K–Ar dating and δO–δD tracing of illitization within and outside the Shea Creek uranium prospect,Athabasca Basin,Canada     

Emmanuel Laverret  Norbert Clauer  Anthony Fallick  Julien Mercadier  Patricia Patrier  Daniel Beaufort  Patrice Bruneton 《Applied Geochemistry》2010

Isotope analyses (K–Ar, δ¹⁸O and δD) were performed on illite from both the sandstone cover and the underlying basement, close to and distant from Shea Creek, an unconformity-type U deposit (Athabasca Basin, Canada); the illite had previously been characterized crystallographically. In the barren areas away from deposit, illite is mainly of the cis-vacant 1M polytype occurring as relatively coarse-grained lath-shaped particles, while it occurs as fine-grained particles of the trans-vacant 1M type next to and in the U mineralized strata. The tectonic-induced hydrothermal system that favored illite crystallization was multi-episodic 1453 ± 2, 1330 ± 20 and probably about 1235 Ma ago. These illite-forming episodes appear to have occurred contemporaneously to those favoring the concentration of the associated U oxides, which were dated independently by the U–Pb method in the Shea Creek deposits and elsewhere in the Athabasca Basin.  相似文献   

Multi-imaging and Bayesian estimation for photon counting with EMCCDs   总被引：1，自引：0，他引：1  

Eric Lantz  Jean-Luc Blanchet  Luca Furfaro  Fabrice Devaux 《Monthly notices of the Royal Astronomical Society》2008,386(4):2262-2270

A multi-imaging strategy is proposed and experimentally tested to improve the accuracy of photon counting with an electron multiplying CCD (EMCCD), by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on one pixel. This strategy is based on Bayesian estimation on each image, with a priori information given by the sum of the images. The method works even for images with large dynamic range, with more improvement in the low light level areas. In these areas, two thirds of the variance added by the EMCCD in a conventional imaging mode are removed, making the physical photon noise predominant in the detected image.  相似文献   

Assessing climate change impacts,sea level rise and storm surge risk in port cities: a case study on Copenhagen   总被引：8，自引：1，他引：7  

Stéphane Hallegatte  Nicola Ranger  Olivier Mestre  Patrice Dumas  Jan Corfee-Morlot  Celine Herweijer  Robert Muir Wood 《Climatic change》2011,104(1):113-137

This study illustrates a methodology to assess the economic impacts of climate change at a city scale and benefits of adaptation, taking the case of sea level rise and storm surge risk in the city of Copenhagen, capital of Denmark. The approach is a simplified catastrophe risk assessment, to calculate the direct costs of storm surges under scenarios of sea level rise, coupled to an economic input–output (IO) model. The output is a risk assessment of the direct and indirect economic impacts of storm surge under climate change, including, for example, production and job losses and reconstruction duration, and the benefits of investment in upgraded sea defences. The simplified catastrophe risk assessment entails a statistical analysis of storm surge characteristics, geographical-information analysis of population and asset exposure combined with aggregated vulnerability information. For the city of Copenhagen, it is found that in absence of adaptation, sea level rise would significantly increase flood risks. Results call for the introduction of adaptation in long-term urban planning, as one part of a comprehensive strategy to manage the implications of climate change in the city. Mitigation policies can also aid adaptation by limiting the pace of future sea level rise.  相似文献   

Late Glacial and Holocene avulsions of the Rio Pastaza Megafan (Ecuador–Peru): frequency and controlling factors     

Carolina Bernal  Frédéric Christophoul  José Darrozes  Jean-Claude Soula  Patrice Baby  José Burgos 《International Journal of Earth Sciences》2011,100(7):1759-1782

The geomorphological study by means of remote sensing imagery of the Rio Pastaza Megafan (Ecuador and northern Peru) reveals the traces of numerous avulsions. One hundred and eight avulsion sites have been defined. The location of these sites, the available radiocarbon ages as well as historical maps of the seventeenth century, enable us to propose an evolution history of the migration and avulsions of the Rio Pastaza since the Last Glacial Maximum. The first avulsions of the Río Pastaza occurred after the LGM in a zone close to and roughly parallel to the sudandean front, where the developed avulsion gave a distributive pattern to the ancient stream of the Río Pastaza in an area located between the modern Río Morona and Pastaza, where they caused the Rio Pastaza to develop a fan-like distributary pattern. This is interpreted as a response to thrust-related forelimb tilt, progressively shifting eastward the Rio Pastaza and the apex of the megafan. This sequence of events ended with the Great Diversion of the Rio Pastaza towards the modern Rios Corrientes and Tigre. Avulsions occurred in the Tigre-Corrientes Area between 9200 and 8,500 years Cal BP. Afterwards, the Río Pastaza was diverted to its present-day north–south course. This last significant avulsion occurred before AD 1691. In the area located between the modern Río Morona and Pastaza, avulsion frequency—probably overestimated—ranges between 100 and 200 years. In the Ríos Tigre and Corrientes area, avulsion frequency—probably underestimated—ranges from 300 to 400 years. Regional tectonics is likely to have triggered most of the avulsions in the Morona Pastaza area but its influence is restricted to this area. The factors controlling the avulsions in the Tigre-Corrientes area are less clear because the frequently described “hydrologic”-driven avulsion as observed in areas characterized by contrasted hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the Rio Pastaza.  相似文献   

