Leeside Sediment Fallout Patterns and the Stability of Angular Bedforms

Hand, Bryce M.; Bartberger, Charles E.

doi:10.1306/212f8d05-2b24-11d7-8648000102c1865d

Cited by 6 publications

(5 citation statements)

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“…The fine structure of cross-strata in lithofacies St + Sh suggests that many of the cross-strata were not formed by simple avalanching along lee slopes of bedforms. Cross strata of lithofacies St + Sh with tangential terminations, wide-ranging dip magnitudes, and laterally continuous laminae are similar to those termed accretionary cross-stratification by Imbrie and Buchanan (1965) and those produced experimentally during the transition of dunes to upper flat beds (Hand and Bartberger, 1988). The process of formation of these cross-strata may involve traction transport over both stoss and lee surfaces of bedforms (Imbrie and Buchanan 1965;Hand and Bartberger, 1988) and/or continuous avalanching (grain flow) accompanied by intense grain fall (Hunter and Kocurek, 1986).…”

Section: Sandstone-dominated Lithofaciessupporting

confidence: 67%

“…Cross strata of lithofacies St + Sh with tangential terminations, wide-ranging dip magnitudes, and laterally continuous laminae are similar to those termed accretionary cross-stratification by Imbrie and Buchanan (1965) and those produced experimentally during the transition of dunes to upper flat beds (Hand and Bartberger, 1988). The process of formation of these cross-strata may involve traction transport over both stoss and lee surfaces of bedforms (Imbrie and Buchanan 1965;Hand and Bartberger, 1988) and/or continuous avalanching (grain flow) accompanied by intense grain fall (Hunter and Kocurek, 1986). These processes are thought to involve higher bedform-migration velocities and higher depositional rates than normal grain-flow processes.…”

Section: Sandstone-dominated Lithofaciessupporting

confidence: 67%

“…These processes are thought to involve higher bedform-migration velocities and higher depositional rates than normal grain-flow processes. Field evidence and sedimenttransport theory suggest that so-called accretionary crossstrata are deposited under flowing water that is deep relative to the bedform height (Imbrie and Buchanan, 1965) and does not undergo flow separation from the bed at convex-up bedform crests (Hand and Bartberger, 1988). These processes are thought to involve higher bedform-migration velocities and higher depositional rates than normal grainflow processes.…”

Section: Sandstone-dominated Lithofaciesmentioning

confidence: 99%

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Stratigraphy, sedimentology, and paleontology of the Lower Eocene San Jose Formation in the central portion of the San Juan Basin, northwest New Mexico

Smith¹,

Lucas²

1991

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The lower Eocene San Jose Formation in the central portion of the San Juan Basin of New Mexico consists of the Cuba Mesa, Regina, Llaves, and Tapicitos Members. Well-log data indicate that, from its 100 m thickness, the Cuba Mesa Member thins towards the center of the basin and pinches out to the northeast by latitude 36 deg. 40' N, longitude 107 deg. 19' W. The Regina Member crops out most extensively in the study area and decreases in sandstone-to-mudrock ratio to the north. The Llaves and Tapicitos Members occur only in the highest locales of the area, are thin due to erosion, and are not mappable as separate units.Well-log data and 1275 m of measured sections in the Regina, Llaves, and Tapicitos Members indicate that strata in the study area are made up of approximately 35% medium- to coarse-grained sandstone and 65% fine-grained sandstone and mudrock. Sedimentology and sediment-dispersal patterns in the study area suggest deposition by generally south-flowing streams that had sources to the northwest, northeast, and east. Low-sinuosity, sand-bedded, braided(?) streams shifted laterally across approximately 1 km wide channel belts to produce sheet sandstones that are prominent throughout the formation. Levees separated channel environments from floodplain and local lacustrine areas. Avulsion relocated channels periodically to areas on the floodplain, resulting in the typically disconnected sheet sandstones within muddy overbank sediments of the Regina Member.Fossil plants from lacustrine strata of the Regina Member at Santos Peak are the only flora described from the San Jose Formation. They indicate a humid, forested environment in the depositional basin. Fossil vertebrates from the Regina Member include the mammal taxa Phenacolemur praecox, Oxyaena forcipata, Ectoganus gliriformis, Esthonyx bisulcatus, Coryphodon molestus, Hyopsodus miticulus, Phenacodus primaevus, and Hyracotherium angustidens. These taxa support correlation with the Almagre local fauna of the Regina Member in the east-central San Juan Basin. They are thus indicative of a middle Wasatchian (Lysitean) age, about 53 Ma.

