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Alessandro Cantelli - One of the best experts on this subject based on the ideXlab platform.
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High Resolution, Millennial-Scale Patterns of Bed Compensation on a Sand-Rich Intraslope Submarine Fan, Western Niger Delta Slope
2018Co-Authors: Zane Richards Jobe, Nick C Howes, Zoltan Sylvester, Alessandro Cantelli, Ru Smith, Ciaran O'byrne, Matthew A. Wolinsky, Carlos Pirmez, Andrew Parker, Niall C SloweyAbstract:Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of Submarine Channel and intraslope Submarine fan deposits. The Submarine Channel enters an 8 km long x 8 km wide intraslope basin, where more than 100 m of deposits form an intraslope Submarine fan. Lobe deposits in the intraslope Submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique dataset indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope Submarine fans do not necessarily correlate with sand presence and/or quality.Core and radiocarbon age data indicate that sand beds progressively stack southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
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Facies architecture of Submarine Channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zane R. Jobe, Zoltan Sylvester, Nick Howes, Carlos Pirmez, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
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facies architecture of Submarine Channel deposits on the western niger delta slope implications for grain size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zoltan Sylvester, Nick Howes, Carlos Pirmez, Zane R. Jobe, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
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high resolution millennial scale patterns of bed compensation on a sand rich intraslope Submarine fan western niger delta slope
Geological Society of America Bulletin, 2017Co-Authors: Zane Richards Jobe, Zoltan Sylvester, Nick Howes, Andrew O Parker, Alessandro Cantelli, R D A Smith, Ciaran Obyrne, Matthew A. Wolinsky, Carlos Pirmez, Niall C SloweyAbstract:Near-seafloor core and seismic reflection-data from the western Niger Delta continental slope document the facies, architecture, and evolution of Submarine Channel and intraslope Submarine fan deposits. The Submarine Channel enters an 8-km-long by 8-km-wide intraslope basin, where more than 100 m of deposits form an intraslope Submarine fan. Lobe deposits in the intraslope Submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique data set indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope Submarine fans do not necessarily correlate with sand presence and/or quality. Core and radiocarbon age data indicate that sand beds southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand rich, ∼2 km wide × 6 km long, and >1 m thick and was deposited rapidly over ∼4000 yr, from 18 to 14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea-level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
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A Polynomial Model for Lateral Thickness Decay of Submarine Channel–Levees
Journal of Sedimentary Research, 2014Co-Authors: Alessandro Cantelli, Jasim ImranAbstract:Abstract Active and relic Channels with extensive levees are common on the seafloor adjacent to the continental margin. Exponential, power-law, and logarithmic functions have been proposed by others to describe the lateral thickness decay of Submarine levees. In the present study, experiments have been conducted to study Submarine levee growth by flow stripping at a Channel bend. Various functions have been fitted to the data. The results show that a third-order polynomial function best describes the levee thickness in the cross-stream direction near a Submarine Channel bend. Generalized model coefficients are derived as functions of deposit thickness adjacent to the Channel bank. The model is applied to experimental data obtained by others as well as levee shapes derived from seismic data. In both cases, satisfactory agreements are found. The proposed model can be a useful tool for stratigraphic modeling of Submarine Channel–levee systems and fill gaps in field data.
Jeff Peakall - One of the best experts on this subject based on the ideXlab platform.
