The evolution of a Holocene banner bank controlled by morphodynamics and structural setting of a macrotidal coast: Saint-Brieuc Bay (NW-EUROPE)

Type Article
Date 2021-09
Language English
Author(s) Traoré Kalil1, Menier David1, Gensac Erwan1, Le Roy Pascal2, Lambert Clément1, Bessin Paul3, Pédoja Kevin4, Duperret Anne5, Le Gall Romain1
Affiliation(s) 1 : Laboratoire Géoscience Océan, UMR 6538, CNRS, Université Bretagne Sud, Campus de Tohannic, 56000 Vannes, France
2 : Laboratoire Géoscience Océan, UMR 6538, CNRS, IUEM, Université Bretagne Occidentale, 29280 Plouzané, France
3 : Laboratoire de Planétologie et Géodynamique, UMR 6112, CNRS, Le Mans Université, Avenue Olivier Messiaen, 72085 Le Mans CEDEX 9, France
4 : Laboratoire Morphodynamique Continentale et Côtière, UMR 6143, CNRS, Université Caen Normandie, campus 1, 2-4, Rue des Tilleuls, 14000 Caen cedex, France
5 : Laboratoire Ondes et Milieux Complexes, UMR 6294, CNRS, Université Le Havre Normandie, 53 rue de Prony, CS, 80540, 76058 Le Havre cedex, France
Source Geoscience Frontiers (16749871) (Elsevier BV), 2021-09 , Vol. 12 , N. 5 , P. 101183 (16p.)
DOI 10.1016/j.gsf.2021.101183
Keyword(s) Sand banks, Banner bank, Holocene climate, Geomorphology, Sea level rise, Tidal gyre.
Abstract

The morphology and internal structure of the Horaine Bank (Bay of Saint-Brieuc, NW France) are described based on multibeam echosounder and high-resolution seismic datasets coupled with vibro-core data. The Horaine Bank shows large-scale bedforms in the lee of a submerged rocky shoal, which allowed defining it as a Banner Bank. The internal structure of the sandbank reveals four seismic units (U1–U4) on a Cambrian basement (U0). The basal unit U1 is interpreted as reworked lowstand fluvial sediments those infilled micro incised valleys during a rise in sea level. This unit is overlain by paleo-coastal barrier sand-spit (U2) whose development was controlled by swell in the context of a rapid rise in sea level. The successive prograding unit (U3) is interpreted as flooding deposits in continuity with unit U2. The unit U4 is characterized by oblique reflectors oriented in two opposite directions. This last unit, dated post 3500 yr BP, corresponds to migrating dunes superimposed on the bank and observable in the high-resolution bathymetric data. The strong correlation between tidal currents and the apparent clockwise migration of dune crests suggests the presence of a tidal gyre controlling the current dynamics of most of the Horaine bank dunes. This study proposes a new model for the construction of banner banks characterized by the gradual transition of a sand spit to a banner bank during marine transgression and ensuing hydrodynamic variability.

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Traoré Kalil, Menier David, Gensac Erwan, Le Roy Pascal, Lambert Clément, Bessin Paul, Pédoja Kevin, Duperret Anne, Le Gall Romain (2021). The evolution of a Holocene banner bank controlled by morphodynamics and structural setting of a macrotidal coast: Saint-Brieuc Bay (NW-EUROPE). Geoscience Frontiers, 12(5), 101183 (16p.). Publisher's official version : https://doi.org/10.1016/j.gsf.2021.101183 , Open Access version : https://archimer.ifremer.fr/doc/00685/79660/