The researchers observed that the Cretaceous Congo River was largely flowing to the north west, with sediments mainly derived from the geological provinces to the south east. (This is the same direction the Congo River currently flows in.)
But by the Oligocene (roughly 34-23m years ago), the river had reversed course entirely, flowing to the south east.
Since changing the direction of a river’s flow requires a major reorganisation of continental topography (picture the Amazon River flowing west, towards the Andes), the researchers conclude that uplift of eastern Africa was already underway some 25m years ago.
The changing record of this ancient river’s flow direction now demonstrates when and where the uplift of the eastern African continent began. The first step in the break-up of Africa is well-underway.