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1.
Cold seep deposits of Beauvoisin (Oxfordian; southeastern France) and Marmorito (Miocene; northern Italy): microbially induced authigenic carbonates 总被引：12，自引：0，他引：12
J. Peckmann V. Thiel W. Michaelis P. Clari C. Gaillard L. Martire J. Reitner 《International Journal of Earth Sciences》1999,88(1):60-75
The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are
found to be associated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito
("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative
δ13Ccarbonate values, respectively. Highly positive values (+15‰) reflect the use of 13C-enriched CO2 produced by methanogenesis. Low δ13C values of the Marmorito carbonates (–30‰) indicate the oxidation of seepage-derived hydrocarbons. Likewise, the δ13C content of specific tail-to-tail linked isoprenoids, biomarkers for archaea, was found to be strikingly depleted in these
samples (as low as –115‰). The isotopic signatures corroborate that archaea were involved in the cycling of seepage-derived
organic carbon at the ancient localities. Another Miocene limestone ("Marmorito limestone") shows a strong imprint of methanotrophic
bacteria as indicated by δ13C values of carbonate as low as –40‰ and biomarker evidence. Epifluorescence microscopy and field-emission scanning electron
microscopy revealed that bacterial biofilms were involved in carbonate aggregation. In addition to lucinid bivalves previously
reported from both localities, we infer that sponges from Beauvoisin and tube worms from Marmorito depended on chemosynthesis
as well. Low δ13C values of nodules related to sponge taphonomy (–27‰) indicate that sponges might have been linked to an enhanced hydrocarbon
oxidation. Tube worm fossils from Marmorito closely resemble chemosynthetic pogonophoran tube worms from Recent cold seeps
and are embedded in isotopically light carbonate (δ13C –30‰).
Received: 13 October 1998 / Accepted: 5 February 1999 相似文献
2.
D. Minniti P.W. Lucas J.P. Emerson R.K. Saito M. Hempel P. Pietrukowicz A.V. Ahumada M.V. Alonso J. Alonso-Garcia J.I. Arias R.M. Bandyopadhyay R.H. Barbá B. Barbuy L.R. Bedin E. Bica J. Borissova L. Bronfman G. Carraro M. Catelan J.J. Clariá G. Pietrzynski 《New Astronomy》2010,15(5):433-443
We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 h of observations with the 4-m VISTA telescope during 5 years (2010–2014), covering ～109 point sources across an area of 520 deg2, including 33 known globular clusters and ～350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9–2.5 μm) and a catalogue of more than 106 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars. 相似文献
3.
Several arguments that justify establishing a revised abundance calibration for DDO photometry of population I red giants
are presented. The components of the blanketing vector in the DDOC(45–48) vsC(42–45) diagram are determined for late-type dwarfs and giants. We have redefined the DDO cyanogen anomaly and calibrated
it against metallicity. The sample of field giants now available with abundances derived from high dispersion spectroscopy
is substantially larger than previously available, leading to a more accurate abundance calibration. Iso-abundance lines in
theC(41–42) vsC(42–45) diagram have been determined for population IG and K giants and an iterative method for deriving abundances of these
stars is described. We show that the new DDO abundances are in very good agreement with those derived from high dispersion
spectroscopy. The new method improves by about 0.1 dex the DDO abundances derived for early G and/or late K giants, with respect
to the δCN method of Janes (1975). 相似文献
4.
Freshly cleaved (001) natural muscovite was chemically characterized by X-ray Photoelectron Spectroscopy (XPS). The investigated
muscovite crystals have composition ranging from pure end member to phengitic muscovite. XPS provides experimental evidence
that the chemical composition of the near-surface region differs from the bulk. This difference is not due to analytical problems,
but to extreme surface sensitivity of XPS. Depth profiling was also carried out after tilting of 60° or 70° of the sample
along an axis perpendicular to [001]. After tilting of phengitic muscovite, the concentration of Al increases and of K decreases,
and therefore Al is the topmost monolayer. Repulsion between the octahedral and tetrahedral sheets, stacking faults or more
probably interlayered phases (gibbsite-like) are responsible for the cleavage. Possible perturbations of surface chemistry
due to X-ray radiation and Ar+ ion sputtering have also been investigated. X-ray radiation is negligeable, but Ar+ ion sputtering introduces important structural modifications, perturbation of the chemical environment of elements and minor
chemical variations.
Received: 13 November 1996 / Revised, accepted: 21 March 1997 相似文献
5.
The Monferrato is a key area of the Alps-Apennine junction. It consists of a Tertiary succession, resting on Apennine-related units, in turn overridden by the Alpine basement. The superficial expression of this crustal discontinuity is the Rio Freddo deformation zone, separating the Alpine-related Torino hill domain from the Monferrato. Stratigraphic analyses allow the recognition of different fault-bounded Oligo-Miocene successions, interpreted as tectonostratigraphic units. Some of these corresponded to high-standing blocks, others to subsiding basins. The facies distribution reflects a transpressional tectonic regime. In this general framework of wrench tectonics, sedimentation was influenced by palaeoceanographic factors during the early and latest Burdigalian, while tectonics played the dominant role during the Aquitanian and the late Burdigalian. The uniform extent and the unconformable basal boundary of the Langhian deposits suggest that the different tectonostratigraphic units presently composing the Monferrato area were in place by Langhian times. 相似文献
6.
