Identification of arid phases during the last 50 cal. ka BP from the Fuentillejo maar‐lacustrine record (Campo de Calatrava Volcanic Field,Spain)     

Juana Vegas  Blanca Ruiz‐Zapata  José E. Ortiz  Luis Galán  Trinidad Torres  Ángel García‐Cortés  María J. Gil‐García  Alfredo Pérez‐González  José L. Gallardo‐Millán 《第四纪科学杂志》2010,25(7):1051-1062

Geochemical (element analysis, molecular analysis of organic compounds), physical, palynological, mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in Fuentillejo maar‐lake in the Central Spanish Volcanic Field of Campo de Calatrava, in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies. The upper 20 m of core FUENT‐1 show variations in clastic input, water chemistry, vegetation and organic fraction sources in the lake throughout the Late Pleistocene and Holocene. The temporal framework provided by ¹⁴C accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal. ka BP. Arid phases identified in the FUENT‐1 sequence are correlated to Heinrich events (HE) and to stadials of the Dansgaard/Oeschger (D/O) cycles. Siliciclastic facies with high magnetic susceptibility values, high Juniperus pollen content, a low Paq index (aquatic macrophysics proxy index), a decrease in the relative percentage of the n‐C₂₇ and an increase in the n‐C₃₁ alkanes are indicative of arid and colder climatic events related to HE 2, HE 1 and the Younger Dryas (YD). Similar short cold and arid phases during the Holocene were identified at 9.2–8.6, 7.5–7 and 5.5–5 cal. ka BP. In dolomite–mud facies, the pollen data show an increase in the herbs component, mainly – Chenopodiaceae, Artemisia and Ephedra – steppe taxa; a low Paq index, a decrease in the relative percentage of the n‐C₂₇ alkane and an increase in the n‐C₃₁ alkane are also observed. This facies was probably the result of lower lake levels and more saline–alkaline conditions, which can be interpreted as linked to arid–warm periods. These warm and arid phases were more frequent during Marine Isotope Stage (MIS) 3 and the interstadials of MIS 2. HE 4, HE 2, HE 1 and the YD in core FUENT‐1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the D/O cycles but do not imply increasing humidity in the area. Fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the North Atlantic region at millennial scale during the last 50 cal. ka BP. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

La frana di Grassura (Fraz. di Cravagliana) in Val Mastellone     

Prof. Dott. Alfredo Boni 《Pure and Applied Geophysics》1947,10(1-2):192-194

Riassunto Breve descrizione ed analisi dei movimenti franosi verificatisi a Grassura (Cravagliana) nel Gennaio e nel Marzo 1947.

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Summary Short report on the rockfalls occured at Grassura (Cravagliana) in January and March 1947.

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Seismic vulnerability assessment and fragility analysis of pre-code masonry buildings in Portugal     

Bernardo  Vasco  Campos Costa  Alfredo  Candeias  Paulo  Costa  An&#;bal 《Bulletin of Earthquake Engineering》2022,20(11):6229-6265

Bulletin of Earthquake Engineering - Despite the fact that in recent years Portugal has not seen the occurrence of high-magnitude earthquakes, it remains threatened by these events due to its...  相似文献   

Spatial and temporal variation of natural recharge in the semi-arid valley of Aguascalientes,Mexico     

Martín Hernández-Marín  Lilia Guerrero-Martínez  Alfredo Zermeño-Villalobos  Lorena Rodríguez-González  Thomas J. Burbey  Jesús Pacheco-Martínez  Sergio I. Martínez-Martínez  Norma González-Cervantes 《Hydrogeology Journal》2018,26(8):2811-2826

The investigation involves a temporal and spatial analysis to characterize recharge in the Aguascalientes valley in central Mexico. The results are based on a two-part methodological strategy using a geospatial and numerical analysis. Results from the geospatial analysis are based on the analytical hierarchical process (AHP) method, which involves developing a zoning map that qualifies the conditions for groundwater recharge in the valley. In addition, one-dimensional numerical modeling based on the van Genuchten equation was applied for various soil column configurations to estimate the transit time of recharge through the vadose zone. The analysis was performed over a 20-year period from 1995 to 2015. The results of the geospatial analysis indicate that the optimal area for groundwater recharge is the lower zone of the valley, particularly the portion influenced by surface discontinuities. The shortest estimated period of recharge for water to pass through the vadose zone is approximately 4.25 years.  相似文献   

