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Matthieu J.b. Cartigny - One of the best experts on this subject based on the ideXlab platform.
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cyclic steps review and aggradation based classification
Earth-Science Reviews, 2020Co-Authors: Arnoud Slootman, Matthieu J.b. CartignyAbstract:Abstract Cyclic steps are a type of upper flow-regime Bedform consisting of trains of upstream- and upslope-migrating bed undulations. The overriding flow is characterised by a series of hydraulic jumps occurring in the troughs of the undulations. Cyclic steps form in open-channel flows such as rivers and comprise a common Bedform in subaqueous density flows in oceans, lakes and reservoirs. Cyclic steps are associated with alternating Froude-subcritical and Froude-supercritical flow on respectively the stoss side and lee side of individual Bedforms. The transition between these flow states is embodied by the hydraulic jump in the trough of the Bedform, leading to the permanent or quasi-permanent morphology of cyclic steps. Over the past decade, numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash, fluvial, delta and turbidite environments as reviewed here. Cyclic steps were previously discriminated as net-depositional (climbing), transportational and net-erosional (falling) in different parts of sedimentary systems. The following cyclic step descriptors, with distinct depositional signatures, are proposed: fully depositional, partially depositional, transportational, partially erosional and fully erosional. Partially depositional cyclic steps are most common. They are associated with backset-bedded sets (high aggradation rate) and nested scours filled with massive-to-backset-bedded deposits (low aggradation rate). The new classification can be used as a predictive tool in the reconstruction of modern and ancient sedimentary successions using repeat bathymetry, seismic reflection or outcrop data. It is applied in three turbidite case studies: classical deep-sea system, small-scale delta slope and line-sourced carbonate slope.
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Origin of spectacular fields of submarine sediment waves around volcanic islands
Earth and Planetary Science Letters, 2018Co-Authors: Ed L. Pope, Peter J. Talling, Martin Jutzeler, Matthieu J.b. Cartigny, James Shreeve, Ian C. Wright, Richard J. WysoczanskiAbstract:Understanding how large eruptions and landslides are recorded by seafloor morphology and deposits on volcanic island flanks is important for reconstruction of volcanic island history and geohazard assessment. Spectacular fields of Bedforms have been recognised recently on submerged flanks of volcanic islands at multiple locations worldwide. These fields of Bedforms can extend over 50 km, and individual Bedforms can be 3 km in length and 150 m in height. The origin of these Bedform fields, however, is poorly understood. Here, we show that Bedforms result from eruption-fed supercritical density flows (turbidity currents) in some locations, but most likely rotational landslides at other locations. General criteria are provided for distinguishing between submarine Bedforms formed by eruptions and landslides, and emphasise a need for high resolution seismic datasets to prevent ambiguity. Bedforms associated with rotational landslides have a narrower source, with a distinct headscarp, they are more laterally confined, and internal Bedform structure does not suggest upslope migration of each Bedform. Eruption-fed density currents produce wide fields of Bedforms, which extend radially from the caldera. Internal layers imaged by detailed seismic data show that these Bedforms migrated up-slope, indicating that the flows that produced them were Froude supercritical. Due to the low density contrast between interstitial fluid and sediment, the extent and dimensions of submarine eruption-fed Bedforms is much greater than those produced by pyroclastic density currents on land.
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Turbidity Current Bedforms
Atlas of Bedforms in the Western Mediterranean, 2016Co-Authors: Matthieu J.b. Cartigny, George PostmaAbstract:Turbidity currents in the submarine seascape are what river flows are in terrestrial landscapes. While rivers transport sediment from the mountains through valleys towards the sea, turbidity currents transport sediment from the shallow marine realms through canyons towards the deeper abyssal plains. The large scale architecture of both systems is remarkably similar. Yet, there are some fundamental differences between rivers and turbidity currents, the most fundamental one being their density difference; the density of river water is thousand times denser than its surrounding air, while the density of a turbidity current can never be more than twice as dense as its ambient water. In addition, rivers do not depend on their sediment load to flow, while turbidity (density) currents do need the sediment derived excess density to flow. These physical differences change their morphodynamics on the Bedform scale. Present day high-resolution seafloor observations show that turbidity current path ways are covered with Bedforms that are fundamentally different from those that occur in river channels. In this chapter we point out these differences and present a 3D Bedform stability diagram for turbidites.
