Seismic stratigraphy of the Guinea Plateau before, during and after the opening of the Equatorial Atlantic Gateway

The Guinea Plateau contains an ∼200 Myr stratigraphic record, encompassing the mid-Cretaceous opening of the Equatorial Atlantic Gateway (EAG). Here we present new 2D seismic data to constrain the structural and stratigraphic evolution of the plateau. Seismic stratigraphic analysis reveals five megasequences of ∼25–65 Myr duration: M1, a Jurassic synrift sequence with prominent seaward-dipping reflections; M2, a late Jurassic–Early Cretaceous post-rift carbonate platform; M3, a late Early Cretaceous transform clastic-dominated sequence; M4, an Albian–Maastrichtian ocean–continent transform to post-transform sequence; and M5, a Maastrichtian–recent passive margin sequence with low sedimentation rates. These megasequences also contain prominent transgressive–regressive cycles of 5–10 Myr duration, interpreted to be the result of dynamic topography.

The boundary between M3 and M4 is a major erosional unconformity documenting the final continental break-up during the opening of the EAG. Above this, a pronounced Albian to Cenomanian/Turonian marine transgression resulted in marine inundation of the plateau. Structural deformation continued into the early Cenomanian along the Guinea Marginal Ridge, a potential structural barrier that restricted marine connection across the EAG. Bulk geochemical data from the shallow Guinea Plateau indicate that enhanced carbon burial in this setting was primarily driven by the deposition of reworked, oxidized organic matter during an oceanic anoxic event, independent of gateway opening.