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1.
Boubacar KANE Pierre Y. JULIEN 《国际泥沙研究》2007,22(2):114-119
An extensive database of reservoir sedimentation surveys throughout continental United States is compiled and analyzed to determine specific degradation SD relationships as function of mean annual rainfall R, drainage area A, and watershed slope S. The database contains 1463 field measurements and specific degradation relationships are defined as function of A, R and S. Weak trends and significant variability in the data are noticeable. Specific degradation measurements are log normally distributed with respect to R, A, and S and 95% confidence intervals are determined accordingly. The accuracy of the predictions does not significantly increase as more independent variables are added to the regression analyses. 相似文献
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JEAN‐FRANÇOIS GHIENNE FLAVIA GIRARD JULIEN MOREAU JEAN‐LOUP RUBINO 《Sedimentology》2010,57(5):1175-1198
Climbing dune‐scale cross‐statification is described from Late Ordovician paraglacial successions of the Murzuq Basin (SW Libya). This depositional facies is comprised of medium‐grained to coarse‐grained sandstones that typically involve 0·3 to 1 m high, 3 to 5 m in wavelength, asymmetrical laminations. Most often stoss‐depositional structures have been generated, with preservation of the topographies of formative bedforms. Climbing‐dune cross‐stratification related to the migration of lower‐flow regime dune trains is thus identified. Related architecture and facies sequences are described from two case studies: (i) erosion‐based sandstone sheets; and (ii) a deeply incised channel. The former characterized the distal outwash plain and the fluvial/subaqueous transition of related deltaic wedges, while the latter formed in an ice‐proximal segment of the outwash plain. In erosion‐based sand sheets, climbing‐dune cross‐stratification results from unconfined mouth‐bar deposition related to expanding, sediment‐laden flows entering a water body. Within incised channels, climbing‐dune cross‐stratification formed over eddy‐related side bars reflecting deposition under recirculating flow conditions generated at channel bends. Associated facies sequences record glacier outburst floods that occurred during early stages of deglaciation and were temporally and spatially linked with subglacial drainage events involving tunnel valleys. The primary control on the formation of climbing‐dune cross‐stratification is a combination between high‐magnitude flows and sediment supply limitations, which lead to the generation of sediment‐charged stream flows characterized by a significant, relatively coarse‐grained, sand‐sized suspension‐load concentration, with a virtual absence of very coarse to gravelly bedload. The high rate of coarse‐grained sand fallout in sediment‐laden flows following flow expansion throughout mouth bars or in eddy‐related side bars resulted in high rates of transfer of sands from suspension to the bed, net deposition on bedform stoss‐sides and generation of widespread climbing‐dune cross‐stratification. The later structure has no equivalent in the glacial record, either in the ancient or in the Quaternary literature, but analogues are recognized in some flood‐dominated depositional systems of foreland basins. 相似文献
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ADRIAAN JANSZEN JULIEN MOREAU ANDREA MOSCARIELLO JÜRGEN EHLERS JENS KRÖGER 《Sedimentology》2013,60(3):693-719
Deep, elongated incisions, often referred to as tunnel valleys, are among the most characteristic landforms of formerly glaciated terrains. It is commonly thought that tunnel valleys were formed by meltwater flowing underneath large ice sheets. The sedimentary infill of these features is often highly intricate and therefore difficult to predict. This study intends to improve the comprehension of the sedimentology and to establish a conceptual model of tunnel‐valley infill, which can be used as a predictive tool. To this end, the densely sampled, Pleistocene tunnel valleys in Hamburg (north‐west Germany) were investigated using a dataset of 1057 deep wells containing lithological and geophysical data. The stratigraphic correlations and the resulting three‐dimensional lithological model were used to assess the spatial lithological distributions and sedimentary architecture. The sedimentary succession filling the Hamburg area tunnel valleys can be subdivided into three distinct units, which are distinguished by their inferred depositional proximity to the ice margin. The overall trend of the succession shows a progressive decrease in transport energy and glacial influence through time. The rate of glacial recession appears to have been an important control on the sedimentary architecture of the tunnel‐valley fill. During periods of stagnation, thick ice‐proximal deposits accumulated at the ice margin, while during rapid recession, only a thin veneer of such coarse‐grained sediments was deposited. Ice‐distal and non‐glaciogenic deposits (i.e. lacustrine, marine and terrestrial) fill the remaining part of the incision. The infill architecture suggests formation and subsequent infill of the tunnel valleys at the outer margin of the Elsterian ice sheet during its punctuated northwards recession. The proposed model shows how the history of ice‐sheet recession determines the position of coarse‐grained depocentres, while the post‐glacial history controls the deposition of fines through a progressive infill of remnant depressions. 相似文献
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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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Rosalía ROJAS 《国际泥沙研究》2002,17(4)
1 INTRODUCTION Erosion and sedimentation embody the processes of detachment, transport, and deposition of soil particles. Erosion and subsequent deposition can cause major problems. Erosion reduces productivity of cropland, sediment degrades water quality and may carry soil adsorbed polluting chemicals. Deposition in irrigation canals, stream channels and reservoirs reduces structural capacity and requires costly removal. Ideally, an erosion model should describe the physical processes… 相似文献
