Assessment of groundwater circulation in La Gomera aquifers (Canary Islands, Spain) from their hydrochemical features     

María Leal  Javier Lillo  Álvaro Márquez 《Environmental Earth Sciences》2014,71(1):23-30

La Gomera (Canary Islands, Spain) does not show water scarcity like other islands of the Archipelago. However, the study of its aquifers is paramount as nearly 60 % of the water supplies are covered with spring water. According to the currently accepted hydrogeological model, La Gomera presents an upper aquifer consisting of perched groundwater bodies. Below this hydrogeological unit, the General Saturated Zone or basal groundwater is placed. The model also establishes the presence of flows through them. Many perched groundwater bodies are located under Garajonay National Park where most of the springs are found. Therefore, if upper and lower aquifers are truly connected and new wells are built, the new extractions could affect Garajonay ecosystems. With the aim of identifying spring groups and related potential areas of water transfer, hydrochemical and statistical analyses (principal component analysis and cluster analysis) have been applied. This study shows the great compositional variability of groundwaters, precluding the identification of spring groups, hydrochemical patterns and, therefore, the transfer areas with no possibility of assessing the potential impact of a water demand increase on the Garajonay National Park ecosystems from the present data. Only the springs belonging to group II of the cluster analysis could indicate a transfer area. The lack of conclusive results could be due to: (1) great compositional variability of volcanic materials; (2) unequal influence of marine aerosols; (3) irregular distribution of rainfall; (4) different grades of soils development; and (5) the occurrence of partially disconnected water bodies giving as a result a complex hydrogeological system.  相似文献   

Exceptional silica speleothems in a volcanic cave: A unique example of silicification and sub‐aquatic opaline stromatolite formation (Terceira,Azores)     

Raquel Daza Brunet  María Ángeles Bustillo Revuelta 《Sedimentology》2014,61(7):2113-2135

Silica stromatolites occur in a number of modern hydrothermal environments, but their formation in caves is very rare. The silica stromatolitic speleothems of the Branca Opala cave (Terceira Island, Azores), however, provide an excellent opportunity for their study. These formations may be analogous to ancient silica stromatolites seen around the world. Petrographic, mineralogical and geochemical analyses were undertaken on the silica speleothems of the above cave, and on the silica‐tufa deposits outside it, with the aim of understanding their genesis. The possible hydrothermal origin of their silica is discussed. X‐ray diffraction analyses showed opal‐A to be the sole silica phase. Negligible ordering of this opal‐A showed ageing to be insignificant, as expected for recent silica deposits. Most of the silica speleothems examined were definable as sub‐aquatic opaline stromatolites that are not currently growing. Optical microscopy clearly revealed a lower microlaminated, an intermediate and an upper microlaminated zone within the stromatolites. Stromatolite types (I, II and III) were classified with respect to their internal structure and distribution throughout the cave. Scanning electron microscopy showed silicified bacterial filaments within the stromatolites, the silicified plant remains and the silica‐tufa deposits. Bacteria therefore played a major role in the precipitation of the opal‐A. Plasma emission/mass spectrometry showed major, minor and rare earth elements to be present in only small quantities. The rare earth elements were mainly hosted within volcanic grains. Rapid silica precipitation from highly super‐saturated water would explain the intense silicification of the plant remains found inside and outside the cave. The opaline stromatolites, the silica‐tufa deposits and the above‐mentioned intense general silicification suggest a local hydrothermal source for the silica. Indeed, these deposits strongly resemble plant‐rich silica sinter associated with low‐temperature hot spring deposits that include bacterial filaments. However, no geochemical signals that might indicate a hydrothermal origin could be found.  相似文献   

Geochemistry,provenance and tectonic setting of the Late Cambrian–Early Ordovician Seydişehir Formation in the Çaltepe and Fele areas,SE Turkey     

