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Russell B. Wynn - One of the best experts on this subject based on the ideXlab platform.
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Turbidity current Sediment Waves on irregular slopes: observations from the Orinoco Sediment–Wave field
Marine Geology, 2002Co-Authors: Gemma Ercilla, Belen Alonso, Russell B. Wynn, Jesús BarazaAbstract:Abstract The Orinoco Sediment–Wave field covers an area of at least 29 000 km2 on the southern margin of the Orinoco Valley, at a water depth of 4400–4825 m. Wave dimensions are highly variable across the Wave field, with Wavelengths of 110–2600 m, and Wave heights of 1–15 m. Slope gradients are also very variable, with values of 0.14–0.48°. Overall, the Sedimentary sequence on the upslope Wave flanks is about 40% thicker than that on the downslope flanks, leading to upslope Wave migration in the manner of antidunes. In addition, reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks, suggesting that a higher proportion of coarser Sediment occurs on the upslope flank. An unconfined turbidity current origin is proposed for the Orinoco Sediment Waves, based upon detailed analysis of regional stratigraphic/seismic facies, and Sediment Wave distribution, morphology and dimensions. Sediment Waves are not related to flows passing along (or spilling out of) the Orinoco Valley, or to bottom currents flowing parallel to the slope. Turbidity currents responsible for Wave generation are interpreted as originating from slope failures on the adjacent Venezuela, Guyana and Suriname continental margins. Simple numerical modelling has enabled turbidity current flow characteristics across the Orinoco Sediment Waves to be estimated: internal Froude number=0.7–1.1, flow thickness=24–645 m, and flow velocity=31–82 cm s−1. A key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in Wave dimensions across the Wave field. The irregular gradient of the present-day Wave field is partly a reflection of the irregular bounding surface of the Sediment Waves, which is represented by mass-flow deposits and associated mud diapirs. The changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents, which in turn control the Wave dimensions. Generally, on lower gradients beyond minor breaks of slope, flow thickness increases and flow velocity decreases, leading to an increase in Wavelength and a decrease in height.
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Classification and characterisation of deep-water Sediment Waves
Marine Geology, 2002Co-Authors: Russell B. Wynn, Dorrik A. V. StowAbstract:Deep-water Sediment Waves can be classified using a combination of grain size and Wave-forming process, although in some cases one or other of these criteria may be indeterminable. Sediment Waves are generated beneath currents flowing across the seabed, in the form of either downslope-flowing turbidity currents or alongslope-flowing bottom currents. Waves formed by either process show varying characteristics, depending on whether they are constructed of coarse- or fine-grained Sediments. Sediment Wave studies over the last five decades are reviewed, and clear trends can be discerned. Early descriptive studies in the 1950s and 1960s relied almost exclusively on seismic reflection profiles, and the Wave-forming process was often a subject of much debate. In the 1970s and 1980s the quality of Sediment Wave datasets increased, with sidescan sonar, deep-sea drilling and numerical modelling all applied to Sediment Wave studies. Consequently, the Wave-forming process became more easily identifiable, and models for the growth of bottom current and turbidity current Sediment Waves were introduced. Most studies from the 1990s onwards have focussed on turbidity current Sediment Waves, in response to the increasing demand for data from turbidite systems from the hydrocarbon exploration and production industry. Studies of bottom current Sediment Waves during this period have focussed on the applications to palaeoceanography, in response to the recent boom in climate change studies. The main focus of this paper is the characterisation of both fine- and coarse-grained, turbidity and bottom current Sediment Waves, including the depositional environment, Wave morphology, Wave Sediments and migration, and the Wave-forming process. In addition, criteria for distinguishing between fine-grained bottom current and turbidity current Waves are discussed, and also for identifying other Wave-like features formed by different processes, such as creep folds. Although in many Sediment Wave studies the dominant Wave-forming process is easy to determine, in others it is likely that a more complex combination of processes has occurred. Further studies should concentrate on methods for identifying these processes and how they interact, and also investigate the exact mechanisms for the initiation and evolution of Sediment Wave fields.
