Sedimentology and Stratigraphy of Large River Deposits: Recognition and Preservation Potential in the Rock Record

Fielding, Christopher R.

doi:10.1002/9781119412632.ch7

“…Despite careful work connecting braided river morphodynamics to bar morphology and migration (e.g., Germanoski and Schumm, 1993;Lunt et al, 2004;Ashworth et al, 2011;Schuurman and Kleinhans, 2015;Fielding, 2022) and detailed descriptions of ancient deposits (e.g., Miall, 1988;Bridge, 1993;Lunt et al, 2004;Bridge and Lunt, 2006;Fielding et al, 2018;Chamberlin and Hajek, 2019;Cardenas et al, 2020;Barefoot et al, 2022), specific connections between braided river kinematics and bar deposit preservation are lacking. Facies models suggest that braided river deposits are dominated by laterally extensive and amalgamated sand bodies that comprise multiple bar deposits, channel floor cross-strata and occasional pockets of low-flow or abandonment fines (Miall, 1985(Miall, , 1988Gibling, 2006;Lynds and Hajek, 2006;Hajek et al, 2010;Ashworth et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

The fate of bars in braided rivers

Alpheus,

Hajek

2024

Preprint

0

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Ancient river deposits are important archives of past landscape conditions on planetary surfaces. On Earth, they host valuable groundwater, energy resources, and carbon-storage potential. Reconstructing details of paleochannel forms and movements refines our understanding of the controls on river behavior under different climate, landcover, and tectonic conditions, and improves predictions and models of subsurface reservoirs. While studies have shown detailed connections between channel kinematics and bar-deposit architecture in meandering river systems, similar connections between braided river movements and preserved braided river deposits have not been established. Here we explore the potential for connecting braided river deposits to paleochannel movements, form, and flow conditions, and we evaluate the controls on bar preservation using synthetic stratigraphy generated with a numerical morphodynamic model. We investigate how attributes of channel morphodynamics, like channel widening or braiding intensity, impact bar deposits’ preservation, scale, geometry, and architecture. We then assess how the scale, preservation, and facies composition of bar deposits reflect formative flow conditions of the channel. Our results demonstrate that no diagnostic signature of braided channel morphodynamics is recorded in bar-deposit geometry, facies, or preservation patterns. Rather, the unique local history of thread movements combines stochastically to preserve or rework bar deposits, and the timing of channel avulsion is the dominant control on bar preservation. Our results also show that representative paleochannel flow conditions will likely be accurately reflected in aggregate observations of braid bar deposits within channel-belt sandbodies at a regional or member/formation scale. These results demonstrate the need for broad sampling and statistical approaches to subsurface prediction and paleo-flow reconstruction in ancient, braided river deposits.

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“…Large rivers are defined by a number of characteristics including large basin drainage areas, channel length, water discharges and sediment fluxes (Hovius, 1998; Potter & Hamblin, 2006; Gupta, 2007; Best, 2019; Best & Fielding, 2019; Fielding, 2022). Although the dominance of multi‐channel systems is well‐documented in large rivers (Latrubesse, 2008; Galeazzi et al ., 2021), there is a comparative paucity of studies concerning their depositional dynamics, largely intrinsic to their scale and the resulting logistical issues involved in their study.…”

Section: Introductionmentioning

confidence: 99%

Morphodynamics and depositional architecture of mid‐channel bars in large Amazonian rivers

Almeida,

Galeazzi,

Best

et al. 2024

Sedimentology

5

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Large rivers are characterized by large water discharges, high suspended sediment fluxes and low slope, and typically display multiple channels that are separated by large complex bars. The most common channel style found in these rivers is characterized by the alternating presence of single and multiple channel threads. Mid‐channel compound bars separate a main deeper channel from shallower secondary channels, leading to low‐order braiding and low to moderate sinuosity. Despite the importance of this type of river for global terrestrial sediment transport and the interpretation of ancient fluvial successions, integrated depositional models for large multi‐channel rivers are still not fully developed. This paper interprets the channel morphodynamics and depositional architecture of such large rivers by investigating the distinctive features of their laterally‐accreting mid‐channel bars in the Solimões–Amazonas River. This is achieved by examination of temporal series of satellite images, quantification of bedforms using multibeam echosounding surveys, analysis of shallow seismic and ground penetrating radar surveys of selected areas, and on‐site field observations and sample collections. Such mid‐channel bars produce directional variability in planform scroll bar accretion of up to 180°. As these bars – and their associated channels – evolve, they become progressively shallower, due to the bifurcation of the two channels and the resultant partitioning of discharge that leads to a gradual reduction in transport capacity within the outer channel. The preserved successions of this process in the alluvial plain are characterized by fining‐upward trends, with larger cross‐strata sets at mid‐depths and internal erosional surfaces marking distinct cycles of bar development with potentially differing palaeocurrent trends. The new depositional models proposed for these mid‐channel bars and channels constitute a basis for the recognition of large multi‐channel river deposits in the ancient rock record.

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The Fate of Bars in Braided Rivers

Alpheus,

Hajek

2024

The Sedimentary Record

0

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Ancient river deposits are important archives of past landscape conditions on planetary surfaces. On Earth, they host valuable groundwater, energy resources, and carbon-storage potential. Reconstructing details of paleochannel forms and movements refines our understanding of the controls on river behavior under different climate, landcover, and tectonic conditions, and improves predictions and models of subsurface reservoirs. While studies have shown detailed connections between channel kinematics and bar-deposit architecture in meandering river systems, similar connections between braided river movements and preserved braided river deposits have not been established. Here we explore the potential for connecting braided river deposits to paleochannel movements, form, and flow conditions, and we evaluate the controls on bar preservation using synthetic stratigraphy generated with a numerical morphodynamic model. We investigate how attributes of channel morphodynamics, like channel widening or braiding intensity, impact bar deposits’ preservation, scale, geometry, and architecture. We then assess how the scale, preservation, and facies composition of bar deposits reflect formative flow conditions of the channel. Our results demonstrate that no diagnostic signature of braided channel morphodynamics is recorded in bar-deposit geometry, facies, or preservation patterns. Rather, the unique local history of thread movements combines stochastically to preserve or rework bar deposits, and the timing of channel avulsion is the dominant control on bar preservation. Our results also show that representative paleochannel flow conditions will likely be accurately reflected in aggregate observations of braid bar deposits within channel-belt sandbodies at a regional or member/formation scale. These results demonstrate the need for broad sampling and statistical approaches to subsurface prediction and paleo-flow reconstruction in ancient, braided river deposits.

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Sedimentology and Stratigraphy of Large River Deposits: Recognition and Preservation Potential in the Rock Record

Cited by 3 publications

References 116 publications

The fate of bars in braided rivers

The fate of bars in braided rivers

Morphodynamics and depositional architecture of mid‐channel bars in large Amazonian rivers

The Fate of Bars in Braided Rivers

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