DRADEM campaign - 2016 July - Scientific report

The DRADEM campaign was performed from July 9th to 21th 2016 on board the Pourquoi Pas?, in the Exclusive Economic Zones of Suriname and French Guyana. This campaign belongs to a program dedicated to geological investigations of the Demerara plateau, following the GUYAPLAC (2003) and IGUANES (2013) campaigns, and before the MARGATS campaign (2016). The aims of the DRADEM campaign were to map the continental slope of the transform margin north of the Demerara plateau, and to dredge the rocks outcropping in the slope. We completed the bathymetric mapping of the continental slope, including part of the edged of the Demerara plateau. These new bathymetric data confirm the segmentation of the transform margin in three parts with very different morphologies. In addition, two circular structures were interpreted as mud volcanoes, one on the northern edge of the plateau, the other one in the distal part of the Orinoco deep sea fan. Twelve dredges were performed between 4700 and 3500 m depths. Four from these twelve did not recovered rocks. The eight others brought back variables amounts of rocks, often encrusted, but of various natures: sediments (breccia, coarse sandstones, sandstones with plants debris, sandstones with shells, clayey ooze), micro-granular rocks and metamorphic rocks (including mylonite). The nature of the rocks was determined from macroscopic observation of the rocks, which are currently altered. Of course, these determinations need to be validated and specified by onshore further studies. Anyway, most of these rocks were previously unknown in this area, and they will strongly influence our understanding of the structure and evolution of this margin. They evidence huge vertical displacements that brought back to the surface some of these rocks that formed in a deep setting.