Exploratory and Instantaneous Swimming Speeds of Amphidromous Fish School in Shallow-Water Coastal Lagoon Channels     

Patrice Brehmer  Jean Guillard  Pablo I. Caballero Pinzon  Pascal Bach 《Estuaries and Coasts》2011,34(4):739-744

Fish school swimming speeds is essential for ecological and management studies. The multibeam sonar in horizontal beaming provided dynamic echo traces of mobile fish schools. We used two school swimming speed indicators: the average of a series of instantaneous speed values, and the exploratory speed. These swimming speeds were estimated for each fish school observed on the basis of their Euclidian position within the sonar beams. The average ISS values per school ranged from 0.15 m s⁻¹ to 4.46 m s⁻¹, while the ESS values per school were lower, ranging from 0.04 m s⁻¹ to 3.77 m s⁻¹. Multibeam sonar technology makes it possible to measure fish school swimming speeds in their natural habitat at small spatio-temporal scales. This methodology can therefore be used to analyse in situ their movements, and has a wide range of applications in behavioural studies and management purposes.  相似文献   

The 2011 expedition to the El'gygytgyn impact structure,Northeast Russia: Toward a new geological map for the crater area     

Ulli Raschke  Patrice Tristan Zaag  Ralf Thomas Schmitt  Wolf Uwe Reimold 《Meteoritics & planetary science》2014,49(6):978-1006

El'gygytgyn is a 3.6 Ma, 18 km diameter, impact crater formed in an approximately 88 Ma old volcanic target in Northeast Siberia. The structure has been the subject of a recent ICDP drilling project. In parallel to those efforts, a Russian‐German expedition was undertaken in summer 2011 to investigate the permafrost soil, lake terraces, and the volcanic rocks of the southern and eastern crater rim. This provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure. Samples from 43 outcrops were collected and analyzed petrographically and geochemically. The results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs, at the scale of 1:50,000. Compositions of our rock suites are compared with the lithologies of the 2009 ICDP drill core. The ignimbrite described as lower bedrock in the ICDP drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface. The suevite sequence exposed in the ICDP drill core is a mixture of all observed target rocks at their respective proportions in the area. In contrast to previous studies, the calculated average target composition of El'gygytgyn takes the contribution of the basic target rocks into consideration: mafic and intermediate rocks approximately 7.5%, and felsic rocks approximately 92.5%.  相似文献   

An experimental investigation of Arctic haze at Alert,N.W.T., March 1985     

N.B.A. Trivett  L.A. Barrie  J.W. Bottenheim  J.‐P. Blanchet  G. den Hartog  R.M. Hoff 《大气与海洋》2013,51(3):341-376

Abstract

Arctic haze has been attributed to industrial pollution released at mid‐latitudes. Our current understanding has been pieced together from routine meteorological data, ground‐based air chemistry observations and limited aircraft measurements. This study investigates the relationship between synoptic boundary‐layer meteorology and the composition of the near‐surface atmosphere during the polar sunrise at Alert, N.W.T. A secondary objective is to characterize the influence of local activity on the atmospheric composition at a site for a new baseline monitoring station and at a location where aerosol chemistry and grab‐flask samples for CO₂ have been made for many years. Detailed measurements of the vertical distribution of aerosols were obtained from an upward‐looking lidar to complement the ground‐based measurements. Meteorological profiles of the near‐surface boundary layer were obtained from both free‐flying and tethered balloons. Near‐surface measurements were made of aerosol physical and chemical properties, O₃, NO₂, NO/NO_x, Peroxyacetylnitrate (PAN) and hydrocarbons.

The study period was characterized by prolonged periods with strong surface inversions, which were broken up occasionally by intrusions of cold air into the warmer air aloft. Lidar observations showed that ice crystals often accompanied aerosols and were responsible for reducing visibility below 30–40 km. There was a strong correlation between aerosol mass in the diameter size range 0.15 to 1.5 μm and total SO₄ ⁼ . PAN found at concentrations of about 200 ppt(v) was the main carrier of atmospheric nitrogen. Aerosol trace elements were divisible into anthropogenic soil, mixed soil/anthropogenic sea salt and halogens. Vertical transport in the surface boundary layer, as regulated by the strength of the surface radiation inversion, may play an important role in influencing the chemical composition of the air at the ground. The location of the new baseline monitoring laboratory was found to be generally windier and warmer than the lower altitude weather station, and the influence of local activity was found to be minimal.  相似文献   

