New 40Ar/39Ar and U/Pb geochronology constrains the depositional age of the Middle Miocene fossil locality known as Napudet on the west side of Lake Turkana in Kenya. Napudet is the type locality for Nyanzapithecus alesi, represented by a remarkably complete fossil skull of an infant ape. Abundant fossil trees in the stratigraphic section (“Emunyan beds”) from which the N. alesi specimen was exhumed indicate that Napudet was a Middle Miocene forest. 40Ar/39Ar geochronology from basalt flows brackets the depositional age of the Emunyan beds between 14.05 ± 0.34 Ma and 13.52 ± 0.13 Ma (2σ). A laser ablation U/Pb dating approach based on geochemical image mapping of carbonate petrified wood found within the Emunyan beds yields ages of 13.19 ± 0.61 Ma using a Tera-Wasserburg diagram to correct for common Pb and 14.11 ± 0.95 Ma using a total−Pb/U−Th isochron (2σ). Both ages are consistent with the bracketing basalts and provide an opportunity to examine different approaches for dating carbonates. Carbonate U/Pb dating represents an exciting avenue for directly dating terrestrial sequences.
Cox et al. (Mon,) studied this question.