Field evidence for disequilibrium dynamics in preserved fluvial cross-strata: A record of discharge variability or morphodynamic hierarchy?

Lyster, Sinead; Whittaker, Alexander C.; Hajek, Elizabeth; Ganti, Vamsi

doi:10.1016/j.epsl.2021.117355

Cited by 17 publications

(25 citation statements)

References 51 publications

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“…A two‐parameter Gamma distribution describes the trough scour depths, similar to the bedform heights (e.g., Paola & Borgman, 1991) (Figure 3c), and the scale parameter of this distribution is inversely proportional to the parameter a that describes the set thickness distribution (Figure 4d; Paola & Borgman, 1991). Moreover,

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)\approx 0.88

across all transport stages, indicating that deviations of CV (D st ) from the empirical range of 0.88 ± 0.30 (Bridge, 1997) can be attributed to the influence of flood variability and/or the coevolution of dunes in the presence of barforms (Ganti et al., 2020; Leary & Ganti, 2020; Lyster et al., 2022). These results suggest that the variability‐dominated preservation model can be used to interpret outcrop observations so long as

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)\approx 0.88

(Bridge, 1997; Leary & Ganti, 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Together, experiments and theory indicate that mean formative bedform heights are 2.9 ± 0.7 times the mean set thickness under low net aggradation rates. Moreover, the variability‐dominated preservation model predicts that the coefficient of variation of the preserved set thickness (

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)

) is a near‐constant value of 0.88—a condition often observed in steady‐state experiments but seldom observed in outcrops (Lyster et al., 2022). Numerical, experimental, and field studies show that preservation ratio of bedforms, the ratio of the mean D st and mean bedform heights, and

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)

can change due to flow variability and the coevolution of river dunes and bars—scenarios characterized by high localized angles of bedform climb (Reesink et al., 2015; Ganti et al., 2020; Leary & Ganti, 2020; Paola et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Transport Stage on Preserved Fluvial Cross Strata

Das

Ganti

Bradley

et al. 2022

Geophysical Research Letters

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Fluvial cross strata are depositional products of bedform migration that record formative flow and sediment transport conditions on planetary bodies. Bedform evolution varies with transport stage even under constant flow depths, but our understanding of how prevailing sediment transport conditions affect preserved cross strata is limited. Here, we analyzed experimental bedform evolution and preserved set thickness spanning threshold‐of‐motion to suspension‐dominated transport conditions at multiple equilibrium flow depths. Results show that bedform trough depth and mean preserved set thickness have a parabolic dependence on transport stage, with maximum values observed at intermediate transport stages. Our results indicate that transport stage is a key control on the flow‐depth‐normalized set thickness but set thickness is a poor indicator of flow depth. Thus, the dependence of bedform dimensions on transport stage should be considered in paleohydraulic reconstruction, and the analysis of set thickness may aid in the estimation of ancient fluvial sediment flux.

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\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)\approx 0.88

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)\approx 0.88

(Bridge, 1997; Leary & Ganti, 2020).…”

Section: Discussionmentioning

confidence: 99%

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)

\mathrm{C}\mathrm{V}\left({D}_{\mathrm{s}\mathrm{t}}\right)

Section: Introductionmentioning

confidence: 99%

The Influence of Transport Stage on Preserved Fluvial Cross Strata

Das

Ganti

Bradley

et al. 2022

Geophysical Research Letters

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“…While independent insights generally point to ever-wet perennial systems in which the largest discharge events were sustained (e.g., Figure 1c,d), further work is required to identify the causes of the largest discharge events. Recent work on the Last Chance Ferron Sandstone documented abundant evidence for bedform disequilibrium dynamics, which may provide insights into formative flow durations (Lyster et al, 2022b). Assuming that bedform disequilibrium dynamics reflect near-instantaneous flow variability, Lyster et al (2022b) estimated total flood durations of order a few hours to a few days, consistent with floods caused by heavy rains, torrential storms, and sub-tropical or extra-tropical storms, which are typical of perennial systems.…”

Section: Independent Insights Into Intermittencymentioning

confidence: 99%

“…Further, where associated depositional volumes have robust age constraints, reconstructed sediment fluxes can be used to estimate sediment transport intermittency factors (e.g., Hayden et al, 2021b). This approach is increasingly useful given an ever-expanding repertoire of methods to reconstruct channel morphologies from fluvial strata, many of which are now incorporated into frameworks that carefully consider uncertainty (e.g., Greenberg et al, 2021;Hayden et al, 2021b;Lyster et al, 2022a;Lyster et al, 2022b;Wood et al, 2022).…”

