Experimental erosion of North Pacific red clay

doi:10.1016/0025-3227(74)90044-9

Marine Geology

Volume 17, Issue 1, August 1974, Pages M51-M60

https://doi.org/10.1016/0025-3227(74)90044-9 Get rights and content

Abstract

Threshold erosion velocities for plane beds of pelagic red clay were established by ten experimental runs in a recirculating salt-water flume. Even with water content as high as 82%, observable erosion of the sediment required a velocity equivalent to a bottom current of about 30 cm/sec. Sediment beds to which manganese nodules were added, simulating an abyssal nodule field, were eroded by much slower flows (e.g., by the equivalent of a 12 cm/sec current at 84% water content). These experimentally derived values may be useful approximations of critical current speeds on the deep-sea floor, though very slow erosion may well occur there at lower speeds, especially in the presence of benthic fauna.

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Furthermore, limited studies have focused on the erosion rate of fine-grained marine sediments that are of calcareous nature similar to the ones investigated in this study. The few studies investigating these type of sediments such as calcareous ooze (Southard et al., 1971) and clay (Lonsdale and Southard, 1974) focus mostly on the initiation of motion. Hence, the relationship between the erosion rate of fine-grained marine sediment (in particular calcareous NWS sediments) and their basic soil characteristics is poorly understood.
Laboratory experiments have been carried out to investigate the erosion behaviour of a number of marine sediments which were reconstituted and sieved in various ways to ensure a large variation in soil properties such as (i) particle size distribution (including median grain size and fines content), (ii) bulk density, and (iii) hydraulic permeability. Based on the experimental results, it was found that for finer marine sediments the erosion rate at a given shear stress was sensitive to changes in these soil properties. No unique relationship was found between changes in the erosion rate and changes in the bulk density or fines content. More specifically, we find that the erosion rate at a given shear stress reduces with increases in density and fines content, but by an amount that is different for different sediments. In contrast, we show that there appears to be a unique relationship between permeability and erosion rate, such that permeability may be used to predict the erosion rate for the marine sediments at any density. By reinterpreting existing experimental results in the literature, we find that this same relationship between permeability and erosion rate is apparent for quartz sediments. We propose an empirical relationship, which fits well the erosion rate behaviour of finer sediments close to the threshold shear stress.
Performance investigation of micro- and nano-sized particle erosion in a 90° elbow using an ANFIS model
2015, Powder Technology
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However, abrupt diversion in the flow direction in a 90-degree elbow would cause great change in the motion and distribution of solid particles, thus leading to considerable difference in E–C behavior at different locations of the elbow [1]. A large number of experimental investigations have been performed regarding the topic of erosion–corrosion in the past years such as studies done by Lonsdale and Southard [2], Gulden [3], and Saravanan, Surappa and Pramila Bai [4]. However, numerical techniques, with all the recent advances, were not successful in producing results with reasonable accuracy.
The accuracy of soft computing technique was employed to predict the performance of micro- and nano-sized particle erosion in a 3-D 90° elbow. The process, capable of simulating the total and maximum erosion rate with adaptive neuro-fuzzy inference system (ANFIS), was constructed. The developed ANFIS network was with three neurons in the input layer, and one neuron in the output layer. The inputs included particle velocity, particle diameter, and volume fraction of the copper particles. The size of these particles was selected in the range of 10 nm to 100 μm. Numerical simulations have been performed with velocities ranging from 5 to 20 m/s and for volume fractions of up to 4%. The governing differential equations have been discretized by the finite volume method for ANFIS training data extraction. The ANFIS results were compared with the CFD results using root-mean-square error (RMSE) and coefficient of determination (R²). The CFD results show that an improvement in predictive accuracy and capability of generalization can be achieved by the ANFIS approach. The following characteristics were obtained: ANFIS model can be used to forecast the maximum and total erosion rate with high reliability and therefore can be applied for practical purposes.
Geomorphological and geochemical evidence (<sup>230</sup>Th anomalies) for cross-equatorial currents in the central Pacific