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Flow processes and sedimentation in Submarine Channel bends
Marine and Petroleum Geology, 2020Co-Authors: Jeff Peakall, Gareth M. Keevil, Kathryn J. Amos, P. William Bradbury, Sanjeev GuptaAbstract:Copyright © 2007 Published by Elsevier Ltd.Turbidity currents in sinuous Submarine Channels are an important mechanism for transporting terrestrial sediments to deep water, and their deposits are of increasing importance as hydrocarbon exploration targets. Despite this, the architecture and dynamics of Submarine Channel systems are not well understood. Analogies are often drawn with fluvial systems due to similarities between their planform shapes even though differences in Channel evolution and hydrodynamics have been noted. A key question is the nature of deposition within Submarine Channel bends; in particular at inner bends where point bars form in alluvial meandering rivers. Recent experimental and numerical work has demonstrated that the fluid dynamics of Submarine Channel bend flow are markedly different from rivers. Notably, a reversal in the orientation of secondary (helical) flow at bend apices occurs in Submarine Channels. The potential influence of these differences in fluid dynamics on deposition within Submarine Channel bends is investigated herein. We report the results of a series of physical experiments in which solute-driven gravity currents were run through pre-formed sinuous Channels containing mobile beds. These experiments reveal sedimentation patterns characterised by accumulation zones downstream of bend apices and erosion zones at outer bends. These patterns are broadly analogous to the point bars and outer-bank pools observed in meandering rivers, demonstrating that the longitudinal flow component dominates over the cross-stream component, as also occurs in rivers. However, the data suggest that the reversal in direction of the cross-stream flow component compared with subaerial flows is important in determining the position and morphology of ‘point bars’ relative to bend apices. From analogy with fluvial compound Channels, and fluvial theory, this reversal in secondary flow cell orientation is also expected to influence the spatial variations of grain size in Submarine Channel ‘point-bar’ deposits.Jeff Peakall, Kathryn J. Amos, Gareth M. Keevil, P. William Bradbury and Sanjeev Guptahttp://www.elsevier.com/wps/find/journaldescription.cws_home/30452/description#descriptio
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Flow structure in sinuous Submarine Channels: Velocity and turbulence structure of an experimental Submarine Channel
Marine Geology, 2020Co-Authors: Gareth M. Keevil, James L. Best, Jeff Peakall, Kathryn J. AmosAbstract:Copyright © 2006 Elsevier B.V. All rights reserved.Submarine Channels have long been considered analogous to meandering fluvial Channels due to their similar planform geometry, and this has given rise to strong analogies in terms of the fluid dynamics of these Channel types. However, there is a paucity of direct measurements detailing the structure of velocity or sediment concentration, and nothing is known about the structure of secondary flow, within Submarine Channels. Within fluvial Channels, secondary circulation has been shown to be an important control of erosion, deposition, lateral sediment transport and overall bend stability. This paper presents a series of experiments in which saline gravity currents flowed through a submerged, fixed-form, sinuous Channel model. Ultrasonic Doppler velocity profiling provided high-resolution, three-dimensional visualisation of flow fields, thereby allowing the first quantitative visualisation of velocity profiles and secondary flows of a saline gravity current within a sinuous Submarine Channel. The same model was also used to measure the structure of flow within a subaerial Channel, thereby providing a detailed comparison between a Submarine and fluvial Channel. The data reveal that secondary flow cells in Submarine Channels are best developed at bend apexes and that the basal component of the flow cell moves from the inside to the outside of the bend, in a reversed direction to that expected from models of fluvial bend flow. These results are of prime importance when assessing the validity of comparisons between Submarine and fluvial Channels, and the role of secondary flow cells in the migration and evolution of meander bends. This work demonstrates that the fundamental flow processes controlling the evolution and migration of Submarine and fluvial Channels may be very different, and suggest that the form and evolution of Submarine Channels may also show different properties to their fluvial counterparts.http://www.sciencedirect.com/science/journal/0025322
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the geomorphology of Submarine Channel systems of the northern line islands ridge central equatorial pacific ocean
Frontiers in Earth Science, 2020Co-Authors: James V. Gardner, Jeff Peakall, Andy Armstrong, Brian R CalderAbstract:More than 844,000 km2 of the northern Line Islands Ridge mapped with multibeam bathymetry and backscatter provide unprecedented views of the geomorphology of this isolated area in the central equatorial Pacific Ocean. A compilation of all available multibeam data in the area reveals six extensive Submarine dendritic Channel systems that encompass a combined drainage area that exceeds 60,000 km2. The Channel systems are incised into the surface of basins surrounded by small guyots and seamounts that make up a discontinuous rim around the summit of the northern Line Island Ridge. The Channels have mostly straight or gently curved well-developed tributaries and main reaches. Although the Line Island Ridge has been dated at 86 to 68 Ma old, the Channels occur on the surface and are not buried by any significant sediment accumulations. Levees are very rare along the Channel banks and no Submarine fans were found where the Channels merge with the adjacent abyssal basins. There is sparse evidence of slope failures or landslides throughout the ridge. The presence of plunge pools below the northwest escarpment, together with the well-defined Channel incisions, suggests the Channels might be relatively recent (perhaps late Neogene or even younger) features developed long after the ridge subsided more than a kilometer below sea level.