Section: New Opportunities To Constrain Flow and Sediment Transport I...mentioning

confidence: 99%

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Constraining flow and sediment transport intermittency in the geological past

Lyster¹,

Whittaker²,

Farnsworth³

et al. 2022

Preprint

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Quantitative investigations of ancient rivers usually provide insights into either instantaneous or mean flow conditions. There is a critical gap between these timescales of investigation which reflects the intermittency of flow and sediment transport, and closing this gap is crucial to fully explore the dynamics and evolution of ancient fluvial landscapes. Here, we combine fluvial stratigraphic datasets, flow and sediment transport models, and paleoclimate general circulation model (GCM) results to develop new methods to estimate intermittency in the geological past, specifically flow intermittency factors (Iw) and sediment transport intermittency factors (Is). We illustrate these methods for the Upper Cretaceous Last Chance Ferron Sandstone, Utah, USA. For sand-transporting flow conditions in Last Chance Ferron rivers, we estimate Iw values of 0.54−0.90, which imply that channel-forming flows were sustained for the majority of the year, consistent with perennial systems in which relatively large discharges are sustained. In contrast, for gravel-transporting flow conditions, Iw values of 0.28−0.38 suggest that the largest formative flows may have occupied Last Chance Ferron rivers for nearly a third of the year, which could be explained by a monsoonal system in which high magnitude discharge events are sustained, or a subtropical system in which high magnitude discharge events have short durations but high frequencies. Meanwhile, Is values of 0.075−0.15 suggest that annual sediment budgets could have been transported in as little as 10 days, but up to 2 months, if channel-forming conditions were sustained, and highlight that small changes to the duration of channel-forming conditions could significantly impact sediment budgets. These results are consistent with independent facies- and proxy-based insights into Last Chance Ferron rivers, which point to a perennially wet system characterized by a monsoonal or subtropical discharge regime. Our results highlight new opportunities to use paleoclimate GCMs to constrain intermittency in the geological past. Going forward, paleoclimate GCMs will be particularly useful where the rock record is incomplete or inaccessible, or where stratigraphic approaches are limited, and will enable us to tackle pertinent research questions pertaining to past surface processes on both Earth and other planets.

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Flow depth estimates and avulsion behaviour in alluvial stratigraphy (Willwood Formation, Bighorn Basin, Wyoming, USA)

Foreman,

Sutherland,

Todd

et al. 2023

The Depositional Record

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The size and geometry of river channels play a central role in sediment transport and the character of deposition within alluvial basins across spatiotemporal scales spanning the initiation of grain movement to the filling of accommodation generated by subsidence. This study compares several different approaches to estimating palaeoflow depths from fluvial deposits in the early Palaeogene Willwood Formation of north‐west Wyoming, USA. Fluvial story heights (n = 60) and mud plug thicknesses (n = 13) are statistically indistinguishable from one another and yield palaeoflow depth estimates of 4 to 6 m. The vertical relief on bar clinoforms (n = 112) yields smaller flow depths, by a factor of ca 0.3, with the exception that the largest bar clinoforms match story heights and mud plug estimates. This observation is consistent with modern river data sets that indicate unit bar clinoforms do not capture the reach‐mean bank‐full flow depths except in rare circumstances. Future studies should use story heights (i.e. compound bar deposits) and mud plugs to estimate bank‐full flow depths in alluvial strata. Additionally, the thickness of multi‐storied fluvial sandbodies (n = 102) and overbank cycles composed of paired crevasse splay and palaeosol deposits (n = 45) were compared. The two depositional units display statistically indistinguishable mean and median values. Building upon previous depositional models, these observations suggest basin rivers aggraded approximately one flow depth prior to major avulsion. This avulsion process generated widespread crevasse splay deposition across the floodplain. Once the main river channel stem was reestablished, overbank flooding and palaeosol development dominated floodplain settings. The depositional model implies river aggradation autogenically generated topography in the basin that was effectively filled during the subsequent avulsion. This constitutes a meso‐timescale (103–104 years) compensational pattern driven by morphodynamics that may account for the high completeness of fossil and palaeoclimate records recovered from the basin.

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Field evidence for disequilibrium dynamics in preserved fluvial cross-strata: A record of discharge variability or morphodynamic hierarchy?

Cited by 17 publications

References 51 publications

The Influence of Transport Stage on Preserved Fluvial Cross Strata

The Influence of Transport Stage on Preserved Fluvial Cross Strata

Constraining flow and sediment transport intermittency in the geological past

Flow depth estimates and avulsion behaviour in alluvial stratigraphy (Willwood Formation, Bighorn Basin, Wyoming, USA)

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