No major thermal event on the mid-Cretaceous Côte d'Ivoire–Ghana Transform Margin     

T. Wagner  & T. Pletsch 《地学学报》2001,13(3):165-171

Transient mid-Cretaceous thermal uplift induced by lateral heating from passing oceanic lithosphere is often invoked as a mechanism for the formation of the Côte d'Ivoire–Ghana basement ridge in the Equatorial Atlantic. This heating event should have affected mid-Cretaceous sedimentary rocks along the ridge. However, organic maturity and clay mineral data on the thermal evolution of these rocks suggest that burial temperatures did not exceed 80 °C and that palaeo–geothermal gradients are not anomalous. Optical petrography and the stratigraphic pattern of temperature-sensitive parameters indicate that higher palaeotemperature estimates are related to admixtures of preheated, detrital organic and inorganic matter. Erosion brought the sediments to their present shallow burial depths. Lack of evidence for significant thermal alteration implies that either thermal exchange between oceanic and continental lithosphere along the Côte d'Ivoire–Ghana Transform Margin was negligible, or that lateral heating by oceanic lithosphere was not strong enough to affect the sedimentary cover of the basement ridge.  相似文献   

Pleistocene mass-flow deposits of basaltic hyaloclastite on a shallow submarine shelf,South Iceland     

Steffen G Bergh  Gudmundur E Sigvaldason 《Bulletin of Volcanology》1991,53(8):597-611

A Pleistocene subaqueous, volcanic sequence in South Iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units. Emplacement occurred on a distal submarine shelf in drowned valleys along the southern coast of Iceland. The higher sea level was caused by eustatic sea-level change, probably towards the end of a glaciation. This sequence, nearly 700 m thick, rests unconformably on eroded flatlying lavas and sedimentary rocks of likely Tertiary age. A Standard Depositional Unit, describing the flows of hyaloclastite, starts with compact columnar-jointed basalt overlain by cubejointed basalt, and/or pillow lava. This in turn is overlain by thick unstructured hyaloclastite containing aligned basalt lobes, and bedded hyaloclastite at the top. A similar lithofacies succession is valid for proximal to distal locations. The flows were produced by repeated voluminous extrusions of basaltic lava from subaquatic fissures on the Eastern Rift Zone of Iceland. The fissures are assumed to lie in the same general area as the 1783 Laki fissure which produced 12 km³ of basaltic lava. Due to very high extrusion rates, the effective water/melt ratio was low, preventing optimal fragmentation of the melt. The result was a heterogeneous mass of hyaloclastite and fluid melt which moved en masse downslope with the melt at the bottom of the flow and increasingly vesicular hyaloclastite fragments above. The upper and distal parts of the flow moved as low-concentration turbulent suspensions that deposited bedded hyaloclastite.  相似文献   

Organo- and lithofacies of glacial-interglacial deposits in the Norwegian-Greenland Sea: Responses to paleoceanographic and paleoclimatic changes     

T Wagner  R Henrich 《Marine Geology》1994,120(3-4):335-364

Based on a multiparameter approach a combined litho- and organofacies concept was developed for glacial and interglacial sediment sections along an E-W transect through the central part of the Norwegian-Greenland Sea (NGS).

Modern and past surface water regimes are clearly displayed by specific litho- and organofacies patterns. Interglacial conditions reveal specific Atlantic water associated lithofacies (A and B3) in the eastern and central sector of the Norwegian-Greenland Sea (NGS). Corresponding interglacial organofacies in general are not well correlated to lithofacies due to strong diagenetic degradation of labile, e.g. autochthonous organic matter (OM). While in near-surface sediments a marine-dominated organofacies (I-1) is preserved under Atlantic water masses, this correlation is not evident for lower Holocene and Isotope Stage 5 deposits. However, during Isotopic Event 5.5.1 increased proportions of marine OM are recorded in a high accumulating core on the Vøring Plateau. Glaciomarine background lithofacies (B and C) indicate minor input of ice rafted debris (IRD) and seasonal variable sea-ice cover. Corresponding organofacies (II-1, non-oxidized and II-2, oxidized) are dominated by allochthonous OM. Most spectacular are glacial diamictons (Lithofacies E and F) evidencing short-term sediment pulses due to a sudden disintegration of far advanced tide water ice margins on the outer shelves. These diamictons bear specific organofacies (III-1 and III-2) with a clear predominance of terrigenous and reworked OM.

