North Atlantic contourite sand channels

Akhmetzhanov, A.; Kenyon, Neil H.; Habgood, E.; Mollen, A. S. Van Der; Nielsen, Tove; Ivanov, M.K.; Shashkin, Pavel

doi:10.1144/gsl.sp.2007.276.01.02

Cited by 17 publications

(7 citation statements)

References 44 publications

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“…Some work has been carried out on the adjacent shallow water sediments on the continental shelf (Nelson et al ., , ; Maldonado et al ., ; Lobo et al ., ), the adjacent channel and sediment wave sectors (Akhmetzhanov et al ., ; Hanquiez et al ., ), as well as within the Strait of Gibraltar (Kelling & Stanley, ; Esteras et al ., ). Focused studies on the region most proximal to the Strait of Gibraltar, however, remain limited to a very few.…”

Section: Gulf Of Cadiz: Geological and Oceanographic Settingmentioning

confidence: 99%

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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Section: Gulf Of Cadiz: Geological and Oceanographic Settingmentioning

confidence: 99%

Textural characteristics and facies of sand‐rich contourite depositional systems

et al. 2018

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“…Contourite drifts formed by oceanographic contour currents also display a strong influence of Coriolis forces [34]. Akhmetzhanov et al [35] document a number of striking examples where there are lateral asymmetries of erosion and deposition driven by saline gravity currents in the Gulf of Cadiz and near the Faeroe Bank Channel. In most of the sandy channels that they studied, erosion preferentially occurred on the right-hand side of the mean flow direction, and deposition to the left-hand side, consistent with the shift in velocity maxima sketched in figure 4d.…”

Section: Field Observations Of Sinuous Channel-levee Systemsmentioning

confidence: 99%

The possible role of Coriolis forces in structuring large-scale sinuous patterns of submarine channel–levee systems

Wells

Cossu

2013

Phil. Trans. R. Soc. A.

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Submarine channel–levee systems are among the largest sedimentary structures on the ocean floor. These channels have a sinuous pattern and are the main conduits for turbidity currents to transport sediment to the deep ocean. Recent observations have shown that their sinuosity decreases strongly with latitude, with high-latitude channels being much straighter than similar channels near the Equator. One possible explanation is that Coriolis forces laterally deflect turbidity currents so that at high Northern latitudes both the density interface and the downstream velocity maximum are deflected to the right-hand side of the channel (looking downstream). The shift in the velocity field can change the locations of erosion and deposition and introduce an asymmetry between left- and right-turning bends. The importance of Coriolis forces is defined by two Rossby numbers, Ro W = U / Wf and Ro R = U / Rf , where U is the mean downstream velocity, W is the width of the channel, R is the radius of curvature and f is the Coriolis parameter. In a bending channel, the density interface is flat when Ro R ∼−1, and Coriolis forces start to shift the velocity maximum when | Ro W |<5. We review recent experimental and field observations and describe how Coriolis forces could lead to straighter channels at high latitudes.

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“…Consequently the interpreted seismic survey reveals that a considerable part of channel strata is composed by mass‐wasted material distinctly reworked by bottom currents, but that aggradation of sediment occurs in the channel axis in parallel with the core of contourite drifts (Figs 3 and 11). This also contrast with the location of coarse‐grained sediment in the Rockall Trough and Southwest Iberia (Akhmetzhanov et al . 2007), known to occur in axial regions of contourite channels.…”

Section: Discussionmentioning

confidence: 61%

“…Comparisons among the interpreted seismic data an 2‐D seismic data from Akhmetzhanov et al . (2007), and the depositional models of Viana et al .…”

Section: Morphometric Analysismentioning

confidence: 99%

A 3-D morphometric analysis of erosional features in a contourite drift from offshore SE Brazil

Alves¹

2010

Geophysical Journal International

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S U M M A R YA contourite drift from offshore Brazil is mapped in detail and investigated using state-of-theart 3-D seismic data. The aim was to review the relevance of erosional features in contourite drifts accumulated on continental slopes. Topographically confined by growing salt diapirs, the mapped contourite ridge is limited by two erosional features, a contourite moat and a turbidite channel, showing multiple slide scars on it flanks. Associated with the latter features are thick accumulations of high-amplitude strata, probably comprising sandy/silty sediment of Miocene to Holocene age. The erosional unconformities are mostly observed in a region averaging 3.75 km away from the axes of a channel and a moat, whose deposits interfinger with continuous strata in central parts of the contourite drift. The multiple unconformities observed are mostly related to slide scars and local erosion on the flanks of the drift. This work demonstrates that the existence of widespread unconformities within contourite drifts on continental slopes: (1) may not be as prominent as often documented, (2) are often diachronic and interfinger with correlative hiatuses or aggraded strata in axial regions of contourite drifts. Although less widespread than regional, or ocean-scale unconformities, these diachronous features result in significant hiatuses within contourite drifts and are, therefore, potentially mappable as relevant (regional-scale) unconformities on 2-D/3-D seismic data. Thus, without a full 3-D morphometric analysis of contourite drifts, significant errors may occur when estimating major changes in the dynamics of principal geostrophic currents based on single-site core data, or on direct correlations between stratigraphic surfaces of distinct contourite bodies.

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North Atlantic contourite sand channels

Cited by 17 publications

References 44 publications

Textural characteristics and facies of sand‐rich contourite depositional systems

Textural characteristics and facies of sand‐rich contourite depositional systems

The possible role of Coriolis forces in structuring large-scale sinuous patterns of submarine channel–levee systems

A 3-D morphometric analysis of erosional features in a contourite drift from offshore SE Brazil

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