Shock-induced mechanical deformations in biotites from crystalline rocks of the ries crater (Southern Germany)     

Hartmut Schneider 《Contributions to Mineralogy and Petrology》1972,37(1):75-85

Mechanical deformation features in shocked biotites from crystalline rocks of the Ries crater are: kink bands, planar elements, and plastic lattice deformations as determined by X-ray investigations.Kink bands can be observed in micas of various pressure histories (stages 0, I, II and less frequently stage III of shock metamorphism). Kink bands in shocked micas are less symmetrical than kinks of static origin. Asymmetry increases with increasing dynamic pressures. Moreover, kink band width is sensitive against changing peak pressures. Distribution of kinked and undistorted micas within a rock permits to fix the shock front direction. Shock-induced kinks in micas are produced by various gliding processes in the cleavage plane (001).Planar elements seldom occur in biotites of shock stages II and III and have never been described in endogenic rocks. Up to now orientations of planar elements parallel to (111), (1¯11), (112) and (11¯2) have been determined. Planar elements are interpreted as planes of plastic lattice gliding. {[110]} is supposed to be the main gliding direction. In the same pressure region other plastic lattice deformations have been determined. They are orientated parallel to (001), (100) and (¯132) or (201) which results from single crystal X-ray investigations and may represent planes of plastic lattice gliding. The dependency of formation of gliding planes and gliding directions on increasing dynamic pressures will be discussed.  相似文献   

Comments on ‘a note on the upper boundary conditions for turbulence models in the neutral atmosphere’, by D. M. Deaves     

J. M. Schneider  F. T. M. Nieuwstadt 《Boundary-Layer Meteorology》1983,26(2):203-204

  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   

Flood-borne sediment analysis of the Hoanib River, northwestern Namibia     

K. Leggett  J. Fennessy  S. Schneider 《Journal of Arid Environments》2005,62(4):587-596

The suspended sediment contained in six flood events in the Hoanib River catchment during the wet season of 1999/2000 were analysed for volatile (or low molecular weight) fine particulate organic material (FPOM), higher molecular weight FPOM and the total organic carbon (TOC). Samples were evaporated to dryness at 80 °C, then heated in a high temperature oven to 250, 550 and 850 °C. The results show that the amount of sediment carried during the flood events varied between 1.54 and 31.27 g/L, with an average of 14.62 g/L. The amount of suspended sediment in the flood-waters (2.789–616.359×10⁶ kg) was found to be dependent on the timing and duration of the flood event. The largest percentage of organic material was found in the volatile FPOM fraction (5.77±6.26%), with lesser amounts being found in the higher molecular weight FPOM (3.36±0.62%) and TOC (4.93±1.86%) fractions.  相似文献   

Southwest African climate independent of Atlantic sea surface temperatures during the Younger Dryas     

Lydie M. Dupont  Jung-Hyun Kim  Ralph R. Schneider  Ning Shi 《Quaternary Research》2004,61(3):318-324

To investigate land–sea interactions during deglaciation, we compared proxies for continental (pollen percentages and accumulation rates) and marine conditions (dinoflagellate cyst percentages and alkenone-derived sea surface temperatures). The proxies were from published data from an AMS-radiocarbon-dated sedimentary record of core GeoB 1023-5 encompassing the past 21,000 years. The site is located at ca. 2000 m water depth just north of the Walvis Ridge and in the vicinity of the Cunene River mouth. We infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation. After the Antarctic Cold Reversal, southeast Atlantic sea surface temperatures no longer influenced the vegetation development in the Kalahari. Stronger trade winds during the Antarctic Cold Reversal and the Younger Dryas period probably caused increased upwelling off the coast of Angola. A southward shift of the Atlantic anti-cyclone could have resulted in both stronger trade winds and reduced impact of the Westerlies on the climate of southwestern Africa.  相似文献   

Climate variability and change in Bulgaria during the 20th century   总被引：1，自引：1，他引：1  

V. Alexandrov  M. Schneider  E. Koleva  J.-M. Moisselin 《Theoretical and Applied Climatology》2004,79(3-4):133-149

Summary Climate data used for climate variability and change analyses, must be homogeneous, to be accurate. The data currently used in the Météo-France homogenization procedure, which does not require computation of regional reference series, was applied to precipitation and average air temperature series in Bulgaria. The Caussinus-Mestre method, with a double-step procedure, was used to detect multiple breaks and outliers in the long-term series of precipitation and average air temperature. A two factor linear model was applied for break correction. The homogenization procedure was run till all or most break risk was gone. Analysis of climate variability and change in Bulgaria during the 20^th century was done on already homogenized precipitation and average air temperature series. The statistical significance of the trends obtained was evaluated by the coefficient of Spearman rank correlation. The variations of annual precipitation in Bulgaria showed an overall decrease. The country has experienced several drought episodes during the 20^th century, most notably in the 1940s and 1980s. Seasonal precipitation in spring shows a positive trend at most weather stations across the country. The trend for summer and autumn precipitation is negative. A statistically significant increasing trend of winter precipitation in north Bulgaria was detected. No significant warming trend in the country was found during the last century inspite of the warming observed during the last two decades. Summer in Bulgaria tends to be warmer from the beginning of the 1980s. There is a statistically significant increasing trend of average air temperature during the winter season at the weather stations near the Danube river (north Bulgaria) during the periods 1901–2000 and 1931–2000.  相似文献   

Late Permian non-marine–marine transitional profiles in the central Southern Permian Basin, northern Germany     

B. Legler  U. Gebhardt  J. W. Schneider 《International Journal of Earth Sciences》2005,94(5-6):851-862

The transition from Rotliegend to Zechstein within the Southern Permian Basin is one from continental desert to a marine environment. During the Upper Rotliegend II a huge playa lake existed there. This lake was temporarily influenced by precursors of the Zechstein transgression. Therefore the mega-playa evolved into a sabkha system. One of these early marine ingressions is known from an outcrop in Schleswig-Holstein. Laminated silt- and claystones, deposited within a standing water body, are intercalated in siltstones of a salt-flat environment. The lake sediments are characterised by high frequency cyclicity, shown by the sedimentary record and also by palaeontological data. The section contains fresh water as well as brackish-marine and marine fauna. Climatically forced cycles interact with marine incursions. After the Zechstein transgression had flooded the basin completely, sedimentation was controlled by sea-level fluctuations. Two sections, in the southern North Sea and in Schleswig-Holstein, are presented in this paper. Cyclicities with different frequencies controlled the sedimentation of the Kupferschiefer (T1) and the Werra Carbonate (Ca1). Sediments of the North Sea sequence were deposited within a shallow bay at the margin of an elevation. Therefore, the high frequency cyclicity became obvious within the sedimentary patterns and in the faunal content.  相似文献   

Climatic Change Editorial Policy 2006     

Stephen H. Schneider 《Climatic change》2006,74(1-3):1-3

  相似文献   

A geometric model for linear-array-based terrestrial panoramic cameras   总被引：1，自引：0，他引：1  

Danilo  Schneider  Hans-Gerd  Maas 《The Photogrammetric Record》2006,21(115):198-210

  相似文献   

The Exosolar Planets Program of the COROT satellite     

Rouan  D.  Baglin  A.  Copet  E.  Schneider  J.  Barge  P.  Deleuil  M.  Vuillemin  A.  Léger  A. 《Earth, Moon, and Planets》1998,81(1):79-82

Earth, Moon, and Planets -  相似文献