Chemical and isotopic characterization of hydrocarbon gas traces in porewater of very low permeability rocks: The example of the Callovo-Oxfordian argillites of the eastern part of the Paris Basin     

Alain Prinzhofer  Jean Pierre Girard  Stphane Buschaert  Yvon Huiban  Sonia Noirez 《Chemical Geology》2009,260(3-4):269-277

A methodology has been developed to determine chemical and carbon isotopic compositions of trace amounts of hydrocarbon gas compounds (methane, ethane, propane, iso- and normal-butane) present as dissolved compounds in the porewater of the low permeability Callovo-Oxfordian argillites in eastern Paris Basin, France. Results indicate that the studied hydrocarbons contain significant amounts of ethane, butane and propane, in addition to methane. Carbon isotopic compositions reflect primarily thermogenic origin (thermal cracking of organic matter), and lack of any significant biodegradation. Because temperature did not exceed 50 °C in the studied argillites, investigated hydrocarbons must have originated in hotter/deeper organic-bearing formations, possibly Stephanian coals. Data supports the predominance of high maturity thermogenic gas in the upper part of the Callovo-Oxfordian, and low maturity thermogenic gas mixed with minor bacterially produced methane in the lower part of the formation. A mixing between three end-member gases models quite well the data: one thermogenic gas with a low maturity (42% methane, with a δ¹³C of − 53‰), a gas with higher maturity (55% methane, with a δ¹³C of − 47‰) and a bacterial gas (99.45% methane, with a δ¹³C of − 80‰). This study illustrates that migration of hydrocarbon gases can take place in rocks with very low permeability and porosity, such as compacted mudrocks, given enough time. It further suggests that the studied fluid migration and transfer in aquitards would help characterization and understanding of fluid movements in sedimentary basins, as a complement to studies focused on water aquifers and hydrocarbon reservoirs. Chemical and isotopic composition of dissolved hydrocarbons in porewater can be used as natural tracers of fluid circulation in sedimentary basins, in addition to more conventional tracers.  相似文献   

Tracking the isostatic and eustatic signals in an end Ordovician–early Silurian deglacial sedimentary record (Algeria – Libya border)     

Flavia Girard  Rmy Deschamps  Jean‐Franois Ghienne  Stphane Rouss  Jean‐Loup Rubino 《Sedimentology》2019,66(3):1042-1066

To elucidate the signature of isostatic and eustatic signals during a deglaciation period in pre‐Pleistocene times is made difficult because very little dating can be done, and also because glacial erosion surfaces, subaerial unconformities and subsequent regressive or transgressive marine ravinement surfaces tend to amalgamate or erode the deglacial deposits. How and in what way can the rebound be interpreted from the stratigraphic record? This study proposes to examine deglacial deposits from Late‐Ordovician to Silurian outcrops at the Algeria–Libya border, in order to define the glacio–isostatic rebound and relative sea‐level changes during a deglaciation period. The studied succession developed at the edge and over a positive palaeo‐relief inherited from a prograding proglacial delta that forms a depocentre of glaciogenic deposits. The succession is divided into five subzones, which depend on the topography of this depocentre. Six facies associations were determined: restricted marine (Facies Association 1); tidal channels (Facies Association 2); tidal sand dunes (Facies Association 3); foreshore to upper shoreface (Facies Association 4); lower shoreface (Facies Association 5); and offshore shales (Facies Association 6). Stratigraphic correlations over the subzones support the understanding of the depositional chronology and associated sea‐level changes. Deepest marine domains record a forced regression of 40 m of sea‐level fall resulting from an uplift caused by a glacio‐isostatic rebound that outpaces the early transgression. The rebound is interpreted to result in a multi‐type surface, which is interpreted as a regressive surface of marine erosion in initially marine domains and as a subaerial unconformity surface in an initially subaerial domain. The transgressive deposits have developed above this surface, during the progressive flooding of the palaeo‐relief. Sedimentology and high‐resolution sequence stratigraphy allowed the delineation of a deglacial sequence and associated sea‐level changes curve for the studied succession. Estimates suggest a relatively short (<10 kyr) duration for the glacio‐isostatic uplift and a subsequent longer duration transgression (4 to 5 Myr).  相似文献   