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Generation and migration of coarse-grained Sediment Waves in turbidity current channels and channel–lobe transition zones
Marine Geology, 2002Co-Authors: Russell B. Wynn, David J.w. Piper, M.j.r. GeeAbstract:Large-scale Sediment Waves, composed of gravels and sands, have been studied using deep-water sidescan systems. New data are presented from submarine channels off the Canary Islands and from canyon mouths off Portugal. Data from other areas are briefly reviewed, including a re-interpretation of data from Laurentian Fan, in order to summarise the varied morphology and setting of these bedforms. Coarse-grained Sediment Waves are found in the proximal, dominantly bypassing areas of deep-water turbidite systems, within canyons, channels and channel-lobe transition zones. Wave heights are in the region of 1-10 m, and Wavelengths are up to several hundred metres. The distribution of Waves, and sparse Sedimentological evidence from modern and ancient Sediment Wave fields, suggests that initial transport and deposition of coarse Sediment occurs within a high-density turbidity current, and not as a non-Newtonian debris flow. In some cases the development of pronounced Wave asymmetry, and evidence of Wave disruption and reworking, suggests that the Wave morphology is at least partially controlled by a later phase of low-density turbidity flow. Grain size also appears to exert some control on Wave morphology, for example, gravel-rich Waves have a greater height for the same Wavelength than sand-rich Waves. Coarse-grained Sediment Waves are often difficult to recognise on the seafloor because of reworking or burial by younger turbidity currents, and are equally difficult to recognise in outcrop because of their large size
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Initiation and evolution of turbidity current Sediment Waves in the Magdalena turbidite system
Marine Geology, 2002Co-Authors: Gemma Ercilla, Belen Alonso, Russell B. Wynn, Jesús BarazaAbstract:This study describes an extensive Sediment–Wave field in the Magdalena Turbidite System, Caribbean Sea, Colombia, which occupies an area of at least 15000 km2 on the continental slope (3330–>3800 m). The Waves display Wavelengths up to 1.9 km, Wave heights up to 18 m, and crestlines that are aligned roughly parallel to the regional bathymetric contours. Preferential deposition on the upslope Wave flank has led to upslope migration, in the manner of antidunes. The Magdalena Sediment Waves are interpreted as forming beneath unconfined turbidity currents, which may result from the downslope evolution of slumps and mass flows. The unconfined turbidity currents are derived from several point sources along the continental slope and spread laterally as they flow downslope. This has led to the formation of a laterally extensive Sediment–Wave field. Simple numerical modelling estimates that the turbidity currents responsible for Wave generation were near- or super-critical, with flow thickness and velocity estimated at 40–160 m, and 36–82 cm s-1 respectively. However, later phases of Wave growth were not dependent on specific flow conditions. The most important aspect of this study is that the entire Sediment–Wave unit, from the basal boundary to the present-day seafloor, has been investigated using ultra high-resolution seismic profiles. The Sediment–Wave unit rests upon an irregular discontinuity that marks a recent change in the Sedimentary regime of the Magdalena Turbidite System, from channelised to unchannelised gravity flows. Above this boundary, the Sediment Waves display a growth pattern characterised by an increase in Wave dimensions. In addition, the Wave dimensions appear to become more regular through time. However, breaks of slope in the lower bounding surface of the Wave field have produced variations in Wave morphology that are still visible at the present-day seafloor. This indicates that there is a close relationship between variations in slope angle and turbidity current flow characteristics, which in turn leads to variations in Wave morphology
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Generation and migration of coarse-grained Sediment Waves in turbidity current channels and channel–lobe transition zones
Marine Geology, 2002Co-Authors: Russell B. Wynn, David J.w. Piper, M.j.r. GeeAbstract:Large-scale Sediment Waves, composed of gravels and sands, have been studied using deep-water sidescan systems. New data are presented from submarine channels off the Canary Islands and from canyon mouths off Portugal. Data from other areas are briefly reviewed, including a re-interpretation of data from Laurentian Fan, in order to summarise the varied morphology and setting of these bedforms. Coarse-grained Sediment Waves are found in the proximal, dominantly bypassing areas of deep-water turbidite systems, within canyons, channels and channel-lobe transition zones. Wave heights are in the region of 1-10 m, and Wavelengths are up to several hundred metres. The distribution of Waves, and sparse Sedimentological evidence from modern and ancient Sediment Wave fields, suggests that initial transport and deposition of coarse Sediment occurs within a high-density turbidity current, and not as a non-Newtonian debris flow. In some cases the development of pronounced Wave asymmetry, and evidence of Wave disruption and reworking, suggests that the Wave morphology is at least partially controlled by a later phase of low-density turbidity flow. Grain size also appears to exert some control on Wave morphology, for example, gravel-rich Waves have a greater height for the same Wavelength than sand-rich Waves. Coarse-grained Sediment Waves are often difficult to recognise on the seafloor because of reworking or burial by younger turbidity currents, and are equally difficult to recognise in outcrop because of their large siz
Dorrik A. V. Stow - One of the best experts on this subject based on the ideXlab platform.
