Major ion geochemistry of groundwaters from southern Nevada and eastern California, USA     

周小平  KEVINH．JOHANNESSON 《中国地球化学学报》2000,19(1):1-22

The dissolved ionic constitutents of groundwaters are,in part,a recored of the minerals and rocks in aquifers through which the water has flowed.The chemical composition and association of these major ions in groundwaters have been used to trace groundwater flow paths and sources,In general,the chemical compostion of water in carbonate-rock aquifers in dominated by calcium,magnesium,and bicarbonate,whereas sodium,chloride,and sulfate can be dominant ions in the water that comes from volcanic aquifers or clay minerals.Since the 1990‘s,we have dealt with the geochemistry of groundwaters from more than 100 springs and wells in southern Nevada and eastrn california ,USA for major solutes and trace elements.This paper compiles the hydrochemical data of major ions of these groundwaters.Based on major ion geochemistry,groundwaters from southern Nevada and eastern California can be classified as carbonate aquifer water,volcanic aquifer water,and mixing water (either mixing of cabonate and volcanic aquifer waters or mixing with local recharges),Piper and stiff diagrams of major ions have graphically shown the general chemical characteristics,classification,and mixing relationships of groundwaters from southern Nevada and eastern California.  相似文献   

Defining drivers of nitrogen stable isotopes (δ15N) of surface sediments in temperate lakes     

Morgan Botrel  Irene Gregory-Eaves  Roxane Maranger 《Journal of Paleolimnology》2014,52(4):419-433

The nitrogen stable isotopic signature (δ¹⁵N) of sediment is a powerful tool to understand eutrophication history, but its interpretation remains a challenge. In a large-scale comparative approach, we identified the most important drivers influencing surface sediments δ¹⁵N of 65 lakes from two regions of Canada using proxies that reflect watershed nitrogen (N) sources, internal lake microbial cycling and productivity. Across regions, we found that water column total nitrogen (TN),  %N in the sediments and lake morphometric variables were the best predictors of sedimentary δ¹⁵N, explaining 66 % of its variation. Significant relationships were also found between sediment δ¹⁵N and human-derived N load ( \( R_{{{\text{adj}} .}}^{2} \)  = 0.23, p < 0.001), the latter being a strong predictor of TN ( \( R_{{{\text{adj}} .}}^{2} \)  = 0.68, p < 0.001). Despite a relatively strong overall relationship, variation partitioning revealed an interesting difference in the dominant variable that influenced regional δ¹⁵N. Alberta lake sedimentary δ¹⁵N signature was dominated by human derived N load. In contrast, internal processing appeared to be more important in Quebec lakes, where sediment δ¹⁵N was best explained by  %N in the sediments and lake volume. Overall, our findings support the use of δ¹⁵N in paleolimnological investigations to reconstruct changing N sources to lakes but also highlight that regions may have distinctive drivers. Interpretations of sediment δ¹⁵N are likely to be strongest when multiple lines of evidence are employed and when placed in a regional context.  相似文献   

Seismic hazard assessment in central Ionian Islands area (Greece) based on stress release models     

Irene Votsi  George M. Tsaklidis  Eleftheria E. Papadimitriou 《Acta Geophysica》2011,59(4):701-727

The long-term probabilistic seismic hazard of central Ionian Islands (Greece) is studied through the application of stress release models. In order to identify statistically distinct regions, the study area is divided into two subareas, namely Kefalonia and Lefkada, on the basis of seismotectonic properties. Previous results evidenced the existence of stress transfer and interaction between the Kefalonia and Lefkada fault segments. For the consideration of stress transfer and interaction, the linked stress release model is applied. A new model is proposed, where the hazard rate function in terms of X(t) has the form of the Weibull distribution. The fitted models are evaluated through residual analysis and the best of them is selected through the Akaike information criterion. Based on AIC, the results demonstrate that the simple stress release model fits the Ionian data better than the non-homogeneous Poisson and the Weibull models. Finally, the thinning simulation method is applied in order to produce simulated data and proceed to forecasting.  相似文献   

