Structure and stratigraphy of the Turkana rift from seismic reflection data

A multichannel seismic survey was conducted on Lake Turkana, a rift lake occupying a portion of the Eastern Branch of the East African Rift System. This survey revealed the presence of a significant rift structure beneath the lake, the extent and structural details of which had been previously unknown. The lake is underlain by a series of half-graben basins which alternate in polarity along the axis of the lake, and are linked end to end by zones of structural high. These half-graben often have Quaternary volcanic centers located near their latitudinal midpoints. Half-graben basins beneath Turkana deepen progressively to the north, attaining thicknesses of up to 4 km. A deep seismic reflector has been identified, and is believed to correspond to the top of a thick series of Mio-Pliocene flood volcanics. Overlying reflectors are thought to correspond to fluvial, lacustrine and volcano-clastic sediments that are Plio-Pleistocene to Recent in age. The style of rifting beneath Lake Turkana is similar to that observed beneath Lake Tanganyika, which occupies a portion of the Western Branch of the East African Rift System. The most noticeable differences are the abundant volcanism and smaller half-graben size associated with Lake Turkana. These differences may be attributed to the warmer, thinner lithosphere underlying the Eastern Branch as compared to that underlying the Western Branch.