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JEAN‐JACQUES CORNÉE JEAN‐LÈN LÉTICÉE PHILIPPE MÜNCH FRÉDÉRIC QUILLÉVÉRÉ JEAN‐FRÉDÉRIC LEBRUN PIERRE MOISSETTE JUAN‐CARLOS BRAGA MIHAELA MELINTE‐DOBRINESCU LYVANE DE MIN JULIEN OUDET AURAN RANDRIANASOLO 《Sedimentology》2012,59(5):1426-1451
Pliocene and Pleistocene deposits from Grande‐Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation controlled by both rapid sea‐level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 (‘Calcaires inférieurs à rhodolithes’) deposited during the Late Zanclean to Early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal‐rich deposits, which dominate the western part of Grande‐Terre, change to planktonic foraminifer‐rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 (‘Formation volcano‐sédimentaire’, ‘Calcaires supérieurs à rhodolithes’ and ‘Calcaires à Agaricia’) was deposited during the Late Piacenzian to Early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal‐dominated ramp that changes upward into a homoclinal, coral‐dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea‐level fall. Finally, Sequence S4 (‘Calcaires à Acropora’) probably formed during the Calabrian, developing as a coral‐dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in Late Calabrian times. 相似文献
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Laminated anorthosite grading outwards into leucogabbro, gabbro,and monzogabbro occurs in a 2.6-km-diameter funnel-shaped intrusion,cut by a quartz alkali syenite plug and concentric syenite andgranite ring-dykes. The anorthosite-gabbro series is laminatedbut not modally or otherwise texturally layered. The lamination,defined by large tabular plagioclase crystals, forms a set ofinwarddipping cones, the dips of which decrease from 60–45?in the central anorthosite to < 25? in the outer gabbros.Rocks close to the outer contact are medium-grained isotropicgabbros. Plagioclase, forming >80% of the series, generallyhas homogeneous labradorite cores (An62–58 in the wholeseries) and thin strongly zoned rims, which follow progressivelylonger solidus paths from the anorthosites to the gabbros. Allrocks contain a late-magmatic alkali feldspar. Plagioclase isthe main or only cumulus phase, the anorthosites being ad- tomesocumulates and the gabbros orthocumulates. Olivine (FO49–41)is more abundant than clinopyroxene in most of the series. Dependingon quartz content, the syenites and granites are hypersolvusor subsolvus and the depth of crystallization was calculatedto be 5 ? 2 km. A Rb/Sr isochron for the syenites and granites gave an age of399 ? 10 Ma with an initial strontium isotopic ratio of 0.7084? 0.0005. Ten samples from the anorthosite-gabbro scries havean average calculated initial ratio of 0.70582 ? 0-00004 at– 400 Ma, showing that the two series are not comagmatic.The anorthosite-gabbro series has parallel REE trends (LaN/YbN{small tilde} 7–10) with decreasing positive Eu anomaliesand increasing total REE contents from anorthosite to gabbro;two monzogabbros have almost no Eu anomaly. The liquid calculatedto be in equilibrium with the lowest anorthosite has almostno Eu anomaly and its normalized REE pattern lies just abovethose for the monzogabbros. The syenites and granites have complementaryREE patterns with negative Eu anomalies. The inferred parental magma was alkalic and leucotroctoliticwith high TiO2 P2O5, Sr and K/Rb and with low MgO, very similarto parental magmas in the Gardar province, South Greenland.It was probably produced at depth by settling of olivine andclinopyroxene but not of plagioclase, which accumulated by flotation.It is suggested that plagioclase crystals from this lower chamberwere progressively entrained (from 0% in the gabbros to 30–40%in the anorthosites), giving rise to the flow lamination inthe upper chamber. The magma in the lower chamber may have beenlayered, because the plagioclase cores in the anorthosite areconsiderably richer in Or than those in the leucogabbros orgabbros. Overall convection did not occur in the upper chamber,whereas compositional convection occurred in the more slowlycooled central anorthositic adcumulates. 相似文献
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Dominant ideology influences political identity, not only through the production of icons and material artifacts but also through attempts to control and eliminate alternative cultural expressions, such as graffiti. Antigraffiti campaigns seek to define notions of legitimacy and appropriateness in urban landscapes. Inscribing graffiti is an inherently spatial practice, one that provides opportunities for alternative expression. These expressions question the power and authority of dominant sociospatial practices and broaden definitions of citizenship and political appropriateness. In this article we analyze Graffiti Hurts, an organization devoted to the eradication of graffiti, in detail. By framing graffitists as outsiders and criminals, Graffiti Hurts seeks to justify the erasure of graffiti, and in so doing it reinforces exclusionary representations of culture, community, and landscape. 相似文献
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JULIEN ROSSIGNOL OLIVIER MOINE DENIS-DIDIER ROUSSEAU 《Boreas: An International Journal of Quaternary Research》2004,33(2):145-154
We investigated the Upper Pleistocene mollusc sequence in the loess deposit of Buzzard's Roost, Nebraska, and compared the results with those obtained for Eustis, 50 km to the west. Both sequences show similarities in: (i) stratigraphy and magnetic susceptibility implying identical fluctuations in loess deposition, (ii) biostratigraphy which indicates a succession of cold-and-moist to cold-and-dry conditions, and (iii) an increasing trend in mollusc abundance and diversity of species characterizing a climatic and/or environmental improvement. We interpret the variations in both sequences as related to the advance of the James and Des Moines ice lobes towards both sites, which was synchronous with the retreat of the Laurentide Ice Sheet. The occurrence of hygrophilous species in the mollusc record, from the upper sequences of Buzzard's Roost, suggests a moister environment than in Eustis. Our preliminary comparison of both malacological sequences suggests that regional or local, rather than global, influence prevailed over the Great Plains between 20 and 12 kyr BP. 相似文献