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Classification and characterisation of deep-water Sediment Waves
Marine Geology, 2002Co-Authors: Russell B. Wynn, Dorrik A. V. StowAbstract:Deep-water Sediment Waves can be classified using a combination of grain size and Wave-forming process, although in some cases one or other of these criteria may be indeterminable. Sediment Waves are generated beneath currents flowing across the seabed, in the form of either downslope-flowing turbidity currents or alongslope-flowing bottom currents. Waves formed by either process show varying characteristics, depending on whether they are constructed of coarse- or fine-grained Sediments. Sediment Wave studies over the last five decades are reviewed, and clear trends can be discerned. Early descriptive studies in the 1950s and 1960s relied almost exclusively on seismic reflection profiles, and the Wave-forming process was often a subject of much debate. In the 1970s and 1980s the quality of Sediment Wave datasets increased, with sidescan sonar, deep-sea drilling and numerical modelling all applied to Sediment Wave studies. Consequently, the Wave-forming process became more easily identifiable, and models for the growth of bottom current and turbidity current Sediment Waves were introduced. Most studies from the 1990s onwards have focussed on turbidity current Sediment Waves, in response to the increasing demand for data from turbidite systems from the hydrocarbon exploration and production industry. Studies of bottom current Sediment Waves during this period have focussed on the applications to palaeoceanography, in response to the recent boom in climate change studies. The main focus of this paper is the characterisation of both fine- and coarse-grained, turbidity and bottom current Sediment Waves, including the depositional environment, Wave morphology, Wave Sediments and migration, and the Wave-forming process. In addition, criteria for distinguishing between fine-grained bottom current and turbidity current Waves are discussed, and also for identifying other Wave-like features formed by different processes, such as creep folds. Although in many Sediment Wave studies the dominant Wave-forming process is easy to determine, in others it is likely that a more complex combination of processes has occurred. Further studies should concentrate on methods for identifying these processes and how they interact, and also investigate the exact mechanisms for the initiation and evolution of Sediment Wave fields.
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Sedimentary processes in the selvage Sediment Wave field ne atlantic new insights into the formation of Sediment Waves by turbidity currents
Sedimentology, 2000Co-Authors: Russell B. Wynn, Gemma Ercilla, Philip Pe Weaver, Dorrik A. V. Stow, D G MassonAbstract:An integrated geophysical and Sedimentological investigation of the Selvage Sediment-Wave field has revealed that the Sediment Waves are formed beneath unconfined turbidity currents. The Sediment Waves occur on the lower continental rise and display Wavelengths of up to 1 km and Wave heights of up to 6 m. Wave Sediments consist of interbedded turbidites and pelagic/hemipelagic marls and oozes. Nannofossil-based dating of the Sediments indicates a bulk Sedimentation rate of 2·4 cm 1000 years-1, and the Waves are migrating upslope at a rate of 0·28 m 1000 years-1. Sediment provenance studies reveal that the turbidity currents maintaining the Waves are largely sourced from volcanic islands to the south. Investigation of existing models for Sediment-Wave formation leads to the conclusion that the Selvage Sediment Waves form as giant antidunes. Simple numerical modelling reveals that turbidity currents crossing the Wave field have internal Froude numbers of 0·5-1·9, which is very close to the antidune existence limits. Depositional flow velocities range from <6 to 125 cm-1. There is a rapid increase in Wavelength and flow thickness in the upper 10 km of the Wave field, which is unexpected, as the slope angle remains relatively constant. This anomaly is possibly linked to a topographic obstacle just upslope of the Sediment Waves. Flows passing over the obstacle may undergo a hydraulic jump at its boundary, leading to an increase in flow thickness. In the lower 15 km of the Wave field, flow thickness decreases downslope by 60%, which is comparable with results obtained for other unconfined turbidity currents undergoing flow expansion
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Sedimentary processes in the Selvage Sediment‐Wave field, NE Atlantic: new insights into the formation of Sediment Waves by turbidity currents
