LACUSTRINE DYNAMICS IN A HIGH-AGGRADATION RIFT SETTING, THE NEOGENE TURKANA BASIN OF EAST AFRICA

Rift basin lakes are sensitive to a complex set of controls including accommodation, sediment flux and climate. The Plio-Pleistocene lakes of the Turkana Basin record a variety of responses to the interplay among these factors. The high-resolution tephrostratigraphic framework and extensive outcrop exposure of these deposits allows a detailed analysis of the dynamics of seven major lacustrine intervals since ca. 4.2 Ma. Three of these lake phases demonstrate a dominant tectonic control, with a superimposed climatic record resolvable to the millennial scale. Other lacustrine intervals appear to be primarily forced by climatic signals. Throughout the Plio-Pleistocene record, the high sediment flux of the Turkana Basin matches or nearly matches accommodation space production. This near balance results in significant intervals of sediment overfill, breaking lacustrine continuity, but also results in high-accumulation lacustrine episodes, with extremely detailed sedimentary archives. Clastic sediment influx is locally replaced by intensive biogenic production, and a well developed record of environmentally sensitive facies and components. Fossil indicators in the sedimentary record also reflect details of hydrographic connections with a broader aquatic network, with important implications for exchange between both biological and hydrological systems. Improved analysis of outcrop exposures and new tools for their investigation are opening new insight into the interplay between the major controls on these lacustrine systems, and proposed drilling may furnish even more complete core-based archives of this unusual rift setting.