》2005,20(12):2252-2282

The thermal effect induced by the Morrón de Mateo volcanic dome (Cabo de Gata volcanic region, Spain) on the adjacent bentonitised tuffaceous beds has been studied as a natural analogue of the thermal behaviour of the bentonite-engineered barrier of a geological radwaste repository. These bentonites consist mainly of Fe-rich smectites and were formed in equilibrium with seawater at temperatures between 75 and 95 °C, according to the δ¹⁸O and δD values. In contrast, bentonites from other localities in the region consist mainly of Al-smectites, formed in equilibrium with meteoric water below 25 °C.This investigation is focussed on the detection of the chemical differences between smectites from proximal and distal zones to the dome, as well as to test whether the temperatures calculated based on the O and H isotopic values correspond to their formation or transformation. The initial hypothesis was that the chosen smectites could be formed under marine conditions, being later transformed and isotopically re-equilibrated as a result of the intrusion. To check this hypothesis, a detailed mineralogical, chemical, geochemical and isotopic study has been performed on the smectitised tuffaceous materials and the overlaying biocalcarenites outcropping near and far from the dome.The results show that distal smectites are dioctahedral Al-smectites, similar to those from other deposits in the region, while proximal smectites are Fe- and Mg-rich smectites, showing two evolutionary trends on a Fe–Mg–Al ternary diagram. Similar features are observed when their structural formulae are plotted on the muscovite–celadonite–pyrophylite diagram. Thus, they plot in the smectite domain with interlayer charge less than 1, which is mainly due to octahedral substitution for distal smectites, while for proximal ones it is caused by both octahedral and tetrahedral substitutions. In this ternary diagram, the domains of both proximal and distal smectites are partially overlapped. The coexistence of di- and trioctahedral smectites was only detected in one proximal sample. Further, proximal biocalcarenites are enriched in Fe-rich dolomite in relation to the distal ones.The ⁸⁷Sr/⁸⁶Sr and δ¹³C values in carbonates and δD in smectites indicate equilibrium with seawater. In contrast, δ¹⁸O values of carbonates and smectites indicate that they were transformed and re-equilibrated between 40 and 90 °C, and between 55 and 66 °C, respectively, independently of their location with respect to the dome.These data suggest that the transformation of calcite into Mg–Fe-carbonates and the occurrence of Fe- and Mg-rich smectites near to the dome resulted from a chemically induced process at similar temperatures. The compositional differences among samples suggests that Fe, Mg and minor Mn were supplied by a contaminant plume originated from the dome, migrating through the sediments and becoming more diluted away from the source. The absence of a well-defined thermal gradient in the system could be due to the small size, semi-closed and shallow character of the basin, as well as to its high underlying volcanic activity.Finally, the results are discussed in terms of analogue processes that can be expected in the bentonite barrier of a radwaste geological repository.  相似文献   

Geometry of half-grabens containing a mid-level viscous décollement     

Ruth Soto  Antonio M. Casas-Sainz†  Pedro del Río‡ 《Basin Research》2007,19(3):437-450

In this work, we explore by means of analogue models how different basin-bounding fault geometries and thickness of a viscous layer within the otherwise brittle pre-rift sequence influence the deformation and sedimentary patterns of basins related to extension. The experimental device consists of a rigid wooden basement in the footwall to simulate a listric fault. The hangingwall consists of a sequence of pre-rift deposits, including the shallow interlayered viscous layer, and a syn-rift sequence deposited at constant intervals during extension. Two different geometries exist of listric normal faults, dip at 30 and 60° at surface. This imposes different geometries in the hangingwall anticlines and their associated sedimentary basins. A strong contrast exists between models with and without a viscous layer. With a viscous décollement, areas near the main basement fault show a wide normal drag and the hangingwall basin is gently synclinal, with dips in the fault side progressively shallowing upwards. A secondary roll-over structure appears in some of the models. Other structures are: (1) reverse faults dipping steeply towards the main fault, (2) antithetic faults in the footwall, appearing only in models with the 30° dipping fault and silicone-level thicknesses of 1 and 1.5 cm and (3) listric normal faults linked to the termination of the detachment level opposite to the main fault, with significant thickness changes in the syn-tectonic units. The experiments demonstrate the importance of detachment level in conditioning the geometry of extensional sedimentary basins and the possibility of syncline basin geometries associated with a main basement fault. Comparison with several basins with half-graben geometries containing a mid-level décollement supports the experimental results and constrains their interpretation.  相似文献   

