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JULIEN BOURGET SEBASTIEN ZARAGOSI NADINE ELLOUZ‐ZIMMERMANN NICOLAS MOUCHOT THIERRY GARLAN JEAN‐LUC SCHNEIDER VALENTINE LANFUMEY SIGFRIED LALLEMANT 《Sedimentology》2011,58(2):376-406
This study investigates the morphology and Late Quaternary sediment distribution of the Makran turbidite system (Makran subduction zone, north‐west Indian Ocean) from a nearly complete subsurface mapping of the Oman basin, two‐dimensional seismic and a large set of coring data in order to characterize turbidite system architecture across an active (fold and thrust belt) margin. The Makran turbidite system is composed of a dense network of canyons, which cut into high relief accreted ridges and intra‐slope piggyback basins, forming at some locations connected and variably tortuous paths down complex slopes. Turbidite activity and trench filling rates are high even during the Holocene sea‐level highstand conditions. In particular, basin‐wide, sheet‐like thick mud turbidites, probably related to major mass wasting events of low recurrence time, drape the flat and unchannellized Oman abyssal plain. Longitudinal depth profiles show that the Makran canyons are highly disrupted by numerous thrust‐related large‐scale knickpoints (with gradients up to 20° and walls up to 500 m high). At the deformation front, the strong break of slope can lead to the formation of canyon‐mouth ‘plunge pools’ of variable shapes and sizes. The plunge pools observed in the western Makran are considerably larger than those previously described in sub‐surface successions; the first insights into their internal architecture and sedimentary processes are presented here. Large plunge pools in the western Makran are associated with large scoured areas at the slope break and enhanced sediment deposition downstream: high‐amplitude reflectors are observed inside the plunge pools, while their flanks are composed of thin‐bedded, fine‐grained turbidites deposited by the uppermost part of the turbidity flows. Thus, these architectural elements are associated with strong sediment segregation leading to specific trench‐fill mechanisms, as only the finer‐grained component of the flows is transferred to the abyssal plain. However, the Makran accretionary prism is characterized by strong along‐strike variability in tectonics and fluvial input distribution that might directly influence the turbidite system architecture (i.e. canyon entrenchment, plunge pool formation or channel development at canyon mouths), the sedimentary dynamics and the resulting sediment distribution. Channel formation in the abyssal plain and trench‐fill characteristics depend on the theoretical ‘equilibrium’ conditions of the feeder system, which is related closely to the balance between erosion rates and tectonic regime. Thus, the Makran turbidite system constitutes an excellent modern analogue for deep‐water sedimentary systems with structurally complex depocentres, in convergent margin settings. 相似文献
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Seabirds and fronts: a brief overview 总被引：4，自引：0，他引：4
DAVID C. SCHNEIDER 《Polar research》1990,8(1):17-21
Oceanographic fronts are the sites of enhanced physical and biological activity, including locally concentrated feeding by marine birds. Two general hypotheses relating marine birds to fronts have been developed. The first is that enhanced primary production at fronts increases prey supply through increased animal growth, reproduction, or immigration. The second is that prey patches develop at fronts either through behavioural responses of prey to thermal or salinity gradients, or through interaction between prey behaviour and circulatory patterns. Several recent studies support the second hypothesis. The first hypothesis, that birds benefit from enhanced primary production at fronts, has yet to be evaluated. We need a better understanding of trophic mechanisms at fronts in order to determine (1) the proportion of daily energy requirements extracted by predators at fronts; (2) the proportion of natural mortality of prey populations at fronts; and (3) the probability of contact between seabirds and point source pollutants. 相似文献