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recognition of cyclic steps in sandy and gravelly turbidite sequences and consequences for the bouma facies model
Sedimentology, 2014Co-Authors: George Postma, Kick Kleverlaan, Matthieu J.b. CartignyAbstract:Preservation of cyclic steps contrasts markedly with that of subcritical-flow Bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such Bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south-eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft-sediment deformation (flames) preserved in coarse-tail normal-graded structureless deposits (Bouma Ta), while near-horizontal, massive to stratified top-cut-out turbidite beds are found further down the stoss side of the Bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens-shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top-cut-out turbidite beds. The facies that characterize these Bedforms have traditionally been described as turbidite units in idealized vertical sequences of high-density turbidity currents, but have not yet been interpreted to represent Bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far.
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Morphodynamics and sedimentary structures of Bedforms under supercritical-flow conditions: New insights from flume experiments
Sedimentology, 2013Co-Authors: Matthieu J.b. Cartigny, George Postma, Dario Ventra, Jan H. Van Den BergAbstract:Supercritical-flow phenomena are fairly common in modern sedimentary environments, yet their recognition and analysis remain difficult in the stratigraphic record. This fact is commonly ascribed to the poor preservation potential of deposits from high-energy supercritical flows. However, the number of flume data sets on supercritical-flow dynamics and sedimentary structures is very limited in comparison with available data for subcritical flows, which hampers the recognition and interpretation of such deposits. The results of systematic flume experiments spanning a broad range of supercritical-flow Bedforms (antidunes, chutes-and-pools and cyclic steps) developed in mobile sand beds of variable grain sizes are presented. Flow character and related Bedform patterns are constrained through time-series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of some widely used Bedform stability diagrams in the supercritical-flow domain, clarifying in particular the morphodynamic relations between antidunes and cyclic steps. The onset of antidunes is controlled by flows exceeding a threshold Froude number. The transition from antidunes to cyclic steps in fine to medium-grained sand occurs at a threshold mobility parameter. Sedimentary structures associated with supercritical Bedforms developed under variable aggradation rates are revealed by means of combining flume results and synthetic stratigraphy. The sedimentary structures are compared with examples from field and other flume studies. Aggradation rate is seen to exert an important control on the geometry of supercritical-flow structures and should be considered when identifying supercritical Bedforms in the sedimentary record.
George Postma - One of the best experts on this subject based on the ideXlab platform.
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Turbidity Current Bedforms
Atlas of Bedforms in the Western Mediterranean, 2016Co-Authors: Matthieu J.b. Cartigny, George PostmaAbstract:Turbidity currents in the submarine seascape are what river flows are in terrestrial landscapes. While rivers transport sediment from the mountains through valleys towards the sea, turbidity currents transport sediment from the shallow marine realms through canyons towards the deeper abyssal plains. The large scale architecture of both systems is remarkably similar. Yet, there are some fundamental differences between rivers and turbidity currents, the most fundamental one being their density difference; the density of river water is thousand times denser than its surrounding air, while the density of a turbidity current can never be more than twice as dense as its ambient water. In addition, rivers do not depend on their sediment load to flow, while turbidity (density) currents do need the sediment derived excess density to flow. These physical differences change their morphodynamics on the Bedform scale. Present day high-resolution seafloor observations show that turbidity current path ways are covered with Bedforms that are fundamentally different from those that occur in river channels. In this chapter we point out these differences and present a 3D Bedform stability diagram for turbidites.
