Sediment dynamics of a sandy contourite: the sedimentary context of the Darwin cold-water coral mounds,Northern Rockall Trough |
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Authors: | V A I Huvenne D G Masson A J Wheeler |
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Institution: | (1) National Oceanography Centre, Southampton, European Way, Southampton, SO14 3ZH, UK;(2) University College Cork, Cork, Ireland |
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Abstract: | Grainsize, mineralogy and current-meter data from the Northern Rockall Trough are presented in order to characterise the sandy
contourite that forms the sedimentary environment of the Darwin cold-water coral mounds, and to investigate the impact of
this environment on the mound build-up. Large clusters of small cold-water coral mounds, 75 m across and 5 m high, have been
found southwest of the Wyville Thomson Ridge, at 900–1,100 m water depth. Their present-day sedimentary environment consists
of a subtly sorted sandy contourite, elongated NE–SW, roughly parallel to the contours. Critical erosional and depositional
current speeds were calculated, and trends in both the quartz/feldspar and foraminifera fractions of the sands show a bi-directional
fining from bedload/erosion-dominated sands in the NE to suspension/deposition-dominated sediments in the SW and towards the
S (downslope). This is caused by a gradual reduction in governing current speed, linked to a reduction in slope gradient,
and by the increasing distance from the current core in the downslope direction. No specific characteristics were found distinguishing
the mound sediments from the surrounding sands: they fit in the overall spatial pattern. Some mound cores show hints of a
fining-upward trend. Overall the mound build-up process is interpreted as a result of sediment baffling. |
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Keywords: | Cold-water corals Sandy contourites Sediment transport Continental margin Northern Rockall Trough |
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