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181.
Guillaume Backé Graham Baines David Giles Wolfgang Preiss Andrew Alesci 《Marine and Petroleum Geology》2010
The Adelaide Basin in Australia is a complex of late Neoproterozoic to Early Cambrian rift and sag basins which was inverted during the Cambro–Ordovician Delamerian Orogeny. The deposition of evaporitic sediments during the earliest stage of basin development in the late Neoproterozoic (Willouran age) played a major role in the subsequent tectonic evolution of the basin. Previous studies have shown that early mobilization, vertical transport and withdrawal of the evaporites influenced the sedimentation during the late Neoproterozoic and Early Cambrian. The evaporites also influenced deformation during the inversion of the basin and the development of the Delamerian fold and thrust belt. However, the control exerted by basement structures in the deposition of the evaporitic beds and the role of these tectonic structures in the later inversion of the basin have been poorly constrained. 相似文献
182.
Fabrice Hollender Cécile Cornou Aline Dechamp Kaveh Oghalaei Florence Renalier Emeline Maufroy Clément Burnouf Sylvette Thomassin Marc Wathelet Pierre-Yves Bard Vincent Boutin Clément Desbordes Isabelle Douste-Bacqué Laetitia Foundotos Cédric Guyonnet-Benaize Vincent Perron Julie Régnier Agathe Roullé Mickael Langlais Deborah Sicilia 《Bulletin of Earthquake Engineering》2018,16(6):2337-2365
Data provided by accelerometric networks are important for seismic hazard assessment. The correct use of accelerometric signals is conditioned by the station site metadata quality (i.e., soil class, VS30, velocity profiles, and other relevant information that can help to quantify site effects). In France, the permanent accelerometric network consists of about 150 stations. Thirty-three of these stations in the southern half of France have been characterized, using surface-wave-based methods that allow derivation of velocity profiles from dispersion curves of surface waves. The computation of dispersion curves and their subsequent inversion in terms of shear-wave velocity profiles has allowed estimation of VS30 values and designation of soil classes, which include the corresponding uncertainties. From a methodological point of view, this survey leads to the following recommendations: (1) perform both active (multi-analysis surface waves) and passive (ambient vibration arrays) measurements to derive dispersion curves in a broadband frequency range; (2) perform active acquisitions for both vertical (Rayleigh wave) and horizontal (Love wave) polarities. Even when the logistic contexts are sometimes difficult, the use of surface-wave-based methods is suitable for station-site characterization, even on rock sites. In comparison with previous studies that have mainly estimated VS30 indirectly, the new values here are globally lower, but the EC8-A class sites remain numerous. However, even on rock sites, high frequency amplifications may affect accelerometric records, due to the shallow relatively softer layers. 相似文献
183.
Azevedo JS Braga ES Favaro DT Perretti AR Rezende CE Souza CM 《Marine pollution bulletin》2011,62(12):2724-2731
Santos-São Vicente estuary, located in São Paulo State, Brazil, has a history of contamination by inorganic chemicals such as mercury (Hg). In the 1980s the Cubatão was considered one of the most polluted sites in the world as a consequence of the intense industrial activities located in the city close to the estuary. To provide data and evaluate the local biota, total mercury (THg) contents were determined in sediments and in fish, Cathorops spixii, from different areas of the Santos-São Vicente estuary. For comparison, samples were also collected in a non-polluted system with similar hydrochemistry characteristics, the Cananeia estuary. The water characteristics and THg levels in sediment and fish samples confirmed a high human influence in the Santos-São Vicente estuary. The lowest THg values, observed in Cananeia, were evidence of low anthropogenic influence. High values observed in Santos-São Vicente show the necessity for a monitoring program. 相似文献
184.
Marcelo Marchesin Deborah da Paixão Vasconcellos 《Astrophysics and Space Science》2014,352(2):443-460
We study a highly symmetric nine-body problem in which eight positive masses, called the primaries, move four by four, in two concentric circular motions such that their configuration is always a square for each group of four masses. The ninth body being of negligible mass and not influencing the motion of the eight primaries. We assume all the nine masses are in the same plane and that the masses of the primaries are \(m_{1}=m_{2}=m_{3}=m_{4}=\tilde{m}\) and m 5=m 6=m 7=m 8=m and the radii associated to the circular motion of the bodies with mass \(\tilde{m}\) is λ∈[λ 0,1] and for the bodies with mass m is 1. We prove the existence of central configurations which characterize such arrangement of the primaries and we study the influence of the parameter λ, the ratio of the radii of the two circles, on the masses m and \(\tilde{m}\) . We use a synodical system of coordinates to eliminate the time dependence on the equations of motion. We show the existence of equilibria solutions symmetrically distributed on the four quadrants and their dependence on the parameter λ. Finally, we show that there can be 13, 17 or 25 equilibria solutions depending on the size of λ and we investigate their linear stability. 相似文献
185.
T.B. McCord A. Coradini F. Capaccioni G. Filacchione P. Cerroni K.H. Baines J.-P. Bibring E. Bussoletti D.P. Cruikshank V. Formisano Y. Langevin R.M. Nelson B. Sicardy 《Icarus》2004,172(1):104-126
The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of <90°, resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible 13C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data. 相似文献
186.
