Abstract
During the end of the lower Cretaceous, the connection between the South and the Central Atlantic accretionary axis led to the oblique opening of the Equatorial Atlantic, and to the separation of Africa and South America by alternating transform and rift margins. At the western end of the Equatorial Atlantic, we investigate the structure of the Cretaceous margins surrounding the Demerara plateau, north of French Guiana and Suriname. These margins were previously described as transform northward and divergent eastward. From the bathymetry and deep structures, we propose to divide the northern transform into three margin segments, with two transform segments separated by a divergent one. These two transform margins are very different, the north-western one being linear and associated with a steep and erosive continental slope, the north-eastern one consisting of several faults and ridges en echelon disposed. In between, the divergent margin appear to be a pull-apart basin localised by structures inherited from the previous Jurassic rifting. Additionally, the eastern divergent margin can have been localised by a thermal anomaly tentatively related to a hotspot. It is proposed that the deformation has been first localised in divergent (rift) basins, subsequently connected by transform faults. The structure of the transform fault varies with the offset between adjacent rift basins: large offset forms a linear transform, short (less than 200 km) offset forms en echelon structures.