Indirect estimation of bedload flux from modern sand-bed rivers and ancient fluvial strata

Mahon, Robert; McElroy, Brandon

doi:10.1130/g40161.1

Cited by 31 publications

(41 citation statements)

References 20 publications

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“…These methods complement traditional geochemical tracers (Weltje & von Eynatten, ), enhancing available methods for reconstructing sediment source areas and providing new constraints on paleosediment flux estimates. Detrital zircon studies provide an independent line of evidence for sediment flux estimates that compliment reconstructions achieved from deposit texture (Mahon & McElroy, ) or isopach reconstruction (Allen et al, ). Combining sediment provenance with other attributes measured from stratigraphic sections will help reduce uncertainty associated with nonunique solutions.…”

Section: Future Directionsmentioning

confidence: 77%

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

et al. 2020

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Climate, tectonics, and life influence the flux and caliber of sediment transported across Earth's surface. These environmental conditions can leave behind imprints in the Earth's sedimentary archive, but signals of climate, tectonic, and biologic change are not always present in the stratigraphic record. Deterministic and stochastic surface dynamics collectively act as a stratigraphic filter, impeding the burial and preservation of environmental signals in sedimentary deposits. Such impediments form a central challenge to accurately reconstructing environmental conditions through Earth's history. Emergent and self‐organized length and timescales in landscapes, which are themselves influenced by regional environmental conditions, define spatial and temporal sedimentation patterns in basins and fundamentally control the likelihood of environmental signal preservation in sedimentary deposits. Properly characterizing these scales provides a key avenue for incorporating the known “imperfections” of the stratigraphic record into paleoenvironmental reconstructions. These insights are necessary for answering both basic and applied science questions, including our ability to reconstruct the Earth system response to prior episodes of climate, tectonic, or land cover change.

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Section: Future Directionsmentioning

confidence: 77%

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

et al. 2020

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“…This empirical relationship predicts relatively accurately the bankfull geometry of vegetated rivers (Figure ). Similar empirical relationships are often used to infer paleohydraulic conditions from fluvial deposits on Earth (e.g., Mahon & McElroy, ) and Mars (e.g., Jacobsen & Burr, ). However, the degree to which such relationships may be applied to unvegetated systems, such as pre‐Silurian (e.g., Eriksson et al, ; Mukhopadhyay et al, ) or Martian (e.g., Jacobsen & Burr, ) rivers, is not well understood.…”

Section: Discussionmentioning

confidence: 99%

“…Bank‐strengthening grain sizes can be estimated by inspection of fine intervals and fed into a bank‐cohesion model (equations –). Paleo‐channel width can then be estimated by iteratively solving equation , using the inferred W / h combined with estimates of paleo‐bed slope (e.g., from bed stress estimates, bed grain size, and flow depth; Lynds et al, ; Trampush et al, ; Mahon & McElroy, ; Figure ). For example, consider a putative ancient channel‐bed deposit from an Amargosa‐like river (Ielpi, ), with grain sizes of ~100 μm and that contains ~1‐m‐tall bar forms and current ripples with wavelengths of ~11 cm.…”

Section: Discussionmentioning

confidence: 99%

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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“…Two modern rivers representing end‐member braided and meandering planforms, the North Loup River (Nebraska, USA) and Trinity River (Texas, USA), are used for comparisons in this study. The North Loup River is a sand‐bed braided river that has been used before as a modern analogue to ancient fluvial strata (Mohrig et al , 2000; Mahon & McElroy, 2018). The North Loup River represents a reasonable analogue to understand bar and bedform processes occurring in the formative channels of the Ruby Ranch Member, because widths and depths are similar.…”

Section: Introductionmentioning

confidence: 99%

The anatomy of exhumed river‐channel belts: Bedform to belt‐scale river kinematics of the Ruby Ranch Member, Cretaceous Cedar Mountain Formation, Utah, USA

et al. 2020

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Many published interpretations of ancient fluvial systems have relied on observations of extensive outcrops of thick successions. This paper, in contrast, demonstrates that a regional understanding of palaeoriver kinematics, depositional setting and sedimentation rates can be interpreted from local sedimentological measurements of bedform and barform strata. Dune and bar strata, channel planform geometry and bed topography are measured within exhumed fluvial strata exposed as ridges in the Ruby Ranch Member of the Cretaceous Cedar Mountain Formation, Utah, USA. The ridges are composed of lithified stacked channel belts, representing at least five or six re-occupations of a single-strand channel. Lateral sections reveal well-preserved barforms constructed of subaqueous dune cross-sets. The topography of palaeobarforms is preserved along the top surface of the outcrops. Comparisons of the channelbelt centreline to local palaeotransport directions indicate that channel planform geometry was preserved through the re-occupations, rather than being obscured by lateral migration. Rapid avulsions preserved the state of the active channel bed and its individual bars at the time of abandonment. Inferred minimum sedimentation durations for the preserved elements, inferred from crossset thickness distributions and assumed bedform migration rates, vary within a belt from one to ten days. Using only these local sedimentological measurements, the depositional setting is interpreted as a fluvial megafan, given the similarity in river kinematics. This paper provides a systematic methodology for the future synthesis of vertical and planview data, including the droneequipped 2020 Mars Rover mission, to exhumed fluvial and deltaic strata.

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Indirect estimation of bedload flux from modern sand-bed rivers and ancient fluvial strata

Cited by 31 publications

References 20 publications

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

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

The anatomy of exhumed river‐channel belts: Bedform to belt‐scale river kinematics of the Ruby Ranch Member, Cretaceous Cedar Mountain Formation, Utah, USA

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