Hall C M, Walter R C, Westgate J A, York D
Nature. 1984;308(5954):26-31. doi: 10.1038/308026a0.
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.
火山灰凝灰岩是一种亚碱性流纹质空降沉积物，可能由混合岩浆喷发形成。它是中阿瓦什地区上新世沉积物中一种独特的、可定年的区域等时标志层，在地层上位于两个新的化石人科动物发现之间。基于对斜长石、流纹质玻璃和玄武质玻璃的40Ar/39Ar分析，以及对锆石的裂变径迹分析，我们估计其年龄为380 - 400万年。这意味着相关的人科动物头骨碎片至少有390万年的历史。
