Cyclic steps and related supercritical bedforms: Building blocks of deep-water depositional systems, western North America

Covault, Jacob A.; Kostic, Svetlana; Paull, C. K.; Sylvester, Zoltán; Fildani, Andrea

doi:10.1016/j.margeo.2016.12.009

Cited by 103 publications

(98 citation statements)

References 69 publications

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“…This is likely caused by the loss of confinement in the CLTZ environment that allows the flow to distribute sediment across a wider surface, reducing bed thickness and thinning rates. The narrow distribution of high net‐to‐gross found within the CLTZs supports the erosion documented in these deposits (Carvajal et al, ; Covault et al, ; Wynn et al, ) and suggests that mud is being bypassed and/or eroded (Figure ).…”

Section: Results and Analysis Of Event‐bed Geometriessupporting

confidence: 60%

Quantification of the bed‐scale architecture of submarine depositional environments

Fryer

Jobe

2019

The Depositional Record

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Submarine channel and fan deposits form the largest sediment accumulations on Earth and host significant reservoirs for hydrocarbons. While many studies of ancient fan deposits describe architectural variability along 2D transects (e.g. axis‐to‐fringe, proximal‐to‐distal), these relationships are often qualitative and are rarely quantified at the event‐bed scale. In order to enable quantitative comparison of the fine‐scale architecture of submarine depositional environments, 56 bed‐scale outcrop correlation panels from five broadly categorized environments (channel, levee, lobe, channel‐lobe transition zone, CLTZ and basin plain) were digitized. Measured architectural parameters (bed thickness, bed thinning rates, lateral correlation distance, net‐to‐gross) provide a large (n = 28,525) and statistically robust framework to compare event‐bed architectures within and between environments. “Thinning rate” data (i.e. the lateral rate of change of bed thickness) clearly differentiate deposits from different submarine depositional environments, helping to quantify generally accepted models for proximal‐to‐distal evolution of stratigraphic architecture. The thinning rates of sandstone beds and mudstone‐dominated intervals vary predictably between environments. For example, the highest sandstone thinning rates occur in channel deposits (0.2–6 cm/m; P10 and P90 values here and below) and decrease to lobe (0.1–1.6 cm/m), CLTZ (0.2–0.9 cm/m), levee (0.0024–0.078 cm/m) and basin‐plain deposits (0.000017–0.0054 cm/m). These quantitative relationships provide valuable insights for downslope flow evolution and the construction of stratigraphic architecture in submarine settings. Due to intra‐environment variability, net‐to‐gross is highly variable and thus (when considered alone) is not a diagnostic indicator of depositional environment. Submarine lobe deposits show the most variability in event bed thickness, thinning rate and net‐to‐gross, likely due to the inherent facies variability and differing boundary conditions. To explore this variability, lobe deposits were sub‐classified based on position (proximal, distal) and effective confinement (unconfined, semiconfined, confined) to provide a more detailed sub‐environment analysis. Unconfined lobe deposits show a proximal‐to‐distal increase in sandstone thickness and decrease in mudstone thickness, supporting conceptual models. Confined lobe deposits have thicker sandstone and mudstone beds and lower net‐to‐gross values as compared to unconfined and semiconfined lobes, supporting a sediment trapping mechanism by confinement. These quantified bed‐scale parameter comparisons enable the recognition of architectural similarities and differences within and between environments, demonstrating the need for more quantitative studies of bed‐scale heterogeneity. The results from this study are immediately applicable to parameterizing forward stratigraphic models, constraining property distribution in reservoir models, and probabilistic determination of depositional environment ...

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Section: Results and Analysis Of Event‐bed Geometriessupporting

confidence: 60%

Quantification of the bed‐scale architecture of submarine depositional environments

Fryer

Jobe

2019

The Depositional Record

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“…Coarse-grained sediment waves and bars have also been described from studies of the modern seafloor (Piper et al, 1985;Wynn et al, 2002;Paull et al, 2011;Gamberi et al, 2013;Kostic, 2014;Covault et al, 2017;Hage et al, 2018). These are typically larger than the bedforms described here, with wavelengths on the order of tens to hundreds of metres and heights from 1 to 10 m. These features are generally interpreted as antidunes or cyclic-steps formed under Froudesupercritical flow Postma and Cartigny, 2014).…”

Section: Comparison To Other Overbank Sand Bars and Bedformsmentioning

confidence: 57%

Supercritical flows overspilling from bypass‐dominated submarine channels and the development of overbank bedforms