The influence of petrophysical properties on the salt weathering of porous building rocks   总被引：1，自引：0，他引：1  

D. Benavente  N. Cueto  J. Martínez-Martínez  M. A. García del Cura  J. C. Cañaveras 《Environmental Geology》2007,52(2):215-224

The influence of pore structure, water transport properties and rock strength on salt weathering is evaluated by means of a thorough rock characterisation and a statistical analysis. The pore structure was described in terms of its porosity, pore size distribution (quantified by mean pore radius) and specific surface area, density and water transport was characterised by means of water permeability (saturated flow) and capillary imbibition (unsaturated flow); whilst the rock strength test was carried out using uniaxial compressive strength, compressional and shear wave velocities, dynamic elastic constants and waveform energy and attenuation were obtained from the digital analysis of the transmitted signal. A principal component analysis and a stepwise multiple regression model was carried out in order to examine the direct relationships between salt weathering and petrophysical properties. From the principal component analysis, two main components were obtained and assigned a petrophysical meaning. The first component is mostly linked to mechanical properties, porosity and density whereas the second component is associated with the water transport and pore structure. Salt weathering, quantified by the percentage of weight loss after salt crystallisation, was included in both principal components, showing its dependence on their petrophysical properties. The stepwise multiple regression analysis found that rock strength has a predominant statistical weight in the prediction of salt weathering, with a minor contribution of water transport and pore structure parameters.  相似文献   

On the effect of subinertial phenomena on the internal lee waves generation in the Strait of Gibraltar     

José J. del Alonso Rosario  M. Arias Ballesteros  P. Villares Durán 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(3):259-272

The generation of internal lee waves (ILW) in the Strait of Gibraltar takes place in the main sill where the tidal flow interacts with a submarine obstacle. The tidal flow is perturbed by subinertial phenomena of different nature summarized in the subinertial currents that can inhibit the ILW generation. The authors present an attempt to randomize the problem by the introduction of a Gaussian noise in the Taylor–Goldstein equation. The random number sets are generated from the statistical distribution of the previously isolated random part of the subinertial currents from experimental data taken in the area during the Gibraltar Experiment 94–96. The effect of the noise is translated into a continuous spreading of the spectrum around the solution of the noise-free problem. A stability analysis is carried out in order to determine the single neutral modes of oscillations and the phase space is divided onto regions of stability and instability as a function of the inflowing subinertial current. The methodology and results could be useful for the design and timing of oceanographic surveys in straits where the ILWs occur.  相似文献   

The conductivity distribution in the North German sedimentary basin derived from widely spaced areal magnetotelluric measurements     

W. Losecke  K. Knödel  W. Müller 《Geophysical Journal International》1979,58(1):169-179

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A Miocene algal assemblage dominated by Pediastrum leonensis n. sp. (Chlorophyceae) from Patagonia, Argentina: paleoenvironmental implications     

Guillermo Tell  María del C. Zamaloa 《Journal of Paleolimnology》2004,32(3):247-254

Taxonomic identification of Pediastrum species in an Early Miocene assemblage from southeast Patagonia, Argentina, is used to assess paleoecological conditions. Pediastrum leonensis n. sp. is described based on unique features of the coenobia morphology. It belongs to the P. kawraiskyi–mustersii–patagonicum complex and has no known living counterpart. This group seems to have a long evolutionary history in the region. P. kawraiskyi and P. mustersii are recorded for the first time in pre-Quaternary deposits and their presence suggests a depositional environment represented by a cold stenothermal lake conditions, indicating a temperate to a cold-temperate climate.  相似文献   