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The orientations and morphologies of sedimentary bedforms tend to reflect the more extreme currents capable of re-suspending particles or influencing patterns of non-deposition and deposition, hence it is not surprising that the furrow orientations bear little relation to the expected eastward geostrophic current (Reid, 1997). That the furrows appear over the carbonate ooze despite the low current speeds and occur less commonly in the carbonate poor area north of the Clipperton Fracture Zone may originate from a smaller threshold of erosion; Lonsdale and Southard (1974) found half or lower threshold velocities of carbonate ooze compared with red clay. The furrows lie oblique to the peak tidal currents in Fig. 8, which are strongest in the NW and SE quadrants, where they approach 3 cm s−1.
Shallow broad elongated sediment depressions and ridges are revealed in multibeam echo-sounder data collected over the carbonate ooze in the central equatorial Pacific. These features, otherwise called “furrows”, have orientations that appear locally distorted by seabed topography as expected of contour-trending currents but at regional scale typically cross contours at high angles. In places, complex patterns suggest that formative currents have a strong time-varying component. From direction indicators, the movement of bottom waters is north to south on average, though with some movement locally south to north. There is a modest 18° average change in orientation crossing from north to south of the equator, with features to the south oriented clockwise of those to the north. This is as expected for a partly developed bottom Ekman layer, with currents in the layer deflected by the Coriolis effect with opposing senses either side of the equator. The features are less prominent on and immediately south of the equator. We evaluated these observations along with reported ²³⁰Th accumulation rates in sediment cores, which are curiously enhanced along the equator, an observation that has been previously interpreted as suggesting transport of ²³⁰Th bound to particles to the equator.
Limited current meter and other data and physical oceanographic models help to explain these observations. Data from current meters 1° north of the equator show a highly asymmetric mesoscale eddy motion here, aligned with the furrows. Phase relationships between near-bed and upper ocean currents suggest an indirect coupling of upper-ocean eddies with the lower ocean. The bottom Ekman layer is predicted theoretically to thicken towards the equator. The resulting reduced bed shear stress may explain the ²³⁰Th deposition and more weakly developed furrows at the equator. Given evidence that equatorial accumulation rates of ²³⁰Th and extraterrestrial ³He both fluctuated over the Late Pleistocene, we explore how the ideas presented here could help to explain how the geochemical anomalies relate to physical oceanographic processes.
Reverse engineering mother nature - Shale sedimentology from an experimental perspective
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Citation Excerpt :
The classical studies by Hjulström (1955) and Sundborg (1956) showed that muds require larger current velocities for erosion than sands due to cohesive forces, and that, depending on the degree of consolidation, mud erosion may require current velocities of the same order of magnitude as those needed for the erosion and transport of gravel. Subsequent work by for example Parthenaides (1965), Southard et al. (1971), and Lonsdale and Southard (1974) confirmed these general relationships, and also showed that the subject of mud erosion is much more complex than what originally could have been expected (Migniot, 1968; Einsele et al., 1974). Ongoing research (e.g. Schieber et al., 2007a), as well as careful observations of the rock record (e.g. Macquaker and Gawthorpe, 1993; Schieber, 1999), clearly show that shales and mudstones were by no means all deposited by low energy processes and that they most likely record a much wider array of depositional parameters than currently appreciated.
Experimental study of the sedimentology of shales can take a variety of forms. At its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior, or one can manipulate mud in a tank or bucket to gain insights into its rheology. This approach was championed over a century ago by Sorby, and the insights gained can be quite profound. More recently, tank and settling tube experiments of animal-sediment interactions, compaction behavior, and sediment unmixing via re-suspension have proven to be highly informative in spite of their simplicity. Flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms. In flume experiments, however, it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments. Although much flume work on muds has been conducted by hydraulic engineers, the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different (though not mutually exclusive) products from such experiments. Engineers and hydrologists are commonly concerned with quantifying fluid flow properties, whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions. Recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand. Mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds. The latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water. There are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology.
