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81.
Floréal Solé Corentin Noiret Delphine Desmares Sylvain Adnet Louis Taverne Thierry De Putter Florias Mees Johan Yans Thomas Steeman Stephen Louwye Annelise Folie Nancy J.Stevens Gregg F.Gunnell Daniel Baudet Nicole Kitambala Yaya Thierry Smith 《地学前缘(英文版)》2019,10(3):1039-1063
The early Paleogene is critical for understanding global biodiversity patterns in modern ecosystems. During this interval, Southern Hemisphere continents were largely characterized by isolation and faunal endemism following the breakup of Gondwana. Africa has been proposed as an important source area for the origin of several marine vertebrate groups but its Paleogene record is poorly sampled, especially from sub-Saharan Africa. To document the early Paleogene marine ecosystems of Central Africa, we revised the stratigraphic context of sedimentary deposits from three fossil-rich vertebrate localities: the Landana section in the Cabinda exclave(Angola), and the Manzadi and Bololo localities in western Democratic Republic of Congo.We provide more refined age constraints for these three localities based on invertebrate and vertebrate faunas, foraminiferal and dinoflagellate cyst assemblages, and carbon isotope records. We find an almost complete absence of Danian-aged rocks in the Landana section, contrary to prevailing interpretations over the last half a century(only the layer 1, at the base of the section, seems to be Danian). Refining the age of these Paleocene layers is crucial for analyzing fish evolution in a global framework, with implications for the early appearance of Scombridae(tunas and mackerels) and Tetraodontiformes(puffer fishes). The combination of vertebrate fossil records from Manzadi and Landana sections suggests important environmental changes around the K/Pg transition characterized by an important modification of the ichthyofauna. A small faunal shift may have occurred during the Selandian. More dramatic is the distinct decrease in overall richness that lasts from the Selandian to the Ypresian. The Lutetian of West Central Africa is characterized by the first appearance of numerous cartilaginous and bony fishes. Our analysis of the ichthyofauna moreover indicates two periods of faunal exchanges: one during the Paleocene, where Central Africa appears to have been a source for the European marine fauna, and another during the Eocene when Europe was the source of the Central Africa fauna. These data indicate that Central Africa has had connections with the Tethyian realm. 相似文献
82.
Sylvain Eschenbrenner Jacques Dorel Jean-Pierre Viode 《Pure and Applied Geophysics》1980,118(2):807-822
Résumé En 1977, deux profils sismiques ont été réalisés en Martinique, un dans la région volcanique de la Montagne Pelée, l'autre dans la partie est de l'île. Le premier couvrait des distances de 3 à 23 km et le second de 2 à 50 km.Les structures superficielles du volcan sont interprétées par un modèle à trois couches. Sur une couche déjà connue, à 6,1 km/s nous trouvons, avec une épaisseur de 0,4 à 2,6 km, une vitesse de 4,3 km/s. En surface et jusqu'à une profondeur de 0,8 à 1,4 km la vitesse est d'environ 2,7 à 2,9 km/s.Dans la partie est de la Martinique, il existe une vitesse élevée-6,5 km/s—à partir d'une profondeur faible, de l'ordre de 3 km.
In 1977, two seismic profiles were carried out in Martinique, one in the area of Montagne Pelée volcano, and the second in the eastern part of the island. The length of the first profile ranges from 3 to 23 km and the second from 2 to 50 km. The interpretation shows that the superficial structures of the volcano may be characterized by a three layer model: in the first layer the compressional velocity is about 2.7 to 2.9 km/s, the thickness varying from 0.8 to 1.4 km. The second layer has a velocity of 4.3 km/s and the thickness goes from 0.4 to 2.6 km. The deeper layer known at Leeward West Indies has a 6.1 km/s velocity.The second profile shows that the eastern part of Martinique is marked by a high velocity of 6.5 km/s, found at a depth of 3 km.相似文献
83.
