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Cross‐sectional outputs from the forward stratigraphic models: (A) incisional, (B) incisional to aggradational, and (C) primarily aggradational. Right: real‐world analogue line drawing examples. Model cross‐section locations shown in Figure 1. Real‐world analogue line drawing examples based on (A) the Zaire (Babonneau et al., 2002; redrawn from part of their figure 13), (B) the Benin‐Major (Deptuck et al., 2007; redrawn from part of their figure 6) and, (C) the Amazon (Pirmez et al., 2000; redrawn from their figure 1D)
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Interpretation of deep‐water channel deposits is challenging because the spatial arrangement of their constituent lithologies is highly variable. This variability is often thought to be a signature of complex interactions between controlling boundary conditions and processes. A three‐dimensional forward stratigraphic model of a sinuous meandering c...
Citations
... The migration of channel threads in braided rivers significantly impacts fluvial landscapes, and sedimentary deposits Morris et al., 2022;Steel et al., 2022;Wickert et al., 2013). This study analyzes the style of channel thread migration in a specific laboratory experiment and finds that patterns of migration exhibit spatial trends. ...
River channels shape landscapes through gradual migration and abrupt avulsion. Measuring the motion of braided rivers, which have multiple channel threads, is particularly challenging, limiting predictions for landscape evolution and fluvial architecture. To address this challenge, we extended the capabilities of image‐based particle image velocimetry (PIV)—a technique for tracking channel threads in images of the surface—by adapting it to analyze topographic change. We applied this method in a laboratory experiment where a straight channel set in non‐cohesive sediment evolved into a braided channel under constant water and sediment fluxes. Topography‐based PIV successfully tracked the motion of channel threads if displacements between observations were less than the channel‐thread width, consistent with earlier results from image‐based PIV. We filtered spurious migration vectors with magnitudes less than the elevation grid spacing, or with high uncertainties in magnitude and/or direction. During braided channel initiation, migration rates varied with the channel planform development, showing an increase as incipient meanders developed, a decrease during the transitional braiding phase, and consistently low values during the established braiding phase. In this experimental setup, migration rates varied quasi‐periodically along stream at the half scale of initial meander bends. Lateral migration with respect to the mean flow direction was much more pronounced than streamwise migration, accounting for approximately 80% of all detected motion. Results demonstrate that topography‐based PIV has the potential to advance predictions for bank erosion and landscape evolution in natural braided rivers as well as bar preservation and stratigraphic architecture in geological records.
... In terms of three-dimensional stratigraphic datasets, we start our analysis with a stratigraphic forward model of meandering river deposits. We used the open-source Python package meanderpy (Sylvester et al., 2019;Sylvester et al., 2021;Morris et al., 2022; https://github. com/zsylvester/meanderpy) to generate this model. ...
... The channel in the model used here only undergoes lateral migration; that is, there is no incision or aggradation (but see Morris et al., 2022 andMorris et al., 2024 for models of submarine channels with significant incision and aggradation). A block diagram that was generated with stratigraph illustrates the plan-view meandering pattern at the end of the simulation (Fig. 6). ...
Time-elevation plots and chronostratigraphic diagrams are valuable for understanding and analyzing stratigraphy when time-elevation data, or some approximation of them, are available, for example in flume experiments, numerical models, and three-dimensional seismic reflection surveys. We developed a Python module called 'stratigraph', aimed at the reproducible analysis and visualization of stratigraphy, and we use it here to explore data from forward stratigraphic models of meandering channels, the eXperimental EarthScape (XES) facility XES-02 experiment, and two experiments that were conducted at the Tulane University Sediment Dynamics and Stratigraphy Laboratory. We use these tools to generate and visualize three-dimensional chronostratigraphic diagrams, compute maps of stratigraphic completeness and other stratigraphic attributes, and explore the nature of the erosional surfaces. We show that, using a 3D Wheeler diagram, it is possible to create maps of important stratigraphic attributes, in addition to the conventional thickness maps. There are six fundamental stratigraphic attributes that are direct consequences of a quantitative chronostratigraphic approach, as follows. (1) Sediments that were preserved after deposition have a thickness and (2) a duration; normalized by the total time, this duration of preserved deposition is called stratigraphic completeness. (3) The duration of deposition of sediment that was eroded later (called vacuity); (4) the thickness of these sediments is the eroded thickness. (5) At any given geographic location, erosion occurs some of the time, and the duration of these erosive periods is the fifth quantity. (6) Finally, it is quite common that neither significant deposition nor erosion takes place for some time and the duration of this stasis can be considered at every location. These maps give an overview of where erosion or deposition dominate in a source-to-sink system, and for how long; and they make it possible to quickly identify sites with both a high degree of stratigraphic completeness and a significant thickness.