Mehmet Muzaffer Karadağ 《Chemie der Erde / Geochemistry》2014

The major, trace and rare earth element (REE) contents of metapelite (MPL), metapsammite (MPS) and metamarl (MM) samples from the Cambro-Ordovician Seydi?ehir Formation were analyzed to investigate their provenance and tectonic setting. The MPS, MPL, and MM samples have variable SiO₂ concentrations, with average values of 72.36, 55.54, and 20.95 wt%, moderate SiO₂/Al₂O₃ ratios (means of 6.88, 3.23, and 3.80), moderate to high Fe₂O₃ + MgO contents (means of 5.14, 9.55, 3.56 wt%), and high K₂O/Na₂O ratios (means of 3.26, 3.64, 2.90), respectively. On average, the chemical index of alteration (CIA) values of the MPS and the MPL are 65.87 and 71.96, respectively, while the chemical index of weathering (CIW) values are 74.54 and 85.09, respectively. These data record an intermediate to high degree of alteration (weathering) of plagioclase to illite/kaolinite in the samples’ provenance. The chondrite-normalized REE patterns of all the sample groups are similar and are characterized by subparallel light rare earth elements (LREE)-enriched, relatively flat heavy rare earth elements (HREE) patterns with pronounced Eu anomalies (mean of 0.69) and moderate fractionation [average (La/Yb)_N = 8.7]. Plots of sediments in ternary diagrams of La, Th, Sc and elemental ratios (La/Sc, Th/Sc, Cr/Th, Eu/Eu*, La/Lu, Co/Th, La/Sc and Sc/Th), which are critical for determining provenance, and REE patterns indicate that the metaclastic units of the Seydi?ehir Formation were derived dominantly from felsic to intermediate magmatic rocks and not from a mafic source. The La–Sc–Th and Th–Sc–Zr/10 ternary diagrams of the Seydi?ehir Formation are typical of continental island arc/active continental margin tectonic settings. The geologic location and geochemistry of the Seydi?ehir Formation suggest that it was deposited in an Andean-type retroarc foreland basin during the Late Cambrian–Early Ordovician period. The Neoproterozoic intermediate to felsic magmatic rocks and metaclastic sediments with felsic origins of the Sand?kl?–Afyon Basement Complex (SBC) and their equivalent units, which are thought to be overlain by the younger units in the study area, may be the dominant source rocks for the Seydi?ehir Formation.  相似文献   

City of Bingöl in May 2003: Assessment of strong ground motion records     

U Çeken  G Beyhan  H H Selim 《Journal of Earth System Science》2014,123(2):381-394

The main shock of Bingöl earthquake (M _W = 6.4) recorded by six accelerometers in the area occurred at 03:27 local time on May 1, 2003. The largest acceleration value of north–south component was recorded as 545.5 cm/s² at the nearest station which it is 12 km away from the epicenter of earthquake. Especially, 0.15 s short period was observed when high spectral acceleration value occurred. An acceleration value greater than 50 gal was recorded at the BNG (Bingöl) station and structural damage occurred within 6.5 s was very important for the near source and strong ground motion seismology. The recorded peak acceleration values were greater than the estimated empirical acceleration values. However, the structural damage was not as high and widespread as expected. This occurrence was explained by considering the factors of earthquake source, frequency content, effective duration, effective acceleration value, local soil conditions, rupture direction and attenuation.  相似文献   

Representing Spain: cultural image and geographic knowledge in National Geographic’s articles on Spain (1888–1936)     

Jacobo García-Álvarez  Paloma Puente-Lozano  Juan-Manuel Trillo-Santamaría 《GeoJournal》2014,79(5):539-556

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The Geomorphological Context of Medieval Juslibol Castle in the Middle Reaches of the River Ebro,Spain     

Jos L. Pea‐Monn  Virginia Rubio‐Fernndez  Luis A. Longares‐Aladrn  Francisco J. Gutirrez‐Gonzlez  Fernando Prez‐Lambn  Carlos Laliena‐Corbera 《Geoarchaeology》2014,29(6):448-461

An interdisciplinary non‐invasive research strategy combining the analysis of archival documents, detailed geomorphological mapping, Quaternary stratigraphic studies, analysis of ceramics, and radiocarbon dating was designed to reconstruct the evolution of the Mezimegeer–Juslibol Castle, northeastern Spain. This fortress had great strategic importance in the siege and conquest of the nearby Islamic city of Saraqusta by the Christians in A.D. 1118. The castle and moat complex was built in the mid‐10th century. In the mid‐12th century, its rapid degradation began, as it is shown by this geoarchaeological study of the sediments in the moats. Its present state of decay is due to later erosion that is promoted by the unstable bedrock of Miocene gypsum, highly deformed gravels that form a Pleistocene fluvial terrace, and the environmental aridity.  相似文献   

