Benedict Aduomahor, Debora Duarte, Thomas Wagner, Tom Dunkley Jones, Uisdean Nicholson

The Guinea Plateau contains a ~200-million-year 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 My duration: M1, a Jurassic syn-rift sequence with prominent seaward-dipping reflections; M2, a late Jurassic- Early Cretaceous post-rift carbonate platform; M3, a late Early Cretaceous syn-transform clastic-dominated sequence; M4, an Albian-Maastrichtian 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 My duration, interpreted to be the result of dynamic topography.

The boundary between M3 and M4 is a major erosional unconformity documenting final continental breakup 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, oxidised organic matter during OAE, independent of gateway opening.