The Late Pleistocene distribution of vicuñas (Vicugna vicugna) and the “extinction” of the gracile llama (“Lama gracilis”): New molecular data     

Jaco Weinstock  Beth Shapiro  Alfredo Prieto  Juan Carlos Marín  Benito A. González  M. Thomas P. Gilbert  Eske Willerslev 《Quaternary Science Reviews》2009,28(15-16):1369-1373

We present the results of a palaeogenetic analysis of two Late Pleistocene camelids originating in southern Chile. Our analysis of two mitochondrial DNA fragments (control region and cytochrome b gene) reveals that these specimens do not belong to an extinct taxon, but rather to extant vicuña (Vicugna vicugna), whose modern distribution is restricted to the extreme elevations of the Andes, more than 3500 km to the north of where these specimens originated. Our results also suggest fossil specimens from Patagonia that are currently assigned to the extinct taxon Lama gracilis, may actually belong to V. vicugna, implying a continuous distribution of the latter from the southern tip of South America to the Andes during the Final Pleistocene. The haplotypes of both specimens are not present in modern populations, suggesting a loss of genetic diversity concomitant with the contraction of the vicuña geographical distribution during the Final Pleistocene or early Holocene.  相似文献   

Discriminant analysis as a method of predicting mineral occurrence potentials in central Norway     

Alfredo E. Prelat 《Mathematical Geology》1977,9(4):343-367

The statistical technique of discriminant analysis is used to define target areas for detailed general exploration given only general geological information and aeromagnetic anomaly blues. In the test area, located in Central Norway, on-going exploration surveys have revealed the presence of mineralization; however, it still has not been determined if any of the sites will beeconomically feasible. The area was divided into 1400 1-km × 1-km cells by superimposing square grid on 1:50,000-scale geological and geophysical maps. Later the area was divided into two subareas based on major differences in each area's geology. A number of geological natures and the aeromagnetic anomaly values were coded systematically in each cell. The cells representing an advanced degree of exploration were chosen as control cells in each of the subareas. The geological and geophysical parameters were transformed, by means of relatively simple transformations, to produce near-normal frequency distributions. A discriminant function was then obtained by discriminant analysis to divide the control data into two groups, cells with presence of mineral occurrence and cells without mineral occurrence. the discriminant function obtained for the control area proved to be relevant both geologically and statistically. Consequently, the discriminant equation was applied to cells outside the control area. The cells were assigned to one of the two groups by entering the geologic factors pleasured from the maps into the discriminant model. The exploration potential of a large number of cells was evaluated by this procedure. To test the results, field work including geochemical sampling was carried out in the cells with highest probability of mineral occurrance The field work results have shown that the application of discriminant analysis to geological information at 1:50,000 scale with 1-km × 1-km cells combined with a careful selection of techniques for transforming the variables is a feasible method for predicting gaeralization, and as such could become a valuable tool for mining exploration.This paper was presented at Symposium 116.3, Quantitative Strategy for Exploration, held as part of the 25th International Geological Congress, Sydney, Australia, August 1976.  相似文献   

The classical tests of cosmology with a simple Kantowski-Sachs model     

Alfredo B. Henriques 《Astrophysics and Space Science》1996,235(1):129-140

The classical tests of cosmology are applied to a simple cosmological model based on the Kantowski-Sachs metric and the results compared with those obtained for the standard model, based on the FRW metric. It is seen that for a large class of KS models the observations will not be able to distinguish between these models and the standard model. Some comments are also made with respect to the possibility of other tests, those involving the primordial nucleosynthesis and the generation of large scale structure, to constrain the acceptable KS models.  相似文献   

Long-Term Profiles of Wind and Weibull Distribution Parameters up to 600 m in a Rural Coastal and an Inland Suburban Area   总被引：1，自引：1，他引：0  

Sven-Erik Gryning  Ekaterina Batchvarova  Rogier Floors  Alfredo Peña  Burghard Brümmer  Andrea N. Hahmann  Torben Mikkelsen 《Boundary-Layer Meteorology》2014,150(2):167-184

