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161.
From outwash to coastal systems in the Portneuf–Forestville deltaic complex (Québec North Shore): Anatomy of a forced regressive deglacial sequence 下载免费PDF全文
Pierre Dietrich Jean‐François Ghienne Mathieu Schuster Patrick Lajeunesse Alexis Nutz Rémy Deschamps Claude Roquin Philippe Duringer 《Sedimentology》2017,64(4):1044-1078
Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km2) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km3) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year?1), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year?1), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations. 相似文献
162.
Bruno Castelle B. G. Ruessink Philippe Bonneton Vincent Marieu Nicolas Bruneau Timothy D. Price 《地球表面变化过程与地形》2010,35(7):771-781
Double sandbar systems are common morphological features along sandy, wave‐dominated, micro‐ to meso‐tidal coastlines. In the companion paper, we demonstrated how various alongshore inner‐bar rip‐channel patterns can develop through morphological coupling to an alongshore‐variable outer bar. The simulated coupling patterns are, however, scarcely observed in the field. Instead, inner‐bar rip channels more often possess remarkably smaller and more variable alongshore length scales, suggesting that coupling mechanisms do not play a substantial role in the overall double‐sandbar dynamics. Here we use a numerical model to show that the relative importance of self‐organization and morphological coupling changes in favour of the latter with an increase in waterdepth variability along the outer‐bar crest. Furthermore, we find that the typical alongshore variability in inner‐bar rip‐channel scale is indicative of a mixture of self‐organization and morphological coupling rather than self‐organization alone. Morphological coupling may thus be more important to understanding and predicting the evolution of inner‐bar rip channels than previously envisaged. Copyright © 2010 John Wiley and Sons, Ltd. 相似文献
163.
164.
Philippe Gueguen Véronique Jolivet Clotaire Michel Anne-Sophie Schveitzer 《Bulletin of Earthquake Engineering》2010,8(2):327-338
Over recent years there has been a growing interest in the building frequency analysis for earthquake and structural engineering
fields using ambient vibrations. Simultaneously, velocity measurements with LASER remote sensing techniques have gained more
interest for several applications. This paper details the comparison of the frequency analysis obtained using sensitive velocimeter
sensor and coherent LIDAR (Light Detection and Ranging) sensor, and applied to one RC existing building. Ambient vibrations
recordings were processed using the Frequency Domain Decomposition method for defining the frequencies and mode shapes of
the building target, while LASER remote sensing approach used coherent LIDAR method for velocity and frequency measurement.
The results of the two systems are discussed. A good agreement is observed, which let us conclude on the ability of the coherent
LIDAR to assess the frequency of existing buildings for structural and earthquake engineering fields at long range and without
any retroreflector on the structure. 相似文献
165.
Oliver Gunther Philippe Picouet Jean-Marc Saglio Michel Scholl Vincent Oria 《International journal of geographical information science》2013,27(7):639-655
Spatial joins are join operations that involve spatial data types and operators. Spatial access methods are often used to speed up the computation of spatial joins. This paper addresses the issue of benchmarking spatial join operations. For this purpose, we first present a WWW-based benchmark generator to produce sets of rectangles. Using a Web browser, experimenters can specify the number of rectangles in a sample, as well as the statistical distributions of their sizes, shapes, and locations. Second, using the generator and a well-defined set of statistical models we define several tests to compare the performance of three spatial join algorithms: nested loop, scan-and-index, and synchronized tree traversal. We also added two real-life data sets from the Sequoia 2000 storage benchmark. Our results show that the relative performance of the different techniques mainly depends on the selectivity factor of the join predicate. All of the statistical models and algorithms are available on the Web, which allows for easy verification and modification of our experiments. 相似文献
166.