Sheathed prokaryotic filaments,major components of Mid-Cretaceous French amber microcoenoses     

Vincent Girard  Gérard Breton  Luc Brient  Didier Néraudeau 《Journal of Paleolimnology》2009,42(3):437-447

Prokaryotes were the first organisms to colonize Earth, but little evidence of their existence has been found in the fossil record. Recent studies of amber, a fossil resin from gymnosperms or angiosperms, have revealed a number of rarely fossilized microorganisms. Several amber-bearing localities of Mid-Cretaceous age in southwestern France (Charentes and Aude regions) led to the discovery of a rich and diverse biota of resin-preserved microorganisms. These amber microcoenoses are dominated by sheathed prokaryotic filaments similar to those of the cyanobacterium Palaeocolteronema cenomanensis Breton and Tostain (2005) and to those of the bacterium Leptotrichites resinatus Schmidt 2005. These sheathed filaments appear as peripheral cortexes around some pieces of amber from the Charentes outcrops and as peripheral dark areas on amber from the Aude locality. Macroscopic and microscopic features, as well as measurements of phycocyanin concentrations from the filaments, made it possible to identify two different taxa. The sheathed filaments from Charentes correspond to P. cenomanensis. They were growing in freshwater ponds when amber trapped them. Those of the Aude outcrop represent L. resinatus. The latter were probably trapped in less humid environments than were P. cenomanensis filaments.  相似文献   

Geophysical characterisation of karstic networks – Application to the Ouysse system (Poumeyssen,France)     

Roger Guérin  Jean-Michel Baltassat  Marie Boucher  Konstantinos Chalikakis  Pierre-Yves Galibert  Jean-François Girard  Valérie Plagnes  Rémi Valois 《Comptes Rendus Geoscience》2009,341(10-11):810-817

In the framework of the management of karstic aquifers, geophysical reconnaissance can be used to locate conduits and caves, and to characterise the surrounding limestone matrix. Suitable characterisation of heterogeneities in the karstic environment is, however, challenging for ground-based geophysical methods. The present article describes the results, and evaluates the response and accuracy of combined geophysical measurements carried out at the Poumeyssen test site in France, involving electrical resistivity imaging (ERI), magnetic resonance sounding (MRS), “mise-à-la-masse” electrical mapping, and seismic tomography. This site provides the opportunity to study a relatively wide, shallow, water-filled conduit whose location and shape are known from topographic work carried out by cave divers. Seismic and MRS provided the exact location and width of the conduit, to within a few meters. The seismic and electrical data suggest that the limestone medium surrounding the conduit is not homogeneous.  相似文献   

An evaluation of Arctic cloud and radiation processes during the SHEBA year: simulation results from eight Arctic regional climate models   总被引：1，自引：1，他引：0  

K. Wyser  C. G. Jones  P. Du  E. Girard  U. Willén  J. Cassano  J. H. Christensen  J. A. Curry  K. Dethloff  J.-E. Haugen  D. Jacob  M. Køltzow  R. Laprise  A. Lynch  S. Pfeifer  A. Rinke  M. Serreze  M. J. Shaw  M. Tjernström  M. Zagar 《Climate Dynamics》2008,30(2-3):203-223