Sedimentology, 2000Co-Authors: Russell B. Wynn, Gemma Ercilla, Philip Pe Weaver, Dorrik A. V. Stow, Douglas G. MassonAbstract:An integrated geophysical and Sedimentological investigation of the Selvage Sediment-Wave field has revealed that the Sediment Waves are formed beneath unconfined turbidity currents. The Sediment Waves occur on the lower continental rise and display Wavelengths of up to 1 km and Wave heights of up to 6 m. Wave Sediments consist of interbedded turbidites and pelagic/hemipelagic marls and oozes. Nannofossil-based dating of the Sediments indicates a bulk Sedimentation rate of 2·4 cm 1000 years-1, and the Waves are migrating upslope at a rate of 0·28 m 1000 years-1. Sediment provenance studies reveal that the turbidity currents maintaining the Waves are largely sourced from volcanic islands to the south. Investigation of existing models for Sediment-Wave formation leads to the conclusion that the Selvage Sediment Waves form as giant antidunes. Simple numerical modelling reveals that turbidity currents crossing the Wave field have internal Froude numbers of 0·5-1·9, which is very close to the antidune existence limits. Depositional flow velocities range from
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Turbidity current Sediment Waves on the submarine slopes of the western Canary Islands
Marine Geology, 2000Co-Authors: Russell B. Wynn, Douglas G. Masson, Dorrik A. V. Stow, Philip Pe WeaverAbstract:Two Sediment Wave fields have been identified on the flanks of the western Canary Islands of La Palma and El Hierro, using a high-quality 2-D and 3-D dataset that includes GEOSEA and TOBI imagery, 3.5-kHz profiles, and short Sediment cores. The La Palma Sediment Wave field covers some 20,000 km2 of the continental slope and rise, and consists of Sediment Waves with Wave heights of up to 70 m and Wavelengths of up to 2.4 km. The Wave crestlines have a complex morphology, with common bifurcation and a clear sinuosity. Waves have migrated upslope through time. Cores recovered from the Wave field contain volcaniclastic turbidites interbedded with pelagic/hemipelagic layers. The Wave field is interpreted as having formed beneath unconfined turbidity currents. A simple, previously published, two-layer model is applied to the Waves, revealing that they formed beneath turbidity currents flowing at 10–100 cm/s−1, with a flow thickness of 60–400 m and a Sediment concentration of 26–427 mg/l. The El Julan Sediment Wave field lies within a turbidity current channel on the southwest flank of El Hierro. The Sediment Waves display Wave heights of about 6 m and Wavelengths of up to 1.2 km. The Waves are migrating upslope, and migration is most rapid in the centre of the channel where the flow velocity is highest. This Wave field has been formed by channelised turbidity currents originating on the flanks of El Hierro
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Seismic features diagnostic of contourite drifts
Marine Geology, 1999Co-Authors: Jean-claude Faugères, Dorrik A. V. Stow, Patrice Imbert, Adriano R VianaAbstract:Abstract The Sedimentary construction of oceanic margins is most often carried out by the combined action of gravitational processes and processes related to bottom (contour) currents. One of the major difficulties encountered in the interpretation of seismic profiles crossing such margins is the differentiation of these two types of deposit, especially where they display very complicated imbricated geometries. The aim of this paper, therefore, is to derive criteria for the recognition of contourite vs. turbidite deposits, based on the analysis of many seismic profiles from both published and unpublished sources. The following features are the most diagnostic for the recognition of contourite drifts. At the scale of the basin, four different drift types can be distinguished according to the morphostructural context, their general morphology and the hydrodynamic conditions. These are: contourite-sheeted drifts (including abyssal sheets and slope-plastered sheets), elongate-mounded drifts (detached and separated types), channel-related drifts (including lateral and axial patch drifts and downstream contourite fans), and confined drifts trapped in small, tectonically active basins. At the scale of the drift, three features provide the best diagnostic criteria for recognising contourite deposits on seismic profiles: major discontinuities that can be traced across the whole drift and represent time lines corresponding to hydrological events, lenticular, convex-upward depositional units with a variable geometry, and a specific style of progradation–aggradation of these units that is influenced by interaction of the bottom current with Coriolis force and with the morphology. At the scale of depositional units, the seismofacies show a wide variety of reflector characteristics, many of which are very similar to those observed in turbidite series. Distinction between Sediment Wave seismofacies deposited by turbidity currents and bottom currents still remains ambiguous.
