An Alternative Protocol for Single Zircon Dissolution with Application to (U‐Th‐Sm)/He Thermochronometry          下载免费PDF全文

Bouchaïb Tibari  Arnaud Vacherat  Martin Stab  Raphaël Pik  Delphine Yeghicheyan  Pascal Hild 《Geostandards and Geoanalytical Research》2016,40(3):365-375

Zircon (U‐Th‐Sm)/He (ZHe) thermochronometry is a powerful tool that has been widely used in geology to constrain the exhumation histories of orogens. In this study, we present an alternative protocol for dissolving zircon grains for determination of parent nuclides. This new alkali fusion procedure developed at the SARM (Service d'Analyse des Roches et des Minéraux) in Nancy, France, is fast (requiring only 2 d, including cleaning steps) and offers several advantages over conventional methods by avoiding: (i) use of HF pressure dissolution and (ii) complete removing of grains from the metal microvials. After dissolution, U, Th and Sm were measured using an ICP‐MS. We tested the new procedure on two different ZHe reference materials, the Fish Canyon Tuff and Buluk Tuff; these provided precision values for ZHe‐age estimations of 9 and 6% (1s), respectively. In addition, using this method, zircons from the Buluk Tuff are shown to be chemically more homogenous and more suitable for assessing the uncertainty of the entire integrated procedure.  相似文献   

Identifying influence areas with connectivity analysis – application to the local perturbation of heterogeneity distribution for history matching     

Véronique Gervais  Mickaële Le Ravalec 《Computational Geosciences》2018,22(1):3-28

Numerical representations of a target reservoir can help to assess the potential of different development plans. To be as predictive as possible, these representations or models must reproduce the data (static, dynamic) collected on the field. However, constraining reservoir models to dynamic data – the history-matching process – can be very time consuming. Many uncertain parameters need to be taken into account, such as the spatial distribution of petrophysical properties. This distribution is mostly unknown and usually represented by millions of values populating the reservoir grid. Dedicated parameterization techniques make it possible to investigate many spatial distributions from a small number of parameters. The efficiency of the matching process can be improved from the perturbation of specific regions of the reservoir. Distinct approaches can be considered to define such regions. For instance, one can refer to streamlines. The leading idea is to identify areas that influence the production behavior where the data are poorly reproduced. Here, we propose alternative methods based on connectivity analysis to easily provide approximate influence areas for any fluid-flow simulation. The reservoir is viewed as a set of nodes connected by weighted links that characterize the distance between two nodes. The path between nodes (or grid blocks) with the lowest cumulative weight yields an approximate flow path used to define influence areas. The potential of the approach is demonstrated on the basis of 2D synthetic cases for the joint integration of production and 4D saturation data, considering several formulations for the weights attributed to the links.  相似文献   

Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine,south Brittany): Depositional history and late Holocene climatic and environmental signals     

Philippe Sorrel  Bernadette Tessier  François Demory  Agnès Baltzer  Firas Bouaouina  Jean-Noël Proust  David Menier  Camille Traini 《Continental Shelf Research》2010,30(10-11):1250-1266

The late Holocene is of particular interest to our understanding of the evolution of coastal sedimentary systems because this period encompasses warmer and cooler periods, and rising sea level in northern Europe. Based on an approach combining AMS ¹⁴C, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine (south Brittany), we document the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany. Correlation between sedimentary archives revealed the main sedimentary infilling phases during the last 6000 years. Four units (U1–U4) are recognized in the coastal sediment wedge of the system, corresponding to the stepwise marine invasion of the bay. We show that (1) marine inundation, due to the steep morphology of the bedrock, is diachronous between distal and proximal records. A time lag of ～1000 years is inferred over a distance of less than 5 km; (2) in the outer areas, the sedimentation has been condensed since 3000 years; (3) proximal estuarine archives offer the best record of sedimentary processes covering the last 2000 years, including the Medieval Warm Period (MWP).Correlations in proximal records in the Bay of Vilaine assess the connection between coastal sedimentary dynamics, climatic conditions and anthropogenic activities during the MWP. We match the preservation of clay deposits to increased river-borne suspended matter transported to the estuary probably as a result of accelerated land-use development (higher soil erosion) in the catchment area between ca. 880 and 1050 AD. Because the preservation of estuarine sedimentary successions is favoured when coastal wave sediment reworking is minimal, it is proposed that the prevailing climatic regime in south Brittany during the MWP likely resembled to that of the preferred negative phase of the North Atlantic Oscillation (NAO). Our data are fairly consistent with other late Holocene records from northern Europe including the Atlantic seaboard. However, they outline the difficulty in interpreting climatic and anthropogenic signatures in coastal sedimentary records where high-resolution chronologies required to unravel their respective influences are still missing.  相似文献   

