Echofacies interpretation of Pleistocene to Holocene contourites on the Demerara plateau and abyssal plain

• Published in: Interpretation
• Main Authors: Tallobre, Cédric, Loncke, Lies, Droz, Laurence, Marsset, Tania, Uusõue, Mirjam, Roest, Walter, Fanget, Anne-sophie, Bassetti, Maria-angela, Giresse, Pierre, Bayon, Germain
• Format: Article in Journal/Newspaper
• Language: English
• Published: Society of Exploration Geophysicists 2021
• Subjects: NADW
• Online Access: https://archimer.ifremer.fr/doc/00680/79223/86918.pdf; https://doi.org/10.1190/INT-2020-0159.1; https://archimer.ifremer.fr/doc/00680/79223/

Off French Guiana and Surinam, NADW and AABW oceanic currents contour the Demerara marginal plateau, which promotes the formation of contourites. We have studied these contourites thanks to a new compilation of high-resolution sub-bottom profiles calibrated by sedimentary cores. The echo-facies and isopach maps we constructed highlight a sedimentary distribution parallel to the isobaths. The presence of moats along the slope is confirmed by the observation of parallel, elongated, sedimentary depleted zones and echo-facies strongly affected by diffraction hyperbola and transparent echo-facies. We interpret these features to be related to eroded slopes and Mass Transport Deposits. In contrast, the sedimentary drifts we mapped are characterized by elongated and thick slope-parallel depocentres displaying bedded echo-facies with wave-like bedforms. According to our interpretation, they result from interactions between currents and the seafloor. Seismic wipe-outs frequently affect those drifts, possibly resulting from high water or organic contents.