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Section: Sandstone-dominated Lithofaciessupporting

confidence: 67%

Section: Sandstone-dominated Lithofaciessupporting

confidence: 67%

Section: Sandstone-dominated Lithofaciesmentioning

confidence: 99%

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Stratigraphy, sedimentology, and paleontology of the Lower Eocene San Jose Formation in the central portion of the San Juan Basin, northwest New Mexico

Smith¹,

Lucas²

1991

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“…In cases where the deposition of suspended sediment plays an integral part in the dune dynamics, this increase in mean settling trajectory length could ultimately lead to the diffusion of dune properties (e.g. flattening or increased wave length) and, as particles moving in suspension have higher average velocities than particles moving in contact with the bed, higher bedform translation velocities (Hand and Bartberger, 1988;Prent and Hickin, 2001;McElroy and Mohrig, 2009;Parsons and Best, 2013;Naqshband et al, 2014). In cases where suspended sediment is not a significant driver of dune dynamics, increased trajectory lengths would lead to higher instances of particle 'bypassing' for individual dunes (Mohrig and Smith, 1996;Naqshband et al, 2014).…”

Section: Implications For Suspended-sediment Concentrations and Bedfomentioning

confidence: 99%

“…The flux of suspended-bed sediment is dependent on the balance of sediment deposition due to particle settling relative to sediment entrainment from the channel bed (Raudkivi, 1998). Sediment settling in bedform fields has been shown to influence the dimensions and translation velocities of those bedforms (Hand and Bartberger, 1988;Bennett et al, 1998;Parsons and Best, 2013;Naqshband et al, 2014;Bradley and Venditti, 2019). Despite this importance, precise simulation of particle-settling processes is often neglected in geomorphic models in favour of assuming a singular particle-settling velocity, typically set as the still-water particle-settling velocity (van Rijn and Tan, 1985;Paola et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Sand settling through bedform‐generated turbulence in rivers

Yuill

Wang

Meselhe

et al. 2020

Earth Surf Processes Landf

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Fluvial bedforms generate a turbulent wake that can impact suspended-sediment settling in the passing flow. This impact has implications for local suspended-sediment transport, bedform stability, and channel evolution; however, it is typically not well-considered in geomorphologic models. Our study uses a three-dimensional OpenFOAM hydrodynamic and particle-tracking model to investigate how turbulence generated from bedforms and the channel bed influences medium sand-sized particle settling, in terms of the distribution of suspended particles within the flow field and particle-settling velocities. The model resolved the effect of an engineered bedform, which altered the flow field in a manner similar to a natural dune. The modelling scenarios alternated bed morphology and the simulation of turbulence, using detached eddy simulation (DES), to differentiate the influence of bedform-generated turbulence relative to that of turbulence generated from the channel bed. The bedform generated a turbulent wake that was composed of eddies with significant anisotropic properties. The eddies and, to a lesser degree, turbulence arising from velocity shear at the bed substantially reduced settling velocities relative to the settling velocities predicted in the absence of turbulence. The eddies tended to advect sediment particles in their primary direction, diffuse particles throughout the flow column, and reduced settling likely due to production of a positively skewed vertical-velocity fluctuation distribution. Study results suggest that the bedform wake has a significant impact on particle-settling behaviour (up to a 50% reduction in settling velocity) at a scale capable of modulating local suspended transport rates and bedform dynamics.

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Computer-assisted paleocurrent determination from trough cross-stratification

Suresh

1990

Computers & Geosciences

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Leeside Sediment Fallout Patterns and the Stability of Angular Bedforms

Cited by 6 publications

References 0 publications

Stratigraphy, sedimentology, and paleontology of the Lower Eocene San Jose Formation in the central portion of the San Juan Basin, northwest New Mexico

Stratigraphy, sedimentology, and paleontology of the Lower Eocene San Jose Formation in the central portion of the San Juan Basin, northwest New Mexico

Sand settling through bedform‐generated turbulence in rivers

Computer-assisted paleocurrent determination from trough cross-stratification

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