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recognition of cyclic steps in sandy and gravelly turbidite sequences and consequences for the bouma facies model
Sedimentology, 2014Co-Authors: George Postma, Kick Kleverlaan, Matthieu J.b. CartignyAbstract:Preservation of cyclic steps contrasts markedly with that of subcritical-flow Bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such Bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south-eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft-sediment deformation (flames) preserved in coarse-tail normal-graded structureless deposits (Bouma Ta), while near-horizontal, massive to stratified top-cut-out turbidite beds are found further down the stoss side of the Bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens-shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top-cut-out turbidite beds. The facies that characterize these Bedforms have traditionally been described as turbidite units in idealized vertical sequences of high-density turbidity currents, but have not yet been interpreted to represent Bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far.
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Morphodynamics and sedimentary structures of Bedforms under supercritical-flow conditions: New insights from flume experiments
Sedimentology, 2013Co-Authors: Matthieu J.b. Cartigny, George Postma, Dario Ventra, Jan H. Van Den BergAbstract:Supercritical-flow phenomena are fairly common in modern sedimentary environments, yet their recognition and analysis remain difficult in the stratigraphic record. This fact is commonly ascribed to the poor preservation potential of deposits from high-energy supercritical flows. However, the number of flume data sets on supercritical-flow dynamics and sedimentary structures is very limited in comparison with available data for subcritical flows, which hampers the recognition and interpretation of such deposits. The results of systematic flume experiments spanning a broad range of supercritical-flow Bedforms (antidunes, chutes-and-pools and cyclic steps) developed in mobile sand beds of variable grain sizes are presented. Flow character and related Bedform patterns are constrained through time-series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of some widely used Bedform stability diagrams in the supercritical-flow domain, clarifying in particular the morphodynamic relations between antidunes and cyclic steps. The onset of antidunes is controlled by flows exceeding a threshold Froude number. The transition from antidunes to cyclic steps in fine to medium-grained sand occurs at a threshold mobility parameter. Sedimentary structures associated with supercritical Bedforms developed under variable aggradation rates are revealed by means of combining flume results and synthetic stratigraphy. The sedimentary structures are compared with examples from field and other flume studies. Aggradation rate is seen to exert an important control on the geometry of supercritical-flow structures and should be considered when identifying supercritical Bedforms in the sedimentary record.
Christian Winter - One of the best experts on this subject based on the ideXlab platform.
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a unified model of ripples and dunes in water and planetary environments
arXiv: Geophysics, 2019Co-Authors: Christian Winter, Orencio Duran Vinent, Bruno Andreotti, Philippe ClaudinAbstract:Subaqueous and aeolian Bedforms are ubiquitous on Earth and other planetary environments. However, it is still unclear which hydrodynamical mechanisms lead to the observed variety of morphologies of self-organized natural patterns such as ripples, dunes or compound Bedforms. Here we present simulations with a coupled hydrodynamic and sediment transport model that resolve the initial and mature stages of subaqueous and aeolian Bedform evolution in the limit of large flow thickness. We identify two types of Bedforms consistent with subaqueous ripples and dunes, and separated by a gap in wavelength. This gap is explained in terms of an anomalous hydrodynamic response in the structure of the inner boundary layer that leads to a shift of the position of the maximum shear stress from upstream to downstream of the crest. This anomaly gradually disappears when the bed becomes hydrodynamically rough. By also considering the effect of the spatial relaxation of sediment transport we provide a new unifying framework to compare ripples and dunes in planetary environments to their terrestrial counterparts.
