The origin of groundwater arsenic and fluorine in a volcanic sedimentary basin in central Mexico: a hydrochemistry hypothesis     

Iván Morales-Arredondo  Ramiro Rodríguez  Maria Aurora Armienta  Ruth Esther Villanueva-Estrada 《Hydrogeology Journal》2016,24(4):1029-1044

A groundwater sampling campaign was carried out in the summer of 2013 in a low-temperature geothermal system located in Juventino Rosas (JR) municipality, Guanajuato State, Mexico. This groundwater presents high concentrations of As and F^? and high Rn counts, mainly in wells with relatively higher temperature. The chemistry of major elements was interpreted with different methods, like Piper and D’Amore diagrams. These diagrams allowed for classification of four groundwater types located in three hydrogeological environments. The aquifers are hosted mainly in alluvial-lacustrine sediments and volcanic rocks in interaction with fault and fracture systems. The subsidence, faults and fractures observed in the study area can act as preferential channels for recharge and also for the transport of deep fluids to the surface, especially in the basin plain. The formation of a piezometric dome and the observed hydrochemical behavior of groundwater suggest a possible origin of the As and F^?. Geochemical processes occurring during water–rock interaction are related to high concentrations of As and F^?. High temperatures and alteration processes (like rock weathering) induce dissolution of As and F^?-bearing minerals, increasing the content of these elements in groundwater.  相似文献   

The rise of the diptera‐microbial mat interactions during the Cenozoic: consequences for the sedimentary record of saline lakes     

M. Esther Sanz‐Montero  José‐Pedro Calvo  M. Angeles García del Cura  Concepción Ornosa  Raimundo Outerelo  J. Pablo Rodríguez‐Aranda 《地学学报》2013,25(6):465-471

Shoreline gypsiferous sediments of an inland lake in central Spain furnishes valuable insight into reconstructions of early sedimentary changes related to shore fly–microbial mat interactions in fossil gypsum precipitating saline lake systems. The association of adult and larval forms of Ephydra (Diptera) with microbial matgrounds overlying the lake margin results in the formation of gypsiferous meniscate back‐filled burrows that provide an analogue for recurring, extensively developed trace fossils that occur in Cenozoic, but not older, lacustrine gypsum rocks. In this setting, sediment burrowing by ephydridae hinders significant preservation of microbialites. The overwhelming rise of Diptera at the onset of the Cenozoic resulted in extensive feeding and dwelling activity and contributed to reshape the saline aquatic habitat where microbial mats thrived, thus leading to the formation of specific trace fossils that are illustrative of the existence of microbes in the paleoenvironment.  相似文献   

The Cretaceous sediment-hosted copper deposits of San Marcos (Coahuila,Northeastern Mexico): An approach to ore-forming processes     

Donají García-Alonso  Carles Canet  Eduardo González-Partida  Ruth Esther Villanueva-Estrada  Rosa María Prol-Ledesma  Pura Alfonso  Juan Antonio Caballero-Martínez  Rufino Lozano-Santa Cruz 《Journal of South American Earth Sciences》2011,31(4):432-443

In the San Marcos ranges of Cuatrociénegas, NE Mexico, several sediment-hosted copper deposits occur within the boundary between the Coahuila Block, a basement high mostly granitic in composition and Late Paleozoic to Triassic in age, and the Mesozoic Sabinas rift basin. This boundary is outlined by the regional-scale synsedimentary San Marcos Fault. At the basin scale, the copper mineralization occurs at the top of a ～1000 m thick red-bed succession (San Marcos Formation, Berrisian), a few meters below a conformable, transitional contact with micritic limestones (Cupido Formation, Hauterivian to Aptian). It consists of successive decimeter-thick roughly stratiform copper-rich horizons placed just above the red-beds, in a transitional unit of carbonaceous grey-beds grading to micritic limestones. The host rocks are fine- to medium-grained arkoses, with poorly sorted and subangular to subrounded grains. The detrital grains are cemented by quartz and minor calcite; besides, late iron oxide grain-coating cement occurs at the footwall unmineralized red-beds. The source area of the sediments, indicated by their modal composition, is an uplifted basement. The contents of SiO₂ (40.70–87.50 wt.%), Al₂O₃ (5.91–22.00 wt.%), K₂O (3.68–12.50 wt.%), Na₂O (0.03–2.03 wt.%) and CaO (0.09–3.78 wt.%) are within the ranges expected for arkoses. Major oxide ratios indicate that the sedimentary-tectonic setting was a passive margin.The outcropping copper mineralization essentially consists in a supergene assemblage of chrysocolla, malachite and azurite. All that remains of the primary mineralization are micron-sized chalcocite grains shielded by quartz cement. In addition, pyrite subhedral grains occur scattered throughout the copper-mineralized horizons. In these weathered orebodies copper contents range between 4.24 and 7.72 wt.%, silver between 5 and 92 ppm, and cobalt from 8 to 91 ppm. Microthermometric measurements of fluid inclusions in quartz and calcite crystals from footwall barren veinlets gave temperatures of homogenization between 98 °C and 165 °C, and ice-melting temperatures between ?42.5 °C and ?26.1 °C.The primary copper mineralization formed during the early diagenesis, contemporary with the active life of the Sabinas Basin. The mineralizing fluids were dense, near neutral, moderately oxidized brines that originally formed from seawater that, driven by gravity, infiltrated to the deepest parts of the basin and dissolved evaporites. As a result, they became hydrothermal fluids of moderate temperature capable of leaching high amounts of copper. The source of this metal could be mafic detrital grains and iron oxides of the underlying Jurassic and Lower Cretaceous red-beds. Copper precipitation took place when the brines passed through the redox boundary marked by the transition from red- to grey-beds. The upward movement of the brines was promoted by a high heat flow that allowed their convective circulation and their ascent along the synsedimentary San Marcos Fault.  相似文献   