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a novel mixing mechanism in sinuous seafloor Channels implications for Submarine Channel evolution
Geomorphology, 2018Co-Authors: R M Dorrell, Jeff Peakall, C Burns, Gareth M. KeevilAbstract:Previous experimental studies of density currents in sinuous seafloor Channels have almost exclusively studied hydrodynamics either by considering time independent, instantaneous, flow measurements or by compiling time-averaged flow measurements. Here we present a novel study of the time dependent dynamics of a density driven flow in a sinuous Channel fed by a source of constant discharge. The experiments show that whilst source conditions may be temporally steady, flow conditions are temporally unsteady with timescales of flow variation driven by flow interaction with Channel topography. Temporal variations reveal that both downstream and cross-stream flows vary significantly from time average observations and predictions, across scales larger than those predicted for turbulence in equivalent straight Channels. Large-scale variations are shown to increase the average production of turbulence across the height of the flow, providing a new mechanism for enhanced mixing of sediment within gravity currents. Further such large-scale variations in flow conditions are recorded in the change in orientation of near-bed secondary flow, providing a plausible mechanism to reduce the cross-stream transport of bedload material and explain the ultimate stabilisation of sinuous seafloor Channel systems.
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Keynote Speech - Physical Modelling of Submarine Channel Deposits - Towards First Order Prediction
Second Conference on Forward Modelling of Sedimentary Systems, 2016Co-Authors: Jeff PeakallAbstract:Process-product studies have been critical to the development of process sedimentology over the past few decades, with the ability to measure flows, and later examine the resulting deposits, removing much of the ambiguity associated with previous interpretations. However, perhaps uniquely for large geomorphic systems on Earth, there are no field-scale process-product studies of Submarine Channels. In fact, there are remarkably few direct measurements even of the flow dynamics as a result of the difficulties of measuring these powerful, infrequent, and often inaccessible flows. Over the past decade, physical experimentation has provided the first process-product studies for model Submarine Channel systems, enabling us to link flow behaviour and sedimentation patterns. This has been supplemented by numerical simulations. Synthesise of these observations, in the context of our direct knowledge of Submarine Channels, enables an overview of Submarine Channel flow dynamics to be derived, along with process-orientated intra-Channel architecture models for low and high latitude systems. These studies reveal that Submarine Channel processes and deposits change globally (latitudinally), and as a function of geological time, moving us towards a first order prediction of Submarine Channel deposits based on palaeolatitude and age.
Ian A. Kane - One of the best experts on this subject based on the ideXlab platform.
