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Location of main features in study area offshore from northwest Africa.a, The Agadir canyon (stippled), Agadir basin, Seine and Madeira abyssal plains; channel network between Agadir basin and Madeira abyssal plain (grey shade); Canary debris flow (CDF; shaded brown); debris avalanches (DA) from Canary Islands1, 2, 3, 4, 5, 6, 7. The path of the flow that deposited bed 5 is shown by arrows. Box indicates area shown in c. Bathymetric contours spaced at 500 m intervals. b, Change in seafloor gradient (red line) plotted against distance along flow path. c, Location of cores (filled circles), debris-flow deposit (debrite), and the location of the cross-sections shown in  (28–48) and in Supplementary Figs 4 and 5 (the three bold black lines) in Agadir basin.

Location of main features in study area offshore from northwest Africa.a, The Agadir canyon (stippled), Agadir basin, Seine and Madeira abyssal plains; channel network between Agadir basin and Madeira abyssal plain (grey shade); Canary debris flow (CDF; shaded brown); debris avalanches (DA) from Canary Islands1, 2, 3, 4, 5, 6, 7. The path of the flow that deposited bed 5 is shown by arrows. Box indicates area shown in c. Bathymetric contours spaced at 500 m intervals. b, Change in seafloor gradient (red line) plotted against distance along flow path. c, Location of cores (filled circles), debris-flow deposit (debrite), and the location of the cross-sections shown in (28–48) and in Supplementary Figs 4 and 5 (the three bold black lines) in Agadir basin.

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Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass...

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... flow deposits were correlated between cores using sand-fraction com- position, the ratio of coccolith species within mud, magnetic susceptibility, colour, thickness, and relative position of layers within the core 3,6 (for example, Supplementary Fig. 1). Ratios of coccolith nannofossil species within hemipela- gic mud were used to date the flows 2-6 , together with an oxygen isotope stra- tigraphy. ...

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... All rights reserved Settling velocities in numerical models of the kinematics of sediment-laden flows should therefore account for the hindered settling effect more often to avert under predictions of deposit runout distances. Conversely, the results of this study imply that the strong hindered settling effect, even at low suspended sediment concentrations and particularly for fine, non-cohesive sediment, helps to explain the high efficiency of bottom-hugging sediment gravity flows in the deep-marine environment, and the long distance of transport of their sediment load (Talling et al., 2007). The strong hindered settling effect thus helps to maintain the main driving force of sediment gravity flows, which is the density difference between the flow and the ambient water. ...
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A revision of the popular equation of Richardson and Zaki (1954a, Transactions of the Institute of Chemical Engineering, 32, 35–53) for the hindered settling of suspensions of non‐cohesive particles in fluids is proposed, based on 548 datasets from a broad range of scientific disciplines. The new hindered settling equation enables predictions of settling velocity for a wide range of particle sizes and densities, and liquid densities and viscosities, but with a focus on sediment particles in water. The analysis of the relationship between hindered settling velocity and particle size presented here shows that the hindered settling effect increases as the particle size decreases, e.g., a 50% reduction in settling velocity is reached for 0.025 mm silt and 4 mm pebbles at particle concentrations of 13% and 25%, respectively. Moreover, hindered settling starts to influence the settling behaviour of sediment particles at volumetric concentrations of merely a few percent. For example, the particle settling velocity in flows that carry 5% silt is reduced by at least 22%. These observations suggest that hindered settling greatly increases the efficiency of natural flows to transport sediment particles, but also particulate carbon and pollutants, such as plastics, over large distances.
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Chapter
One of the most important topics still to be clarified regarding the sedimentology of the Yanchang Formation in the Ordos Basin is the occurrence of hyperpycnites. The present contribution shows convincingly that hyperpycnites are well developed in Oil Member 7 of the formation. They extend from distributary estuaries into the deep lake and have intercalations of dark shales and tuffs, and they coexist with debrites and turbidites as a result of the progradation of subaqueous fans. The study makes clear that the origination of hyperpycnal flows was controlled mainly by episodic tectonic movements and the humid climate. The hyperpycnites have important implications for the possible presence of unconventional petroleum reservoirs because the flows supplied not only large amounts of coarse grains and organic material to the deep-water fine-grained central lake sediments, but also resulted in a high total organic carbon content. The coarse-grained layers serve as reservoir rocks, whereas the fine-grained layers form seals.
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