Emergent facies patterns within fluvial channel belts

Willis, Brian J.; Sech, Richard P.

doi:10.1002/9781119424437.ch19

Cited by 14 publications

(14 citation statements)

References 61 publications

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Section: Discussionmentioning

confidence: 99%

“…12). Different styles of planform evolution can occur under a variable ratio between lateral shift and vertical aggradation of channels, giving rise to a wide spectrum of combinations, which can influence the thickness of channel-belt deposits (Willis & Sech, 2019a), and the morphology of their basal and top surfaces (Ghinassi et al, 2016). Latero-vertical shift of channels controls geometry of point-bar bodies, along with inter-bar connectivity (Colombera et al, 2017;Willis & Sech, 2019b), especially where aggradation allows adjacent bar bodies to overlap.…”

Section: Point-bar Brink and Channel Thalweg: From 2d Trajectories Tomentioning

confidence: 99%

“…However, studies that document the lateral and vertical shift of both the point‐bar brink and channel thalweg (De Mowbray, 1983; Nanson & Croke, 1992; Makaske, 2001; Rajchl & Uličný, 2005; Rieu et al ., 2005; Ghinassi et al ., 2014; Fielding, 2015; Ielpi et al ., 2015; Brivio et al ., 2016; Candel et al ., 2017; Boaga et al ., 2018; Finotello et al ., 2018; Cosma et al ., 2019), suggest that, where the rate of aggradation is high (for example, millimetres to centimetres per year) relative to the rate of lateral channel migration (for example, centimetres to decimetres per year), geometries of resulting point‐bar bodies can differ substantially from those of classical tabular sedimentary bodies. Development of point‐bar geometries, and their internal stratal architectures, are also influenced by the different styles of bar planform evolution (Willis & Tang, 2010; Ghinassi et al ., 2013, 2016; Yan et al ., 2017; Willis & Sech, 2019a). However, even though the planform transformations of meander bends (i.e.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An integrated approach to determine three‐dimensional accretion geometries of tidal point bars: Examples from the Venice Lagoon (Italy)

et al. 2020

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Low rates of lateral migration (centimetres to decimetres per year) combined with relatively high rates of vertical accretion (millimetres to centimetres per year) recorded in microtidal channels of the Venice Lagoon (Italy) give rise to point-bar geometries and internal facies arrangements that differ substantially from widely accepted models of point-bar sedimentary architecture. In this study, field data from the Venice Lagoon are combined with a three-dimensional forward stratigraphic model, the 'Point-Bar Sedimentary Architecture Numerical Deduction' (PB-SAND), to predict the stratal geometries of point bars formed in aggradational settings. The PB-SAND uses a combined geometric and stochastic modelling approach that can be constrained by field evidence. The model applied determines the geometry of four point bars generated by 9 to 11 m wide channels cutting through salt marshes. An iterative best-fit modelling approach has been used to obtain multiple simulations for each case study, each of which fits the observations derived from the analysis of time-series historical aerial photographs and 44 sedimentary cores. Results demonstrate how the geometry of the bars is determined by the development of two key stratal surfaces: the point-bar brink and channel-thalweg surfaces. These surfaces are defined by the progressive translation and vertical shift of the point-bar brink (i.e. break of slope between bar top and bar slope) and the channel thalweg (i.e. deepest part of the channel) during bar evolution. The approach is used to: (i) reconstruct three-dimensional point-bar geometries; (ii) propose alternative reconstructions; (iii) provide insight to drive the acquisition of additional data to better constrain the proposed models; and (iv) provide insight into the mechanism of bar growth for slowly migrating channels in settings subject to relatively high rates of aggradation. This study highlights how interaction between styles of planform transformation and latero-vertical shifts of meandering channels can determine the geometry of related sedimentary bodies. Keywords Aggradation, channel-thalweg trajectory, point-bar brink trajectory, tidal meander, Venice Lagoon. negligible with respect to lateral migration processes. Hence, point bars are commonly described as purely laterally accreting bodies

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Section: Discussionmentioning

confidence: 99%

Section: Point-bar Brink and Channel Thalweg: From 2d Trajectories Tomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An integrated approach to determine three‐dimensional accretion geometries of tidal point bars: Examples from the Venice Lagoon (Italy)

et al. 2020

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“…As fluvial meanders evolve, they commonly undertake lateral expansion, downstream translation and apex rotation, whereby the dominant direction of channel migration can change repeatedly through various stages of bar development (Jackson, 1976; Makaske & Weerts, 2005; Ielpi & Ghinassi, 2014; Ghinassi et al ., 2016). Through the alternation of stages of meander‐bend expansion, translation and rotation, point‐bar deposits accumulated in the earlier stages of bar development can experience multiple episodes of partial erosion, and this can give rise to sedimentary architectures characterized by the juxtaposition of lateral‐accretion packages with different accretion directions, as evidenced by complex mosaics of scroll‐bar sets observed in planforms of modern rivers (Durkin et al ., 2015; Strick et al ., 2018; Durkin et al ., 2019; Johnston & Holbrook, 2019; Willis & Sech, 2019a). In parallel with variations in the dip azimuth and inclination of bar‐accretion surfaces, bathymetric variations that exist along sinuous channels, such as depth changes across riffles and pools, may also cause variability in the thickness of channel‐belt deposits in three‐dimensions (Willis & Tang, 2010; Ielpi & Rainbird, 2015; Willis & Sech, 2019a).…”

