Geochemical evolution and salinization of a coastal aquifer via seepage through peaty lenses     

Nicolò Colombani  Micòl Mastrocicco 《Environmental Earth Sciences》2016,75(9):798

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Origins of metamorphic lode gold deposits: Implications of stable isotope data from the central Rocky Mountains,Canada     

R. P. Shaw  R. D. Morton  J. Gray  H. R. Krouse 《Mineralogy and Petrology》1991,43(3):193-209

Summary The stable isotope geochemistry of native gold-bearing quartz veins contained within low-grade metasedimentary strata in the central Canadian Rocky Mountains, British Columbia is examined. The data augment previous geological and geochemical studies.Vein pyrite ³⁴S values cluster between + 14.2 and + 16.3 (CDT). Coeval galenas exhibit ³⁴S values between + 11.4 and 13.3. Pyrite-galena geothermometry reveals a mean temperature of mineralization of 300 ± 43°C. Comparison of ³⁴S values for the vein pyrites, with values for pyrite porphyroblasts in country rocks suggests that vein sulfur was probably derived from the host rocks.¹⁸O(SMOW) values of host quartzites and pelites cluster between + 12.0 and + 13.5, and + 9.5 and + 10.5, respectively. Auriferous vein quartz exhibits ¹⁸O values between + 13.0 and + 15.0. Veins were likely deposited from fluids undergoing post-peak metamorphic cooling.Vein inclusion fluids exhibit values between –105 and –124 (SMOW). Combined O-H-isotope data are most compatible with a source fluid involving chemically- and isotopically-evolved meteoric waters.The critical role of H-isotope data in the evaluation of source fluids for such mesothermal gold lodes is stressed. The paucity of H-isotope data pertaining to the study of lode gold deposits in similar low-grade metasedimentary domains suggests that the involvement of meteoric waters may at times be overlooked.

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Der Ursprung metamorphogener Gold-Ganglagerstätten: Bedeutung stabiler Isotopendaten aus den zentralen Rocky Mountains, Kanada

Zusammenfassung Die vorliegende Arbeit befaßt sich mit der Untersuchung der Geochemie stabiler Isotope goldführender Quarzgänge in schwach metamorphen Sedimenten der zentralen Rocky Mountains in Britisch Kolumbien, Kanada. Die Resultate ergänzen früher publizierte geologische und geochemische Daten.Die ³⁴S-Werte von Gang-Pyrit liegen zwischen + 14.2 und + 16.3 (CDT); gleichzeitig gebildeter Bleiglanz hat ³⁴S-Werte von + 11.4 bis + 13.3. Die Isotopengeothermo metrie des Pyrits und Bleiglanzes ergibt eine mittlere Mineralisationstemperatur von 300°C + 43° für diese beiden Minerale. Vergleiche der 8345-Werte des Gang-Pyrits mit denen von Pyrit-Porphyroblasten des Nebengesteins lassen für die Gang-Pyrite eine Herkunft des Schwefels aus dem Nebengestein als wahrscheinlich erscheinen.Die ¹⁸O-Werte von Quarziten und Peliten, die als Nebengesteine auftreten, streuen von + 12.0 bis + 13.5 (SMOW), beziehungweise von +9.5 bis + 10.5 Quarz goldführender Gänge hat ¹⁸O-Werte, die zwischen + 13.0 und + 15.0 (SMOW) liegen. Er wurde als Gangfüllung wahrscheinlich bei sinkenden Temperaturen aus post metamorphen wäßrigen Lösungen abgesetzt.Flüssigkeitseinschlüsse von Gangmineralien zeigen D-Werte von -105 bis -124 (SMOW). Die H-O-Isotope sind deshalb ein Hinweis dafür, daß als mineralisierende Lösungen isotopisch veränderte meteorische Wässer in Betracht zu ziehen sind. Bei der Deutung der Herkunft der mineralisierenden wäßrigen Lösungen von mesothermalen Goldgängen muß die Kenntnis der H-Isotope als kritisch betrachtet werden. Die Seltenheit mit der H-Isotopendaten dieses Lagerstättentyps in der Literatur diskutiert werden, dürfte ein wesentlicher Grund dafür sein, daß die Rolle meteorischer Wässer bei der Genese mesothermaler, in Metasedimenten liegender Goldgänge, vielfach übersehen wurde.