The spatial and temporal distribution of grain‐size breaks in turbidites     

Christopher J. Stevenson  Peter J. Talling  Douglas G. Masson  Esther J. Sumner  Michael Frenz  Russell B. Wynn 《Sedimentology》2014,61(4):1120-1156

Grain‐size breaks are surfaces where abrupt changes in grain size occur vertically within deposits. Grain‐size breaks are common features in turbidites around the world, including ancient and modern systems. Despite their widespread occurrence, grain‐size breaks have been regarded as exceptional, and not included within idealized models of turbidity current deposition. This study uses ca 100 shallow sediment cores, from the Moroccan Turbidite System, to map out five turbidite beds for distances in excess of 2000 km. The vertical and spatial distributions of grain‐size breaks within these beds are examined. Five different types of grain‐size break are found: Type I – in proximal areas between coarse sand and finer grained structureless sand; Type II – in proximal areas between inversely graded sand overlain by finer sand; Type III – in proximal areas between sand overlain by ripple cross‐laminated finer sand; Type IV – throughout the system between clean sand and mud; and Type V – in distal areas between mud‐rich (debrite) sand and mud. This article interprets Types I and V as being generated by sharp vertical concentration boundaries, controlled by sediment and clay concentrations within the flows, whilst Types II and III are interpreted as products of spatial/temporal fluctuations in flow capacity. Type IV are interpreted as the product of fluid mud layers, which hinder the settling of non‐cohesive grains and bypasses them down slope. Decelerating suspensions with sufficient clay will always form cohesive layers near to bed, promoting the generation of Type IV grain‐size breaks. This may explain why Type IV grain‐size breaks are widespread in all five turbidites examined and are commonplace within turbidite sequences studied elsewhere. Therefore, Type IV grain‐size breaks should be understood as the norm, not the exception, and regarded as a typical feature within turbidite beds.  相似文献   

Dinoflagellate Cyst Assemblages in Surface Sediments from Three Shallow Mediterranean Lagoons (Sardinia,North Western Mediterranean Sea)     

Cecilia T. Satta  Sílvia Anglès  Esther Garcés  Nicola Sechi  Silvia Pulina  Bachisio Mario Padedda  Daniela Stacca  Antonella Lugliè 《Estuaries and Coasts》2014,37(3):646-663

The present study identified and quantified dinoflagellate cysts in surface sediments from three Mediterranean lagoons. Sediment samples were recovered from 11 stations in May 2009 at Cabras Lagoon, eight stations in May 2010 at Corru S'Ittiri Lagoon, and five stations in May 2011 at Santa Giusta Lagoon. Fifty-three dinoflagellate cyst morphotypes were identified. Sixteen species are first reports for the lagoons, and two for the Mediterranean Sea. Moreover, a new Scrippsiella species was discovered in Cabras. Seven harmful algal species were identified, primarily belonging to the potentially toxic genus Alexandrium. Total cyst abundance, number of morphotypes, and assemblages varied among lagoons, and each lagoon showed a distinct morphotype composition. A degree of heterogeneity was also detected within lagoon. Cabras and Santa Giusta cyst assemblages were characterised by morphotypes belonging to the autotrophic genus Scrippsiella, whereas Corru S'Ittiri assemblages showed dominance of heterotrophic morphotypes, including Protoperidinium cf tricingulatum. Differentiation among lagoons was also evident according to environmental conditions. Salinity proved to be a fundamental variable in determining total cyst abundance, morphotype number, and composition. This study was among the first to examine dinoflagellate cyst composition in coastal lagoons, especially from the Mediterranean region, and contributed data that increased our knowledge of cyst-producing dinoflagellates in these environments.  相似文献   

Deep solid-state equilibration and deep melting of plagioclase-free spinel peridotite from the slow-spreading Mid-Atlantic Ridge, ODP Leg 153     

Thomas M. Will  Esther Schmädicke  Hartwig E. Frimmel 《Mineralogy and Petrology》2010,100(3-4):185-200