Karen Guihou Julien Marmain Yann Ourmières Anne Molcard Bruno Zakardjian Philippe Forget 《Ocean Dynamics》2013,63(7):793-808
The Northern current is the main circulation feature of the North-Western Mediterranean Sea. While the large-scale to mesoscale variability of the northern current (NC) is well known and widely documented for the Ligurian region, off Nice or along the Gulf of Lions shelf, few is known about the current instabilities and its associated mesoscale dynamics in the intermediate area, off Toulon. Here, we took advantage of an oceanographic cruise of opportunity, the start of a HF radar monitoring programme in the Toulon area and the availability of regular satellite sea surface temperature and chlorophyll a data, to evaluate the realism of a NEMO-based regional high-resolution model and the added value brought by HF radar. The combined analysis of a 1/64° configuration, named GLAZUR64, and of all data sets revealed the occurrence of an anticyclonic coastal trapped eddy, generated inside a NC meander and passing the Toulon area during the field campaign. We show that this anticyclonic eddy is advected downstream along the French Riviera up to the study region and disturbs the Northern current flow. This study aims to show the importance of combining observations and modelling when dealing with mesoscale processes, as well as the importance of high-resolution modelling. 相似文献
167.
Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania 总被引:1,自引:0,他引:1
Matthieu Perrault Philippe Gueguen Alexandru Aldea Sorin Demetriu 《地震工程与工程振动(英文版)》2013,12(4):643-658
The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied: (1) adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson's criteria, (2) computation of the structure's response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements (IM), and (3) construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ) as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology. 相似文献
168.
River restoration measures are becoming increasingly popular and are leading to dynamic river bed morphologies that in turn result in complex water level distributions in a river. Disconnected river branches, nonlinear longitudinal water level profiles and morphologically induced lateral water level gradients can evolve rapidly. The modeling of such river‐groundwater systems is of high practical relevance in order to assess the impact of restoration measures on the exchange flux between a river and groundwater or on the residence times between a river and a pumping well. However, the model input includes a proper definition of the river boundary condition, which requires a detailed spatial and temporal river water level distribution. In this study, we present two new methods to estimate river water level distributions that are based directly on measured data. Comparing generated time series of water levels with those obtained by a hydraulic model as a reference, the new methods proved to offer an accurate and faster alternative with a simpler implementation. 相似文献
169.
Pauline Robert Christopher W. Mckindsey Gwénaëlle Chaillou Philippe Archambault 《Marine pollution bulletin》2013,66(1-2):92-104
This study reports the results of a field experiment using benthic mesocosms that examined dose-dependent effects of mussel biodeposition on the benthic environment. Mesocosms were placed in the natural sea bottom and subjected to one of eight levels of biodeposition (from 0 to 1400 mussels m?2). Most analyses indicated non-linear (i.e., threshold) effects. Sediment characteristics changed significantly between 200 and 400 mussels m?2 as did multivariate community structure. Community structure effects were characterised by changes in abundances of species that are very sensitive or tolerant to organic loading. The multivariate AZTI Marine Biotic Index (M-AMBI) indicated that the benthic status changed from High to Good in all mesocosms receiving biodeposits. Sediments acted as a sink for oxygen (O2), but results suggest O2 sediment demand was not sensitive enough to evaluate organic loading impacts. Results from this and improved experiments can be used to determine the environmental carrying capacity of sites for bivalve culture. 相似文献
170.
The re-vegetation of soils contaminated by potentially harmful metals is generally considered a suitable option to reduce the metal dispersion in surrounding environments. A continuous flow experiment was conducted to quantitatively assess the effect of Italian ryegrass (Lolium multiflorum Lam.) root activity on the weathering of smithsonite (ZnCO3), a common Zn mineral. At the end of the experiment (10 days), the total amount of Zn released by smithsonite was increased by a factor of 2.25 in the presence of plants. This increase was due not only to plant uptake but also to the enhancement of the Zn release into leachates. The rate of Zn release from smithsonite to leachates was 2.9 × 10−4 μg g−1 s−1 and 1.5 × 10−4 μg g−1 s−1 in the presence and the absence of plants, respectively. The strong correlation (r = 0.95; p < 0.001) between concentrations of Zn and dissolved organic C (DOC) produced by the rhizosphere activity in leachates indicated that organic root exudates and secretions were closely involved in smithsonite weathering. Although the results are derived from laboratory study, and further in situ investigations over the long term are needed, they clearly highlighted that plants can enhance metal release into the environment by accelerating mineral weathering. Therefore, it is suggested that the ability of plants to alter metal phases in soils should be further taken into account when re-vegetation strategies are proposed for the rehabilitation of metal-polluted soils. 相似文献