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A unified model of ripples and dunes in water and planetary environments
Nature Geoscience, 2019Co-Authors: Orencio Duran Vinent, Philippe Claudin, Bruno Andreotti, Christian WinterAbstract:Terrestrial and planetary subaqueous and aeolian ripples and dunes can be compared in a unified framework, according to simulations with a hydrodynamic and sediment transport model. Subaqueous and aeolian Bedforms are ubiquitous on Earth and other planetary environments. However, it is still unclear which hydrodynamic mechanisms lead to the observed variety of morphologies of self-organized natural patterns such as ripples, dunes or compound Bedforms. Here we present simulations with a coupled hydrodynamic and sediment transport model that resolve the initial and mature stages of subaqueous and aeolian Bedform evolution in the limit of large flow thickness. We identify two types of Bedforms consistent with subaqueous ripples and dunes, and separated by a gap in wavelength. This gap is explained in terms of an anomalous hydrodynamic response in the structure of the inner boundary layer that leads to a shift of the position of the maximum shear stress from upstream to downstream of the crest. This anomaly gradually disappears when the bed becomes hydrodynamically rough. By also considering the effect of the spatial relaxation of sediment transport we provide a new unifying framework to compare ripples and dunes in planetary environments to their terrestrial counterparts.
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residual currents and Bedform migration in a natural tidal inlet knudedyb danish wadden sea
Geomorphology, 2016Co-Authors: S Fraccascia, Christian Winter, Verner Brandbyge Ernstsen, Dierk HebbelnAbstract:Abstract The morphology and hydrodynamics of the natural tidal inlet Knudedyb in the Danish Wadden Sea were investigated by the analysis of high resolution bathymetric data and hydrodynamic numerical modeling. In contrast to the expected anticlockwise pattern similar to the other inlets in the Wadden Sea, a clockwise tidal residual current was found, which drives the sediment transport and results from the presence of a confluent meander bend. The channel is draped by Bedforms of several hierarchical scales (on average, approximately 155 m long and 2.3 m high), with average sizes decreasing from south to north and seaward (i.e., westward). Primary Bedforms in the area are mostly asymmetric ebb-directed and migrate in the ebb direction in the order of 3 m yr− 1. Bedform sections at the northern channel flank show more symmetrical profiles; crests migrate flood-ward, leading to crestal flexing in the central channel. Lateral recirculation cells develop during ebb tide on both sides of the channel seaward of a bend, before the tidal reversal occurs in the rest of the model domain. As a result of the longer flood phase, a main clockwise residual eddy exists in the middle reach of the channel. Bedform migration patterns and hydrodynamic simulations reveal that the pronounced tidal asymmetry in the channel is enhanced by the effects of the channel morphology on the confined flow (at low tide).
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Predicting bed form roughness: the influence of lee side angle
Geo-Marine Letters, 2016Co-Authors: Alice Lefebvre, Christian WinterAbstract:Flow transverse Bedforms (ripples and dunes) are ubiquitous in rivers and coastal seas. Local hydrodynamics and transport conditions depend on the size and geometry of these Bedforms, as they constitute roughness elements at the bed. Bedform influence on flow energy must be considered for the understanding of flow dynamics, and in the development and application of numerical models. Common estimations or predictors of form roughness (friction factors) are based mostly on data of steep Bedforms (with angle-of-repose lee slopes), and described by highly simplified Bedform dimensions (heights and lengths). However, natural Bedforms often are not steep, and differ in form and hydraulic effect relative to idealised Bedforms. Based on systematic numerical model experiments, this study shows how the hydraulic effect of Bedforms depends on the flow structure behind Bedforms, which is determined by the Bedform lee side angle, aspect ratio and relative height. Simulations reveal that flow separation behind Bedform crests and, thus, a hydraulic effect is induced at lee side angles steeper than 11 to 18° depending on relative height, and that a fully developed flow separation zone exists only over Bedforms with a lee side angle steeper than 24°. Furthermore, the hydraulic effect of Bedforms with varying lee side angle is evaluated and a reduction function to common friction factors is proposed. A function is also developed for the Nikuradse roughness ( k _s), and a new equation is proposed which directly relates k _s to Bedform relative height, aspect ratio and lee side angle.