Gemma Ercilla - One of the best experts on this subject based on the ideXlab platform.
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quaternary Sedimentation and origin of the orinoco Sediment Wave field on the demerara continental rise ne margin of south america
Marine Geology, 2002Co-Authors: E Gonthier, J C Faugeres, A Gervais, Gemma Ercilla, Belen Alonso, J BarazaAbstract:Abstract New core data from a Sediment–Wave field on the Demerara Outer Ridge show that the Waves are mainly built from turbidity currents that flow northwards down the Demerara margin. The contour currents circulating parallel and obliquely to the margin are apparently not as important to Wave formation as previously proposed. Detailed analysis of the Sedimentary facies of cores taken on the crest and flank of a Sediment Wave indicates that fine-grained turbiditic deposits are dominant. Hemipelagic/pelagic deposits are interbedded with the turbidites. Sediment redistribution by contour currents was only evidenced by the presence of peculiar clay mineral assemblages and microfaunal associations, as well as some Sedimentary structures such as truncations and cross-bedding. The turbiditic processes were active during the Last Glacial. In contrast, the Holocene is characterised by pelagic Sedimentation. A combination of seismic and core data suggests that the Sediment Waves result from predominantly turbiditic depositional processes interacting with minor contour currents and synSedimentary deformation processes.
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Turbidity current Sediment Waves on irregular slopes: observations from the Orinoco Sediment–Wave field
Marine Geology, 2002Co-Authors: Gemma Ercilla, Belen Alonso, Russell B. Wynn, Jesús BarazaAbstract:Abstract The Orinoco Sediment–Wave field covers an area of at least 29 000 km2 on the southern margin of the Orinoco Valley, at a water depth of 4400–4825 m. Wave dimensions are highly variable across the Wave field, with Wavelengths of 110–2600 m, and Wave heights of 1–15 m. Slope gradients are also very variable, with values of 0.14–0.48°. Overall, the Sedimentary sequence on the upslope Wave flanks is about 40% thicker than that on the downslope flanks, leading to upslope Wave migration in the manner of antidunes. In addition, reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks, suggesting that a higher proportion of coarser Sediment occurs on the upslope flank. An unconfined turbidity current origin is proposed for the Orinoco Sediment Waves, based upon detailed analysis of regional stratigraphic/seismic facies, and Sediment Wave distribution, morphology and dimensions. Sediment Waves are not related to flows passing along (or spilling out of) the Orinoco Valley, or to bottom currents flowing parallel to the slope. Turbidity currents responsible for Wave generation are interpreted as originating from slope failures on the adjacent Venezuela, Guyana and Suriname continental margins. Simple numerical modelling has enabled turbidity current flow characteristics across the Orinoco Sediment Waves to be estimated: internal Froude number=0.7–1.1, flow thickness=24–645 m, and flow velocity=31–82 cm s−1. A key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in Wave dimensions across the Wave field. The irregular gradient of the present-day Wave field is partly a reflection of the irregular bounding surface of the Sediment Waves, which is represented by mass-flow deposits and associated mud diapirs. The changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents, which in turn control the Wave dimensions. Generally, on lower gradients beyond minor breaks of slope, flow thickness increases and flow velocity decreases, leading to an increase in Wavelength and a decrease in height.
