Abstract: Controls on Sedimentation in a Plio-Pleistocene Fluvial-Dominated Rift Basin, the Turkana Basin of East Africa

Craig S. Feibel

The Turkana basin of northern Kenya and southern Ethiopia has existed as an elongate, extensional basin since the early Pliocene. Throughout this time, the basin has been dominated by a through-flowing fluvial system, in which both water and sediment supply derive from the Ethiopian Highlands, some 200 km north of and roughly 2000 m higher than the depositional basin. Three controlling factors are reflected in sedimentation patterns and character of the Plio-Pleistocene strata in the basin. Tectonic control, in the form of asymmetrical subsidence along a series of alternating half-grabens, produced variations in thickness, accumulation rates and ultimately exposure. Climatic control is apparent in changes in depositional process at local and regional scales. Short-term climatic effect as well as long-term trends are documented. The influence of climate must be viewed as a complex control, with local climate at variance with the climatic regime in the critical headwater region. Volcanism was an important short-term control in the Plio-Pleistocene. Local volcanism, in the form of lava flows, is implicated in the initiation of short-term lake phases in the basin. Explosive volcanism in the fluvial source area for the basin episodically choked fluvial systems and caused a breakdown of the channel pattern. Present-day Lake Turkana is interpreted as a relatively young feature, produced by major structural reorganization of the basin beginning about 0.5 Ma. Since then, tectonics and climate have been the dominant controls on sedimentation in the current lacustrine basin.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994