Eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank (Celtic Sea)

Reynaud, Jean‐Yves; Tessier, Bernadette; Proust, Jean‐Noël; Dalrymple, Robert W.; Marsset, Tania; Batist, Marc De; Bourillet, Jean‐François; Lericolais, Gilles

doi:10.1046/j.1365-3091.1999.00244.x

Cited by 63 publications

(48 citation statements)

References 61 publications

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“…The sinuous pattern of the base of most of the sets in Unit 3 (Fig. 5) would then correspond to the migration path of the scour pits developed in front of the dunes (Reynaud et al, 1999c). Only the uppermost, deeply incised channel forms (Fig.…”

Section: Older Dynamicsmentioning

confidence: 95%

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The offshore Quaternary sediment bodies of the English Channel and its Western Approaches

Reynaud

Tessier

Auffret

et al. 2003

J Quaternary Science

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After a short review of present-day surficial sediments on the sea-floor of the English Channel and its Western Approaches, this paper summarises recent results on the Present-Quaternary sandy accumulations (tidal bank systems), based on sea-floor imaging, very high-resolution seismic surveys and a few piston cores. The English Channel, a typical funnel-shaped tidal shelf, is presently starved of terrigenous sediments. Most of mobile sediments at the sea-floor are autochthonous, either skeletal carbonates or siliciclastic sands reworked from old littoral deposits or incised valley fills. Three zones are considered: 1 the Central (and western Central) Channel, which is a bedload parting zone characterised by a pebbly lag making up the sole of the Quaternary sediments throughout the shelf area; 2 the Eastern Channel, a flood-dominated area characterised by medium to fine siliciclastic sands, mainly of aeolian periglacial origin; 3 the Western Approaches, an ebb-dominated area with a polygenic sediment cover characterised by coarse, carbonate-rich, gravelly to muddy sands of marine to glaciomarine origin, with a diachronous faunal content. These sediments are sourced by reworking of a former littoral barrier or incised valley fills. The seismic stratigraphy of Quaternary sediment accumulations (10-50 m) points to the predominant control of tidal dynamics, together with the general interplay between the Channel morphology and the sea-level story. The thickest deposits in the Eastern Channel and Western Approaches are built up into bank systems. Whereas the interpretation of the active Eastern Channel banks finds a general agreement, the 'moribund' banks in the Western Approaches (i.e. the southern Celtic Banks) remains under debate, owing to the lack of long cores. In our hypothesis, both systems were built up during the last post-glacial sea-level rise. The Celtic Banks would represent the tidal transgressive systems tract whereas the Eastern Channel banks correspond to the highstand systems tract. The architecture of both bank systems is studied from two examples, the Bassure de Baas bank in the Eastern Channel and the Kaiser Bank in the Western Approaches. Both examples show transgressive features. The Bassure de Baas exhibits from base to top: an estuarine mouth barrier, a wave erosion surface, a shoreface bank and finally a 'classic' tidal bank. By contrast, the Kaiser Bank consists of the offshore reworking of fully marine deposits. Its base would correspond to the amalgamation of the last glacial sea-level fall with a strong tidal ravinement surface. From base to top, the bank underwent: tidal-bar accretion, very large dune-field aggradation, perched-channels incision, storm erosion and deposition.This interpretation still needs to be modelled. For instance, the channels perched at the top of the Kaiser Bank point to an erosional peak, which could be related to a tidal resonance episode within the Western Approaches basin.

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Section: Older Dynamicsmentioning

confidence: 95%

“…5) must have been incised by flow processes, but not necessarily subaerially. They could represent tidal swatchways across the bank crest (Reynaud et al, 1999c).…”

Section: Older Dynamicsmentioning

confidence: 99%

The offshore Quaternary sediment bodies of the English Channel and its Western Approaches

Reynaud

Tessier

Auffret

et al. 2003

J Quaternary Science

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“…The coupling of the glacio-hydroisostatic rebound resulting from the influence of the British ice-sheet would have significantly enhanced the relative sea-level fall (Wingfield, 1995). In this perspective, the Celtic Banks could be tidal sand banks wholly reworked at the last post-glacial sea-level rise from former lowstand deposits (Bouysse et al, 1976;Pantin and Evans, 1984;Tessier, 1997;Marsset et al, 1999;Reynaud et al, 1999b). However, these hypotheses remain speculative as no samples of the banks core are available (Reynaud, 1996).…”