Transgressive dunefield landforms and vegetation associations,Doña Juana,Veracruz, Mexico     

Patrick Hesp  Marisa Martinez  Graziela Miot da Silva  Natalia Rodríguez‐Revelo  Erika Gutierrez  Adriana Humanes  Daniela Laínez  Irene Montaño  Verónica Palacios  Agustín Quesada  Lorena Storero  Gabriela González Trilla  Carolina Trochine 《地球表面变化过程与地形》2011,36(3):285-295

Transgressive dune fields often comprise a multiplicity of landforms where vegetation processes largely affect landform dynamics, which in turn, also affect vegetation processes. These associations have seldom been studied in detail. This paper examines four separate landform types in a complex coastal transgressive dunefield located in the central Gulf of Mexico, in order to assess the relationships between dunefield habitat, local environmental factors, vegetation associations and landform evolution. Topographic surveys using tape and clinometer were conducted in conjunction with vegetation survey transects at four locations across the Doña Juana dunefield. Vegetation surveys allowed the estimation of relative plant cover of each plant species found along the transects. A large variety of landforms were found at the Doña Juana Dunefield: deflation plains, gegenwalle (counter) ridges, transverse dune trailing ridges, blowouts and parabolic dunes, aklé (fish‐scale shaped) dunefields and precipitation ridges, with plant species associations developing on these different landforms equally variable. Flood tolerant species were located in the lower parts (deflation plain and gegenwalle ridges) whereas the older and dryer parts were covered by coastal matorral shrubs. Burial‐tolerant species were dominant in the most mobile areas (blowouts and aklé dunefield and margin). The dune trailing ridge, with relatively milder conditions, showed the highest richness, with no dominant species. A dual interaction was found such that colonizing species both create and affect topography, and in turn, topography determines vegetation association and succession patterns. In coastal dunes, the vegetation and abiotic environment (namely the different landforms and the inherent micronevironmental variability) interact tightly and generate a complex and highly dynamic biogeomorphic system where substrate mobility and colonization processes reinforce one another in positive feedback. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Short‐term versus medium‐term monitoring for detecting gully‐erosion variability in a Mediterranean environment     

Irene Marzolff  Johannes B. Ries  Jean Poesen 《地球表面变化过程与地形》2011,36(12):1604-1623

This study investigates how medium‐term gully‐development data differ from short‐term data, and which factors influence their spatial and temporal variability at nine selected actively retreating bank gullies situated in four Spanish basin landscapes. Small‐format aerial photographs using unmanned, remote‐controlled platforms were taken at the gully sites in short‐term intervals of one to two years over medium‐term periods of seven to 13 years and gully change during each period was determined using stereophotogrammetry and a geographic information system. Results show a high variability of annual gully retreat rates both between gullies and between observation periods. The mean linear headcut retreat rates range between 0·02 and 0·26 m a^–1. Gully area loss was between 0·8 and 22 m² a^–1 and gully volume loss between 0·5 to 100 m³ a^–1, of which sidewall erosion may play a considerable part. A non‐linear relationship between catchment area and medium‐term gully headcut volume change was found for these gullies. The short‐term changes observed at the individual gullies show very high variability: on average, the maximum headcut volume change observed in 7–13 years was 14·3 times larger than the minimum change. Dependency on precipitation varies but is clearly higher for headcuts than sidewalls, especially in smaller and less disturbed catchments. The varying influences of land use and human activities with their positive or negative effects on runoff production and connectivity play a dominant role in these study areas, both for short‐term variability and medium‐term difference in gully development. The study proves the value of capturing spatially continuous, high‐resolution three‐dimensional data using small‐format aerial photography for detailed gully monitoring. Results confirm that short‐term data are not representative of longer‐term gully development and demonstrate the necessity for medium‐ to long‐term monitoring. However, short‐term data are still required to understand the processes – particularly human activity at varying time scales – causing fluctuations in gully erosion rates. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Calibration of cosmogenic Cl production rates from Ca and K spallation in lava flows from Mt. Etna (38°N, Italy) and Payun Matru (36°S, Argentina)     

