Journal ArticleNew Discovery of Oligocene Strata in the Topernawi Formation, Turkana County, KenyaSousa, F; Cox, S; Hemming, S; Rasbury, T; Steponaitis, E; Hatton, K; Saslaw, M; Henkes, G; Princehouse, P; Vitek, N; Nengo, INew field observations and 40 Ar/ 39 Ar geochronology reveal that the Topernawi Formation of the Ekitale Basin, northern Turkana Depression, Turkana County, Kenya was deposited entirely during the Oligocene between 29.7 ± 0.5 Ma and 29.24 ± 0.08 Ma. These bracketing ages are determined via new 40 Ar/ 39 Ar geochronology on a basaltic lava flow at the base of the section and a felsic ignimbrite near the top. A newly discovered basal unit and interbedded lava flow result in a new total sedimentary thickness of 92 m. The Topernawi Formation is the oldest dated syn-rift sedimentary section in the northern Turkana Depression.Frontiers in Earth Science2022-02-0310552372Frontiers in earth sciences101-91863-4621https://doi.org/2437782East Africa Rift systemOligocenehominid evolutionstratigraphygeochronologyTurkana BasinTurkana DepressionNational Science Foundation