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Initiation and evolution of turbidity current Sediment Waves in the Magdalena turbidite system
Marine Geology, 2002Co-Authors: Gemma Ercilla, Belen Alonso, Russell B. Wynn, Jesús BarazaAbstract:This study describes an extensive Sediment–Wave field in the Magdalena Turbidite System, Caribbean Sea, Colombia, which occupies an area of at least 15000 km2 on the continental slope (3330–>3800 m). The Waves display Wavelengths up to 1.9 km, Wave heights up to 18 m, and crestlines that are aligned roughly parallel to the regional bathymetric contours. Preferential deposition on the upslope Wave flank has led to upslope migration, in the manner of antidunes. The Magdalena Sediment Waves are interpreted as forming beneath unconfined turbidity currents, which may result from the downslope evolution of slumps and mass flows. The unconfined turbidity currents are derived from several point sources along the continental slope and spread laterally as they flow downslope. This has led to the formation of a laterally extensive Sediment–Wave field. Simple numerical modelling estimates that the turbidity currents responsible for Wave generation were near- or super-critical, with flow thickness and velocity estimated at 40–160 m, and 36–82 cm s-1 respectively. However, later phases of Wave growth were not dependent on specific flow conditions. The most important aspect of this study is that the entire Sediment–Wave unit, from the basal boundary to the present-day seafloor, has been investigated using ultra high-resolution seismic profiles. The Sediment–Wave unit rests upon an irregular discontinuity that marks a recent change in the Sedimentary regime of the Magdalena Turbidite System, from channelised to unchannelised gravity flows. Above this boundary, the Sediment Waves display a growth pattern characterised by an increase in Wave dimensions. In addition, the Wave dimensions appear to become more regular through time. However, breaks of slope in the lower bounding surface of the Wave field have produced variations in Wave morphology that are still visible at the present-day seafloor. This indicates that there is a close relationship between variations in slope angle and turbidity current flow characteristics, which in turn leads to variations in Wave morphology
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Sedimentary processes in the selvage Sediment Wave field ne atlantic new insights into the formation of Sediment Waves by turbidity currents
Sedimentology, 2000Co-Authors: Russell B. Wynn, Gemma Ercilla, Philip Pe Weaver, Dorrik A. V. Stow, D G MassonAbstract:An integrated geophysical and Sedimentological investigation of the Selvage Sediment-Wave field has revealed that the Sediment Waves are formed beneath unconfined turbidity currents. The Sediment Waves occur on the lower continental rise and display Wavelengths of up to 1 km and Wave heights of up to 6 m. Wave Sediments consist of interbedded turbidites and pelagic/hemipelagic marls and oozes. Nannofossil-based dating of the Sediments indicates a bulk Sedimentation rate of 2·4 cm 1000 years-1, and the Waves are migrating upslope at a rate of 0·28 m 1000 years-1. Sediment provenance studies reveal that the turbidity currents maintaining the Waves are largely sourced from volcanic islands to the south. Investigation of existing models for Sediment-Wave formation leads to the conclusion that the Selvage Sediment Waves form as giant antidunes. Simple numerical modelling reveals that turbidity currents crossing the Wave field have internal Froude numbers of 0·5-1·9, which is very close to the antidune existence limits. Depositional flow velocities range from <6 to 125 cm-1. There is a rapid increase in Wavelength and flow thickness in the upper 10 km of the Wave field, which is unexpected, as the slope angle remains relatively constant. This anomaly is possibly linked to a topographic obstacle just upslope of the Sediment Waves. Flows passing over the obstacle may undergo a hydraulic jump at its boundary, leading to an increase in flow thickness. In the lower 15 km of the Wave field, flow thickness decreases downslope by 60%, which is comparable with results obtained for other unconfined turbidity currents undergoing flow expansion
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Sedimentary processes in the Selvage Sediment‐Wave field, NE Atlantic: new insights into the formation of Sediment Waves by turbidity currents
Sedimentology, 2000Co-Authors: Russell B. Wynn, Gemma Ercilla, Philip Pe Weaver, Dorrik A. V. Stow, Douglas G. MassonAbstract:An integrated geophysical and Sedimentological investigation of the Selvage Sediment-Wave field has revealed that the Sediment Waves are formed beneath unconfined turbidity currents. The Sediment Waves occur on the lower continental rise and display Wavelengths of up to 1 km and Wave heights of up to 6 m. Wave Sediments consist of interbedded turbidites and pelagic/hemipelagic marls and oozes. Nannofossil-based dating of the Sediments indicates a bulk Sedimentation rate of 2·4 cm 1000 years-1, and the Waves are migrating upslope at a rate of 0·28 m 1000 years-1. Sediment provenance studies reveal that the turbidity currents maintaining the Waves are largely sourced from volcanic islands to the south. Investigation of existing models for Sediment-Wave formation leads to the conclusion that the Selvage Sediment Waves form as giant antidunes. Simple numerical modelling reveals that turbidity currents crossing the Wave field have internal Froude numbers of 0·5-1·9, which is very close to the antidune existence limits. Depositional flow velocities range from
Michael E. Glinsky - One of the best experts on this subject based on the ideXlab platform.
