Luminescence evidence for two Middle Pleistocene interglacial events at Tourville, northwestern France     

SANDA BALESCU  MICHEL LAMOTHE  JEAN-PIERRE LAUTRIDOU 《Boreas: An International Journal of Quaternary Research》1997,26(1):61-72

The infrared stimulated luminescence (IRSL) dating method is applied to alkali feldspar coarse grains from the two distinct Middle Pleistocene interglacial estuarine deposits of Tourville, located along the Seine Valley. The upper deposit (unit D), previously dated at 200 ka by ESR on in situ shells and correlated with a stage 7 high sea-level stand (186–245 ka), yields a measured IRSL age of 176 ± 21 ka. The lower deposit (unit B) assigned to a distinctly older high sea-level event (stage 9: 303–339 ka) yields a measured IRSL age of 273 ± 28 ka. The nearby stage 7 raised beach of Sangatte, in Northwestern France, previously dated by TL on quartz (229 ± 18 ka) yields a measured IRSL age of 186 ± 19 ka. These IRSL age estimates systematically underestimate the expected geological ages. This could be due to the long-term fading or instability of the luminescence signal in alkali feldspars. The correction for long-term fading has been tested on these samples. At Tourville, it yields corrected IRSL ages of 196 ± 23ka and 314 ± 32ka, for the upper and lower units respectively and, at Sangatte, a corrected IRSL age of 206 ± 20 ka. These corrected IRSL age estimates are in better agreement with the expected geological ages. This study demonstrates the potential of the feldspar luminescence dating method to provide chronological information on Middle Pleistocene interglacial estuarine sediments within the North Sea-English Channel Basin.  相似文献   

Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador)   总被引：4，自引：1，他引：3  

SAMANIEGO  PABLO; MARTIN  HERVE; MONZIER  MICHEL; ROBIN  CLAUDE; FORNARI  MICHEL; EISSEN  JEAN-PHILIPPE; COTTEN  JOSEPH 《Journal of Petrology》2005,46(11):2225-2252

In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the Wadati–Benioff zone and favouring slab partialmelting. KEY WORDS: adakites; ⁴⁰Ar/³⁹Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes  相似文献   

Quantification of carbon dioxide, methane, nitrous oxide and chloroform emissions over Ireland from atmospheric observations at Mace Head     

SÉBASTIEN BIRAUD  PHILIPPE CIAIS  MICHEL RAMONET  PETER SIMMONDS  VICTOR KAZAN  PATRICK MONFRAY  SIMON O'DOHERTY  GERARD SPAIN  S. GERRARD JENNINGS 《Tellus. Series B, Chemical and physical meteorology》2002,54(1):41-60

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Evaluation of 2001 springtime CO transport over West Africa using MOPITT CO measurements assimilated in a global chemistry transport model     

STÉPHANIE PRADIER  JEAN-LUC ATTIÉ  MICHEL CHONG  JUAN ESCOBAR  VINCENT-HENRI PEUCH  JEAN-FRANÇOIS LAMARQUE  BORIS KHATTATOV  DAVID EDWARDS 《Tellus. Series B, Chemical and physical meteorology》2006,58(3):163-176

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Données isotopiques (8786/Sr) et changements hydrologiques depuis 15 000 ans sur l'Altiplano andin     