... Following the methods of Covault et al. (2021), centrelines of channel elements were interpreted, which stack to form a channel belt (see fig. 5 of Covault et al., 2021;Morris et al., 2022), also known as a channel complex (Campion et al., 2000;Sprague et al., 2005;McHargue et al., 2011b). meandergraph, a directed graph approach, was used to reconstruct the kinematic evolution of the channel system (Speed et al., 2024; https:// github. ...
... However, disorganised channel stacking is unlikely within large erosional valleys, which confine the basal high-velocity and concentration core of channel-forming turbidity currents (Pirmez & Imran, 2003;Sylvester et al., 2011), even in cases of extremely large sediment discharge (Covault et al., 2021). The base of a valley-confined system might show an apparently disorganised pattern, but this is the result of a migrating, laterally erosive channel that leaves behind a fragmentary depositional record (Sylvester et al., 2011;Covault et al., 2016;Morris et al., 2022). However, deposition of a large landslide, or a few landslides, could fill a submarine channel or valley, thereby promoting channel avulsion or resetting the system such that subsequent channel patterns bear no resemblance to earlier ones (e.g., Figure 10). ...
Landslides are among the largest mass movements on Earth. As such, the deposits of landslides, also known as mass‐transport deposits, are significant architectural elements of continental margins, especially those receiving sediment from large deltas. Landslide dams have been shown to alter the courses of rivers and submarine channels. However, there are fewer examples of landslides completely filling submarine channels and examples of the subsequent stratigraphic evolution. A three‐dimensional seismic‐reflection dataset (<90 Hz) from the deep‐water (>1500 m) Taranaki Basin, offshore the North Island of New Zealand, was used to explore the response of a sequence of channel deposits to landslide filling. The basal channel system initially meandered like a river, with successive channel positions in close proximity, as it aggraded >250 ms two‐way travel time. This systematic, organised evolution is governed by the memory of early channel evolution, which sets the sea floor geomorphology that guides channel‐forming turbidity currents. Later, a channel approximately twice as wide as underlying channels cut off a number of channel bends, probably as a result of an increase in the discharge of channel‐forming turbidity currents. This last channel was filled with submarine landslides, which transported and deposited sediment as debris flows based on the presence of blocks within a matrix comprising chaotic, lower amplitude seismic facies. These debris‐flow deposits smoothed over the sea floor, effectively wiping the memory of channel evolution. As a result, the subsequent channel pattern bears no resemblance to the basal system. Submarine‐channel resetting by landslide filling is common in settings with frequent catastrophic basin‐margin collapses, like offshore New Zealand.
... Each channel belt resulted from the migration and aggradation of a single channel, represented by its centreline, starting from a nearly straight path up until the avulsion of the whole path. Simulated channel belts corresponded to stage 1 described by Morris et al. (2022) where channel sinuosity and belt width rapidly increased until the first bend cutoffs. ...
... The avulsion period was set to 4000 iterations, which corresponds to the time of the first cutoffs. Simulated channel belts were 5-10 km wide and the average channel sinuosity before avulsion was about 2.25, which is in the range of channel-belt widths and sinuosity measurements in natural systems (Deptuck et al. 2007;Morris et al. 2022). The channel aggradation intensity was set to 2 m every 100 iterations, which yields 78 m of total aggradation (i.e. ...
... The channel stacking pattern is a key element for submarine channel interpretations in terms of channel evolution history, changes of extrinsic or intrinsic parameters such as flow properties and high impact reservoir connectivity (Clark and Pickering 1996;Mayall and O'Byrne 2002;Deptuck et al. 2007;Macauley and Hubbard 2013;Morris et al. 2022). This study shows that inside a single channel complex (sensu Abreu et al. 2003) a large variety of recorded channel stacking patterns may be observed without changes in external forcings. ...
