Early Post-rift of transform margins: the african margins of the Equatorial Atlantic
Résumé
We investigated the structural variability of the African Equatorial Atlantic margin, and, in particular, the stratigraphic
architecture of the early post-rift sedimentary wedges (Upper Cretaceous). A major segmentation of the
margin results from the obliquity of each segment with respect to the direction of the transform faults bounding
the 3 main depocenters (Sierra Leone-Liberia, Ivory-Coast, Ghana-Togo-Benin). It produced margin segments
with various widths of the crustal necking zone (very narrow transform segments vs wider divergent segments)
and of the continent-ocean transition. Also, along transform segments, only the distal part of the early post-rift
sedimentary wedge was preserved whereas, along divergent segments, the whole wedge has been preserved. As
a difference, the late post-rift stage wedge (Cenozoic) has been well preserved on both types of segment. We interpret
this differential preservation, during the early post-rift stage, as the result of different histories of vertical
movements along segments having different extension obliquities. Faster early post-rift uplift is expected along
transform segments because of their very narrow necking domain amplifying the flexural response of the lithosphere
to stretching and erosion/sedimentation transfers. This resulted in sediment bypass and shelf erosion of
the proximal sedimentary wedge along transform segments whereas accommodation allowed for the sedimentary
wedge to be preserved, at the same time, along divergent segments. During the following late post-rift stage, the
differential behavior was smoothed out