Evidence for mantle exhumation along the Arabian margin in the Zagros (Kermanshah area, Iran)     

Jean-Christophe Wrobel-Daveau  Jean-Claude Ringenbach  Saeid Tavakoli  Geoffrey M. H. Ruiz  Pierre Masse  Dominique Frizon de Lamotte 《Arabian Journal of Geosciences》2010,3(4):499-513

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A two‐step process for the reflooding of the Mediterranean after the Messinian Salinity Crisis     

François Bache  Speranta‐Maria Popescu  Marina Rabineau  Christian Gorini  Jean‐Pierre Suc  Georges Clauzon  Jean‐Louis Olivet  Jean‐Loup Rubino  Mihaela Carmen Melinte‐Dobrinescu  Ferran Estrada  Laurent Londeix  Rolando Armijo  Bertrand Meyer  Laurent Jolivet  Gwénaël Jouannic  Estelle Leroux  Daniel Aslanian  Antonio Tadeu Dos Reis  Ludovic Mocochain  Nikola Dumurdžanov  Ivan Zagorchev  Vesna Lesić  Dragana Tomić  M. Namık Çağatay  Jean‐Pierre Brun  Dimitrios Sokoutis  Istvan Csato  Gülsen Ucarkus  Ziyadin Çakır 《Basin Research》2012,24(2):125-153

The Messinian Salinity Crisis is well known to have resulted from a significant drop of the Mediterranean sea level. Considering both onshore and offshore observations, the subsequent reflooding is generally thought to have been very sudden. We present here offshore seismic evidence from the Gulf of Lions and re‐visited onshore data from Italy and Turkey that lead to a new concept of a two‐step reflooding of the Mediterranean Basin after the Messinian Salinity Crisis. The refilling was first moderate and relatively slow accompanied by transgressive ravinement, and later on very rapid, preserving the subaerial Messinian Erosional Surface. The amplitude of these two successive rises of sea level has been estimated at ≤500 m for the first rise and 600–900 m for the second rise. Evaporites from the central Mediterranean basins appear to have been deposited principally at the beginning of the first step of reflooding. After the second step, which preceeded the Zanclean Global Stratotype Section and Point, successive connections with the Paratethyan Dacic Basin, then the Adriatic foredeep, and finally the Euxinian Basin occurred, as a consequence of the continued global rise in sea level. A complex morphology with sills and sub‐basins led to diachronous events such as the so‐called ‘Lago Mare’.This study helps to distinguish events that were synchronous over the entire Mediterranean realm, such as the two‐step reflooding, from those that were more local and diachronous. In addition, the shoreline that marks the transition between these two steps of reflooding in the Provence Basin provides a remarkable palaeogeographical marker for subsidence studies.  相似文献   

1750?years of large rainfall events inferred from particle size at East Lake, Cape Bounty, Melville Island, Canada     

Fran?ois Lapointe  Pierre Francus  Scott F. Lamoureux  Meriem Sa?d  Stéphanie Cuven 《Journal of Paleolimnology》2012,48(1):159-173

Annual grain-size variation was measured on the varved (annually laminated) lacustrine sediment from Cape Bounty East Lake using an innovative image analysis system. About 7100 images were acquired using a scanning electron microscope and processed to obtain measurement of particles from 2845 varves. Several particle-size distributions indices were calculated and can be linked to high-energy sedimentary facies. Moreover, the coarse grain size (98th percentile) of these high-energy facies is strongly correlated with summer rainfall (and also summer temperature) of instrumental data from nearby stations. Particle-size distributions show a similar trend through time, especially for the standard deviation and the 98th percentile. Climatic reconstruction suggests that Cape Bounty recently experienced an unprecedented increase of rainfall events since ~AD 1920. On the other hand, changes in varve thickness are weakly correlated with the particle-size distribution. Altogether, these results highlight the need to obtain annual grain-size data to identify a meteorological signal.  相似文献   

Changes in coronal condensations emission after solar bursts at microwaves     

Pierre Kaufmann  E. Scalise Jr.  P. Marques Dos Santos 《Solar physics》1970,15(1):195-201

The amount of circular polarization of the total solar radio emission at 7 GHz present permanent changes after the occurrence of certain radio bursts associated with larger flares. For isolated S-components, associated with such flares the changes of the polarization degree _sranges between 0.004 to 0.1, and appears to be a function of the flare importance. A semi-qualitative interpretation associates _swith magnetic field reductions at the S-component, agreeing fairly well with a flare mechanism based on collisionless dissipation of magnetic energy, corresponding to energies in the range of 10³⁰ to 10³² ergs, assuming an average model for the coronal condensations.  相似文献   

Solar physics at Mackenzie University,São Paulo,Brazil     

Pierre Kaufmann 《Solar physics》1968,3(2):360-363

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Liquidus surfaces of ultracalcic primitive melts: formation conditions and sources   总被引：4，自引：1，他引：3  

Etienne?MédardEmail author  Max?W.?Schmidt  Pierre?Schiano 《Contributions to Mineralogy and Petrology》2004,148(2):201-215