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estimation of roughness lengths and flow separation over compound Bedforms in a natural tidal inlet
Continental Shelf Research, 2013Co-Authors: Alice Lefebvre, Verner Brandbyge Ernstsen, Christian WinterAbstract:Abstract The hydraulic effect of asymmetric compound Bedforms on tidal currents was assessed from field measurements of flow velocity in the Knudedyb tidal inlet, Denmark. Large asymmetric Bedforms with smaller superimposed ones are a common feature of sandy shallow water environments and are known to act as hydraulic roughness elements in dependence with flow direction. The presence of a flow separation zone on the Bedform lee was estimated through analysis of the measured velocity directions and the calculation of the flow separation line. The Law of the Wall was used to calculate roughness lengths and shear velocities from log–linear segments sought on transect-averaged and single-location velocity profiles. During the ebb tide a permanent flow separation zone was established over the steep (10–20°) lee sides of the ebb-oriented primary Bedforms, which generated a consequent drag on the flow. During the flood, no flow separation was induced by the gentle (2°) lee side of the primary Bedforms except over the steepest (10°) part of the lee side where a small separation zone was sometimes observed. As a result, hydraulic roughness was only due to the superimposed Bedforms. The parameterized flow separation line was found to underestimate the length of the flow separation zone of the primary Bedforms. A better estimation of the presence and shape of the flow separation zone over complex Bedforms in a tidal environment still needs to be determined; in particular the relationship between flow separation zone and Bedform geometry (asymmetry, relative height or slope of the lee side) is unclear. This would improve the prediction of complex Bedform roughness in tidal flows.
Joseph Calantoni - One of the best experts on this subject based on the ideXlab platform.
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observations of Bedform migration and bedload sediment transport in combined wave current flows
Journal of Geophysical Research, 2019Co-Authors: M E Wengrove, D L Foster, Thomas C Lippmann, M A De Schipper, Joseph CalantoniAbstract:Bedload transport is an important mechanism for sediment flux in the nearshore. Yet few studies examine the relationship between Bedform evolution and net sediment transport. Our work contributes concurrent observations of Bedform mobility and bedload transport in response to wave dominant, current dominant, and combined wave-current flows in the nearshore. Bedload sediment flux from migrating Bedforms during combined wave-current conditions accounted for at least 20% more bedload transport when compared with wave dominant flows and at least 80% more than current-dominant flows. Bedforms were observed to transport the most sediment during periods with strong currents, with high-energy skewed waves, and while Bedform orientation and transport direction were aligned. Regardless of flow type, Bedform migration rates were directly proportional to the total kinetic energy contained in the flow field. Eleven bedload transport models formulated to be used in combined flows (both shear and energetics based) were compared with sediment flux estimated from measured Bedform migration. An energetics based sediment transport model was most representative for our data.
M E Wengrove - One of the best experts on this subject based on the ideXlab platform.
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observations of Bedform migration and bedload sediment transport in combined wave current flows
Journal of Geophysical Research, 2019Co-Authors: M E Wengrove, D L Foster, Thomas C Lippmann, M A De Schipper, Joseph CalantoniAbstract:Bedload transport is an important mechanism for sediment flux in the nearshore. Yet few studies examine the relationship between Bedform evolution and net sediment transport. Our work contributes concurrent observations of Bedform mobility and bedload transport in response to wave dominant, current dominant, and combined wave-current flows in the nearshore. Bedload sediment flux from migrating Bedforms during combined wave-current conditions accounted for at least 20% more bedload transport when compared with wave dominant flows and at least 80% more than current-dominant flows. Bedforms were observed to transport the most sediment during periods with strong currents, with high-energy skewed waves, and while Bedform orientation and transport direction were aligned. Regardless of flow type, Bedform migration rates were directly proportional to the total kinetic energy contained in the flow field. Eleven bedload transport models formulated to be used in combined flows (both shear and energetics based) were compared with sediment flux estimated from measured Bedform migration. An energetics based sediment transport model was most representative for our data.