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

Abstract

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. ᭧

Cold-Water Coral Habitats in Submarine Canyons of the Bay of Biscay

“…It is a passive margin containing three parts; the Celtic, Armorican and Aquitaine margins (Zaragosi et al, 2000). Within this study, the Bay of Biscay was defined using geological boundaries (see Bourillet et al, 2006) therefore including all three margins, as the Celtic margin is part of the Celtic Sea according to hydrographical terms.…”

“…These canyons contain several morphological features, such as cliffs, mainly formed in the head of the canyons by regressive erosion from the bottom to the top of the canyon . There are three main deep-sea drainage systems: (i) the Petite Sole drainage basin on the Celtic margin, comprising the canyons from Sorlingues to Hermine, (ii) the Chapelle drainage basin, comprising the canyons from Blackmud to Guilcher, (Bourillet and Lericolais, 2003) and, (iii) the West Brittany drainage basin, comprising the canyons from Brest to Douarnenez (Zaragosi et al, 2000(Zaragosi et al, , 2001. Zone 1 is under the influence of tidal currents of the English Channel (Zaragosi et al, 2001) and is linked with the drainage basins of rivers, such as the Seine, via the Channel paleo-river .…”

The Dangeard and Explorer canyons, South Western Approaches UK: Geology, sedimentology and newly discovered cold-water coral mini-mounds

“…High-energy hydrodynamics characterise the Celtic Margin with spring tides and storm surges influencing the transport of sediment from the near shore to the shelf-edge and margin slope (Kenyon and Stride, 1970, Reynaud et al, 1999and Zaragosi et al, 2000. The study area is influenced by two main water masses: an upper layer described as the Eastern North Atlantic Water (ENAW; a component of the North Atlantic Current) from the thermocline (a seasonal surface layer of up to 50-100 m thickness) down to 800 m water depth; and the Mediterranean Outflow Water (MOW) from 800 m to 1200 m water depth (Dullo et al, 2008, Le Boyer et al, 2013and van Weering et al, 1998.…”

“…The Explorer and Dangeard canyons presented in this paper are part of the Grande Sole drainage basin ( Fig. 1), which was fed by melt water from the Irish Sea sourced from the disintegrating British Ice Sheets (Zaragosi et al, 2000 andZaragosi et al, 2006). The Grande Sole drainage system feeds the Celtic deep-sea fan system via the Whittard Canyon (Fig.…”

Deep-sea echinoderm oxygen consumption rates and an interclass comparison of metabolic rates in Asteroidea, Crinoidea, Echinoidea, Holothuroidea and Ophiuroidea

“…The Nazaré and Setúbal Canyons (JC10) intersect the western Iberian margin between 38°N and 39°30ЈN off the coast of Portugal (Arzola et al, 2008). The Whittard Canyon (JC36) intersects the Celtic margin at ~10°45ЈW (Zaragosi et al, 2000).…”