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Turbidity current flow over an obstacle and phases of Sediment Wave generation
Journal of Geophysical Research: Oceans, 2012Co-Authors: Moshe Strauss, Michael E. GlinskyAbstract:We study the flow of particle-laden turbidity currents down a slope and over an obstacle. A high-resolution 2D computer simulation model is used, based on the Navier-Stokes equations. It includes poly-disperse particle grain sizes in the current and substrate. Particular attention is paid to the erosion and deposition of the substrate particles, including application of an active layer model. Multiple flows are modeled from a lock release that can show the development of Sediment Waves (SW). These are stream-wise Waves that are triggered by the increasing slope on the downstream side of the obstacle. The initial obstacle is completely erased by the resuspension after a few flows leading to self consistent and self generated SW that are weakly dependant on the initial obstacle. The growth of these Waves is directly related to the turbidity current being self sustaining, that is, the net erosion is more than the net deposition. Four system parameters are found to influence the SW growth: (1) slope, (2) current lock height, (3) grain lock concentration, and (4) particle diameters. Three phases are discovered for the system: (1) "no SW", (2) "SW buildup", and (3) "SW growth". The second phase consists of a soliton-like SW structure with a preserved shape. The phase diagram of the system is defined by isolating regions divided by critical slope angles as functions of current lock height, grain lock concentration, and particle diameters.
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turbidity current flow over an erodible obstacle and phases of Sediment Wave generation
Journal of Geophysical Research, 2012Co-Authors: Moshe Strauss, Michael E. GlinskyAbstract:[1] We study the flow of particle-laden turbidity currents down a slope and over an obstacle. A high-resolution 2-D computer simulation model is used, based on the Navier-Stokes equations. It includes poly-disperse particle grain sizes in the current and substrate. Particular attention is paid to the erosion and deposition of the substrate particles, including application of an active layer model. Multiple flows are modeled from a lock release that can show the development of Sediment Waves (SW). These are stream-wise Waves that are triggered by the increasing slope on the downstream side of the obstacle. The initial obstacle is completely erased by the resuspension after a few flows leading to self consistent and self generated SW that are weakly dependant on the initial obstacle. The growth of these Waves is directly related to the turbidity current being self sustaining, that is, the net erosion is more than the net deposition. Four system parameters are found to influence the SW growth: (1) slope, (2) current lock height, (3) grain lock concentration, and (4) particle diameters. Three phases are discovered for the system: (1) “no SW,” (2) “SW buildup,” and (3) “SW growth”. The second phase consists of a soliton-like SW structure with a preserved shape. The phase diagram of the system is defined by isolating regions divided by critical slope angles as functions of current lock height, grain lock concentration, and particle diameters.