Irene Schimmelpfennig  Lucilla Benedetti  Raphaël Pik  Pete Burnard  Robert Finkel  Katja Ammon 《Geochimica et cosmochimica acta》2011,75(10):2611-9

Published cosmogenic ³⁶Cl production rates from Ca and K spallation differ by almost a factor of 2. In this paper we determine production rates of ³⁶Cl from Ca and K in samples of known age containing little Cl. Ca-rich plagioclases and K-feldspars were separated from a total of 13 samples collected on the surfaces of four basaltic lava flows at Mt. Etna (38°N, Italy) and from a trachyte lava flow at Payun Matru volcano (36°S, Argentina). Eruption ages, determined by independent methods, range between 0.4 and 32 ka. Sample site elevations range between 500 and 2500 m. Corresponding scaling factors were calculated using five different published scaling models, four of which consider paleo-geomagnetic field variations integrated over the exposure durations. The resulting five data sets were then analyzed using a Bayesian statistical model that incorporates the major inherent uncertainties in a consistent way. Spallation production rates from Ca and K, considering all major uncertainties, are 42.2 ± 4.8 atoms ³⁶Cl (g Ca)⁻¹ a⁻¹ and 124.9 ± 8.1 atoms ³⁶Cl (g K)⁻¹ a⁻¹ normalized to sea level and high latitude using the scaling method of Stone (2000). Scaling models that account for paleo-geomagnetic intensity changes yield very similar mean values (at most +4%). If the uncertainties in the independent ages are neglected in the Bayesian model, the calculated element specific production rates would be about 12% higher. Our results are in agreement with previous production rate estimations both for Ca and K if only low Cl (i.e. ?20 ppm) samples are considered.  相似文献   

Changes in tropical Atlantic interannual variability from a substantial weakening of the meridional overturning circulation   总被引：1，自引：1，他引：0  

Irene Polo  Buwen W. Dong  Rowan T. Sutton 《Climate Dynamics》2013,41(9-10):2765-2784

In response to a substantial weakening of the Atlantic Meridional Overturning Circulation (AMOC)—from a coupled ocean–atmosphere general circulation model experiment—significant changes in the interannual variability are found over the tropical Atlantic, characterized by an increase of variance (by ~150 %) in boreal late spring-early summer and a decrease of variance (by ~60 %) in boreal autumn. This study focuses on understanding physical mechanisms responsible for these changes in interannual variability in the tropical Atlantic. It demonstrates that the increase of variability in spring is a consequence of an increase in the variance of the El Niño-Southern Oscillation, which has a large impact on the tropical Atlantic via anomalous surface heat fluxes. Winter El Niño (La Niña) affects the eastern equatorial Atlantic by decreasing (increasing) cloud cover and surface wind speed which is associated with anomalous downward (upward) short wave radiation and reduced (enhanced) upward latent heat fluxes, creating anomalous positive (negative) sea surface temperature (SST) anomalies over the region from winter to spring. On the other hand, the decrease of SST variance in autumn is due to a deeper mean thermocline which weakens the impact of the thermocline movement on SST variation. The comparison between the model results and observations is not straightforward owing to the influence of model biases and the lack of a major MOC weakening event in the instrumental record. However, it is argued that the basic physical mechanisms found in the model simulations are likely to be robust and therefore have relevance to understanding tropical Atlantic variability in the real world, perhaps with modified seasonality.  相似文献   

Physical properties and structure of the lower crust revealed by one- and two-dimensional modelling     

K.-J. Sandmeier  W. Walde  F. Wenzel 《Geophysical Journal International》1987,89(1):339-344

