Nature 308, 26 - 31 (01 March 1984); doi:10.1038/308026a0

Geochronology, stratigraphy and geochemistry of Cindery Tuff in Pliocene hominid-bearing sediments of the Middle Awash, Ethiopia

C. M. Hall^*, R. C. Walter^†, J. A. Westgate^† & D. York^*

^*Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7
^†Department of Geology, Scarborough College, University of Toronto, West Hill, Ontario, Canada M1C 1A4

Cindery Tuff is a subalkaline, rhyolitic air-fall deposit that was probably produced by a mixed-magma eruption. It is a distinctive, datable, regional isochronous marker bed within the Pliocene sediments of the Middle Awash district, and is stratigraphically situated between two new fossil hominid discoveries. Based on ⁴⁰Ar/³⁹Ar analyses of plagioclase, rhyolitic glass and basaltic glass, as well as fission-track analyses of zircons, we estimate its age to be 3.8−4.0 Myr. This implies that associated hominid skull fragments are at least 3.9 Myr old.

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