Oxygen and organic carbon fluxes in sediments of the Bay of Biscay     

Aurélia Mouret  Pierre Anschutz  Bruno Deflandre  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Henri Etcheber  Jean-Marie Jouanneau  Antoine Grémare  Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540

The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O₂ consumption and POC burial rates. Benthic O₂ distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O₂ consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O₂ fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O₂ profiles. The rupture in the gradient of O₂ microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O₂ fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O₂ fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O₂ penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.  相似文献   

Test of the vibrational modelling for the λ-type transitions: Application to the α-β quartz transition     

Joëlle Castex  Michel Madon 《Physics and Chemistry of Minerals》1995,22(1):1-10

Vibrational modelling is at the present time the only known way to predict the heat capacities of the Earth's mantle minerals at high-pressure and high-temperature. To test the validity of this method for λ-type transitions, we have applied it to the α-β quartz transition (T ₀=846±1 K). Raman spectra of quartz were recorded up to 900 K. Measured frequency shifts of the α-quartz Raman modes were then used in conjunction with available high-pressure Raman data to calculate intrinsic mode anharmonicity, through the parameter a _i=(?Lnv_i/?T)_v. Vibrational modelling of the heat capacity at constant volume, Cv, and at constant pressure, Cp, including anharmonic corrections deduced from the a _i parameters, are compared to experimental data. Taking into account the soft-mode associated to the α-β quartz transition, the model reproduces the excess of Cp related to the transition. Then, this study confirms that detecting a soft-mode from vibrational data allows one to predict λ-type transitions. However, when modelling the thermodynamic properties, the contribution of a soft-mode cannot be established from spectroscopic data. Therefore, one needs first to determine this contribution in order to predict the heat capacities of Earth's mantle minerals displaying λ-type transitions. In α-quartz, this contribution has been determined as 0.007% of the total number of the optic modes in the model of the density of states.  相似文献   

Chronostratigraphy and paleoclimatic meaning of cryogenic deformations in the Central European loess     

Brigitte van Vliet-Lanoë Dr. 《GeoJournal》1991,24(2):157-163

Cryoturbations in loess reflect cold and wet environments but not necessarily permafrost. Only flat bottomed cryoturbations are indicative of it. Outside the permafrost zone they occur during the wet period of the last glaciation: during the early Weichselian, the lower pleniglacial, the end of the middle pleniglacial and the late glacial. Their morphology ist related to the frost susceptibility of the superimposed layers, expressed in form of differential frost heaving, ruled by the drainage quality and the frost susceptibility gradient. Their diagenesis is discussed.  相似文献   

U-Pb dating of an early paleozoic bimodal magmatism in the french Massif Central and of its further metamorphic evolution     

Christian Pin  Joël Lancelot 《Contributions to Mineralogy and Petrology》1982,79(1):1-12

In the Marvejols area (Southern french Massif Central), the gneissic Marvejols supergroup is overthrust on the metasedimentary “Série du Lot”, deposited in part prior to 540 Ma. The allochtonous terranes are characterized by the occurrence of a leptyno-amphibolitic group, a complex association of mafic and felsic rocks of igneous and sedimentary derivation. A 480±10 Ma age has been obtained by U-Pb dating of zircons, for the crystallization of both mafic and felsic meta-igneous rocks. These rocks were emplaced during an important extensional tectonics. Relics of eclogites, pyrigarnites, coronite gabbros and HP-trondhjemites are clear evidence for a further HP-HT event dated at 415±6 Ma on zircons from a HP trondhjemite. Subsequently, the Marvejols supergroup underwent an amphibolite facies metamorphism with incipient mobilization dated at 345±10 Ma. Rifting and thinning of the continental crust in Cambro-Ordovician times appears to be a major geodynamic feature which could account for the thermal events often referred to the “Caledonian” orogeny. The Silurian (415 Ma) age of the HP episode is clearly older than the main Variscan tectonometamorphic event; it is in agreement with Rb-Sr dating of the Moldanubian granulites and with some radiometric data from Southern Brittany (France). These results point to a compressive phase, probably in a subduction context, in view of the high pressures reached (15–20 Kb), after the Cambro-Ordovician distensive phase. The main final tectono-metamorphic paroxysm (blocking of subduction process and continental collison ?) is not prior to the end of Devonian (340–350 Ma) and is related to the Variscan orogeny s.s  相似文献   

The atmospheric electric agitation and its origin     

H. Israël 《Pure and Applied Geophysics》1959,42(1):140-142

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Remarks concerning the “ten-year-period” of atmospheric electricity     

Prof. Dr. Hans Israël 《Meteorology and Atmospheric Physics》1968,17(1):88-89

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Buchbesprechungen     

F. Steinhauser  W. Mörikofer  H. Israël  M. Toperczer 《Meteorology and Atmospheric Physics》1953,6(1):114-128

Ohne Zusammenfassung  相似文献