B. Kneller - One of the best experts on this subject based on the ideXlab platform.
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deep water Sediment Wave formation linear stability analysis of coupled flow bed interaction
Journal of Fluid Mechanics, 2011Co-Authors: Lutz Lesshafft, Eckart Meiburg, Brendon Hall, B. KnellerAbstract:A linear stability analysis is carried out for the interaction of an erodible Sediment bed with a Sediment-laden, stratified flow above the bed, such as a turbidity or bottom current. The fluid motion is described by the full, two-dimensional Navier-Stokes equations in the Boussinesq approximation, while erosion is modelled as a diffusive flux of particles from the bed into the fluid. The stability analysis shows the existence of both Tollmien-Schlichting and internal Wave modes in the stratified boundary layer. For the internal Wave mode, the stratified boundary layer acts as a Wave duct, whose height can be determined analytically from the Brunt-Vaisala frequency criterion. Consistent with this criterion, distinct unstable perturbation Wavenumber regimes exist for the internal Wave mode, which are associated with different numbers of pressure extrema in the wall-normal direction. For representative turbidity current parameters, the analysis predicts unstable Wavelengths that are consistent with field observations. As a key condition for instability to occur, the base flow velocity boundary layer needs to be thinner than the corresponding concentration boundary layer. For most of the unstable Wavenumber ranges, the phase relations between the Sediment bed deformation and the associated wall shear stress and concentration perturbations are such that the Sediment Waves migrate in the upstream direction, which again is consistent with field observations.
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Deep-water Sediment Wave formation: linear stability analysis of coupled flow/bed interaction
Journal of Fluid Mechanics, 2011Co-Authors: Lutz Lesshafft, Eckart Meiburg, Brendon Hall, B. KnellerAbstract:A linear stability analysis is carried out for the interaction of an erodible Sediment bed with a Sediment-laden, stratified flow above the bed, such as a turbidity or bottom current. The fluid motion is described by the full, two-dimensional Navier-Stokes equations in the Boussinesq approximation, while erosion is modelled as a diffusive flux of particles from the bed into the fluid. The stability analysis shows the existence of both Tollmien-Schlichting and internal Wave modes in the stratified boundary layer. For the internal Wave mode, the stratified boundary layer acts as a Wave duct, whose height can be determined analytically from the Brunt-Vaisala frequency criterion. Consistent with this criterion, distinct unstable perturbation Wavenumber regimes exist for the internal Wave mode, which are associated with different numbers of pressure extrema in the wall-normal direction. For representative turbidity current parameters, the analysis predicts unstable Wavelengths that are consistent with field observations. As a key condition for instability to occur, the base flow velocity boundary layer needs to be thinner than the corresponding concentration boundary layer. For most of the unstable Wavenumber ranges, the phase relations between the Sediment bed deformation and the associated wall shear stress and concentration perturbations are such that the Sediment Waves migrate in the upstream direction, which again is consistent with field observations.
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Deep-water Sediment Wave formation: Linear stability analysis of coupled flow/bed interaction
Journal of Fluid Mechanics, 2011Co-Authors: Lutz Lesshafft, B. Hall, E. Meiburg, B. KnellerAbstract:A linear stability analysis is carried out for the interaction of an erodible Sediment bed with a Sediment-laden, stratified flow above the bed, such as a turbidity or bottom current. The fluid motion is described by the full, two-dimensional Navier-Stokes equations in the Boussinesq approximation, while erosion is modelled as a diffusive flux of particles from the bed into the fluid. The stability analysis shows the existence of both Tollmien-Schlichting and internal Wave modes in the stratified boundary layer. For the internal Wave mode, the stratified boundary layer acts as a Wave duct, whose height can be determined analytically from the Brunt-Val frequency criterion. Consistent with this criterion, distinct unstable perturbation Wavenumber regimes exist for the internal Wave mode, which are associated with different numbers of pressure extrema in the wall-normal direction. For representative turbidity current parameters, the analysis predicts unstable Wavelengths that are consistent with field observations. As a key condition for instability to occur, the base flow velocity boundary layer needs to be thinner than the corresponding concentration boundary layer. For most of the unstable Wavenumber ranges, the phase relations between the Sediment bed deformation and the associated wall shear stress and concentration perturbations are such that the Sediment Waves migrate in the upstream direction, which again is consistent with field observations. © 2011 Cambridge University Press.