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

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Abstract
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 2 new fossil hominid discoveries. Based on 40Ar/39Ar analyses of plagioclase, rhyolitic glass and basaltic glass, and fission-track analyses of zircons, its age is estimated to be 3.8-4.0 million yr. This implies that associated hominid skull fragments are at least 3.9 million yr old.