Kevin H. Baines Pierre Drossart Miguel A. Lopez-Valverde Sushil K. Atreya Christophe Sotin Thomas W. Momary Robert H. Brown Bonnie J. Buratti Roger N. Clark Philip D. Nicholson 《Planetary and Space Science》2006,54(15):1552-1562
We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119–147]. in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 μm. For CH3D, the prominent Q branch of the ν2 fundamental band of CH3D near 4.55 μm is apparent. CO2 emissions from the strong v3 vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32±15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is 2.9±1.5×1014 kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (0.5–1.0 Gyr), we find a mean CO atmospheric production rate of 6±3×105 kg yr−1. Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779–784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8±0.9×10−4, based on an average methane surface emission rate over the past 0.5 Gyr of 1.3×10−13 gm cm−2 s−1 as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi:10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer–Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is 0.02 km3 yr−1, a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant active geological processes reshaping the surface of Titan. 相似文献
187.
Hydrologic recovery after wildfire is critical for restoring the ecosystem services of protecting of human lives and infrastructure from hazards and delivering water supply of sufficient quality and quantity. Recovery of soil‐hydraulic properties, such as field‐saturated hydraulic conductivity (Kfs), is a key factor for assessing the duration of watershed‐scale flash flood and debris flow risks after wildfire. Despite the crucial role of Kfs in parameterizing numerical hydrologic models to predict the magnitude of postwildfire run‐off and erosion, existing quantitative relations to predict Kfs recovery with time since wildfire are lacking. Here, we conduct meta‐analyses of 5 datasets from the literature that measure or estimate Kfs with time since wildfire for longer than 3‐year duration. The meta‐analyses focus on fitting 2 quantitative relations (linear and non‐linear logistic) to explain trends in Kfs temporal recovery. The 2 relations adequately described temporal recovery except for 1 site where macropore flow dominated infiltration and Kfs recovery. This work also suggests that Kfs can have low hydrologic resistance (large postfire changes), and moderate to high hydrologic stability (recovery time relative to disturbance recurrence interval) and resilience (recovery of hydrologic function and provision of ecosystem services). Future Kfs relations could more explicitly incorporate processes such as soil‐water repellency, ground cover and soil structure regeneration, macropore recovery, and vegetation regrowth. 相似文献
188.
Deborah Painter 《Geology Today》2017,33(4):138-141
In south‐central Pennsylvania, USA, is the world's only Upper Silurian/lower Devonian period shallow water marine reef, located deep within a cave and operated for the tourist trade. Other unusual features in the cave include black basaltic rock, the presence of nearly perfect clear calcite crystals and varied cave decorations. The reef is primarily composed of stromatoporoids with brachiopods and crinoids and is part of the Upper Silurian Jersey Shore Member of the Keyser Formation siliciclastics and carbonates. Just outside the cave itself is a transition to the Devonian New Creek and Corriganville formations, also siliciclastics and carbonates. In these formations are the only actual fossil corals in the vicinity of the cave discovered by Boy Scouts in 1928 by climbing through a natural entrance. ‘Wonderland Coral Caverns’ was opened to the public in the 1930s and closed in the 1980s until a safer entrance could be created. The cave is the result of the Alleghanian Orogeny in which Silurian and Devonian sedimentary strata were buried without metamorphism beneath the encroaching northwest African continental mass as the proto‐Atlantic Ocean and the Rheic Ocean closed. The mass eroded completely and the resulting sediments were transported to the west of modern day Pennsylvania, leaving a karst topography and a well preserved fossil reef. 相似文献
189.
Deborah P. Ruffle Eric Herbst 《Monthly notices of the Royal Astronomical Society》2001,322(4):770-778
The photodissociation of surface species, caused by photons from the cosmic-ray-induced and background interstellar radiation fields, is incorporated into our combined gas-phase and grain-surface chemical models of quiescent dense interstellar cores. For the cores studied here, only cosmic-ray-induced photons are important. We find that photodissociation alters gas-phase and surface abundances mainly at large cloud ages (≳ 106–7 yr). The abundances of those surface species, such as H2 O, that are readily reproduced on the surface following photodissociation are not strongly affected at any time. The abundances of surface species that are, on the other hand, reformed slowly via surface reactions possessing activation energy (e.g. CH3 OH) are reduced, while the abundances of associated surface photoproducts (e.g. CO) increase. In the gas phase, inclusion of surface photodissociation tends to increase molecular abundances at late times, slightly improving the agreement with observation for TMC-1. 相似文献
190.
We present an analysis of VIRTIS-M-IR observations of 1.74 μm emission from the nightside of Venus. The 1.74 μm window in the near infrared spectrum of Venus is an ideal proxy for investigating the evolution of middle and lower cloud deck opacity of Venus because it exhibits good signal to noise due to its brightness, good contrast between bright and dark regions, and few additional sources of extinction beside the clouds themselves. We have analyzed the data from the first 407 orbits (equivalent to 407 Earth days) of the Venus Express mission to determine the magnitude of variability in the 1.74 μm radiance. We have also performed an analysis of the evolution of individual features over a span of roughly 5–6 h on two successive orbits of Venus Express. We find that the overall 1.74 μm brightness of Venus has been increasing through the first 407 days of the mission, indicating a gradual diminishing of the cloud coverage and/or thickness, and that the lower latitudes exhibited more variability and more brightening than higher latitudes. We find that individual features evolve with a time scale of about 30 h, consistent with our previous analysis. Analysis of the evolution and motion of the clouds can be used to estimate the mesoscale dynamics within the clouds of Venus. We find that advection alone cannot explain the observed evolution of the features. The measured vorticity and divergence in the vicinity of the features are consistent with evolution under the influence of significant vertical motions likely driven by a radiative dynamical feedback. We measure a zonal wind speed of around 65 m/s, and a meridional wind speed around 2.5 m/s by tracking the motion of the central region of the features. But we also find that the measured wind speeds depend strongly on the points chosen for the wind speed analysis. 相似文献