A petrological investigation of abyssal, plagioclase-free spinel peridotite drilled during ODP cruise 153 in the North Atlantic revealed that the peridotite represent refractory, partial residual mantle material that experienced depletion of incompatible trace elements during upper mantle melting. The degree of partial melting as estimated from spinel compositions was c. 12%. Fractionated middle and heavy rare earth elements imply polybaric melting, with c. 1–4% initial melting in the garnet peridotite stability field and subsequent partial melting of ~7–10% in the spinel peridotite stability field. Geothermobarometric investigations revealed that the solid-state equilibration of the spinel peridotite occurred at some 1,100–1,150°C and c. 20–23 kbar, corresponding to an equilibration depth of c. 70?±?5 km and an unusually low thermal gradient of some 11–17°C/km. A thermal re-equilibration of the peridotite occurred at ~850–1,000°C at similar depths. Naturally, the initial mantle melting in the garnet-peridotite stability field must have commenced at depths greater than 70?±?5 km. It is likely that the residual peridotite rose rapidly through the lithospheric cap towards the ridge axis. The exhumation of the abyssal peridotite occurred, at least in parts, via extensional detachment faulting. Given the shallow to moderate dip angles of the fault surfaces, the exhumation of the peridotite from its equilibration depth would imply an overall ridge-normal horizontal displacement of c. 50–160 km if tectonic stretching and detachment faulting were the sole exhumation mechanism.  相似文献   

Can Jupiters be found by monitoring Galactic bulge microlensing events from northern sites?     

Yiannis Tsapras  Rachel A. Street  Keith Horne  Alan Penny  Fraser Clarke  Hans Deeg  Francisco Garzon  Simon Kemp  Maria Rosa Zapatero Osorio  Alejandro Oscoz Abad  Santiago Madruga Sanchez  Carlos Eiroa  Alcione Mora  Antxon Alberdi  rew Cameron  John K. Davies  Roger Ferlet  Carol Grady  Allan W. Harris  Javier Palacios  reas Quirrenbach  Heike Rauer  Jean Schneider  Dolf de Winter  Bruno Merin  Enrique Solano 《Monthly notices of the Royal Astronomical Society》2001,325(3):1205-1212

In 1998 the EXPORT team monitored microlensing event light curves using a charge-coupled device (CCD) camera on the IAC 0.8-m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic bulge sources make a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1-m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass.  相似文献   

The Global/Regional Integrated Model system (GRIMs)   总被引：5，自引：0，他引：5  

Song-You Hong  Hoon Park  Hyeong-Bin Cheong  Jung-Eun Esther Kim  Myung-Seo Koo  Jihyeon Jang  Suryun Ham  Seung-On Hwang  Byoung-Kwon Park  Eun-Chul Chang  Haiqin Li 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(2):219-243

  相似文献   

Coastal inshore waters in the NW Mediterranean: Physicochemical and biological characterization and management implications     

Eva Flo  Esther Garcés  Marta Manzanera  Jordi Camp 《Estuarine, Coastal and Shelf Science》2011

The physicochemical and biological characteristics of coastal waters form a gradient extending from land to ocean. In the Mediterranean this gradient is particularly large, due to the sea’s weak tides. Within coastal waters, those waters in contact with land are called coastal inshore waters (CIW), defined herein as between 0 and 200 m from the shoreline. Here we present the first physicochemical and biological characterization of CIW of the NW Mediterranean Sea. This case study is based on 19 years of data collected from coastal inshore (CIW; 0–200 m), nearshore (CNW; 200–1500 m), and offshore (COW; >1500 m) waters of the Catalan coast. Analyses of these data showed that the physicochemical and biological characteristics of CIW differ significantly from those of CNW and COW due to: (1) significantly higher concentrations of dissolved inorganic nutrients (nitrate = 11.07 μM, nitrite = 0.52 μM, ammonium = 6.43 μM, phosphate = 0.92 μM, silicates = 5.99 μM) and chlorophyll-a (=2.42 μg/L) in CIW than in either CNW or COW (in some cases up to one order of magnitude); (2) a greater variability of dissolved inorganic nutrients and chlorophyll-a in CIW than in CNW and COW, and (3) the presence of a mostly urban population and the effects of river inflows as a primary source of CIW variability but with minimal impact on CNW or COW. In addition, the risk of eutrophication was found to be highest in CIW, placing human and environmental interests at greater risk than in the outermost coastal waters. The results highlight the importance of considering the distinctive physicochemical and biological properties of CIW in future coastal waters studies. This is of major importance in assessments of eutrophication and coastal water quality, not only to identify the pressure–impact relationships but also to allow the timely detection of local environmental problems and thus avoid endangering the unique communities of CIW and ensuring the sustainability of human activities. In conclusion, CIW characterization is essential to integrate coastal zone management.  相似文献   

Climate changes and human activities recorded in the sediments of Lake Estanya (NE Spain) during the Medieval Warm Period and Little Ice Age   总被引：2，自引：0，他引：2  

Mario Morell��n  Blas Valero-Garc��s  Pen��lope Gonz��lez-Samp��riz  Teresa Vegas-Vilarr��bia  Esther Rubio  Maria Rieradevall  Antonio Delgado-Huertas  Pilar Mata  ��scar Romero  Daniel R. Engstrom  Manuel L��pez-Vicente  Ana Navas  Jes��s Soto 《Journal of Paleolimnology》2011,46(3):423-452

A multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42°02?? N, 0°32?? E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and ²¹⁰Pb and ¹³⁷Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150?C1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300?C1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years.  相似文献