Modern sedimentation and geochemical imprints in sediments from the NW Madagascar margin

Type Article
Date 2020-08
Language English
Author(s) Pastor Lucie1, Brandily Christophe1, Schmidt S.2, Miramontes E.3, Péron Maela1, Appere Dennis1, Chéron Sandrine4, Boissier AudreyORCID4, Jouet Gwenael5
Affiliation(s) 1 : IFREMER, Centre de Bretagne, REM/EEP, Laboratoire Environnement Profond, F-29280 Plouzané, France
2 : UMR5805 EPOC, CNRS, OASU, Université de Bordeaux, 33615 Pessac, France
3 : MARUM – Center for Marine and Environmental Sciences, University of Bremen, Klagenfurter Straße 2-4, Bremen 28359, Germany
4 : IFREMER, Centre de Bretagne, REM/GM, Laboratoire Cycles Géochimiques et Ressources, F-29280 Plouzané, France
5 : IFREMER, Centre de Bretagne, REM/GM, Laboratoire Géodynamique et Enregistrement Sédimentaire, F-29280 Plouzané, France
Source Marine Geology (0025-3227) (Elsevier BV), 2020-08 , Vol. 426 , P. 106184 (11p.)
DOI 10.1016/j.margeo.2020.106184
WOS© Times Cited 4
Keyword(s) Episodic sedimentation, Madagascar margin, Betsiboka river, Mahavavy river, Progradation, methane, Geochemistry, Sediment

The NW Madagascar continental margin receives high loads of terrigenous particulate organic matter during the wet season and especially linked to extreme events, originating from two major rivers, the Betsiboka and the Mahavavy Rivers. This particulate matter contains a high content of iron minerals from the weathering of red ferruginous/ferralitic soils of Madagascar. The presence of pockmarks, i.e. gas or fluid expulsion features on the continental slope, testifies to past/present methane migration through the sedimentary column, associated with early diagenetic processes. This study globally aims at deciphering the interactions between episodic sedimentation and geochemical processes influenced by fluids upward migration, using a sediment trap mooring and interface sediment cores at two sites on the continental slope. The present-day sedimentation along this margin undergoes two patterns. During the wet season, high continental fluxes generally result in an increase in particle fluxes on the slope. Longshore currents may deflect river plumes alongslope resulting in some periods of low particle flux on the slope during the wet season. During the dry season, the particles collected in the water column are probably originated from sediment remobilization from the shelf and slope. The observed progradation of the Mahavavy River delta and prodelta between 1984 and 2016 argues for an increase in temporary connections of the river with the canyon head during extreme events, inducing pulsed sedimentation offshore. This pulsed sedimentation could be responsible for enhancing pyritization on surface sediments, due to higher inputs of terrigenous organic matter and iron oxides. Finally, methane upward migration also influences the pyritization process through anaerobic oxidation of methane using sulfate as an electron acceptor and methanotrophs associated with this reaction significantly impact the δ13C of organic carbon towards more negative values.

Full Text
File Pages Size Access
Author's final draft 40 14 MB Open access
11 12 MB Access on demand
10 684 KB Access on demand
Top of the page