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differentiating Submarine Channel related thin bedded turbidite facies outcrop examples from the rosario formation mexico
Sedimentary Geology, 2017Co-Authors: Larissa Hansen, Ian A. Kane, Richard H T Callow, Ben KnellerAbstract:Abstract Thin-bedded turbidites deposited by sediment gravity flows that spill from Submarine Channels often contain significant volumes of sand in laterally continuous beds. These can make up over 50% of the Channel-belt fill volume, and can thus form commercially important hydrocarbon reservoirs. Thin-bedded turbidites can be deposited in environments that include levees and depositional terraces, which are distinguished on the basis of their external morphology and internal architecture. Levees have a distinctive wedge shaped morphology, thinning away from the Channel, and confine both Channels (internal levees) and Channel-belts (external levees). Terraces are flat-lying features that are elevated above the active Channel within a broad Channel-belt. Despite the ubiquity of terraces and levees in modern Submarine Channel systems, the recognition of these environments in outcrop and in the subsurface is challenging. In this outcrop study of the Upper Cretaceous Rosario Formation (Baja California, Mexico), lateral transects based on multiple logged sections of thin-bedded turbidites reveal systematic differences in sandstone layer thicknesses, sandstone proportion, palaeocurrents, sedimentary structures and ichnology between Channel-belt and external levee thin-bedded turbidites. Depositional terrace deposits have a larger standard deviation in sandstone layer thicknesses than external levees because they are topographically lower, and experience a wider range of turbidity current sizes overspilling from different parts of the Channel-belt. The thickness of sandstone layers within external levees decreases away from the Channel-belt while those in depositional terraces are less laterally variable. Depositional terrace environments of the Channel-belt are characterized by high bioturbation intensities, and contain distinctive trace fossil assemblages, often dominated by ichnofabrics of the echinoid trace fossil Scolicia. These assemblages contrast with the lower bioturbation intensities that are recorded from external levee environments where Scolicia is typically absent. Multiple blocks of external levee material are observed in the depositional terrace area where the proximal part of the external levee has collapsed into the Channel-belt; their presence characterizes the Channel-belt boundary zone. The development of recognition criteria for different types of Channel-related thin-bedded turbidites is critical for the interpretation of sedimentary environments both at outcrop and in the subsurface, which can reduce uncertainty during hydrocarbon field appraisal and development.
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Submarine Channel evolution terrace development and preservation of intra Channel thin bedded turbidites mahin and avon Channels offshore nigeria
Marine Geology, 2017Co-Authors: Larissa Hansen, Ian A. Kane, Michal Janocko, Benjamin Charles KnellerAbstract:Abstract Terraces on the modern seafloor are defined as topographically flat areas above the active Submarine Channel thalweg but within the confines of the Channel-belt. They have been described from many modern Submarine Channels, but the controls on terrace distribution, evolution and stacking patterns are not well understood. In this study, we describe the architecture of the Mahin and Avon Channel-belts and their associated terraces, located offshore Nigeria towards the northwest of the Niger Delta. The studied Channel sections are The surfaces defining the bases of the terrace bodies have been mapped along both Channels using high-resolution 3D seismic data. Spectral decomposition of the data reveals subtle variations in seismic character that highlight sedimentological detail that can otherwise not be recognized, allowing us to suggest the processes responsible for terrace formation and terrace body composition. The contrasting evolution of the two Channels is reflected in the morphology and architecture of their terraces. While the Mahin terrace bodies show a predictable pattern, typically consisting of stacked Channel-fill and overbank deposits in a circular planform shape (shape controlled by cut-off Channel bends), the deposits of the Avon terrace bodies up-dip of the confluence with the Mahin are dominated by overbank deposits, with the planform terrace shape heavily controlled by the topography of the underlying Channel-belt deposits. This study shows how spatially and temporally associated Channels can have markedly different architectures. The evolution of the Channel and the abundance and stacking patterns of compositional elements within terrace bodies are shown to be linked.
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Global (latitudinal) variation in Submarine Channel sinuosity
Geology, 2012Co-Authors: Jeff Peakall, Gareth M. Keevil, William Mccaffrey, Douglas G. Masson, Ian A. Kane, Ransome CorneyAbstract:Current classifications of Submarine Channels and fans link Channel sinuosity to gradient, and in turn to sediment caliber, with end members being high-sinuosity, low-gradient, fine-grained systems and low-sinuosity, high-gradient, coarse-grained systems. However, the most sinuous modern Submarine Channels, such as the Amazon, Bengal, Indus, and Zaire, along with ancient sinuous Submarine Channels, are located in equatorial regions. Here we quantitatively compare slope versus latitude controls on Submarine Channel sinuosity and show that the latitudinal control is strong, while that of slope is weak. Variation in sinuosity with latitude is shown to occur uniquely in Submarine Channels; no comparable relationship is observed for terrestrial river Channels. Possible causal mechanisms for this latitudinal variation are explored, focusing on the influence of the Coriolis force, flow type, and sediment type. Although climate does not vary straightforwardly with latitude, climatic controls on flow and sediment type may explain some of the latitudinal variation; Coriolis force, however, varies with latitude alone and produces an excellent fit to the observed sinuosity-latitude distribution. Regardless of which control predominates, latitudinal global variation in Channel sinuosity should have changed over geologic time. Since deposit architecture and facies are linked directly with sinuosity, Submarine Channel deposits should also systematically vary in space and time.
