STRATIGRAPHIC EVOLUTION OF THE TURKANA BASIN, EASTERN AFRICA

The Turkana Basin preserves a record of rift-related accumulation dating back to the Mesozoic Central African Rift System (CARS), but primarily associated with the development of the Cenozoic East African Rift System (EARS). Over 50 years of outcrop investigations have documented volcanic and sedimentary stratigraphy, often closely associated with the spectacular paleontological and archaeological discoveries of the region. Extensive subsurface work has been undertaken as part of petroleum exploration, including seismic profiling and boreholes. Limited scientific drilling has recovered high-resolution records of environmental proxies. The modern Turkana Basin provides a living laboratory through which to examine interactions among tectonic, volcanic and sedimentary systems, climate dynamics, and the responses of modern communities to various aspects of change.

Basin fill includes some seven km of rift-related volcanics (basalts, phonolites, rhyolites) along with a diverse array of sedimentary strata reflecting lacustrine and fluvial depositional systems. CARS strata are composed of coarse alluvial deposits in a non-volcanic rift setting. EARS accumulation is dominated by early rift volcanic strata, which in late Oligocene through Miocene times are punctuated by thick lacustrine packages (Lokichar Basin) and scattered fluvial sequences that preserve important vertebrate fossil assemblages. The modern configuration of the basin developed in early Pliocene times, and hosted a complex fluvio-lacustrine system that persists to the present day. The latter is notable for abundant distal silicic tephra providing markers for correlation and age control. Legacy and on-going geologic mapping, outcrop and subsurface investigations provide a detailed record of the spatial and temporal dynamics in this long-lived archive of geologic history.