![]() | Activity of the turbidite levees of the Celtic-Armorican margin (Bay of Biscay) during the last 30,000 years: Imprints of the last European deglaciation and Heinrich events Auteur(s) : Toucanne, Samuel Zaragosi, S Bourillet, Jean-francois Naughton, F Cremer, M Eynaud, F Dennielou, Bernard Éditeur(s) : Elsevier Résumé : High-resolution sedimentological and micropaleontological studies of several deep-sea cores retrieved from the levees of the Celtic and Armorican turbidite systems (Bay of Biscay - North Atlantic Ocean) allow the detection of the major oscillations of the British-Irish Ice Sheet (BIIS) and 'Fleuve Manche' palaeoriver discharges over the last 30,000 years, which were mainly triggered by climate changes. Between 30 and 20 cal ka, the turbiditic activity on the Celtic-Annorican margin was weak, contrasting with previous stratigraphic models which predicted a substantial increase of sediment supply during low sea-level stands. This low turbidite deposit frequency was most likely the result of a weak activity of the 'Fleuve Manche' palaeoriver and/or of a reduced seaward transfer of sediments from the shelf to the margin. However, two episodes of turbiditic activity increase were detected in the Celtic-Armorican margin, during Heinrich events (HE) 3 and 2. This strengthening of the turbiditic activity was triggered by the meltwater releases from European ice sheets and glaciers favouring the seaward transfer of subglacial material, at least via 'Fleuve Manche' palaeoriver. At around 20 cal ka, a significant increase of turbidite deposit frequency occurred as a response to the onset of the last deglaciation. The retreat of the European ice sheets and glaciers induced a substantial increase of the 'Fleuve Manche' palaeoriver discharges and seaward transfer of continentally-derived material into the Armorican turbidite system. The intensification of the turbiditic activity on the Celtic system was directly sustained by the widespread transport of subglacial sediments from the British-Irish Ice Sheet (BIIS) to the Celtic Sea via the Irish Sea Basin. A sudden reduction of turbiditic activity in the Armorican system, between ca. 19 and 18.3 cal ka, could have been triggered by the first well known abrupt sea-level rise ('meltwater pulse', at around 19 cal ka) favouring the trapping of sediment in the 'Fleuve Manche' palaeoriver valleys and the decrease of the seaward transfer of continentally-derived material. The maximum of turbiditic activity strengthening in the Celtic-Armorican margin, between ca. 18.3 and 17 cal ka, was induced by the decay of European ice sheets and glaciers producing the most extreme episode of the 'Fleuve Manche' palaeoriver runoff and a great seaward transfer of subglacial material into the Bay of Biscay, Between ca. 17.5 and 16 cal ka, the turbiditic activity significantly decreased in both Celtic and Armorican turbidite systems in response to a global re-advance of glaciers and ice sheets in Europe. The last episode of ice sheet retreat, between ca. 16 and 14 cal ka, is well expressed in the Celtic system by a new increase of the turbiditic activity. The major episode of sea-level rise at around 14 cal ka ('Meltwater Pulse 1A'), precluding the seaward transfer of sediments, induced the end of turbiditic activity in both the Celtic and the Armorican system. Although two main phases of global sea-level rise seem to have had an effect on the Celtic-Armorican margin, this work proposes the BUS retreat and associated riverine discharges as the main trigger mechanisms of the turbiditic activity in this region during the last 30,000 years. Marine Geology (0025-3227) (Elsevier), 2008 , Vol. 247 , N. 1-2 , P. 84-103 Droits : 2008 Elsevier B.V. All rights reserved http://archimer.ifremer.fr/doc/2008/publication-3729.pdf DOI:10.1016/j.margeo.2007.08.006 http://archimer.ifremer.fr/doc/00000/3729/ | Partager Voir aussi Turbidites Heinrich events LGM Last deglaciation Palaeoriver Fleuve Manche British irish ice sheet Bay of Biscay Télécharger |
![]() | Evolution du fleuve Manche depuis l'oligocène : stratigraphie et géomorphologie d'une plateforme continentale en régime périglaciaire Auteur(s) : Lericolais, Gilles Éditeur(s) : Unersité Bordeaux I Résumé : Ce travail propose un scénario de reconstruction de l'histoire du fleuve Manche depuis son origine supposée oligocène, basé sur l'interprétation de données numériques de géophysique très haute résolution (sismique sparker, et multifaisceaux EM100) acquises par l'IFREMER au cours d'une série de campagnes qui ont été réalisées dans le cadre du programme SEDIMANCHE. Les techniques de traitement utilisées (sismique, imagerie et cartographique) apportent des éléments nouveaux témoins de l'existence et du passé du fleuve qui a drainé au cours des périodes de bas niveau marin plio-quaternaires, une grande partie de l'Europe du Nord-Ouest. Droits : Université Bordeaux I http://archimer.ifremer.fr/doc/00034/14504/11848.pdf http://archimer.ifremer.fr/doc/00034/14504/ | Partager |
![]() | The impact of the last European deglaciation on the deep-sea turbidite systems of the Celtic-Armorican margin (Bay of Biscay) Auteur(s) : Zaragosi, Sébastien Bourillet, Jean-francois Eynaud, Frédérique Toucanne, Samuel Denhard, Benjamin Van Toer, Aurélie Lanfumey, Valentine Éditeur(s) : Springer Résumé : The compilation of results obtained on three giant piston cores from the Whittard, Shamrock and Guilcher turbidite levees reveals a high-resolution stratigraphic record for the Bay of Biscay. Due to the abundance of reworked sediments in these sedimentary environments, a specific methodological approach, based on an X-ray-assisted subsampling phase associated with sedimentological, geochemical and micropalaeontological analyses, was implemented. With an accurate chronological framework, this multi-proxy investigation provides observations on the 'Fleuve Manche' palaeoriver and the British-Irish Ice Sheet (BIS) histories over the last 20,000 years. The results obtained highlight the direct influence of the decay of the BIS on the Bay of Biscay deep-sea clastic sedimentation during the last European deglacial phase. During this period, the annual BIS cycle of meltwater seems enough to generate seasonal turbidity currents associated with exceptional sedimentation rates in all the Celtic and Armorican turbidite systems. With very high sedimentation rates, the turbidite levees represent the main deep-sea clastic depositional area. Long coring combined with a very careful subsampling method can provide continuous high-resolution palaeoenvironmental signals. Geo-Marine Letters (0276-0460) (Springer), 2006-12 , Vol. 26 , N. 6 , P. 317-329 Droits : 2006 Springer Science+Business Media http://archimer.ifremer.fr/doc/2006/publication-2142.pdf DOI:10.1007/s00367-006-0048-9 http://archimer.ifremer.fr/doc/00000/2142/ | Partager |