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global latitudinal variation in Submarine Channel sinuosity reply
Geology, 2012Co-Authors: Jeff Peakall, Gareth M. Keevil, Douglas G. Masson, Ian A. Kane, Mathew G Wells, Remo Cossu, William D Mccaffrey, Ransome CorneyAbstract:Current classifications of Submarine Channels and fans link Channel sinuosity to gradient, and in turn to sediment caliber, with end members being high-sinuosity, low-gradient, fine-grained systems and low-sinuosity, high-gradient, coarse-grained systems. However, the most sinuous modern Submarine Channels, such as the Amazon, Bengal, Indus, and Zaire, along with ancient sinuous Submarine Channels, are located in equatorial regions. Here we quantitatively compare slope versus latitude controls on Submarine Channel sinuosity and show that the latitudinal control is strong, while that of slope is weak. Variation in sinuosity with latitude is shown to occur uniquely in Submarine Channels; no comparable relationship is observed for terrestrial river Channels. Possible causal mechanisms for this latitudinal variation are explored, focusing on the influence of the Coriolis force, flow type, and sediment type. Although climate does not vary straightforwardly with latitude, climatic controls on flow and sediment type may explain some of the latitudinal variation; Coriolis force, however, varies with latitude alone and produces an excellent fit to the observed sinuosity-latitude distribution. Regardless of which control predominates, latitudinal global variation in Channel sinuosity should have changed over geologic time. Since deposit architecture and facies are linked directly with sinuosity, Submarine Channel deposits should also systematically vary in space and time.
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sedimentological criteria to differentiate Submarine Channel levee subenvironments exhumed examples from the rosario fm upper cretaceous of baja california mexico and the fort brown fm permian karoo basin s africa
Marine and Petroleum Geology, 2011Co-Authors: Ian A. Kane, David M HodgsonAbstract:Two scales of levee confinement are commonly recognised from Submarine Channel-levee systems on the seafloor and in the subsurface. Large-scale external levees bound the entire system whilst smaller-scale internal levees bound individual thalweg Channels within the Channel-belt. Although thin beds are commonly identified in core and well logs, their origin, and consequently their stratigraphic significance is currently poorly understood. This knowledge gap stems, in part, from the lack of unambiguously identified outcrop analogues of Channel-levees, and in particular the lack of identifiable internal and external levees. Here we report from two exhumed Channel-levee systems where both scales of confinement can be recognised: the Rosario Fm. of Baja California, and the Fort Brown Fm. of South Africa. A suite of characteristic sedimentary features are recognised from internal and external levees respectively: internal levees are characterised by structures indicative of complexity in the waxing-waning style of overspill, interactions with topography and flow magnitude variability; in contrast, external levees are characterised by structures indicative of simple surge-like waning flows, relatively uniform flow directions, laterally extensive beds, and a lack of erosive events. Using these observations, together with published literature, we propose a simple nomenclatural scheme for levee sub-environments, and criteria to differentiate between levee sub-environments in core or outcrop.
Zoltan Sylvester - One of the best experts on this subject based on the ideXlab platform.
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The stratigraphic evolution of a Submarine Channel: Linking seafloor dynamics to depositional products
Journal of Sedimentary Research, 2020Co-Authors: Stephen M. Hubbard, Zoltan Sylvester, Zane R. Jobe, Brian W. Romans, Jacob A. Covault, Andrea FildaniAbstract:ABSTRACT We investigate the relationship between the cross-sectional geomorphic expression of a Submarine Channel as observed on the seafloor and the stratigraphic product of long-lived erosion, bypass, and sediment deposition. Specifically, by reconstructing the time–space evolution of an individual Channel fill (i.e., Channel element) exposed in outcrop, we establish a genetic link between thick-bedded Channel-element-axis sandstone to thinly interbedded Channel-element-margin deposits. Although the bounding surface between axis sandstone and margin thin beds is sharply defined, it is composed of a series of geomorphic surface segments of various ages; as such, the composite stratigraphic surface (∼ 17 m relief) was formed from numerous incision events that repeatedly sculpted the conduit. By demonstrating the origin of the stratigraphic surface, we conclude that geomorphic surfaces with 2–7 m of erosional relief were largely responsible for the observed intra-Channel-element architecture (and ultimately, the composite 17-m-thick element). The widely documented Channel element axis-to-margin architecture is a product of Submarine-Channel thalweg dynamics, primarily recording interactions between the seafloor and the basal high-concentration layers of Channelized turbidity currents.
