Modern and ancient amalgamated sandy meander‐belt deposits: recognition and controls on development

Hartley, Adrian J.; Owen, Amanda; Weissmann, Gary S.; Scuderi, L. A.

doi:10.1002/9781119424437.ch14

Cited by 12 publications

(16 citation statements)

References 97 publications

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“…This idea is consistent with recent observations of a modern point‐bar deposit along a highly mobile unvegetated river meander in the Toiyabe Basin, NV (Ielpi & Lapôtre, ), which is dominated by sand‐sized materials with little intercalated mud. If found to be representative of other unvegetated meandering streams, the observed stratigraphy in the Toiyabe Basin is inconsistent with heterolithic lateral accretion sets being diagnostic of river meandering (as also suggested by, e.g., Hartley et al, ; McMahon & Davies, ; Swan et al, ).…”

Section: Discussionmentioning

confidence: 84%

“…It remains unclear, however, whether the interpreted paucity of pre-Silurian single-thread rivers reflects a true scarcity of such rivers before the advent of land plants, a lack of refined facies models applicable to nonheterolithic meandering systems (Hartley et al, 2015(Hartley et al, , 2018, or selective preservation of sandier deposits in the absence of vegetation. There is also a possibility that some Precambrian fluvial mudstones were misinterpreted as marine in the absence of fossils (McMahon & Davies, 2018a).…”

Section: Single-thread and Meandering Riversmentioning

confidence: 99%

“…There is also a possibility that some Precambrian fluvial mudstones were misinterpreted as marine in the absence of fossils (McMahon & Davies, ). Despite being rarely recognized (e.g., Gibling et al, ; Hartley et al, ; McMahon & Davies, ), at least some single‐thread rivers existed long before plants colonized land (Long, , ; Ielpi & Rainbird, ; Santos & Owen, ; Ielpi et al, , 2017). Moreover, some single‐thread rivers meander on Earth today in the virtual absence of macroscopic plant life (Matsubara et al, ; Ielpi, ; Ielpi & Lapôtre, ‐b; Santos et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

et al. 2019

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Flume experiments and field observations show that bank vegetation promotes the formation of narrow and deep single‐thread channels by strengthening riverbanks. Consistent with this idea, the pre‐Silurian fluvial record generally consists of wide monotonous sand bodies often interpreted as deposits of shallow braided rivers, whereas single‐thread rivers with muddy floodplains become more recognizable in Silurian and younger rocks. This shift in the architecture of fluvial deposits has been interpreted as reflecting the rise of single‐thread rivers enabled by plant life. The deposits of some single‐thread rivers, however, have been recognized in pre‐Silurian rocks, and recent field studies have identified meandering rivers in modern unvegetated environments. Furthermore, single‐thread‐river deposits have been identified on Mars, where macroscopic plants most likely never evolved. Here we seek to understand the formation of those rarely recognized and poorly characterized single‐thread rivers in unvegetated landscapes. Specifically, we quantitatively explore the hypothesis that cohesive muddy banks alone may enable the formation of single‐thread rivers in the absence of plants. We combine open‐channel hydraulics and a physics‐based erosion model applicable to a variety of bank sediments to predict the formation of unvegetated single‐thread rivers. Consistent with recent flume experiments and field observations, results indicate that single‐thread rivers may form readily within muddy banks. Our model has direct implications for the quantification of riverbank strengthening by vegetation, understanding the hydraulic geometry of modern and ancient unvegetated rivers, interpreting pre‐Silurian fluvial deposits, and unraveling the hydrologic and climate history of Mars.

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Section: Discussionmentioning

confidence: 84%

Section: Single-thread and Meandering Riversmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

et al. 2019

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“…Long (2011) suggested that sandy meandering systems could be identified within pre-vegetation alluvium by measuring the directional relationships between foresets and their underlying bounding surfaces. The commonness of sinuous pre-vegetation channel planforms was subsequently considered in multiple studies (e.g., de Almeida et al, 2016;Santos and Owen, 2016;Hartley et al, 2018;Ielpi et al, 2018;McMahon and Davies, 2018c), with the general consensus arising that, while much evidence of genuine pre-vegetation sinuosity may have gone unrecognized (or be unrecognizable), sinuous channel planforms were almost certainly less common on Earth in the absence of biological stabilizing agents, prior to the evolution of land plants. Since the widespread preservation of mud is an important element for more easily classifying fluvial style, we add the caveat that it may be more difficult to diagnose fluvial style in pre-vegetation successions.…”

Section: Recent Studies Of Pre-vegetation Alluvium (2010-2019)mentioning

confidence: 99%

Physical and biological functioning in Proterozoic rivers: evidence from the archetypal pre-vegetation alluvium of the Torridon Group, NW Scotland