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P. A. MAYEWSKI T. BRACEGIRDLE I. GOODWIN D. SCHNEIDER N. A. N. BERTLER S. BIRKEL A. CARLETON M. H. ENGLAND J‐H. KANG A. KHAN J. RUSSELL J. TURNER I. VELICOGNA 《第四纪科学杂志》2015,30(5):391-395
Climate model results suggest that future climate change in Antarctica will be accompanied by continued strengthening and poleward contraction of the Southern Ocean westerly wind belt. Paleoclimate records suggest past changes in the westerly winds can be abrupt and that healing of the Antarctic ozone hole could lead to poleward contraction of the westerlies and increased meridional atmospheric transport of warm air regionally into Antarctica. An abrupt shift to more meridional circulation could lead to notable changes in moisture availability for extra‐Antarctic regions, increased Antarctic ice sheet disintegration and more rapid sea‐level rise. 相似文献
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Spatial autocorrelation in marine birds 总被引：1，自引：0，他引：1
DAVID C. SCHNEIDER 《Polar research》1990,8(1):89-97
All marine organisms exhibit some degree of spatial autocorrelation, which is the tendency for high (or low) densities to occur in proximity, rather than at random in the ocean. Autocorrelation occurs at scales ranging from the length of the organism to thousands of kilometres. Autocorrelation results from a wide variety of mechanisms, many of which act at characteristic scales. Consequently, some insight into causal mechanisms can be obtained from exploratory analysis of the scale and intensity of autocorrelation of abundance or behaviour, and the scale and intensity (coherence) of cross-correlation with environmental variables such as water temperature or prey abundance. This paper uses seabird counts along extended transects to illustrate standard measures of autocorrelation and cross-correlation. A brief discussion of exploratory and confirmatory analysis of autocorrelated data on marine birds follows. 相似文献
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Résumé Le débit de pointe de la crue annuelle de période de retour donnée T est estimé à l'aide de la formule QT=ATpSα pour le tronçon supérieur du cours d'eau Aar à l'amont de Berne. S représente la surface du bassin versant et ATα sont les paramètres du bassin. Le débit QT est déterminé sur la base des mesures faites en chaque station, après correction des courtes séries et des erreurs d'échantillonage éventuelles. Les paramètres AT et a sont calculés à partir d'une régression linéaire établie entre le logarithme des valeurs de QT et de S. Connaissant la relation qui lie l'abscisse curviligne l à la surface du bassin versant en un point quelconque du cours d'eau, la relation QT = QT(S) permet de déterminer le profil de la pointe de la crue annuelle de période T le long de la rivière: QT = QT(l). 相似文献
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The current study focuses on the application of a three-dimensional numerical model for the prediction of morphological bed changes. The sediment deposition in a reservoir during a 10-year-flood was investigated and the results of the simulation were validated with data derived from a physical model study. Because of the small grain sizes in the prototype, synthetic granulate was used in the physical model. The numerical computation domain was a reproduction of the physical model, including the grain sizes and the density of the particles, in order to ensure comparability. The CFD code SSIIM, which solves the RANS-equations in three-dimensions, was used for the simulations. The sediment transport in SSIIM is divided into suspended sediment transport, computed by solving the convection-diffusion equation, and bed-load transport, calculated by an empirical formula. The results of the numerical simulation correspond well to the results of the physical model study. The simulated location and the pattern of the sediment deposition in the reservoir are an accurate representation of the observed distribution in the physical model. 相似文献
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陆相盆地中的海侵层序特征:中欧盆地三叠系与松辽盆地白垩系对比研究 总被引：5，自引：0，他引：5
中欧盆地三叠系是典型的海陆过渡相沉积，松辽盆地白垩系是含有海侵事件记录的陆相河湖盆地。两盆地的共同特点是：①大陆克拉通上长期发育的大型坳陷盆地；②靠近古大洋和（或）有向海通道；③主要由互层状泥岩、粉砂岩、碳酸盐岩和膏盐层组成；④无典型海相化石，可能发育有半咸水和（或）高盐度生物；⑤海侵层中自生矿物的δ^34S,δ^13C,δ^18O同位素比值及介质盐度指数（Sr/Ba）、碱度指数（Ca Mg)／（Si Al）、还原性指标（Zn Ni)/Ga、硫沉积通量指数（归一化硫含量）等显著高于相邻层位背景值。 相似文献