Dynamics of the turbidity maximum zone in a macrotidal estuary (the Gironde,France): Observations from field and MODIS satellite data     

David Doxaran  Jean-Marie Froidefond  Patrice Castaing  Marcel Babin 《Estuarine, Coastal and Shelf Science》2009,81(3):321-332

Over a 1-year period, field and satellite measurements of surface water turbidity were combined in order to study the dynamics of the turbidity maximum zone (TM) in a macrotidal estuary (the Gironde, France). Four fixed platforms equipped with turbidity sensors calibrated to give the suspended particulate matter (SPM) concentration provided continuous information in the upper estuary. Full resolution data recorded by the moderate resolution imaging spectroradiometer (MODIS) sensors onboard the Terra and Aqua satellite platforms provided information in the central and lower estuary twice a day (depending on cloud cover). Field data were used to validate a recently developed SPM quantification algorithm applied to the MODIS ‘surface reflectance’ product. The algorithm is based on a relationship between the SPM concentration and a reflectance ratio of MODIS bands 2 (near-infrared) and 1 (red). Based on 62 and 75 match-ups identified in 2005 with MODIS Terra and Aqua data, the relative uncertainty of the algorithm applied to these sensors was found to be 22 and 18%, respectively.Field measurements showed the tidal variations of turbidity in the upper estuary, while monthly-averaged MODIS satellite data complemented by field data allowed observing the monthly movements of the TM in the whole estuary. The trapping of fine sediments occurred in the upper estuary during the period of low river flow. This resulted in the formation of a highly concentrated TM during a 4-month period. With increasing river flow, the TM moved rapidly to the central estuary. A part of the TM detached, moved progressively in the lower estuary and was finally either massively exported to the ocean during peak floods or temporary trapped (settled) on intertidal mudflats. The massive export to the ocean was apparently the result of combined favorable environmental conditions: presence of fluid mud near the mouth, high river flow, high tides and limited wind speeds. The mean SPM concentration within surface waters of the whole estuary showed strong seasonal variations but remained almost unchanged on a 1-year-basis. These observations suggest that the masses of suspended sediments exported toward the ocean and supplied by the rivers were almost equivalent during the year investigated (2005). Results show the usefulness of information extracted from combined field and current ocean color satellite data in order to monitor the transport of suspended particles in coastal and estuarine waters.  相似文献   

Structures tectoniques et contraintes de cheminement des eaux dans les aquifères karstiques du barrois (Lorraine/Champagne,France)     

Alain Devos  Stéphane Jaillet  Patrice Gamez 《Geodinamica Acta》2013,26(3-4):249-257

Résumé

Entre Lorraine et Champagne, dans l’est du Bassin parisien, au contact des calcaires portlandiens du Barrois et des sables et argiles crétacés du Perthois, se développe un karst couvert. Le paysage de côtes est ici perturbé par une tectonique souple (synclinal de Treveray) et cassante (fossé d’effon-drement de la Marne) déterminant l’organisation spatiale des écoulements. En période d’étiage, les méthodes hydrologiques (profils hydrologiques lissés, traçages), permettent de montrer l’influence de cette tectonique d’ondulation et de basculement sur l’écoulement des rivières barroises (Saulx, Marne). Fractures et microfractures influencent la zone de transit vertical des eaux du karst (zone des puits) tandis que les failles compartimentent les aquifères (système du Rupt-du-Puits, 21 km de conduits, 13 km²). Les méthodes d’études hydrologiques, confirment le basculement de la région vers l’ouest déduit des comparaisons de nivellement. © Elsevier, Paris  相似文献   

A Method for Monitoring the Heat Flux from an Urban District with a Single Infrared Remote Sensor     

Aurélien Hénon  Patrice G. Mestayer 《Boundary-Layer Meteorology》2014,153(2):277-303

The proposed methodology relies on the modelling capabilities of the thermo-radiative model Solene to simulate the heat and radiation energy exchanges between an actual urban district and the atmosphere. It is based on the comparison of the simulated upward infrared and sensible heat flux diurnal cycles that may be measured by elevated sensors above the three-dimensional scene, as a function of sensor position: the heat flux is a function of an equivalent surface temperature given by the infrared sensor and an equivalent heat transfer coefficient deduced from Solene simulations with the actual geometry. The method is tested against measurements obtained in the city centre of Toulouse, France during an experimental campaign in 2004–2005. To improve the computation of the heat exchanges between air and building surfaces a new algorithm is first implemented, based on an empirical model of the wind distribution within street canyons. This improvement is assessed by a direct comparison of the simulated brightness surface temperatures of the Toulouse city centre to measurements obtained with an airborne infrared sensor. The optimization of the infrared remote sensor position is finally analyzed as a function of its height above the mean roof level: it allows evaluation of the heat flux from an urban district when the three different classes of surfaces (roofs, walls, grounds) have similar contributions to the infrared flux towards the sensor, and to the heat flux into the atmosphere.  相似文献