The electrical conductivity of eclogites measured by two methods     

Marcela Laštovičková  Reviewer J. Buben 《Studia Geophysica et Geodaetica》1975,19(4):394-398

  相似文献   

Groundwater recharge in a sedimentary basin in semi-arid Mexico   总被引：9，自引：1，他引：8  

Jürgen?MahlknechtEmail author  Jean?F.?Schneider  Broder?J.?Merkel  Ignacio?Navarro de León  Stefano?M.?Bernasconi 《Hydrogeology Journal》2004,12(5):511-530

Recharge mechanisms and the hydrochemical evolution of groundwater in a semi-arid, 6,840-km², intermountain basin in central Mexico were investigated using stable isotopes and major chemical constituents. Ionic ratio analysis helped to conceptualize and quantify in part the subsequent geochemical evolution in the aquifer system. Mass balance models (PHREEQC) were used to interpret and rectify the geochemical properties of the aquifer. The recharge conditions have not changed noticeably during the last several thousands of years. The recharge mechanisms are accompanied by leaching of meteoric salts on and near the ground surface during major rain events, which previously accumulated after minor rain events. Rapid and diffuse infiltration can be excluded. Indirect infiltration from wadis (arroyos) and depressions (playas) with little mixing in shallow groundwater contrasts with a high degree of mixing for water with deep circulation. The prevailing source of major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) is weathering of carbonates and albite, followed by exchange reactions on clays and hydroxides. Ca²⁺/Na⁺ exchange may interchange along the flow path with reverse (Na⁺/Ca²⁺) exchange, although the Ca²⁺/Na⁺ option is prevalent. Meteoric Ca and Mg inputs are relatively small; however, meteoric Na is insignificant. Irrigation return flow plays an important role in the western part of the study area, giving rise to elevated sulfate and chloride concentrations.

---

Resumen Se han investigado los mecanismos de recarga y la evolución hidroquímica de las aguas subterráneas en una cuenca semiárida e intermontanosa de México central, de 6.840 km². Para ello, se han utilizado isótopos estables y los constituyentes químicos mayores. El análisis de las relaciones iónicas ha servido para conceptuar y cuantificar en parte su evolución geoquímica posterior dentro del sistema acuífero. Se ha recurrido a modelos de balance de masas (PHREEQC) para interpretar y rectificar las propiedades geoquímicas del acuífero. Las condiciones de recarga no han cambiado de forma apreciable durante los últimos miles de años. Los mecanismos de recarga se ven acompañados por el lixiviado de las sales meteóricas sobre y cerca de la superficie del terreno durante los episodios principales de lluvia, las cuales son acumuladas en episodios menores de lluvia. Se puede excluir la infiltración rápida y difusa. La infiltración indirecta desde arroyos ( wadis) y depresiones ( playas), que apenas se mezcla con las aguas subterráneas someras, contrasta con un elevado nivel de mezcla con el agua de circulación profunda. La fuente dominante de cationes mayores (calcio, magnesio, sodio, potasio) es la meteorización de los carbonatos y albita, mientras que las reacciones de intercambio en las arcillas e hidróxidos son menos importantes. El intercambio ión calcio-ión sodio puede ser reemplazado a lo largo de una línea de flujo por el intercambio opuesto (ión sodio-ión calcio), aunque la primera es prioritaria. Las aportaciones meteóricas de calcio y magnesio son relativamente pequeñas, mientras que la de sodio es insignificante. Los retornos de riego desempeñan un papel importante en la parte occidental del área de estudio, dando lugar a concentraciones elevadas de sulfato y cloruro.

