Abstract The Turkana magmatic rift (Northern Kenya) initiated at 45 Ma as one of the nucleation zones of rifting in the East African Rift. It forms an anomalously broad-rifted zone ( c. 200 km) striking with a north—south trend and lying within a NW—SE topographic depression, floored on both sides of the Turkana area by Cretaceous rifts in the Sudan and Anza plains. From a compilation of available data, combined with newly acquired remote sensing and DEM dataset, we propose a five-stage tectono-magmatic model for the Turkana rift evolution (45–23 Ma; 23–15 Ma; 15–6 Ma; 6–2.6 Ma and 2.6 Ma—Present). The corresponding ‘restored’ maps clearly show the changing spatial distribution of magmatism and fault/basin network with time, hence supplying some clues about dynamics of continental extension. First-order basement-rooted transverse faults zones are identified and their influence on nucleation and propagation of strain is demonstrated, whereas the role of magmatic ‘soft-spots’ as concentrating strain is minimized. Blocking of deformation as well as rift jump and lateral transfer of strain are discussed in relation to various types of fault interaction (dip direction, strikes and acute/ obtuse angle of the intersecting faults). The causal links between rift nucleation ‘cells’ and inherited transverse weakness zones in the Turkana rift might also exist elsewhere along the eastern branch of the East African Rift, hence suggesting a complex and discontinuous mode of rift propagation.

Abstract Lacustrine diatomaceous deposits are widespread in the East African Rift System, occurring in Miocene to Holocene sedimentary units. Problems in their classification can be clarified with a common set of well-defined terms, including: diatomite, siliciclastic diatomite, subdiatomite, diatominc, and diatom-poor. Additional descriptors refer to lamination, fragmentation, and dissolution. Diatom taphonomy and assemblage alteration reflect sedimentation, interface, and analysis controls, including: dissolution, settling rates, fragmentation, and floral mixing. The spatial and temporal distribution of East African diatomaceous deposits, especially in the Kenya and Malawi Rifts, suggest specific models for the development of a variety of diatomaceous facies. The models are based on factors that control the availability of diatom nutrients, including: fluvial inputs, water depth, seasonality of rainfall, wind regimes and their influence on upwelling and overturn, and turbidity currents. In turn, these factors reflect tectonic and geomorphic setting, drainage basin geology and resultant water chemistry, and climatic setting.