Sylvain Huon Francis E. GroussetDidier Burdloff Gérard BardouxAndré Mariotti 《Geochimica et cosmochimica acta》2002,66(2):223-239
Organic carbon (OC) and total nitrogen (TN) concentrations and stable isotope ratios (δ13C, δ15N) of fine (<50 μm) size fractions of deep-sea sediments from the central North Atlantic were employed to identify changes in sources of organic matter over the past 50 ka BP. Ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs (averages ± 1σ: OC/TN = 7.6 ± 0.8; δ13C = −22.8 ± 1.0‰; δ15N = 5.5 ± 0.6‰). δ13C, OC, and TN concentrations shift to higher values during the Holocene, indicating a gradual decrease of fine terrigenous supply to the North Atlantic. The unchanged δ15N record between last glacial and Holocene stages indicates that the central North Atlantic region remained oligotrophic at least during the past 50 ka BP, but additional studies are required to support this result in terms of nitrogen oceanic budget. During the phases of enhanced ice-rafted detrital supply corresponding to prominent Heinrich events (HL1, HL2, HL4, and HL5), fine-sized sedimentary organic matter has lower OC and TN concentrations, contrasting sharply with those of ambient glacial sediments. Lower δ13C (down to −28‰) and δ15N (down to 1.6‰) values and high OC:TN ratios (up to 14.7 ± 1.1) are found for HL1, HL2, and with lesser extent for HL4. These values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter-bearing rock sources of the underlying geological basement. During HL5, only the δ13C offset records the input of fine size ice-rafted organic matter. Gradually changing soil development conditions during the time interval covering HL5 to HL1 (marine isotope stages 5 to 2), as well as varying erosion levels, have been hypothesized on the basis of constant δ13C, increasing OC/TN and decreasing δ15N values. 相似文献
84.
Simulation of Meteorological Fields Within and Above Urban and Rural Canopies with a Mesoscale Model 总被引:3,自引:4,他引:3
Accurate simulation of air quality at neighbourhood scales (on order of 1-km horizontal grid spacing) requires detailed meteorological fields inside the roughness sub-layer (RSL). Since the assumptions of the roughness approach, used by most of the mesoscale models, are unsatisfactory at this scale, a detailed urban and rural canopy parameterisation, called DA-SM2-U, is developed inside the Penn State/NCAR Mesoscale Model (MM5) to simulate the meteorological fields within and above the urban and rural canopies. DA-SM2-U uses the drag-force approach to represent the dynamic and turbulent effects of the buildings and vegetation, and a modified version of the soil model SM2-U, called SM2-U(3D), to represent the thermodynamic effects of the canopy elements. The turbulence length scale is also modified inside the canopies. SM2-U(3D) assesses the sensible and latent heat fluxes from rural and urban surfaces in each of the computational layers inside the canopies by considering the shadowing effect, the radiative trapping by the street canyons, and the storage heat flux by the artificial surfaces. DA-SM2-U is tested during one simulated day above the city of Philadelphia, U.S.A. It is shown that DA-SM2-U is capable of simulating the important features observed in the urban and rural RSL, as seen in the vertical profiles of the shear stress, turbulent kinetic energy budget components, eddy diffusivity, potential air temperature, and specific humidity. Within the canopies, DA-SM2-U simulates the decrease of the wind speed inside the dense canopies, the skirting of the flow around the canopy blocks, warmer air inside the vegetation canopy than above open areas during the night and conversely during the day, and constantly warmer air inside the urban canopy. The comparison with measurements shows that the surface air temperature above rural and urban areas is better simulated by DA-SM2-U than by the `standard version' of MM5. 相似文献
85.
Seismic Microzonation: A Comparison between Geotechnical and Seismological Approaches in Pointe-à-Pitre (French West Indies) 总被引:1,自引:0,他引:1
Benoit LeBrun Anne-Marie Duval Pierre-Yves Bard Olivier Monge Myriam Bour Sylvain Vidal Hubert Fabriol 《Bulletin of Earthquake Engineering》2004,2(1):27-50
Pointe-à-Pitre, the main city of Guadeloupe in the French West Indies, has on several occasions been partially destroyed by
major historical earthquakes. Moreover, a post-seismic assessment of the damage from the 1985 Montserrat earthquake indicates
that the town is prone to site effects. Consequently, from 1996 to 1998, BRGM conducted a seismic microzonation study based
on geotechnical and geological data. At the same time, three seismological studies were being conducted – two based on earthquake
recordings using a time-series analysis and the classical spectral ratio (CSR) method (CETE/LCPC and BRGM), and the third
based on noise measurement at 400 points using the horizontal-to-vertical noise ratio (HVNR) method (CETE/LCPC). The objective
of this paper is not to carry out a new microzonation study by taking into account all the results, but rather to show in
what respects the results of these different methods are in agreement or not. A comparison of the results of the seismological
studies with the geotechnical microzonation shows that they are in fairly good agreement, albeit with some discrepancies.
