Formation and evolution of glauconite in the Demerara Contourite depositional system related to NADW circulation changes during late Quaternary (French Guiana)

Abstract The Demerara Plateau is a marginal plateau which forms a bathymetric relief on the sea floor. Here, contouritedeposits have been studied in detail, following the recent discovery of contouritesequences likely related to the bottom currents and linked both to contour current and peculiar sea-floor morphology. A chronostratigraphic framework, based on δ 18 O relative variations and palaeomagnetic events in sediment cores allows correlating sediment processes to current intensity changes and major climate phases (glacial or interglacial). The studied sediments are enriched in glauconiticgrains. In addition, the glauconitemineralogical maturity can easily correlate to low sedimentation rate and slightly energetic bottom currents on the seafloor. Based on these data and using the glauconitic authigenicmineral as proxy for inferring the degree of winnowingat the sediment-water interface, we might put forward the hypothesis that the intensity of NADW is higher during the glacial stages and lower during interglacialperiods.