Chapter 9. Albertine Rift stratigraphy 1: sedimentary architecture

A persistent problem that has hampered a general understanding of Albertine Rift early continental rift basins has been the lack of a high-resolution stratigraphic framework within which to correlate sediments across their onshore outcrop. Crucial to resolving this problem is resolving how the 3D stacking architecture of sediments is controlled by a combination of evolving rift basin structure and the glacial climatic cyclicity experienced at the Equatorial Tropics of East Africa during deposition. Rift basin structural styles and subsidence rates are modelled and their merits discussed in the light of the field evidence gathered from around the Albertine Rift. After establishing the mechanism of structural development in the basins, the impact of glacially driven climatic oscillations on sedimentary lithofacies is also incorporated to produce a combined glacial climatic cyclicity model for Albertine Rift basin evolution. This superimposes lake level transgressive–regressive cyclicity upon a tectonic regime of fault propagation and depocentre retreat away from rift margins. The model predicts the resulting stratigraphic architecture that should develop in outcrop areas, and is supported by field evidence of not only lithofacies characteristic of arid (glacial) and wet (interglacial) climatic conditions but also cycles of 3D terrace development, channel incision and sediment backfilling.