ANNE COUDRAIN  MICHEL LOUBET  THOMAS CONDOM  AMAL TALBI  PIERRE RIBSTEIN  BERNARD POUYAUD 《水文科学杂志》2013,58(2):293-306

Abstract

In catchments characterized by spatially varying hydrological processes and responses, the optimal parameter values or regions of attraction in parameter space may differ with location-specific characteristics and dominating processes. This paper evaluates the value of semi-distributed calibration parameters for large-scale streamflow simulation using the spatially distributed LISFLOOD model. We employ the Shuffled Complex Evolution Metropolis (SCEM-UA) global optimization algorithm to infer the calibration parameters using daily discharge observations. The resulting posterior parameter distribution reflects the uncertainty about the model parameters and forms the basis for making probabilistic flow predictions. We assess the value of semi-distributing the calibration parameters by comparing three different calibration strategies. In the first calibration strategy uniform values over the entire area of interest are adopted for the unknown parameters, which are calibrated against discharge observations at the downstream outlet of the catchment. In the second calibration strategy the parameters are also uniformly distributed, but they are calibrated against observed discharges at the catchment outlet and at internal stations. In the third strategy a semi-distributed approach is adopted. Starting from upstream, parameters in each subcatchment are calibrated against the observed discharges at the outlet of the subcatchment. In order not to propagate upstream errors in the calibration process, observed discharges at upstream catchment outlets are used as inflow when calibrating downstream subcatchments. As an illustrative example, we demonstrate the methodology for a part of the Morava catchment, covering an area of approximately 10 000 km². The calibration results reveal that the additional value of the internal discharge stations is limited when applying a lumped parameter approach. Moving from a lumped to a semi-distributed parameter approach: (i) improves the accuracy of the flow predictions, especially in the upstream subcatchments; and (ii) results in a more correct representation of flow prediction uncertainty. The results show the clear need to distribute the calibration parameters, especially in large catchments characterized by spatially varying hydrological processes and responses.  相似文献   

Using TOPMODEL towards identifying and modelling the hydrological patterns within a headwater,humid, tropical catchment     

HELENA MOLIOV  MICHEL GRIMALDI  MIKE BONELL  PIERRE HUBERT 《水文研究》1997,11(9):1169-1196

Increasing pressure on the tropical environment requires a more thorough understanding of hydrological processes as part of reconciling the conflicting demands of economic development vis-à-vis sustainable land management. Using TOPMODEL, a physically based semi-distributed topohydrological model, we test its validity in modelling the stream flow dynamics (hydrograph) in a 1 ha tropical rainforest catchment in French Guiana. Another objective is through field validation of TOPMODEL to ascertain possible runoff generation mechanisms. The field validation of the temporal and spatial hydrodynamics across a rainfall–runoff event reveals that TOPMODEL may be suited for applications to this particular tropical rainforest environment; in fact, this is possibly the first successful application of such a model within the humid tropics. The main reasons why the model was successful are the presumed low hydraulic conductivities of the subsoil, coupled with the absence of an additional deep groundwater body, the contribution from which has caused difficulties in application of topographically, ‘physically’ based runoff models elsewhere in the humid tropics. © 1997 John Wiley & Sons, Ltd.  相似文献   

Accelerator mass spectrometry measurements and model calculations of iron-60 production rates in meteorites     

K. KNIE  S. MERCHEL  G. KORSCHINEK  T. FAESTERMANN  U. HERPERS  M. GLORIS  R. MICHEL 《Meteoritics & planetary science》1999,34(5):729-734

Abstract— The cosmogenic radionuclide ⁶⁰Fe (T_1/2 = 1.49 Ma) was measured in two iron meteorites as well as in the magnetic fractions of a stony-iron and a stony meteorite by means of accelerator mass spectrometry (AMS). The measured ⁶⁰Fe/Fe ratios range from 1.5 × 10-¹⁴ to 6.3 × 10-¹⁴ and show a significant correlation to the respective concentrations of Ni, which is the main target element. The resulting ⁶⁰Fe specific activities correspond to production rates in meteorites in the order of 1 dpm/kg Ni. In addition, model calculations of depth- and size-dependent ⁶⁰Fe production rates were performed. Although there are no experimental data for the production cross sections, our measurements are in surprisingly good agreement with the theoretical predictions using production cross sections that were determined by computer model calculations.  相似文献   

Seasonal predictability of tropical rainfall: probabilistic formulation and validation     

MICHEL DÉQUÉ 《地球，A辑:动力气象学与海洋学》2001,53(4):500-512

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Holocene palaeoenvironments at the timberline in the French Alps—a multidisciplinary approach     

LUCIEN TESSIER  JACQUES-LOUIS DE BEAULIEU  MICHEL COUTEAUX  JEAN-LOUIS EDOUARD  PHILIPPE PONEL  CHRISTIANE ROLANDO  MICHEL THINON  RE THOMAS  KAZIMIR TOBOLSKI 《Boreas: An International Journal of Quaternary Research》1993,22(3):244-254

