⁴⁰Ar/³⁹Ar age spectra from the KBS Tuff, Koobi Fora Formation

Area of Science:

• Geochronology
• Volcanic stratigraphy
• Paleoanthropology

Background:

• The KBS Tuff is a critical marker bed in the Koobi Fora Formation, Kenya, vital for dating early hominin sites.
• Previous geochronological studies using Ar-Ar and K-Ar methods yielded conflicting dates for the KBS Tuff.

Purpose of the Study:

• To resolve the conflicting age data for the KBS Tuff.
• To establish a precise and reliable age for this key geological marker bed.

Main Methods:

• Argon-40/Argon-39 (Ar-40/Ar-39) age spectra analysis.
• Analysis of anorthoclase phenocrysts from three pumice clasts within the KBS Tuff.

Main Results:

• Nearly ideal flat Ar-40/Ar-39 age spectra patterns were obtained, indicating minimal post-crystallization disturbance.
• Concordant ages of 1.88 ± 0.02 million years were determined for the KBS Tuff.
• The new Ar-40/Ar-39 data confirm the KBS Tuff's age and resolve prior dating conflicts.

Conclusions:

• The KBS Tuff is now very well-dated at 1.88 ± 0.02 million years.
• This precise dating enhances the chronological framework for the Koobi Fora Formation and paleoanthropological research in the region.