Contourite Drifts and Associated Bedforms

Esentia, Ibimina Pepple; Stow, Dorrik; Smillie, Zeinab

doi:10.1007/978-3-319-57852-1_16

Cited by 14 publications

(14 citation statements)

References 68 publications

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“…There are at least three different bottom current types that can be recognised as operating in deep-water settings [6,57,58], including (a) wind-driven bottom currents, (b) thermohaline bottom currents and (c) deep-water tidal bottom currents, both barotropic and baroclinic. Internal waves (including baroclinic tides) oscillate along the interface between two water masses of different densities.…”

Section: Bottom Currentsmentioning

confidence: 99%

Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites

2020

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The distinction between turbidites, contourites and hemipelagites in modern and ancient deep-water systems has long been a matter of controversy. This is partly because the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap. In addition, the three facies types commonly occur within interbedded sequences of continental margin deposits. The nature of these end-member processes and their physical parameters are becoming much better known and are summarised here briefly. Good progress has also been made over the past decade in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics are summarised here in terms of standard facies models and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. A three-scale approach to distinction for all deep-water facies types should be attempted wherever possible, including large-scale (oceanographic and tectonic setting), regional-scale (architecture and association) and small-scale (sediment facies) observations.

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Section: Bottom Currentsmentioning

confidence: 99%

Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites

2020

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“…Contourites are those sediments deposited or substantially reworked by bottom currents (Stow et al ., ). In areas with long‐term deposition, they can construct large mounded drifts (contourite drifts) in a variety of shapes and sizes, which may be elongated up to several hundreds of kilometres along the continental margin (Rebesco et al ., ; Esentia et al ., ). The characteristics of the fine‐grained sediments collected from these mounded drifts are now well‐constrained thanks to early facies and textural studies (Stow & Lovell, ; Gonthier et al ., ; Stow & Piper, ).…”

Section: Introductionmentioning

confidence: 97%

Textural characteristics and facies of sand‐rich contourite depositional systems

et al. 2018

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This work presents a detailed study of CONTOURIBER and Integrated Ocean Drilling Program 339 sediment data targeting sand-rich contourites in the Eastern Gulf of Cadiz. All of the collected sediments are interpreted as contourites (deposited or reworked by bottom currents) on the basis of oceanographic setting, seismic and morphometric features, and facies characteristics. A variety of sandy and associated facies are found across the study area including: (i) bioturbated muddy contourites; (ii) mottled silty contourites; (iii) very fine mottled and fine-grained bioturbated sandy contourites; (iv) massive and laminated sandy contourites; and (v) coarse sandy/ gravel contourites. The thickest sands occur within contourite channels and there is a marked reduction in sand content laterally away from channels. Complementary to the facies descriptions, grain-size analysis of 675 samples reveals distinctive trends in textural properties linked to depositional processes under the action of bottom currents. The finest muddy contourites (<20 lm) show normal grain-size distributions, poor to very poor sorting, and zero or low skewness. These are deposited by settling from weak bottom currents with a fine suspension load. Muddy to fine sandy contourites (20 to 200 lm) trend towards better sorting and initially finer and then coarser skew. These are typical depositional trends for contourites. As current velocity and carrying capacity increase, more of the finest fraction remains in suspension and bedload transport becomes more important. Clean sandy contourites (>200 lm) are better sorted. They result from the action of dominant bedload transport and winnowing at high current speeds. The results highlight the importance of bottom current velocity, sediment supply and bioturbational mixing in controlling contourite facies. Despite growing interest in their hydrocarbon exploration potential, contourite sands have remained poorly understood. This research therefore has important implications for developing current understanding of these deposits and aiding the correct interpretation of deep marine sands and depositional processes. 2223

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“…We therefore conclude that locally in the Holocene and perhaps during other full interglacials near bottom currents were strong enough to modify the sea floor. On the other hand, clear current scour moats or other features typically associated with prolonged formation of contourite drifts (van Rooij et al, 2007;Esentia et al, 2018) were Figure 8C, including Desmophyllum dianthus coral graveyard. See Figure 9B for surficial geology layer, and see Figure 7C for underlying ROV-derived bathymetry below (D).…”