An attempt is made to reconstruct the palaeoenvironmental Holocene history at the timberline on the basis of the analysis of various palaeoecological proxy indicators available on a marshy area and its surroundings in the Taillefer Massif (Isère. France). The multidisciplinary approach involves analyses of pollen assemblages. plant macrofossils, coleoptera remains. subfossil trunks extracted from lakes or peat-bogs. and charcoals derived from the surrounding soils. This enables definition of the respective roles of five forest taxa ( Pinus uncinata Mill., Pinus cembra L., Larix decidua Mill., Abies alba Mill, and Picea abies L. Karsten) in the evolution of high altitude forests during the Holocene. Pinus uncinata was present on the plateau throughout the Holocene. Larix and Pinus cembra were present only during two periods: 7500-5000 BP and 3500-2000 BP. All trees disappeared from the plateau at about 2000 BP, while, at lower altitude. Abies was replaced by Picea. The action of both climate and early human impact can explain these changes.  相似文献   

Rheological Transitions During Partial Melting and Crystallization with Application to Felsic Magma Segregation and Transfer   总被引：26，自引：7，他引：19  

VIGNERESSE  JEAN LOUIS; BARBEY  PIERRE; CUNEY  MICHEL 《Journal of Petrology》1996,37(6):1579-1600

We consider the rheological behaviour of felsic magma in thezone of partial melting and during subsequent crystallization.We also introduce and combine concepts (mushy zone, percolationtheory, granular flow, shear localization) derived from thenon-geological literature and apply them to field observationson migmatites and granites. Segregation and transportation offelsic magmas is commonly observed in association with non-coaxialdeformation, suggesting that gravity forces have limited influenceduring magma segregation. Solid to liquid and liquid to solidtransitions are shown to be rheologically different, which infirmsthe concept of a unique rheological critical melt percentagefor both transitions. Four stages are examined, which dependon the melt fraction present. (1) A minimum of 8% melt by volume must first be produced toovercome the liquid percolation threshold (LPT) above whichmelt pockets can connect, thus allowing local magma displacement.Transport of the liquid phase is amplified by deformation towarddilatant sinks and is restricted to a very local scale. Thiscorresponds to partially molten domains illustrated by incipientmigmatites. (2) When more melt (20–25%) is present, a melt escapethreshold (MET) allows segregation and transport of the meltand part of the residual solid phase, over large distances.This corresponds to segregation and transfer of magma towardsthe upper crust. (3) Segregation of magma also occurs during granite emplacementand crystallization. In a flowing magma containing few particles(20%), particles rotate independently within the flow, defininga fabric. As soon as sufficient crystals are formed, they interactto construct a rigid skeleton. Such a random loose packed frameworkinvolves 55% solids and corresponds to the rigid percolationthreshold (RPT). Above the RPT, clusters of particles can sustainstress, and the liquid fraction can still flow. The only remainingpossibilities for rearranging particles are local shear zones,often within the intrusion rim, which, as a consequence, developsdilatancy. This stage of segregation during crystallizationis totally different from that of magma segregation during incipientmelting. (4) Finally, the system becomes totally locked when random closepacking is reached, at 72–75% solidification; this isthe particle locking threshold (PLT). The introduction of four thresholds must be viewed in the contextof a two-fold division of the cycle that generates igneous rocks,first involving a transition from solid to liquid (i.e. partialmelting) and then a transition from liquid to solid (i.e. crystallization).Neither transition is simply the reverse of the other. In thecase of melting, pockets of melt have to be connected to afforda path to escaping magma. This is a bond-percolation, in thesense of physical percoloation theory. In the case of crystallization,randomly distributed solid particles mechanically interact,and contacts between them can propagate forces. Building a crystalframework is a site-percolation, for which the threshold ishigher than that of bond-percolation. For each transition twothresholds are applicable. The present approach, which basicallydiffers from that based on a unique critical melt fraction,expands and clarifies the idea of a first and a second percolationthreshold. One threshold in each transition (LPT and RPT, respectively)corresponds to a percolation threshold in the sense of physicalpercolation theory. Its value is independent of external forces,but relies on the type and abundance of minerals forming thematrix within which melt connectivity is developing. The exactvalue of the second threshold (MET or PLT) will vary accordingto external forces, such as deformation and the particle shape. KEY WORDS: migmatites; partial melting; granites; magma segregation; magma solidification ^*Corresponding author. Telephone: 33 03 83 44 19 00. Fax: 33 03 83 44 00 29. e-mail: jlv{at}cregu.cnrs-nancy.fr  相似文献