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Fei Ai Michael Strasser Benedict Preu Till J. J. Hanebuth Sebastian Krastel Achim Kopf 《Geo-Marine Letters》2014,34(5):399-417
Submarine landslides are common along the Uruguayan and Argentinean continental margin, but size, type and frequency of events differ significantly between distinct settings. Previous studies have proposed sedimentary and oceanographic processes as factors controlling slope instability, but also episodic earthquakes have been postulated as possible triggers. However, quantitative geotechnical slope stability evaluations for this region and, for that matter, elsewhere in the South Atlantic realm are lacking. This study quantitatively assesses continental slope stability for various scenarios including overpressure and earthquake activity, based on sedimentological and geotechnical analyses on three up to 36 m long cores collected on the Uruguayan slope, characterized by muddy contourite deposits and a locus of landslides (up to 2 km3), and in a canyon-dominated area on the northern Argentinean slope characterized by sandy contourite deposits. The results of shear and consolidation tests reveal that these distinct lithologies govern different stability conditions and failure modes. The slope sectors are stable under present-day conditions (factor of safety >5), implying that additional triggers would be required to initiate failure. In the canyon area, current-induced oversteepening of weaker sandy contourite deposits would account for frequent, small-scale slope instabilities. By contrast, static vs. seismic slope stability calculations reveal that a peak ground acceleration of at least 2 m/s2 would be required to cause failure of mechanically stronger muddy contourite deposits. This implies that, also along the western South Atlantic passive margin, submarine landslides on open gentle slopes require episodic large earthquakes as ultimate trigger, as previously postulated for other, northern hemisphere passive margins. 相似文献
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A marked increase in manganese content from shallow to deep marine lithofacies can be observed within the carbonate fraction of the Middle Ordovician sequence in eastern Tennessee. The distribution of manganese is controlled by: (1) the original aragonite and calcite mineralogy of shallow and deep marine environments, respectively; (2) preferential substitution of manganese for calcium in the rhombohedral structure of calcite; (3) anoxic depositional and diagenetic environments; and (4) possibly, volcanism. 相似文献
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The organic reef is a special type of carbonate reservoir which always dominates the spatial distribution, reserves and accumulations of natural gas. However, it is difficult to determine the organic reef’s internal structure and gas reservoirs due to numerous adverse factors such as the low resolution of seismic data, depth of burial, strong anisotropy, irregular spatial distribution and complex internal structure. A case study of wavelet decomposition and reconstruction technology applied to elucidate the features of organic reef reservoirs in the Changxing formation from Yuanba gas field shows that the seismic record reconstructed by high frequency signal can adequately describe the internal properties of organic reef reservoirs. Furthermore, the root mean square amplitude ratio of both low and high frequency data obtained from the reconstructed seismic data clearly show spatial distribution of gas and water in reef reservoirs. 相似文献
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The Effects of Building Representation and Clustering in Large-Eddy Simulations of Flows in Urban Canopies 总被引：3，自引：3，他引：0
Elie Bou-Zeid Jan Overney Benedict D. Rogers Marc B. Parlange 《Boundary-Layer Meteorology》2009,132(3):415-436
We perform large-eddy simulations of neutral atmospheric boundary-layer flow over a cluster of buildings surrounded by relatively
flat terrain. The first investigated question is the effect of the level of building detail that can be included in the numerical
model, a topic not yet addressed by any previous study. The simplest representation is found to give similar results to more
refined representations for the mean flow, but not for turbulence. The wind direction on the other hand is found to be important
for both mean and turbulent parameters. As many suburban areas are characterised by the clustering of buildings and homes
into small areas separated by surfaces of lower roughness, we look at the adjustment of the atmospheric surface layer as it
flows from the smoother terrain to the built-up area. This transition has unexpected impacts on the flow; mainly, a zone of
global backscatter (energy transfer from the turbulent eddies to the mean flow) is found at the upstream edge of the built-up
area. 相似文献
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Sediment dynamics and geohazards off Uruguay and the de la Plata River region (northern Argentina and Uruguay) 总被引：1，自引：0，他引：1
Sebastian Krastel Gerold Wefer Till J. J. Hanebuth Andrew A. Antobreh Tim Freudenthal Benedict Preu Tilmann Schwenk Michael Strasser Roberto Violante Daniel Winkelmann 《Geo-Marine Letters》2011,31(4):271-283