Some of the diamictons seem to occur contemporaneous with the so called “Heinrich-layers” H1 and H2, suggesting a common trigger-mechanism for the almost simultaneous disintegration of huge continental ice masses along the shelves of North America and the eastern margin of the NGS.

Application of a combined organo- and lithofacies concept provides essential information on spatial and temporal variations of water mass characteristics, the oceanic effects of ice sheet dynamics and circulation models.  相似文献   

Late-Quaternary supply of terrigenous organic matter to the Congo deep-sea fan (ODP site 1075): implications for equatorial African paleoclimate   总被引：3，自引：1，他引：3  

J. Holtvoeth  T. Wagner  B. Horsfield  C. Schubert  U. Wand 《Geo-Marine Letters》2001,21(1):23-33

Late-Quaternary sections (about 1 Ma) from the Congo deep-sea fan (ODP Leg 175, site 1075) were used to reconstruct the terrigenous organic matter supply to the easternmost equatorial Atlantic Ocean. Variations in quantity and quality of the riverine organic matter reflect the interaction between the paleoclimatic development within the continental catchment area and the paleoceanographic conditions in the Congo river plume. To characterize the delivery of organic matter from terrigenous and marine sources, we used elemental and bulk carbon isotopic analyses, Rock-Eval pyrolysis, lignin chemistry, and organic petrology. High-amplitude fluctuations occurring about every 15-25 ka reveal a mainly precessional control on organic sedimentation. Results from Rock-Eval pyrolysis indicate a mixed kerogen type III/II, as would be anticipated in front of a major river. Fluctuations in T_max from Rock-Eval pyrolysis demonstrate pronounced cyclic changes in the delivery of low- and high-mature organic matter. Contribution of the low-mature organic fraction was strongest during warm climates supporting enhanced marine production offshore of the Congo. Organic petrological observations confirm the existence of abundant terrigenous plant tissues, both non-oxidized (vitrinite) and oxidized (inertinite). Charcoal-like organic matter (fusinite) is attributed to periods of increased bush fires in the continental hinterland, and implies more arid climatic conditions. Results from ratios of specific phenolic lignin components suggest that terrigenous organic matter in Late-Quaternary sections of site 1075 mainly derives from non-woody angiosperm tissue, i.e., grasses and leaves. Correlation between the amount of specific lignin phenols and the bulk '¹³C_org signature fosters the conclusion that an appreciable amount of the terrigenous organic fraction derives from C4 plant matter. This may cause an underestimation of the terrigenous proportion of bulk organic matter when assessments are based on bulk carbon isotopic signatures alone.  相似文献   

The starburst in the Wolf-Rayet nucleus of the Liner NGC 6764     

A. Eckart  M. Cameron  R. Genzel  N. Nakai  S. Wagner 《Astrophysics and Space Science》1993,205(1):29-35

We present high resolution millimeter, near-infrared, and optical data on the Wolf-Rayet nucleus of the Liner NGC 6764. The millimeter¹²CO(1-0) maps were obtained using the Nobeyama Millimeter Interferometer. Near-infrared images in the K-band continuum and the 2.12µm H₂, 2.06µm He I, 2.17µm Br, and 1.64µm [Fe II] lines were taken with the MPE imaging spectrometer FAST at the William Herschel Telescope on La Palma, Spain. The optical data were obtained at the 3.5m telescope on Calar Alto, Spain. The measurements indicate a strong concentration of molecular gas and a massive starburst at the nucleus of NGC 6764. The interferometric position velocity map of the nucleus shows the presence of distinct molecular cloud complexes with an apparently asymmetric velocity field shifted towards the blue with respect to the systemic velocity of 2420 km s^–1. The distribution of the 2.12µm H₂ line flux exhibits extensions approximately perpendicular to the bar which are in agreement with structural features in VLA radio maps and IRAM 30m maps of the¹²CO(2–1) line emission. This may represent evidence for combination of a nuclear outflow and a central oval distortion of gas predicted by gas dynamical calculations as a response to a bar like potential. A detailed investigation of the Wolf-Rayet-feature at 466 nm indicates that it is spatially extended on a scale of a few arcseconds.  相似文献   