The results indicate that the seismological methods and the geotechnical data are highly complementary and should be used
together in compiling seismic transfer-function microzonation maps.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
Alain Izart Jacques Beauchamp Daniel Vachard Abdel-Ilah Tourani Mohammed Essamani 《Journal of African Earth Sciences》1997,24(4):445-454
Marine deposits of Visean age are well exposed in the Marrakesh area. Two third order sequences are identified in the central High Atlas and Jebilet: SA, which is of Middle Visean age (CM); SB of Upper Visean age (Cf6αβγ); and a complex with olistoliths of Upper Visean-Lower Namurian age (Cf6δ-Cf7). The SA and SIB sequences consist of a relative low-lying system tract with turbidites, a retrograde transgressive system tract and a prograde high-lying system tract. The relative low level comprises a turbiditic fan fed by tectonic uplift, which does not strictly coincide with eustatic processes. The transgressive system tract retrogrades firstly on the slope during tectonic reactivation with slumps, channels and silty levees, secondly on the shelf edge with a mixture of turbiditic and storm deposits and finally on the shelf with storm deposits and reef building. The high level system tract progrades on the shelf by a delta fan. This model is similar to sequences described in Spain and Italy by Mutti (1992), where tectonism is dominant.Nevertheless, eustasy, as described by Vail et al. (1977) played a part, since the same sequences are found in the chart of Ross and Ross (1987): S1, which of Middle Visean age (Cf5) and S2 which is of Upper Visean age (Cf6αβγ). Only the comparison between regional sequences described in Morocco and the sequences of the European platform allow tectonics and eustasy to be taken into consideration. 相似文献
87.
88.
Martin Piringer Sylvain Joffre Alexander Baklanov Andreas Christen Marco Deserti Koen De Ridder Stefan Emeis Patrice Mestayer Maria Tombrou Douglas Middleton Kathrin Baumann-Stanzer Aggeliki Dandou Ari Karppinen Jerzy Burzynski 《Boundary-Layer Meteorology》2007,124(1):3-24
The specific problems of determining and simulating the surface energy balance (SEB) and the mixing height (MH) over urban
areas are examined. The SEB and MH are critical components of algorithms and numerical models for the urban boundary layer,
though the constituent parts of the SEB and the MH are not routinely measured by national weather services. Parameterisations
are thus needed in applications. In this investigation, several recently developed algorithms and models for estimating the
SEB and MH were applied to new datasets and assessed. Results are discussed in terms of the need for spatial resolution and
the parameters needed to describe the urban atmosphere. Limitations of models are identified and recommendations for further
development and observations are given. Having identified gaps in knowledge, key findings from new urban experiments and numerical
modelling for the SEB and MH are given. The diurnal cycle for the SEB is significantly different from rural conditions—urban
heat storage is needed in urban parameterisations. The urban MH is increased over the rural MH, as shown by several numerical
schemes and careful sodar analyses. This work has been carried out within the COST-715 Action “Meteorology applied to urban
air pollution problems (1998–2004). COST 715 reached a consensus proposing representatively sited measurements of meteorological
parameters and turbulent fluxes above roof-tops, and recognised that such data are needed to improve numerical models of the
urban surface processes. 相似文献
89.
The potential of correlating high-resolution Synthetic Aperture Radar images to estimate local water-level variations is analysed based on observing the motions of floating structures. By computing range and azimuth offsets on a COSMO-SkyMed multi-temporal data-set in an area of the French Atlantic Coast, displacement signatures were detected in several harbours of the region. They can be associated with specific floating structures, whose vertical motion is mostly driven by tides. Although the image resolution is not the best achievable for the COSMO-SkyMed sensor, comparison with ground-based tide information revealed that the obtained space-borne measurements are consistent with the tide gauges to a decimetric accuracy. Even if the requirements for traditional users of tidal data are not met by the current revisit time of the COSMO-SkyMed constellation, the method proposed here provides complementary measures, which are already well aligned to requirements of users concerned with long-term sea-level variation and river or lake water stocks. 相似文献
90.
Fores Benjamin Champollion Cdric Lesparre Nolwenn Pasquet Sylvain Martin Aurlie Nguyen Frdric 《Hydrogeology Journal》2021,29(6):2077-2089
Hydrogeology Journal - A hydrogeophysical field experiment was conducted on a karst hydrosystem in the south of France to investigate groundwater transfer and storage variability at a scale of a... 相似文献