McMahon

Davies

2019

SJG

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In modern rivers, vegetation affects hydrological, geomorphological and sedimentological functioning, so extant fluvial systems can provide only partial analogues for those rivers that operated before the evolution of land plants. However, pre-vegetation rivers were the norm for the first 90% of Earth's history and so a better understanding of their sedimentary product can provide insights into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth. In addition to a short review of the history of research into pre-vegetation alluvium, this paper presents a fieldwork-based case study of the later Proterozoic Torridon Group, which contains some of the most extensive and easily accessible exposures of pre-vegetation alluvium worldwide. Three alluvial architectural deposits have been recognized: (1) channel-bedform deposits (c. 80%); (2) barform deposits (c. 20%); and (3) out-of-channel deposits (≪1%). Channel-bedform deposits have erosional bases and most frequently stack vertically to form thick multistorey channel-bedform sequences. The preferential preservation of these deposits, which record the deepest parts of river channels, suggests that channel migration had a dominant control on preservation in the Torridon Group. Less frequently, channel-bedform deposits pass upwards into a genetically related barform deposit. Barform preservation in these instances is interpreted to be due to channel avulsion, which protected the barforms from reworking. Channel-bar thickness, measured from the basal erosional surface of a channel-bedform deposit to the top of its associated barform deposit, indicates minimum water depths of 1.7 to 8.0 m. Downstream-accreting barform deposits are most frequent, but lateral and upstream modes of accretion are also well represented. Dominant southeastward-palaeoflow directions imply that the Torridonian rivers were sourced from the Grenvillian Mountain Belt. The preserved architectural deposits and narrow dispersal of palaeocurrent data are explained by interpreting the Torridon Group as the alluvium of dominantly low-sinuosity rivers, with signatures recording autogenic fluvial adjustments. In the few rare instances where out-of-channel deposits are preserved, they contain fossil evidence for microbial mats, which prove that not all Proterozoic river systems were wholly abiotic. The overall characteristics of the Torridon alluvium, in terms of its ubiquitous highly tabular beds of sand-grade or coarser material, make it an archetypal example of pre-vegetation alluvium as known globally.Thematic collection: This article is part of the SJG Collection on Early-Career Research available at: https://www.lyellcollection.org/cc/SJG-early-career-research

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“…Riverscapes contain a wide range of planforms, a spectrum rarely reflected in interpretations of ancient alluvium. Most geological studies group successions as the product of particular end-member river types (braided, meandering) and whilst these generalizations are largely the result of a lack of traceable evidence at outcrop (Kleinhans et al, 2010), they have nonetheless resulted in widespread skepticism of ancient palaeochannel interpretations (Bridge, 1993;Miall, 2006b;Ethridge, 2011;Hartley et al, 2015Hartley et al, , 2018Fielding et al, 2018). Improved confidence in the interpretation of such channel-scale planforms is necessary to determine if any 'norm' system-scale depositional style (i.e.…”

Section: Introductionmentioning

confidence: 99%

Experimental distributive fluvial systems: Bridging the gap between river and rock record

Scheltinga

McMahon

Dijk

et al. 2020

The Depositional Record

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A debate has called into question as to which fluvial channel patterns are most widely represented in the stratigraphic record, with some advocating that distributive fluvial systems (DFS) predominate and others that a broad diversity of fluvial styles may become preserved. Critical to both sides is the adequate recognition of original channel planform from geological outcrops separated from their formative processes by millions or even billions of years. In this study the river and rock record are linked through experimentally created DFSs with both aggrading channel beds and floodplains. This approach allows depositing processes and deposited strata to be studied in tandem. Proximal areas comprise coarse, amalgamated channel‐fills with scarce fine‐grained floodplain material. The overall spread of sandbody dimensions become far more varied in medial stretches, with an overall reduction in mean width and depth. In these areas channel‐fills may be sand‐rich or mud‐rich and, following avulsion, all channels are covered by floodplain sediment. Channels, levees and splays form discrete depositional bodies each with varying aspect ratios; a novel breadth of deposits and morphologies in aggrading experiments largely concurrent with proposed trends indicative of DFSs. The proportion of floodplain material increases distally, resulting in decreased interconnectedness of distal channel‐fills. Muddy floodplain sediments significantly change DFSs behaviour and subsequent stratigraphic architecture by enhancing bank stability and reducing avulsion through the filling of floodbasins. The laboratory methods utilised here open up the possibility of controlled experimentation on the effects and mechanisms of DFSs sedimentation, which is important since the modelled stratigraphic trends are rarely so tractable in ancient geological outcrop belts.

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Modern and ancient amalgamated sandy meander‐belt deposits: recognition and controls on development

Cited by 12 publications

References 97 publications

Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

Model for the Formation of Single‐Thread Rivers in Barren Landscapes and Implications for Pre‐Silurian and Martian Fluvial Deposits

Physical and biological functioning in Proterozoic rivers: evidence from the archetypal pre-vegetation alluvium of the Torridon Group, NW Scotland

Experimental distributive fluvial systems: Bridging the gap between river and rock record

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