Eight atmospheric regional climate models (RCMs) were run for the period September 1997 to October 1998 over the western Arctic Ocean. This period was coincident with the observational campaign of the Surface Heat Budget of the Arctic Ocean (SHEBA) project. The RCMs shared common domains, centred on the SHEBA observation camp, along with a common model horizontal resolution, but differed in their vertical structure and physical parameterizations. All RCMs used the same lateral and surface boundary conditions. Surface downwelling solar and terrestrial radiation, surface albedo, vertically integrated water vapour, liquid water path and cloud cover from each model are evaluated against the SHEBA observation data. Downwelling surface radiation, vertically integrated water vapour and liquid water path are reasonably well simulated at monthly and daily timescales in the model ensemble mean, but with considerable differences among individual models. Simulated surface albedos are relatively accurate in the winter season, but become increasingly inaccurate and variable in the melt season, thereby compromising the net surface radiation budget. Simulated cloud cover is more or less uncorrelated with observed values at the daily timescale. Even for monthly averages, many models do not reproduce the annual cycle correctly. The inter-model spread of simulated cloud-cover is very large, with no model appearing systematically superior. Analysis of the co-variability of terms controlling the surface radiation budget reveal some of the key processes requiring improved treatment in Arctic RCMs. Improvements in the parameterization of cloud amounts and surface albedo are most urgently needed to improve the overall performance of RCMs in the Arctic.  相似文献   

Further Characterisation of the 91500 Zircon Crystal   总被引：28，自引：2，他引：28  

Michael Wiedenbeck  John M. Hanchar  William H. Peck  Paul Sylvester  John Valley  Martin Whitehouse  reas Kronz  Yuichi Morishita  Lutz Nasdala  J. Fiebig  I. Franchi  J.-P. Girard  R.C. Greenwood  R. Hinton  N. Kita  P.R.D. Mason  M. Norman  M. Ogasawara  P.M. Piccoli  D. Rhede  H. Satoh  B. Schulz-Dobrick  O. Skår  MJ. Spicuzza  K. Terada  A. Tindle  S. Togashi  T. Vennemann  Q. Xie  Y.-F. Zheng 《Geostandards and Geoanalytical Research》2004,28(1):9-39

This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses.  相似文献   

Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series   总被引：3，自引：0，他引：3  

Jacques Leterrier  René C. Maury  Pierre Thonon  Danielle Girard  Michèle Marchal 《Earth and Planetary Science Letters》1982,59(1):139-154

Uranium contents and²³⁴U/²³⁸U activity ratios have been determined for groundwaters from the Lincolnshire Limestone artesian aquifer in eastern England. Changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone. The western part of the aquifer, closest to recharge, is dominated by oxidising groundwaters which then enter a reducing zone towards the east, where there is an abrupt decrease in Eh and the chlorinity of the groundwaters begins to increase. Uranium contents in the oxidising zone range from 0.7 to 3.4 μg kg^?1 and²³⁴U/²³⁸U activity ratio of this dissolved uranium is close to unity, the equilibrium value. The uranium content decreases abruptly when the grounwaaters enter the reducing zone, averaging 0.04 μg kg^?1 east of the oxidation/reduction barrier. Simultaneously with the decrease in uranium content, there is an increase in²³⁴U/²³⁸U activity ratio and this ratio increases to a maximum within 7 km of the oxidation/reduction barrier. This increase in activity ratio is attributed to enhanced²³⁴U solution due to²³⁴Th recoil from uraniferous fissure surfaces east of the oxidising zone. The activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to²³⁴Th recoil from the oolith surfaces. However, the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium.²³⁴Th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium-bearing surfaces in the process of oolith cementation.  相似文献   

Escaped introduced sea bass (Dicentrarchus labrax) infected by Sphaerospora testicularis (Myxozoa) reach maturity in coastal habitats off Canary Islands     

Kilian Toledo‐Guedes  Pablo Sanchez‐Jerez  Jaume Mora‐Vidal  Dominique Girard  Alberto Brito 《Marine Ecology》2012,33(1):26-31

Aquaculture activities have introduced European sea bass (Dicentrarchus labrax) along the coasts of some of the Canary Islands. We present the first record of simultaneous male and female gonad maturation of escaped sea bass in the wild, indicating that this species is finding its essential fish habitat (EFH). Individuals with ripe gonads were only caught during January and February 2009, although the maturation and spawning season may last from November to February in the studied area (Tenerife island). Bass infected by Sphaerospora testicularis were found and the incidence of the parasite was checked. This represents the southernmost record of the parasite, probably introduced together with sea bass stock. The results are discussed from the point of view of risk assessment and the ecology of invasions being valuable for aquaculture management in Central North Atlantic and Mediterranean areas.  相似文献   

