Froude supercritical flow processes and sedimentary structures: New insights from experiments with a wide range of grain sizes
Ono, Kenya; Plink-Björklund, Piret; Eggenhuisen, Joris T.; Cartigny, Matthieu J.B.
(2021) Sedimentology, volume 68, issue 4, pp. 1328 - 1357
(Article)
Abstract
Recognition of Froude supercritical flow deposits in environments that range from rivers to the ocean floor has triggered a surge of interest in their flow processes, bedforms and sedimentary structures. Interpreting these supercritical flow deposits is especially important because they often represent the most powerful flows in the geological record.
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Insights from experiments are key to reconstruct palaeo-flow processes from the sedimentary record. So far, all experimentally produced supercritical flow deposits are of a narrow grain-size range (fine to medium sand), while deposits in the rock record often consist of a much wider grain-size distribution. This paper presents results of supercritical-flow experiments with a grain-size distribution from clay to gravel. These experiments show that cyclic step instabilities can produce more complex and a larger variety of sedimentary structures than the previously suggested backsets and ‘scour and fill’ structures. The sedimentary structures are composed of irregular lenses, mounds and wedges with backsets and foresets, as well as undulating planar to low-angle upstream and downstream dipping laminae. The experiments also demonstrate that the Froude number is not the only control on the sedimentary structures formed by supercritical-flow processes. Additional controls include the size and migration rate of the hydraulic jump and the substrate cohesion. This study further demonstrates that Froude supercritical flow promotes suspension transport of all grain sizes, including gravels. Surprisingly, it was observed that all grain sizes were rapidly deposited just downstream of hydraulic jumps, including silt and clay. These results expand the range of dynamic mud deposition into supercritical-flow conditions, where local transient shear stress reduction rather than overall flow waning conditions allow for deposition of fines. Comparison of the experimental deposits with outcrop datasets composed of conglomerates to mudstones, shows significant similarities and highlights the role of hydraulic jumps, rather than overall flow condition changes, in producing lithologically and geometrically complex stratigraphy.
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Keywords: Cyclic steps, foreset and backset, Froude supercritical flow deposits, gravel lenses, scour and fill, sedimentary structure hierarchy, upward fining stratigraphy, Taverne, Geology, Stratigraphy
ISSN: 0037-0746
Publisher: Wiley Online Library
Note: Funding Information: This work was funded by the INPEX Corporation and the RioMAR Consortium (BHP Billiton, Chevron, Devon, Eni, ExxonMobil, Petrom, Shell, Statoil, Wintershall and Woodside). Thony van der Gon‐Netscher is acknowledged for technical support in the Eurotank Flume Laboratory, which made this work possible. Regarding the grain‐size analysis, João Alexandre is thanked for the technical discussion and Coen Mulder is thanked for the technical assistance. M.J.B. Cartigny is funded through a Royal Society Research Fellowship. We also thank Sedimentology reviewers Jörg Lang, Jean Francois Ghienne, and the Associate Editor Alexandre Normandeau for constructive comments. Funding Information: This work was funded by the INPEX Corporation and the RioMAR Consortium (BHP Billiton, Chevron, Devon, Eni, ExxonMobil, Petrom, Shell, Statoil, Wintershall and Woodside). Thony van der Gon-Netscher is acknowledged for technical support in the Eurotank Flume Laboratory, which made this work possible. Regarding the grain-size analysis, Jo?o Alexandre is thanked for the technical discussion and Coen Mulder is thanked for the technical assistance. M.J.B. Cartigny is funded through a Royal Society Research Fellowship. We also thank Sedimentology reviewers J?rg Lang, Jean Francois Ghienne, and the Associate Editor Alexandre Normandeau for constructive comments. Publisher Copyright: © 2019 The Authors. Sedimentology © 2019 International Association of Sedimentologists
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