High-resolution 40Ar/39Ar geochronology of the Koobi Fora Tuff Complex, Turkana Basin: Implications for the hominin bearing strata of the Early Pleistocene (1.6–1.4 Ma)

Volcaniclastic ash deposits (tuffs) within the Turkana Basin in Kenya act as temporal markers to constrain the extensive fossil-rich sediments of the Koobi Fora Formation. By using geochemical fingerprinting and precise geochronology this study improves the temporal and spatial resolution of the Koobi Fora, Lower Koobi Fora and Karari Blue tuffs within the Koobi Fora Tuff Complex. Utilising a Bayesian approach to single-grain anorthoclase ages this study presents ages of 1.49257 ± 0.00186 (2σ) Ma for the Karari Blue Tuff, 1.49430 ± 0.00142 (2σ) Ma for the Koobi Fora Tuff and 1.51561 ± 0.00090 (2σ) Ma for the Lower Koobi Fora Tuff. These results provide highly precise (<0.1 % uncertainties) anchoring ages for the stratigraphy of the Okote Member, implying an older age for the base of the Koobi Fora Tuff Complex (>1.51561 ± 0.00090 Ma). The implications of the ∼30 ka revision of the Lower Koobi Fora Tuff indicates older dates for significant hominin fossil sites in the Ileret (Area 1A) and Koobi Fora (Area 103) regions. The ages of the three tuffs provide the highest precision ages of the Koobi Fora Tuff Complex thus far and have important implications in the Koobi Fora Formation and correlates across the Turkana Basin.