Semi-Implicit Scheme for the DWD Lokal-Modell     

S. Thomas  C. Girard  G. Doms  U. Schättler 《Meteorology and Atmospheric Physics》2000,73(1-2):105-125

Summary  The fourth generation of numerical weather prediction (NWP) models is currently under development at the Deutscher Wetterdienst (DWD) consisting of a global grid point model (GME) and limited-area Lokal-Modell (LM). The nonhydrostatic fully compressible LM has been designed to meet high-resol ution regional fore-cast requirements at meso-β and meso-γ scales. The initial LM implementation is based on the NCAR/Penn State MM5 with the addition of a novel generalized terrain-following coordinate and rotated lat-lon grid. A fully 3D semi-implicit time-stepping scheme has been implemented by retaining the full buoyancy term instead of the approximate form found in MM5. In contrast with earlier schemes, mass-lumping is not applied to simplify the elliptic operator on an Arakawa-C/Lorenz grid. The resulting variable-coefficient elliptic problem is solved using a minimal residual Krylov iterative method with line relaxation preconditione rs. The new semi-implicit scheme is compared with a variant of the Klemp–Wilhelmson split-explicit scheme (horizontal explicit, vertical implicit) on the basis of computational efficiency and accuracy at resolutions ranging from 7 km to 400 m. Both idealized 3D mountain wave flows and naturally occuring flows are analyzed. Below the tropopause, the 3D semi-implicit scheme can be more efficient for low Mach number M ≪ 1 flows when the number of small time steps Δt _s of the split-explicit approach increases with the sound-speed Courant number. Revised October 7, 1999  相似文献   

Exploring the spatiotemporal variability of the snow water equivalent in a small boreal forest catchment through observation and modelling     

Achut Parajuli  Daniel F. Nadeau  François Anctil  Annie-Claude Parent  Benjamin Bouchard  Médéric Girard  Sylvain Jutras 《水文研究》2020,34(11):2628-2644

In snow-fed catchments, it is crucial to monitor and model the snow water equivalent (SWE), particularly when simulating the melt water runoff. SWE distribution can, however, be highly heterogeneous, particularly in forested environments. Within these locations, scant studies have explored the spatiotemporal variability in SWE in relation with vegetation characteristics, with only few successful attempts. The aim of this paper is to fill this knowledge gap, through a detailed monitoring at nine locations within a 3.49 km² forested catchment in southern Québec, Canada (47°N, 71°W). The catchment receives an annual average of 633 mm of solid precipitation and is predominantly covered with balsam fir stands. Extracted from intensive field campaign and high-resolution LiDAR data, this study explores the effect of fine scale forest features (tree height, tree diameter, canopy density, leaf area index [LAI], tree density and gap fraction) on the spatiotemporal variability in the SWE distribution. A nested stratified random sampling design was adopted to quantify small-scale variability across the catchment and 1810 manual snow samples were collected throughout the consecutive winters of 2016–17 and 2017–18. This study explored the variability of SWE using coefficients of variation (CV) and relating to the LAI. We also present existing spatiotemporal differences in maximum snow depth across different stands and its relationship with average tree diameter. Furthermore, exploiting key vegetation characteristics, this paper explores different approaches to model SWE, such as multiple linear regression, binary regression tree and neural networks (NN). We were unable to establish any relationship between the CV of SWE and the LAI. However, we observed an increase in maximum snow depth with decreasing tree diameter, suggesting an association between these variables. NN modelling (Nash-Sutcliffe efficiency [NSE] = 0.71) revealed that, snow depth, snowpack age and forest characteristics (tree diameter and tree density) are key controlling variables on SWE. Using only variables that are deemed to be more readily available (snow depth, tree height, snowpack age and elevation), NN performance falls by only 7% (NSE = 0.66).  相似文献