Age of the earliest Paleolithic sites in the northern part of the Armenian Highland by SHRIMP-II U–Pb geochronology of zircons from volcanic ashes

Abstract

Understanding the earliest period of hominid dispersal from Africa to Eurasia requires reliable ages. Since artifacts are not suitable for direct dating, geochronology of an artifact host-rock matrix is the only robust approach. Possible matrix contamination limits the application of bulk mineral analysis, but the spatially selective secondary ionization mass spectrometry (SIMS) technique allows screening of contaminants. In two recently discovered Early Paleolithic sites in the northern Armenian Highland, the stratigraphic sequence includes ash-bearing volcanic layers with zircon autocrysts, suitable for SIMS U–Pb dating. At the Karakhach site, zircons from the ash-bearing volcanic layers yielded single age populations. This suggests that the layers were formed during multiple eruptions and were not reworked. Zircon crystallization ages of 1.942 ± 0.046 Ma, 1.804 ± 0.030 Ma, and 1.750 ± 0.020 Ma are close to eruptions and therefore date the enclosed Early Acheulian lithic artifacts. For artifacts underneath the oldest ash layer, the zircon age indicates the minimum age of artifacts. These results identify the Karakhach as the oldest Early Acheulian site in Eurasia. At the Kurtan site, the dated ash layer underlies palaeosols containing Early-Middle Acheulian artifacts. The stratigraphic succession at this site implies that the U–Pb zircon age of 1.432 ± 0.028 Ma from the ash is nearly coeval with the beginning of human occupation at the site.