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1.
Jean Carlos Montero-Serrano Viviane Bout-Roumazeilles Nicolas Tribovillard Thomas Sionneau Armelle Riboulleau Aloys Bory Benjamin Flower 《Quaternary Science Reviews》2009,28(27-28):3333-3347
Cored sediments from the Pigmy Basin, northern Gulf of Mexico, were analyzed in order to better constrain late deglacial and early Holocene paleoenvironmental and sedimentary changes in response to North American climate evolution. Mineralogical and geochemical proxies indicate the succession of two sedimentary regimes: dominantly detrital during the deglaciation (15–12.9 cal ka BP) whereas biogenic contribution relatively increased later on during the Younger Dryas and early Holocene (12.9 and 10 cal ka BP). Geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the Mississippi River rather than modifications of redox conditions in the basin. Specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode (Meltwater Spike) described or modeled in previous marine or continental studies. During this episode, most parameters display “stair-step-like” – pattern variations highlighting three successive steps within the main meltwater flow. Variations in grain-size and clay mineral assemblage recorded in the Pigmy Basin indicate that the erosional regime was very strong on land during the first part of the Meltwater Spike, and then milder, inducing more subtle modifications in the sedimentary regime in this part of the Gulf. Specific geochemical and mineralogical signatures (notably, clay minerals and trace metal geochemistry) pinpoint a dominant origin from NW North America for detrital particles reflecting meltwater outflow from the south-western Laurentide Ice Sheet (LIS) margin during the most intense freshwater discharge. The observed decrease of the sedimentation rate from about 200 to 25 cm/ka at ca 12.9 ka evidenced a drastic decrease of erosional processes during late phase of discharge, consistently with the hypotheses of major reduction of meltwater flow. The major modification at 12.9 cal ka BP is interpreted to result from both modifications of the main Mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the Younger Dryas, and the increase of sea-surface temperature linked to insolation. Finally, slight grain-size modifications suggest that some freshwater discharges may have episodically reached the Gulf of Mexico after the Younger Dryas reflecting possible small adjustments of the postglacial hydrological regime. 相似文献
2.
The circulation of an injected fluid in the deep granite of the Soultz-sous-Forêts HDR (‘Hot Dry Rock’) site causes important textural and mineralogical modifications. In order to determine the potential crystallization sequences along the fluid pathway, several experiments under thermal gradient were conducted at 600 bar (between 300 and 200 °C). After 40 days, the observed sequences of the newly formed products along the thermal gradient are always as follows, from high to low temperatures: quartz, feldspars, and finally interstratified clays, this implying a significant mobility of aluminium in the solution. To cite this article: A. Baldeyrou et al., C. R. Geoscience 335 (2003). 相似文献
3.
Estelle Arbellay Markus Stoffel Armelle Decaulne 《Boreas: An International Journal of Quaternary Research》2013,42(3):568-574
Dendrogeomorphic research has long relied on scarred trees to reconstruct the frequency of mass‐movement processes. Injuries have mostly been dated macroscopically by counting the tree rings formed after wounding. Tree‐ring anatomical anomalies induced by cambial injury, in contrast, have only recently been recognized as proxy records of past events. We investigated 12 sub‐arctic downy birch (Betula pubescens Ehrh.) trees scarred by snow avalanches in Norway and Iceland. Earlywood vessel lumina were measured for each tree in the xylem tissue bordering the scars. Seven successive rings were examined, namely two control rings laid down prior to wounding and five rings in the wound xylem. We provide evidence that snow‐avalanche‐induced wounding resulted in atypically narrow earlywood vessels over at least two years. Our data demonstrate that wound‐associated vessel anomalies represent tangible markers of mass‐movement processes, and as such make a viable tool for reconstructing past events. Similar dendrogeomorphic studies based on tree‐ring anatomy can be readily conducted with other mass‐movement processes, as well as with other broad‐leaved tree species. Ultimately, this new approach will foster increment coring over more invasive sampling techniques. 相似文献
4.