Section: The Sand Banksmentioning

confidence: 99%

“…Thus the cut-and-fill facies would correspond to stacked fluvial and deltaic channels and the flat, parallel-bedded facies would correspond either to estuarine bay or to marine sediments. Because of the absence of barrier remnants below the possible wave ravinement surface, Reynaud et al (1999b) favoured an estuarine interpretation for this latter facies. Whatever the case, the whole valley filling would represent sequences of deposits laid down during at least five cycles of relative sealevel variations.…”

Section: Detailed Architecture Of the Palaeovalley Infillmentioning

confidence: 99%

The ‘Fleuve Manche’: the submarine sedimentary features from the outer shelf to the deep‐sea fans

Bourillet

Reynaud

Baltzer

et al. 2003

J Quaternary Science

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Bathymetric, seismic and coring surveys have been carried out since the beginning of the 1990s on the outer shelf, the slope and the continental rise of the Western Approaches margin. Most of the sedimentary features studied belong to a sedimentary system built up since the Oligocene and fed by a palaeoriver, the 'Fleuve Manche' that flowed in the English Channel during eustatic lowstands. A geomorphological map details the spatial distributions of the palaeovalleys on the outer shelf, the drainage-basin-like organised canyons on the slope and the channel-levee and lobe complexes on the rise. The obvious channel-canyon connections and the assessed palaeovalley-canyon links demonstrate that the 'Fleuve Manche' was the single source for terrigeneous fluxes of the Armorican Deep Sea Fan when it was one of two sources of the Celtic Deep Sea Fan. Amongst parameters controlling the sedimentation, two factors play a major role. (i) Subsidence controlled the possibly Messinian riverine incision, the turbidite activities during lowstands, as well as marine infilling of the seawards part of the 'Fleuve Manche'. (ii) Quaternary sedimentary supplies were influenced by the melting ice-sheets and the connections with the onshore catchment basins.

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“…These elongated, parallel banks oriented at right angles to the shelf break are up to 35 m high, 5-7 km wide and 40-180 km long. The processes, which have controlled their deposition, are still uncertain: erosional remnants of lowstand nearshore deposits (Berné et al, 1998;Marsset et al, 1999) or totally reworked transgressive shelf deposits (Reynaud et al, 1999b). Whatever the case, these banks are located at the front of a former lowstand estuarine or deltaic system.…”

Section: Regional Settingmentioning

confidence: 99%

Physiography and recent sediment distribution of the Celtic Deep-Sea Fan, Bay of Biscay

et al. 2000

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The Celtic Deep-Sea Fan located in the northwestern part of the Bay of Biscay is a middle sized fan with a surface area of more than 30,000 km 2 . The whole system is a mature mud/sand-rich submarine fan on a passive margin. Multi-beam echo sounder data, 3.5 kHz seismic and 12 Küllenberg cores were examined to define the fan morphology, the lithological characteristics, the sedimentary processes and the relationship between the evolution of the fan deposits and the environmental conditions on the Celtic continental shelf.The upper fan is characterised by the presence of two distinct tributary systems: (1) the Whittard system with a large, persistent, slightly sinuous channel, which is linked to the southern end of the Irish Sea River system; and (2) the Shamrock system, with a moderate sized channel, which is linked to the western end of the English Channel River system. The middle and lower fan corresponds to divergent braided secondary channels and associate lobes. Successive lobe elements, without important relief, were generated during periodic avulsions of middle fan channels.The lithological, palaeontological, and geochemical analyses on cores show the evolution of sedimentation since the last glaciation. During the last lowstand and rise of sea-level frequent low-density turbidity currents were predominant and deposited sediments throughout the whole fan system. They were initiated at the front of a deltaic environment on the Celtic outer-shelf. During the high sea-level conditions, occasional high-density turbidity currents and/or non-cohesive debris flows occur and were responsible for sand deposition in the middle-lower fan. They are derived from reworked sands due to the highenergy conditions on the outer shelf. Thus for the Celtic Fan, the variations of the hydrodynamic conditions on the outer Celtic Shelf seem to be the primary control on facies shift and fan growth. ᭧

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Eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank (Celtic Sea)

Cited by 63 publications

References 61 publications

The offshore Quaternary sediment bodies of the English Channel and its Western Approaches

The offshore Quaternary sediment bodies of the English Channel and its Western Approaches

The ‘Fleuve Manche’: the submarine sedimentary features from the outer shelf to the deep‐sea fans

Physiography and recent sediment distribution of the Celtic Deep-Sea Fan, Bay of Biscay

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