An investigation of the long-term variability of wind profiles for wind energy applications is presented. The observations consists of wind measurements obtained from a ground-based wind lidar at heights between 100 and 600 m, in combination with measurements from tall meteorological towers at a flat rural coastal site in western Denmark and at an inland suburban area near Hamburg in Germany. Simulations with the weather research and forecasting numerical model were carried out in both forecast and analysis configurations. The scatter between measured and modelled wind speeds expressed by the root-mean-square error was about 10 % lower for the analysis compared to the forecast simulations. At the rural coastal site, the observed mean wind speeds above 60 m were underestimated by both the analysis and forecast model runs. For the inland suburban area, the mean wind speed is overestimated by both types of the simulations below 500 m. When studying the wind-speed variability with the Weibull distribution, the shape parameter was always underestimated by the forecast compared to both analysis simulations and measurements. At the rural coastal site although the measured and modelled Weibull distributions are different their variances are nearly the same. It is suggested to use the shape parameter for climatological mesoscale model evaluation. Based on the new measurements, a parametrization of the shape parameter for practical applications is suggested.  相似文献   

Heterogeneous seepage at the Nopal I natural analogue site, Chihuahua, Mexico     

Patrick F. Dobson  Teamrat A. Ghezzehei  Paul J. Cook  J. Alfredo Rodríguez-Pineda  Lourdes Villalba  Rodrigo De la Garza 《Hydrogeology Journal》2012,20(1):155-166

A study of seepage occurring in an adit at the Nopal I uranium mine in Chihuahua, Mexico, was conducted as part of an integrated natural analogue study to evaluate the effects of infiltration and seepage on the mobilization and transport of radionuclides. An instrumented seepage collection system and local automated weather station permit direct correlation between local precipitation events and seepage. Field observations recorded between April 2005 and December 2006 indicate that seepage is highly heterogeneous with respect to time, location, and quantity. Seepage, precipitation, and fracture data were used to test two hypotheses: (1) that fast flow seepage is triggered by large precipitation events, and (2) that an increased abundance of fractures and/or fracture intersections leads to higher seepage volumes. A few zones in the back adit recorded elevated seepage volumes immediately following large (>20 mm/day) precipitation events, with transit times of less than 4 h through the 8-m thick rock mass. In most locations, there is a 1?C6 month time lag between the onset of the rainy season and seepage, with longer times observed for the front adit. There is a less clear-cut relation between fracture abundance and seepage volume; processes such as evaporation and surface flow along the ceiling may also influence seepage.  相似文献   

Structural and biological control of the Cenozoic epithermal uranium concentrations from the Sierra Pe?a Blanca, Mexico     

Samuel Angiboust  Mostafa Fayek  Ian M. Power  Alfredo Camacho  Georges Calas  Gordon Southam 《Mineralium Deposita》2012,47(8):859-874

Epithermal uranium deposits of the Sierra Pe?a Blanca are classic examples of volcanic-hosted deposits and have been used as natural analogs for radionuclide migration in volcanic settings. We present a new genetic model that incorporates both geochemical and tectonic features of these deposits, including one of the few documented cases of a geochemical signature of biogenic reducing conditions favoring uranium mineralization in an epithermal deposit. Four tectono-magmatic faulting events affected the volcanic pile. Uranium occurrences are associated with breccia zones at the intersection of fault systems. Periodic reactivation of these structures associated with Basin and Range and Rio Grande tectonic events resulted in the mobilization of U and other elements by meteoric fluids heated by geothermal activity. Focused along breccia zones, these fluids precipitated under reducing conditions several generations of pyrite and uraninite together with kaolinite. Oxygen isotopic data indicate a low formation temperature of uraninite, 45–55°C for the uraninite from the ore body and ～20°C for late uraninite hosted by the underlying conglomerate. There is geochemical evidence for biological activity being at the origin of these reducing conditions, as shown by low δ³⁴S values (～?24.5‰) in pyrites and the presence of low δ¹³C (～?24‰) values in microbial patches intimately associated with uraninite. These data show that tectonic activity coupled with microbial activity can play a major role in the formation of epithermal uranium deposits in unusual near-surface environments.  相似文献