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Crustal and Depositional Architecture of the Demerara Rise, Suriname, as Related to the Opening of the Atlantic Ocean


The Demerara Rise is a three-sided drowned plateau of sedimentary strata offshore Suriname. The Rise demarcates the division between the Central and Equatorial Atlantic opening history, showing Geology pertaining to both. Reconstructions of the closure of the Equatorial Atlantic during Early Aptian juxtapose the Rise with the Guinea Plateau, Guinea. The Aptian-Albian Equatorial opening is caused by a dextral transcurrent separation from Guinea and E-W extensional rifting along the Rise's north and east sides. The transcurrent displacement from Guinea is the likely cause for Aptian-?Early Albian inversion of basement faults and folding of the pre-Albian section, which increases in intensity northward toward the bounding paleo-transform. Westward of the Rise, the total sedimentary section is thicker than to the east, owing to an older phase of rifting. Plate reconstructions show that the continental crust beneath Great Bank, Bahamas, fits into the orthogonal “elbow” of the Guyana-west Demerara margin for roughly Oxfordian time, indicating that seafloor spreading relating to Central Atlantic opening began at a NNE-SSW spreading center which migrated to the WNW. The Rise is predicted to have a Middle Jurassic rift history that evolved into passive margin sedimentation in Oxfordian-Barremian time prior to uplift and inversion pertaining to the opening of the Equatorial Atlantic. The Trinidad-Guyana margin is a sinistral transcurrent or transtensional margin along which the south flank of the Bahamas (now overthrust by the Cuban Arc) migrated WNW. The stratal package beneath the “Albian unconformity” shows impressive growth with bed sets thickening westward to depths approaching 20 km. It is not clear if this “growth” is entirely fault controlled or a response of progradation of clastic sequences from the future Equatorial rift zone to the Central Atlantic margin. There appears to be a zone of moderate magmatic rifting in the western margin of the Rise, which is consistent with volcanism affecting the conjugate Bahamian basement. A NW-SE fault zone cuts the northern Rise, causing flower-like deformation in the pre-Albian section that probably relates to Equatorial Atlantic opening. The very large folds and inversion structures beneath the unconformity affect most of the sedimentary section.