The first-and second-order extinction coefficients in theUBVRI and DDO systems are derived for the first time at CASLEO. They define an extinction curve which is discussed in the framework of atmospheric absorption theory. From this curve the first-order extinction coefficients for the Washington and Strömgren systems are inferred. From a photometric point of view, CASLEO occupies a preferred place among the observatories of the world. A comparison of theUBV extinction coefficients obtained at Bosque Alegre with previous determinations supports the conclusion that the sky transparency at this station has deteriorated in the ultraviolet in the last years.Visting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba y San Juan, Argentina. 相似文献
7.
J. J. Clariá 《Astrophysics and Space Science》1979,66(1):201-209
Interstellar reddening, the ratio [Fe/H], effective temperatures, surface gravities, and masses for twelve clump stars at the blue end of the giant branch and for seven non-clump red giant members in NGC 7789 have been determined from existingUBV andDDO photoelectric data. For the metal abundance and helium content of the clump stars we foundZ0.01 andY0.38, respectively. The masses of the red giants are found to be higher than those of the clump stars. On average, the masses of the clump stars are about half of the turnoff point mass. We conclude that the clump stars could have undergone mass loss before reaching their helium core burning phase of evolution. This conclusion arises from an analysis of the several sources entering our mass determination. 相似文献
8.
CCD BVI Johnson–Cousins photometry of the open cluster candidates Pismis 23 and BH 222 is presented. Both the analysis of the colour-magnitude diagrams and star counts performed in the regions of these two objects support their physical reality. For Pismis 23 we derive E(B?V) = 2.0 ± 0.1, E(V?I) = 2.6 ± 0.1, a distance from the Sun d= (2.6 ± 0.6) kpc and an age of (300 ± 100) Myr, while for BH 222 we obtain E(V?I) = 2. 4 ± 0.2, d= (6.0 ± 2.7) kpc and (60 ± 30) Myr. Both objects, located beyond the Sagittarius arm, are among the most reddened and distant open clusters known in the direction towards the Galactic centre. 相似文献
9.
We present CCD photometry in the Washington system C and T1 passbands down to T1 ～ 19.5 magnitudes in the fields of Czernik 26, Czernik 30, and Haffner 11, three poorly studied open clusters located in the third Galactic quadrant. We measured T1 magnitudes and C ? T1 colors for a total of 6472 stars distributed throughout cluster areas of 13.6′ × 13.6′ each. Cluster radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Based on the best fits of isochrones computed by the Padova group to the (C ? T1, T1) color-magnitude diagrams (CMDs), we derived color excesses, heliocentric distances and ages for the three clusters. These are characterized by a relatively small angular size and by a high field star contamination. We performed a firm analysis of the field star contamination of the CMDs and examined different relationships between the position in the Galaxy of known open clusters located within 1 kpc around the three studied ones, their age and their interstellar visual absorption. We confirm previous results in the sense that the closer the cluster birthplace to the Galactic plane, the higher the interstellar visual absorption. We also found that the space velocity dispersion perpendicular to the Galactic plane diminishes as the clusters are younger. The positions, interstellar visual absorptions, ages, and metallicities of the three studied clusters favor the hypothesis that they were not born in the recently discovered Canis major (CMa) dwarf galaxy before it was accreted by the Milky Way. 相似文献
10.
Results fromCMT
1T2 1T2 broad-band and DDO intermediate-band photometry are presented for G and K giants in the old open clusters NGC. 2482,
NGC 3680, and IC 4651. Two independent photometric criteria have been used to separate red field stars from the physical members
of the clusters. Recent calibrations of the DDO andCMT
1T2 systems have been used to derive reddening, distance moduli, metallicities, effective temperatures, and surface gravities.
Rough estimates of masses have also been made. The giants of NGC 2482 and IC 4651 have CN strengths nearly identical to the
Hyades giants, while those of NGC 3680 are slightly richer in CN than the nearby K giants.CMT1T2 abundance analysis in NGC 2482 and NGC 3680 yield [Fe/H]MT = - 0.1 ± 0.1 as derived from the iron lines, while abundances derived from the CNO - contaminated (C - M) index are 0.4 dex higher. BothCMT
1T2 and DDO data support the conclusion that 1C 4651, with [Fe/H] = + 0.2 ± 0.1, is on the metalrich side of the distribution
of intermediate and old open clusters. Finally, the mass results suggest that the clump stars in NGC 3680 and. IC 4651 could
have undergone mass loss before reaching their helium core burning phase of evolution.
Supported in part by the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) of Argentina.
Visiting astronomer of Cerro Tololo Inter-American Observatory supported by the National Science Foundation under contract
No. AST 74-04128. 相似文献