Ecological and agricultural productivity indices and their dynamics in a sub-humid/semi-arid region from central Mexico   总被引：1，自引：0，他引：1  

W. Ritter Ortíz  E. Juregui Ostos  S. Guzmn Ruíz  A. Estrada Betancourt  H. Muoz Nava  J. Surez Snchez  Ma. del Carmen Corona Vargas 《Journal of Arid Environments》2004,59(4):675

Using precipitation data from a semi-arid region in the highlands of central Mexico, historical values of productivity are assessed. Production models based on climatic indices are discussed. An empirical rain simulation equation shows that it is possible to reproduce the expected values of productivity from observed ecosystems and agricultural yields. A graphical method is proposed to estimate intrinsic growth rate and maximum sustainable yield. Spatial rainfall variability induced by orographic effects, introduces a chaotic semicyclic behavior as expected in a logistic simulation equation. Resilience and predictable drought-productivity tendencies can also be derived from this model.  相似文献   

Hydrogeological Investigation of Hydrocarbon Contamination of Ground Water in Albolote (Granada, Spain)     

J. Cruz-Sanjulián  M. Olías  M. del  Valle  J.C. Rubio 《Ground Water Monitoring & Remediation》1992,12(3):188-194

In July 1988, hydrocarbons were detected in wells in the urban area of Albolote, near Granada, Spain, near the border of the "Vega de Granada" alluvial aquifer. According to available hydrogeological data, the contamination was attributed to leaks in the underground pipelines of a nearby (300m) industrial factory, where the loss of 40,000 to 50,000 liters of gasoline had been detected some weeks before. A complete hydrogeological investigation was then undertaken, involving, among other techniques: (a) an inventory of the existing wells in the area; (b) the preparation of piezometric maps; (c) the application of electrical geophysical methods; (d) the drilling of piezometers and new pumping wells between the urbanized area and the leak point; (e) the improvement of the pluviometric and piezometric control by the installation of a pluviograph and several limnigraphs; (f) the sampling, initially daily and finally weekly, in a 20-well observation network, also used for piezometric control; and (g) the geostatistical study of the analytical data. The contamination plume, extended in the direction of the flow lines, has a length of 500m and a width of less than 50m, and appears to have occurred mainly in a paleochannel. Hydrocarbons (1600 liters) were recovered by pumping and by using absorbent blankets, as well as by a gas and liquid suction method. Hydrocarbon concentrations have continuously decreased. However, sporadic increases, associated with rainfall, have been observed suggesting the presence of retained hydrocarbons in the unsaturated zone. The rate of decrease in hydrocarbon concentrations has currently slowed, particularly in the less affected zone. As a means of activating the cleaning up of the unsaturated zone, an artificial recharging method has been designed.  相似文献   

Unusual twinning features in large primary gypsum crystals formed in salt lake conditions, Middle Miocene, Madrid Basin, Spain: palaeoenvironmental implications—reply     

J. P. Rodríguez-Aranda  J. M. Rouchy  J. P. Calvo  S. Ordez  M. A. García del Cura 《Sedimentary Geology》1995,100(1-4)

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Harmonic emission and polarization of millisecond radio spikes     

A. O. Benz  M. Güdel 《Solar physics》1987,111(1):175-180

The spectral distribution of millisecond radio spikes observed by the Zürich spectrometers in the 200–1100 MHz range has been studied. In one event out of a total of 36 we have found clearly developed harmonic structure. The ratio between the two bands of emission was 1:1.39 ± 0.01. We have also determined the sense of circular polarization of the spike events and compared it to the magnetic polarity of the leading spot of the flaring active region. According to the Leading Spot Rule the majority of the events (10 out of 13) were emitted in the ordinary mode.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.  相似文献