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With 4 Figures  相似文献   

Network Topology and City Accessibility of the Commercial Internet     

David C. Wheeler  Morton E. O'Kelly 《The Professional geographer》1999,51(3):327-339

The rapid growth in this decade of World Wide Web access through the Internet is supported by a complex matrix of telecommunications infrastructure. This paper presents an overview of the history of the Internet and recent efforts to measure its structure and performance, and examines the spatial organization of the commercial Internet backbone. The research presented in this paper differs from previous Internet measurement work in that we apply network analysis methods to evaluate Internet connectivity. Transportation network analysis techniques are applied to measure 1) connectivity of individual service provider networks and 2) accessibility of cities to Internet service. The results reveal many different strategies implemented by service providers in network design as well as large differences in levels of accessibility of cities and regions in the United States. There is also an apparent disparity between population and city accessibility to the Internet.  相似文献   

Reclamation influence and background geochemistry of neutral saline soils in the Po River Delta Plain (Northern Italy)     

Dario Di Giuseppe  Barbara Faccini  Micòl Mastrocicco  Nicolò Colombani  Massimo Coltorti 《Environmental Earth Sciences》2014,72(7):2457-2473

Reclaimed neutral saline sulphate soils constitute a large part of the eastern part of Po Plain lowlands, where intensive agricultural activities take place. The knowledge of their geochemical features is essential to develop the best management practices capable to preserve this threatened environment. With this aim, three boreholes were drilled in an agricultural field and a typical reclaimed soil profile has been characterized for major and trace element, pH, electrical conductivity, redox conditions and water-soluble anions and ammonium. Statistical analysis (cluster analysis and principal component analysis) has been used to understand the relationship between elements and grain size. The soil profile is characterized by high salinity and high organic matter contents responsible for high chloride, sulphate, and ammonium concentrations. Heavy metal content is naturally high, since Po Plain sediments are the result of ultramafic rocks erosion; in addition, organic matter tends to concentrate heavy metals by adsorption, mainly in peaty horizons. As a consequence of chemical and zootechnical fertilization, high NO₃ ^? contents have been found in the top soil, thus enhancing the risk of nitrate discharge in the water system, especially in relation to extreme climatic events.  相似文献   

Origin of Carboniferous sandstones fringing the northern margin of the Wales‐Brabant Massif: insights from detrital zircon ages     

Andrew Morton  Colin Waters  Mark Fanning  Ian Chisholm  Matt Brettle 《Geological Journal》2015,50(5):553-574

A study of detrital zircon age populations in Namurian–Westphalian (Carboniferous) sandstones in the southern Central Pennine Basin of the UK has revealed considerable complexity in their provenance history. The Pendleian–Marsdenian Morridge Formation, which is known to have been derived from the Wales‐Brabant Massif to the south on the basis of palaeocurrent and petrographic information, is dominated by zircons ultimately derived from the Caledonian belt to the north. These zircons were recycled from sandstones of northern origin that had been previously deposited over the massif during Middle to Late Devonian times. The Morridge Formation also includes Late Neoproterozoic zircons of local Wales‐Brabant Massif origin. The south lobe of the Yeadonian Rough Rock has been previously interpreted as having a complex provenance including sediment of northern origin interbedded with sediment ascribed to a Wales‐Brabant Massif source. However, the zircon spectrum lacks a Late Neoproterozoic component that would have been diagnostic of input from the Wales‐Brabant Massif, and the provenance history of the Rough Rock south lobe therefore remains enigmatic. The Langsettian Ludgbridge Conglomerate is dominated by Late Neoproterozoic zircons of Wales‐Brabant Massif origin, but even in this evidently proximal deposit, the provenance is complex since the main zircon group (ca. 640 Ma) cannot be matched with known local Neoproterozoic basement sources. The data either indicate the presence of hitherto‐unknown magmatic rocks of this age adjacent to the South Staffordshire coalfield or indicate that the zircons were recycled from sediment with a more distal origin. Finally, the Duckmantian Top Hard Rock contains zircons that can be reconciled with a source in the Irish Caledonides, consistent with the palaeocurrent evidence, supplemented by zircons derived from the Wales‐Brabant Massif, possibly including the Monian Composite Terrane of Anglesey. The study reinforces the important message that failure to recognize the presence of recycled zircon could lead to erroneous reconstructions of sediment provenance and transport history. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Use of shallow groundwater temperature profiles to infer climate and land use change: interpretation and measurement challenges          下载免费PDF全文