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Submarine Channels "swept" downstream after bend cutoff in salt basins
2018Co-Authors: Jacob Covault, Zoltan Sylvester, Michael R Hudec, Can Ceyhan, Dallas DunlapAbstract:Channel-bend expansion and downstream translation, as well as vertical movements by aggradation and incision, set the stratigraphic architecture of Channelized depositional systems. Early work on Submarine-Channel evolution has suggested that downstream translation is rare. We propose that downstream translation of bends might be common in deep-water salt-tectonic provinces, where complex topography can localize Channel pathways that promote meander cutoffs and the generation of high-curvature bends. We use three-dimensional seismic-reflection data from a region with salt-influenced topography in the Campos basin, offshore Brazil, to characterize the structural geometry of a salt diapir and stratigraphic architecture of an adjacent ~18 km-long reach of a Submarine-Channel system. We interpret the structural and stratigraphic evolution, including meander-cutoff development near the salt diapir followed by ~10 km of downstream translation of a Channel bend. We test the stratigraphic evolution with a simple numerical model of Channel meandering. This integrated subsurface characterization and stratigraphic modeling study sheds light on the processes and controls of Submarine-Channel downstream translation, which might be common in rapidly deforming settings, such as salt basins, that promote localized subsidence, meander cutoffs, and rapidly translating, high-curvature bends.
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High Resolution, Millennial-Scale Patterns of Bed Compensation on a Sand-Rich Intraslope Submarine Fan, Western Niger Delta Slope
2018Co-Authors: Zane Richards Jobe, Nick C Howes, Zoltan Sylvester, Alessandro Cantelli, Ru Smith, Ciaran O'byrne, Matthew A. Wolinsky, Carlos Pirmez, Andrew Parker, Niall C SloweyAbstract:Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of Submarine Channel and intraslope Submarine fan deposits. The Submarine Channel enters an 8 km long x 8 km wide intraslope basin, where more than 100 m of deposits form an intraslope Submarine fan. Lobe deposits in the intraslope Submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique dataset indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope Submarine fans do not necessarily correlate with sand presence and/or quality.Core and radiocarbon age data indicate that sand beds progressively stack southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
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Facies architecture of Submarine Channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zane R. Jobe, Zoltan Sylvester, Nick Howes, Carlos Pirmez, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
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facies architecture of Submarine Channel deposits on the western niger delta slope implications for grain size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zoltan Sylvester, Nick Howes, Carlos Pirmez, Zane R. Jobe, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
Carlos Pirmez - One of the best experts on this subject based on the ideXlab platform.
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High Resolution, Millennial-Scale Patterns of Bed Compensation on a Sand-Rich Intraslope Submarine Fan, Western Niger Delta Slope
2018Co-Authors: Zane Richards Jobe, Nick C Howes, Zoltan Sylvester, Alessandro Cantelli, Ru Smith, Ciaran O'byrne, Matthew A. Wolinsky, Carlos Pirmez, Andrew Parker, Niall C SloweyAbstract:Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of Submarine Channel and intraslope Submarine fan deposits. The Submarine Channel enters an 8 km long x 8 km wide intraslope basin, where more than 100 m of deposits form an intraslope Submarine fan. Lobe deposits in the intraslope Submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique dataset indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope Submarine fans do not necessarily correlate with sand presence and/or quality.Core and radiocarbon age data indicate that sand beds progressively stack southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
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Facies architecture of Submarine Channel deposits on the western Niger Delta slope: Implications for grain‐size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zane R. Jobe, Zoltan Sylvester, Nick Howes, Carlos Pirmez, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
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facies architecture of Submarine Channel deposits on the western niger delta slope implications for grain size and density stratification in turbidity currents
Journal of Geophysical Research, 2017Co-Authors: Zoltan Sylvester, Nick Howes, Carlos Pirmez, Zane R. Jobe, Michele Bolla Pittaluga, Alessandro Frascati, Daniel Minisini, Alessandro CantelliAbstract:High-resolution bathymetry, seismic reflection, and piston core data from a Submarine Channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the Channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the Channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above Channel thalweg and/or distance from Channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-Channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for Submarine Channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.