The continental margin off Uruguay and northern Argentina is characterized by high fluvial input by the de la Plata River and a complex oceanographic regime. Here we present first results from RV Meteor Cruise M78/3 of May?CJuly 2009, which overall aimed at investigating sediment transport processes from the coast to the deep sea by means of hydroacoustic and seismic mapping, as well as coring using conventional tools and the new MARUM seafloor drill rig (MeBo). Various mechanisms of sediment instabilities were identified based on geophysical and core data, documenting particularly the continental slope offshore Uruguay to be locus of submarine landsliding. Individual landslides are relatively small with volumes <2km3. Gravitational downslope sediment transport also occurs through the prominent Mar del Plata Canyon and several smaller canyons. The canyons originate at a midslope position, and the absence of buried upslope continuations strongly suggests upslope erosion as main process for canyon evolution. Many other morphological features (e.g., slope-parallel scarps with scour geometries) and abundant contourites in a 35-m-long MeBo core reveal that sediment transport and erosion are controlled predominantly by strong contour currents. Despite numerous landslide events, their geohazard potential is considered to be relatively small, because of their small volumes and their occurrence at relatively deep water depths of more than 1,500?m. 相似文献
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Minitope coral islands represent one third of the islands located in the tropical Indo-Pacific. Subsistence farming and extensive agriculture dominate the traditional structure of income. As the lack of natural resources, infrastructure and capital restrict the developmental changes, the islands' natural environment has been utilized as economic potential. Planning and realization of land use systems introduced have, however, often been based on an insufficient data basis and have often inadequately considered the consequences of human impacts on the natural environment and its controlling factors. The result was environmental degradation and ecological destruction, affecting also the population's socioeconomic situation and in some cases rendering alternative land use impossible. Therefore, the long-term utilization of coral islands and, hence, the economic development of those countries require a specific development strategy. Based on the environmental and socioeconomic consequences of touristic utilization of coral islands in the Maldivian Archipelago, the model for a sustainable development strategy and its aims are derived, and the objectives, the conceptual structure, and the way of establishing them organizationally and administratively are presented. 相似文献
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Chronology of cirque glaciation,Colorado front range 总被引：2，自引：0，他引：2
James B. Benedict 《Quaternary Research》1973,3(4):584-599
Moraines and rock glaciers in Front Range cirques record at least four, and possibly five, intervals of Holocene glacier expansion. The earliest and most extensive was the Satanta Peak advance, which deposited multiple terminal moraines near present timberline shortly before 9915 ± 165 BP. By 9200 ± 135 BP, timberline had risen to at least its modern elevation; by 8460 ± 140 BP, patterned ground on Satanta Peak moraines had become inactive. Although a minor ice advance may have occurred just prior to 7900 ± 130 BP, there is no evidence that glaciers or perennial snowbanks survived in the Front Range during the “Altithermal” maximum (ca. 6000–7500 BP), or during a subsequent interval of alpine soil formation (ca. 5000–6000 BP).Glaciers were larger during the Triple Lakes advance (3000–5000 BP) than at any other time during Neoglaciation. Minimum ages of 4485 ± 100 BP, 3865 ± 100 BP, and ca. 3150 BP apply to a threefold sequence of Triple Lakes deposits in Arapaho Cirque. After an important interval of soil formation and cavernous weathering, glaciers and rock glaciers of the Audubon advance (950–1850 BP) reoccupied many cirques, and perennial snowbanks blanketed much of the area above present timberline; although the general Audubon snow cover had begun to melt from valley floors by 1505 ± 95 BP, expanded snowbanks lingered on tundra ridge crests until 1050–1150 BP, and glaciers persisted is sheltered cirques until at least 955 ± 95 BP. Following a minor interval of ice retreat, glaciers of the Arapaho Peak advance (100–300 BP) deposited multiple moraines in favorably oriented cirques.Interpretation of Holocene glacial deposits in the Southern and Central Rocky Mountains has been hampered by (1) a heavy reliance upon relative-dating criteria, many of which are influenced by factors other than age; (2) the assumption that glacial advances in high-altitude cirques can be correlated directly with alluvial deposition in far-distant lowlands; and (3) the assumption that glacial advances have necessarily been synchronous throughout the Rocky Mountain region and the world. Although Holocene glacier fluctuations in the Front Range are believed to reflect changes in regional climate, the Front Range chronology does not have particularly close analogs in other parts of North America. Better-dated local sequences are needed before the hypothesis of global synchroneity can be adequately evaluated; until synchroneity has been proven, long-distance correlations and worldwide cycles of recurring glaciation will remain unconvincing. 相似文献