40Ar/39Ar eruption ages of Turkana Basin tuffs: millennial-scale resolution constrains palaeoclimate proxy tuning models and hominin fossil ages

The Turkana Basin in NW Kenya and SW Ethiopia hosts remarkable fossil-rich sediments that are central to our understanding of early hominin evolution, with interbedded volcanic tuffs providing critical time markers. However, the resolution of existing Early Pleistocene-Pliocene ages is limited to c. 20-60 kyr, inhibiting the evaluation of climatic and environmental drivers of evolution. We present high-precision, single-feldspar Ar-40/Ar-39 age and elemental data for four stratigraphically significant tuffs. These samples exhibit variably dispersed age distributions correlated with feldspar compositional trends, interpreted to indicate the partial retention of inherited Ar-40 related to crustal `cold storage' and rapid melt infiltration preceding eruption. We evaluated various statistical methods and calculated astronomically calibrated Bayesian age estimates of 1879.1 +/- 0.6 ka (+/- 2.4 ka including external errors) for the Kay Behrensmeyer Site (KBS)/H2 Tuff, 1837.4 +/- 0.9 ka (+/- 2.4 ka) for the Malbe/H4 Tuff, 1357.5 +/- 1.8 ka (+/- 2.5 ka) for the Chari/L Tuff and 1315.4 +/- 1.9 ka (+/- 2.5 ka) for the Gele Tuff. Our results permit refined age constraints for important early Homo fossils, including the cranium KNM-ER1813 (Homo habilis) and various Homo erectus fossils. The KBS Tuff age also provides an important calibration locus for orbital tuning of palaeoclimate proxy records, revealing the complex interplays between palaeoclimate and geological drivers of sedimentation.

Automated summary

The Turkana Basin in NW Kenya and SW Ethiopia contains valuable fossil deposits that shed light on early hominin evolution. By using high-precision dating techniques, researchers were able to refine the age estimates of important fossils and better understand the climatic and environmental factors that influenced human evolution.