Channel kinematics play a pivotal but underappreciated role in determining submarine meandering channel stacking patterns. A stratigraphic forward model is here applied to turbidite systems to generate synthetic stratigraphic architectures and to compare channel trajectories recorded on cross-sections with the kinematics of meander bends. Various channel stacking patterns -which may be classified into four types- are obtained from a single set of constant parameters. This variety of stacking patterns observed from one 2D section to another is thus autogenic. It is the consequence of the 3D migration of meander bends. It reflects the number of consecutive bends that have intercepted the cross-section, which depends on the channel downstream migration rate. These 3D effects alone are sufficient to explain variations of apparent migration rate and the reversal of migration direction. As a result, sigmoidal geometries can be preserved in aggrading systems without significant change of channel geometry or varying aggradation and migration rates. Finally, despite these 3D effects, stratigraphic mobility numbers still provide good constraints on bend kinematics. These results should apply to meandering rivers and other meandering systems.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6610936
... Using a forward stratigraphic model, we evaluate the hypothesis that the increasing sinuosity of a channel results in a concurrent decrease in the channel slope by geometrical necessity, and this decrease in slope promotes deposition from turbidity currents and aggradation of the system. Therefore, autogenic processes intrinsic to the channel system can play a role in determining vertical movements of the channel, i.e. its trajectory (Sylvester et al. 2011;Morris et al. 2022). We show evidence that the processes documented here could be applied to other channel-levee systems such as the Amazon, in addition to giving insights into the processes governing the evolution of deepwater channel systems more generally. ...
... We propose that the increasing sinuosity and reducing slope of the channel may have enhanced deposition from the turbidity currents flowing through it, driving aggradation. This control is significant because it suggests that processes intrinsic to the channel system can play a role in determining the vertical migration of a channel through time, i.e. its trajectory (Sylvester et al. 2011;Covault et al. 2016;Morris et al. 2022). Each preserved channel element is likely to be the result of numerous sediment-gravity flows (Hubbard et al. 2020;Talling et al. 2022); simultaneous lateral migration and aggradation is unlikely to happen from a single flow. ...
... This behaviour is governed by a meandering algorithm based on linking the lateral migration rate to the local and upstream weighted curvature of the channel (Howard and Knutson 1984). This approach has been used to model a range of deep-water channel systems (Sylvester et al. 2011;Covault et al. 2016Covault et al. , 2020Sylvester and Covault 2016;Morris et al. 2022). To evaluate the influence of decreasing slope on the vertical movements of the channel through time, we use a simplified stream power law, in which erosion rate is a linear function of the bed shear stress: ...
There has been debate over the processes acting on deep-water channels with comparisons made to the evolution of meandering fluvial systems. We characterized a three-dimensional seismic-reflection dataset of the Joshua deep-water channel-levee system located in the eastern Gulf of Mexico and interpreted 13 horizons showing its kinematic evolution over a 25 km reach. Over this reach, we documented channel migration through systematic bend expansion and downstream translation, which was sustained through channel aggradation as sinuosity increased from 1.25 to 2.3 at abandonment. An abrupt decrease in sinuosity was associated with a neck cutoff, which changed the subsequent migration direction of the channel in that locality. These processes are analogous to the evolution of meandering fluvial systems. We show increasing channel sinuosity correlates to a reduction in channel slope and hypothesize this promoted increasingly depositional turbidity currents that led to channel aggradation. Using a simple forward stratigraphic model in which vertical movements of the channel are governed by a stream power law, we show how aggradation can be driven autogenically. Trends in sinuosity, aggradation and slope are in broad agreement between the Joshua and the model. This highlights the potential importance of intrinsic channel processes as a control on system evolution.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6610896.v1
Active submarine channel bases are marked by large erosional features, such as knickpoints and plunge pools. Their presence in ancient channel-fills has rarely been documented, meaning their importance in submarine channel morphodynamics requires investigation. Using seismic reflection data calibrated by wells from a buried submarine channel-fill, we document erosional features 100s m long and 10s m deep, here interpreted as knickpoints and a plunge pool, and provide a mechanistic process for their transfer into the stratigraphic record for the first time. Channel incision patterns are interpreted to record a transient uplift in an otherwise subsiding depocentre. Local structural complexities in the channel slope formed zones of preferential scouring. A switch to a depositional regime preserved the irregular channel base inhibiting their upstream migration and smoothing of the channel base. Their formation and preservation record responses to salt tectonics and provide a unique snapshot of the formative processes of an ancient submarine channel. The presence of these exceptional basal scours indicates that headward erosion processes did not operate rapidly, challenging the paradigm that knickpoint migration controls channel evolution. Our results show that the primary erosion of the main channel surface, and long-term channel evolution, are dominated by far more gradual processes.