The polarization of X-ray emission of some solar flares in July 1974     

I. P. Tindo  A. I. Shuryghin  W. Steffen 《Solar physics》1976,46(1):219-227

Preliminary results of polarization measurements at three solar flares of July 5 and 6, 1974, are given. The measurements were performed at h 15 keV with Thomson-scattering polarimeter on the Intercosmos 11 satellite.At the decay phase of the flare on July 5 we obtained P = 3.4–5.0%, which did not exclude some contribution from non-thermal processes. At the flares of July 6 we found P =1.0–1.9% and P = 0.1–2.0%, respectively: neither value exceeds the level of statistical fluctuations.Presented at XVIII COSPAR Meeting (VARNA, May–June 1975), contribution III.B.2.9.  相似文献   

Geometry and accuracy of reflecting points in bistatic satellite altimetry     

J. Kostelecký  J. Klokočník  C.A. Wagner 《Journal of Geodesy》2005,79(8):421-430

The analysis of the time and space distribution of specular (reflecting) points in bistatic altimetry between GPS and CHAMP satellites or SAC-C (taken as examples) is extended from Wagner and Klokočník (2003 J. Geod 77: 128–138). We demonstrate a significantly higher number and density of reflecting points in bistatic altimetry in comparison with traditional monostatic altimetry. After an outline of our older accuracy assessment for the vertical position of the reflecting point, we add a new independent derivation and compare both approaches. We account for orbit errors of both the transmitters (GPS) and receiver (CHAMP) satellites, and the measurement (delay) error. We found that the accuracy of the vertical position of the reflecting point decreases only slowly with increasing off-nadir angle and that the orbit errors must be accounted for if decimeter and better accuracy is required. In this paper, we do not study errors such as state of the ocean, technical parameters of the receiving system, and atmospheric corrections.  相似文献   

Particle size dependent response of aerosol counters     

A. Ankilov  A. Baklanov  M. Colhoun  K. -H. Enderle  J. Gras  Yu. Julanov  D. Kaller  A. Lindner  A. A. Lushnikov  R. Mavliev  F. McGovern  T. C. O'Connor  J. Podzimek  O. Preining  G. P. Reischl  R. Rudolf  G. J. Sem  W. W. Szymanski  A. E. Vrtala  P. E. Wagner  W. Winklmayr  V. Zagaynov 《Atmospheric Research》2002,62(3-4)

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.  相似文献   

Common-Reflection-Surface Stack for Converted Waves     

Bergler  Steffen  Duveneck  Eric  Höcht  German  Zhang  Yonghai  Hubral  Peter 《Studia Geophysica et Geodaetica》2002,46(2):165-175

The finite-offset (FO) common-reflection-surface (CRS) stack has been shown to be able to handle not only P-P or S-S but also arbitrarily converted reflections. It can provide different stack sections such as common-offset (CO), common-midpoint (CMP) and common-shot (CS) sections with significantly increased signal-to-noise ratio from the multi-coverage pre-stack seismic data in a data-driven way. It is our purpose in this paper to demonstrate the performance of the FO CRS stack on data involving converted waves in inhomogeneous layered media. In order to do this we apply the FO CRS stack for common-offset to a synthetic seismic data set involving P-P as well as P-S converted primary reflections. We show that the FO CRS stack yields convincing improvement of the image quality in the presence of noisy data and successfully extracts kinematic wavefield attributes useful for further analyses. The extracted emergence angle information is used to achieve a complete separation of the wavefield into its P-P and P-S wave components, given the FO CRS stacked horizontal and vertical component sections.  相似文献   

The Cretaceous and younger thermal history of the KTB site (Germany): apatite fission-track data from the Vorbohrung     

D. A. Coyle  G. A. Wagner  E. Hejl  R. Brown  P. Van den Haute 《International Journal of Earth Sciences》1997,86(1):203-209

A detailed fission-track analysis was carried out on 41 apatite samples from the 4001-m-deep pilot hole of the German Continental Deep Drilling Program (KTB). The investigations include dating by the population method and length measurements of horizontal confined tracks. Age and length information indicate that all samples above the present-day partial annealing zone cooled from temperatures above 120?°C in the Cretaceous. The top two kilometres of the profile show less variation of age with depth than was expected. Modelling of the profile indicates that the distribution of fission track ages with depth requires that the profile was disturbed during or after cooling through the partial annealing zone. Modelling of individual samples reveals that at least the upper 2?km experienced reverse faulting, effectively thickening the upper part of the rock column by up to 1000?m in the Tertiary. A present-day partial annealing zone for apatite was observed between 2000 and 4000?m (～60–110?°C). This confirms earlier in situ observations of the position of the partial annealing zone.  相似文献