Summary. Data from a refraction and a reflection seismic survey in the Black Forest, southwest Germany, are used for extensive one- and two-dimensional modelling. The data are available along approximately the same line, and therefore the same piece of crust is probed by two seismic methods. We utilize this favorable circumstance for detailed model calculations concerning both data sets. Lower crustal properties vary on the scale of a wavelength and thus full solutions of the elastic equations are required: the Reflectivity Method for the evaluation of refraction seismograms and numerical solutions of the acoustic wave equation for the reflection response. Details of the geometry and physical properties of the lamination are derived. Vertical layering on a scale of 100 m is found; horizontal extent of reflecting elements is in the range of a few hundreds of meters; rocks with velocities between 5.6 and 7.2 km/s constitute the lower crust.  相似文献   

Dry granular masses impacting on rigid obstacles: numerical analysis and theoretical modelling     

Redaelli  Irene  di Prisco  Claudio  Calvetti  Francesco 《Acta Geotechnica》2021,16(12):3923-3946

Acta Geotechnica - The assessment of the time evolution of the impact force exerted by dry flowing masses on rigid obstacles is mandatory for the dynamic design of sheltering structures and the...  相似文献   

Mantle derived crystal-poor rhyolitic ignimbrites: Eruptive mechanism from geochemical and geochronological data of the Piedra Parada caldera,Southern Argentina     

Eugenio Aragon  Antonio Castro  Juan Diaz-Alvarado  Lucio Pinotti  Fernando D'eramo  Manuel Demartis  Jorge Coniglio  Irene Hernando  Carmen Rodriguez 《地学前缘(英文版)》2018,9(5):1529-1553

Trace elements, isotopic modeling and U-Th-Pb SHRIMP zircon age constraints are used to reconstruct the eruption history and magmatic processes of the Piedra Parada Caldera. In the early Eocene, the crystal-poor Barda Colorada ignimbrite(BCI), having 15% micro-porphyritic crystals with respect to magmatic components, erupted a volume estimated in more than 300 km~3. The Piedra Parada caldera is located in the Patagonian Andes foreland, at the southern end of the calderas field of the Pilcaniyeu Volcanic Belt(PVB). This belt is related to an extensional tectonic setting as a result of the collision of the Farallon-Aluk ridge with South America, which enabled the development of a transform ocean/continental plate margin followed by the detachment of the Aluk plate and the opening of a slab window. The BCI extra-caldera Plateau is a 100 m thick deposit, having a lower unit with high silica(Si O_2 76 wt.%),potassium poor rhyolitic composition(trondhjemitic like magma), and an upper unit with normal to high potassium rhyolitic composition(granitic like magma). A trace elements modeling of the BCI units shows that the BCI lower and upper units did not evolve from fractionation or immiscibility in the shallow magma reservoir. The BCI also have a primitive isotopic signature(initial87 Sr/86 Sr =0.7031-0.7049 and ε_(Nd)= +3.4 to +3.65). Thus, tectonic, compositional and isotopic constraints suggest the fast ascent of high silica magmas to a shallow reservoir, and point to an upper mantle origin for these rhyolitic magmas in a transitional(Orogenic-Anorogenic) tectono-magmatic setting. U-Th-Pb SHRIMP zircon crystallization ages of the Syn-caldera stage BCI units(56 -51.5 Ma) show a protracted life of 5 Ma for this caldera reservoir. The age of 52.9 ± 0.3 Ma is considered the best fit for the possible maximum age for the caldera collapse. The Late-caldera magmatism has trachyandesitic and rhyolitic compositions.The trace element modeling suggests that these rhyolites evolve from the trachyandesites and do not evolve from the BCI residual magma. The trachyandesites have U-Th-Pb SHRIMP zircon crystallization ages of 52 ± 1 Ma, suggesting that the caldera eruption was triggered by the arrival of the trachyandesitic magma.  相似文献