Nature and rates of fine-sedimentation on a mid-shelf: "La Grande Vasiere" (Bay of Biscay, France)

Type Article
Date 2007-09
Language English
Author(s) Dubrulle C1, 2, Jouanneau J2, Lesueur P1, Bourillet Jean-FrancoisORCID3, Weber O2
Affiliation(s) 1 : Univ Caen, CNRS, UMR Morphodynam Continentale & Cotiere M2C 6143, F-14000 Caen, France.
2 : Univ Bordeaux 1, CNRS, UMR 5805, EPOC, F-33405 Talence, France.
3 : IFREMER, DRO GM, F-29280 Plouzane, France.
Source Continental Shelf Research (0278-4343) (Elsevier), 2007-09 , Vol. 27 , N. 16 , P. 2099-2115
DOI 10.1016/j.csr.2007.05.002
WOS© Times Cited 14
Keyword(s) Bay of Biscay, Continental shelf, Sedimentation rate, Radionuclides, Fine sediment fraction, Mud
Abstract The study area, "La Grande Vasiere" (LGV), stretches out on the French Atlantic continental shelf (at ca. 100 m water depth), along 250 km from the Glenan Islands at the north to the southwest of Rochebonne at the south. Box-cores were sampled in this mid-shelf area during four cruises in June 1995, and in April, June and September 2002. They were investigated using sedimentologicat approaches (X-radiographs and grain-size analyses) and radionuclide studies (Pb-210 geochronology and excess Th-234). The main results are: (1) the surficial sediments are generally organized into a decimetrescale fining up sequence which can be the result of extreme storms; (2) an upper mixing layer of 7-20cm reflects an important biological benthic activity and/or the impact of fishing (i.e. trawlers); (3) a thin (i.e. a few mm) surficial mud-rich layer is the result of the present-day sedimentation; (4) an apparent annual sedimentation rate of 1-3 mm is recorded in several loci of the study area. Some seasonal variations appear, corresponding to the deposition of fine material from April to September, and to the reworking and the re-suspension during the winter. This fine material is the result of the decantation of estuarine plumes, mainly the Loire and the Vilaine rivers, over the study area. LGV ties (1) under the influence of a winter-to-spring thermo-hatine wedge that acts as a filter for the transfer of fine river-borne material to the slope and the open sea, and (2) below water depths where the mean swell action permits sedimentation, mainly in summer.

From the point of view of the nature of its sediments, LGV is not a mud-belt, but a heterolithic and patchy sandy area that is submitted to increasing silting with environmental changes, on a seasonal-time scale.

(c) 2007 Elsevier Ltd. All rights reserved.
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