Jean Carlos Montero-Serrano Manuel Martínez Armelle Riboulleau Nicolas Tribovillard Gonzalo Márquez José Vicente Gutiérrez-Martín 《Marine and Petroleum Geology》2010
The early Miocene Pedregoso Formation is one of the numerous formations rich in organic matter within the stratigraphic record of the Urumaco Trough, in the central area of the Falcón Basin. Due to its lithological characteristics and stratigraphic position, this formation is of great interest regarding the basin's petroliferous systems. The evaluation of various inorganic and organic geochemical parameters indicates that the organic matter is primarily of marine origin, deposited in a marine carbonate environment typical of reefal systems, under oxic-to-dysoxic conditions. The low variability in the TOC concentrations and in the distributions of the biomarkers extracted from the samples suggests that the paleoenvironmental conditions and the organic-matter supply remained approximately constant throughout the sedimentation of this unit. The Pedregoso type-II organic matter (marine origin) and initial organic richness value (∼1.8%) suggest that this unit has probably generated hydrocarbons within the Urumaco Trough. However, present-day thermal maturity parameters reveal that the Pedregoso organic matter is overmature (dry gas window), indicating that this unit is only capable to generate gas. In addition, the geothermal gradient, maturity parameters, and the maximum paleotemperature estimated in this study suggest that the Pedregoso Formation reached a maximum burial depth the ∼6.5 km, consistent with the value obtained from data of stratigraphic thickness in the Urumaco Trough. This implies that the thermal anomaly that affected the basin during the Late Eocene–Early Miocene did not reach the central part of the basin, and therefore, the organic matter maturation in this unit is due to the sedimentary burial. 相似文献
5.
The development of ecosystem-based indicators requires the broadening of a view of the community, from fish species to all the species (macrobenthic and fish) correctly captured by a given sampling gear. Many scientific surveys already have such integrated databases. The present note aims to demonstrate that existing databases, herein from dedicated coastal nursery surveys, are actually underexploited. Such databases contain information on non-commercial taxa, which could greatly improve our knowledge on the organisation and functioning of coastal ecosystems. Using two datasets, a “complete” dataset composed of commercial and not-commercial epibenthic trawled species (fish and invertebrate) and a “subset” dataset characterized by commercial and routinely surveyed species (mainly fish and cephalopods), different measures of functional diversity are compared to identify the functional gains of including epibenthic species. The results show that, when included in the analyses, epibenthic taxa provide gains of functional information, associated mainly with the community feeding traits, i.e. organisms composing the primary and secondary consumer levels of the coastal nursery food web. Failure to include some of the primary (zooplanktivores and suspension feeders) and secondary consumers (detritivores–scavengers) in coastal survey analyses may, for instance, hamper our understanding of energy flux between the benthic and water column compartments of these ecosystems. The results also suggest that the exclusion of some taxa associated with these two food web compartments, may lead to the underestimation of the functional redundancy in coastal ecosystems. 相似文献
6.
Maria-Fernanda Romero-Sarmiento Armelle RiboulleauMarco Vecoli Gerard J.-M. Versteegh 《Organic Geochemistry》2011,42(6):605-617
Twenty one core samples of Late Ordovician to Early Devonian age from sections in southern Tunisia, North African Platform (Gondwana) and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content (e.g. acritarchs, prasinophytes, chitinozoans, cryptospores and trilete spores). In addition to several biomarkers of algal/bacterial origin, long chain n-alkanes that might be derived from land plants, as well as the terrestrial diterpane, norabietane, were found. Several land plant-derived biomarkers, such as retene, cadalene, simonellite, tetrahydroretene and C19 isohexylalkyl naphthalene were observed in the aromatic fractions. While these terrestrial biomarkers could be clearly recognized in the middle Silurian-lower Devonian samples, their presence in the upper Ordovician-lower Silurian sediments is more doubtful, because of much lower relative abundances. The land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores, derived from bryophytes and tracheophytes, which covered the emerged areas around the Ghadamis Basin during the Silurian and Devonian. The early tracheophytes (e.g. Cooksonia, lycophytes and zosterophylls) are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of Middle Silurian to Early Devonian age. 相似文献
7.
The surface radiation budget over South America in a set of regional climate models from the CLARIS-LPB project 总被引：1，自引：0，他引：1
Natalia L. Pessacg Silvina A. Solman Patrick Samuelsson Enrique Sanchez José Marengo Laurent Li Armelle Reca C. Remedio Rosmeri P. da Rocha Caroline Mourão Daniela Jacob 《Climate Dynamics》2014,43(5-6):1221-1239
The performance of seven regional climate models in simulating the radiation and heat fluxes at the surface over South America (SA) is evaluated. Sources of uncertainty and errors are identified. All simulations have been performed in the context of the CLARIS-LPB Project for the period 1990–2008 and are compared with the GEWEX-SRB, CRU, and GLDAS2 dataset and NCEP-NOAA reanalysis. Results showed that most of the models overestimate the net surface short-wave radiation over tropical SA and La Plata Basin and underestimate it over oceanic regions. Errors in the short-wave radiation are mainly associated with uncertainties in the representation of surface albedo and cloud fraction. For the net surface long-wave radiation, model biases are diverse. However, the ensemble mean showed a good agreement with the GEWEX-SRB dataset due to the compensation of individual model biases. Errors in the net surface long-wave radiation can be explained, in a large proportion, by errors in cloud fraction. For some particular models, errors in temperature also contribute to errors in the net long-wave radiation. Analysis of the annual cycle of each component of the energy budget indicates that the RCMs reproduce generally well the main characteristics of the short- and long-wave radiations in terms of timing and amplitude. However, a large spread among models over tropical SA is apparent. The annual cycle of the sensible heat flux showed a strong overestimation in comparison with the reanalysis and GLDAS2 dataset. For the latent heat flux, strong differences between the reanalysis and GLDAS2 are calculated particularly over tropical SA. 相似文献
8.