---

Résumé Les mécanismes de recharge et lévolution hydrochimique de leau souterraine dans un bassin de montagne de 6 840 km² en zone semi-aride, dans le centre du Mexique, ont été étudiés au moyen des isotopes stables et des composés chimiques majeurs. Lanalyse des rapports ioniques a aidé à conceptualiser et à quantifier en partie lévolution géochimique qui en résulte, dans le système aquifère. Des modèles de bilan de masse (PHREEQC) ont été utilisés pour interpréter et corriger les propriétés de laquifère. Les conditions de recharge nont pas changé notablement au cours des derniers millénaires. Les mécanismes de recharge sont accompagnés, durant les épisodes majeurs de précipitation, dun lessivage, à la surface du sol et à son voisinage, de sels météoriques accumulés auparavant pendant les petits épisodes de pluie. Linfiltration rapide et diffuse peut être exclue. Linfiltration indirecte à partir des oueds (arroyos) et des dépressions (playas) avec un faible mélange dans la nappe superficielle contraste avec le degré élevé de mélange de leau avec les circulations profondes. La source prépondérante des cations majeurs (Ca²⁺, Mg²⁺, Na⁺, K⁺) est laltération des carbonates et des feldspaths ; léchange de cations avec les argiles et les hydroxydes est moins important. Léchange de Ca²⁺ avec Na⁺ peut sinverser le long des axes découlements pour donner un échange de Na⁺ avec Ca²⁺, bien que le cas Ca²⁺/Na⁺ soit prépondérant. Les apports météoriques de Ca et de Mg sont relativement faibles, cependant que celui de Na météorique est insignifiant. Lécoulement par retour dirrigation joue un rôle important dans la partie occidentale de la région étudiée, produisant un accroissement des concentrations élevées en sulfate et en chlorure.

  相似文献   

Oxygen isotope compositions of phosphate from arvicoline teeth and Quaternary climatic changes, Gigny, French Jura     

Nicolas Navarro  Christophe Lécuyer  Sophie Montuire  Cyril Langlois 《Quaternary Research》2004,62(2):172-182

Oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high- and mid-latitudes. An oxygen isotope fractionation equation was determined by using present-day European arvicoline (rodents) tooth phosphate: δ¹⁸O_p = 20.98(±0.59) + 0.572(±0.065) δ¹⁸O_w. This fractionation equation was applied to the Late Pleistocene karstic sequence of Gigny, French Jura. Comparison between the oxygen isotope compositions of arvicoline tooth phosphate and Greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence. According to the δ¹⁸O value of meteoric water-mean air temperature relationships, the δ¹⁸O value of arvicoline teeth records variations in mean air temperatures that range from 0° to 15°C.  相似文献   

Temperature profiles in the earth of importance to deep electrical conductivity models   总被引：3，自引：0，他引：3  

Vladimír Čermák  Marcela Laštovičková 《Pure and Applied Geophysics》1987,125(2-3):255-284

Deep in the Earth, the electrical conductivity of geological material is extremely dependent on temperature. The knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models. The measured values of the terrestrial heat flow, radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere. Various methods of deep temperature calculations are presented and discussed. Characteristic geotherms are proposed for major tectonic provinces of Europe and it is shown that the existing temperatures on the crust-upper mantle boundary may vary in a broad interval of 350–1,000°C. The present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200–1,000°C. It is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity-versustemperature data into the conductivity-versus-depth data.  相似文献   

Diatom paleoecology of the Mar Chiquita lagoon delta,Argentina   总被引：1，自引：0，他引：1  

Marcela A. Espinosa 《Journal of Paleolimnology》1994,10(1):17-23

A 68 cm thick outcrop of diatomaceous sediments at the head of Mar Chiquita Lagoon on the Argentine coast near Buenos Aires provides evidence of Holocene paleoenvironmental changes related to sea level changes and freshwater input to the lagoon system. Salinity tolerances of extant diatom taxa were used for the reconstruction and multivariate analytical techniques were applied to reduce subjective interpretations of the diatom percentage data.The basal half of the record was deposited before 3000 years ago and fossil diatoms indicate generally freshwater conditions with one fluctuation in mesohalobous diatoms suggesting brackish water conditions at a depth of about 60 cm. Polyhalobous (marine) diatoms characterize the record after 3000 years ago and large numbers of epiphytic diatoms indicate salt marsh environments with episodic seawater fluctuations to supratidal levels. Freshwater diatoms returned at the top of the outcrop, presumably as a result of the restriction of the historic marine inlet to the lagoon and the effects of freshwater inflow to the basin.This is the second in a series of papers published in this issue on Paleolimnology in Southern South America. Dr. C. A. Fernández served as guest editor for these papers.  相似文献   

Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian,Gzhelian, Pennsylvanian,Bohemian Massif), their timing,and possible trigger mechanism     

Marcela Stárková  Karel Martínek  Radek Mikuláš  Nicholas Rosenau 《International Journal of Earth Sciences》2015,104(5):1277-1298

  相似文献   

The nautiloid Family Eothinoceratidae from the Floian of the Central Andean Basin (NW Argentina and South Bolivia)     

Marcela Cichowolski  Beatriz G. Waisfeld  Norberto E. Vaccari  Larisa Marengo 《Geological Journal》2015,50(6):764-782

A single confidently dated species of cephalopod is so far known in the Tremadocian of the southern Central Andean Basin (NW Argentina and southern Bolivia). This species belongs to the Eothinoceratidae and has a strong affinity mainly with Avalonia. During the Floian, a notable increase in diversity took place, with the appearance of a variety of families represented by several genera, in particular, within the Family Eothinoceratidae. In addition to the previously described species from southern Bolivia, we evaluate the other records of that family from the Central Andean Basin, and propose the following new taxa: Saloceras sikus sp. nov., Saloceras quena sp. nov., Mutveiceras gen. nov., and Mutveiceras cienagaensis sp. nov. We also describe Margaritoceras diploide, Margaritoceras sp., and Mutveiceras sp. From a palaeogeographic perspective, the cephalopod fauna shows affinities mainly with those of England, Wales, and the Montagne Noire (cold water Gondwana and peri‐Gondwana). As with other cephalopod faunas of mid to high palaeolatitudes, eothinoceratids occur along with other cephalopods forming assemblages of low morphological diversity. We interpret the forms described here as demersal with a subvertical poise, but capable of making rapid buoyancy changes, living in a wide spectrum of shallow offshore to shoreface settings. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The inner structure of ΛCDM haloes – II. Halo mass profiles and low surface brightness galaxy rotation curves     

E. Hayashi  J. F. Navarro  C. Power  A. Jenkins  C. S. Frenk  S. D. M. White  V. Springel  J. Stadel  T. R. Quinn 《Monthly notices of the Royal Astronomical Society》2004,355(3):794-812

  相似文献   

Hiding cusps in cores: kinematics of disc galaxies in triaxial dark matter haloes     

Eric Hayashi  Julio F. Navarro † 《Monthly notices of the Royal Astronomical Society》2006,373(3):1117-1124

  相似文献   

Ancient Forests in European drylands: Holocene palaeoecological record of Mazarrón,south-eastern Spain     

José S. Carrión  Elena Fierro  Milagros Ros  Manuel Munuera  Santiago Fernández  Juan Ochando  Gabriela Amorós  Francisca Navarro  Tomás Rodríguez-Estrella  Saúl Manzano  Penélope González-Sampériz  Ana Moreno 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(4):512-525

This paper presents a new Holocene palaeoecological record from coastal south-eastern Spain, a region characterised by high plant species diversity, varied physiography, high risk of desertification, and a history of human pressure on the landscape that stretches to antiquity. The pollen sequence shows four main vegetation phases: the first characterised by mixed forests of Pinus and evergreen Quercus accompanied by broad-leaved mesophilous trees, and a diversity of Mediterranean scrub; the second phase is characterised by mesophytic decline and expansion of Artemisia; a third, mid-Holocene phase of thermo-mesophytic maxima with prevalence of forested landscapes; and, finally, the progressive opening of the landscape with sparse pines, halo-xerophytic grasslands and sclerophyllous brushwood. The current treeless situation of south-eastern Spain is a relatively recent feature resulting from a dramatic change in the ecological structure of the regional landscapes. This paper stresses the continued vulnerability of these arid systems in the face of a changing climate. This sequence adds to previous palaeobotanical records (pollen and charcoal) and archaeological reports to suggest that deforestation started earlier in low-elevation areas and river basins than in the inland mountains and platforms, a factor that appears in connection to human exploitation of the natural environment.  相似文献