Characterization of Colliery Spoils in León: Potential Uses in Rural Infrastructures     

Joaquín Ferreras Cadierno  Manuel Ignacio Guerra Romero  Andrés Juan Valdés  Julia Mª Morán del Pozo  Julia García González  Desirée Rodríguez Robles  José Vallepuga Espinosa 《Geotechnical and Geological Engineering》2014,32(2):439-452

One of the bases of sustainable development is the responsible management of natural resources, and this is the approach which has been adopted by developed countries as regards management of all kinds of waste, through the establishment of management strategies based on prevention, reuse and recycling. This article present the results of a physical, chemical and geotechnical characterization of colliery spoils stored in slag heaps in the Ciñera-Matallana coal mining area in León, Spain. The primary objectives of this research were to determine the suitability of this mining waste for use as granular material in rural and civil engineering infrastructures and to classify it according to national and international road construction standards. On the basis of the results obtained, they are proposed several possible uses (foundation and core layers in track and road embankments, granular sub-base for light traffic and top layers of embankments), although it should be noted the need for mechanical treatments as crushing or sieving and the recommendation of use of sulphate resistant cement to avoid the possible problems.  相似文献   

Fluid Inclusion and Stable Isotope Studies at Don Sixto,a Precious Metal Low Sulfidation Deposit in Mendoza Province,Argentina     

Ana Cecilia Mugas Lobos  María Florencia Márquez‐Zavalía 《Resource Geology》2013,63(4):350-359

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (～4 km²), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (T_h) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaCl_equiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaCl_equiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ¹⁸O_H2O = ?6.92 up to ?3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ³⁴S_H2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.  相似文献   

Trace metal and radionuclide pollution in marine sediments of the Aegean Sea (Izmir Bay and Didim)     

S. Aközcan  A. Uğur Görgün 《Environmental Earth Sciences》2013,69(7):2351-2355

To determine radioactivity and trace metal levels, surface sediments were collected from two important areas (?zmir Bay and Didim) in the Aegean Sea region of Turkey, and were analyzed for concentrations of ²¹⁰Po, ²¹⁰Pb and trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn). The average ²¹⁰Po and ²¹⁰Pb massic activities in sediments varied in the range of 24 ± 5 to 126 ± 6 Bq kg^?1 dry wt. and 18 ± 3 to 59 ± 4 Bq kg^?1 dry wt., respectively. Izmir Bay exhibited the highest polonium activities in sediments, likely due to specific sedimentation processes and other sediment characteristics. The trace metal results showed that the Izmir Bay is facing trace metal pollution. The metal concentrations in sediment samples are low compared to those from the other neighboring marine environments.  相似文献   

Assessment of the physico-mechanical behaviour of gypsum-lime repair mortars as a function of curing time     

Jesús Igea Romera  Sagrario Martínez-Ramírez  Pilar Lapuente  María Teresa Blanco-Varela 《Environmental Earth Sciences》2013,70(4):1605-1618

Gypsum-based mortars were widely used during the Mudejar artistic period in Spain from the 12th to 16th century. During restoration works, compatibility between the new repair mortars and the original components is essential for an adequate intervention on the monument. The increasing interest of knowing the properties of the gypsum-lime-based mortars for restoration purposes justifies the research carried out. Different mortars compatible with traditional building materials were elaborated by varying the binder proportions, the type of aggregates, the binder/aggregate ratios and the curing time. The main goal of this paper is to characterize the mechanical behaviour and the pore structure of the mortars as a function of curing time. The influence between the different variables used to prepare the mortars and the development of the carbonation process over time is also considered. Mechanical strength and porosity measurements as well as X-ray diffraction and thermal analysis were performed after curing times of 1, 28 and 90 days. The results obtained confirmed a progressive increase in mechanical strength linked to the carbonation of the mortars prepared. Less lime binder and also aggregate contents showed the highest rise in strength over time, related to the highest initial porosity which favoured the carbon dioxide flow. The use of siliceous aggregates (GL-QS mortars) obtained the best results in the development of physico-mechanical properties over curing time. The knowledge obtained from the studied mortars provides practical information to establish a suitable mortar mixture for restoration works on historic buildings and modern architecture where gypsum-lime-based mortars are used.  相似文献