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high resolution millennial scale patterns of bed compensation on a sand rich intraslope Submarine fan western niger delta slope
Geological Society of America Bulletin, 2017Co-Authors: Zane Richards Jobe, Zoltan Sylvester, Nick Howes, Andrew O Parker, Alessandro Cantelli, R D A Smith, Ciaran Obyrne, Matthew A. Wolinsky, Carlos Pirmez, Niall C SloweyAbstract:Near-seafloor core and seismic reflection-data from the western Niger Delta continental slope document the facies, architecture, and evolution of Submarine Channel and intraslope Submarine fan deposits. The Submarine Channel enters an 8-km-long by 8-km-wide intraslope basin, where more than 100 m of deposits form an intraslope Submarine fan. Lobe deposits in the intraslope Submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique data set indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope Submarine fans do not necessarily correlate with sand presence and/or quality. Core and radiocarbon age data indicate that sand beds southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand rich, ∼2 km wide × 6 km long, and >1 m thick and was deposited rapidly over ∼4000 yr, from 18 to 14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea-level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
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rapid adjustment of Submarine Channel architecture to changes in sediment supply
Journal of Sedimentary Research, 2015Co-Authors: Zane R. Jobe, Zoltan Sylvester, Nick Howes, Andrew O Parker, Niall C Slowey, Carlos PirmezAbstract:Abstract Changes in sediment supply and caliber during the last ∼ 130 ka have resulted in a complex architectural evolution of the Y Channel system on the western Niger Delta slope. This evolution consists of four phases, each with documented or inferred changes in sediment supply. Phase 1 flows created wide (1,000 m), low-sinuosity (1.1) Channel forms with lateral migration and little to no aggradation. During Phase 2, the Y Channel system began to aggrade, creating more narrow (300 m) and sinuous (1.4) Channel forms with many meander cutoffs. This system was abandoned at ∼ 130 ka, perhaps related to rapid relative sea-level rise during Marine Isotope Stage (MIS) 5. Phase 3 flows were mud-rich and deposited sediment on the outer bends of the Channel form, resulting in the narrowing (to 250 m), straightening (to a sinuosity of 1.22), and aggradation of the Y Channel system. Renewed influx of sand into the Y Channel system occurred with Phase 4 at ∼ 50 ka, during MIS 3 sea-level fall. The onset of Phase 4 is marked by the initiation of the Y′ tributary Channel, which re-established sand deposition in the Y Channel system. Flows entering the Y Channel from the Y′ Channel were underfit, resulting in inner levee deposition that is most prevalent on outer banks, acting to further straighten (1.21) and narrow (to 200 m wide) the Y Channel. The inner levees accumulated quickly as the flows sought equilibrium, with deposition rates > 200 cm/ky. Marked by the presence of the last sand bed, abandonment occurred at ∼ 19 ka in the Y Channel and ∼ 15 ka in the Y′ Channel and is likely related to progressive abandonment due to shelf-edge delta avulsion and/or progressive sea level rise associated with Melt Water Pulse 1-A. The muddy, 5-meter-thick Holocene layer has thickness variations that mimic those seen in the sandy part of Phase 4, suggesting that dilute, muddy flows continue to affect the modern Y Channel system. This unique dataset allows us to unequivocally link changes in Submarine Channel architecture to variations in sediment supply and caliber. Changes in the updip sediment routing system (i.e., the Channel “plumbing”) are shown to have profound implications for Submarine Channel architecture and reservoir connectivity.