CaO-rich, Al₂O₃-poor ultracalcic primitive melts occur at mid-ocean-ridges, back-arc basins, ocean islands and volcanic arcs. They are subdivided into a nepheline-normative alkaline-rich, silica-poor group uniquely found in arcs and in hypersthene-normative fairly refractory melts which occur in all of the above environments. The high CaO contents (to 19.0 wt%) and CaO/Al₂O₃ ratios (to 1.8) exclude an origin from fertile lherzolites at volatile-absent conditions. Experimental investigation of the liquidus of a hypersthene-normative and a nepheline-normative ultracalcic melt results in quite distinct pressure-temperature conditions of multiple saturation: whereas the hypersthene-normative liquid saturates in olivine + clinopyroxene at 1.2 GPa and 1,410°C, this occurs at 0.2 GPa and 1,220°C for the nepheline-normative ultracalcic liquid. Our results in combination with melting experiments from the literature suggest that hypersthene-normative melts result from melting of a refractory olivine + clinopyroxene ± orthopyroxene source at elevated mantle temperatures. Contrasting, nepheline-normative ultracalcic melts form from wehrlitic cumulates in the arc crust; to account for the high alkaline and low silica contents, and the relatively low temperatures, source wehrlites must have contained amphibole.  相似文献   

Geochemical influences on H40/1 bacteriophage inactivation in glaciofluvial sands     

Raymond?FlynnEmail author  Daniel?Hunkeler  Christine?Guerin  Christine?Burn  Pierre?Rossi  Michel?Aragno 《Environmental Geology》2004,45(4):504-517

Geochemical heterogeneities may cause spatial variations in virus inactivation rates resulting from interactions with minerals leading to differences in natural disinfection capacity within an aquifer. Column studies investigating the interaction of the bacteriophage H40/1 with natural sands sampled from the Kappelen test site (Kappelen), Bern, Switzerland indicated that inactivation rates are higher for adsorbed bacteriophages than for those suspended in groundwater. Moreover, breakthrough curves obtained from field-based tracer tests at Kappelen indicated that the adsorbed H40/1 is inactivated in-situ at comparable rates. Statistical analyses of mineralogical data failed to demonstrate significant spatial variations in aquifer composition either across the site or with depth. In contrast hydrochemical analyses of groundwater samples collected at Kappelen demonstrated that iron-reducing groundwater occurs below aerobic waters. Tracer breakthrough curves indicate that H40/1 survival is not affected by variable redox conditions. Investigation results suggest that spatial geochemical variability does not significantly affect H40/1s inactivation rate at Kappelen.  相似文献   

Detection of methane in the martian atmosphere: evidence for life?     

Vladimir A. Krasnopolsky  Jean Pierre Maillard 《Icarus》2004,172(2):537-547

Using the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH₄ band at 3.3 μm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH₄ mixing ratio is 10±3 ppb. Total photochemical loss of CH₄ in the martian atmosphere is equal to , the CH₄ lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH₄ during its diffusion through the regolith may be significant. There are no processes of CH₄ formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of CH₄ by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas” on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured CH₄ abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases.  相似文献   

The orbital period distribution of subdwarf-B binaries     

Luisa Morales-Rueda  Pierre F.L. Maxted  Tom R. Marsh 《Astrophysics and Space Science》2004,291(3-4):299-306

We present the results of a 3.5 year long campaign to measure orbital periods of subdwarf-B (sdB) star binaries. We directly compare our observed orbital period distribution with that predicted by using binary population synthesis. Up to now, most of our systems seem to have been formed through two of the formation channels discussed by Han et al. (2003, MNRAS 341, p. 669), i.e. the first and the second common envelope ejection (CE) channels. At this point, thanks to the long baseline of our observations, we are starting to detect also very long orbital period systems. These have probably come from a complete different formation path, the first stable Roche Lobe overflow (RLOF) channel in which the first mass transfer phase is stable. This channel is expected to lead to the formation of very wide binaries with typical orbital periods ranging from 1 month to 1 year.  相似文献   

The extent of chronic marine oil pollution in southeastern Newfoundland waters assessed through beached bird surveys 1984-1999     

Wiese FK  Ryan PC 《Marine pollution bulletin》2003,46(9):1090-1101

The Grand Banks south of Newfoundland provide year-round feeding habitat for tens of millions of seabirds of numerous species, an abundance and diversity unparalleled in the North Atlantic. Dense ship traffic routes traverse this productive environment as vessels travel the Great Circle Route between Europe and North America. Oiled seabirds have washed up on beaches in Newfoundland for many decades. Most oil on their feathers is heavy fuel oil mixed with lubricants, the mixture found in bilges of large vessels. Beached bird surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland is among the highest in world. Sixty two percent of all dead birds found over the 16-year period had oil on their feathers; 74% during the last five years. Auks, especially Thick-billed Murres (Uria lomvia), are the most affected. The mean number of oiled birds per kilometer was 0.77 and thus higher than in other regions of the world during a comparable time period (0.02-0.33). Oiling rates correlated with weather patterns and degree of the regional murre hunt, indicate that illegal dumping of oil may occur year round, and point out that it is critical to assess all possible environmental and anthropogenic factors influencing the number of clean and oiled dead birds found on beaches before inferring trends in oiling rates over time.  相似文献