Erodibility of pelagic carbonate ooze in the northeast Atlantic
2003, Journal of Experimental Marine Biology and Ecology
Shipboard erosion experiments were conducted on retrieved carbonate ooze sediments using the suction-stirring flume instrument of Gust and Muller [Gust, G., Muller, V., 1997. Interfacial hydrodynamics and entertainment functions of currently used erosion devices. Burt, N.T., et al. (Eds.) Cohesive Sediments. Wiley, Chichester, pp. 149–176] at two differing localities (site A, 3800 m water depth; site B, 1100 m water depth) in the eastern North Atlantic. Step-wise increases in bottom stress were used to sequentially erode the surface sediment layers. Surficial sediment layers at both sites are moderately resistant to fluid stress, with erosion rates during periods of subthreshold fluid stress of the order 10⁻³ kg m⁻² s⁻¹. Tidal flows in excess of ∼18 cm s⁻¹ at 1 m above the bottom would be necessary to induce any significant erosion. Seabed sediments of site A possess a higher erodibility in comparison to site B: significant erosion occurs at a lower applied friction velocity (u_*crit.=1.0–1.2 cm s⁻¹), time-averaged erosion rates are higher by ∼25% and ultimately nearly twice as much sediment is entrained into suspension at the end of the experiment. Site B sediment, for which u_*crit.=1.4–1.6 cm s⁻¹, is slightly finer texturally and slightly more compact. However, the presence of interlocking silica spicules from the benthic sponge species Pheronema and Hyalonema within the sediment matrix at site B is suggested as the principal reason for the differing erodibility. Direct observation of the size spectra of particles in suspension during active erosion suggests that low interfacial stresses (u_*∼0.2–0.4 cm s⁻¹) winnow clay clusters, complete and broken coccolith tests and small Foraminifera species from the sediment matrix, whilst progressively higher stresses entrain sequentially larger particles, including larger benthic and planktonic Foraminifera bodies. The supposition of Miller and Komar [Sedimentology 24 (1977) 709–721] that sand-size Foraminifera should be entrained by lower fluid stresses is not borne out, most probably due to cohesive forces associated with the sediment matrix. The implications of these experiments to natural resuspension events and bottom nepheloid layer formation are discussed.
Abyssal current influence on the southwest Bermuda Rise and surrounding region
1996, Marine Geology
Echograms (3.5 kHz) and bottom photographs reveal that the northward flowing Antarctic Bottom Water (AABW) has strongly influenced the modern depositional regime on the southwest Bermuda Rise. The spatial distribution of echo character types, the orientation and nature of current-controlled structures, and limited current meter data show that AABW flows with varying intensities along three primary pathways around and over the southwest Bermuda Rise. The main core of AABW flows clockwise around the eastern and western flanks of the southern Bermuda Rise, roughly parallel to the 5400 m isobath. This current bifurcates at 28°30′N, 69°W where a portion flows northeast over the southwest Bermuda Rise and the remainder continues north along the physiographic boundary between the southwest Bermuda Rise and the Hatteras Abyssal Plain. Secondary ribbons of AABW branch off the main core of AABW during its southerly journey along the southeastern Bermuda Rise, and flow west through fracture zones. Finally, a diffuse, northward flowing AABW sweeps the entire southwest Bermuda Rise.
A progression of current-controlled bedforms occurs beneath the main path of the AABW reflecting the spatially varying current velocities and sediment supply. The main core of AABW flows west through the narrow Vema Gap creating erosional furrows along the border between the southwest Bermuda Rise and the Vema Gap. Current velocities greater than 20 cm s⁻¹ are inferred from the bedforms in this region. Farther north along the southwestern edge of the Bermuda Rise, sediment waves become more prevalent. This transition from erosional to more depositional bedforms results from diminished current velocities (5–15 cm s⁻¹) and increased sediment supply. Although some of these bedforms on the southwest Bermuda Rise appear to be relict, their orientation is consistent with current meter data and abyssal current direction inferred from bottom photographs.

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^☆: Contribution of the Scripps Institution of Oceanography, New Series.

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Letter sectionExperimental erosion of North Pacific red clay☆

Abstract

Deep-Sea Res.

Erosional current marks of weakly cohesive mud beds

J. Sed. Petrol.

A literature review on erosion and deposition of cohesive soils

Photographing manganese nodules on the ocean floor

Oceanol. Int.

Petrology of Sedimentary Rocks

Sedimentary provinces of the North Pacific

Letter section
Experimental erosion of North Pacific red clay☆