Section: Introductionmentioning

confidence: 99%

Controls on fluvial meander‐belt thickness and sand distribution: Insights from forward stratigraphic modelling

2021

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Fluvial point-bar evolution commonly involves multiple stages of bar development driven by changes in the style of meander transformations. Complicated planform morphologies are widely recognized in remote-sensing imagery, but the relationships between meander-bend evolutionary behaviour and stratigraphic architecture, facies distribution, and sand volumes remain poorly understood. This study applies a geometric forward stratigraphic model (Point-Bar Sedimentary Architecture Numerical Deduction -'PB-SAND') to simulate the internal sedimentary architecture of 24 meanderbelt segments that evolved via a broad range of meander-bend transformation styles. Modelling inputs are constrained by channel trajectories inferred from high-resolution Light Detection and Ranging (LiDAR) datasets, lithological information from a sedimentological database (Fluvial Architecture Knowledge Transfer System -'FAKTS') and geological knowledge of trends in point-bar lithology (for example, decrease in sand proportion with sinuosity, downstream of bend apices, and beyond the transition from point-bar to counter-point-bar deposits) and in channel bathymetry (depth variations across pools and riffles). Modelling results are used to explore how the relative distribution of sand and mud is controlled by the styles of point-bar transformation, quantified by the relative degree of meander translation versus expansion, and by the amount of bend rotation. The 24 models are classified into three groups based on cluster analysis of their mean migration angle, mean apex rotation, mean sinuosity, standard deviation of channel circular variance and preservation ratio; these quantities are known to be controlled by meander transformation types. Quantitative comparisons across these groups and relationships between metrics of planform change and quantifications of point-bar deposits demonstrate how meander planform evolution controls point-bar thickness and sand volume. Locally, the thickness of sand in bar deposits is controlled by the interplay of facies trends and spatial variations in bar thickness that reflect bathymetric changes, both related to local hydrodynamics. The proposed workflow establishes linkages between planform morphologies and three-dimensional facies distributions; it can be employed to characterize the distribution of subsurface porous volumes where the planform history of meander bends can be reconstructed.

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“…Conversely, mud-dominated abandoned channel elements commonly have thin, sand-rich components in their basal-most part, which permit the flow of fluids through overall low-permeability channel-plug deposits (Donselaar & Overeem, 2008). Consequently, the internal distribution of lithofacies inside these bodies exerts a major control on porous fluid-flow pathways (Bridge, 1982;Brownlie, 1983;Sun et al, 2001aSun et al, , 2001bWillis & Sech, 2019a, 2019b. Knowledge of the expected internal facies arrangement within architectural elements is therefore an essential requirement for effective groundwater or hydrocarbon reservoir evaluation (e.g., Jackson & Muggeridge, 2000;Jackson et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Combined inverse and forward numerical modelling for reconstruction of channel evolution and facies distributions in fluvial meander-belt deposits

Parquer

Yan

Colombera

et al. 2020

Marine and Petroleum Geology

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The sedimentary record of meandering rivers contains a diverse and complex set of lithological heterogeneities, which impact natural resource management. Different methods exist to model such accumulated successions present in the subsurface by integrating knowledge of system evolutionary behaviour and geometries visible on seismic time or stratal slices. With reference to case-study examples, we review, discuss and employ two of these methods: (i) ChaRMigS generates possible scenarios for channel evolution and meander cutoffs by a reverse migration process; (ii) PB-SAND is a forward stratigraphic model which simulates fluvial point-bar geometry and facies distributions from known palaeo-channel geometries. We introduce a workflow to demonstrate how these two methods can be applied in combination to predict fluvial meander-belt facies distributions, using a subsurface dataset on a Pleistocene succession from the Gulf of Thailand where abandoned channels are visible on seismic time slices, but for which bar-accretion geometries and the exact timing of channel abandonment are unclear. Results show the value of a combined modelling approach to automate the stochastic generation of facies distributions constrained by seismic interpretations.

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Emergent facies patterns within fluvial channel belts

Cited by 14 publications

References 61 publications

An integrated approach to determine three‐dimensional accretion geometries of tidal point bars: Examples from the Venice Lagoon (Italy)

An integrated approach to determine three‐dimensional accretion geometries of tidal point bars: Examples from the Venice Lagoon (Italy)

Controls on fluvial meander‐belt thickness and sand distribution: Insights from forward stratigraphic modelling

Combined inverse and forward numerical modelling for reconstruction of channel evolution and facies distributions in fluvial meander-belt deposits

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