Early Oligocene stratigraphic turnover on the west Africa continental margin: a signature of the Tertiary greenhouse‐to‐icehouse transition?

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Abstract
The post‐rift stratigraphy on the west African margin is characterized by aggradation of a carbonate ramp during Late Cretaceous to Eocene epochs and progradation of a terrigenous wedge from Oligocene to the Present. Such first‐order structure has been attributed in the past to geodynamic forcing. However, comparison of the stratigraphic record of the margin with eustasy, δ18O and 87Sr/86Sr curves, shows a close temporal relationship with the Tertiary climate cooling, an increase of continental weathering, and a long‐term lowering of sea level. We suggest that the transition from low‐amplitude, high‐frequency sea‐level changes during the greenhouse period to high‐amplitude, high‐frequency sea‐level changes during the icehouse period may account for: (i) the switch from an aggrading carbonate ramp to a prograding clastic wedge, and (ii) the enhanced continental weathering and increased terrigenous influx to the margin.