Nicolò Colombani  Beatrice Maria Sole Giambastiani  Micòl Mastrocicco 《水文研究》2016,30(14):2512-2524

Temperature is often used to infer the effect of land use and climate conditions on aquifers. Reliable data are needed to examine the temperature behaviour in the subsurface; thus, the use of robust acquisition techniques is unavoidable. Three temperature measurement techniques were applied to assess the sources of bias that could occur during temperature logging in a shallow Quaternary coastal aquifer in Ferrara (Northern Italy). Open borehole temperature logging, multilevel sampling straddle packers isolated temperature measurements within a flow cell above ground and multilevel sampling straddle packers isolated temperature measurements via an in‐well level logger (MLS‐IW) were compared for several coastal monitoring wells to gain insights on the limitations of each technique. Results show that the source of bias between the three applied techniques are different: (i) the open borehole temperature logging method tends to record heat convection through the open borehole and is not representative of the aquifer temperature distribution; (ii) the multilevel sampling straddle packers isolated temperature measurements within a flow cell above ground method is swayed by the air temperature and the heating of the submersible pump used to lift groundwater above ground; and (iii) the MLS‐IW provides the most reliable vertical thermal profiling both in summer and winter, because groundwater temperature is directly measured at the selected monitoring depth. The implementation of a 1D flow model demonstrates that if precise temperature profiles are needed to infer the influence that land use and climate changes have on groundwater, the MLS‐IW method is a reliable method that could be applied to existing monitoring wells. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Paired bedrock and boulder 10Be concentrations resulting from early Holocene ice retreat near Jakobshavn Isfjord,western Greenland     

Lee B. Corbett  Nicolás E. Young  Paul R. Bierman  Jason P. Briner  Thomas A. Neumann  Dylan H. Rood  Joseph A. Graly 《Quaternary Science Reviews》2011,30(13-14):1739-1749

We measured in situ cosmogenic ¹⁰Be in 16 bedrock and 14 boulder samples collected along a 40-km transect outside of and normal to the modern ice margin near Sikuijuitsoq Fjord in central-west Greenland (69°N). We use these data to understand better the efficiency of glacial erosion and to infer the timing, pattern, and rate of ice loss after the last glaciation. In general, the ages of paired bedrock and boulder samples are in close agreement (r² = 0.72). Eleven of the fourteen paired bedrock and boulder samples are indistinguishable at 1σ; this concordance indicates that subglacial erosion rates are sufficient to remove most or all ¹⁰Be accumulated during previous periods of exposure, and that few, if any, nuclides are inherited from pre-Holocene interglaciations. The new data agree well with previously-published landscape chronologies from this area, and suggest that two chronologically-distinct land surfaces exist: one outside the Fjord Stade moraine complex (～10.3 ± 0.4 ka; n = 7) and another inside (～8.0 ± 0.7 ka; n = 21). Six ¹⁰Be ages from directly outside the historic (Little Ice Age) moraine show that the ice margin first reached its present-day position ～7.6 ± 0.4 ka. Early Holocene ice margin retreat rates after the deposition of the Fjord Stade moraine complex were ～100–110 m yr^?1. Sikuijuitsoq Fjord is a tributary to the much larger Jakobshavn Isfjord and the deglaciation chronologies of these two fjords are similar. This synchronicity suggests that the ice stream in Jakobshavn Isfjord set the timing and pace of early Holocene deglaciation of the surrounding ice margin.  相似文献   

