--> The transform margin of the northern Demerara plateau (offshore Suriname, French Guiana)

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The transform margin of the northern Demerara plateau (offshore Suriname, French Guiana)


Offshore Suriname and French Guiana, the Demerara marginal plateau is a submarine continental relief at the intersection of two oceanic domains: the Jurassic Central Atlantic and the Early Cretaceous Equatorial Atlantic. Its northern border is characterized by a narrow continent-ocean transition zone, 10 to 40 km wide between the Plateau and the oceanic crust. From IGUANES geophysical campaign, three domains can be defined along this margin by different characteristics (Go to Search and Discovery to see Figure).

Western domain (A): at the north-western corner of the Demerara Plateau, the transition zone is narrow and corresponds to the linear, steep and eroded continental slope. The continental slope is probably lined up with the oceanic fracture zone identified eastward on seismic lines. The trace of the vertical transform fault corresponds to the trench located at the bottom of the continental slope.

Central domain (B): in the central part, the transition zone widens and recent sediments overly 5 km-wide southward (towards the plateau) tilted blocks. They are truncated by a planar erosional surface.

Eastern domain (C): In the north-eastern corner of the Plateau, the transition zone displays a very steep erosive slope ocean ward and a more gentle slope towards the Plateau. It is characterized by two left-lateral en echelon ridges correlated with positive gravity anomalies. These ridges are quite similar in shape to the marginal ridges observed along some transform margins. This domain should therefore represent a transform continental margin and its connection with the divergent margin southward.

From these new observations, we interpret the northern edge of the Demerara Plateau as a transtensive or oblique rift zone between two transform continental margins.