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

Abstract

Off French Guiana and Suriname, North Atlantic Deep Water and Antarctic Bottom Water 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 subbottom profiles calibrated by sedimentary cores. The echofacies and isopach maps that 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 echofacies strongly affected by diffraction hyperbola and transparent echofacies. We interpret these features to be related to eroded slopes and mass-transport deposits. In contrast, the sedimentary drifts that we mapped are characterized by elongated and thick slope-parallel depocenters displaying bedded echofacies with wave-like bedforms. According to our interpretation, they result from interactions between the currents and the seafloor. Seismic wipeouts frequently affect those drifts, possibly resulting from high water or organic contents.