An ocean observation system for monitoring the affects of climate change on the ecology and sustainability of pelagic fisheries in the Pacific Ocean     

Simon J. Nicol  Valerie Allain  Graham M. Pilling  Jeff Polovina  Marta Coll  Johann Bell  Paul Dalzell  Peter Sharples  Robert Olson  Shane Griffiths  Jeffrey M. Dambacher  Jock Young  Antony Lewis  John Hampton  Jesus Jurado Molina  Simon Hoyle  Karine Briand  Nic Bax  Patrick Lehodey  Peter Williams 《Climatic change》2013,119(1):131-145

Climate change presents an emerging challenge to the sustainable management of tuna fisheries, and robust information is essential to ensure future sustainability. Climate and harvest affect tuna stocks, populations of non-target, dependent species and the ecosystem. To provide relevant advice we need an improved understanding of oceanic ecosystems and better data to parameterise the models that forecast the impacts of climate change. Currently ocean-wide data collection in the Pacific Ocean is primarily restricted to oceanographic data. However, the fisheries observer programs that operate in the region offer an opportunity to collect the additional information on the mid and upper trophic levels of the ecosystem that is necessary to complement this physical data, including time-series of distribution, abundance, size, composition and biological information on target and non-target species and mid trophic level organisms. These observer programs are in their infancy, with limited temporal and spatial distribution but recent international and national policy decisions have been made to expand their coverage. We identify a number of actions to initiate this monitoring including: consolidating collaborations to ensure the use of best quality data; developing consistency between sub-regional observer programmes to ensure that they meet the objectives of ecosystem monitoring; interrogating of existing time series to determine the most appropriate spatial template for monitoring; and exploring existing ecosystem models to identify suitable indicators of ecosystem status and change. The information obtained should improve capacity to develop fisheries management policies that are resilient and can be adapted to climate change.  相似文献   

On the use of marine radar imagery for estimation of properties of the directional spectrum of the sea surface     

Joseph R. Buckley  Morton Allingham  Réjean Michaud 《大气与海洋》2013,51(1):195-213

Abstract

The “sea clutter” observable on a standard marine navigation radar has long been recognized as a potential source of information about sea state. In the last decade a number of researchers have published “directional wave spectra” calculated from marine radar images. Our group has continued this line of research using a unique radar system that digitizes and stores radar images eight bits deep directly related to the strength of the radar backscatter.

Our system was deployed on the CSS Hudson during the Grand Banks ERS‐1 SAR Wave Spectrum Validation Experiment cruise in November 1991. We collected in excess of 3000 sea surface backscatter images. From this dataset we have produced a number of directional spectra in an effort to understand the performance of the sensor and to compare it with other wave determining instruments and models.

Analysis has shown a strong azimuthal asymmetry both in the strength of the backscattered signal and in the relative strength of spectral peaks. This asymmetry is similar inform to that observed in scatterometer data. Unbiased estimation of the “true” image spectrum requires removal of these asymmetries. This estimation has been accomplished through calculation and removal of a non‐linear multi‐parameter least‐squares model of the backscatter from each image, and averaging of spectra from many look directions. The resulting spectra compare favourably with those calculated from directional wave buoy data, satellite and aircraft SARs and other directional wave measurements and models.  相似文献   

An evaluation of evapotranspiration in tropical central Africa     

F. I. Morton 《水文科学杂志》2013,58(5):527-529

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