Section: Mound Form Distribution and Probable Originmentioning

confidence: 99%

“…The range of biogenic and abiogenic processes responsible for mound formation is considerable. Some examples of the more common abiotic processes of mound formation, include tectonism and block-faulting (e.g., Laughton et al, 1972;Sibuet, 1992;Moscardelli et al, 2013, reviewed by Cormier andSloan, 2018); magmatic volcanism (e.g., Wiles et al, 2014, reviewed by Casalbore, 2018, and diapirism (e.g., Laughton et al, 1972), often associated with rifting or failed rifts; salt diapirs (e.g., Laughton et al, 1972;Parson et al, 1984), mud volcanoes and similar structures related to fluid escape (e.g., Barrett et al, 1988;Bolton et al, 1988;Enachescu, 2004;Burton-Ferguson et al, 2006, reviewed by Mazzini andEtiope, 2017); cold-seeps and authigenic carbonate precipitation (reviewed by Ceramicola et al, 2018); some types of contourite drifts (reviewed by Esentia et al, 2018) and submerged subaerial erosion features such as karst (Hart, 1977;Parson et al, 1984;Dronov, 1993;Immenhauser and Rameil, 2011;Taviani et al, 2012). Biogenic mounds in the deep sea include, a variety of types of biogenic carbonate mound formation including cold-water coral reefs and mounds (e.g., Hovland et al, 1994;Huvenne et al, 2003;Roberts et al, 2003, reviewed by Lo Iacono et al, 2018, and siliciclasticdominated sponge reefs (e.g., Conway et al, 2005;Howell et al, 2016) and microbial mounds (e.g., Riding and Awramik, 2000).…”

Section: Introductionmentioning

confidence: 99%

Enigmatic Deep-Water Mounds on the Orphan Knoll, Labrador Sea

et al. 2020

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Deep-sea mounds can have a variety of origins and may provide hard-substrate features in depths that are normally dominated by mud. Orphan Knoll, a 2 km high bedrock horst off northeast Newfoundland, hosts more than 200 mounds, or mound complexes, of unknown composition, in water depths of 1720-2500 m. Most mounds are 10-600 m high, with average mound height 187 m, and 1-3 km wide. The study objective was to characterize the size, shape, orientation, and composition of the enigmatic Orphan Knoll mounds, in order to determine their age and origin. Archival ship-based side-scan sonar, multibeam sonar, airgun, high-resolution sparker and 3.5 kHz acoustic sub-bottom profiling, and newly acquired ship-based multibeam sonar, video transects by remotely operated vehicle (ROV), rock samples, and near-bottom multibeam sonar data were analyzed. Four mounds were studied during two ROV dives. Archival sidescan sonar data show > 200 mounds. Sparker profiles show that the mound crests are covered by condensed stratified Quaternary sediment and airgun seismic data show faults reaching near the seafloor. New multibeam sonar data show mounds are dominantly conical to elliptical in shape, but without preferred orientation or alignment. Remotely operated vehicle (ROV) transects and near-bottom multibeam showed that three mounds were rounded and symmetrically arranged, while a fourth was more asymmetrical, with steep faces on the southwestern and southeastern flanks, where finely bedded to massive sedimentary bedrock outcropped dipping 15-45 • SW. Rock samples from the mounds include Eocene calcareous ooze and mid-Miocene bedded pelagic limestone. Thick ferromanganese crusts were found on many surfaces, obscuring possible outcrops from physical sampling. Polymetallic nodules were found on the slope of one mound. Ice-rafted detritus, including igneous and metamorphic rocks and Paleozoic limestone and dolostone, was common in the sediments immediately surrounding the mounds. Quaternary sub-fossil solitary scleractinian corals accumulated over a span of at least 0.18 Ma at the base of one mound. The presence of uplifted condensed Eocene-Miocene rocks on the mounds and faulting in seismic profiles suggest uplift during Frontiers in Marine Science | www.frontiersin.org 1 January 2020 | Volume 6 | Article 744 Meredyk et al. Orphan Knoll Mounds reactivation of old rift-related faults during the Neogene, with seabed mass wasting creating residual mounds, which were then draped by Quaternary proglacial muds. Sculpting of hemipelagic Quaternary sediment by bottom currents probably contributed to mound morphology.

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Contourite Drifts and Associated Bedforms

Cited by 14 publications

References 68 publications

Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites

Distinguishing between Deep-Water Sediment Facies: Turbidites, Contourites and Hemipelagites

Textural characteristics and facies of sand‐rich contourite depositional systems

Enigmatic Deep-Water Mounds on the Orphan Knoll, Labrador Sea

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