Armelle Charrié-Duhaut Jacques Connan Mike Darnell Jorge Spangenberg Ewa Szymczyk Adry Bissada Pierre Albrecht 《Organic Geochemistry》2009,40(5):647-665
The wreck U Pezzo, excavated within the Saint Florent Gulf in northern Corsica was identified as the pink, Saint Etienne, a merchant ship which sank on January 31, 1769. In order to determine the composition of organic materials used to coat the hull or to waterproof different parts of the pink, a study of several samples, using molecular biomarker and carbon isotopic analysis, was initiated. The results revealed that the remarkable yellow coat, covering the outside planks of the ship’s bottom under the water line, is composed of sulfur, tallow (of ox and not of cetacean origin) and black pitch which corresponds to a mixture called “couroi” or “stuff”. Onboard ropes had been submitted to a tarring treatment with pitch. Hairs mixed with pitch were identified in samples collected between the two layers of the hull or under the sheathing planking. The study also provides a key model for weathering of pitch, as different degrees of degradation were found between the surface and the heart of several samples. Accordingly, molecular parameters for alteration were proposed. Furthermore novel mixed esters between terpenic and diterpenic alcohols and the free major fatty acids (C14:0, C16:0, C18:0) were detected in the yellow coat. 相似文献
9.
Edward Derbyshire Armelle Billard Brigitte Van Vliet-Lanoë Jean-Pierre Lautridou Mauro Cremaschi Cnr 《第四纪科学杂志》1988,3(2):147-169
In 1985, a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western Europe was initiated jointly by laboratories in Leicester, Meudon, Caen, Milan, Cardiff and Southampton, involving a limited amount of comparative work on the loess from types sites in the Loess Plateau of central China. Preliminary results include the following: (1) Experimental procedures in particle size analysis, clay sample preparation and microscopy have been standardised in all cooperating groups; distinctive fabrics indicative of depositional mechanisms have been recognised. (2) Comparison of aeolian, colluvial and alluvial silt by laser-scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re-deposited by slope processes and flowing water. (3) The variability in the anisotropy of the limon à doublet facies has been assessed by image analysis of scanning electron microscopy (SEM) and optical microscopy. Strong anisotropy has also been measured in thin section imagery of loess from Normandy and Poland as the product of freezing and thawing. This is confirmed by scanning electron microscopy and by experimental freezing of some silts. (4) The clay fabric and mineralogy in western European loess differ from those in Chinese loess, especially in the case of semi-arid deposits. (5) Distribution of CaCO3, using thin sections and SEM analysis, has been determined for loess from Normandy and the Rhǒne valley in France and for some Chinese loess, At Saint Vallier, zones of CaCO3 concentration occur masking much of the original (loess) sedimentary skeleton which is a locally reworked loessic silt with some laminations. Despite considerable scatter, the palaeomagnetic results indicate a reversed polarity throughout, placing the whole Saint Vallier sequence in the Matuyama chron. These preliminary results suggest the existence of two different palaeoenvironments: one typified by central China, with arid glacials and humid interglacials; and the other represented by western Europe, with generally high humidities. There was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern Italy than in western littoral Europe. 相似文献
10.
Armelle Anthoine 《地震工程与结构动力学》2006,35(7):851-866
This paper explains how to control in displacement any force proportional loading. Such a procedure makes it possible to derive the complete (i.e. including the possible softening branch) response curve of a structure along any radial loading path in the force space. This is exactly what is required in the so‐called pushover analysis used in the seismic assessment of structures. The proposed procedure is simple in the sense that it can be easily implemented in any classical (displacement‐based) finite element code through a standard displacement control loading process. Furthermore, it leads to an interesting definition of the controlled degree‐of‐freedom, which, in the case of the pushover analysis, could substitute the classical roof displacement. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献