Magnetic fabric of Bengal fan sediments: Holocene record of sedimentary processes and turbidite activity from the Ganges-Brahmaputra river system

Type Article
Date 2020-12
Language English
Author(s) Moreno Eva1, Caroir Fabien2, Fournier Lea3, Fauquembergue Kelly3, Zaragosi Sébastien3, Joussain Ronan4, Colin Christophe4, Blanc-Valleron Marie-Madeleine5, Baudin François6, de Garidel-Thoron Thibault7, Valet Jean Pierre8, Bassinot Franck9
Affiliation(s) 1 : Laboratoire d'Océanographie et du Climat: Expérimentations et approches numériques, UMR 7159 CNRS, IRD, Sorbonne Université/MNHN/IPSL. Boîte 100 - 4, place Jussieu, 75252 Paris cedex 05, France
2 : UMR 8187, LOG, Laboratoire d'Océanologie et de Géosciences, Université Lille, CNRS, Université Littoral Côte d'Opale, F 59000 Lille, France
3 : UMR CNRS 5805 EPOC, OASU, Université de Bordeaux, Allée Geoffroy Saint-Hilaire - CS 50023, 33615 Pessac cedex, France
4 : CNRS, GEOPS, Université Paris-Saclay, 91405, Orsay, France
5 : CR2P, UMR 7207, Muséum National d'Histoire Naturelle, 43 Rue Buffon - CP38, Paris, France
6 : ISTeP - Institut des Sciences de la Terre Paris, Sorbonne Université, 4 place Jussieu, CP 117, 75005 Paris, France
7 : CNRS, IRD, Coll. de France, INRAE, CEREGE, Aix-Marseille Université, Technopôle de l'Arbois - BP80, 13545 Aix-en-Provence cedex 04, France
8 : Institut De Physique Du Globe De Paris, 1, Université de Paris, 1 rue Jussieu, 75238 Paris cedex 05, France
9 : Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
Source Marine Geology (0025-3227) (Elsevier BV), 2020-12 , Vol. 430 , P. 106347 (13p.)
DOI 10.1016/j.margeo.2020.106347
Keyword(s) Bengal fan, Holocene, Turbidite activity, Magnetic fabric, Magnetic mineralogy
Abstract

We present here a study based on the Anisotropy of Magnetic Susceptibility (AMS) and magnetic mineralogy carried out on the composite core MD17&18taken from the eastern levee of the active channel of the middle Bengal Fan in the Indian Ocean. Based on C-14 dating, the sedimentary sequence covers 9.8 ka in 39 m of sediment. It therefore records at very high resolution the variations in continental material exported to the ocean by the Ganges-Brahmaputra river system during the Holocene.

This sequence was divided into two units according to turbidite activity: Unit 1 from 9.8 to 9.2 ka cal. Representing 39 m of coarse-grained turbidite sequences (coarse silts to fine sands) and extremely high sedimentation rates. Unit 2 of 9.2 ka cal. BP to the present characterized by a sharp decrease in the sedimentation rate, the presence of fine-grained turbidites characterized by strong decrease in the ln(Ti/Ca) ratio.

Our AMS results indicate that the magnetic fabric is highly sensitive to the mode of deposition. The turbidite sequences are clearly characterized by very high F and Pj values, not only of the coarse-grained turbidite levels in unit 1, but also of the fine turbidites in unit 2. We suggest that this strong degree of anisotropy is the result of the strong and rapid deposition during the turbidite sequences which induces an additional compaction effect.

Furthermore, LT SIRM measurements revealed that the magnetic minerals representative of the Ganges and Brahmaputra drainage area are magnetite, hematite and goethite. A higher supply in fine-grained magnetite was observed during the turbidite sequences in phase with an increase in sediment grain size.

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Moreno Eva, Caroir Fabien, Fournier Lea, Fauquembergue Kelly, Zaragosi Sébastien, Joussain Ronan, Colin Christophe, Blanc-Valleron Marie-Madeleine, Baudin François, de Garidel-Thoron Thibault, Valet Jean Pierre, Bassinot Franck (2020). Magnetic fabric of Bengal fan sediments: Holocene record of sedimentary processes and turbidite activity from the Ganges-Brahmaputra river system. Marine Geology, 430, 106347 (13p.). Publisher's official version : https://doi.org/10.1016/j.margeo.2020.106347 , Open Access version : https://archimer.ifremer.fr/doc/00652/76388/