Identification of a contouritic deposit system and associated sedimentary processes on the Demerara Plateau (Guiana margin)

• Main Author: Tallobre, Cedric
• Other Authors: Centre de Formation et de Recherche sur les Environnements Méditérranéens (CEFREM), Université de Perpignan Via Domitia (UPVD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Perpignan, Lies Loncke, Marie-Angela Bassetti
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2017
• Subjects: Demerara plateau; Marginal plateau; Contourite; Glaucony; Plateau de Demerara; Plateau marginal; Glauconie; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Le Plateau; NADW
• Online Access: https://tel.archives-ouvertes.fr/tel-01492880; https://tel.archives-ouvertes.fr/tel-01492880/document; https://tel.archives-ouvertes.fr/tel-01492880/file/these_tallobre_Cedric_2017.pdf

The Demerara Plateau is a marginal plateau located along the French Guyana and Surinam margin. Thanks to the recent data acquired during the IGUANES cruise, with geophysical data and sedimentary cores, some sedimentary structures illustrate a strong current influence on the recent building of this margin. The sedimentary geometries suggest the presence of a Contourite Depositional System (CDS). The seafloor is marked by the presence of longitudinal structures formed by the current activity: giant flute clasts or comet marks, and longitudinal waves. Based on the chirp data analysis and on cores, some sedimentary domains are identified on the Demerara marginal plateau. The intermediate and the lower marginal plateaus are affected by contouritic process with two moats and a mounded elongated drift. This contourite is likely induced by the NADW circulation. The contourite on this plateau is made of glauconitic rich sediments inside the moat showing the winnowing effect induced by the bottom currents. The detailed study of sedimentary cores associated with a chronostratigraphic framework allows identifying the sedimentation features depending on current intensity through time. The glaucony authigenic mineral is used as a main proxy, coupled with grain-size and facies analyses, for inferring the degree of winnowing at the sediment-water interface. On the Demerara plateau, the sedimentation suggests low sediment accumulation rates and quite energetic bottom currents during ice periods.The presence of contourites along the Demerara Plateau and along other marginal plateaus shows the strong impact of such deep-sea marginal bathymetric reliefs on the oceanic circulation. Le plateau de Demerara est un plateau marginal situé le long de la marge de la Guyane française et du Surinam. Grâce aux données récentes acquises lors de la campagne IGUANES, avec des données géophysiques et des carottes sédimentaires, certaines structures sédimentaires illustrent une forte influence du courant sur la construction récente de cette ...