McArthur

Kane²,

Bozetti

et al. 2019

The Depositional Record

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Overbank deposits of submarine channels are typically thin-bedded, fine-grained and predominantly characterized by a series of sedimentary structures interpreted to record a relatively simple history of waning flow. Here, a new type of bedform indicative of Froude-supercritical flow is reported from successions of thin-bedded turbidites interpreted as channel overbank deposits in the Upper Cretaceous Rosario Formation, Baja California, Mexico. A link is demonstrated between the development of overbank deposits in the form of depositional terraces or internal levees and contemporaneously active sediment transport, bypass and deposition of coarsergrained material in a channel. The overbank bedforms overlie an erosion surface and contain a suite of sedimentary structures indicative of initially Froude-supercritical flow conditions and a progressive waning of flow strength. In some cases, a stacked repetition of facies is interpreted to record a rejuvenation of flow energy. The characteristic sedimentary sequence observed is as follows: (a) long wavelength, low amplitude erosional surface with superimposed scours; (b) antidune backsets; (c) upper stage plane-parallel lamination; (d) subcritical climbing ripples; (e) supercritical climbing ripples; (f) lower stage planar laminated tops; (g) a sharp upper surface.The exact vertical sequence of sedimentary structures encountered varies depending on the point of observation with respect to the bedform crest and distance from the parent channel. The recognition of these distinctive bedforms allows for interpretation of sediment bypass and proximity to a channel thalweg. These bedforms have not hitherto been described and provide a further example of the range of flow processes operating in submarine channel-levee systems, which aids depositional environment interpretation in both subsurface and outcrop studies. K E Y W O R D SBaja California, deep-marine, Rosario Formation, slope channels, turbidity currents, Upper Cretaceous |McARTHUR eT Al.

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“…Transportational cyclic steps in open‐channel flows, which are neither net‐erosive nor net‐depositional (Parker & Izumi, ), have been modelled experimentally in flume tanks (Taki & Parker, ; Cartigny et al ., ) and modelled numerically using depth‐averaged models (Fagherazzi & Sun, ). Cyclic steps in subaqueous settings have been modelled in flume experiments (Spinewine et al ., ) and with depth‐averaging numerical models (Fildani et al ., ; Kostic & Parker, ; Kostic et al ., ; Cartigny et al ., ; Kostic, , ; Covault et al ., , ). These studies have provided valuable insight into the development and mechanics of cyclic steps, by exploring how average flow velocity, sediment concentration and flow thickness vary over the length of the bedform wavelength (Fig.…”

Section: Introductionmentioning

confidence: 99%

Morphodynamics and depositional signature of low‐aggradation cyclic steps: New insights from a depth‐resolved numerical model

et al. 2017

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Bedforms related to Froude‐supercritical flow, such as cyclic steps, are increasingly frequently observed in contemporary fluvial and marine sedimentary systems. However, the number of observations of sedimentary structures formed by supercritical‐flow bedforms remains limited. The low number of observations might be caused by poor constraints on criteria to recognize these associated deposits. This study provides a detailed quantification on the mechanics of a fluvial cyclic step system, and their depositional signature. A computational fluid‐dynamics model is employed to acquire a depth‐resolved image of a cyclic step system. New insights into the mechanics of cyclic steps shows that: (i) the hydraulic jump is, in itself, erosional; (ii) there are periods over which the flow is supercritical throughout and there is no hydraulic jump, which plays a significant role in the morphodynamic behaviour of cyclic steps; and (iii) that the depositional signature of cyclic steps varies with rate of aggradation. Previous work has shown that strongly aggradational cyclic steps, where most of the deposited sediment is not reworked, create packages of backsets, bound upstream and downstream by erosive surfaces. Here, the modelling work is focussed on less aggradational conditions and more transportational systems. The depositional signature in such systems is dominated by an amalgamation of concave‐up erosional surfaces and low‐angle foresets and backsets creating lenticular bodies. The difference between highly aggradational cyclic steps and low‐aggradation steps can be visible in outcrop both by the amount of erosional surfaces, as well as the ratio of foreset to backset, with backsets being indicative of more aggradation.

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Cyclic steps and related supercritical bedforms: Building blocks of deep-water depositional systems, western North America

Cited by 103 publications

References 69 publications

Quantification of the bed‐scale architecture of submarine depositional environments

Quantification of the bed‐scale architecture of submarine depositional environments

Supercritical flows overspilling from bypass‐dominated submarine channels and the development of overbank bedforms

Morphodynamics and depositional signature of low‐aggradation cyclic steps: New insights from a depth‐resolved numerical model

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